JPH0926719A - Image heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the temp. distribution in the longitudinal direction within a fixing nip uniform and to make it possible to supply uniform heat energy to a recording material by changing the distance between an excitation coil/core and the heating layer of a fixing film. SOLUTION: The magnetic flux generated by the current impressed on the coil 18 by an excitation circuit is introduced to a high permeability core 17 to generate eddy current in the heating layer of the fixing film 10. In such a case, the Joule heat generated in the heating layer of the fixing film 10 by the magnetic field generated in the excitation coil 18 and the core 17 is changed by the distance between the excitation coil 18 and the core 17 and the heating layer. The heat generation value is larger as the distance is shorter. The radiation quantity in the longitudinal direction of a press roller increases toward the end. The heat generated at the end of the heating layer of the fixing film 10 must be increased in order to obtain the temp. distribution uniform in the fixing nip. The distance between the excitation coil 18 and the fixing film 10 is so set as to be made shorter toward the end from the central part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating device of a type in which heat energy is applied to an image carrier (recording material) directly from or through a film, and particularly to an image of an electrophotographic device, an electrostatic recording device or the like. The present invention relates to an image heating device which is used in a forming apparatus and fixes an unfixed image.

[0002]

2. Description of the Related Art As an increasing heat device represented by a heat fixing device, a contact heating system such as a heat roller system or a film heating system has been widely used.

Among them, in a color fixing device having a maximum of four toner layers, a halogen heater is heated to heat a toner image through a core metal of a fixing roller and a rubber elastic layer.

Japanese Patent Publication No. 5-9027 proposes to generate an eddy current in the fixing roller by magnetic flux and generate heat by Joule heat.

By utilizing the generation of the eddy current in this way, the heat generation position can be brought closer to the toner, and the efficiency of energy consumption can be improved as compared with the heat roller using the halogen lamp.

[0006]

However, in the above-mentioned fixing method, since a fixing roller having a large heat capacity is heated, quick start cannot be achieved even with the best efficiency. Further, in Japanese Patent Publication No. 5-9027, when an eddy current is generated in a cylindrical body to generate Joule heat, the exciting coil and the exciting iron core are heated, the amount of magnetic flux is reduced, and heat generation becomes unstable.

Further, the heat efficiency is not sufficient due to the heat radiation to the inside of the roller.

Other methods using a halogen heater are inefficient because they once convert energy into light.

Further, in a color image recording apparatus, a maximum of four toner layers may be overlapped, and if the interface between the recording material and the toner layer is not sufficiently heated, fixing failure occurs.

Therefore, in color roller fixing, a halogen heater is also provided in the pressure roller, but there is a drawback that quick start cannot be realized. Further, there is a drawback that the heat capacity is large and the power consumption is large.

Therefore, there is a method in which a film having a small heat capacity is used to heat the conductive layer of the film by electromagnetic induction heating. However, in the longitudinal direction of the pressure roller, the heat radiation area at the end is larger than at the center. Therefore, the heat radiation amount becomes larger at the end portion. For this reason, a uniform temperature distribution cannot be obtained in the fixing nip, and the temperature is lowered at the end portion, so that sufficient thermal energy cannot be supplied to the recording material and the toner on the recording material at the end portion. There was a problem that was offset.

[0012]

