JP2008134307A - Image heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image heating device for lessening a temperature difference generated by different Curie temperature even when using a material having the different Curie temperature for a center part and an end. <P>SOLUTION: The image heating device inscribes a heating roller in a non-magnetic body outer layer roller and an outer layer roller, is composed of a ferromagnetic body inner layer roller end 1, center, and end 2, composed as center<end 1≈end 2 in each Curie temperature, and achieves a fixing unit having approximately uniform temperature distribution. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing unit of an electrophotographic image forming apparatus, in particular, a heating fixing unit using an induction heating method, and a heating rotator provided in the fixing unit.

  In an apparatus using an electrophotographic process such as an electrophotographic copying machine, an electrostatic printer, or a facsimile, an image is formed on a recording material by the following image process. The electrostatic latent image formed by exposing the photosensitive member, which is a charged image carrier, is developed with toner. The toner image formed on the photoconductor is transferred onto a recording material to be conveyed by a transfer unit. The toner on the recording material is a nip formed by a heating roller formed by forming a releasable resin film on the surface of a cylindrical metal core, and a pressure roller in pressure contact with the elastic roller on the surface. By passing through the part, it is fixed on the recording material by pressure and heat. As the fixing device, a fixing device in which a halogen heater is provided inside the heating roller and the heating roller is heated by the radiant heat of the halogen heater is widely used.

  In recent years, from the viewpoint of heat exchange efficiency and start-up time, an induction heating type fixing device has been proposed in which the heating roller itself generates heat by an induced current generated by magnetic flux.

  For example, as disclosed in Patent Document 1, a magnetic flux generated by applying a high-frequency voltage to a coil by a high-frequency power source generates an eddy current in a cored bar portion of a heating roller made of magnetic iron-based metal, and generates heat. ing.

  Further, in the above method, a temperature detection member that detects the temperature of the heating roller temperature is provided, and temperature control that controls energization to the coil based on the output of the temperature detection member is employed.

  On the other hand, a configuration has been proposed in which the surface temperature of the heating roller is controlled using a characteristic that the relative magnetic permeability called a Curie point is significantly reduced, as in Patent Document 2. According to this structure, it has the merit that it is not necessary to use the temperature detection member like patent document 1. FIG.

  However, when the Curie temperature of the heating roller is set to the image heating temperature, the following problem occurs. That is, since the heat radiation from the heating roller at the end is larger than that at the center, the temperature at the end is lower than the image heating temperature. As a result, if the maximum size paper that can be passed is continuously fed, a sufficient amount of heat is not applied to the end of the heating roller, resulting in a fixing failure.

  In order to prevent this, there is a configuration in which a Curie point temperature is set at a temperature in anticipation of a temperature drop at the end portion of the heating roller, and a coil with improved end portion heating efficiency as in Patent Document 3 is used. However, in this case, since the Curie point temperature and the image heating temperature are different, there is a problem that it is difficult to control the temperature of the central portion.

Therefore, the above-described problem can be solved by using a material having a Curie temperature near the image heating temperature at the center and using a material having a temperature that takes into account the temperature decrease.
Japanese Patent Publication No. 5-9027 Japanese Patent No. 2975435 JP 2000-029332 A

  However, if materials having different Curie temperatures are made into an integral roller and the temperature is adjusted without providing a temperature detecting member, the temperature on the end side becomes high. In particular, the portion having a distance from the end portion of the region where the Curie temperature is high has a lower heat dissipation amount than the end portion, and thus the temperature is higher than that of the end portion. And, if the heat transfer is made only at the joint part of different materials, the amount of heat transfer is small, so that the temperature difference cannot be greatly reduced. As a result, the image is sufficiently heated compared to the surrounding area only, and uneven heating of the image occurs.

  Therefore, the present invention provides a coil that generates magnetic flux, a Curie temperature that is the first Curie temperature, a first member that generates heat due to the magnetic flux generated by the coil, and a second Curie temperature that is higher than the first Curie temperature. And a second member that generates heat by the magnetic flux generated by the coil, and a rotatable image heating member that heats an image on a recording material at a temperature near the first Curie temperature. The image heating member includes a metal member, the first member is provided on the center side in the rotation axis direction, the second member is provided on the end side in the rotation axis direction, and the first member and the The second member is integral with the metal member.

