JP2003077645A - Heater and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heater which can suppress temperature rise in the area of a heating medium where no paper exists without changing the size of the heater or wasteful overheating of a magnetic flux shield plate. SOLUTION: In the heater comprising the heating medium having a conductive layer and an induction heating source for heating the heating medium by the induction heating, a flexible, magnetic flux shield member for shielding a part of the magnetic flux reaching the heating medium is disposed between the heating medium and the induction heating source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic copying machine, a printer, a facsimile, a composite machine thereof, and the like, and a heating device for heating and melting a developer on an unfixed image to fix it on a recording material. The present invention relates to an image forming apparatus including a heating device.

[0002]

2. Description of the Related Art In an electrophotographic copying machine, the toner (developer) of a toner image (unfixed image) transferred onto a recording material, which is a recording medium to be conveyed, is melted by heat to perform the recording. A heating device for fusing onto the material is provided. In this heating device, in order to raise the temperature at a high speed, a fixing roller, which is a heating medium, is made thin and has a small diameter, a rotating body of resin film is pressed against the rotating body from the inside, and a thin metal rotating body is guided. Although heating by heating is known, all of them are intended to reduce the heat capacity of a rotating body which is a heating medium and to heat with a heat source having high heating efficiency.

Although a non-contact heating source is also used, in view of cost and energy efficiency, in an image forming apparatus such as a copying machine, a thin rotary member is brought into contact with a recording material to form a recording material on the recording material. Many heating devices of the type that heat and melt the developer have been proposed.

However, when a thin rotating body is used as a heating medium in order to reduce the heat capacity, the heat transfer coefficient in the axial direction is not good because the cross-sectional area of the cross section perpendicular to the axis is extremely small. This tendency becomes more remarkable as the wall thickness becomes thinner, and it becomes even lower for materials such as resins having low thermal conductivity. When the thermal conductivity is λ, the temperature difference between the two points is θ1−θ2, and the length is L, the heat quantity Q transferred per unit time is expressed by Q = λ · f (θ1−θ2) / L It is also clear from Fourier's law that it is done.

This is not a problem when a recording material having the full length in the longitudinal direction of the rotating body, that is, a recording material having a maximum paper passing width is passed through and fixed, but a recording material having a small width and a small size is used. When the paper is continuously passed, the temperature in the non-paper-passing area of the rotating body rises above the temperature control temperature, and the temperature difference between the temperature in the paper-passing area and the temperature in the non-paper-passing area becomes extremely large. There was a problem.

Therefore, due to such temperature unevenness of the heating medium in the longitudinal direction, there is a possibility that the heat resistant life of the peripheral member made of the resin material may be shortened or the thermal damage may be caused.
Further, when a large-sized recording material is passed immediately after a small-sized recording material is continuously passed, there is a possibility that paper wrinkles, skew, or fixing unevenness may occur due to partial temperature unevenness. There is also a problem.

The temperature difference between the paper passing area and the non-paper passing area increases as the heat capacity of the recording material conveyed is large and the throughput (the number of prints per unit time) is increased. Therefore, when the heating device is composed of a thin-walled, low-heat-capacity rotating body, it is difficult to apply it to a copying machine having a high throughput.

On the other hand, in a heating device using a halogen lamp or a heating resistor as a heating source, it is known that the heating source is divided and selectively energized so as to heat a region according to the sheet passing width. There is. Further, even in a heating device using an induction coil as a heating source, there is one in which the heating source is similarly divided and selectively energized.

However, if a plurality of heating sources are provided or divided, the control circuit is complicated and the cost is increased accordingly, and the number of divisions is further increased in order to cope with recording materials of various widths. The cost will be higher.
Moreover, if a thin rotary member is used as the heating medium, the temperature distribution near the boundary when divided is discontinuous and non-uniform, which may affect the fixing performance.

Therefore, between the heating medium and the induction heating source,
It has been proposed so far to dispose a magnetic flux shielding means for shielding a part of the magnetic flux reaching the heating medium from the induction heating source and to provide a displacement means for changing the position of the magnetic flux shielding means (Japanese Patent Laid-Open No. 9-17889). , Japanese Patent Laid-Open No. 10-74009). In the present invention, by providing the magnetic flux shielding means and moving the magnetic flux, the magnetic flux reaching from the induction heating source is shielded except the necessary portion, and the heat generation itself is suppressed, so that the heat generation range is controlled and the temperature is raised. It is possible to control the heat distribution of the heating medium.

