JP2001242732A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device of electromagnetic induction heating in which the temperature control of a toner heating medium can be performed stably. SOLUTION: The fixing device has a heating roller consisting of magnetic metals heated by electromagnetic induction, a fixing roller disposed in parallel to the heating roller, a heat-resistant belt trained around the heating roller and the fixing roller, heated by the heating roller and rotated by these rollers, and a pressure roller press-contacted to the fixing roller through the heat- resistant belt, rotating with respect to the heat-resistant belt and forming a fixing nip part. By this configuration, the temperature control of the toner heating medium can be performed stably, and the fixing of a toner image can be performed stably.

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, a printer, etc., and more specifically, to the fixing of a toner image using an electromagnetic induction heating system. It concerns the device.

[0002]

2. Description of the Related Art In recent years, market demands for energy saving and speeding up of image forming apparatuses such as printers, copiers, and facsimile machines have become stronger. 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.

In an image forming apparatus, an unfixed toner image is formed on a recording material sheet, printed paper, photosensitive paper, electrostatic recording by an image transfer method or a direct method by an image forming process such as electrophotographic recording, electrostatic recording, or magnetic recording. It is formed on a recording material such as paper. As a fixing device for fixing an unfixed toner image, a contact heating type fixing device such as a heat roller system, a film heating system, and an electromagnetic induction heating system is widely used.

A heat roller type fixing device basically includes a rotating roller pair of a fixing roller having a heat source such as a halogen lamp therein to control the temperature to a predetermined temperature, and a pressing roller pressed against the fixing roller. And The recording material is introduced and conveyed to a contact portion of these rotating roller pairs, a so-called fixing nip portion,
The unfixed toner image is melted and fixed by heat and pressure from the fixing roller and the pressure roller.

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 support member via a thin fixing film having heat resistance, and the fixing film is slidably moved with respect to the heating member. Heat is supplied to the recording material via the film material. In this fixing device, as a heating element, for example, a ceramic heater having a resistance layer on a ceramic substrate such as alumina (Al2O3) or aluminum nitride (AlN) having characteristics such as heat resistance, insulation, and good thermal conductivity is used. use. Since this fixing device can use a thin film and low heat capacity as the fixing film, it has higher heat transfer efficiency than the heat roller type fixing device, shortens the warm-up time, and enables quick start and energy saving. Will be possible.

As a fixing device of the electromagnetic induction heating type, in Japanese Patent Application Laid-Open No. Hei 8-22206, Joule heat is generated by eddy current generated in a magnetic metal member by an alternating magnetic field, and a heating element including the metal member is heated by electromagnetic induction. Technology has been proposed.

The configuration of the electromagnetic induction heating type fixing device will be described below.

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

As shown in FIG. 5, a conventional fixing device includes an exciting coil unit 18 and a magnetic metal member 19 serving as a heating unit.
A heat-resistant cylindrical film 17 wrapped around the film inner surface guide 21 with the magnetic metal member 19 in contact with the inner wall; and a magnetic metal member 19. And a pressure roller 22 for rotating the film 17 while pressing the film 17 at the position to form a fixing nip N with the film 17.

The film 17 has a thickness of 100 μm or less,
Preferably a single-layer film such as PTFE, PFA, FEP having heat resistance of 50 μm or less and 20 μm or more, or polyimide, polyamideimide, PEEK, PES,
PTFE, PFA, F
A composite layer film coated with EP or the like is used.

The film inner surface guide 21 is made of PEE.
The heating body 20 is made of a member having rigidity and heat resistance formed of a resin such as K or PPS. The heating body 20 is fitted into a substantially central portion of the film inner surface guide 21 in the longitudinal direction.

The pressure roller 22 comprises a core 22a and a heat-resistant rubber layer 22b provided around the core 22a and having good releasability, such as silicone rubber. Bearings and biasing means (neither is shown)
Thus, it is disposed so as to press against the magnetic metal member 19 of the heating element 20 with the film 17 interposed therebetween with a predetermined pressing force. The pressing roller 22 is driven to rotate counterclockwise by a driving unit (not shown).

