JP2002236429A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the abnormal temperature rise of a toner heating medium heated by the electromagnetic induction of an induction heating means. SOLUTION: This fixing device is provided with a heating roller 1 heated by the electromagnetic induction of the induction heating means, a fixing roller arranged in parallel with the roller 1, a heat-resistant belt 3 stretched and laid over the roller 1 and the fixing roller, heated by the roller 1 and rotated by the rollers, a pressure roller made to press-contact with the fixing roller through the belt 3, rotating in a forward direction with respect to the belt 3 and forming a fixing nip part, a switching element 16 applying a current to an exciting coil 7, a switching element driving means 17 driving the element 16, and a temperature sensitive operation member 12 connected to the power source line of the driving means 17 in series and stopping power supply to the driving means 17 when the sensed temperature becomes equal to or above the specified one.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an electrostatic recording type image forming apparatus such as a copying machine, a facsimile, and a printer, and more particularly to a fixing device of an electromagnetic induction heating system. .

[0002]

2. Description of the Related Art In recent years, market demands for energy saving and high speed have been increasing for image forming apparatuses such as printers, copiers, and facsimile machines. And
In order to achieve these required performances, it is important to improve the thermal efficiency of the fixing device used in the image forming apparatus.

Here, the image is transferred (indirectly) by an appropriate image forming process means such as electrophotographic recording, electrostatic recording, or magnetic recording.
As a fixing device for fixing the unfixed toner image formed by the direct or direct method to recording materials such as recording material sheets, printing paper, photosensitive paper, electrostatic recording paper, etc., a heat roller method, a film heating method, electromagnetic induction A fixing device of a contact heating type such as a heating type is widely used.

A fixing device of a heat roller type has a rotating roller pair of a fixing roller having a heat source such as a halogen lamp therein and adjusted to a predetermined temperature, and a pressing roller pressed against the fixing roller. The recording material is introduced into a contact portion of the pair of rotating rollers, a so-called fixing nip portion, and nipped and conveyed, and the unfixed toner image is melted and fixed by heat and pressure from the fixing roller and the pressure roller. is there.

Further, a fixing device of a film heating system is disclosed in, for example, JP-A-63-313182 and
63679 and the like.

In this apparatus, a recording material is brought into close contact with a heating member fixed and supported by a supporting member via a thin fixing film having heat resistance, and the heating member is slidably moved with respect to the heating member. Is supplied to the recording material via the film material. In this fixing device, as a heating body, for example, a ceramic substrate such as alumina (Al ₂ O ₃ ) or aluminum nitride (AlN) having characteristics such as heat resistance, insulation, and good thermal conductivity, and heat is generated by energization. Since a ceramic heater based on a configuration having a resistance layer on this substrate can be used as a fixing film having a thin film and low heat capacity, the heat transfer efficiency is higher than that of a heat roller type fixing device, and the warm-up is achieved. Time can be shortened, and quick start and energy saving can be achieved.

As an electromagnetic induction heating type fixing device, Japanese Patent Publication No. 8-22206 discloses an eddy current generated in a magnetic metal member by an alternating magnetic field to generate Joule heat, and a heating element including the metal member is generated by the Joule heat. It has been proposed to generate magnetically induced heat.

Hereinafter, the configuration of a magnetic induction heating type fixing device will be described. Here, FIG. 5 is a schematic diagram showing a fixing device using a conventional electromagnetic induction heating method.

As shown in FIG. 5, the fixing device is provided with a heating element 23 which is an electromagnetic induction heating structure comprising an exciting coil unit 21 having a coil wound thereon and a magnetic metal member 22 as a heating section. A film inner guide 24 and a heat-resistant cylindrical film 20 surrounding the film inner guide 24 with the magnetic metal member 22 facing the inner wall.
And a pressure roller 2 that presses against the film 20 at the position of the magnetic metal member 22 to form a fixing nip portion N with the film 20 and that rotates the film 20 by rotation.
And 5.