According to the present invention, there is provided a rotating body having a heat generating layer, and a pressing member forming a nip with the rotating body.
An exciting coil for generating an alternating magnetic field for generating an eddy current by applying a magnetic field to the heat generating layer, and the image carrier is sandwiched and conveyed between the rotating body and the pressing member. In the image heating device for applying thermal energy, the distance between the exciting coil and the heat generating layer is changed in the direction orthogonal to the rotating direction of the rotating body.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 10 is a sectional view of an electrophotographic color printer using the present invention. 101 is a photoconductor drum made of an organic photoconductor or an amorphous silicon photoconductor, 1
Reference numeral 02 denotes a charging roller for uniformly charging the photoconductor drum 101, and 110 denotes a signal from an image signal generator (not shown) which is turned on / off by a laser beam to cause an electrostatic latent image on the photoconductor drum 101. It is a laser optical box that forms an image. 1
Reference numeral 03 is a laser beam, and 109 is a mirror. The electrostatic latent image on the photosensitive drum 101 is visualized by selectively attaching toner by the developing device 104. The developing device 104 is
The photoconductor drum 10 includes a color developing device for yellow Y, magenta M, and cyan C and a developing device B for black.
1 is developed and the toner image is transferred to the intermediate transfer drum 1
05 are sequentially overlaid to obtain a color image. The intermediate transfer body drum 105 has an elastic layer having a medium resistance and a surface layer having a high resistance on a metal drum, and applies a bias potential to the metal drum to transfer a toner image by a potential difference from the photosensitive drum 101. . On the other hand, the recording material P sent from the paper feed cassette by the paper feed roller is sent between the transfer roller 106 and the intermediate transfer drum 105 so as to be synchronized with the electrostatic latent image on the photoconductor drum 101. Transfer roller 10
6 supplies an electric charge having a polarity opposite to that of the toner from the back surface of the recording material P to transfer the toner image on the intermediate transfer body drum 105 onto the recording material. In this way, the recording material on which the unfixed toner image is placed is subjected to heat and pressure by the heat fixing device 100, is permanently fixed on the recording material, and is discharged to a paper discharge tray (not shown). . The toner and the paper dust remaining on the photoconductor drum 101 are removed by the cleaner 107, and the toner and the paper dust remaining on the intermediate transfer drum 105 are removed by the cleaner 108. repeat.

The image heating apparatus according to this embodiment will be described below.

(1) Overall Structure of Image Heating Apparatus--FIG. 2 FIG. 2 is a sectional view of the image heating apparatus according to the present invention.

The fixing film 10 rotates in the direction of the arrow,
The film guide 16 ensures pressurization to the nip portion and stability of conveyance of the film.

Further, the film guide 16 also has a function of supporting the high magnetic permeability core 17 and the coil 18. The high-permeability core 17 is preferably made of a material used for a transformer core, such as ferrite or permalloy, and more preferably 100.
It is preferable to use ferrite, which has a small loss even at a frequency of kHz or higher.

An exciting circuit (FIG. 4) is connected to the coil 18, and this circuit can generate a high frequency of 20 kHz to 500 kHz with a switching power supply. The recording material P on which the unfixed toner T is placed is passed through a nip N formed by the pressure roller 30 and the fixing film 10 to perform heat fixing.

The principle of heating in this nip is that the magnetic flux generated by the current applied to the coil 18 by the exciting circuit (FIG. 4) is guided to the high permeability core 17 and the fixing film 1
An eddy current is generated in the heating layer 1 of 0. Heat is generated by this eddy current and the specific resistance of the heat generating layer 1.

The generated heat heats the recording material P conveyed to the nip N through the elastic layer 2 and the release layer 3 and the toner T on the recording material P. In the nip N, the toner T is melted, passed through the nip, and then cooled to form a permanently fixed image.

(2) Heat distribution-FIG. 1 The relationship between the exciting coil 18 and the core 17 and the fixing film 10 is shown in FIG. In FIG. 1, A, B, and
The cross-sectional views at the position of C are A-section, B-section,
C-section. In FIG. 1, as typical values of the distance between the fixing film 10 and the exciting coil 18, the distances between the uppermost line of the coil 17 and the fixing film 10 are d _A , d _B and d _C.

The Joule heat generated in the heat generating layer 1 of the fixing film 10 by the magnetic field generated in the exciting coil 18 and the core 17 changes depending on the distance between the exciting coil 18 and the core 17 and the heat generating layer 1, and the closer the distance is, the closer. The amount of heat generation increases.

The heat radiation amount in the longitudinal direction of the pressure roller 30 increases toward the end. This is because the heat radiation area at the end of the pressure roller 30 is larger than that at the center.
Therefore, in order to obtain a uniform temperature distribution in the fixing nip N, the heat generation amount at the end of the heat generating layer 1 of the fixing film 10 must be increased.

Therefore, the exciting coil 18 and the fixing film 1
The distance of 0 is set so that the distance becomes closer from the center to the end. That is, it is set so that d _A = d _C > d _B. As a result, a uniform temperature distribution can be obtained in the fixing nip N.

FIG. 8 shows the temperature distribution of the fixing nip, the heat generation distribution of the heat generating layer of the fixing film, and the heat radiation distribution of the pressure roller.