When the pressure roller 22 is driven to rotate, a frictional force is generated between the pressure roller 22 and the film 17 so that a rotational force acts on the film 17.
Slides and rotates while being in close contact with the magnetic metal member 19.

When the heating body 20 reaches a predetermined temperature, the film 17 in the fixing nip portion N and the pressure roller 22
In between, a recording material 11 having an unfixed toner image T formed by an image forming unit (not shown) is introduced. Recording material 1
Reference numeral 1 denotes a state in which the heat of the magnetic metal member 19 is applied to the recording material 11 via the film 17 by being conveyed through the fixing nip N between the pressure roller 22 and the film 17, and the unfixed toner image T is recorded. It is fused and fixed on the 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 17 and is conveyed to a paper discharge tray (not shown).

As described above, in the fixing device of the electromagnetic induction heating system, the magnetic metal member 19 as the induction heating means is brought close to the toner image T of the recording material 11 through the film 17 by utilizing the generation of the eddy current. And the heating efficiency is further improved as compared with the film heating type fixing device.

Among the image forming apparatuses, a fixing apparatus in a full-color image forming apparatus is required to have a capability of sufficiently heating and melting a thick toner particle layer laminated in four or more layers. In order to achieve this requirement, a fixing device of the electromagnetic induction heating type uses a 200 μm film on the film surface in order to sufficiently wrap the toner image and uniformly heat and fuse it.
A rubber elastic layer of about m is required.

[0018]

However, when the surface of the film is coated with an elastic layer of silicon rubber or the like of about 200 μm, the thermal response of the elastic layer becomes poor due to the low thermal conductivity of the elastic layer. The temperature difference between the inner surface of the film and the outer surface in contact with the toner becomes very large.

For this reason, it becomes difficult to control the temperature of the surface of the film, which is the toner heating medium, which greatly affects the fixing performance of the toner.

An object of the present invention is to provide an electromagnetic induction heating type fixing device capable of stably controlling the temperature of a toner heating medium.

[0021]

A fixing device according to the present invention comprises a heating roller made of magnetic metal and heated by electromagnetic induction, a fixing roller arranged in parallel with the heating roller,
An endless belt-shaped toner heating medium that is stretched over the heating roller and the fixing roller, is heated by the heating roller, and is rotated by these rollers, is pressed against the fixing roller via the toner heating medium, and And a pressure roller that rotates in the forward direction to form a fixing nip.

Further, according to the present invention, induction heating of the toner heating medium can be performed more efficiently by using a magnetic metal as the base material of the toner heating medium.

According to the configuration of the present invention, the toner heating medium is sent to the fixing nip portion in a state where the difference in temperature between the front and back surfaces is reduced. Therefore, it is possible to stably control the temperature of the toner heating medium and stably fix the toner image.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS. In these drawings, the same members are denoted by the same reference numerals, and duplicate description is omitted.

The fixing device shown in FIG. 1 includes a heating roller 1 heated by electromagnetic induction of an induction heating means 6, a fixing roller 2 arranged in parallel with the heating roller 1, and a heating roller 1 and a fixing roller 2. An endless belt-shaped heat-resistant belt (toner heating medium) 3 which is stretched and heated by the heating roller 1 and rotated in the direction of arrow A by rotation of at least one of these rollers, and a fixing roller via the belt 3 2 and a pressure roller 4 rotating in the forward direction with respect to the belt 3.

The heating roller 1 is made of a hollow cylindrical magnetic metal member such as iron, cobalt, nickel or an alloy of these metals. The heating roller 1 has an outer diameter of, for example, 20 mm, a thickness of, for example, 0.3 mm, and has a low heat capacity. It has a fast configuration.

