JP2009180818A - Fixing unit and image forming apparatus equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing unit, capable of attaining both shortening of the warm-up time of a heating roller and securement of mechanical strength, and to provide an image forming apparatus equipped therewith. <P>SOLUTION: The fixing unit 20 for fixing a toner image transferred to a recording medium M on the recording medium M is equipped with the heating roller 30 fixing the toner image on the recording medium M, by heating the toner image on the recording medium M, and a pressure roller 40 holding the recording medium M between the heating roller 30 and the pressure roller. The heating roller 30 includes a cylindrical and hollow roller base material 35; a magnetic flux generating part 36, provided inside the roller base material 35 and generating magnetic flux; a heating layer 31, provided on the roller base material 35 and heating the toner image, by generating heat by magnetic flux; and a heat-insulating layer 33 provided between the roller base material 35 and the heating layer 31 and having heat insulation properties of preventing heating of the heating layer 31 from being transmitted to the magnetic flux generating part 36. The roller base material 35 is constituted of non-magnetic and non-conductive rigid member. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixing unit that fixes a toner image transferred onto a recording medium onto the recording medium, and an image forming apparatus including the fixing unit.

  Conventionally, as a fixing unit for fixing a toner image transferred onto a recording medium onto the recording medium, one disclosed in Patent Document 1 is known. The fixing unit of Patent Document 1 includes a heating roller (heat generation layer) that heats a toner image on a recording medium and fixes the toner image on the recording medium, and a pressure roller that sandwiches the recording medium between the heating rollers. And an induction coil that is disposed inside the heating roller and generates heat by the magnetic flux, and a cylindrical heat insulating material (heat insulating layer) that is disposed between the heating roller and the induction coil.

The heating roller can generate heat up to a predetermined temperature by the magnetic flux from the induction coil, and receives a pressure from the pressure roller when the recording medium is sandwiched between the pressure roller and the heating roller is constant with respect to the pressure. It is manufactured from a magnetic material such as stainless steel or iron so as to have a mechanical strength of
JP 2000-105516 A

  In recent years, it has been required to shorten the warm-up time of the fixing unit, that is, to shorten the time required for the heating roller to generate heat up to a predetermined temperature. If the thickness of the heating roller is reduced, the heat capacity of the heating roller is reduced, so that the heating roller can be heated to a predetermined temperature in a short time. However, if the thickness of the heating roller is reduced to meet the above requirement, it becomes difficult to ensure the mechanical strength. As described above, in the fixing unit of the cited document 1, it is difficult to obtain both shortening of the warm-up time of the heating roller and ensuring of the mechanical strength.

  Therefore, in view of the above problems, the present invention provides a fixing unit capable of obtaining both shortening of the warm-up time of the heating roller and ensuring of mechanical strength, and an image forming apparatus including the fixing unit. Objective.

  In order to achieve the above object, a fixing unit according to the present invention fixes a toner image transferred onto a recording medium onto the recording medium, and heats the toner image on the recording medium. A heating rotator for fixing the toner image on the recording medium; and a pressure rotator for sandwiching the recording medium between the heating rotator. The heating rotator is provided on a cylindrical and hollow rotator base, a magnetic flux generator provided inside the rotator base, and generates a magnetic flux, on the rotator base, A heat generating layer that generates heat by magnetic flux and heats the toner image, and is provided between the rotating body base and the heat generating layer to prevent the heat of the heat generating layer from being transmitted to the magnetic flux generation unit. And a heat insulating layer having heat insulating properties. The rotating body substrate is a fixing unit made of a non-magnetic and non-conductive rigid member. The rigid member is preferably a ceramic material.

  According to the fixing unit of the present invention, since the rotating body substrate provided with the heat insulating layer and the heat generating layer is manufactured from a rigid member, for example, a ceramic material, the heating rotating body is recorded between the pressure rotating body. The mechanical strength with respect to the pressure received from the pressurizing rotary body along the longitudinal direction of the rotary base material when the medium is sandwiched can be obtained. Moreover, since the rotor base material is non-magnetic and non-conductive, it does not prevent the magnetic flux from the magnetic flux generating part from reaching the heat generating layer. Therefore, the heat generating layer can reach the temperature at which the toner image can be heated and fixed on the recording medium in a short time. Thus, according to the fixing unit of the present invention, both shortening of the warm-up time of the heating rotator and ensuring of the mechanical strength can be obtained.

