JP4962201B2 - Fixing device, heat generating roller, and image forming apparatus using the same - Google Patents

Description

  The present invention relates to a fixing device used in an image forming apparatus such as an electrophotographic or electrostatic recording type copying machine, a facsimile machine, or a printer. In particular, an unfixed image formed with toner is printed on paper or the like by an electromagnetic induction heating method. The present invention relates to a fixing device that heats and fixes the recording material, a heat generating roller used in the fixing device, and an image forming apparatus using the fixing device.

  In recent years, efforts for energy saving of fixing devices used in copying machines, facsimiles, printers, and the like have been actively studied. And as an influential configuration, it has been actively studied to adopt an electromagnetic induction heating method. In the electromagnetic induction heating type fixing device, an alternating current is applied to the exciting coil, and an alternating magnetic flux is generated around the exciting coil. An induced current is generated when the generated alternating magnetic flux is linked to the conductor, and heat generated in the conductor by the induced current is used for fixing an unfixed image.

  FIG. 20 is a schematic cross-sectional view of a conventional fixing device. In the fixing device, a heat generating layer made of a ferromagnetic metal is formed on the inner surface of a high-rigidity hollow roller made of a highly heat-conductive nonmagnetic metal. The heat generating layer is heated by the included exciting coil. With such a configuration, rotational stability is secured against an increase in pressure, and a non-sheet passing portion region during continuous feeding of a narrow recording material is maintained at a predetermined temperature. (For example, refer to Patent Document 1).

  FIG. 21 is a view for explaining the structure of a heating roller of a conventional fixing device. The fixing device is a hollow first roller made of a first metal and having a length corresponding to a predetermined paper size. And a second roller that is fitted to the outer periphery of the first roller and is slightly longer than the maximum sheet size that can be fixed, and extends in the axial direction of the first and second rollers. And a current application means for selectively applying a first frequency current or a second frequency current to the coil, and selectively applying a current frequency current corresponding to the paper size. Then, the first or second roller corresponding to the current frequency is selectively heated to switch overheating range. (For example, refer to Patent Document 2).

Further, in order to solve the problem of excessive temperature rise in the non-sheet passing portion region, it is conceivable to perform self-temperature control using a magnetic shunt metal (also referred to as a temperature-sensitive magnetic metal) whose Curie temperature is set to a predetermined temperature as a heating element. . FIG. 22 is a view showing a conventional heat roller composed of two layers of a temperature-sensitive magnetic material and a non-magnetic conductor, and the heat roller has a layer of the temperature-sensitive magnetic material that is equal to or larger than the width of the paper passage area. It is considered that the induction coil has a width smaller than the width of the induction coil, and the magnetic field is not weakened even at the end of the paper passing area, and uniform heat generation can be obtained. (For example, refer to Patent Document 3).
Japanese Patent Laid-Open No. 11-167981 JP-A-10-207269 JP 2006-267419 A

  However, in the configuration in which the heat generating layer made of ferromagnetic metal is formed on the inner surface of the conventional high heat conductive nonmagnetic metal high rigidity roller, the heat generating layer has a small heat capacity, but the high heat conductive nonmagnetic metal has a thick wall. Is set to withstand the applied pressure, its heat capacity is large and the warm-up time cannot be shortened. Further, the highly rigid hollow roller of high heat conductivity non-magnetic metal conducts heat and escapes from both end portions to the support member and the like, so that the temperature at both end portions decreases and temperature unevenness occurs. If the heat generation distribution of the induction coil is adjusted and corrected in order to solve this problem, there is a problem that the amount of applied power increases.

  Further, in the configuration in which one of the two conventional length rollers is selectively heated by currents of two frequencies, the current application means is complicated and expensive, and the size of the recording material that can be handled is large. Limited. Furthermore, the heat capacity is large, and it is not possible to shorten the warm-up, and the first roller and the coil in the part where the magnetic field lines pass through the first roller through the second roller and the part through which the first roller passes without passing through the second roller There is a problem that a uniform heat generation cannot be obtained due to a different bonding state.

  Further, in the heat roller in which the two layers of the conventional temperature-sensitive magnetic metal and the nonmagnetic conductor are configured as shown in FIG. 22, the heat generated in the temperature-sensitive magnetic metal is entirely transmitted by the nonmagnetic conductor. The region of the nonmagnetic conductor that is in contact with the temperature-sensitive magnetic metal also extends outside the region of the temperature-sensitive magnetic metal, and the end of the nonmagnetic conductor is further connected to the bearing and the drive gear. Since they are in contact with each other, heat flows to and is released from the end portion of the nonmagnetic conductor, so that the temperature at both end portions of the temperature-sensitive magnetic metal decreases. In order to eliminate such a local decrease in temperature, it is conceivable to correct the heat generation distribution of the coil. However, if the predetermined temperature is obtained for the entire sheet passing area after the correction, the applied power increases. become. Furthermore, since the nonmagnetic conductive layer is formed over the entire heat roller, there is a problem that its heat capacity is large and it is difficult to shorten the warm-up.

  The present invention solves the conventional problems such as those described above, and in the heat generating means made of a magnetic shunt material, a thin layer of a nonmagnetic conductive layer that is wider than the width of the recording material and narrower than the width of the magnetic shunt material. The provided structure shortens the warm-up and prevents temperature unevenness due to heat conduction to the edges, and ensures overheating of the non-passing part of the recording material when narrower recording material is continuously passed. An object of the present invention is to provide a fixing device that prevents the applied power and reduces the applied power, a heat generating roller used in the fixing device, and an image forming apparatus using the fixing device.

  In order to achieve the above object, the present invention provides a fixing device that heats and presses a recording material having an image formed of a color material on a surface to fix the color material on the recording material. And at least a part of the magnetic field formed by the excitation means, a heating means that generates heat by penetrating the magnetic field lines of the magnetic field, and the recording material and the heating means are brought into contact with each other. The heat generating means includes a magnetically permeable conductive layer and a nonmagnetic conductive layer, wherein the permeable conductive layer is magnetic at room temperature. However, the magnetically permeable material and the non-magnetic conductive layer are formed of an image of the recording material to be fixed by the apparatus. In at least one direction on the surface The length of the magnetically permeable conductive layer is formed longer than the length of the recording material, and the length of the nonmagnetic conductive layer is longer than the length of the recording material and shorter than the length of the magnetically permeable conductive layer. It is assumed that

  A fixing device that heats and presses a recording material having an image formed of a color material on the surface to fix the color material on the recording material; an excitation means that forms a magnetic field; and at least a part of the excitation device A heating means for generating heat by penetrating the magnetic field lines of the magnetic field into the inside, and a pressurizing means for bringing the recording material and the heating means into contact with each other and applying pressure therebetween The heat generating means includes a magnetically permeable conductive layer and a nonmagnetic conductive layer, wherein the magnetically permeable conductive layer has magnetism at room temperature but becomes magnetic at a predetermined temperature or higher. The magnetically permeable conductive layer and the nonmagnetic conductive layer are in at least one direction on the surface on which the image of the recording material to be fixed by the device is formed. The length of the magnetically permeable conductive layer is It is formed longer than the length of the recording material, and the length of the nonmagnetic conductive layer is longer than the length of the recording material and shorter than the length of the magnetically permeable conductive layer, and is formed approximately equal to the length of the excitation means. It is good as it is.

  Further, an exciting means for forming a magnetic field is provided on a fixing device in which an image is formed of a color material on the surface and the recording material moving relative to the apparatus is heated and pressed to fix the color material on the recording material. And at least a portion of the heating means that is in the magnetic field formed by the excitation means and generates heat by penetrating the magnetic field lines of the magnetic field, and the traveling recording material and the heating means are brought into contact with each other. And a pressurizing means for applying a pressure therebetween, wherein the heat generating means includes a magnetically permeable conductive layer and a nonmagnetic conductive layer, wherein the permeable conductive layer is at room temperature. It is made of a magnetic shunt material that has magnetism but loses magnetism at a predetermined temperature or more, and the magnetically permeable conductive layer and the nonmagnetic conductive layer at least move relative to the heat generating means. Orthogonal to the direction of travel The width of the magnetically permeable conductive layer is formed wider than the sheet passing width of the recording material, and the width of the nonmagnetic conductive layer is wider than the sheet passing width of the recording material and the permeable conductive The width of the layer may be narrower than that of the excitation means.

  In addition, the roller is disposed in a magnetic field formed by the excitation means and generates heat by penetrating the magnetic field lines of the magnetic field. An image is formed of a color material on the surface and moves in contact with the roller. A heating roller for heating the recording material so that the coloring material is fixed on the recording material has a permeable conductive layer and a nonmagnetic conductive layer, and the permeable conductive layer is magnetic at room temperature. It is made of a magnetic shunt material that loses magnetism at a predetermined temperature or more, and the magnetically permeable conductive layer and the nonmagnetic conductive layer are in a width direction that is perpendicular to the moving direction of the moving recording material. The width of the magnetically permeable conductive layer is formed wider than the paper passing width of the recording material, and the width of the nonmagnetic conductive layer is wider than the paper passing width of the recording material and smaller than the width of the magnetically permeable conductive layer. The shape is almost equal to the width of the excitation means Or as being.

  In the present invention, the heat capacity of the heat generating means is small due to the above configuration. When the heating means is below the Curie temperature, the lines of magnetic force from the excitation means penetrate into the magnetically permeable conductive layer and generate heat rapidly. On the other hand, for example, when a recording material having a narrow width is continuously passed and the temperature exceeds the Curie temperature, the magnetic field lines from the excitation means penetrate the magnetically permeable conductive layer and penetrate into the nonmagnetic conductive layer in that region. Induces current. This induced current generates a repulsive magnetic field that acts in a direction that cancels the magnetic field generated by the exciting means, and greatly attenuates the magnetic flux from the exciting means. As a result, since the magnetic flux density is reduced, the amount of heat generation is reduced, and the excessive temperature rise is suppressed.

  As described above, the heating means according to the present invention has at least one direction on the surface on which the image of the recording material is formed (for example, a direction orthogonal to the moving direction when the recording material moves relative to the heating means The width of the nonmagnetic conductive layer having a relatively high thermal conductivity is slightly longer than the length of the recording material, so that the nonmagnetic conductive layer does not cover the end of the heating means. Generally, it is possible to prevent heat from flowing out to the support of the fixing device through a support receiving portion provided at the end of the heat generating means. In addition, the nonmagnetic conductive layer according to the present invention can be coupled with the fact that the thickness may be thin, so that the increase in heat capacity is small, and thus the increase in warm-up time can be suppressed.

  In addition, since most of the heat is not conducted from the area in contact with the recording material to the end, it is only conducted slightly through the magnetically permeable conductive layer having low thermal conductivity and flows out to the end of the heating means. It is possible to reduce the temperature unevenness in the contact area, and further, it is possible to eliminate the correction of the heat generation distribution by the excitation means and to reduce the power applied to the fixing device.

  As described above, the present invention provides quick start-up during warm-up, and suppression of excessive temperature rise outside the recording material width (outside the area where the heating means contacts the recording material), for example, during continuous paper feeding. Both, for example, can effectively prevent deterioration of the rubber material and damage to the bearing member, and further prevent the heat outflow from the end of the heating means to reduce temperature unevenness, There is an effect that the applied power can be reduced.