The fixing roller 2 includes a metal core 2a made of metal such as stainless steel, for example, and an elastic member 2b in which heat-resistant silicone rubber is solid or foamed to cover the core 2a. Then, in order to form a contact portion having a predetermined width between the pressing roller 4 and the fixing roller 2 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 elastic member 2b has a thickness of about 3 to 8 mm and a hardness of 15 to 50 ° (As
ker hardness: about 6 to 25 in JIS A hardness). With this configuration, since the heat capacity of the heating roller 1 is 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 belt 3 stretched between the heating roller 1 and the fixing roller 2 is heated at a contact portion W 1 of the heating roller 1 heated by the induction heating means 6. Then, the inner surface of the belt 3 is continuously heated by the rotation of the rollers 1 and 2, and as a result, the entire belt is heated.

As shown in FIG. 3, the belt 3 has a heat generating layer 3a made of a metal having magnetic properties such as iron, cobalt, nickel or the like or an alloy based on them, and a heating layer 3a covering the surface thereof. And a release layer 3b made of an elastic member such as silicone rubber or fluorine rubber provided as described above.

If the above-described composite layer belt is used, even if foreign matter is mixed between the belt 3 and the heating roller 1 for some reason, for example, a gap is generated, the heat generation layer 3a of the belt 3 is caused by electromagnetic induction. Since the belt 3 itself generates heat due to the heat generation, the temperature non-uniformity is small, and the fixing reliability is increased.

The thickness of the heat generating layer 3a is preferably about 20 μm to 50 μm, and more 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 during the rotation of the belt causes damage such as cracks and cracks in the composite layer belt.

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. In this case, the surface layer of the 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 belt 3 becomes small, and the belt surface temperature drops rapidly in the toner fixing step, so that the fixing performance cannot be sufficiently secured. . Also, the release layer 3b
If the thickness of the belt 3 is larger than 300 μm, the heat capacity of the belt 3 increases, and the time required for warm-up increases. In addition, in the toner fixing step, the surface temperature of the belt is less likely to decrease, so that the aggregation effect of the melted toner at the exit of the fixing unit is not obtained, and the releasability of the belt decreases, so that the toner adheres to the belt. Hot offset occurs.

The inner surface of the heat generating layer 3a may be coated with a resin for the purpose of preventing metal oxidation and improving the contact with the heating roll 1.

As the base material of the belt 3, instead of the heat generating layer 3a made of the above-mentioned metal, a fluororesin, a polyimide resin, a polyamide resin, a polyamideimide resin, a PE
A heat-resistant resin layer such as an EK resin, a PES resin, or a PPS resin may be used.

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

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 thermal conductivity of the resin is small, so that the heat transfer efficiency from the heating roller 1 to the release layer 3b of the belt 3 is reduced, and the fixing performance is reduced. I do.

The pressure roller 4 has a metal core 4a made of a metal cylindrical member having high thermal conductivity such as copper or aluminum.
And an elastic member 4b provided on the surface of the metal core 4a and having high heat resistance and toner releasing property. SUS may be used for the metal core 4a in addition to the above metals.

The pressure roller 4 presses the fixing roller 2 via the belt 3 to form the fixing nip N. In the present embodiment, the hardness of the pressure roller 4 is compared with that of the fixing roller 2. When the recording material 11 is hardened, the pressure roller 4 bites into the fixing roller 2 (and the belt 3), and the bite causes the recording material 11 to follow the circumferential shape of the surface of the pressure roller 4. This has the effect of making it easier to separate from the surface. The outer diameter of the pressure roller 4 is about 30 mm, which is the same as that of the fixing roller 2, but the wall pressure is 2 to 5 mm.
It is thinner than the fixing roller 2 and its hardness is 20-60 °
(Asker hardness: 6 to 25 degrees in JIS A hardness) and is harder than the fixing roller 2 as described above.

As shown in FIGS. 1 and 2A and 2B, the induction heating means 6 for heating the heating roller 1 by electromagnetic induction
An exciting coil 7 serving as a magnetic field generating means;
Is wound around the coil guide plate 8. The coil guide plate 8 has a semi-cylindrical shape disposed close to the outer peripheral surface of the heating roller 1. As shown in FIG. 2B, the excitation coil 7 is formed by moving a single long excitation coil wire along the coil guide plate 8. The heating roller 1 is wound alternately in the axial direction. The length around which the coil is wound is the same as the area where the belt 3 and the heating roller 1 are in contact.