  In a preferred embodiment of the present invention, the magnetic flux generation unit includes a cylindrical bobbin that is concentric with the rotating body substrate and extends in the longitudinal direction of the rotating body base, and a magnetic core disposed inside the bobbin; And a coil wound around the circumferential surface of the cylindrical bobbin.

  According to this configuration, since the coil is wound around the peripheral surface of the bobbin extending in the longitudinal direction of the rotating body substrate, the magnetic flux is uniformly distributed outward in the radial direction of the bobbin, that is, toward the heat generation layer. be able to. Therefore, the rotating base material is interposed between the magnetic flux generation part and the heat generation layer, so that the magnetic coupling degree between the magnetic flux generation part and the heat generation layer is ensured even when the distance between the magnetic flux generation part and the heat generation layer increases. Is possible. As a result, even if the distance between the magnetic flux generation part and the heat generation layer is large, the heat generation efficiency of the heat generation layer can be improved.

  In another preferred embodiment of the present invention, a plurality of the magnetic cores are arranged inside the bobbin so as to be movable in the longitudinal direction of the rotating body substrate. According to this configuration, it is possible to adjust the magnetic flux distribution range along the longitudinal direction by moving the plurality of magnetic cores in the longitudinal direction of the rotating base material. Therefore, the heat generation range in the heat generation layer can be adjusted along the longitudinal direction. Accordingly, when the recording medium is, for example, a sheet, the toner image on the sheet can be heated and fixed on the sheet according to the size of the sheet.

In a further preferred embodiment of the present invention, when the distance between the heat generating layer and the coil is D1 and the distance between the magnetic core and the coil is D2 when viewed from the axial center of the heating rotating body, A fixing unit that satisfies Equation (1).
(1) D1> D2

  According to this configuration, the magnetic coupling degree between the magnetic core and the coil is set to be larger than the magnetic coupling degree between the heat generating layer and the coil, so that the magnetic flux generated from the coil is generated according to the arrangement of the magnetic core. Can be guided smoothly. This makes it easy to adjust the heat generation range of the heat generation layer. Accordingly, by appropriately adjusting the arrangement of the magnetic cores, temperature sagging and the like can be suppressed at both ends of the heat generating layer in the longitudinal direction of the rotating body base material. In addition, since the heat generation range of the heat generation layer greatly depends on the arrangement of the magnetic core, the heat generation range adjustment performance by moving the magnetic core can be improved.

  In a further preferred embodiment of the present invention, the fixing unit further includes a blower arranged so as to be able to cool the magnetic flux generating part by flowing air inside the rotating body substrate. According to this configuration, since the rotating body base material is manufactured from a ceramic material, cooling air from the cooler is prevented from reaching the heat generating layer through the rotating body base material and cooling the heat generating layer. It is possible to cool only the magnetic flux generator.

  In a further preferred embodiment of the present invention, there is provided an image forming apparatus comprising: a transfer unit that transfers a toner image formed on a photosensitive drum to a recording medium; and the fixing unit that fixes the toner image to the recording medium. provide.

  According to the fixing unit and the image forming apparatus including the fixing unit according to the present invention, it is possible to obtain both shortening of the warm-up time of the heating rotator and ensuring of the mechanical strength.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic diagram of an image forming apparatus including a fixing unit according to an embodiment of the present invention. The image forming apparatus 10 is, for example, a printer, and includes a sheet storage unit 12 that stores sheets M (recording medium) to be used for printing processing, and one sheet fed out from the sheet bundle M1 stored in the sheet storage unit 12. A transfer unit 13 for performing an image transfer process on the paper M and a fixing unit 20 for performing a fixing process on the paper M subjected to the transfer process by the transfer unit 13 are incorporated in the apparatus main body 11. The paper discharge unit 15 for discharging the paper M on which the fixing process has been performed by the fixing unit 20 is provided at the top of the apparatus main body 11.