  The first embodiment of the present invention is a fixing device that heats and presses a recording material on which an image is formed with a color material and fixes the color material on the recording material. The fixing device includes an exciting unit that forms a magnetic field, a heating unit that is at least partially in the magnetic field formed by the exciting unit, and that generates heat by penetrating the magnetic field lines of the magnetic field, and the recording material. And pressurizing means for bringing the heat generating means into contact with each other and applying pressure therebetween. The heat generating means includes a magnetically permeable conductive layer and a nonmagnetic conductive layer. Here, the magnetically permeable conductive layer is made of a magnetic shunt material that has magnetism at room temperature but loses magnetism at a predetermined temperature or higher, and the magnetically permeable conductive layer and the nonmagnetic conductive layer include the device. The length of the magnetically permeable conductive layer is longer than the length of the recording material in at least one direction on the surface of the recording material on which the image is fixed, and the nonmagnetic conductive layer Is longer than the length of the recording material and shorter than the length of the magnetically permeable conductive layer.

  Such heat generating means of the fixing device has a small heat capacity. When the temperature is equal to or lower than the Curie temperature, the magnetic lines of force from the excitation means penetrate into the magnetically permeable conductive layer and generate heat rapidly. On the other hand, when the temperature exceeds the Curie temperature, in that region, the magnetic field lines from the excitation means penetrate the magnetically permeable conductive layer and penetrate the nonmagnetic conductive layer to induce an induced current. This induced current generates a repulsive magnetic field that acts in a direction that cancels the magnetic field generated by the exciting means, and greatly attenuates the magnetic flux from the exciting means. As a result, since the magnetic flux density is reduced, the amount of heat generation is reduced, and the excessive temperature rise is suppressed.

  Thus, the heat generating means of this embodiment is such that a nonmagnetic conductive layer having a relatively high thermal conductivity is not applied to the end of the heat generating means in at least one direction on the surface of the recording material on which the image is formed. Therefore, heat can be prevented from flowing out to the support of the fixing device or the like through a support receiving portion that is generally provided at the end of the heat generating means. In addition, coupled with the fact that the thickness of the nonmagnetic conductive layer may be as thin as about 0.015 mm, the increase in heat capacity is small, and thus the increase in warm-up time can be suppressed.

  In addition, since most of the heat is not conducted from the area in contact with the recording material to the end, it is only conducted slightly through the magnetically permeable conductive layer having low thermal conductivity and flows out to the end of the heating means. It is possible to reduce the temperature unevenness in the contact area, and further, it is possible to eliminate the correction of the heat generation distribution by the excitation means and to reduce the power applied to the fixing device.

  As described above, the present embodiment can realize both the rapid start-up at the time of warm-up and the suppression of the excessive temperature rise outside the area where the heat generating means is in contact with the recording material. It is possible to prevent heat from flowing out from the end of the heat generating means, and to reduce applied power in addition to reducing temperature unevenness.

  The second embodiment of the present invention is a fixing device that heats and presses a recording material having an image formed of a color material on the surface to fix the color material on the recording material. The fixing device includes an exciting unit that forms a magnetic field, a heating unit that is at least partially in the magnetic field formed by the exciting unit, and that generates heat by penetrating the magnetic field lines of the magnetic field, and the recording material. And pressurizing means for bringing the heat generating means into contact with each other and applying pressure therebetween. The heat generating means includes a magnetically permeable conductive layer and a nonmagnetic conductive layer. Here, the magnetically permeable conductive layer is made of a magnetic shunt material that has magnetism at room temperature but loses magnetism at a predetermined temperature or higher, and the magnetically permeable conductive layer and the nonmagnetic conductive layer include the device. The length of the magnetically permeable conductive layer is longer than the length of the recording material in at least one direction on the surface of the recording material on which the image is fixed, and the nonmagnetic conductive layer Is longer than the length of the recording material and shorter than the length of the magnetically permeable conductive layer, and is substantially equal to the length of the excitation means.

  The heat generating means of such a fixing device has a smaller heat capacity than the heat generating means in the first embodiment and is less in heat capacity. When the temperature is equal to or lower than the Curie temperature, the magnetic lines of force from the excitation means penetrate into the magnetically permeable conductive layer and generate heat rapidly. On the other hand, when the temperature exceeds the Curie temperature, in that region, the magnetic field lines from the excitation means penetrate the magnetically permeable conductive layer and penetrate the nonmagnetic conductive layer to induce an induced current. This induced current generates a repulsive magnetic field that acts in a direction that cancels the magnetic field generated by the exciting means, and greatly attenuates the magnetic flux from the exciting means. As a result, since the magnetic flux density is reduced, the amount of heat generation is reduced, and the excessive temperature rise is suppressed.

  As described above, in the heat generating means of this embodiment, the length of the nonmagnetic conductive layer having a relatively high thermal conductivity is substantially equal to the length of the excitation means in at least one direction on the surface of the recording material on which the image is formed. Since the nonmagnetic conductive layer can be made not to cover the end of the heating means because it is just slightly longer than the length of the recording material, heat is generally applied to the fixing device support through a support receiving portion provided at the end of the heating means. Can be prevented from leaking. In addition, coupled with the fact that the thickness of the nonmagnetic conductive layer may be as thin as about 0.015 mm, the increase in heat capacity is optimized over the heat generating means in the first embodiment, and thus the warm-up time is small. This increase can be suppressed more optimally than the heat generating means in the first embodiment.

  In addition, since most of the heat is not conducted from the area in contact with the recording material to the end, it is only conducted slightly through the magnetically permeable conductive layer having low thermal conductivity and flows out to the end of the heating means. It is possible to reduce the temperature unevenness in the contact area, and further, it is possible to eliminate the correction of the heat generation distribution by the excitation means and to reduce the power applied to the fixing device.

  As described above, the present embodiment can realize both the rapid start-up at the time of warm-up and the suppression of the excessive temperature rise outside the area where the heat generating means is in contact with the recording material. Besides preventing the heat from flowing out from the end of the heat generating means and reducing the temperature unevenness, the applied power can be reduced more optimally than the heat generating means in the first embodiment.

  In the third fixing device according to the present invention, a recording material on which a color material is formed and a recording material that moves relative to the device is heated and pressed to place the coloring material on the recording material. A fixing device for fixing. The fixing device includes: an excitation unit that forms a magnetic field; and a heating unit that is at least partially in the magnetic field formed by the excitation unit and generates heat by penetrating the magnetic field lines of the magnetic field. And pressurizing means for bringing the recording material and the heat generating means into contact with each other and applying pressure therebetween. The heat generating means includes a magnetically permeable conductive layer and a nonmagnetic conductive layer. Here, the magnetically permeable conductive layer is made of a magnetic shunt material that has magnetism at room temperature but loses magnetism at a predetermined temperature or higher, and the magnetically permeable conductive layer and the nonmagnetic conductive layer are at least the In the width direction, which is a direction perpendicular to the moving direction of the recording material that moves relative to the heat generating means, the width of the magnetically permeable conductive layer is formed wider than the sheet passing width of the recording material. The width of the layer is wider than the sheet passing width of the recording material and narrower than the width of the magnetically permeable conductive layer, and is formed substantially equal to the width of the excitation means.

  Such heat generating means of the fixing device has a small heat capacity. When the temperature is equal to or lower than the Curie temperature, the magnetic lines of force from the excitation means penetrate into the magnetically permeable conductive layer and generate heat rapidly. On the other hand, when a recording material with a narrow width is continuously passed and the temperature outside the recording material exceeds the Curie temperature, the magnetic field lines from the excitation means penetrate the permeable conductive layer in the region outside the recording material width. It penetrates into the nonmagnetic conductive layer and induces an induced current. This induced current generates a repulsive magnetic field that acts in a direction to cancel the magnetic field generated by the exciting means, and greatly attenuates the magnetic flux from the exciting means. As a result, since the magnetic flux density is reduced, the amount of heat generation is reduced, and the excessive temperature rise is suppressed.

  Thus, the heat generating means of this embodiment has a width of the nonmagnetic conductive layer having a relatively high thermal conductivity in the width direction, which is a direction orthogonal to the moving direction of the recording material that moves relative to the heat generating means. Since the nonmagnetic conductive layer is not applied to the support receiving portion of the heat generating means because it is substantially equal to the width of the excitation means and slightly wider than the sheet passing width of the recording material, heat can be applied to the support of the fixing device through the support receiving portion. It can prevent outflow. In addition, coupled with the fact that the thickness of the nonmagnetic conductive layer may be as thin as about 0.015 mm, the increase in heat capacity is small, and thus the increase in warm-up time can be suppressed.

  Also, since most of the heat is not conducted outside the width of the recording material, it is conducted only slightly through the magnetically permeable conductive layer having a low thermal conductivity and flows out to the end portion. Further, it is possible to eliminate the correction of the heat generation distribution by the excitation means, and to reduce the power applied to the fixing device.

  As described above, the present embodiment can achieve both the rapid start-up at the time of warm-up and the suppression of the excessive temperature rise outside the recording material width at the time of continuous paper feeding. It is possible to prevent heat from flowing out from the end portion and reduce applied power in addition to reducing temperature unevenness.

  The fourth embodiment of the present invention is a fixing device according to the third embodiment, wherein the heat generating means is a cylindrical heat generating roller that can rotate around an axis inside itself. The magnetically permeable conductive layer and the nonmagnetic conductive layer are integrally rotated with the rotation of the heat generating roller in the peripheral portion of the cylinder, and the nonmagnetic conductive layer is the excitation means. Between the magnetically permeable conductive layers.

  Such a fixing device can realize both rapid start-up at the time of warm-up and suppression of excessive temperature rise outside the area where the heating means contacts the recording material. In addition to being able to effectively prevent damage to the bearing member and the bearing member, and further preventing heat from flowing out from the end of the heat generating means, reducing temperature unevenness and reducing applied power, the roller is cylindrical Therefore, a wide nip can be formed with a small applied pressure, and the load can be further reduced.

  The fifth embodiment of the present invention is a fixing device according to the third embodiment, wherein the heat generating means is a hollow cylindrical heat generating roller that can rotate around an axis inside itself. The magnetically permeable conductive layer and the nonmagnetic conductive layer are integrally rotated with the rotation of the heat generating roller in the peripheral portion of the cylinder, and the nonmagnetic conductive layer is the excitation means. Between the magnetically permeable conductive layers.

  Such a fixing device can realize both rapid start-up at the time of warm-up and suppression of excessive temperature rise outside the area where the heating means contacts the recording material. In addition to being able to effectively prevent damage to the bearings and bearing members, and further preventing heat from flowing out from the end of the heating means, reducing temperature unevenness and reducing applied power, the roller is cylindrical Therefore, it is possible to form a wide nip with a small applied pressure, and the load can be reduced.Furthermore, a low heat capacity with a hollow roller can realize a quick start-up and further reduce the load. is there.

  The sixth embodiment of the present invention is characterized in that, in the third embodiment, the magnetically permeable conductive layer has a layer surface facing the exciting means in the width direction.

  Since such a fixing device is disposed so as to face each other, it can penetrate the magnetically permeable conductive layer without attenuation of the magnetic lines of force, so that efficient heat generation is possible at a temperature equal to or lower than the Curie temperature.

  The seventh embodiment of the present invention is characterized in that, in the third embodiment, a nonmagnetic conductive layer is in close contact with the magnetically permeable conductive layer.