The film 20 has a thickness of 100 μm.
m, preferably 50 μm or less, and a single-layer film of PTFE, PFA, FEP or the like having a heat resistance of 20 μm or more, or polyimide, polyamideimide, PEE
PTF on the outer surface of film such as K, PES, PPS
A composite layer film coated with E, PFA, FEP or the like is used.

The film inner surface guide 24 has a rigidity made of a thermosetting resin such as PEEK or PPS.
The heating body 23 is made of a heat-resistant member, and is fitted into a substantially central portion of the lower surface of the film inner surface guide 24.

The pressure roller 25 comprises a core metal 25a and a heat-resistant rubber layer 25b provided around the core metal 25a and having good releasability such as silicone rubber. (Not shown) so that the film 20 is pressed against the magnetic metal member 22 of the heating body 23 with a predetermined pressing force. Then, it is rotationally driven counterclockwise by a driving means (not shown).

The rotation of the pressure roller 25 generates a frictional force between the pressure roller 25 and the film 20, and the rotational force acts on the film 20.
Slides and rotates while closely contacting the magnetic metal member 22 of the heating body 23.

When the heating element 23 rises to a predetermined temperature, the film 20 in the fixing nip portion N formed by the heating element 23 and the pressure roller 25 via the film 20.
The recording material 11 having the unfixed toner image T formed by the image forming unit (not shown) is introduced between the recording material 11 and the pressure roller 25. Then, the recording material 11 is sandwiched between the pressure roller 25 and the film 20 and conveyed through the fixing nip N, so that the heat of the magnetic metal member 22 of the heating element 23 is transferred through the film 20 to the recording material 11. And recording material 1
1 is fused and fixed on the recording material 11. At the exit of the fixing nip N, the recording material 11 that has passed is separated from the surface of the film 20 and conveyed to a paper discharge tray (not shown).

Japanese Patent Application Laid-Open No. 7-295414 discloses a structure in which an electromagnetic induction heating member is provided outside a cylindrical rotary heating member and a temperature sensor is provided outside a region heated by the electromagnetic induction heating member. ing.

Further, Japanese Patent Application Laid-Open No. 7-319312 discloses that an electromagnetic induction heating member is provided inside a cylindrical rotary heating member and a temperature detecting element is provided outside the cylindrical rotary heating member at a position facing the electromagnetic induction heating member. Is disclosed.

[0017]

In a fixing device of the electromagnetic induction heating type, a safety device such as a thermostat is provided at a position outside the heat generating member and opposed to the electromagnetic induction heating member, and a heat generating portion due to runaway such as temperature control is provided. In order to prevent an abnormal rise in temperature, a safety device for shutting off commercial power is used.

However, the safety device that shuts off the commercial power supply requires a large current to flow, and therefore has a large heat capacity. Therefore, the response speed of the safety device is slow with respect to the heating speed of the heating member, and the rotating heating member is rapidly operated. In some cases, the temperature of the rotating heat generating member itself may cause damage such as thermal deformation.

Accordingly, an object of the present invention is to provide an electromagnetic induction heating type fixing device which can prevent an abnormal temperature rise of a toner heating medium heated by electromagnetic induction of an induction heating means.

[0020]

In order to solve this problem, a fixing device according to the present invention comprises a heating roller which is made of a magnetic metal member and is heated by electromagnetic induction of an induction heating means; An endless belt-shaped toner heating medium that is stretched between the arranged fixing roller, the heating roller and the fixing roller, heated by the heating roller and rotated by these rollers, and pressed against the fixing roller via the toner heating medium. A pressure roller that rotates in the forward direction with respect to the toner heating medium to form a fixing nip portion; a switching element that supplies current to an excitation coil that generates a magnetic field in the induction heating means; and a switching element that drives the switching element. Element driving means, connected in series to the power supply line of the switching element driving means, It is obtained by the structure having the temperature-sensitive actuating member for stopping the power supply to the movement means.