According to this configuration, the area of the heating roller 1 that 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 belt 3 are in contact with each other is maximized, the efficiency of heat transfer to the belt 3 is increased.

The excitation coil 7 has an oscillation circuit connected to a drive power source (not shown) whose frequency is variable.

Outside the excitation coil 7, a semi-cylindrical excitation coil core 9 made of a ferromagnetic material such as ferrite is fixed to the excitation coil core support member 10 and is arranged 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 excitation coil 7 has a frequency of 10 kHz from the drive power supply.
~ 1MHz high frequency alternating current, preferably 20kHz ~
A high frequency alternating current of 800 kHz is fed, thereby generating an alternating magnetic field. The alternating magnetic field acts on the heating layer 3a of the heating roller 1 and the belt 3 in the contact area W1 between the heating roller 1 and the heat-resistant belt 3 and in the vicinity thereof, and a direction B in which the change of the alternating magnetic field is prevented inside these. An eddy current I flows through.

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

The belt 3 heated in this manner is detected by a temperature sensor having a high thermal response such as a thermistor disposed in contact with the inner surface of the belt 3 near the entrance side of the fixing nip N. Means 5 detects the belt inner surface temperature.

According to the above configuration, since the temperature detecting means 5 does not damage the surface of the belt 3, the fixing performance is continuously maintained, and the temperature immediately before entering the fixing nip portion N of the belt 3 is detected. Is done. Then, by controlling the input power to the induction heating means 6 based on a signal output based on this temperature information, the temperature of the belt 3 is reduced to, for example, 18
Stably maintained at 0 ° C.

As described above, according to the present embodiment, the fixing nip portion N is formed by the belt 3 heated by the heating roller 1 heated by the induction heating means 6 and the pressure roller 4. When the toner image T formed on the recording material 11 in the image forming unit (not shown) is introduced into the fixing nip N, the belt 3 is in a state where the difference between the surface temperature and the back surface temperature is small. At the fixing nip N. Therefore, the so-called overshoot in which the belt surface temperature becomes excessively high with respect to the set temperature is suppressed, and the temperature control of the belt 3 as the toner heating medium can be stably performed.

Therefore, in the fixing step, the belt 3 maintained at a constant temperature comes into contact with the toner image T, and stable fixing quality can be secured.

Next, the second fixing device of this embodiment will be described.

As shown in FIG. 4, in the second fixing device, the induction heating means 12 is fixed to the exciting coil 13, the coil guide plate 14 around which the exciting coil 13 is wound, and the exciting coil core supporting member 16. And an excitation coil core 15 disposed close to the outside of the excitation coil 13.

In the present apparatus, the heating region is a substantially quarter region W2 shorter than the contact region when the induction heating means 12 has a substantially quarter cylindrical shape and a semi-cylindrical shape.

In this way, the size of the induction heating means 12 can be reduced, so that the size of the fixing device can be reduced and the cost of parts can be reduced.

As described above, according to the present invention, the fixing nip portion is formed by the toner heating medium heated by the heating roller heated by the induction heating means and the pressure roller.
The toner heating medium is sent to the fixing nip in a state where the difference between the front and back surface temperatures is small, and an effective effect that the temperature of the toner heating medium can be stably controlled can be obtained.

[0056]

The effects of the present invention are summarized as follows.

If the base material of the belt-shaped toner heating medium is made of a magnetic metal member, the toner heating medium itself generates heat by electromagnetic induction even if a gap is formed between the toner heating medium and the heating roller. It is possible to obtain high fixing reliability with less temperature unevenness.

If the base material of the toner heating medium is made of a heat-resistant resin member, the toner heating medium can easily adhere to the heating roller in accordance with the curvature of the heating roller. Good communication becomes possible.

