JPH0980939A - Heating device for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent irregularities in an image caused by the effect of magnetic field by generating the magnetic field on a downstream side of the center of a nip between a film and a pressure roller in the rotating direction of the film and within the nip, and heating the film, thereby performing fixation. SOLUTION: A conductive layer 19 is formed by plating a film base material 18 consisting of resin such as polyimide with Ni, and the layer 19 is coated with a releasing layer 20 consisting of silicone resin, etc., so that the film 17 is constituted. A stay for holding the traveling of the film 17 supports a coil 21 wound round a core material 22. Within the nip between the film 17 and the pressure roller 24, the magnetic field is generated on the downstream side of the center of the nip in the rotating direction (arrow (a)) of the film 17, and a recording material P is heated and pressured to melt and fix a toner image T. Therefore, the magnetic toner unfixed image is pressured and held on the upstream side of the nip hardly affected by the magnetic field, and then fixed by passing through the heating part where the magnetic field is generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for generating an eddy current by utilizing electromagnetic induction to heat an object to be heated while it is being conveyed. In particular, it is used in a heat fixing device used for fixing a toner image formed on a recording material, which is an object to be heated, by an electrophotographic method or an electrostatic recording method, and heating and melting the toner image to permanently fix the toner image.

[0002]

2. Description of the Related Art As a heating device, a heat-resistant film, a heating element fixedly supported on one side of the film with the film inside, and a heating element disposed on the other side of the heating element so as to face the heating element. A heating member has a pressing member that adheres the heating member to the heating member through the film, and is heated by passing the heating member through a nip portion formed by pressure contact between the heating member and the pressing member. There is a film heating type heating device that heats a material through the film with the heating body.

This apparatus is suitable for electrophotography, electrostatic recording, magnetic recording, etc. in image forming apparatuses such as copiers, laser beam printers, facsimiles, microfilm reader printers, image display (display) devices and recorders. Recording material (electrofax sheet, electrostatic recording sheet, transfer material sheet, printing paper, etc.) using toner made of heat-meltable resin by image forming process means
Image (unfixed toner image) corresponding to the target image information formed on the surface of the paper by direct method or indirect (transfer) method
Can be utilized as an image heating and fixing device for performing heat fixing processing as a permanently fixed image on the surface of the recording material carrying the image.

Further, it can also be used, for example, in an apparatus for heating a recording material carrying an image to modify the surface properties (such as polishing) and an apparatus for post-processing. Alternatively, it can be used for heating or drying while conveying a sheet-like object.

Conventionally, for example, a heat roller system has been widely used as a heating device of a recording material for heating and fixing an image. This system basically consists of a metallic roller equipped with a heater inside and a pressure roller with elasticity that comes into pressure contact with the metallic roller. The image is heated, pressed and fixed.

However, in such a heat roller system,
Due to the large heat capacity of the roller, it took a very long time to raise the roller surface to the fixing temperature.

Therefore, in order to quickly execute the image output operation, the temperature of the roller surface must be adjusted to a certain temperature even when the machine is not in use.

That is, it takes a long time to warm up, and it is necessary to provide a standby state and always keep the fixing roller in a heated state in order to speed up the first printing.

Various systems and configurations such as a flash heating system, an open heating system, and a hot plate heating system are known and put into practical use. US Patent No. 35787
A belt heating system is also known as described in Japanese Patent Specification No. 97.

Recently, the above-mentioned film heating type heat fixing device, that is, a fixedly supported heating body (thermal heater), a heat resistant film (fixing film) conveyed while being pressed against the heater, and the film An unfixed image formed and carried on the surface of the recording material is heated on the surface of the recording material by applying heat from the heater to the recording material through the film A heat fixing device for fixing has come into use.

