JP2014139613A - Fixing unit and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing unit which is capable of suppressing impedance increase, when a temperature becomes a Curie temperature or higher by weakening the demagnetization effect of a part of a demagnetization part, with a simple structure and without strength decrease and to provide an image forming apparatus.SOLUTION: The fixing unit is an electromagnetic overheat type fixing unit and comprises: an exciting coil generating a magnetic flux; a heating part electromagnetically induced by the magnetic flux from the exciting coil; a temperature-sensitive magnetic part which is oppositely arranged on the side away from the exciting coil of the heating part and becomes a nonmagnetic body from a ferromagnetic body, when the temperature reaches the Curie temperature; and a demagnetization part 54 generating a repulsive magnetic flux for canceling the magnetic flux of the exciting coil by the magnetic flux from the exciting coil, after passing through the temperature-sensitive magnetic part. A mesh type groove 54A is provided in a part except both ends in the width direction of a paper, in the surface on the side of the temperature-sensitive magnetic part of the demagnetization part 54.

Description

  The present invention relates to a fixing unit that fixes toner on a sheet, a fixing device including a heating unit that heats the fixing unit, and an image forming apparatus.

  In recent years, from the viewpoint of energy saving, it has become necessary to shorten the rise time from the start of heating of the fixing device until the paper can be passed. Therefore, a fixing device using a heat roller or a belt using an IH heater as a heat source using electromagnetic induction heating having higher heat exchange efficiency than a conventional halogen heater has been proposed.

  In this electromagnetic induction heating type fixing device, since the heat generating portion is thin, it is difficult to control the temperature distribution in the paper width direction. For this reason, heat is taken away by the paper in the paper passing area of the fixing unit (the area where the paper is passed), but heat is not taken away by the paper in the non-paper passing area (the area where the paper is not passed). Becomes too high.

  In view of this, an electromagnetic induction heating type fixing device has been proposed in which a demagnetizing portion that generates a repulsive magnetic flux that cancels the magnetic flux of the exciting coil is used to prevent overheating of the fixing portion. The fixing device further includes a temperature-sensitive magnetic portion that changes from a ferromagnetic material to a non-magnetic material when the temperature is equal to or higher than the Curie temperature, between the exciting coil and the demagnetizing portion. With the above configuration, when the fixing unit is overheated and the temperature-sensitive magnetic unit becomes equal to or higher than the Curie temperature, the magnetic flux from the exciting coil passes through the temperature-sensitive magnetic unit and reaches the demagnetizing unit, thereby generating an eddy current. Due to this eddy current, a repulsive magnetic flux that cancels the magnetic flux from the exciting coil is generated in the demagnetizing portion, thereby preventing overheating (Patent Document 1).

  However, when the above fixing device reaches the Curie temperature even when it is below the Curie temperature at the start of heating, the magnetic flux of the exciting coil is canceled out, so the impedance applied to the power supply rises extremely and the power load increases. Depending on the situation, there was a problem that the power was turned off.

  Thus, for example, a technique has been proposed in which the center of the demagnetization part is narrowed to partially weaken the demagnetization effect at the center of the demagnetization part (Patent Document 2). However, in this case, the degaussed portion becomes extremely weak against twisting, and thus may be distorted when thermally expanded. In addition, there is also described a technique in which the electrical resistance at the center of the demagnetization part is changed to partially weaken the demagnetization effect at the center of the demagnetization part (Patent Document 3). However, there is a problem that the central portion needs to be provided as a separate member and the structure becomes complicated.

  The present invention has been made in view of the above circumstances, and the impedance is increased when the temperature becomes equal to or higher than the Curie temperature by weakening the demagnetizing effect of a part of the demagnetized portion without reducing the strength with a simple structure. It is an object of the present invention to provide a fixing device and an image forming apparatus that can suppress the above-described problem.

  In order to solve the above-described problem, the invention according to claim 1 is a fixing device including a fixing unit that fixes toner on a sheet and a heating unit that heats the fixing unit. Are arranged opposite to the exciting coil that generates magnetic flux, a heat generating part that is induction-heated by the magnetic flux from the exciting coil, and a side of the heat generating part away from the exciting coil. A non-magnetic temperature-sensitive magnetic part; and a demagnetizing part that generates a repulsive magnetic flux that cancels the magnetic flux of the exciting coil by the magnetic flux from the exciting coil that has passed through the temperature-sensitive magnetic part. The fixing device according to claim 1, wherein the plurality of concave portions are provided in a portion of the surface on the temperature-sensitive magnetic portion side excluding both ends in the width direction of the paper.

