JP2007010812A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an IH type fixing device achieving the facilitation of the temperature control of a heating roller and securing arranging places for a peeling pawl and a cleaning member on the outer circumference of the heating roller without making the diameter of the heating roller large. <P>SOLUTION: Two heating rollers 11a and 11b composed of conductive members are brought into press-contact with a pressure roller 12, and an IH coil 13 is arranged between the heating rollers 11a and 11b. By applying a high-frequency current to the IH coil 13, the heating rollers 11a and 11b are heated. From a viewpoint that fixing property is improved by making nip width larger, it is also good to lay a fixing belt 14 between the heating rollers 11a and 11b, and bring the heating rollers 11a and 11b into press-contact with the heating roller 12 through the fixing belt 14. It is desirable to use magnetic shunt alloy whose Curie temperature is ≤200°C as the material of the heating rollers 11a and 11b. <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 have been proposed and some of them have been put into practical use. The electromagnetic induction heating type fixing device generates a high frequency magnetic field around the IH coil by flowing a high frequency current through the 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 is caused to generate heat by Joule heat. For example, Patent Document 1 proposes a fixing device in which two heating rollers are brought into pressure contact with a pressure roller and an IH coil is disposed oppositely on the outer periphery of each of the two heating rollers.
Japanese Patent Laying-Open No. 2003-76170 (Claims, FIG. 1)

  However, in the proposed technique, since the IH coil is provided for each of the two heating rollers, the control of the fixing temperature becomes complicated. 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. On the other hand, when the IH coil is arranged inside the heating roller, it is easy to secure the arrangement place of the peeling claw and the cleaning member on the outer periphery of the heating roller, but the diameter of the heating roller is increased and the fixing device is enlarged. In addition, there is a problem that the heat capacity of the heating roller increases and the warm-up time becomes longer.

  The present invention has been made in view of such a conventional problem. The object of the present invention is to easily control the temperature of the heating roller, and to increase the diameter of the heating roller without increasing the diameter of the heating roller. An object of the present invention is to provide an IH-type fixing device that can secure an arrangement place of a peeling claw and a cleaning member.

  According to the present invention, there is provided a pressure roller, two heating rollers made of a conductive member that is in pressure contact with the pressure roller, and a heating excitation coil disposed between the two heating rollers. A fixing device is provided that heats the two heating rollers by passing a high-frequency current through the coil.

  Here, from the viewpoint of improving the fixability by increasing the nip width, it is preferable to hang a belt between the two heating rollers, and press the two heating rollers against the pressure roller via this belt. .

  From the viewpoint of preventing overheating of the heating roller, it is desirable to use a magnetic shunt alloy having a Curie temperature of 200 ° C. or less as the material of the heating roller.

  In the fixing device of the present invention, since the heating roller is directly heated by supplying a high-frequency current to the IH coil, it becomes easy to control the temperature of the heating roller. In addition, since one IH coil is arranged between the two heating rollers and the two heating rollers are heated at the same time, it is possible to secure an arrangement place of the peeling claw and the cleaning member on the outer periphery of the heating roller. Become.

  Further, when a belt is hung between two heating rollers and the two heating rollers are pressed against the pressure roller via the belt, the nip width can be increased and the fixing property can be improved. Further, when a magnetic shunt alloy having a Curie temperature of 200 ° C. or less is used as the material of the heating roller, the surface temperature of the heating roller does not exceed the Curie temperature, so that overheating of the heating roller is effectively prevented.

  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. As will be described later, the toner image is heated and pressed 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 FIGS. 2 and 3, the fixing device 1 of the present invention has two heating rollers 11a and 11b pressed against a pressure roller 12 having an elastic layer formed around a metal shaft member, and the heating roller 11a. The IH coil 13 is disposed between the heating roller 11b and the heating roller 11b. As understood from FIG. 3, the IH coil 13 has substantially U-shaped bobbins 132a and 132b attached to both surfaces of a plate-like ferrite core 131, and the coil 133 is wound around the recesses of the bobbins 132a and 132b. Become. 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 heating roller 11a is measured by the sensor S, and a high frequency current is supplied to the coil 133 from the high frequency inverter power supply 15 so that the surface temperature of the heating roller 11a becomes a predetermined temperature.

  In the fixing device having such a configuration, when a high frequency current flows through the IH coil 13, a high frequency magnetic field is generated around the IH coil 13. This magnetic field causes eddy currents to flow through the heating rollers 11a and 11b, and the heating rollers 11a and 11b are heated by Joule heat. In addition, when the heating rollers 11a and 11b are made of a magnetic material, hysteresis loss due to a high-frequency magnetic field occurs, which also contributes to heating. Accordingly, the warm-up time is remarkably shortened as compared with a fixing device using a conventional halogen heater. Compared to a conventional fixing device in which an IH coil is disposed in each of the heating rollers 11a and 11b, power consumption can be reduced by about 10% under the same fixing conditions.

  The heating rollers 11a and 11b used in the present invention are not particularly limited as long as they are conductive, 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. In addition, it is recommended that the material of the heating rollers 11a and 11b be a magnetic shunt alloy having a characteristic of losing magnetism when the temperature is high, and having a Curie temperature (temperature at which the magnetism disappears) close to the fixing temperature. . When a magnetic shunt alloy is used as the material of the heating rollers 11a and 11b, if the temperature of the heating rollers 11a and 11b exceeds the fixing temperature (Curie temperature), the magnetism is lost and the heating is stopped, so the heating roller temperature becomes abnormally high. Is reliably prevented. This is because when the paper having a narrow axial width is continuously fixed, the surface temperature of the central portion of the heating rollers 11a and 11b through which the paper passes decreases, and the heating rollers 11a and 11b are further controlled to prevent this. The problem that the surface temperature of both sides of the heating rollers 11a and 11b through which the sheet does not pass due to heating rises abnormally can be solved from the material side of the heating roller 11. Examples of the magnetic shunt alloy include an Fe—Ni alloy, and the Curie temperature is adjusted by the Ni content.

  FIG. 4 shows another embodiment of the fixing device according to the present invention. The fixing device of FIG. 4 differs from the fixing device of FIG. 3 in that a fixing belt 14 is suspended between the fixing rollers 11a and 11b. In this fixing device, the heating rollers 11a and 11b are heated by flowing a high-frequency current through the IH coil 13, and the fixing belt 14 is heated by the heating rollers 11a and 11b. In the fixing device having this structure, the fixing belt 14 is suspended, so that the nip width with the pressure roller 12 can be widened, and toner fixing on the paper P can be performed more reliably and stably.

  Examples of the fixing belt 14 include a belt base made of polyimide with a surface coated with PTFE (polytetrafluoroethylene). Here, when conductive particles are contained in the belt base or the belt base is covered with a conductive member, the fixing belt itself is also heated by the IH coil so that the warm-up time can be further shortened. Become.

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. FIG. 3 is a partially enlarged view of the fixing device in FIG. 2. 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 11a, 11b Heating roller 12 Pressure roller 13 IH coil (Excitation coil for heating)
14 Fixing belt 15 High frequency inverter power supply

Claims (3)

A pressure roller, two heating rollers made of a conductive member in pressure contact with the pressure roller, and a heating excitation coil disposed between the two heating rollers,
A fixing device that heats the two heating rollers by passing a high-frequency current through a heating exciting coil.   The fixing device according to claim 1, wherein a belt is suspended between the two heating rollers, and the two heating rollers are pressed against the pressure roller via the belt.   The fixing device according to claim 1, wherein a magnetic shunt alloy having a Curie temperature of 200 ° C. or less is used as the heating roller.

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