JP2007010815A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the heating efficiency of a heating roller from lowering by restraining the temperature rise of an IH coil in an IH type fixing device where the IH coil is incorporated in the heating roller. <P>SOLUTION: The heating roller 11 is formed in a double cylinder state where a first cylindrical body 111 having high resistivity is set on the outside and a second cylindrical body 112 having low resistivity is set on the inside, and the IH coil 13 is provided inside the second cylindrical body 112. A cover part 14 is fit to the side end of the heating roller 11 to seal space between the first and the second cylindrical bodies 111 and 112. From a viewpoint that the uniformization of the surface temperature of the heating roller 11 in a shaft direction is contrived, it is desirable to compose the first cylindrical body 111 of magnetic shunt alloy. From a viewpoint that the temperature rise of the IH coil 13 is restrained further, it is desirable to use a cover which opens the side surface of the second cylindrical body 112 when it is attached to the side end of the heating roller 11 as the cover part 14. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device, and more particularly to a fixing device using electromagnetic induction heating (IH).

  In an electrophotographic image forming apparatus, a heat fixing roller type has been widely used as a fixing device. In this heat fixing roller type fixing device, a pressure roller is brought into pressure contact with a heating roller having a built-in halogen heater, and the transfer paper on which the toner image is placed is passed through the nip portion of both rollers, whereby the toner image is transferred onto the transfer paper. It is melt-fixed on the surface.

  Such a heat fixing roller type fixing device consumes about 70% of the electric power of the entire image forming apparatus. For this reason, in response to increasing awareness of environmental problems in recent years, there is a strong demand from the market for energy saving of fixing devices. In order to save energy of the fixing device, it is effective to shorten the time from when the power is turned on until the temperature reaches the fixable temperature, so-called warm-up time, and low temperature setting during standby.

Therefore, various fixing methods using electromagnetic induction heating (IH) have been proposed and some of them have been put into practical use. The IH type fixing device generates a high frequency magnetic field around the IH coil by flowing a high frequency current through an IH coil arranged inside or outside the heating roller, and generates an eddy current in the heating roller by this magnetic field. The heating roller generates heat by Joule heat (for example, Patent Documents 1 to 3). Since this IH type fixing device directly heats the heating roller itself, it is more efficient than the conventional heat fixing roller method, and can reduce the temperature rise in parts other than the heating roller. Thereby, shortening of warm-up time and low temperature setting during standby are realized.
JP 54-39645 A JP 7-295414 A JP-A-9-258586

  However, when the IH coil is disposed inside the heating roller, the temperature of the IH coil itself increases due to radiant heat from the heating roller, and characteristics such as the resistance value and inductance value of the IH coil may change. When the characteristics of the IH coil change, the heating efficiency decreases, the coil itself melts and causes dielectric breakdown, and there is a possibility that the power source that supplies power to the IH coil may be greatly affected. In order to prevent such a problem, it is conceivable to forcibly cool the IH coil using a cooling fan or the like, but it is not preferable in terms of thermal efficiency to cool while heating.

  On the other hand, when the IH coil is arranged outside the heating roller, forced cooling of the IH coil is not necessary, but there is natural cooling due to the air entering and exiting from both ends of the heating roller and heat conduction. As in the case where the coil is disposed inside, it is inefficient to cool while heating. In addition, it is difficult to secure a place where a peeling claw for peeling the transfer paper after fixing from the heating roller and a cleaning member for cleaning the surface of the heating roller are arranged around the heating roller.

  The present invention has been made in view of such a conventional problem. The object of the present invention is to suppress an increase in the temperature of the IH coil even when the IH coil is disposed inside the heating roller. Moreover, it is an object of the present invention to provide a fixing device that does not lower the heating efficiency of the heating roller.

  According to the present invention, the toner image is fixed to the transfer paper by bringing the heat roller and the pressure member into pressure contact and passing the transfer paper on which the toner image is formed through the nip portion between the heat roller and the pressure member. In the fixing device, the heating roller has a double cylindrical shape, the outer first cylindrical body is configured by a member having a high resistivity, and the inner second cylindrical body is configured by a member having a low resistivity, and the second cylinder. A heating excitation coil is provided in the body, and a lid for sealing the space between the first cylindrical body and the second cylindrical body is provided at the side end of the heating roller so that a high-frequency current flows through the heating excitation coil. The fixing device is characterized in that the first cylindrical body is heated. In this specification, high resistivity means 5.0 μΩ · cm or more, and low resistivity means less than that.

  Here, from the viewpoint of making the heating roller surface temperature uniform in the axial direction, the first cylindrical body is preferably made of a magnetic shunt alloy.

  Further, from the viewpoint of further suppressing the temperature rise of the IH coil, it is preferable that the lid portion opens the side surface of the second cylindrical body when mounted on the side end of the heating roller. In addition, from the viewpoint of preventing pressure increase due to air expansion in the space between the first cylinder and the second cylinder, it is preferable to form a vent hole in the lid.