  According to the present invention, even if materials having different Curie temperatures are used for the central portion and the end portion, the temperature difference caused by the different Curie temperatures can be reduced.

  Hereinafter, the present invention will be described more specifically with reference to examples. The following examples are examples of the best mode of the present invention, but the present invention is not limited to these examples.

(Example 1)
Embodiments of the present invention will be described below in detail with reference to the drawings.

  First, an image forming apparatus using the image heating apparatus of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram of a digital full-color copying machine in which an image heating apparatus is used in the present invention. Hereinafter, the copying operation of the digital full-color copying machine will be described with reference to FIG. In the figure, reference numeral 80 denotes a document reading unit, and 10 denotes a full-color image forming unit. Four image stations are arranged in the full-color image forming unit 10, and each image forming station has photosensitive drums 12a, 12b, 12c, and 12d as image carriers.

  In addition, dedicated charging means (13a, 13b, 13c, and 13d) and laser scanning units (11a, 11b, 11c, and 11d) for irradiating the photosensitive drum with light corresponding to image information are disposed around it. Yes. Developing means (15a, 15b, 15c, 15d) for developing the formed electrostatic latent image is disposed. Further, drum cleaning means (14a, 14b, 14c, 14d) for removing toner remaining on the photosensitive drum after the transfer is disposed. Further, transfer means (16a, 16b, 16c, 16d) for transferring the toner image on the photosensitive drum to the intermediate transfer member or the recording material are arranged. Reference numerals 51a to 51d denote developer containers corresponding to the developing units 14a to 14d, respectively, and are provided directly below the horizontal portion of the laser scanning units 11a to 11d and in line with the vertical portion. The developer is replenished by attaching and detaching the cylindrical developer cartridge. Here, the image forming stations Pa, Pb, Pc, and Pd are for forming a cyan image, a magenta image, a yellow image, and a black image, respectively.

  On the other hand, an endless belt-like intermediate transfer belt 61 is disposed below the photosensitive drums 12a, 12b, 12c, and 12d so as to pass through the image forming stations Pa to Pd. The intermediate transfer belt 61 is stretched around a driving roller 62 and driven rollers 63 and 65, and further provided with a cleaning means 64 for cleaning the surface thereof.

  In this configuration, an electrostatic latent image is first formed on the photosensitive drum 12a by exposure by the charging unit 13a and the laser scanning unit 11a of the first image forming station Pa. The electrostatic latent image is visualized as a cyan toner image by a developer having cyan toner by the developing unit 15a, and the cyan toner image is transferred to the surface of the intermediate transfer belt 61 by the transfer unit 16a.

  On the other hand, while the cyan toner image is transferred onto the intermediate transfer belt 61, a magenta toner image is similarly formed at the second image forming station Pb. Then, the magenta toner image is accurately transferred and transferred onto the intermediate transfer belt 61 which has been transferred at the first image forming station Pa by the transfer unit 16b.

  Thereafter, the yellow image and the black image are also formed in the same manner, and the four color toner images are superimposed on the intermediate transfer belt 61. The four-color toner image on the intermediate transfer belt is transferred by the secondary transfer roller 66 in the paper feed cassette 70 and conveyed by the paper feed roller 71, the transport roller pair 72, and the registration roller pair 73 at the same timing. Transferred onto S (secondary transfer). The recording material S for which the secondary transfer has been completed is heat-fixed at a fixing temperature, which is a preset image heating temperature, on the toner image transferred by the heating roller pair 74, and a full-color image is obtained on the recording material S. .

  The photosensitive drums 12a to 12d, which have been transferred, have residual toner removed from the drums by the cleaning units 14a to 14d, and are prepared for subsequent image formation.

  FIG. 2A is a longitudinal sectional view of the heating roller 1 as an image heating member of the image heating apparatus according to the present invention.