  A predetermined number (one in the embodiment) of paper cassettes 121 is provided in the paper storage unit 12 so as to be detachable from the apparatus main body 11. At the downstream end of the paper cassette 121 (on the right side in FIG. 1), a pickup roller 122 that feeds the paper M one by one from the paper bundle M1 is provided. The sheet M fed from the sheet cassette 121 by driving the pickup roller 122 is fed to the transfer unit 13 via the sheet feeding conveyance path 123 and the registration roller pair 124 provided at the downstream end of the sheet feeding conveyance path 123. It has come to be.

  The transfer unit 13 performs a transfer process on the paper M based on image information transmitted from a computer or the like, and is provided to be rotatable around a drum axis extending in the front-rear direction (a direction perpendicular to the paper surface of FIG. 1). A charger 132, an exposure device 133, a developing device 134, a transfer roller 135, and a cleaning device 136 are arranged from the position immediately above the photosensitive drum 131 in the clockwise direction along the peripheral surface of the photosensitive drum 131. It is formed by.

  The photosensitive drum 131 is for forming an electrostatic latent image and a toner image along the electrostatic latent image on the peripheral surface, and an amorphous silicon layer is laminated on the peripheral surface, thereby forming these images. It is suitable for making it happen.

  The charger 132 forms a uniform charge on the circumferential surface of the photosensitive drum 131 rotating clockwise around the drum axis. In the example shown in FIG. A method of applying a charge to the peripheral surface is adopted. A charging roller that applies a charge while rotating the driven surface while contacting the peripheral surface of the photosensitive drum 131 is used instead of the charger 132 as a member that applies a charge to the peripheral surface of the photosensitive drum 131. Also good.

  The exposure device 133 irradiates the peripheral surface of the rotating photosensitive drum 131 with a laser beam to which intensity is applied based on image information transmitted from an external device such as a computer, and the photosensitive drum 131 is rotated by this. An electrostatic latent image is formed on the peripheral surface of the photosensitive drum 131 by erasing the charge of the portion irradiated with the laser beam on the surface.

  The developing device 134 supplies the toner to the peripheral surface of the photosensitive drum 131 to attach the toner to the portion where the electrostatic latent image is formed on the peripheral surface, whereby the toner image is formed on the peripheral surface of the photosensitive drum 131. It is to be formed.

  The transfer roller 135 transfers a positively charged toner image formed on the peripheral surface of the photosensitive drum 131 to the paper M with respect to the paper M sent to a position immediately below the photosensitive drum 131. A negative charge having a polarity opposite to that of the image is applied to the paper M.

  The sheet M that has reached the position directly below the photosensitive drum 131 is pressed and sandwiched between the transfer roller 135 and the photosensitive drum 131, while the positively charged toner image on the circumferential surface of the photosensitive drum 131 is negatively charged. The paper M is peeled off toward the front surface, whereby the paper M is transferred.

  The cleaning device 136 is for removing the toner remaining on the peripheral surface of the photosensitive drum 131 after the transfer process and cleaning it. The peripheral surface of the photosensitive drum 131 cleaned by the cleaning device 136 goes to the charger 132 again for the next image forming process.

  The fixing unit 20 performs a fixing process by heating the toner image on the paper M that has been transferred by the transfer unit 13. The fixing unit 20 heats the toner image on the paper M to fix the toner image on the paper M. A cylindrical heating roller (heating rotator) 30, and a cylindrical pressure roller (pressure rotator) 40 that is disposed below the heating roller 30 so as to sandwich the paper M between the heating roller 30 and the heating roller 30. Have The heating roller 30 and the pressure roller 40 are disposed in the box body 21. A rotational driving force is applied to the heating roller 30 from an unillustrated driving device and a speed reduction mechanism disposed in the box body 21. As the heating roller 30 is driven to rotate, the pressure roller 40 is driven and rotated. A nip N is formed between the heating roller 30 and the pressure roller 40. The paper M transferred by the transfer unit 13 is fed toward the nip N between the heating roller 30 and the pressure roller 40. By passing through the nip portion N, the sheet M obtains heat from the heating roller 30 and is subjected to a fixing process. The sheet M subjected to the fixing process is discharged to the paper discharge unit 15 through the paper discharge conveyance path 143.