  In such a fixing device, since these layers are in close contact with each other, the heat generated in the magnetically permeable conductive layer is efficiently conducted to the nonmagnetic conductive layer, and the high thermal conductivity of the nonmagnetic conductive layer further increases the temperature. Unevenness can be reduced. Therefore, when the Curie temperature is exceeded, the heat generated by the induced current flowing in the nonmagnetic conductive layer is also conducted to the magnetically permeable conductive layer. Temperature rise can be prevented.

  The eighth embodiment of the present invention is characterized in that, in the third embodiment, the nonmagnetic conductive layer is formed with a thickness smaller than that of the magnetically permeable conductive layer.

  In such a fixing device, the layer thickness is thicker in the permeable conductive layer than in the nonmagnetic conductive layer, so that the magnetic lines of force almost penetrate into the permeable conductive layer and do not penetrate into the nonmagnetic conductive layer. Efficient heat generation is possible when the temperature is equal to or lower than the Curie temperature.

  The ninth embodiment of the present invention is characterized in that, in the third embodiment, the nonmagnetic conductive layer has a specific resistance value smaller than a specific resistance value of the magnetically permeable conductive layer.

  In such a fixing device, when the magnetic field line penetrates into the nonmagnetic conductive layer and the repulsive magnetic field is generated when the Curie temperature is exceeded, the heat generation in the nonmagnetic conductive layer is caused by the heat generation in the magnetically permeable conductive layer. Can also be reduced.

  A tenth embodiment of the present invention is characterized in that, in the third embodiment, the magnetically permeable conductive layer is formed with a thickness of 0.2 to 1.0 mm.

  Such a fixing device can reduce the warm-up time because the magnetic field lines entering the layer do not pass through the layer below the Curie temperature and go out of the layer and have a low heat capacity.

  An eleventh embodiment of the present invention is characterized in that, in the third embodiment, the nonmagnetic conductive layer is formed with a thickness of 0.015 mm to 0.060 mm.

  Such a fixing device can suppress an excessive temperature rise even in such a thin non-magnetic conductive layer, suppresses the applied power, and increases the heat capacity accompanying the addition of the non-magnetic conductive layer. Since the magnetic conductive layer is thin, it can be made light.

A twelfth embodiment of the present invention is characterized in that, in the third embodiment, the nonmagnetic conductive layer has a specific resistance of 7 × 10 ⁻⁸ Ω · m or less.

  Such a fixing device can suppress heat generation in the nonmagnetic conductive layer when the Curie temperature is exceeded.

  In the thirteenth embodiment of the present invention, in the third embodiment, the nonmagnetic conductive layer is formed slightly wider in the width direction than the width of the excitation means wider than the sheet passing width of the recording material. It is characterized by being.

  In such a fixing device, the nonmagnetic conductive layer is formed even when the temperature of the portion where the recording material does not pass in the heat generating unit exceeds the Curie temperature and the lines of magnetic force pass through the magnetically permeable conductive layer. Since the range is larger than the excitation means, the non-magnetic conductive layer surely reduces the magnetic flux and suppresses the excessive temperature rise, so the end of the pressure roller is not abnormally hot and broken. It is possible to reduce temperature unevenness and suppress excessive temperature rise.

  In a fourteenth embodiment of the present invention, in the above third embodiment, the pressing means includes a pressing roller, and the width of the nonmagnetic conductive layer in the width direction is determined by the passage of the recording material. It is characterized in that it is formed to be approximately equal to or slightly wider than the width of the pressure roller wider than the paper width.

  Such a fixing device reliably uses a nonmagnetic conductive layer even when the temperature of the portion where the recording material does not pass in the heat generating unit rises and exceeds the Curie temperature and the magnetic lines of force pass through the magnetically permeable conductive layer. Since excessive temperature rise is suppressed by reducing the magnetic flux, the end of the pressure roller does not become abnormally hot and breaks. Further, the end portion of the nonmagnetic conductive layer does not come into pressure contact with the pressure roller and does not damage the pressure roller.

  A fifteenth embodiment of the present invention is characterized in that, in the third embodiment, the nonmagnetic conductive layer is made of copper and has a thickness of 0.015 mm to 0.060 mm. It is what.

  Such a fixing device can prevent overheating even with such a thin nonmagnetic conductive layer, and is made of copper, and because of its small specific resistance, it generates heat when the Curie temperature is exceeded. Therefore, since the nonmagnetic conductive layer is thin, the increase in heat capacity associated with the addition of the nonmagnetic conductive layer can be minimized and the warm-up can be performed quickly.

  A sixteenth embodiment of the present invention is characterized in that, in the third embodiment, the nonmagnetic conductive layer is made of aluminum and has a thickness of 0.025 mm to 0.060 mm. It is what.

  In such a fixing device, suppression of excessive temperature rise and reduction of applied power can be achieved at low cost.

  A seventeenth embodiment of the present invention is characterized in that, in the third embodiment, the nonmagnetic conductive layer is made of zinc and has a thickness of 0.055 mm to 0.060 mm. It is what.

  In such a fixing device, suppression of excessive temperature rise and reduction of applied power can be achieved at low cost.

  In an eighteenth embodiment of the present invention, in the above third embodiment, the heat generating means further has a protective film on the surface of the nonmagnetic conductive layer. The magnetic conductive layer is formed to be substantially equal to the width.

  In such a fixing device, the masking for forming the nonmagnetic conductive layer and the protective layer may be the same, the workability is good, and the cost can be reduced.

  According to a nineteenth embodiment of the present invention, in the third embodiment, the heat generating means further includes a protective film on the surface of the nonmagnetic conductive layer. Here, the protective layer has a width that is transparent. The magnetic conductive layer is formed to be substantially equal to the width.

  Such a fixing device does not require masking of the protective layer and can prevent oxidation of the entire width of the magnetically permeable conductive layer.

  A twentieth embodiment of the present invention is characterized in that, in the fifth embodiment, the excitation means is disposed inside the hollow of the heat generating roller.

  Such a fixing device can be reduced in size, and further, a cleaning unit that removes unnecessary toner adhering to or remaining on the surface of the heat generation roller because the excitation unit does not exist on the outer peripheral surface side of the heat generation roller. In addition, the recording material separating means can be easily arranged.

  A twenty-first embodiment of the present invention is characterized in that, in the fourth or fifth embodiment, the excitation means is arranged outside the heating roller.

  Such a fixing device can easily prevent the exciting coil from generating heat, and its consumable parts can be easily replaced and maintained.

  A twenty-second embodiment of the present invention is an image forming apparatus including the fixing device according to any one of the first to twenty-first embodiments.

  Such an image forming apparatus has a fast warm-up, small temperature unevenness, and prevents excessive temperature rise in a non-sheet passing portion when a narrow width recording material is continuously passed, and can reduce applied power. is there.

  A twenty-third embodiment of the present invention is a roller that is arranged in a magnetic field formed by excitation means and generates heat by penetrating the magnetic field lines of the magnetic field, and an image is formed on the surface with a coloring material. The heat generating roller heats the recording material that moves in contact with the roller so that the color material is fixed on the recording material. The heat generating roller has a magnetically permeable conductive layer and a nonmagnetic conductive layer. The magnetically permeable conductive layer is made of a magnetic shunt material that has magnetism at room temperature but loses magnetism at a predetermined temperature or more, and the permeable conductive layer and the nonmagnetic conductive layer move. With respect to the width direction that is a direction perpendicular to the moving direction of the recording material, the width of the magnetically permeable conductive layer is formed wider than the sheet passing width of the recording material, and the width of the nonmagnetic conductive layer is the width of the recording material. It is wider than the sheet passing width and narrower than the width of the magnetically permeable conductive layer, and is substantially equal to the width of the excitation means.

  Such a heating roller has a fast warm-up, small temperature unevenness, and prevents an excessive temperature rise in a non-sheet passing portion when a narrow width recording material is continuously passed through the fixing device, thereby reducing applied power. Is possible.

  Hereinafter, embodiments of a fixing device, an image forming apparatus, and a heat generating roller according to the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to this Example.

Example 1
FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to Embodiment 1 of the present invention.

  As shown in the figure, an electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 101 is rotatably disposed in an image forming apparatus main body 100 of this image forming apparatus.

  In FIG. 1, the surface of the photosensitive drum 101 is uniformly charged to a predetermined negative dark potential V0 by the charger 102 while being rotated at a predetermined peripheral speed in the direction of the arrow.

  The laser beam scanner 103 outputs a laser beam 104 modulated in accordance with a time-series electric digital pixel signal of image information input from a host device such as an image reading device or a computer (not shown).

  The uniformly charged surface of the photosensitive drum 101 is scanned and exposed by a laser beam 104. As a result, the absolute value of the potential of the exposed portion of the photosensitive drum 101 decreases to a bright potential VL, and an electrostatic latent image is formed on the surface of the photosensitive drum 101. The electrostatic latent image is reversely developed by the negatively charged toner of the developing device 105 to be a visible image (toner image).

  The developing device 105 includes a developing roller 106 that is driven to rotate.

  The developing roller 106 is disposed to face the photosensitive drum 101, and a thin layer of toner is formed on the outer peripheral surface thereof. A developing bias voltage whose absolute value is smaller than the dark potential V0 of the photosensitive drum 101 and larger than the light potential VL is applied to the developing roller 106. As a result, the toner on the developing roller 106 is transferred only to the portion of the photosensitive drum 101 having the bright potential VL, and the electrostatic latent image is visualized, and an unfixed toner image (hereinafter referred to as “toner”) 111) is formed.

  On the other hand, a recording sheet 109 as a recording material is fed from the sheet feeding unit 107 one by one by a feeding roller 108.

  The fed recording paper 109 passes through a pair of registration rollers 110 and is fed to the nip between the photosensitive drum 101 and the transfer roller 112 at an appropriate timing synchronized with the rotation of the photosensitive drum 101. As a result, the toner image 111 on the photosensitive drum 101 is transferred onto the recording paper 109 by the transfer roller 112 to which a transfer bias is applied.

  The recording paper 109 on which the toner image 111 is formed and supported in this way is guided by the recording paper guide 114 and separated from the photosensitive drum 101, and then the fixing portion of the heat fixing device (hereinafter referred to as “fixing device”) 200. It is conveyed toward. Then, the toner image 111 is heated and fixed by the fixing device 200 on the recording paper 109 conveyed to the fixing portion.

  The recording paper 109 on which the toner image 111 is heated and fixed passes through the fixing device 200 and is then discharged onto a paper discharge tray 115 disposed outside the image forming apparatus main body 100.

  The photosensitive drum 101 from which the recording paper 109 has been separated is subjected to the subsequent image formation by removing residuals such as transfer residual toner on the surface thereof by the cleaning device 113.

  2 and 3 are schematic cross-sectional views illustrating the configuration of the fixing device according to the first embodiment of the present invention. As shown in these drawings, the fixing device 200 includes a heat generation unit 210, a pressure unit 220, a temperature sensor 230, and an excitation unit 240.

  The heat generating means 210 includes at least a heat generating roller 211. The heat generating roller 211 is a cylindrical roller having a diameter of, for example, 40 mm, is supported by the bearing 213 via the heat insulating bush 212, and the toner image is supported on the recording. The paper 109 is rotated so as to be conveyed in the direction of the arrow.

  The heating roller 211 includes at least a magnetically permeable conductive layer (also referred to as a highly permeable conductive layer in contrast to the nonmagnetic conductive layer) 214 and nonmagnetic (in the present invention, nonmagnetic means that the magnetic permeability is that of the permeable conductive layer). A conductive layer 215 (which is low with a clear difference) is laminated. More specifically, FIG. 4 is an enlarged cross-sectional model view of the surface layer portion of the heat roller. As shown in FIG. 4, the highly permeable conductive layer 214, in order from the side closer to the central axis of the heat roller 211, A nonmagnetic conductive layer 215, a protective layer 216, and a release layer 217 are stacked.