  According to the fixing device of the first aspect, since the surface of the demagnetizing portion on the temperature-sensitive magnetic portion side is provided with a plurality of concave portions in the portion excluding both ends in the width direction of the paper, The eddy current is divided and cannot flow due to the concave portion of the magnet, and the magnetic flux of the exciting coil cannot be canceled. As a result, simply by providing a plurality of recesses in the demagnetization part, the structure is simple and the demagnetization effect of a part of the demagnetization part can be weakened without reducing the strength. Can be suppressed.

It is a schematic sectional drawing which shows one Embodiment of the fixing device of this invention. It is a fragmentary sectional view of the heating roller shown in FIG. FIG. 2 is a perspective view of a demagnetizing part shown in FIG. 1. It is a figure which shows an example of the conventional demagnetizing part. (A) is a figure which shows the path | route of the eddy current which flows into the conventional demagnetization part shown in FIG. 4, (B) is a figure which shows the path | route of the eddy current which flows into the demagnetization part of this embodiment shown in FIG. (A) is a figure which shows the repulsion magnetic flux which arises in the conventional demagnetization part shown in FIG. 4, (B) is a figure which shows the repulsion magnetic flux which arises in the demagnetization part of this embodiment shown in FIG. Impedance with respect to temperature was measured for the fixing device using the conventional demagnetizing unit shown in FIG. 4 (conventional product) and the fixing device using the demagnetizing unit of the present embodiment shown in FIG. 3 (product of the present invention). It is a graph which shows a result. It is a perspective view of a demagnetizing part in other embodiments.

  A fixing device and an image forming apparatus according to the present invention will be described with reference to FIGS. The fixing device 1 shown in FIG. 1 is incorporated in an image forming apparatus (not shown). An image forming apparatus (not shown) can form an image on a plurality of types of paper having different sizes in the width direction. Here, the papers having different sizes in the width direction include papers of non-standard sizes in addition to papers of various standard sizes in the A and B rows of JIS dimensions.

  Further, the width direction is a direction orthogonal to the paper conveyance direction. Even if the same paper (for example, A4 paper) is used, if the longitudinal direction is the conveyance direction, the short direction becomes the width direction, and the short direction. Is the transport direction, the longitudinal direction is the width direction.

  As shown in FIG. 1, the fixing device 1 includes a fixing unit 3 that fixes toner T onto a sheet 2, a pressure roller 4 that is disposed in pressure contact with the fixing unit 3, and a heating unit that heats the fixing unit 3. 5 is provided.

  The fixing unit 3 includes a fixing roller 31 and a fixing belt 32 stretched between the fixing roller 31 and a heating roller 53 described later. The fixing roller 31 is provided in a columnar shape or a cylindrical shape, and is provided so as to be rotatable around its central axis. The fixing belt 32 is a belt-like endless belt and is heated by the heating roller 53.

  The pressure roller 4 is provided in a columnar shape or a cylindrical shape, and is provided so as to be rotatable around its central axis. The pressure roller 4 is pressed against the fixing roller 31 through the heated fixing belt 32. When the sheet 2 is sandwiched between the fixing roller 31 and the fixing belt 32 and the pressure roller 4 with the toner T facing the fixing unit 3 side, and the fixing roller 31 and the pressure roller 4 are rotated in the opposite directions, The sheet 2 is conveyed and the toner T is fixed by the heat of the fixing belt 32.

  The heating unit 5 is provided in the heating roller 53, a core 51 made of a magnetic material, an excitation coil 52 wound around the core 51 to generate magnetic flux, a heating roller 53 that is induction-heated by the excitation coil 52, and the heating roller 53. And a demagnetizing part 54.