  The paper discharge unit 15 is formed by recessing the top of the apparatus main body 11, and a paper discharge tray 151 for receiving the discharged paper M is formed at the bottom of the concave recess.

  Hereinafter, the configuration of the fixing unit 20 according to the present embodiment will be described with reference to FIGS. FIG. 2 is a perspective view showing a state in which the heating roller 30 and the pressure roller 40 are arranged in the box body 21. The heating roller 30 and the pressure roller 40 have axes C1 and C2, respectively. The box 21 has a shape extending in the direction of the axis C1 of the heating roller 30 and the axis C2 of the pressure roller 40, that is, the longitudinal direction of the heating roller 30 and the pressure roller 40. In this box 21, the heating roller 30 and the pressure roller 40 are arranged in a state of being opposed to each other in the vertical direction and in contact with each other along the axial centers C1 and C2. The sheet M transferred by the transfer unit 13 is guided to a nip N (FIG. 1) between the heating roller 30 and the pressure roller 40 through an opening (not shown) formed in the box 21.

  FIG. 3 is a cross-sectional view taken along the line AA in FIG. 2 and shows the constituent layers of the heating roller 30 and the pressure roller 40. The heating roller 30 is a cylindrical member having a substantially circular cross section, a heating belt portion 32 that heats the paper M on which the toner image is formed during the fixing process, a concentricity with the heating belt portion 32, and the heating belt. And a magnetic flux generation unit 36 that is disposed inside the unit 32 and generates a magnetic flux to cause the heating belt unit 32 to generate heat by the magnetic flux. An air layer 34 is interposed between the heating belt portion 32 and the magnetic flux generation portion 36. The heating belt portion 32 is configured to be rotatable with respect to the magnetic flux generation portion 36.

  The heating belt portion 32 includes a cylindrical and hollow roller base material (rotary body base material) 35 having an axis C1 as an axis, and heat insulation provided on the outer peripheral surface of the roller base material 35 concentrically with the roller base material 35. And a heat generating layer 31 provided on the outer peripheral surface of the heat insulating layer 33 concentrically with the roller base material 35.

  The roller base 35 is manufactured from a rigid member capable of imparting mechanical strength to the heating roller 30, for example, a ceramic material. This ceramic material is a ceramic material having non-magnetic and non-conductive characteristics, and is preferably mullite or alumina. The thickness of the roller base material 35 is set to 1.0 mm, for example.

  The heat generating layer 31 is formed of an alloy containing nickel and having a thickness of about 40 μm, an elastic layer having elasticity provided on the outer peripheral surface of the heat generating layer base, and an outer peripheral surface of the elastic layer. And a release layer that forms the outermost layer of the heating roller 30. The elastic layer is made of, for example, silicon rubber and has a thickness set to 300 μm. The release layer is obtained, for example, by coating a fluororesin paint (coating agent) such as PFA on the outer peripheral surface of the elastic layer with a thickness in the range of about 10 to 100 μm, for example. This release layer improves the releasability when the toner image is melted and fixed at the nip N between the heating roller 30 and the pressure roller 40.

  The heat insulating layer 33 is made of, for example, silicon sponge having heat insulating properties and elasticity, and heat of the heat generating layer 31 generated by the magnetic flux generating unit 36 to be described later becomes radiant heat (so-called heat) to heat the magnetic flux generating unit 36. In order to prevent the magnetic flux generator 36 from being burned out. The thickness of the heat insulation layer 33 is set to 5.0 mm, for example.

  Further, since the heat insulating layer 33 has elasticity, if the nip portion N is depressed by the pressing force of the pressure roller 40 during the fixing process, the distance between the magnetic flux generating portion 36 and the heat generating layer 31 is minimized. . Thereby, the magnetic coupling degree between the magnetic flux generation part 36 and the heat generating layer 31 can be increased in the nip part N. As a result, the heat generation efficiency in the nip portion N of the heat generation layer 31 can be improved.