Thus, since the temperature-sensitive operating member is disposed on the power supply line of the switching element driving means having a small current value, the heat capacity of the temperature-sensitive operating member can be reduced, and the temperature of the heating roller can be rapidly increased. And the temperature of the toner heating medium heated by electromagnetic induction of the induction heating means can be prevented from rising abnormally.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention relates to a heating roller made of a magnetic metal member and heated by electromagnetic induction of an induction heating means, and a fixing roller arranged in parallel with the heating roller. And an endless belt-shaped toner heating medium that is stretched over a heating roller and a fixing roller, is heated by the heating roller and is rotated by these rollers, and is pressed against the fixing roller via the toner heating medium while heating the toner. A pressure roller that rotates in a forward direction with respect to the medium to form a fixing nip portion, a switching element that passes a current to an excitation coil that generates a magnetic field in the induction heating means, a switching element driving means that drives the switching element, It is connected in series to the power supply line of the switching element driving means and stops supplying power to the switching element driving means when the temperature exceeds a predetermined temperature. The temperature-sensitive operating member is provided on the power supply line of the switching element driving means having a small current value, so that the heat capacity of the temperature-sensitive operating member can be reduced and the fixing device can be heated. This has the effect of reliably following the rapid rise in the temperature of the roller and preventing an abnormal rise in the temperature of the toner heating medium heated by the electromagnetic induction of the induction heating means.

According to a second aspect of the present invention, in the first aspect of the present invention, the temperature-sensitive operating member is a fixing device disposed near an eddy current generating portion of the induction heating member. Since the temperature-sensitive operating member is arranged on the power supply line of the small switching element driving means, the heat capacity of the temperature-sensitive operating member can be reduced, so that the temperature of the heating roller can be rapidly followed. This has the effect that abnormal temperature rise of the toner heating medium heated by the electromagnetic induction of the induction heating means can be prevented.

Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. In these drawings, the same members are denoted by the same reference numerals, and redundant description is omitted.

FIG. 1 is an explanatory view showing a fixing device according to an embodiment of the present invention. FIG. 2A is a sectional view showing an exciting coil of induction heating means in the fixing device shown in FIG. 1, and FIG. 1 is a side view showing an exciting coil of induction heating means in the fixing device of FIG. 1, FIG. 3 is an explanatory view showing generation of an alternating magnetic field and an eddy current by the induction heating means in the fixing device of FIG. 1, and FIG. It is a block diagram showing a circuit configuration for generating a magnetic field in the electromagnetic induction heating means in the device.

The fixing device shown in FIG. 1 is a fixing device of the electromagnetic induction heating type used in the image forming apparatus, and is arranged in parallel with the heating roller 1 heated by electromagnetic induction of the induction heating means 6 and the heating roller 1. Endless belt-shaped heat-resistant belt (toner heating medium) that is stretched between the fixing roller 2 and the heating roller 1 and the fixing roller 2, is heated by the heating roller 1, and rotates in the direction of arrow A by the rotation of the fixing roller 2. 3, and a pressure roller 4 pressed against the fixing roller 2 via the heat-resistant belt 3 and rotated in the forward direction with respect to the heat-resistant belt 3.

As shown in the figure, the fixing device comprises a thermosensitive element having a high thermal response such as a thermistor, and is arranged in contact with the inner surface of the heat resistant belt 3 near the entrance side of the fixing nip N. A temperature detecting means 5 for detecting the temperature of the heat resistant belt 3 is provided. Also, the heating roller 1
The temperature-sensitive operating member 12 such as a temperature fuse, which is a safety device for preventing the thermal runaway of the induction heating means 6 when both ends are opened and the heating is stopped when a predetermined temperature is reached, is reached. Are located.

The heating roller 1 is made of a hollow cylindrical magnetic metal member such as SUS and has an outer diameter of, for example, 20 mm and a thickness of, for example, 0.3 mm. Has become.

The fixing roller 2 comprises a metal core 2a made of, for example, SUS, and an elastic member 2b formed by solidifying or foaming silicone rubber having heat resistance and covering the metal core 2a. In order to form a contact portion having a predetermined width with the pressing roller 4 by the pressing force from the pressing roller 4, the outer diameter is set to about 30 mm, which is larger than that of the heating roller 1. The thickness is about 3 to 8 mm, and the hardness is about 15 to 50 ° (Asker C).