  The core 51 is provided in a bowl shape with a cross-sectional arc covering the heating roller 53, and efficiently guides the magnetic flux generated by the excitation coil 52 to the heating roller 53. The core 51 protrudes from the center in the radial direction toward the heating roller 53, and protrudes in a direction approaching each other from the center core 51 </ b> A along the longitudinal direction of the heating roller 53, and along the longitudinal direction of the heating roller 53. Side core 51B is provided. The exciting coil 52 is wound around the center core 51A in a spiral shape.

  As shown in FIG. 2, the heating roller 53 includes a temperature-sensitive magnetic part 53A provided in a cylindrical shape, and a heat-generating layer 53B as a heat-generating part whose surface is plated on the exciting coil 52 side of the temperature-sensitive magnetic part 53A. It has. The temperature-sensitive magnetic part 53A is disposed opposite to the side farther from the exciting coil 52 than the heat generating layer 53B. The temperature-sensitive magnetic portion 53A is a ferromagnetic material at room temperature, shields the magnetic flux from the exciting coil 52, changes from a ferromagnetic material to a non-magnetic material when the Curie temperature is reached, and transmits the magnetic flux. The temperature-sensitive magnetic part 53A is provided with a Curie temperature of 100 ° C. to 300 ° C. by adjusting the composition.

  The heat generating layer 53B is made of copper, for example, and is plated on the surface of the temperature-sensitive magnetic part 53A. The heat generating layer 53B generates heat by generating eddy current on the surface by the magnetic flux from the exciting coil 52, and generating Joule heat by the electric resistance of the heat generating layer 53B itself.

  For example, as shown in FIG. 3, the demagnetizing unit 54 is provided in a cylindrical shape and is accommodated in the heating roller 53. The demagnetizing part 54 is disposed on the side farther from the exciting coil 52 than the temperature-sensitive magnetic part 53A, and is made of a nonmagnetic material having a lower electrical resistivity than the temperature-sensitive magnetic part 53A such as aluminum. On the surface of the demagnetizing portion 54 on the temperature-sensitive magnetic portion 53A side, a plurality of mesh-shaped grooves 54A (concave portions) are formed in a portion excluding both ends of the paper 2 in the width direction. That is, the plurality of mesh-shaped grooves 54 </ b> A are provided only at the center of the demagnetizing portion 54. The groove 54A is formed by cutting the surface of the demagnetized portion 54.

  The plurality of grooves 54A are provided, for example, in an area through which the paper 2 having the minimum width passes. For example, if the minimum width is A4 length, a mesh-like groove 54A is provided in 210 mm at the center of the demagnetization portion 54, and if it is A5 length, a mesh-like groove 54A is provided in 105mm at the center of the demagnetization portion 54. The depth of the groove 54A is greater than the skin depth of the eddy current flowing in the demagnetizing portion 54 due to the magnetic flux from the exciting coil 52 that has passed through the temperature-sensitive magnetic portion 53A.

  Next, a general operation of the above-described fixing device 1 will be described. First, when the exciting coil 52 is energized by a power supply circuit (not shown), a magnetic flux is generated in the exciting coil 52. When the magnetic flux of the exciting coil 52 reaches the heat generating layer 53B of the heating roller 53, an eddy current is generated in the heat generating layer 53B, an eddy current is generated, and Joule heat is generated by the electric resistance of the heat generating layer 53B itself to generate heat. . As a result, the fixing belt 32 in contact with the heat generating layer 53B is heated.

  While the temperature-sensitive magnetic part 53A is equal to or lower than the Curie temperature, the temperature-sensitive magnetic part 53A is a ferromagnetic body, so the magnetic flux from the excitation coil 52 is shielded by the temperature-sensitive magnetic part 53A and does not reach the demagnetizing part 54. On the other hand, when the temperature-sensitive magnetic part 53A reaches the Curie temperature due to the heat generation of the heat-generating layer 53B, the temperature-sensitive magnetic part 53A changes from a ferromagnetic material to a non-magnetic material, transmits the magnetic flux from the exciting coil 52, and degausses. 54 generates eddy currents on the surface.

  The eddy current generated on the surface of the demagnetizing portion 54 generates a repulsive magnetic flux that is in a direction opposite to the magnetic flux generated in the exciting coil 52. Therefore, the magnetic flux density on the heat generating layer 53B is lowered by the repulsive magnetic flux, and the heat generating layer 53B is heated. Thus, overheating of the fixing belt 32 can be prevented.