  FIG. 2B is a circumferential sectional view of the heating roller.

  The cross section of the heating roller 1 will be described below.

  The innermost cores 300, 400, and 500 are made of iron-based metal and are made into a cylindrical shape by welding the end of a flat plate, and then processed into a predetermined shape through a stretching process and a polishing process. This is a thin-walled air core roller.

  Furthermore, each cored bar is generally set with a different Curie point by changing the composition of the chemical components of its base material.

  In this embodiment, the one whose Curie point is changed by changing the blending amount of Ni in the iron-based metal is mainly used.

  The Curie point temperature of the cored bar 300 that is the first member disposed on the center side of the heating roller 1 in the direction of the rotation axis of the heating roller is adjusted to Tc (180 ° C.). In the present embodiment, since the self-heating control is performed without providing a temperature detection member for detecting the temperature of the heating roller, the image heating temperature is a temperature near the Curie temperature. More specifically, the image heating temperature is configured such that self-heating control is performed within a range of (Curie temperature−10 ° C.) to Curie temperature. Further, the Curie point temperatures of the cored bar 400 as the second member and the cored bar 500 as the third member respectively provided on the end side of the heated roller in the rotation axis direction of the heated roller are Ts (225 ° C.) higher than Tc. ). The setting of Ts is preferably set lower than a temperature of 235 ° C. at which the heat generation efficiency may be lowered due to an increase in the electrical resistance of the coil as the coil temperature increases. Furthermore, it is necessary to set the heat resistance temperature of the image heating apparatus lower than 245 ° C. Each of the core bars 300, 400, and 500 has an inner diameter of 45 mm and an outer diameter of 46 mm.

  Next, a metal roller that is a metal member will be described. This metal roller has an inner diameter that is as small as the outer diameter of the cores 300, 400, and 500. In this embodiment, it is 45.5 mm. The outer diameter is 47.0 mm. A roller main body is formed by press-fitting the metal roller 200 in the order shown in FIG. In the roller body, the core metal and the metal roller are integrated. Here, it is assumed that the metal roller 200 is made of a metal such as aluminum, which is a material having high thermal conductivity. Moreover, it is preferable that the thermal conductivity of the metal roller 200 is higher than the thermal conductivity of the core bars 100, 200, and 300.

  Reference numeral 800 denotes a retainer provided at both ends of the roller.

  A release layer 600 (a fluororesin such as PTFE) that prevents the unfixed toner from adhering to the heating roller core itself when the unfixed toner is melted is provided at a thickness of 50 μm on the outer periphery of the metal roller 200 configured as described above. It has been.

  The heating roller core 200 and the release layer 600 are bonded together by an adhesive 700 that is a binder layer.

  In this embodiment, the release layer is provided on the metal roller, but there is no problem even if an elastic layer is provided between the metal roller and the release layer.

  The configuration of induction heating using the heating roller 1 will be described with reference to FIG.

  Since the heating roller 1 is hollow, the heating roller 1 can be provided with a transmitting coil L1.

  The coil L1 that generates magnetic flux is connected to a smoothing circuit including diodes D1 to D4, a noise filter NF, a capacitor C1, and an oscillation circuit including a switching element TR1, a resonance capacitor C2, a flywheel diode D5, and the like.

  The oscillation circuit is supplied with a commercial power supply (AC) and is oscillated at a high frequency by pulse frequency modulation control of about 20 K to 30 KHz generated from the resonance control circuit. Therefore, an AC magnetic field is generated when a high frequency voltage is applied to the coil L1.

  When this magnetic field interlinks with the thin heating rollers 300, 400, 500 made of iron-based metal, an eddy current is generated on each roller surface, and the roller is heated by Joule heat generated thereby.

  Next, FIG. 4 shows a configuration of a fixing device using the roller.

  The fixing device 301 is provided with a roller pair composed of a pressure roller 302 that contacts the fixing roller 1 and is rotated at a predetermined speed by a driving unit (not shown). Here, the sheet P after image transfer conveyed by a conveying means (not shown) enters from the entrance of the fixing device 301 and passes through the nip portion formed by the roller pair, thereby heating by the fixing roller and the roller pair. The toner image on the paper P is fixed on the paper P by the pressurizing action.