In the present embodiment, the locations of d _A , d _C and d _B are used as typical values in order to represent the distance between the exciting coil 18 and the heat generating layer 1 of the fixing film 10. The purpose is to change the amount of heat generation by changing the distance between 18 and the heat generating layer 1, and does not specify at which position on the cross-sectional view the distance between the exciting coil 18 and the heat generating layer 1 is changed. . Further, d _A = d _C is set at both ends (positions A and C), but d _A > d _C or d _A <d _C due to a difference in heat radiation amount due to a difference in shape of both ends of the pressure roller. Good.

The magnetic flux absorption efficiency is higher if the distance between the exciting coil 18 and the heat generating layer 1 is as close as possible. However, if the distance exceeds 10 mm, the magnetic flux absorption rate decreases, and the distance is within 10 mm. It is better to The distance between the heat generating layer 1 and the exciting coil 18 is set to be about 0.5 mm at the minimum. This is the film guide 16a
This is because a stable shape cannot be obtained with a thickness of 0.5 mm or less.

Although the windings of the exciting coil 18 are arranged in one row in the present embodiment, the windings may be wound in two or more rows.

(3) Concerning Layer Structure of Fixing Film-FIGS. 5 and 61 are heat generating layers made of a metal film or the like as a base layer of the fixing film, more preferably nickel, iron and ferromagnetic S.
It is preferable to use a ferromagnetic metal such as US or nickel-cobalt alloy.

The heat generating layer 1 of the fixing film 10 may be made of a non-magnetic metal, but more preferably a metal such as nickel, iron, magnetic stainless steel, cobalt-nickel alloy or the like, which has good absorption of magnetic flux. The thickness thereof is preferably thicker than the skin depth expressed by the following formula and 200 μm or less. The skin depth σ [m] is expressed as σ = 503 × (ρ / fμ) ^1/2 by the frequency f [Hz], the magnetic permeability μ, and the specific resistance ρ [Ωm] of the excitation circuit.

This shows the depth of absorption of electromagnetic waves used in electromagnetic induction. At deeper points, the intensity of electromagnetic waves is 1 / e or less, and conversely, most of the energy reaches this depth. Is absorbed by (Fig. 7).

The thickness of the heat generating layer 1 is preferably 1 to 100 μm.
m is good. If the thickness of the heat generating layer is less than 1 μm, most of the electromagnetic energy cannot be absorbed, resulting in poor efficiency. Further, if the heat generating layer exceeds 100 μm, the rigidity becomes too high and the bending property deteriorates, which is not practical for use as a rotating body. Therefore, the thickness of the heat generating layer 1 is 1 to 10
0 μm is preferred.

The elastic layer 2 is made of silicone rubber, fluororubber, fluorosilicone rubber or the like, which has good heat resistance and good thermal conductivity.

The thickness of the elastic layer 2 is preferably 10 to 500 μm. The elastic layer 2 has a thickness necessary to guarantee the quality of a fixed image.

When a color image is printed, a solid image is formed over a large area on the recording material P, especially for a photographic image. In this case, if the heating surface (release layer 3) cannot follow the unevenness of the recording material or the unevenness of the toner layer, heating unevenness occurs, and gloss unevenness occurs in the image in a portion with a large amount of heat transfer (a transfer amount) The part with a large amount of heat has a high glossiness,
Low gloss in areas with low heat transfer). Therefore, if the thickness of the elastic layer 2 is 10 μm or less, the unevenness of the image gloss may occur because the unevenness of the recording material or the toner layer cannot be followed. When the thickness of the elastic layer 2 is 1000 μm or more, the thermal resistance of the elastic layer becomes large and it is difficult to realize a quick start. More preferably, the elastic layer 2 has a thickness of 5
0 to 500 μm is preferable.

If the hardness of the elastic layer 2 is too high, it cannot follow the irregularities of the recording material or the toner layer, resulting in uneven image gloss. Therefore, the hardness of the elastic layer is 6
0 ° (JIS-A) or less, more preferably 45 ° (JIS
SA) The following is preferred. The thermal conductivity λ of the elastic layer 2 is 6 × 10
^{-4 to} 2 x 10 ^-3 [cal / cm-sec-deg. ] Is good. Thermal conductivity λ is 6 × 10 ^-4 [cal / cm · sec
Deg. ], The thermal resistance is high,
The temperature rise in the surface layer of the fixing film becomes slow. Thermal conductivity λ is 2 × 10 ⁻³ [cal / cm · sec · de
g. ], The hardness becomes too high and the compression set becomes worse. Therefore, the thermal conductivity λ is 6 ×
10 ^{−4 to} 2 × 10 ⁻³ [cal / cm · sec · de
g. ] Is good. More preferably, 8 × 10 ^{−4 to} 1.5 × 1
0 ^-3 [cal / cm · sec · deg. ] Is good.