  As described above, the repulsive magnetic flux generated in the demagnetizing unit 54 suppresses the magnetic field generated by the exciting coil 52, so that the load on the exciting coil 52 as viewed from the power supply circuit increases and the impedance increases.

  Next, the effect obtained by providing the mesh-shaped groove 54A in the demagnetizing portion 54, which is a feature of the present invention, will be described with reference to FIGS. FIG. 4 shows an example of a conventional demagnetizing unit 54. FIG. 5A is a diagram showing a path of eddy current flowing in the conventional demagnetizing section 54 shown in FIG. 4, and FIG. 5B is a diagram showing eddy current flowing in the demagnetizing section 54 of the present embodiment shown in FIG. It is a figure which shows a path | route. It should be noted that no current flows in the hatched area drawn toward the lower left in the figure, and a large current flows in the hatched area drawn in the lower right. 6A is a diagram showing a repulsive magnetic flux generated in the conventional demagnetizing portion 54 shown in FIG. 4, and FIG. 6B is a diagram showing a repulsive magnetic flux generated in the demagnetizing portion 54 of the present embodiment shown in FIG. is there.

  As shown in FIG. 4, when the plurality of grooves 54A are not provided, an eddy current flows along a path indicated by a dotted arrow in FIG. That is, a looped eddy current flows from one end to the other end in the longitudinal direction of the degaussing portion 54 and returns from the other end to the one end. As a result, as shown in FIG. 6A, a repulsive magnetic flux uniformly indicated by a U-turn arrow is generated along the longitudinal direction.

  On the other hand, when a plurality of grooves 54A are provided as shown in FIG. 3, an eddy current flows along a path indicated by a dotted arrow in FIG. That is, a loop-shaped eddy current that goes from one end in the longitudinal direction of the demagnetizing portion 54 to the front of the central portion where the plurality of grooves 54A are provided, and returns from the front of the central portion to one end in the longitudinal direction, and a plurality of from the other end in the longitudinal direction. A loop-like eddy current flows to the front of the center where the groove 54A is provided and returns from the front of the center to the other end in the longitudinal direction. That is, almost no current flows in the central portion of the demagnetized portion 54 provided with the plurality of grooves 54A, and no repulsive magnetic flux is generated in the center as shown in FIG. This is because the loop of the eddy current is cut and divided by the groove 54A provided beyond the skin depth.

  Therefore, by providing the plurality of grooves 54A, it is possible to weaken the demagnetizing effect only at the central portion of the demagnetizing portion 54. For this reason, although the effect of preventing overheating at the center of the fixing belt 32 is lowered, the center of the fixing belt 32 is a portion corresponding to the paper passing area through which the paper is passed. There is no need to arrange the demagnetizing section 54. The temperature rise becomes a problem at both ends where the paper 2 is not passed. According to the present embodiment, for the convenience of using the threading member, when the demagnetizing part 54 is also arranged at the center of the fixing belt 32, the structure can be simplified by providing the groove 54A at the center of the demagnetizing part 54, and Without degrading the strength, the demagnetizing effect of a part of the demagnetizing portion 54 can be weakened, and an increase in impedance can be suppressed when the temperature becomes equal to or higher than the Curie temperature.

  Further, according to the above-described embodiment, the heat generating layer 53B is formed by plating the surface of the temperature-sensitive magnetic part 53A. Thus, the heat generating layer 53B can be easily formed by plating.

  Further, according to the embodiment described above, the heat generating layer 53B is made of copper. Thereby, induction heating is efficiently performed in the heat generation layer 53B.

  Further, according to the above-described embodiment, the demagnetizing portion 54 is made of aluminum. Thereby, a repulsive magnetic flux is efficiently generated in the demagnetizing portion 54.

  Next, in order to confirm the effect of this embodiment, the present inventors have used the fixing device 1 (conventional product) using the conventional demagnetizing section 54 shown in FIG. 4 and the demagnetization of this embodiment shown in FIG. With respect to the fixing device 1 (product of the present invention) using the section 54, the impedance with respect to temperature was measured. The results are shown in FIG. As is clear from the figure, it was confirmed that by providing a plurality of grooves 54A, the product of the present invention can lower the impedance after the Curie temperature rises compared to the conventional product.