  The magnetic flux generator 36 is configured to be able to heat the heating belt portion 32 by electromagnetic induction, extends concentrically with the axial center C1 of the heating roller 30 and extends in the longitudinal direction of the heating roller 30, and is arranged inside the heating belt portion 32. A cylindrical bobbin 37 made of a liquid crystal polymer, a plurality of magnetic cores 39 having an arcuate cross section centered on an axis C1 disposed in contact with the inner peripheral surface of the bobbin 37, and a bobbin 37 A so-called radial coil (Litz wire) 38 wound around the outer peripheral surface. The magnetic core 39 is, for example, a ferrite core, has a shape extending in the longitudinal direction of the bobbin 37, and is arranged in two rows so as to form an annular core with the two magnetic cores 39 as shown in FIG. Yes.

  When a high frequency current is supplied to the coil 38 from a high frequency power supply (not shown), a magnetic flux is generated from the coil 38. The magnetic flux travels outward in the radial direction of the bobbin 37, passes through the roller base 35 and the heat insulating layer 33 made of a nonmagnetic and nonconductive ceramic material, and reaches the heat generating layer base of the heat generating layer 31. Thereby, magnetic paths P, P1, and P2 (FIG. 4) described later are formed, and the heat generating layer base material generates heat. The toner image on the paper M is melted and fixed at the nip portion N by the heat of the heat generating layer base material.

  Since the coil 38 is wound around the outer peripheral surface of the bobbin 37 extending in the longitudinal direction of the roller base 35, the magnetic flux is uniformly distributed outward in the radial direction of the bobbin 37, that is, toward the heat generating layer 31. Can do. Therefore, since the roller base material 35 and the air layer 34 having a low magnetic permeability are interposed between the magnetic flux generator 36 and the heat generating layer 31, even if the distance between the magnetic flux generator 36 and the heat generating layer 31 increases. It is possible to ensure the degree of magnetic coupling between the magnetic flux generator 36 and the heat generating layer 31. As a result, even if the distance between the magnetic flux generator 36 and the heat generating layer 31 is large, the heat generation efficiency of the heat generating layer 31 can be improved.

Further, the heating roller 30 has a distance between the inner peripheral surface of the heat generating layer 31 and the thickness central portion of the coil 38 as viewed from the axial center C1, and between the outer peripheral surface of the magnetic core 39 and the thickness central portion of the coil 38. When the distance is D2, it is configured to satisfy the following formula (1).
D1> D2 (1)

  By satisfying the expression (1), the magnetic coupling degree between the magnetic core 39 and the coil 38 can be set larger than the magnetic coupling degree between the heat generating layer 31 and the coil 38, so that the magnetic flux generated from the coil 38 can be used as the magnetic core 39. Can be smoothly guided to the heat generating layer 31 according to the arrangement. Thereby, it becomes easy to adjust the heat generating range of the heat generating layer 31. Therefore, by appropriately adjusting the arrangement of the magnetic cores 39, temperature sagging and the like can be suppressed at both ends of the heat generating layer 31 in the longitudinal direction of the roller base 35. In addition, since the heat generation range of the heat generation layer 31 greatly depends on the arrangement of the magnetic core 39, the heat generation range adjustment performance due to the movement of the magnetic core 39 can be improved.

  The pressure roller 40 is arranged concentrically with the axis C2 and is made of a non-magnetic metal roller base (not shown), an elastic layer (not shown) provided on the outer peripheral surface of the roller base, and an outer periphery of the elastic layer. And a release layer (not shown) provided on the surface. Examples of the nonmagnetic metal of the roller base material include aluminum, copper, silver, and austenitic stainless steel. The thickness of the roller base material is set to about 1 to 5 mm, for example, to give mechanical strength to the roller base material. The elastic layer and the release layer of the pressure roller 40 are made of the same material as the elastic layer and the release layer of the heating roller 30.

  A heater (not shown) such as a halogen heater may be disposed inside the pressure roller 40. Since the roller base material of the pressure roller 40 can be heated by this heater, it is possible to maintain the temperature of the pressure roller 40 during the print standby when the heating roller 30 does not rotate. This prevents heat from being removed from the heating roller 30 by the pressure roller 40 at the start of printing or the like, so that the temperature drop of the heating roller 30 can be minimized. As a result, good fixability of the toner image can be ensured.