As shown in FIG. 6, the magnetic flux shielding plate 131 is
It has an arcuate curved surface mainly covering the upper half of the induction coil 118, and corresponds to the non-sheet passing area of the fixing roller 111 when a small-sized recording material (shown by a chain double-dashed line in FIG. 6) is passed. Displacement means 1 to a position (shown by a chain double-dashed line in FIG. 2) covering the induction coil 118 in the axial direction range
Moved by 40.

On the other hand, when a large size recording material is passed, the magnetic flux shielding plate 131 is retracted to the outside of the width of the large size recording material. As described above, the position of the magnetic flux shielding plate 131 is changed by the displacement means 140 according to the sheet passing range of the fixing roller 111, so that it is possible to deal with recording materials of various widths. The paper passing range is configured to obtain information by the size detecting means of the recording material feeding portion, or the fixing roller 11
Alternatively, a plurality of means for detecting the temperature of the pressure roller 113, the pressure roller 113, and the like may be provided along the axial direction to detect the temperature (none of them is shown).

Further, in particular, in the form shown in FIG. 7A or 7B, the thin magnetic flux shielding means 132 is arranged such that the surface area thereof is changed in the axial direction, and the holder 112 is also arranged.
Since the holder is rotatable, the range of the shielded portion can be changed by rotating the holder 112. Therefore, the fixing roller 111 can be set in a very limited space.
It is possible to control the heat distribution of.

[0014]

However, the magnetic flux shielding plate in the conventional example has the following drawbacks.

1) When a recording material having a size smaller than the maximum paper passing width is passed, the induction coil is driven by a motor so that the position of the magnetic flux shielding plate is in the axial range corresponding to the non-sheet passing area of the fixing roller. Is displaced to the position where it covers. This allows
The magnetic flux that reaches the non-sheet passing area of the fixing roller from the induction coil is shielded, and the situation in which the temperature of the fixing roller in the non-sheet passing area rises above the controlled temperature of the fixing roller in the sheet passing area is prevented.

On the other hand, when passing a large-sized recording material, the magnetic flux shield plate is retracted to the outside of the sheet-passing width of the large-sized recording material by driving the motor. As a result, the fixing roller receives the magnetic flux from the induction coil and is uniformly heated. At this time, since a space for retracting the magnetic flux shielding plate is required for the heating device, a large size is required in the axial direction of the fixing roller, and the device is large.

2) When the surface area of the thin magnetic flux shielding means is changed in the axial direction and arranged, and the range of the shielding portion is changed by rotating the holder,
It is possible to control the heat distribution of the fixing roller in an extremely limited space, but the magnetic flux shielding plate is always near the fixing roller regardless of the size of the paper being passed.
The heat of the fixing roller is removed, and the magnetic flux shielding plate is continuously overheated, which causes thermal deterioration.

The present invention has been made in view of the above problems, and an object of the present invention is not to change the size of the apparatus and to prevent wasteful overheating of the magnetic flux shield plate, and the non-sheet passing area of the heating medium. An object of the present invention is to provide an image forming apparatus capable of efficiently controlling the heat distribution regardless of the heating device and the sheet passing mode that can suppress the temperature rise in the above.

[0019]

In order to achieve the above object, the present invention provides a heating apparatus having a heating medium having a conductive layer and an induction heating source for heating the heating medium by induction heating. A flexible magnetic flux shielding member that shields a part of magnetic flux that reaches the heating medium from a source is disposed between the heating medium and the induction heating source.

Further, the present invention is characterized in that the heating device of the image of the image forming apparatus is constituted by the heating device.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1> FIG. 1 is a perspective view of an induction heating type heating apparatus according to Embodiment 1 of the present invention, and FIG. 2 is a sectional view perpendicular to the axis of the heating apparatus.

The induction heating apparatus shown in FIGS. 1 and 2 melts the developer of the unfixed image formed on the recording material 14 which is the recording medium to be conveyed by heat and fuses it onto the recording material 14. A coil unit 10 for generating a high-frequency magnetic field, a heating roller (corresponding to a heating medium) 11 that is heated by the coil unit 10 and is movably provided along the conveyance direction of the recording material 14, and the heating unit. Laura 1
1 and holder 1 (corresponding to an insulating member) fixed at a predetermined distance from 1 and holder 1
2 and the heating roller 11 and a pressure roller 13 that is in pressure contact with these.