Reference numeral 3 denotes a releasing layer, and a material having good releasing property and heat resistance such as fluororesin, silicone resin, fluororesin silicone rubber, fluororubber, silicone rubber, PFA, PTFE, FEP is selected.

The thickness of the release layer 3 is preferably 1 to 100 μm. If the thickness of the release layer 3 is less than 1 μm, there arises a problem that uneven coating of the coating film causes a part having poor releasability or insufficient durability. In addition, when the release layer exceeds 100 μm, there is a problem that heat conduction is deteriorated. In particular, in the case of a resin release layer, the hardness becomes too high, and the effect of the elastic layer 2 is lost.

Further, as shown in FIG. 6, the fixing film 10
The heat insulating layer 4 may be provided in the layer structure. As the heat insulating layer 4, fluororesin polyimide resin, polyamide resin, polyamideimide resin, PEEK resin, PES resin, PP
Heat resistant resins such as S resin, PFA resin, PTFE resin and FEP resin are preferable. The thickness of the heat insulating layer 4 is 10 to 10.
1000 μm is preferred. When the thickness of the heat insulating layer 4 is smaller than 10 μm, the heat insulating effect cannot be obtained, and the durability is insufficient. On the other hand, when it exceeds 1000 μm, the distance from the core 17 and the exciting coil 18 to the heat generating layer 1 becomes large, and the magnetic flux is not sufficiently absorbed in the heat generating layer 1.

Since the heat insulating layer 4 can insulate heat generated in the heat generating layer 1 so as not to go to the inside of the fixing film, the heat supply efficiency to the recording material P side is higher than that in the case without the heat insulating layer 4. Become. Therefore, power consumption can be suppressed.

(4) Pressure roller-FIG. 230 is a pressure roller which is constituted by coating a core metal with silicone rubber, fluororubber, fluororesin or the like. The pressure roller is driven by a drive mechanism (not shown).

Further, in order to supply heat energy to the recording material from the pressure roller side, the pressure roller 30 may be provided with a heating means.

(5) Longitudinal dimension The length L _F of the fixing film and the length L _R of the pressure roller are set to L _F > L _R in order to prevent the pressure roller from being scratched by the film edge. There is.

For the film end, the film end is regulated /
Members 21a and 21b for holding are attached. The film edge holding members 21a and 21b are used for the fixing film 10.
It may be configured to rotate by being driven.

Although the film is driven by the pressure roller in this embodiment, the film may be driven by the drive roller 19 by applying tension to the film by the tension roller 20 as shown in FIG.

As described above, according to the present invention, it is possible to provide an image heating apparatus capable of quick start while maintaining high image quality without causing uneven image gloss.

In this embodiment, since the toner containing the low-softening substance is used as the toner T, the heating and fixing device is not provided with an oil application mechanism for preventing offset.
An oil application mechanism may be provided when a toner containing no low-softening substance is used. Further, a cooling unit may be provided after the fixing nip to perform cooling separation. Also,
Even when a toner containing a low-softening substance is used, oil coating or cooling separation may be performed.

Although the four-color image forming apparatus has been described in the present embodiment, it may be applied to a monochrome or one-pass multi-color image forming apparatus. In this case, the elastic layer 2 may be omitted in the fixing film 10.

(Second Embodiment) In the present embodiment, as shown in FIG. 11, in addition to the configuration of the first embodiment, the distance between the core 17 and the fixing film 10 is changed. There is. Also in the relationship of the distance between the core 17 and the heat generating layer 1 of the fixing film 10, as in the relationship between the exciting coil 18 and the fixing film 10, the shorter the distance, the heat generating layer 1
The amount of heat generated in

Therefore, combining these two effects,
It is possible to make the heat generation amount of the fixing nip uniform.

The core 17 may be formed by one member as shown in FIG. 11, but a plurality of members may be arranged in the longitudinal direction. At this time, some blocks can be arranged stepwise as shown in FIG.