  The highly permeable conductive layer 214 is made of a magnetic shunt material set so that the Curie temperature becomes a predetermined temperature. For example, it has a hollow cylindrical shape with a diameter of 40 mm, a wall thickness of 0.6 mm, and a total length of 385 mm. Molded. Considering the heat capacity of the heat generating roller 211, it is desirable to make the highly magnetically permeable conductive layer 214 thinner to reduce the heat capacity and to quickly raise the temperature of the heat generating roller 211. However, when the thickness of the highly permeable conductive layer 214 is less than the skin depth below the Curie temperature, the magnetic lines of force (magnetic flux) penetrate the highly permeable conductive layer 214 and permeate the nonmagnetic conductive layer 215, as will be described later. The calorific value is decreased, leading to a decrease in the heating rate, etc., which is not preferable. For this reason, it is desirable that the highly magnetically permeable conductive layer 214 is thicker than the skin depth of the magnetic shunt metal forming this layer. Specifically, the thickness of the high magnetic permeability conductive layer 214 is preferably 0.2 mm to 1 mm.

As the magnetic shunt material for forming the high magnetic permeability conductive layer 214, for example, an alloy of iron and nickel or an alloy of iron, nickel, and chromium is used. And the Curie temperature of a magnetic shunt material can be set to predetermined | prescribed temperature by adjusting the mixing | blending of each of these metals. In this embodiment, it is assumed that the Curie temperature of the magnetic shunt material forming the highly permeable conductive layer 214 is set to 210 ° C., which is close to the toner fixing temperature. Therefore, the high magnetic permeability conductive layer 214 exhibits characteristics as a ferromagnetic material when the temperature is 210 ° C. or lower, but exhibits characteristics as a non-magnetic material when the temperature exceeds 210 ° C. In this case, the specific resistance of the magnetic shunt material was 81.5 × 10 ⁻⁸ Ωm. The Curie temperature is not limited to 210 ° C., and may be set to other temperatures.

The nonmagnetic conductive layer 215 is made of, for example, a nonmagnetic material such as copper having a specific resistance of 1.68 × 10 ⁻⁸ Ωm. The outer peripheral surface of the highly permeable conductive layer 214 is plated, metalized, etc. The recording material of the maximum size that can be used (referred to as the maximum recording material in this embodiment, A3 size paper), the recording material on the direction line perpendicular to the running direction when the paper is passed through the apparatus The length [width] of the range through which the sheet passes through, also referred to as the maximum width or simply the width, “maximum recording material width” means the sheet passing width of the maximum recording material, and in this embodiment, the short side of the A3 size paper ) A layer having a thickness of, for example, 0.015 mm, processed over a slightly larger range of 320 mm.

The material of the nonmagnetic conductive layer 215 is preferably a material having a specific resistance of 7 × 10 ⁻⁸ Ωm or less, in addition to copper, aluminum having a specific resistance of 2.7 × 10 ⁻⁸ Ωm, 6.1 × It may be 10 ⁻⁸ Ωm zinc, 1.62 × 10 ⁻⁸ Ωm silver, 2.3 × 10 ⁻⁸ Ωm gold, or the like.

  The thickness of the nonmagnetic conductive layer 215 is preferably about 0.015 mm to 0.06 mm. The thickness of the nonmagnetic conductive layer 215 will be described in detail separately.

  The protective layer 216 is a nickel layer having a thickness of, for example, 2 μm formed on the outer peripheral surface of the nonmagnetic conductive layer 215 with a width equal to that of the nonmagnetic layer 215 by plating, metalizing, or the like. The protective layer 216 covers the surface of the nonmagnetic conductive layer 215, thereby preventing oxidation of the nonmagnetic conductive layer 215 and improving durability, and improving adhesion of the release layer 217 and preventing peeling.

  As the protective layer 216, a thin film having a thickness of about 3 μm using chromium, zinc, or the like may be formed instead of nickel. When the thickness of the protective layer 216 is 1 μm or less, the function as an anti-oxidation layer may be insufficient. On the other hand, when the thickness exceeds 10 μm, the heat capacity increases and it takes time to warm up. The applied power for maintaining the fixing temperature during passage increases, which is not preferable.

  The non-magnetic conductive layer 215 and the protective layer 216 are both formed with the same width, and it is necessary to mask them so that they are not formed at both ends of the highly permeable conductive layer 14 during the forming operation. . In this embodiment, since the formation width is the same, the masking can be used in common, the workability is improved, and the processing cost is reduced.

  The release layer 217 is made of, for example, a fluororesin such as PTFE, PFA, or FEP, and is formed on the outer surface of the protective layer 216 over the same range of 320 mm as the width of the nonmagnetic conductive layer 214. Is, for example, a 20 μm layer.

  Note that a silicone rubber layer may be provided between the protective layer 216 and the release layer 217 so that the heat generating roller 211 has elasticity. Further, it may be formed over a wider range than the nonmagnetic conductive layer 215.

  Referring to FIGS. 2 and 3 again, the pressure unit 220 supports the pressure roller 221 so that both ends of the pressure roller 221 can be rotated by bearings (not shown), and is pressed against the heat generating roller 211 by an urging unit (not shown). A nip through which the recording paper 109 passes is formed.

  The pressure roller 221 rotates around the central axis (clockwise in the figure) so as to convey the recording paper 109 in the direction of the arrow, following the rotation of the heat generating roller 211. Here, the pressure roller 221 is driven by the rotation of the heat generating roller 211, but the pressure roller 221 may be rotated to drive the heat generating roller 211.

  The pressure roller 221 includes an elastic layer 222 having a low thermal conductivity, such as silicone rubber having a hardness of 10 degrees, and a cored bar 223. The elastic layer has an outer diameter of 30 mm and a length of 315 mm. Thus, a predetermined nip is formed with a small urging force.

  In addition, as a material of the elastic layer 222, for example, a heat-resistant resin such as fluororubber and fluororesin, or other foamable resin such as rubber or sponge may be used alone or in a laminated manner. In addition, in order to improve wear resistance and releasability, it is desirable to coat the outer peripheral surface of the elastic layer 222 with a resin such as PTFE, PFA, or FEP or rubber alone or mixed.

  The length of the elastic layer is preferably larger than the maximum recording material width and equal to or smaller than the width of the nonmagnetic conductive layer 215.

  The excitation means 240 includes at least a power source (not shown) and an excitation coil unit 241. The excitation coil unit 241 is held by the insulating holding member 242 in a spiral manner so that the coil 243 is spirally wound and kept inside the heat generating roller 211 at a predetermined interval. Has been. The coil 243 is preferably a litz wire in which thin wires are bundled.

  The exciting coil unit 241 induction-heats the heating roller 211 when a high-frequency current is supplied from a power source (not shown). The exciting coil unit 241 is configured to be able to heat a range of 315 mm slightly narrower than the nonmagnetic conductive layer 215. In addition to the insulating holding member 242, a core member made of ferrite or the like that enhances the coupling of the magnetic circuit may be used for the exciting coil 241. Further, the Litz wire is wound from one end of the heat generating roller 211 to the other end with the magnetic flux extending over the entire circumference of the heat generating roller 211 as in the exciting coil 241 or in a state facing the inner surface of the heat generating roller 211. A configuration may be used, or a configuration in which the inner surface of the heat generating roller 211 is wound so as to face the range of about 180 degrees.

  The insulating holding member 242 holds the coil 243 and ensures insulation. In this embodiment, the insulating holding member 242 has a hollow shaft, and causes an air flow in the hollow during continuous operation. Thus, the heat generation of the coil 243 can be reduced. The shape of the insulating holding member 242 is not limited to a hollow shaft, and may be a shape that matches the shape of the coil 243 such as a solid shaft or an arc shape.

  The temperature sensor 230 is provided in contact with the outer peripheral surface of the heat generating roller 211 and detects the temperature of the heat generating roller 211. When the temperature of the heat generating roller 211 is detected by the temperature sensor 230, for example, a control unit (not shown) instructs the feeding roller 108 to start feeding the recording paper 109, or the AC current from the power source (not shown) to the exciting unit 240 is indicated. Supply is controlled. More specifically, when the temperature sensor 230 detects that the temperature of the heat generating roller 211 has reached a temperature suitable for fixing the toner image 111, an instruction to start the operation of the feeding roller 108 is given by a control unit (not shown). And printing is started. Further, when the temperature sensor 230 detects that the temperature of the heat generating roller 211 is higher than a predetermined threshold, the supply of alternating current from the power source (not shown) to the exciting coil unit 241 is controlled.

  Next, the operation of the fixing device configured as described above will be described.

  FIG. 5 is a diagram for explaining the induced current flowing in the heat generating roller, and shows that the induced current flows through the hatched portion in the drawing.

  First, the case where the temperature of the heat generating roller 211 is equal to or lower than the Curie temperature will be described.

  When the power of the image forming apparatus 100 is turned off or in the sleep state, the temperature of the heat generating roller 211 of the fixing apparatus 200 continues to drop to about room temperature, which is significantly lower than the Curie temperature of 210 ° C. in this embodiment. It has become. When the power is turned on to perform printing or when returning from the sleep state, the heating roller 211 is heated to a temperature suitable for fixing the toner image 111.

  That is, a voltage is applied to the excitation means 240 from a power source (not shown), and an alternating current flows. The frequency of this alternating current is desirably 20 to 100 kHz. In this embodiment, this frequency is set to 20 to 60 kHz. When an alternating current flows through the exciting coil 241, the magnetic flux generated by the exciting coil 241 is linked to the highly permeable conductive layer 214, and near the inner peripheral surface of the highly permeable conductive layer 214 due to the skin effect, FIG. ) Induces an induced current in the hatched portion, and the highly permeable conductive layer 214 generates heat due to Joule heat.

  When the entire heating roller 211 is heated to a fixing temperature suitable for fixing the toner image 111, the temperature of the heating roller 211 is detected by the temperature sensor 230 and stopped by the control circuit. Controlled to keep. In this embodiment, the fixing temperature is set to 180 ° C. (fixing setting temperature), and the power of about 1200 W is applied to the excitation means 240, so that the total width of the maximum recording material width (A3) is about 25. 5 seconds from 25 ° C. The temperature could be raised to the fixing temperature.

  Next, the operation when the recording material is continuously passed will be described.

  FIG. 6 shows the temperature distribution in the width direction of the heat generating roller when continuously passing through the recording paper 109 of different sizes at a speed of 440 mm per second (63 sheets per minute for A4 size paper and 42 sheets per minute for A3 size paper). It is a figure.

  When the maximum recording material width (A3 size in this embodiment) is continuously passed, the entire A3 width is maintained at substantially uniform 180 ° C. as indicated by the broken line in FIG. This is because the recording material contacts over the entire width of the heat generating roller 211 and heat is taken away from the entire passage width.

  On the other hand, when the small A4 portrait is continuously fed, the temperature distribution is as shown by the solid line in FIG.

  That is, the inside of the A4 vertical width where the recording paper 109 contacts is controlled to a constant temperature of 180 ° C., but the recording paper 109 does not touch the outside of the A4 width and heat is not taken away. Here, since the electric power by the excitation unit 240 is input in a range slightly wider than the recording material width, as a result, the temperature of the heat generating roller 211 rapidly increases outside the A4 vertical width and approaches the Curie temperature. Go.