  The heating roller 30 and the pressure roller 40 are in contact with each other via the nip portion N during the fixing process. At this time, the heating roller 30 receives a pressing force from the pressure roller 40 along the longitudinal direction of the heating roller 30, and the heat generating layer 31 and the elastic layer 33 are recessed as shown in FIG. The heating layer base material of the heating layer 31 of the heating roller 30 is a member having a certain mechanical strength, but it cannot be said that the heating layer base material has a sufficient mechanical strength against the pressing force of the pressure roller 40. For this reason, the heating roller 30 may be deformed. However, in the present embodiment, the roller base 35 provided with the heat generating layer 31 is formed of a ceramic material, thereby giving the heating roller 30 mechanical strength that can withstand the pressing force of the pressure roller 40. Therefore, deformation of the heating roller 30 can be prevented.

  A thermistor 43 for detecting the temperature of the outer peripheral surface of the heating roller 30 is disposed at a position spaced a predetermined distance outward in the radial direction of the heating roller 30. The thermistor 43 is a ceramic semiconductor that uses metal oxide as a main raw material and is sintered at a high temperature, and has a negative temperature coefficient that decreases as the temperature rises. That is, the temperature of the heat generating layer 31 is detected. A high-frequency current supplied to a coil 38 (to be described later) is adjusted by a control unit (not shown) based on a signal indicating the outer surface temperature of the heating roller 30 detected by the thermistor 43, and the outer surface temperature of the heating roller 30 is predetermined. The temperature is controlled so as to be maintained.

  4 is a cross-sectional view taken along the line BB in FIG. 2, and a plurality of magnetic cores 39 are arranged in two rows on the inner peripheral surface of the bobbin 37 extending in the longitudinal direction of the heating roller 30 as described above. The arrangement | positioning is shown. The magnetic core 39 has a shape extending along the coil 38 radially wound around the bobbin 37 and parallel to the heat generating layer 31. A magnetic path P through which the magnetic flux generated by the coil 38 passes is formed between the magnetic core 39, the air layer 34, the roller base 35, the heat insulating layer 33, and the heat generating layer 31 having such a shape.

  Among the plurality of magnetic cores 39, the magnetic cores 39 disposed at both ends in the longitudinal direction of the bobbin 37 are disposed so as to be movable in the longitudinal direction along the inner peripheral surface of the bobbin 37. The magnetic core 39 before movement is indicated by a solid line, and the magnetic core 39 after movement is indicated by an imaginary line. The magnetic core 39 before moving forms a magnetic path P <b> 1 among the air layer 34, the roller base 35, the heat insulating layer 33, and the heat generating layer 31. When the magnetic core 39 is moved in the longitudinal direction, the magnetic path P1 is moved in the longitudinal direction to form the magnetic path P2. In other words, the distribution range of the magnetic flux generated by the coil 38 can be adjusted along the longitudinal direction of the heating roller 30. Therefore, the heat generation range in the heat generating layer 31 of the heating belt portion 32 can be adjusted along the longitudinal direction of the heating roller 30. Accordingly, the toner image on the paper M can be heated and fixed on the paper M according to the sizes W1 and W2 of the paper M. In FIG. 4, the magnetic path P1 is formed by moving the magnetic core 39 according to the size W1 of the paper M, while the magnetic path P2 is the magnetic core 39 according to the size W2 of the paper M. It is formed by moving. The amount of movement of the magnetic core 39 can be accurately adjusted by moving it using a stepping motor.

  As shown in FIG. 4, the heating roller 30 is provided with a blower 45, such as a blower fan, which is arranged so as to blow air from one end side of the magnetic flux generation unit 36 toward the multi-end side in order to cool the magnetic flux generation unit 36. I have. Since the roller base material 35 is manufactured from a ceramic material, the cooling air from the blower 45 does not reach the heat generation layer 31 through the roller base material 35 and cool the heat generation layer 31. And only the coil 38 is cooled through the air layer 34 between the roller bases 35.