With such a configuration, since the heat capacity of the pressure roller 1 becomes smaller than the heat capacity of the fixing roller 2, the heating roller 1 is rapidly heated and the warm-up time is reduced.

The heat-resistant belt 3 stretched between the heating roller 1 and the fixing roller 2 is heated at a contact portion W of the heating roller 1 heated by the induction heating means 6. Then, the inner surface of the heat resistant belt 3 is continuously heated by the rotation of the heat resistant belt 3 accompanying the rotation of the fixing roller 2 by the driving means (not shown), and as a result, the entire belt is heated.

Here, the heat resistant belt 3 is made of Ni, Cu,
Heat generation layer 3a based on a metal member having magnetism such as Cr
And a release layer 3b made of an elastic member such as silicone rubber or fluorine rubber provided so as to cover the surface thereof.

According to this, even if foreign matter is mixed between the heat-resistant belt 3 and the heating roller 1 to form a gap for some reason, the heat-generating layer 3a of the heat-resistant belt 3 is not affected by electromagnetic induction. Since the heat-resistant belt 3 itself generates heat due to the heat generation, the temperature non-uniformity is small and the reliability is improved.

The heating layer 3a has a thickness of 20 μm.
m to about 50 μm, and preferably about 30 μm.

If the thickness of the heat generating layer 3a is larger than 50 μm, the strain stress generated during the rotation of the belt increases, causing cracks due to shearing force and extremely lowering the mechanical strength. The thickness of the heat generating layer 3a is 20 μm.
If it is smaller, a thrust load on the belt end caused by meandering at the time of rotation of the belt causes breakage such as cracks and cracks.

On the other hand, the thickness of the release layer 3b is 100
It is desirable that the thickness is about μm to 300 μm, and particularly about 200 μm. By doing so, the surface layer of the heat-resistant belt 3 sufficiently wraps the toner image T formed on the recording material 11, so that the toner image T can be uniformly heated and melted.

If the thickness of the release layer 3b is smaller than 100 μm, the heat capacity of the heat-resistant belt 3 becomes small, and the belt surface temperature drops rapidly in the toner fixing step,
The fixing performance cannot be sufficiently secured. If the thickness of the release layer 3b is larger than 300 μm, the heat capacity of the heat-resistant belt 3 is increased and the time required for warm-up is prolonged. As a result, the effect of coagulating the melted toner at the exit of the fixing unit cannot be obtained, and the so-called hot offset, in which the releasability is reduced and the toner adheres to the belt, occurs.

The base material of the heat resistant belt 3 is N
A heat-resistant resin layer such as a fluororesin, a polyimide resin, a polyamide resin, a polyamideimide resin, a PEEK resin, a PES resin, and a PPS resin is used instead of the heat generating layer 3a made of a metal member such as i, Cu, or Cr. You may.

If the base material is made of a resin layer, which is a resin member having high heat resistance, the heat-resistant belt 3 can easily adhere to the heating roller 1 in accordance with the curvature of the heating roller 1. Is efficiently transmitted to

In this case, the thickness of the resin layer is 20 μm.
m to about 150 μm, particularly about 75 μm. If the thickness of the resin layer is smaller than 20 μm, mechanical strength against meandering during belt rotation cannot be obtained. When the thickness of the resin layer is larger than 150 μm, the heat shielding effect is increased and the heat transfer efficiency from the heating roller 1 to the release layer 3b of the heat resistant belt 3 is reduced, so that the fixing performance is reduced. appear.

The pressure roller 4 is a metal core 4 made of a metal cylindrical member having high heat conductivity such as SUS or aluminum.
a, and an elastic member 4b provided on the surface of the cored bar 4a and having high heat resistance and toner releasing property.