However, when the temperature of the heat generating roller 211 approaches the Curie temperature, the magnetic permeability of that portion suddenly decreases and the magnetism is lost, and as a result, the magnetic flux generated by the exciting coil 241 penetrates the highly permeable conductive layer 214, It penetrates into the nonmagnetic conductive layer 215 formed on the outer peripheral surface. The portion indicated by hatching in FIG. 5B shows a portion where an induced current induced by the magnetic flux generated by the exciting coil 241 flows in this state, and FIG. 5B shows only the highly permeable conductive layer 214. In other words, the induced current flows also in the nonmagnetic conductive layer 215. Then, a repulsive magnetic field is generated in the direction in which the magnetic flux is canceled by the induced current, and the magnetic flux generated by the exciting coil 241 is greatly attenuated. As a result, the heat roller 211 has a specific resistance of the nonmagnetic conductive layer 215 of 1.68 × 10 ⁻⁸ Ω · m and a specific resistance of the high magnetic permeability conductive layer 214 of 81.5 × 10 ⁻⁸ Ω · m. Combined with the small size, the heat generation outside the A4 vertical width is greatly reduced, and there is no further temperature rise to prevent overheating.

  In the present embodiment, the continuous output of 63 sheets per minute can be suppressed to 205 ° C. as indicated by the solid line in FIG. 6, without increasing the interval of passing the recording material or limiting the number of sheets to be continuously passed. Continuous output is now possible.

  Here, in this embodiment, the nonmagnetic conductive layer 215 is formed in a range of 320 mm, which is larger than the maximum recording material width and larger than the heatable range 315 mm of the exciting coil unit 241, and the entire length of the elastic layer 222 of the pressure roller 221. Greater than 315 mm.

  Therefore, when the temperature of the portion of the heat generating roller 211 where the recording material does not pass rises and the magnetic flux exceeds the Curie temperature and passes through the highly permeable conductive layer 214, the region where the nonmagnetic conductive layer 215 is formed is heated. Since it is larger than the possible range, that is, the generation range of the magnetic flux, the nonmagnetic conductive layer 215 can reliably reduce the magnetic flux and suppress the excessive temperature rise. As a result, the end of the pressure roller 221 may be damaged at an abnormally high temperature. Absent. Further, since the elastic layer 222 of the pressure roller 221 is shorter than the nonmagnetic conductive layer 215, the end of the nonmagnetic conductive layer 215 may come into pressure contact with the elastic layer 222 of the pressure roller 221 and damage the elastic layer 222. Absent.

  In this embodiment, only the passage of the A4 vertical size recording material is shown. However, the size of the recording material is not limited to this, and this principle works at any size, and the excessive rise outside the recording material width automatically occurs. Needless to say, the temperature can be reduced.

  The temperature outside the recording material width is affected by the speed of continuous passage, the recording material passage interval, and the thickness of the recording material. This is because the electric power supplied to the entire exciting coil 241 greatly depends on these conditions. However, in most cases, an excessive temperature rise can be suppressed below the Curie temperature, and a highly reliable fixing device can be realized without causing a decrease in the life of the rubber material and damage to the bearing.

  Next, the relationship between the magnetic characteristics of the heat generating roller 211 used in this embodiment, the warm-up time, and the excessive temperature rise when a narrow recording material is continuously passed will be described in detail.

  FIG. 7 shows the temperature characteristics of the relative permeability immediately after the processing of the heat generating roller 211 made of the magnetic shunt material used in this embodiment. In addition, the temperature characteristic of a relative magnetic permeability shows the measured value on the conditions of 45 A / m and a 30 kHz alternating current magnetic field.

  The heating roller 211 is formed by bending and welding a magnetic shunt material made of a plate material having a thickness of about 1 mm into a roll shape, processing the end portion into a cup shape, thinning it by spinning, and having a diameter of 40 mm, a thickness of 0.6 mm, and a length. The roller shape is 385 mm. Of course, the processing method is not limited to this, but it is made into a thin cylindrical body by bending it into a roll and making the tube thin by welding after ironing, or by primary finishing by drawing and finishing by machining. There are ways to do it. In any case, when a thin tube material is used, the magnetic properties of the magnetic shunt material are greatly changed by applying plastic working to the magnetic shunt material and applying a strong mechanical stress.

  FIG. 7 shows the characteristics immediately after the spinning process, and the relative magnetic permeability starts to decrease from around 168 ° C. indicated by Ts and becomes almost non-magnetic at the Curie temperature Tc = 222 ° C. The value Th at which the relative permeability is halved was 204 ° C. Ts means a temperature at which the relative permeability of the magnetic shunt material starts to decrease.

  Next, FIG. 8 shows the characteristics of the heat-generating roller 210 immediately after the processing, which is annealed by holding it at 800 ° C. for 1 hour in an inert gas atmosphere such as nitrogen gas and then gradually cooling it to 200 ° C. or less. It is the heat generating roller 211 of the invention. As can be seen from comparison with FIG. 7, the change in the magnetic permeability becomes sharp after annealing, and the half value Th is 205 ° C., which is almost the same as that before the annealing, but the Curie temperature Tc is 210 ° C., and the relative permeability starts to decrease. The temperature Ts was 195 ° C.

  Here, the nonmagnetic conductive layer 215 is formed after the main annealing treatment, and then the protective layer 216 and the release layer 217 are formed.

  FIG. 9 shows a comparison of warm-up time when the heat generating roller 211 before and after the annealing treatment is used. In FIG. 9, the warm-up time when the heat generating roller 211 after annealing of the present invention is used is shown by a solid line, and the case where the heat generating roller 211 before annealing is used is shown by a broken line. As described above, the heating roller 211 of the present invention indicated by the solid line reaches 180 ° C. in 24.5 seconds, but the heating roller 211 before the annealing treatment indicated by the broken line has a gentle rise in temperature from around 160 ° C. It took about 32 seconds to reach ℃. This is because the Ts (168 ° C.) is lower than the fixing set temperature (180 ° C.) in the heat generating roller 211 before annealing, and a change in magnetic characteristics appears at an early stage around 168 ° C. Under this condition, the magnetic flux penetrating through the highly permeable conductive layer 214 starts to increase from an early stage, the magnetic field penetrates into the nonmagnetic conductive layer 215, and the magnetic flux density decreases due to the repulsive magnetic field caused by the induced current flowing. It is considered that the magnetic coupling between the magnetic conductive layer and the excitation means is weakened and the heat generation efficiency is lowered.

  Next, as a result of continuously passing the A4 vertical size recording material using both of these, when the heat generating roller 211 after the annealing treatment is used under the same conditions, the excessive temperature rise outside the recording material paper width is 205 ° C. or less. However, when the heating roller 211 before the annealing treatment was used, the temperature rose to near 230 ° C. This is because the temperature control in the recording material passage region is 180 ° C., and at this time, the ratio of the magnetic flux penetrating all over the heat generating roller 210 has already increased, and the heat generation efficiency in the portion corresponding to the A4 vertical width is reduced. It is considered that the electric power required for temperature control has increased and the difference in magnetic coupling between the paper passing portion and the non-paper passing portion has become difficult to attach.

  From the above, it is desirable to set the temperature Ts at which the relative permeability starts to decrease as high as possible than the fixing set temperature. However, if the Curie temperature is set to be high according to this, an excessive temperature rise outside the recording material width will occur. Too high and not preferable. The Curie temperature is desirably as low as possible at 220 ° C. or lower in consideration of the heat resistant temperature of the silicone rubber material used for the pressure roller 221.

  The inventors continuously pass the recording material in the A4 vertical direction and the A4 horizontal direction with the heat generating roller 211 with the thickness of the nonmagnetic conductive layer 214 changed, and increase the temperature distribution and fixing temperature in the axial direction of the heat generating roller 211. A comparative study of warm-up time until heating and average applied power was performed.

  Here, FIG. 10 shows the axial temperature distribution of the heat generating roller 211 when the thickness of the nonmagnetic conductive layer 215 is changed and 500 continuous A4 recording materials are continuously passed, and FIG. Similarly, when the thickness of the nonmagnetic conductive layer 215 is changed, the warm-up time until the temperature is raised to 180 ° C. is shown. FIG. 12 shows that 500 sheets of recording material in the A4 horizontal direction and A4 vertical direction are passed continuously. The average applied power is shown.

  As can be seen from FIG. 10, when the nonmagnetic conductive layer 215 is not present, the temperature of the recording material non-passing portion exceeds 240 ° C., but the thickness of the nonmagnetic conductive layer 215 is 0.015 mm to 0.08 mm. Is almost saturated at 205 ° C. The present inventors conducted experiments on the thickness of the nonmagnetic conductive layer 215 of 0.08 mm, 0.03 mm, and 0.015 mm, and the temperatures of the non-passing portions were all saturated at around 205 ° C. The thickness of 0.015 mm has been found to have a great effect in suppressing excessive temperature rise in the non-passing portion.

  In general, the nonmagnetic conductive layer 215 is considered to be difficult to generate heat due to electromagnetic induction, but it is known that when the thickness thereof is set to an appropriate thickness, the resistance increases and heat is generated. Further, when the magnetic flux is limited or shielded by the nonmagnetic conductive layer 215 as in the present embodiment, the nonmagnetic conductive layer 215 generates heat if the thickness is not a certain thickness, and the recording material non-passing portion. It has been said that there are problems such as that the temperature of the exciting coil 241 becomes too high, or that the temperature in the vicinity of the exciting coil 241 becomes too high and the insulating property of the insulating layer of the exciting coil 241 is impaired.

  In the present embodiment, the present inventors have found that if the thickness of the nonmagnetic conductive layer 215 is 0.015 mm, the temperature rise in the non-passing portion of the recording material does not occur. The thinner the non-magnetic conductive layer 215, the greater the resistance and the easier it is to generate heat. However, the non-magnetic conductive layer 215 is in close contact with the highly permeable conductive layer 214, and heat is transferred to the highly permeable conductive layer 214 to some extent. It is inferred that it is balanced with the heat generated by the electric power released and applied inside.

  As shown in FIG. 11, the relationship between the thickness of the nonmagnetic conductive layer 215 and the time required for temperature rise is such that the temperature rise time increases as the thickness of the nonmagnetic conductive layer 215 increases, and the thickness of the nonmagnetic conductive layer 215 is 0. In the case of 0.06 mm, it is about 1.5 seconds longer than in the case where the nonmagnetic conductive layer 214 is not provided. However, the temperature is raised from room temperature to the fixing temperature in about 25.5 seconds, and the effect on practical use is increased. Is insignificant.

  FIG. 12 shows the relationship between the average applied power and the thickness of the nonmagnetic conductive layer when 500 recording materials are passed continuously.