  A core 303 is a ferrite core provided to regulate the direction of the magnetic flux generated by the coil L1.

  Next, the temperature distribution of the fixing roller 1 during the above operation will be described with reference to the temperature distribution diagram of FIG.

  In the configuration diagram in the direction of the rotation axis of the heating roller, those unnecessary for explanation are omitted.

  When the apparatus is operated at the time of start-up to enable the first sheet to pass, the temperature of the heating roller 1 rises from around room temperature.

  First, when the temperature reaches the vicinity of the Curie temperature Tc of the central core 300, the relative permeability of the core 300 is rapidly reduced, so that the heating efficiency is also significantly reduced. For example, when the relative permeability at room temperature is 100, it reaches 1 when the Curie temperature is reached. Therefore, the temperature of the portion where the cored bar 300 is arranged is stabilized in the vicinity of Tc, except when the frequency of the power applied to the coil is significantly changed.

  In the metal cores 400 and 500, the Curie point Ts is set as Tc <Ts. Therefore, even if the temperature of the metal core 300 reaches the Curie temperature Tc, the temperature of the metal cores 400 and 500 continues to rise. However, in this embodiment, since the core bars 400 and 500 are roller end portions, the amount of heat radiation is larger than that at the center portion, so that they are stabilized at a temperature slightly lower than the actual Curie temperature Ts.

  In the present invention, the temperature difference between the cored bar 300 and the cored bar 400, 500 can be reduced by arranging the cored bars 300, 400, 500 inside the metal roller 200 having high thermal conductivity. Here, the temperature distribution in the standby state (standby state) when the recording material is not passed is shown. A temperature distribution in which the metal roller 200 is not provided is indicated by 404. In this case, the heat transfer between the metal cores 400 and 500 and the metal core 300 is limited only to the joint portion, so that the amount of heat transfer is reduced. Moreover, since the amount of heat radiation is smaller on the central side of the core metal 400 and the core metal 500 than on the end side, the temperature is likely to rise. As a result, the temperature distribution tends to be high on the joint side between the core bars. For this reason, when a recording material having the maximum width (W1) that can be passed is passed, the temperature difference between the end portion side and the central portion side becomes large, so that heating unevenness occurs on the image. On the other hand, when the metal roller 200 is provided, the heat transfer between the metal cores 400 and 500 and the metal core 300 is not limited to the joint of the metal cores, and is also performed from the metal roller 200. The temperature difference can be increased and the temperature difference can be reduced. A is a temperature difference when the metal roller 200 is not used, and was 30 ° C. as a result of examination. However, by using the metal roller 200, B could be 10 ° C.

  Reference numerals 402 and 405 denote temperature distributions when the recording material having the maximum width (W1) that can be passed is passed. In the temperature distribution 405 when the metal roller 200 is not provided, a temperature difference of 20 ° C. occurs at the portion C of the end portions of the core bars 400 and 500 for the same reason as described above. On the other hand, in the configuration in which the metal roller 200 is provided, the temperature of the roller in contact with the sheet temporarily decreases because the sheet takes heat from the roller when the sheet passes through the nip, but when the power is turned on, the temperature is near Tc. Will be maintained. When the recording material is continuously passed, the input power is again taken away by the recording material, so that the temperature at the end of the paper passing area of the recording material is not higher than in the standby state (401), The temperature unevenness in the recording material passing area can be reduced (402). On the other hand, in the portions of the rollers 4 and 5, the temperature rises to the vicinity of Ts particularly at the endmost portion not in contact with the paper P.

  Reference numeral 403 denotes a temperature distribution when a recording material having a width smaller than W1 is passed. When the paper P ′ having the paper width W2 substantially equal to the length of the central roller 3 is continuously passed, the roller temperature temporarily decreases in the central portion as in the case of 402, but the temperature near Tc is applied by applying power. Will be maintained. At this time, the temperature of most of the end rollers 4 and 5 rises to near Ts, but does not exceed that (403). This prevents the image heating device from being damaged even if the temperature of the non-sheet passing portion is increased.