  In the fixing device of the present invention, since the second cylinder is disposed between the first cylinder heated by the IH coil and the IH coil, the radiant heat from the first cylinder is blocked by the second cylinder. Thus, heating of the IH coil is prevented. Furthermore, since the sealed space is formed between the first cylindrical body and the second cylindrical body by the lid portion, temperature drop of the first cylindrical body and convective heat transfer to the IH coil are prevented.

  If the first cylindrical body is made of a magnetic shunt alloy, the heating roller surface temperature can be made uniform in the axial direction.

  In addition, when a lid that seals the space between the first cylinder and the second cylinder and at the same time opens the side of the second cylinder, the temperature drop of the first cylinder and the IH coil Temperature rise can be suppressed.

  Further, if a vent hole is formed in the lid portion, it is possible to prevent a pressure increase due to air expansion in the space between the first cylindrical body and the second cylindrical body.

  Hereinafter, the fixing device of the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments.

  FIG. 1 is a schematic view showing an embodiment of a copying machine to which a fixing device according to the present invention is applied. First, the image forming mechanism of the copying machine of FIG. 1 will be described. The surface of the photosensitive drum 70 is uniformly charged positively or negatively by a charging device 71. On the other hand, a document (not shown) is placed on the document placing table 90, and the image data is read by the reading device 91. The read image data is written on the surface of the photosensitive drum 70 by a laser scanner (exposure device) 72, and an electrostatic latent image is formed on the surface of the photosensitive drum 70. Specifically, in the case of the reverse development method, the charge corresponding to the image is removed, and in the case of the regular development method, the charge corresponding to the background is removed to form an electrostatic latent image. Next, the electrostatic latent image on the photosensitive drum 70 is visualized with toner by the developing device 73. At this time, the charging polarity of the toner is the same as the charging polarity of the photosensitive drum 70 in the case of the reversal development method, and is opposite to the charging polarity of the photosensitive drum 70 in the case of regular development.

  On the other hand, the paper P stored in the paper feed cassette 81 is pulled out by the pickup roller 82, sandwiched between the paper feed roller 83 and the separating roller 84, and sent to the conveyance path. Then, the registration roller pair 80 feeds the paper P to the transfer unit at the timing when the toner image on the photosensitive drum 70 reaches the transfer unit. In the transfer portion, the sheet P is sandwiched between the photosensitive drum 70 and the transfer roller 74, and a charge having a polarity opposite to the toner charging polarity is applied to the transfer roller 74. Toner image moves onto the paper P. On the other hand, the toner remaining on the photosensitive drum 70 without moving onto the paper P is removed and collected by the cleaning device 75. The paper P on which the toner image is placed is conveyed to the fixing device 1. Here, the toner image is heated and pressurized by the fixing device 1 and fixed on the paper P. Then, the paper P is sent to the discharge roller pair 86 and discharged to the tray 87.

  As shown in FIG. 2, the fixing device 1 includes a heating roller 11 in which a first cylindrical body 111 having a high resistivity and a second cylindrical body 112 having a low resistivity are doubled coaxially, and rubber or the like as an outermost layer. The pressure roller (pressure member) 12 on which the elastic layer is formed is in pressure contact. In the second cylindrical body 112, the IH coil 13 is disposed in the axial direction. The space between the first cylindrical body 111 and the second cylindrical body 112 is sealed by a lid portion 14 (shown in FIG. 3) attached to the side end of the heating roller 11 as will be described later. This sealed space provides a heat retaining action and suppresses the temperature drop of the first cylindrical body 111, and at the same time, radiant heat and convective heat transfer to the IH coil 13 are prevented in the space, and the temperature of the IH coil 13 rises. Is suppressed.

  The IH coil 13 is formed by attaching substantially U-shaped bobbins 132a and 132b on both surfaces of a plate-like ferrite core 131, and winding the coil 133 around the recesses of the bobbins 132a and 132b. The coil 133 is made of a single copper wire and is wound so as to go around both side surfaces of the ferrite core 131 in the axial direction. In the illustrated embodiment, the coil 133 is wound twice in the recesses of the bobbins 132a and 132b. Thereby, the generated magnetic field can be strengthened. The surface temperature of the first cylindrical body 111 is measured by the sensor S, and a high frequency current is passed through the coil 133 from the high frequency inverter power supply 15 so that the surface temperature of the first cylindrical body 111 becomes a predetermined temperature.

  In the fixing device 1 having such a configuration, a high frequency magnetic field is generated around the IH coil 13 when a high frequency current flows through the IH coil 13. An eddy current flows through the first cylindrical body 111 and the second cylindrical body 112 by this magnetic field. Joule heat is generated in the first cylindrical body 111 having a high resistivity, whereas Joule heat is generated in the second cylindrical body 112 having a low resistivity. Does not occur. That is, only the first cylindrical body 111 is heated by the IH coil 13.