  In FIG. 12, the broken line indicates the relationship between the average applied power and the thickness of the nonmagnetic conductive layer when the A4 paper is passed in the A4 horizontal direction, and the solid line indicates the thickness of the nonmagnetic conductive layer 215 when the A4 paper is passed in the horizontal direction. When the thickness is 0.03 mm, it is increased by about 9 W compared to the case without the nonmagnetic conductive layer 215. When the thickness of the nonmagnetic conductive layer 215 is 0.06 mm, the thickness is about 20 W and 0.08 mm. Increased by about 27.6W. Further, the average applied power in the case of A4 lengthwise paper passing is reduced by about 31 W when the thickness of the nonmagnetic conductive layer 215 is 0.03 mm as compared with the case where the nonmagnetic conductive layer 215 is not provided. When the thickness of the nonmagnetic conductive layer 215 is 0.06 mm, it is almost the same as the case without the nonmagnetic conductive layer. When the thickness of the nonmagnetic conductive layer 215 is 0.08 mm, the nonmagnetic conductive layer 215 is not present. Compared to In the case of the A4 horizontal direction, the heat capacity increases by the thickness of the nonmagnetic conductive layer 215 and the power to maintain the temperature increases. In the case of the A4 vertical direction, when the nonmagnetic conductive layer 215 is not present, This is probably because the recording material non-passing portion has a temperature exceeding 240 ° C., and electric power is consumed for the temperature increase. When the thickness of the nonmagnetic conductive layer 215 is 0.03 mm, the heat capacity is increased, but the temperature of the non-passing portion of the recording material is balanced at 205 ° C., and as a result, the power is estimated to be reduced. Is done. Further, when the thickness of the nonmagnetic conductive layer 215 is 0.08 mm, the influence of the load increase due to the increase in the heat capacity exceeds the amount that the recording material non-passing portion is balanced at 205 ° C. to reduce the power. Is estimated to have increased.

  By setting the thickness of the nonmagnetic conductive layer 215 to 0.015 mm to 0.060 mm, when passing a small-sized recording material, the heat generating roller can be heated to the fixing temperature with the same or less power than when the nonmagnetic conductive layer 215 is not provided. Can be maintained, and overheating of the area where a small-sized recording material does not pass can be prevented. If the thickness of the nonmagnetic conductive layer 215 is greater than 0.06 mm, excessive temperature rise in the non-passing portion can be prevented, but the applied power increases.

  In the present embodiment, the recording materials in the A4 horizontal direction and the A4 vertical direction have been described. However, although there is a difference in the increase / decrease amount of the applied power for other recording materials, it goes without saying that the same tendency is observed.

  Next, FIG. 13 shows the axial temperature distribution of the heat generating roller 211 at the time of A4 horizontal continuous passage, and the solid line is the case where the thickness of the nonmagnetic conductive layer 214 is 0.03 mm and the length is 320 mm. A broken line indicates a temperature distribution when the heat-generating roller 211 of the high magnetic permeability conductive layer 214 is formed over the entire length. As can be seen from FIG. 13, when the non-magnetic conductive layer 214 is formed over the entire length of the heat generating roller 210, the temperature at both ends is lowered and is in a range of 320 mm, which is slightly larger than the width of the maximum recording material that passes. When the nonmagnetic conductive layer 214 is formed, a uniform temperature distribution is shown over almost the entire width of the recording material.

  The heating roller 211 is made of a magnetic shunt metal whose Curie temperature is adjusted to 210 ° C., and its thermal conductivity is as small as 13 W / m · K, and the thermal conductivity of copper formed as the nonmagnetic conductive layer 215. Is as high as 398 W / m · K. When the nonmagnetic conductive layer 215 is formed over the entire length, heat moves through the nonmagnetic conductive layer 215 toward both ends of the heat generation roller 211 other than the heat generation portion by the excitation coil 241, and through the bearing 213 or the like. Heat flows out and temperature unevenness occurs at both ends within the recording material width. When the nonmagnetic conductive layer 215 is formed in the range of 320 mm, the heat is transferred only through the magnetic shunt material having a low thermal conductivity outside the range of the nonmagnetic conductive layer 215, and the heat outflow from the end is extremely small. The temperature became smaller and temperature unevenness did not occur.

  If the width of the nonmagnetic conductive layer 215 is formed to be equal to the width of the maximum recording material, if there is a change in the passing position of the recording material or a fluctuation in the magnetic field generation width due to the exciting coil 241 at the end of the recording material equivalent width, The magnetic conductive layer 215 cannot be reduced, and temperature unevenness may occur. The width of the nonmagnetic conductive layer 215 is preferably slightly larger than the maximum recording material.

  When the nonmagnetic conductive layer 215 is formed over the entire width of the heat generating roller 211, it is possible to adjust the magnetic flux distribution generated by the exciting coil 241 so that there is no temperature unevenness. In this case, the nonmagnetic conductive layer 215 is recorded at the maximum. Compared with the case where it is formed slightly larger than the material width, the applied power increases.

  Further, temperature unevenness due to variations in the magnetic field generated by the exciting coil 241 can be reduced by forming the nonmagnetic conductive layer 214 having a high thermal conductivity.

  Needless to say, in the range where the nonmagnetic conductive layer 214 is formed, even if the magnetic flux generated by the exciting coil 241 is uneven, the temperature unevenness is reduced by its high thermal conductivity.

  The case where copper is used for the nonmagnetic conductive layer 214 has been described, but is not limited to copper, aluminum having a thermal conductivity of 237 W / m · K, zinc having 114.3 W / m · K, 87. The same effect can be obtained with nickel of 9 W / m · K, gold of 294 W / m · K, silver of 418 W / m · K, and the like. In each metal, the specific resistance and the thermal conductivity are different, and the thickness at which the above-described effect is obtained is different. In the experiments of the present inventors, the same effect is obtained in the case of 0.015 mm to 0.060 mm in the case of copper, 0.025 mm to 0.060 mm in the case of aluminum, and 0.055 mm to 0.060 m in the case of zinc. Was found to be obtained.

  As described above, a thin film of the nonmagnetic conductive layer 215 is formed in a slightly wider range than the maximum recording material on the heat generating roller 211 made of the high magnetic permeability conductive layer 214 made of a magnetic shunt material whose Curie temperature is set to a predetermined temperature. By doing so, it is possible to quickly start up, while preventing excessive temperature rise outside the width of the recording material, preventing temperature unevenness and preventing heat from flowing out to the end, and reducing applied power.

  Further, the exciting means 240 is disposed inside the heat generating roller 211, and it is easy to dispose a cleaning means for removing toner remaining on the surface of the heat generating roller 211 and a recording material separating means, and the fixing can be reduced in size. A device can be realized.

(Example 2)
A feature of the second embodiment of the present invention is that an exciting means 240 is disposed outside the heat generating roller 211, and a nonmagnetic conductive layer 215 is formed on the inner surface of a highly magnetically conductive layer 214 made of a magnetic shunt material having a set Curie temperature. The heat generation prevention of the excitation means 240 and the maintainability of the heat generation roller 211 are improved.

  Since the schematic configuration of the image forming apparatus according to the present embodiment is the same as that of the first embodiment (FIG.), The description thereof is omitted. In this embodiment, only the configuration of the fixing device is different from that of the first embodiment.

  14 and 15 are cross-sectional model views showing the configuration of the fixing device according to this embodiment. In these drawings, the same parts as those of the fixing device according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The heat generating roller 211 is a cylindrical roller having a diameter of 34 mm, for example, and rotates around the central axis (counterclockwise in the drawing) so as to convey the recording material 109 on which the toner image is formed and supported in the direction of the arrow.

  The heat generating roller 211 is mainly formed by laminating a highly permeable conductive layer 214 and a nonmagnetic conductive layer 215. The nonmagnetic conductive layer 215 is formed on the inner surface of the roller formed of the highly permeable conductive layer 214. This is different from the first embodiment.

  The highly permeable conductive layer 214 is made of a magnetic shunt metal having a Curie temperature set at 210 ° C., and is formed into a hollow cylindrical shape having a diameter of 34 mm, a wall thickness of 0.3 mm, and a total length of 385 mm.

  The nonmagnetic conductor 215 is made of copper having a thickness of, for example, 0.03 mm, and is formed on the inner surface of a hollow cylinder made of the highly permeable conductive layer 214 by plating. The width is formed over a range of 320 mm which is slightly wider than the maximum recording material.

  The protective layer 216 is made of, for example, nickel having a thickness of 3 μm, and is formed on the surface of the nonmagnetic conductive layer 215 (in this case, the inner surface side) over the same range as the nonmagnetic conductive layer 215.

  The exciting means 240 includes at least an exciting coil unit 241 disposed outside the heat generating roller 211 and a power source (not shown).

  The exciting coil unit 241 includes a coil 243 and a core member 244. The exciting coil unit 241 is formed by turning a litz wire around a half circumference of the heat generating roller 211. When an alternating current flows from a power source (not shown), a magnetic field is generated around it. generate.

  The core member 244 is formed of a magnetic material having a high magnetic permeability and specific resistance, such as ferrite and permalloy, and is disposed so as to cover the coil 243. The core member 244 serves as a path for magnetic flux generated on the opposite side of the heat generating roller 211 from the magnetic flux generated by the coil 243.

  The magnetic field generated by the exciting coil unit 241 is configured to be generated over a range of 315 mm slightly narrower than the width of the nonmagnetic conductive layer 214.

  In addition, since the exciting coil unit 241 according to the present embodiment excites the heat generating roller 211 from the outside of the heat generating roller 211, the work efficiency of replacement and maintenance of parts such as the heat generating roller 211 which is a consumable item is good.

  Next, the heat generation principle of the fixing device configured as described above will be described.

  Also in this embodiment, when the temperature of the heat generating roller 211 is equal to or lower than the Curie temperature, a magnetic flux is generated around the exciting coil unit 241 by an alternating current flowing through the exciting means 240. The generated magnetic flux interlinks with the highly permeable conductive layer 214, induces an induced current on the surface of the highly permeable conductive layer 214 by the skin effect, and causes the surface of the highly permeable conductive layer 213 to generate heat by Joule heat.

  On the other hand, when the temperature of the heat generating roller 211 rises and exceeds the Curie temperature, the highly permeable conductive layer 214 becomes nonmagnetic and the magnetic flux penetrates this layer. The magnetic flux penetrating the highly permeable conductive layer 214 penetrates into the nonmagnetic conductive layer 215, induces an induced current, and this induced current acts in a direction to cancel the magnetic flux to generate a repulsive magnetic field. As a result, the exciting coil The magnetic flux by 241 is greatly attenuated, the magnetic flux density is lowered, and the heat generation amount is lowered. Therefore, even if a recording material having a size smaller than the maximum recording material width is passed, the non-passing portion does not become abnormally high. The nonmagnetic conductive layer 215 is formed slightly wider than the maximum recording material width, and the magnetic flux generation width by the induction coil unit 241 is wider than the maximum recording material width and slightly narrower than the nonmagnetic conductive layer 215. Since the thermal conductivity of the magnetic conductive layer 215 is large, temperature unevenness within the maximum recording material width is reduced. On the other hand, due to the low thermal conductivity of the magnetic shunt material which is the highly magnetically permeable conductive layer 214, the heat outflow to the end portion is reduced. Since it becomes a little and a range slightly wider than the maximum recording material width can be efficiently heated, the applied power can be further reduced.

(Example 3)
The feature of the third embodiment of the present invention is that the exciting means 240 disposed inside, the heat generating means 250 fixed in place of the heat generating roller 211, and the heat generating means 250 are pressed with the fixing belt 260 interposed therebetween to form a nip. In the belt-type fixing device having the pressure unit 220, it is intended to prevent excessive temperature rise of the non-passing portion when passing through a narrow recording material and to reduce applied power.

  Since the schematic configuration of the image forming apparatus according to the present embodiment is the same as that of the first embodiment (FIG. 1), description thereof is omitted. In this embodiment, only the configuration of the fixing device is different from that of the first embodiment.