Similar effects can be obtained by arranging cores having different magnetic permeability as shown in FIG. 12 (b). In this case, the amount of heat generation can be increased from the center to the end by gradually increasing the magnetic permeability from the center to the end.

Furthermore, it is also possible to combine FIG. 12 (a) and 12 (b) to form a structure as shown in FIG. 12 (c).

(Third Embodiment) In the present embodiment, the exciting coil 18 is wound in the winding direction as shown in FIG. 13 in the first embodiment. Also in the winding direction of the coil as in this embodiment, the same effect as in the first embodiment can be obtained.

Also in the present embodiment as in the second embodiment, the same effect can be obtained by changing the distance between the core 17 and the heat generating layer 1 of the fixing film.

As described above, the distance between the exciting coil and the core and the heat generating layer of the fixing film has been changed to make the temperature distribution in the fixing nip uniform. However, in order to positively change the temperature distribution in the fixing nip, The invention may be utilized.

[0057]

As described above, according to the present invention,
By changing the distance between the excitation coil / core and the heat generating layer of the fixing film, the temperature distribution in the fixing nip in the longitudinal direction can be made uniform, and uniform thermal energy can be supplied to the recording material, so toner offset It is possible to obtain a good fixing property with no deterioration.

[Brief description of drawings]

FIG. 1 is a sectional view of an image heating apparatus used in the present invention.

FIG. 2 is a sectional view of the image heating apparatus according to the first embodiment.

FIG. 3 is a front view of the image heating apparatus according to the first embodiment.

FIG. 4 is a perspective view of an exciting coil, a core, and a stay according to the first embodiment.

FIG. 5 is a layer configuration diagram of a fixing film used in the first embodiment.

FIG. 6 is a layer configuration diagram of a fixing film used in the first embodiment.

FIG. 7 is a diagram showing a graph showing the relationship between the depth of a heat generating layer and the intensity of electromagnetic waves.

FIG. 8 is a graph showing a relationship between a fixing nip temperature in the longitudinal direction and heat generation / heat radiation amount.

FIG. 9 is a cross-sectional view of the image heating device used in the first embodiment.

FIG. 10 is a cross-sectional view of the image forming apparatus used in the first embodiment.

FIG. 11 is a front view of the image heating apparatus used in the second embodiment.

FIG. 12 is an array diagram of cores used in the second embodiment.

FIG. 13 is a cross-sectional view of the image heating device used in the third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat generating layer 2 Elastic layer 3 Release layer 4 Thermal insulation layer 10 Fixing film 17 High magnetic permeability core 18 Excitation coil 21a, b Film end part holding member 30 Pressure roller

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Kiyofumi Nakane 3-43-12 Shinkino, Abiko City, Chiba Prefecture

Claims (7)

[Claims] 1. A rotating body having a heating layer, a pressing member forming a nip with the rotating body, and an exciting coil for generating an alternating magnetic field for generating an eddy current by applying a magnetic field to the heating layer. In the image heating device that has, and that applies thermal energy to the image bearing member by sandwiching and conveying the image bearing member between the rotating member and the pressing member, in the direction orthogonal to the rotating direction of the rotating member, the exciting coil and the heat are generated. An image heating device, characterized in that the distance between the layers is changing. 2. A core material around which the exciting coil is wound,
The image heating apparatus according to claim 1, wherein the distance between the core member and the heat generating layer changes in a direction orthogonal to the rotation direction of the rotating body. 3. The excitation coil has a plurality of cores wound around it, and the material of these cores changes in a direction orthogonal to the rotation direction of the rotating body.
Image heating equipment. 4. The image heating apparatus according to claim 1, wherein there is a portion in which the distance between the exciting coil and the rotating body is smaller toward the outside than in the central portion. 5. The rotating body is an endless film, and the layer structure of the film is composed of at least a heat insulating layer, a heat generating layer, an elastic layer and a release layer in this order. Image heating device. 6. The image heating apparatus according to claim 1, wherein the rotating body is an endless film, and the layer structure of the film includes at least a heat insulating layer, a heat generating layer, and a release layer in this order. . 7. The image heating apparatus according to claim 1, wherein the distance between the heat generating layer and the exciting coil varies between 0.5 mm and 10 mm.