The pressure roller 4 is a heat resistant belt 3
The fixing nip N is formed by pressing the fixing roller 2 through the fixing roller 2. However, in this embodiment, the outer diameter of the fixing nip N is increased so that the toner separating action at the exit of the fixing nip N is increased. Same as 2 but about 30mm, but the thickness is 2-5m
m, which is thinner than the fixing roller 2 and has a hardness of 20 to 60.
° (Asker C), which is harder than the fixing roller 2.

As shown in FIG. 2, the induction heating means 6 for heating the heating roller 1 by electromagnetic induction includes an exciting coil 7 as a magnetic field generating means and a coil guide plate 8 around which the exciting coil 7 is wound. Have. Here, the coil guide plate 8 has a semi-circular shape arranged close to the outer peripheral surface of the heating roller 1, and the exciting coil 7 is configured by applying a single long exciting coil wire to the heating roller 1 along the coil guide plate 8. The winding length is the same as the area where the heat-resistant belt 3 and the heating roller 1 are in contact with each other.

According to this, the area of the heating roller 1 which is subjected to electromagnetic induction heating by the induction heating means 6 is maximized,
Since the time during which the surface of the heating roller 1 that is generating heat and the heat-resistant belt 3 are in contact with each other is maximized, the heat transfer efficiency is increased.

Further outside the excitation coil 7, an excitation coil core 9, which is a semicircular arc-shaped member made of a ferromagnetic material such as ferrite, is fixed to the excitation coil core support member 10 and is disposed close to the excitation coil 7. . In the present embodiment, the excitation coil core 9 having a relative magnetic permeability of 2500 is used.

The exciting coil 7 has a high frequency alternating current of 10 kHz to 1 MHz, preferably 20 kHz to 800 kHz.
Is supplied, thereby generating an alternating magnetic field. Then, in the contact area W between the heating roller 1 and the heat resistant belt 3 and in the vicinity thereof, this alternating magnetic field acts on the heating layer 3a of the heating roller 1 and the heat resistant belt 3,
Inside these, an eddy current I flows in a direction B that hinders the change in the magnetic field.

The eddy current I generates Joule heat in accordance with the resistance of the heating roller 1 and the heating layer 3a, and mainly in the contact area between the heating roller 1 and the heat-resistant belt 3 and in the vicinity thereof, The heat-resistant belt 3 having 3b is heated by electromagnetic induction.

The heat-resistant belt 3 thus heated
The temperature of the inner surface of the heat-resistant belt 3 is detected by the temperature detecting means 5 disposed in contact with the inner surface of the heat-resistant belt 3 near the entrance side of the fixing nip N.

Next, the operation at the time of thermal runaway in the fixing device of the electromagnetic induction heating type having such a configuration will be described with reference to FIG.

In FIG. 4, a rectifying element 14 for full-wave rectification of a commercial power supply 13, a resonance capacitor 15 connected in parallel to the exciting coil 7, and a switching device such as an IGBT for supplying a high-frequency current to the exciting coil 7. Elements 16 are connected in series. For example, a DC power supply 18 of 20 V DC is connected to the switching element driving means 17 which is composed of a dedicated IC and drives the gate of the switching element 16 via the temperature-sensitive operation member 12. The control means 19 outputs an on / off signal to the switching element driving means 17 so that the switching element 16 is turned on / off.
It is turned off, and a high-frequency current flows through the exciting coil 7.

Since only about 20 mA needs to be supplied from the DC power supply 18 to the switching element driving means 17 via the temperature-sensitive operating member 12, the temperature-sensitive operating member 12 has a small heat capacity, a small heat capacity and good thermal response. Is used.

Further, both ends of the temperature-sensitive operating member 12 are normally in a short-circuit state, and when the temperature exceeds a predetermined temperature, both ends are in an open state. In the present embodiment, the temperature-sensitive operation member 12 which is short-circuited at 200 ° C. is used.

In such a circuit configuration, the temperature of the heating roller 1 is controlled to about 180 ° C. in a normal state.
Both ends of the temperature-sensitive operating member 12 are in a short-circuit state.