  In the above-described embodiment, a cylindrical shape is used as the demagnetizing portion 54, but the present invention is not limited to this. For example, as shown in FIG. 8, it is conceivable to form the demagnetizing portion 54 in a bowl shape.

  In the above-described embodiment, the plurality of grooves 54A are provided in the region through which the sheet 2 having the minimum width passes, but the present invention is not limited to this. The plurality of grooves 54 </ b> A may be provided in a portion excluding both ends of the demagnetizing unit 54, and may be provided, for example, in an area through which the sheet 2 with high printing frequency passes.

  In the embodiment described above, a plurality of mesh-shaped grooves 54A are provided at the center of the demagnetizing portion 54, but the present invention is not limited to this. For example, the plurality of grooves 54A may be provided in a lattice shape, or may be simply arranged side by side in the lateral direction or the longitudinal direction. It is also conceivable to provide a plurality of fine recesses, for example, so that the eddy current loop can be divided instead of the groove 54A.

  In the embodiment described above, the heat generating layer 53B is provided by plating on the surface of the temperature-sensitive magnetic part 53A, but the present invention is not limited to this. It may not be provided by plating.

  In the above-described embodiment, copper is used as the heat generating layer 53B, but the present invention is not limited to this. As the heat generating layer 53B, any material having good conductivity can be used as long as it generates heat by generating eddy current on the surface by the magnetic flux from the exciting coil 52.

  In the embodiment described above, aluminum is used as the demagnetizing portion 54, but the present invention is not limited to this. The demagnetizing part 54 is a nonmagnetic material having a lower electrical efficiency than the temperature-sensitive magnetic part 53A, and may be made of other materials as long as a repulsive magnetic flux is generated.

  In the above-described embodiment, the heat-sensitive magnetic part 53A plated with the heat generating layer 53B is provided on the heating roller 53 to heat the fixing belt 32. However, the present invention is not limited to this. For example, the fixing belt 32 may be provided with a temperature-sensitive magnetic part 53A plated with the heat generating layer 53B. Further, it may be provided on the fixing roller 31 or a film provided on the surface of the fixing roller 31. That is, the temperature-sensitive magnetic part 53A may be provided as at least one of a film, a roller, and an endless belt.

  The present invention is not limited to the above embodiment. That is, various modifications can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Fixing device 2 Paper 3 Fixing part 5 Heating part 32 Fixing belt (endless belt)
52 Excitation coil 53A Temperature-sensitive magnetic part 53B Heat generation layer (heat generation part)
54 Demagnetizing section 54A Plural grooves (plural recesses)

JP 2000-30850 A JP 2007-279672 A JP 2007-264421 A

Claims (8)

A fixing device comprising: a fixing unit that fixes toner on a sheet; and a heating unit that heats the fixing unit,
The heating unit is
An exciting coil that generates magnetic flux;
A heat generating portion that is induction-heated by magnetic flux from the exciting coil;
A temperature-sensitive magnetic part that is disposed opposite to the side away from the exciting coil of the heat generating part and becomes a non-magnetic substance from a ferromagnetic substance when the Curie temperature is reached,
A demagnetizing part that generates a repulsive magnetic flux that cancels the magnetic flux of the exciting coil by the magnetic flux from the exciting coil that has passed through the temperature-sensitive magnetic part,
The fixing device, wherein the plurality of concave portions are provided in a portion of the surface of the demagnetizing portion on the temperature-sensitive magnetic portion side excluding both ends in the width direction of the paper. The fixing device according to claim 1, wherein the plurality of recesses are configured by a plurality of grooves provided in a mesh shape. The fixing device according to claim 1, wherein the plurality of recesses are configured by a plurality of grooves. The fixing device according to any one of claims 1 to 3, wherein the heat generating part is formed by plating the surface of the temperature-sensitive magnetic part. The fixing device according to claim 1, wherein the heat generating portion is made of copper. The fixing device according to any one of claims 1 to 5, wherein the demagnetizing portion is made of aluminum. The fixing device according to any one of claims 1 to 6, wherein the temperature-sensitive magnetic unit is provided as at least one of a film, a roller, and an endless belt.   An image forming apparatus comprising the fixing device according to claim 1.

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