In the toner heating medium, the base material is 100 μm.
Covering the toner image formed on the recording material with the surface layer of the toner heating medium sufficiently covers the toner image if covered with an elastic release layer having a thickness of m to 300 μm. It becomes possible to do.

If the induction heating means is disposed along the outer peripheral surface of the heating roller over substantially the same length as the contact area between the heating roller and the toner heating medium, the area of the heating roller to be electromagnetically heated by the induction heating means is reduced. The heat transfer efficiency is increased since the time when the surface of the heating roller that is generating heat and the toner heating medium are in contact is also maximized.

If the induction heating means is arranged along the outer peripheral surface of the heating roller over a length shorter than the contact area between the heating roller and the toner heating medium, the size of the induction heating means can be reduced. And the cost of parts can be reduced.

If the outer diameter of the heating roller is smaller than the outer diameter of the fixing roller, the heat capacity of the heating roller becomes smaller than the heat capacity of the fixing roller, so that the heating roller is rapidly heated and the warm-up time can be reduced. become.

If a temperature detecting means for detecting the temperature of the toner heating medium is provided in contact with the toner heating medium on the inner surface side of the toner heating medium near the entrance of the fixing nip portion, the surface of the toner heating medium is damaged. Therefore, the fixing performance is continuously ensured. Further, since the temperature of the toner heating medium immediately before entering the fixing nip is detected, it is possible to stably maintain the temperature of the toner heating medium.

[Brief description of the drawings]

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

FIG. 2A is a cross-sectional view illustrating an arrangement of an excitation coil of an induction heating unit in the fixing device of the present invention. FIG.

FIG. 3 is an explanatory diagram showing generation of an alternating magnetic field and an eddy current in the fixing device of the present invention.

FIG. 4 is an explanatory view showing a fixing device according to another embodiment of the present invention.

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 Belt 4 Pressure roller 5 Temperature detecting means 6 Induction heating means 7 Exciting coil 8 Coil guide plate 9 Exciting coil core 10 Exciting coil core support member 11 Recording material

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tomoyuki Noguchi 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Terms (reference) 2H033 AA02 BA11 BA12 BA25 BA26 BA32 BB18 BB21 BE06 CA07 CA28 CA30 3K059 AA08 AB00 AB19 AB20 AB23 AB27 AB28 AC33 AC73 AD03 AD07 AD15 CD44 CD66 CD75 CD77

Claims (9)

[Claims] A heating roller made of a magnetic metal and heated by electromagnetic induction; a fixing roller disposed in parallel with the heating roller; a heating roller stretched over the heating roller and the fixing roller; Endless belt-shaped toner heating medium which is heated by the rollers and rotated by these rollers, is pressed against the fixing roller via the toner heating medium, and is rotated in the forward direction with respect to the toner heating medium for fixing. A fixing device, comprising: a pressure roller forming a nip portion. 2. A fixing device according to claim 1, wherein said toner heating medium has a base material made of a metal having magnetism. 3. The fixing device according to claim 1, wherein said toner heating medium has a base material made of a resin member having heat resistance. 4. The fixing device according to claim 2, wherein said toner heating medium has a surface of said base material coated with an elastic layer having a thickness of 100 μm to 300 μm. 5. The fixing device according to claim 4, wherein said elastic layer has a releasing property. 6. The apparatus according to claim 1, wherein said induction heating means is disposed along an outer peripheral surface of said heating roller over substantially the same length as a contact area between said heating roller and said toner heating medium. The fixing device according to any one of claims 1 to 5. 7. The apparatus according to claim 1, wherein said induction heating means is disposed along an outer peripheral surface of said heating roller over a length shorter than a contact area between said heating roller and said toner heating medium. 6. The fixing device according to claim 5, 8. The fixing device according to claim 1, wherein the outer diameter of the heating roller is set smaller than the outer diameter of the fixing roller. 9. A method according to claim 1, wherein a temperature detecting means is provided in contact with said toner heating medium on an inner surface side of said toner heating medium near an entrance of said fixing nip portion. The fixing device according to claim 1.