  As described above, in the embodiment having the above-described configuration, the roller base 35 provided with the heat insulating layer 33 and the heat generating layer 31 is manufactured from a rigid member, for example, a ceramic material. The mechanical strength with respect to the pressing force received from the pressure roller 40 along the longitudinal direction of the roller base 35 when the recording medium M is sandwiched between the pressure roller 40 in the portion N can be obtained. In addition, since the roller base 35 is nonmagnetic and nonconductive, it does not prevent the magnetic flux from the magnetic flux generator 36 from reaching the heat generating layer 31. Therefore, the heat generating layer 31 can reach the temperature at which the toner image can be heated and fixed on the recording medium M in a short time. Thus, according to the fixing unit 20 of the present embodiment, both shortening of the warm-up time of the heating roller 30 and ensuring of mechanical strength can be obtained.

  FIG. 5 is a schematic diagram showing a configuration in which the fixing unit 20 is applied to a so-called pressure belt system. In the fixing unit 20, an endless belt 52 stretched between a pair of rollers 50 and 51 is arranged in contact with the heating roller 30 instead of the pressure roller 40. The belt 52 is a substantially intermediate portion between the pair of rollers 50 and 51 and is in contact with the heating roller 30, and the nip portion N is formed between the outer peripheral surface of the intermediate portion and the heating roller 30.

  Also in this configuration, the heating roller 30 receives a pressing force from the belt 52 along the longitudinal direction of the roller base 35 when the recording medium M is sandwiched between the heating roller 30 and the belt 52 at the nip portion N. However, since the roller base 35 of the heating roller 30 is made of a rigid member, for example, a ceramic material, the heating roller 30 can obtain mechanical strength against the pressing force by the belt 52.

1 is a schematic diagram of an image forming apparatus including a fixing unit according to an embodiment of the present invention. FIG. 4 is a perspective view showing a state where a heating roller and a pressure roller of the fixing unit are arranged in a box. It is sectional drawing cut | disconnected along the AA line of FIG. It is sectional drawing cut | disconnected along the BB line of FIG. FIG. 3 is a schematic diagram illustrating a configuration in which a fixing unit is applied to a pressure belt system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 20 Fixing unit 30 Heating roller 31 Heat generation layer 32 Heating belt part 33 Heat insulation layer 34 Air layer 35 Roller base material 36 Magnetic flux generation part 37 Bobbin 38 Coil 39 Magnetic core 40 Pressure roller 50, 51 Roller 52 Belt P, P1, P2 magnetic path

Claims (7)

A fixing unit for fixing a toner image transferred onto a recording medium onto the recording medium,
A heating rotator for heating the toner image on the recording medium to fix the toner image on the recording medium;
A pressure rotator for sandwiching the recording medium with the heating rotator, and
With
The heating rotator is
A cylindrical and hollow rotating body substrate;
A magnetic flux generator provided inside the rotating body base material for generating magnetic flux;
A heating layer that is provided on the rotating body substrate and generates heat by the magnetic flux to heat the toner image;
A heat insulating layer provided between the rotating body base and the heat generating layer and having a heat insulating property to prevent heat of the heat generating layer from being transmitted to the magnetic flux generation unit;
Including
The rotating body substrate is a fixing unit made of a non-magnetic and non-conductive rigid member.   The fixing unit according to claim 1, wherein the rigid member is a ceramic material.   3. The fixing unit according to claim 1, wherein the magnetic flux generation unit is disposed inside the bobbin and a cylindrical bobbin that is concentric with the rotary base material and extends in a longitudinal direction of the rotary base material. A fixing unit including a magnetic core and a coil wound around the circumferential surface of the cylindrical bobbin.   The fixing unit according to claim 3, wherein a plurality of the magnetic cores are arranged so as to be movable in the longitudinal direction of the rotating body base within the bobbin. 5. The fixing unit according to claim 3, wherein a distance between the heating layer and the coil is D <b> 1 and a distance between the magnetic core and the coil is D <b> 2 when viewed from the axial center of the heating rotating body. Then, the fixing unit satisfying the following expression (1).
(1) D1> D2   3. The fixing unit according to claim 2, further comprising a blower arranged to allow air to flow inside the rotating body base so as to cool the magnetic flux generation unit. A transfer unit for transferring a toner image formed on the photosensitive drum to a recording medium;
The fixing unit according to any one of claims 1 to 6, wherein the toner image is fixed to the recording medium.
An image forming apparatus.

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