  Part of the heat generated in the first cylindrical body 111 is used for melting and fixing the toner on the conveyed paper. Further, the other part of the generated heat is released inward from the first cylindrical body 111 and accumulated in the space between the first cylindrical body 111 and the second cylindrical body 112. As shown in FIG. 3, a disc-like lid 14 having a circular opening 141 formed in the center is fitted to both ends of the heating roller 11 and the space is sealed, so that the heat retention by the space is improved. And the temperature fall of the 1st cylindrical body 111 is suppressed. As understood from FIG. 3, both ends of the second cylindrical body 112 are opened by the circular opening 141 formed in the center of the lid 14, so that the temperature increase of the IH coil 13 is effectively suppressed. Become so.

  Note that if the temperature of the sealed space formed by the first cylindrical body 111, the second cylindrical body 112, and the lid 14 rises, air in the space may expand and the lid 14 may come off. It is recommended that a vent 142 be provided.

  When the amount of electric power when 80 sheets of A4 size paper were fixed was measured, it was about 850 W with the conventional heating roller with a built-in IH coil, but it was suppressed to about 800 W with the heating roller used in the present invention. It was. Further, although the surface temperature of the heating roller decreased from 180 ° C. to 100 ° C., it was 4 minutes with the conventional heating roller, but it extended to about 5 minutes with the heating roller used in the present invention.

  The first cylindrical body 111 used in the present invention is not particularly limited as long as it has a high resistivity, but ferromagnetic materials such as iron and nickel are preferable from the viewpoint of dielectric heating efficiency. For example, stainless steel such as SUS430 can also be used. Furthermore, a weak magnetic material or a non-magnetic material may be used. A suitable resistivity is 5.0 μΩ · cm or more, more preferably 6.0 μΩ · cm or more. When the first cylindrical body 111 is made of a magnetic material, hysteresis loss due to a high-frequency magnetic field is generated, which also contributes to heating. Therefore, the material of the first cylindrical body 111 is preferably a material having magnetism. According to such IH heating, the warm-up time is remarkably shortened as compared with a conventional fixing device using a halogen heater.

  In addition, it is recommended that the material of the first cylindrical body 111 be a magnetic shunt alloy having a characteristic of losing magnetism when the temperature is high, and having a Curie temperature (temperature at which magnetism disappears) close to the fixing temperature. . When a magnetic shunt alloy is used as the material of the first cylindrical body 111, if the temperature of the first cylindrical body 111 exceeds the fixing temperature (Curie temperature), the magnetism is lost and the surface is not heated. The temperature is reliably prevented from becoming abnormally high. This is because when the paper having a narrow axial width is continuously fixed, the surface temperature of the central portion of the first cylindrical body 111 through which the paper passes decreases, and the first cylindrical body 111 is further prevented to prevent this. Due to the heating, the problem that the surface temperature of the both sides of the first cylinder 111 through which the paper does not pass rises abnormally can be solved from the material surface of the first cylinder 111. Examples of the magnetic shunt alloy include an Fe—Ni alloy, and the Curie temperature is adjusted by the Ni content.

  The second cylindrical body 112 used in the present invention is not particularly limited as long as it has a low resistivity, and examples thereof include aluminum, copper, and stainless steel. The resistivity is preferably 3.0 μΩ · cm or less, more preferably 2.7 μΩ · cm or less.

  The pressure member 12 used in the present invention is not limited to the roller shape shown in the above embodiment, and a conventionally known member can be used. For example, as shown in FIG. 4, the belt B (between the two rollers 17 a and 17 b) is pressed against the heating roller 11 (FIG. 4A), or the heating roller 11 is not tensioned. For example, pad pressing (the same figure (b)) which press-contacts the pad member 18 via the belt B is mentioned.

1 is a schematic view of an image forming apparatus using a fixing device according to the present invention. 1 is a schematic view showing an embodiment of a fixing device according to the present invention. It is a disassembled perspective view of a heating roller. FIG. 6 is a schematic view showing another embodiment of the fixing device according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixing device S Sensor B Belt 11 Heating roller 12 Pressure roller 13 IH coil (Excitation coil for heating)
14 Lid 15 High Frequency Inverter Power Supply 111 First Cylinder 112 Second Cylinder

Claims (4)

In a fixing device for fixing a toner image to a transfer paper by pressing the heating roller and a pressure member and passing the transfer paper on which the toner image is formed through a nip portion between the heating roller and the pressure member.
The heating roller has a double cylindrical shape, the outer first cylindrical body is composed of a member having a high resistivity, and the inner second cylinder is composed of a member having a low resistivity. Is equipped with an exciting coil for heating,
A lid for sealing the space between the first cylindrical body and the second cylindrical body is provided at the side end of the heating roller,
A fixing device for heating a first cylindrical body by flowing a high-frequency current through a heating exciting coil.   The fixing device according to claim 1, wherein the first cylindrical body is made of a magnetic shunt alloy.   The fixing device according to claim 1, wherein when the lid is attached to a side end of the heating roller, the side surface of the second cylindrical body is opened.   The fixing device according to claim 1, wherein a ventilation hole is formed in the lid portion.

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