If the temperature control does not work for some reason and the thermal runaway state occurs, the temperature of the heating roller 1 rapidly rises, and the temperature of the temperature-sensitive operating member 12 also follows the temperature of the heating roller 1 rapidly. To rise. When the temperature of the temperature-sensitive operating member 12 becomes 200 ° C. or more due to the continuous temperature increase, both ends of the temperature-sensitive operating member 12 are opened, and power is not supplied from the DC power supply 18 to the switching element driving means 17. . Since the output of the switching element driving means 17 is pulled down, when power is not supplied, the gate of the switching element 16 is turned off, no current flows through the exciting coil 7, and the heating of the electromagnetic induction heating means 6 stops.

As described above, according to the present embodiment, since the temperature-sensitive operating member 12 is disposed on the power supply line of the switching element driving means 17 having a small current value, the heat capacity of the temperature-sensitive operating member 12 is reduced. Can be heated roller 1
Reliably follows the rapid temperature rise of This makes it possible to prevent an abnormal rise in the temperature of the heat-resistant belt 3 that is heated by the electromagnetic induction of the induction heating means 6, and to prevent damage to the fixing device due to thermal deformation or the like.

Further, since the temperature-sensitive operating member 12 can be made smaller, the size of the fixing device can be reduced.

[0057]

As described above, according to the present invention, since the temperature-sensitive operating member is disposed on the power supply line of the switching element driving means having a small current value, the heat capacity of the temperature-sensitive operating member can be reduced. As a result, it is possible to reliably follow the rapid rise in the temperature of the heating roller and to prevent an abnormal rise in the temperature of the toner heating medium heated by the electromagnetic induction of the induction heating means. can get.

As a result, an advantageous effect is obtained in that damage due to thermal deformation of the fixing device can be prevented.

Further, according to the present invention, since the temperature-sensitive operation member itself can be reduced, an advantageous effect that the fixing device can be downsized can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a fixing device according to an embodiment of the present invention;

2A is a cross-sectional view illustrating an excitation coil of an induction heating unit in the fixing device of FIG. 1. FIG. 2B is a side view illustrating an excitation coil of the induction heating unit in the fixing device of FIG.

FIG. 3 is an explanatory diagram showing generation of an alternating magnetic field and an eddy current by the induction heating means in the fixing device of FIG. 1;

4 is a block diagram showing a circuit configuration for generating a magnetic field in an electromagnetic induction heating unit in the fixing device of FIG.

FIG. 5 is a schematic view showing a fixing device using a conventional electromagnetic induction heating method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating roller 2 Fixing roller 3 Heat resistant belt (toner heating medium) 4 Pressure roller 6 Induction heating means 7 Exciting coil 12 Temperature sensitive operation member 16 Switching element 17 Switching element driving means N Fixing nip

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazunori Matsuo 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture F-term (reference) 2H033 AA24 BA25 BA31 BA32 BB01 BB18 BB22 BB28 BB33 BB34 BE06 CA07 CA23 CA30 CA45 3K059 AA08 AB19 AC33 AD02 AD34 BD21 CD10 CD75

Claims (2)

[Claims] A heating roller made of a magnetic metal member and heated by electromagnetic induction of an induction heating means; a fixing roller arranged in parallel with the heating roller; and a stretcher between the heating roller and the fixing roller. And an endless belt-shaped toner heating medium which is heated by the heating roller and rotated by these rollers. The toner heating medium is pressed against the fixing roller via the toner heating medium and is directed in a forward direction with respect to the toner heating medium. A pressure roller that rotates to form a fixing nip portion; a switching element that supplies current to an excitation coil that generates a magnetic field in the induction heating means; a switching element driving means that drives the switching element; and the switching element driving means Are connected in series to each other, and when the temperature exceeds a predetermined temperature, power is supplied to the switching element driving means. A fixing device characterized in that it comprises a temperature-sensitive operating member to stop. 2. The fixing device according to claim 1, wherein the temperature-sensitive operating member is disposed near an eddy current generating portion of the induction heating member.