  FIG. 16 is a cross-sectional view illustrating a configuration of the fixing device according to the present exemplary embodiment. In this figure, the same parts as those of the fixing device according to the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The heat generating means 250 is formed in at least an arc shape, and includes a heat generating plate 251 that contacts the fixing belt and transfers heat. The heat generating plate 251 is formed so as to be capable of contacting with a length of about one third of the entire circumference of the fixing belt 260. The heat generating plate 251 includes a highly magnetic conductive layer 252 made of a magnetic shunt material having a set Curie temperature, and a nonmagnetic conductive layer formed on the side (in this case, the outer side) facing the coil across the high magnetic permeability conductive layer 252. Layer 253 is formed. The thickness of the high magnetic permeability conductive layer 252 is formed to, for example, 0.6 mm. The nonmagnetic conductive layer 253 is, for example, formed of aluminum having a thickness of 0.03 mm in a range of 320 mm that is slightly larger than the maximum recording material width, and is fixed at a predetermined position.

  A protective layer 254 made of nickel is formed outside the nonmagnetic conductive layer 253. The protective layer 254 prevents oxidation of the nonmagnetic conductive layer 253, prevents wear of the heat generating means 250 due to contact with the belt, reduces the friction coefficient, and prevents belt meandering and deviation. Instead of nickel, chromium, zinc, or a fluorine resin may be used alone or laminated.

  The fixing belt 260 is guided by the heat generating means 250 and the guide member 270, forms a nip at the pressure contact portion between the heat generating means 250 and the pressure means 220, and the rotation is transmitted by the pressure means 220. The fixing belt 260 is made of a heat-resistant polyimide resin having a diameter of 45 mm and a thickness of 80 μm, and a release layer made of a silicone rubber layer having a thickness of 150 μm and a fluororesin having a thickness of 30 μm is coated on the surface of the substrate. Is formed. The dimensions and material of the fixing belt 260 are not limited to the above, and as the base material, a fluororesin or a PPS resin may be used in addition to the polyimide resin, or a thin metal may be used. Moreover, you may use resin and rubber | gum with favorable mold release characteristics, such as PTFE, PFA, FEP, and fluororubber, individually or in mixture as a release layer.

  The exciting means 240 includes at least an exciting coil unit 241 disposed inside the fixing belt 260 and a power source (not shown). The exciting coil unit 241 includes a coil 243 and a core member 244. The exciting coil unit 241 is formed by rotating a litz wire around one part of about three parts of the fixing belt 260, and is held at a predetermined interval from the heat generating plate 251. When an alternating current flows from a power source (not shown), a magnetic flux is generated around and a magnetic field is formed. The core member 244 is formed of a magnetic material having a high magnetic permeability and specific resistance, such as ferrite or permalloy, and has a substantially T shape so as to face the coil 243. The core member 244 serves as a path for magnetic flux generated on the opposite side of the heat generating means 250 among the magnetic flux generated by the coil 243.

  Next, the operation of the fixing device configured as described above will be described.

  Also in this embodiment, when the heat generating means 250 is below the Curie temperature, a magnetic flux is generated around the exciting coil unit 241 by the alternating current flowing through the exciting means 240. The generated magnetic flux interlinks with the highly permeable conductive layer 252 of the heat generating plate 251 and generates heat near the surface of the highly permeable conductive layer 252 facing the exciting coil unit 241 by the skin effect. The heat generated in the heat generating means 250 is transmitted to the nip portion with the pressure means 220 via the fixing belt 260.

  On the other hand, when a narrow recording material is continuously passed, the temperature of the non-passing portion of the recording material rises and exceeds the Curie temperature. In that case, the highly permeable conductive layer 252 of the heat generating plate 250 becomes nonmagnetic and the magnetic flux penetrates this layer. The magnetic flux penetrating through the highly permeable conductive layer 252 penetrates into the non-magnetic conductive layer 253, induces an induced current, and this induced current acts in a direction to cancel the magnetic flux to generate a repulsive magnetic field. As a result, the magnetic flux density Decreases and the calorific value decreases. Therefore, even if a recording material having a size smaller than the full width is passed, the non-passing portion does not become abnormally hot. In addition, the nonmagnetic conductive layer is formed slightly wider than the maximum recording material width, heat does not flow to the end through the nonmagnetic conductive layer, there is no temperature unevenness, and applied power can be reduced. In this embodiment, the heat capacity of the heat generating plate is small, so that the warm-up time can be shortened and the applied power can be reduced.

Example 4
The fourth embodiment of the present invention is different from the third embodiment in that the exciting unit 240 is disposed outside, and the pressure roller 221 presses the fixing belt 260 against the fixing roller 280 to form a nip. In the fixing device of the belt type that transmits the heat generated by the heat generating means 250 and the heat generated by the heat generating means 250 to the contact portion with the pressurizing means 220 by the fixing belt 260, the non-passing portion when passing through the small size recording material. It is intended to prevent excessive temperature rise and reduce applied power.

  Since the schematic configuration of the image forming apparatus according to the present embodiment is the same as that of the first embodiment (FIG. 1), description thereof is omitted. In this embodiment, only the configuration of the fixing device is different from that of the first embodiment.

  FIG. 17 is a cross-sectional view illustrating the configuration of the fixing device according to the present exemplary embodiment. In these drawings, the same parts as those of the fixing device according to the third embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The fixing belt 260 is an endless belt stretched between the heat generating unit 250 and the fixing roller 280, and transfers heat generated by the heat generating unit 250 to a nip portion formed by the fixing roller 280 and the pressure unit 220.

  The fixing roller 280 is a cylindrical roller having a diameter of, for example, 30 mm. The fixing roller 280 is in pressure contact with the pressing unit 220 via the fixing belt 260 to form a nip portion through which the recording material passes. Then, the fixing roller 280 rotates around the central axis so as to convey the recording material following the transfer of the fixing belt 260 by the rotation of the pressure unit 220. The fixing roller 280 is formed of a material having low thermal conductivity such as silicone rubber having a hardness of JIS-A 10 degrees. The fixing roller 280 may be made of foamed silicone rubber.

  The heat generating means 250 has at least a heat generating plate 251 formed in, for example, an arc shape, and the heat generating plate 251 has a high magnetic permeability conductive layer 252 made of a magnetic shunt material having a set Curie temperature, and a high magnetic permeability conductive layer 252. Is formed of a nonmagnetic layer 253 formed on the side facing the exciting coil unit 241 (in this case, inside), and is held at a predetermined position. The thickness of the highly permeable conductive layer 252 is, for example, 0.6 mm. The nonmagnetic conductive layer 253 is formed, for example, in a range of 320 mm in which aluminum having a thickness of 30 μm is slightly larger than the maximum recording material width.

  A protective layer 254 made of nickel is formed outside the nonmagnetic conductive layer 253, and this protective layer is the same as the protective layer 216 according to the 254 embodiment 1.

  The exciting means 240 includes at least an exciting coil unit 241 disposed outside the fixing belt 260 and a power source (not shown). The exciting coil unit 241 includes a coil 243 and a core member 244. The exciting coil unit 241 is formed by rotating a litz wire in a range of approximately 160 degrees of the heat generating means 250. When an alternating current flows from a power source (not shown), Generate a magnetic field. The core member 244 is formed of a magnetic material having high magnetic permeability and specific resistance, such as ferrite and permalloy, and is disposed so as to cover the coil 243. The core member 244 serves as a path for magnetic flux generated on the opposite side of the heat generating means 250 among the magnetic flux generated by the coil 243.

  In addition, since the exciting coil unit 241 according to the present embodiment excites the heat generating plate 251 from the outside of the fixing belt 260, the work efficiency of replacement and maintenance of parts such as the fixing belt 260 which is a consumable item is good. In the configuration according to this embodiment, the heat generating portion and the nip portion are separated from each other, and each can be optimally set.

  Next, the operation of the fixing device configured as described above will be described.

  Also in this embodiment, when the heat generating means is below the Curie temperature, an alternating current flows through the exciting means 240, thereby generating a magnetic flux around the exciting coil unit 241. The generated magnetic flux generates heat near the surface of the highly permeable conductive layer 252 that constitutes the heat generating plate 251 facing the exciting coil unit 241 by the skin effect. The heat generated in the heat generating means 250 is transmitted to the nip portion with the pressure means 220 via the fixing belt 260.

  On the other hand, when a small-sized recording material is continuously passed, the temperature of the non-passing portion of the recording material rises and exceeds the Curie temperature. In that case, the highly permeable conductive layer 252 becomes non-magnetic and magnetic flux penetrates this layer. The magnetic flux penetrating the highly permeable conductive layer 252 penetrates into the nonmagnetic conductor 253 and induces an induced current. This induced current acts in the direction of canceling the magnetic flux and generates a repulsive magnetic field. Decreases and heat generation decreases. Therefore, even if a recording material having a size smaller than the full width is passed, the non-passing portion does not become abnormally hot. Further, the nonmagnetic conductive layer 253 is formed slightly wider than the maximum recording material width, and heat flow to the end through the nonmagnetic conductive layer 253 is negligible, there is no temperature unevenness, and applied power can be reduced. In this embodiment, the heat capacity of the heat generating plate is small, so that the warm-up time can be shortened and the applied power can be reduced.

(Example 5)
The feature of the fifth embodiment of the present invention is that the thickness of the heat generating layer of the heat generating roller 211 is reduced and the heat generating layer is supported by the shaft and the heat insulating support layer. It is intended to prevent excessive temperature rise of the non-passing portion when passing through the recording material and to reduce applied power.

  Since the schematic configuration of the image forming apparatus according to the present embodiment is the same as that of the first embodiment (FIG. 1), description thereof is omitted. In this embodiment, only the configuration of the fixing device is different from that of the first embodiment.

  18 and 19 are cross-sectional views showing the configuration of the fixing device according to this embodiment. In these drawings, the same portions as those of the fixing device according to the second embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The heat generating unit 210 includes a shaft 262 rotatably supported in order from the inside, a heat insulating support layer 263, and a heat generating roller 270 provided with the heat generating layer 261, and the generated heat is formed by pressure contact of the pressure unit 220. Transmit to the nip.

  The heat generating layer 261 includes a high magnetic permeability conductive layer 264 made of a magnetic shunt material having at least a Curie temperature, a nonmagnetic conductive layer 265, a protective layer 266, and a release layer 267. The high magnetic permeability conductive layer 264 is formed into a thin cylindrical shape having a diameter of 34 mm and a thickness of 0.2 mm, for example.

  The nonmagnetic conductive layer 265 is formed by plating copper on the inner surface of the high magnetic permeability conductive layer 264 over a range of 320 mm with a thickness of 0.015 mm.

  The protective layer 266 is formed on the inner surface of the nonmagnetic conductive layer 265 over a range of 320 mm.

  The release layer 276 is formed over the entire width of the outer peripheral surface of the highly permeable conductive layer 264. Further, an elastic layer such as silicone rubber may be provided between the high magnetic permeability conductive layer 264 and the release layer 276.

  The heat insulating support layer 263 is made of silicone sponge and is disposed between the shaft 262 and the heat generating layer 261, and supports the heat generating layer 261 so that the heat generating layer 261 does not bend and break when pressed by the pressurizing means 220, thereby forming a wide nip. I am letting. The heat insulating support layer 263 is not limited to a silicone sponge, and may be a resin such as fluoro rubber.

  Next, the operation of the fixing device configured as described above will be described.