The pressure roller 13 is rotatably provided in the direction of arrow a in FIG. 2, and is rotated by rotation of the heating roller 11. Recording material 14 on which an unfixed toner image is transferred
Is conveyed in the direction of the arrow b in the figure and is fed toward the nip portion 23 that holds the recording material 14 therebetween. The recording material 14 is
The heated heat roller 11 and the pressure applied from the pressure roller 13 are conveyed to the nip portion 23 while being applied. As a result, the unfixed toner is fixed, and the recording material 14
A fixed toner image is formed on the top.

The recording material 14 that has passed through the nip portion 23 is separated from the heating roller 11 by the separation claw 15 whose front end is in contact with the surface of the heating roller 11, and is conveyed rightward in FIG. The recording material 14 is conveyed by the paper discharge rollers 24 and discharged onto a paper discharge tray (not shown).

The heating roller 11 is a thin hollow metal conductor, and has a conductive layer formed of a conductive magnetic material such as nickel, iron, or SUS430. And
A heat-resistant release layer is formed by coating the outer peripheral surface of the heating roller 11 with a fluororesin. The thickness of the metal layer of the heating roller 11 is 30 μm to 1 mm. Inside the heating roller 11, in order to induce an induced current (eddy current) in the heating roller 11 to generate Joule heat,
A coil unit 10 for generating a high frequency magnetic field is arranged. The coil unit 10 is held inside the holder 12. The holder 12 is fixed to a fixing unit frame (not shown) and is non-rotating.

The coil unit 10 has a core (corresponding to a core material) 16 made of a magnetic material, and an induction coil (corresponding to an induction heating source) 18 for inducing an induction current in the heating roller 11 to heat it. For the core 16, a material having a large magnetic permeability and a small self-loss is preferable, such as ferrite,
Permalloy, sendust, etc. are suitable. The coil unit 10 is housed in the holder 12 so as not to be exposed to the outside.

The holder 12 and the separating claw 15 are made of heat resistant and electrically insulating engineering plastic. The pressure roller 13 includes an axis 19 and the axis 19
And a silicone rubber layer 20, which is a surface-releasing heat-resistant rubber layer, formed on the periphery of the.

A temperature sensor 21 for detecting the temperature of the heating roller 11 is provided above the heating roller 11. The temperature sensor 21 is pressed against the surface of the heating roller 11 so as to face the induction coil 18 across the heating roller 11. The temperature sensor 21 is composed of, for example, a thermistor, and while detecting the temperature of the heating roller 11 with this thermistor, energization to the induction coil 18 is controlled so that the temperature of the heating roller 11 becomes the optimum temperature.

Next, the operation and action of the heating device according to this embodiment will be described.

When a high-frequency current is passed through the induction coil 18, the heating roller 11 is made of magnetic metal, so that the high-frequency induction current is induced to generate heat. Moreover, the induction heating method has a high heat generation efficiency, and since the heating roller 11 is formed thin to reduce the heat capacity, the heating roller 11 is heated at a high speed. The heating roller 11 rotates with the pressure roller 13 while being brought into pressure contact with the pressure roller 13 by obtaining a driving force from a drive source (not shown).

The recording material 14 to which the unfixed toner image has been transferred is sent toward the nip portion 23 between the heating roller 11 and the pressure roller 13 and is heated by the heated heating roller 11. The toner is fixed on the recording material 14 by being conveyed through the nip portion 23 while being applied with the pressure applied from the pressure roller 13. The magnetic flux shielding plate 31 is
It is arranged between the induction coil 18 and the inner surface of the fixing roller 11, and is made of a flexible metal. In this embodiment, a thin aluminum plate having a thickness of about 100 μm is used.

A winding roller 32, which is a conveying and storing means, is arranged at an end of the magnetic flux shielding plate 31, and the magnetic flux shielding plate 31 having flexibility is driven by a motor (not shown).
It is possible to wind up and store. here,
When a recording material having a size smaller than the maximum paper passing width is passed, the magnetic flux shielding plate 31 is not stored as shown in FIG. 2, and a part of the magnetic flux toward the non-sheet passing portion of the fixing roller 11 is passed. The configuration is so arranged that it is shielded. When the paper having the maximum paper-passing width is performed, the magnetic flux shielding plate 31 is wound around the take-up roller 32 to retract, and all the magnetic flux from the induction coil 18 can be directed to the fixing roller 11. The heat distribution of the fixing roller 11 can be controlled in the space. As a result, the heating roller 11 receives the magnetic flux from the induction coil 18 and is uniformly heated.