  As described above, according to the present invention, even when materials having different Curie temperatures are used for the central portion and the end portion, a temperature difference caused by different Curie temperatures can be reduced.

(Example 2)
FIG. 6 is a cross-sectional view of the fixing roller according to another embodiment of the present invention, particularly an enlarged view of contact between the cored bar 300 and the cored bar 400. The contact between the cored bar 500 and the cored bar 300 in this embodiment is the same as that of the cored bar 300 and the cored bar 400.

  When the metal core 300 and the metal core 400 are in close contact with each other as shown in FIG. 6C, depending on the heating state and the heat dissipation state of the roller, the temperature near the contact surface as shown in FIG. Since it is heated to a temperature higher than the Curie point Ts of 2, the temperature of the end region increases, and the temperature difference increases.

  Therefore, if it is configured not to contact directly as shown in FIG. 6A, the temperature difference can be made smaller if the metal core 300 and the metal core 400 are not in contact as shown in FIG. 6B. can do.

  If the distance d is always constant, the fixing method of the inner roller is not limited.

  Thus, as in this embodiment, the metal roller 200 is provided and the cored bar 300 and the cored bars 400 and 500 are brought into a non-contact state.

  With this configuration, even if a material having a different Curie temperature is used for the central portion and the end portion, the temperature difference caused by the different Curie temperature can be reduced.

(Other examples)
FIG. 7 is a cross-sectional view of a roller for explaining another embodiment.

  In the above-described embodiment, the thickness, outer diameter, and inner diameter of the core metal 300, the core metal 400, and the core metal 500 are the same. However, in the present embodiment, the thickness, outer diameter, and inner diameter are different. FIG. 7A shows the core 300 and the core 400 (core 500) having different outer diameters and inner diameters. FIG. 7B shows the core 300 and the core 400 (core 500) having different outer diameters and inner diameters. In the present invention, the thickness, outer diameter, and inner diameter of the cored bar 300, the cored bar 400, and the cored bar 500 are not limited to the same value.

  Further, there is no problem even if the metal roller 200 and the cored bar 300, the cored bar 400, and the cored bar 500 are attached by an adhesive.

Sectional view of the image forming apparatus in Embodiment 1 Sectional drawing of the heating roller in Example 1 Configuration diagram of induction heating device in embodiment 1 The figure showing the section of the fixing device in Example 1. Longitudinal temperature distribution diagram of heating roller in Embodiment 1 Sectional view and temperature distribution diagram of fixing roller in Example 2 Cross-sectional view of the fixing roller in Embodiment 3

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heating roller 6 Release layer 7 Adhesive 301 Image heating apparatus 302 Pressure roller 200 Metal roller 300 Center metal core roller 400 End metal core roller 500 End core metal roller L1 Induction heating coil C2 Resonance capacitor D1 D4 Rectifier diode TR1 Switching element 202 Resonance control circuit 201 Induction heating power supply

Claims (5)

A coil that generates magnetic flux, a Curie temperature is the first Curie temperature, a first member that generates heat due to the magnetic flux generated by the coil, a Curie temperature is a second Curie temperature that is higher than the first Curie temperature, and the coil A second member that generates heat by the generated magnetic flux, and a rotatable image heating member that heats an image on the recording material at a temperature near the first Curie temperature.
The image heating member includes a metal member, the first member is provided on the center side in the rotation axis direction, the second member is provided on the end side in the rotation axis direction, the first member and the second member An image heating apparatus, wherein the member is integral with the metal member.   The image heating apparatus according to claim 1, wherein the thermal conductivity of the metal member is higher than that of the first member and the second member.   The image heating apparatus according to claim 1, wherein the thickness of the metal member is greater than the thickness of the first member and the second member.   The image heating apparatus according to any one of claims 1 to 3, wherein the first member and the second member are arranged with a space therebetween.   The image heating apparatus according to claim 1, wherein the metal member is a roller.

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