  Also in the present embodiment, when the heat generating means 210 is at or below the Curie temperature, an alternating current flows through the exciting means 240, thereby generating a magnetic flux around the exciting coil unit 241. The generated magnetic flux generates heat in the vicinity of the surface of the heat generating layer 261 facing the coil of the highly permeable conductive layer 264 by the skin effect.

  On the other hand, when a narrow recording material is continuously passed, the temperature of the passing portion of the recording material rises and exceeds the Curie temperature. In that case, the highly permeable conductive layer 264 becomes non-magnetic and magnetic flux penetrates this layer. The magnetic flux penetrating through the highly permeable conductive layer 264 penetrates the non-magnetic conductive layer 265 to induce an induced current, and this induced current acts in a direction to cancel the magnetic flux to generate a repulsive magnetic field. Decreases and heat generation decreases. Therefore, even if a recording material having a size smaller than the full width is passed, the non-passing portion does not become abnormally hot. Further, the nonmagnetic conductive layer 265 is formed slightly wider than the maximum recording material width, so that heat does not flow to the end portion through the nonmagnetic conductive layer, there is no temperature unevenness, and a reduction in applied power can be realized.

  Further, since the heat generating means 210 holds the thin heat generating roller 211 with the shaft 262 and the heat insulating support layer 262 and rotates integrally, it is possible to form a wide nip with a small pressing force of the pressurizing means 220. Reduction of friction load can be realized.

  As described above, the fixing device according to the present invention can realize a rapid start-up at the time of warm-up and can simultaneously suppress the excessive temperature rise outside the paper width during continuous paper feeding, It can effectively prevent damage to the bearing member, reduce temperature unevenness, reduce applied power, and is useful for fixing devices that heat and fix unfixed images on recording materials by electromagnetic induction heating. It is.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a cross-sectional model diagram illustrating the configuration of the fixing device according to the first exemplary embodiment of the present invention. FIG. 3 is a longitudinal cross-sectional model diagram showing the configuration of the fixing device in Embodiment 1 of the present invention. 1 is a partial cross-sectional view showing a detailed configuration of a heat generating roller in Embodiment 1 of the present invention. Explanatory drawing of the induced current which flows in the heat-generating roller in Example 1 of this invention FIG. 3 is a temperature distribution diagram of the heat generating roller during continuous paper feeding in Embodiment 1 of the present invention. Temperature characteristic diagram of relative permeability before annealing treatment of magnetic shunt material in Example 1 of the present invention Temperature characteristic diagram of relative permeability of magnetic shunt material in Example 1 of the present invention The figure which showed the temperature rising characteristic of the heat-generating roller at the time of warm-up in Example 1 of this invention FIG. 3 is a temperature distribution diagram of the heat generating roller during continuous A4 vertical paper feeding in Embodiment 1 of the present invention. The figure which showed the relationship between the thickness of the nonmagnetic conductive layer in Example 1 of this invention, and warm-up time The figure which showed the relationship between the electric power at the time of continuous paper_feeding in Example 1 of this invention, and a nonmagnetic conductive layer FIG. 6 is a temperature distribution diagram of the heat generating roller during continuous paper feeding when the width of the nonmagnetic conductive layer in Example 1 of the present invention is changed. Cross-sectional model diagram showing the configuration of the fixing device in Embodiment 2 of the present invention FIG. 6 is a longitudinal cross-sectional model diagram showing a configuration of a fixing device in Embodiment 2 of the present invention. Cross-sectional model diagram showing the configuration of the fixing device in Example 3 of the present invention Cross-sectional model diagram showing the configuration of the fixing device in Example 4 of the present invention Cross-sectional model diagram showing the configuration of the fixing device in Example 5 of the present invention FIG. 10 is a longitudinal cross-sectional model view showing a configuration of a fixing device in Embodiment 5 of the present invention. Cross-sectional model of the main part showing a conventional heat fixing device The figure which shows the structure of the heating roller of the conventional fixing device Sectional view showing the configuration of a conventional image fixing unit

Explanation of symbols

200 Fixing device
210 Heating means 211, 270 Heating roller 214 Highly permeable conductive layer 215 Nonmagnetic conductive layer 220 Pressure means 221 Pressure roller 230 Temperature sensor 240 Excitation means 241 Excitation coil unit 251 Heating plate 260 Fixing belt

Claims (23)

A fixing device that heats and presses a recording material on which an image is formed with a color material and fixes the color material on the recording material,
Excitation means for forming a magnetic field;
At least part of the heat generation means that is in the magnetic field formed by the excitation means and generates heat by penetrating the magnetic field lines of the magnetic field;
A pressure means for bringing the recording material and the heat generating means into contact with each other and applying a pressure therebetween, and
The heat generating means has a magnetically permeable conductive layer and a nonmagnetic conductive layer,
Here, the magnetically permeable conductive layer is made of a magnetic shunt material that has magnetism at room temperature but loses magnetism when a predetermined temperature or higher is reached.
The permeable conductive layer and the non-magnetic conductive layer have a length of the permeable conductive layer in at least one direction on the surface on which the image of the recording material to be fixed by the apparatus is formed. The fixing device is formed longer than the length of the recording material, and the length of the nonmagnetic conductive layer is longer than the length of the recording material and shorter than the length of the magnetically permeable conductive layer. . A fixing device that heats and presses a recording material on which an image is formed with a color material and fixes the color material on the recording material,
Excitation means for forming a magnetic field;
At least part of the heat generation means that is in the magnetic field formed by the excitation means and generates heat by penetrating the magnetic field lines of the magnetic field;
A pressure means for bringing the recording material and the heat generating means into contact with each other and applying a pressure therebetween, and
The heat generating means has a magnetically permeable conductive layer and a nonmagnetic conductive layer,
Here, the magnetically permeable conductive layer is made of a magnetic shunt material that has magnetism at room temperature but loses magnetism when a predetermined temperature or higher is reached.
The permeable conductive layer and the non-magnetic conductive layer have a length of the permeable conductive layer in at least one direction on the surface on which the image of the recording material to be fixed by the apparatus is formed. It is formed longer than the length of the recording material, and the length of the nonmagnetic conductive layer is longer than the length of the recording material and shorter than the length of the magnetically permeable conductive layer, and is formed approximately equal to the length of the excitation means. A fixing device. A fixing device in which an image is formed on a surface with a color material and a recording material that moves relative to the apparatus is heated and pressed to fix the color material on the recording material,
Excitation means for forming a magnetic field;
At least part of the heat generation means that is in the magnetic field formed by the excitation means and generates heat by penetrating the magnetic field lines of the magnetic field;
Including a pressurizing means for bringing the traveling recording material and the heat generating means into contact with each other and applying a pressure therebetween,
The heat generating means has a magnetically permeable conductive layer and a nonmagnetic conductive layer,
Here, the magnetically permeable conductive layer is made of a magnetic shunt material that has magnetism at room temperature but loses magnetism when a predetermined temperature or higher is reached.
The permeable conductive layer and the nonmagnetic conductive layer have at least a width of the permeable conductive layer in a width direction which is a direction perpendicular to the moving direction of the recording material moving relative to the heat generating means. It is formed wider than the sheet passing width of the recording material, and the width of the non-magnetic conductive layer is wider than the sheet passing width of the recording material and smaller than the width of the magnetically permeable conductive layer, and is substantially equal to the width of the excitation means. A fixing device characterized in that the fixing device is provided. The heating means is a cylindrical heating roller that can rotate,
The magnetically permeable conductive layer and the nonmagnetic conductive layer are integrally rotated with the rotation of the heat generating roller in the peripheral portion of the cylinder, and the nonmagnetic conductive layer is the excitation means. The fixing device according to claim 3, wherein the fixing device is formed on a side where the magnetically permeable conductive layer is sandwiched between the fixing device and the fixing device. The heating means is a hollow cylindrical heating roller that can rotate,
The magnetically permeable conductive layer and the nonmagnetic conductive layer are integrally rotated with the rotation of the heat generating roller in the circumferential portion of the cylinder, and the nonmagnetic conductive layer is the excitation means. The fixing device according to claim 3, wherein the fixing device is formed on a side where the magnetically permeable conductive layer is sandwiched between the fixing device and the fixing device. The fixing device according to claim 3, wherein a layer surface of the magnetically permeable conductive layer faces the excitation unit in the width direction. The fixing device according to claim 3, wherein the nonmagnetic conductive layer is in close contact with the magnetically permeable conductive layer. The fixing device according to claim 3, wherein the nonmagnetic conductive layer has a thickness smaller than a thickness of the magnetically permeable conductive layer. The fixing device according to claim 3, wherein the nonmagnetic conductive layer has a specific resistance value smaller than a specific resistance value of the magnetically permeable conductive layer. The fixing device according to claim 3, wherein the magnetically permeable conductive layer has a thickness of 0.2 mm to 1.0 mm. The fixing device according to claim 3, wherein the nonmagnetic conductive layer has a thickness of 0.015 mm to 0.060 mm. The fixing device according to claim 3, wherein the nonmagnetic conductive layer has a specific resistance of 7 × 10 ⁻⁸ Ω · m or less. 4. The fixing according to claim 3, wherein the non-magnetic conductive layer is formed to be slightly wider in the width direction than the width of the exciting unit wider than the sheet passing width of the recording material. apparatus. The pressure means includes a pressure roller,
The non-magnetic conductive layer is characterized in that, in the width direction, the width is substantially equal to or slightly wider than the width of the pressure roller wider than the sheet passing width of the recording material. The fixing device according to claim 3. 4. The fixing device according to claim 3, wherein the nonmagnetic conductive layer is made of copper and has a thickness of 0.015 mm to 0.060 mm. 4. The fixing device according to claim 3, wherein the nonmagnetic conductive layer is made of aluminum and has a thickness of 0.025 mm to 0.060 mm. 4. The fixing device according to claim 3, wherein the nonmagnetic conductive layer is made of zinc and has a thickness of 0.055 mm to 0.060 mm. The heating means further has a protective film on the surface of the nonmagnetic conductive layer,
4. The fixing device according to claim 3, wherein the protective layer has a width substantially equal to a width of the nonmagnetic conductive layer. The heating means further has a protective film on the surface of the nonmagnetic conductive layer,
4. The fixing device according to claim 3, wherein the protective layer has a width substantially equal to a width of the magnetically permeable conductive layer. The fixing device according to claim 5, wherein the exciting unit is disposed inside a hollow of the heat generating roller. The fixing device according to claim 4, wherein the excitation unit is disposed outside the heating roller. An image forming apparatus comprising the fixing device according to any one of claims 1 to 21. A recording medium that is disposed in a magnetic field formed by excitation means and generates heat by penetrating the magnetic field lines of the magnetic field, and an image is formed with a color material on the surface and moves in contact with the roller A heating roller that heats the coloring material to be fixed on the recording material,
A magnetically permeable conductive layer and a nonmagnetic conductive layer;
The magnetically permeable conductive layer is made of a magnetic shunt material that has magnetism at room temperature but loses magnetism at a predetermined temperature or higher,
The magnetically permeable conductive layer and the nonmagnetic conductive layer have a width direction that is a direction perpendicular to the moving direction of the moving recording material, and the width of the permeable conductive layer is larger than the sheet passing width of the recording material. The width of the nonmagnetic conductive layer is wider than the sheet passing width of the recording material and narrower than the width of the magnetically permeable conductive layer, and is substantially equal to the width of the excitation means. Heating roller.

Images