By using the magnetic flux shielding plate 31 as described above, even with the thin heating roller 11, the heat distribution of the heating roller 11 which is heated regardless of the size of the recording material to be fed is controlled. In addition, since heat is not generated except for necessary parts, heat loss is small and energy is saved. Therefore, it becomes possible to reduce the temperature rise in the non-sheet passing area of the heating roller 11,
It is possible to suppress temperature unevenness in the longitudinal direction of the heating roller 11. As a result, high-temperature offset occurs due to partial unevenness in fixability when a large-sized recording material is passed immediately after passing a small-sized recording material, and a large-sized recording material immediately after passing a small-sized recording material is also passed. Paper wrinkles, skew or jam due to temperature unevenness during sheet passing, and temperature rise in the non-sheet passing area of the heating roller 11 such as melting, deformation or damage due to exceeding the heat resistant temperature of the components of the heating device. Problems can be efficiently prevented.

The magnetic flux shield plate 31 is made of copper, which is a non-magnetic material that conducts an induced current and has a small specific resistance.
It is desirable to use a non-magnetic metal material having a low volume resistance value such as aluminum, silver, or an alloy thereof. or,
In addition to the above-mentioned metal alloy, it is also possible to use a non-magnetic material such as SUS304 in a mesh shape in order to enhance flexibility.

The embodiment described above is not intended to limit the present invention, and various modifications can be made. For example, in the above-described embodiment, the induction heating device using the hollow metal roller as the heating medium has been described, but the present invention is not limited to this, and the induction heating device using the heating roller having flexibility. Of course, it can be applied to.

<Second Embodiment> Next, a second embodiment of the present invention will be described.

The first embodiment will be described below with reference to the drawings.
The same members as those shown in FIG.

FIG. 3 is a cross sectional view of an induction heating type heating device according to a second embodiment of the present invention, and FIGS. 4 and 5 are a perspective view and a schematic view of a magnetic flux shielding means used in the heating device.

The magnetic shielding member 33 has a coating layer formed by partially coating silver on a heat resistant base film such as polyimide, and is divided into a coated portion 36 and a non-coated portion 37 as shown in FIG. These are divided according to the paper passing size. For example, when there is A4 size paper with a maximum paper passing width of A3, a portion corresponding to 40 is connected to the coil 18 by driving the winding means 34 and the rewinding means 35. It is conveyed between the fixing rollers 11. Since the coated portion 36 shields the magnetic flux, the non-sheet passing area corresponding thereto does not generate heat. Further, when A3, which is the maximum paper passing width, is passed, the area of 42 is conveyed.

By performing the above operation, stable control is possible.

[0042]

As is apparent from the above description, according to the present invention, a heating device having a heating medium having a conductive layer and an induction heating source for heating the heating medium by induction heating is used. Since a magnetic flux shielding member having flexibility that shields a part of the magnetic flux that reaches the heating medium from the source is arranged between the heating medium and the induction heating source, the size of the device is not changed, and Without causing unnecessary overheating,
The effect that the temperature rise of the heating medium in the non-sheet passing area can be suppressed and the heat distribution can be efficiently controlled regardless of the sheet passing mode is obtained.

[Brief description of drawings]

FIG. 1 is a perspective view of an induction heating type heating device according to a first embodiment of the present invention.

FIG. 2 is a sectional view perpendicular to the axis of the heating device according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view of an induction heating type heating device according to a second embodiment of the present invention.

FIG. 4 is a perspective view of a magnetic flux shielding means used in the heating device according to the second embodiment of the present invention.

FIG. 5 is a schematic diagram of magnetic flux shielding means used in the heating device according to the second embodiment of the present invention.

FIG. 6 is a sectional view perpendicular to the axis of a conventional induction heating type heating device.

FIG. 7 is a perspective view of a magnetic flux shield plate of a conventional induction heating type heating device.

[Explanation of symbols]

11 Heating roller (heating medium) 12 Holder (insulating member) 13 Pressure roller 14 Recording material 16 cores 18 induction coil (induction heating source) 31, 33 Magnetic flux shielding means 32 winding roller 34 Winding means 35 Rewinding means

Claims (4)

[Claims] 1. A heating device having a heating medium having a conductive layer and an induction heating source for heating the heating medium by induction heating, wherein a part of magnetic flux reaching the heating medium from the induction heating source can be shielded. A heating device comprising a magnetic flux shielding member having flexibility arranged between the heating medium and the induction heating source. 2. The heating device according to claim 1, further comprising a storage unit that stores the magnetic flux shielding member. 3. The heating device according to claim 1, wherein the heating device is an image heating fixing device that heats and fixes an image on a recording material as a permanent image. 4. An image forming apparatus comprising the image heating and fixing device according to claim 3.