According to the applicant's earlier proposal, for example, Japanese Patent Laid-Open No.
The system and apparatus disclosed in JP-A-3-13182 belong to this, and a thin heat-resistant film (sheet), a moving driving means for the film, and a fixedly supporting one side of the film with the film inside are arranged. And a pressing member arranged on the other surface side so as to face the heating body and to bring the developed image bearing surface of the recording material to be image-fixed into close contact with the heating body via the film. The film is moved at least at the same speed in the forward direction as the recording material to be image-fixed, which is conveyed and introduced between the film and the pressure member at the time of image fixing, and the heating moving body is sandwiched between the film and the heating member. By passing through a fixing nip portion formed by press contact between the recording material and a pressure member, the developed image bearing surface of the recording material is heated by the heating body through the film to heat the developed image (unfixed toner image). Apply energy to soften and melt Is a device which is based on that to separate the recording material and the film after fixing point passed at the separation point and then.

As the pressing member, generally, a roller body made of silicone rubber or fluororubber having excellent heat resistance and releasing property is often used.

In such a film heating type heat fixing device, a low heat capacity heater can be used as a heater. Therefore, it is possible to save power and shorten the wait time (quick start) as compared with the conventional contact heating method such as the heat roller method and the belt heating method. Further, since the quick start can be performed, preheating during non-printing operation (heating during standby) is not required, and power saving can be achieved in a comprehensive sense.

[0014]

However, in such a fixing device, When a high-rigidity thick film is used, heat conduction becomes poor and the heat capacity of the film becomes large, so that a rapidly heatable state cannot be achieved. 2. If the film is thin, rigidity cannot be obtained, and a traveling control mechanism is required inside the film, resulting in a large and complicated structure. 3. The material of the film that requires heat resistance is limited. Further, since the resin film has a good heat insulating property, heat is accumulated inside the film, and heat resistance is also required for an object arranged inside the film, so that an expensive and limited material has to be used. And the like.

Therefore, the applicant of the present invention has devised a new fixing device for generating heat and heating by electromagnetic induction in order to solve the above-mentioned drawbacks.

In this fixing device, a magnetic field is repeatedly generated and extinguished on the surface of the heating film by applying a high frequency to the coil arranged on the side of the surface of the heating film. As a result, an eddy current is generated in the conductive layer formed on the surface of the heating film substrate, and heat is generated. A recording material carrying a toner image is pressed against the heated film and conveyed to carry out fixing.

However, since the above-mentioned fixing device heats the conductive layer of the film by a magnetic field, when fixing an unfixed image of magnetic toner, the image may be disturbed by the influence of the magnetic field.

[0018]

In a fixing device for generating heat and heating by electromagnetic induction, in the present invention, in the nip between the film and the pressure roller, the downstream side from the center of the nip with respect to the rotating direction of the film. A magnetic field was generated and the film was heated to fix the film. Therefore, the unfixed image of the magnetic toner is pressed and held on the upstream side of the nip where the influence of the magnetic field is small, and then passes through the heat generating portion where the magnetic field is generated and is fixed, so that the image is disturbed by the influence of the magnetic field. There is no possibility of causing.

[0019]

FIG. 3 shows a schematic structure of an example of an image forming apparatus using a heating device according to the present invention as a fixing device. The image forming apparatus of this example is a laser printer using an electrophotographic process.

Reference numeral 1 is a rotary drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as a first image bearing member.
The photosensitive drum 1 is rotationally driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed (process speed), and in the course of the rotation, the primary charger 2 uniformly charges the negative dark potential V _D.

A laser beam scanner 3 outputs a laser beam modulated in accordance with a time series electric digital pixel signal of target image information input from a host device such as an image reading device, a word processor and a computer (not shown). Then, as the surface of the photosensitive drum 1 which has been negatively and uniformly charged by the primary charger 2 is scanned and exposed by the laser beam as described above, the exposed portion has a smaller absolute value of the potential and becomes the bright potential V _L , and the rotary exposure is performed. An electrostatic latent image corresponding to the target image information is formed on the surface of the drum 1.

Next, the latent image is developed by the developing device 4 with a negative toner so as to be reversal-developed (toner is attached to the laser exposure portion _VL ) to be visualized.

The developing unit 4 has a developing sleeve 4a containing a magnet which is driven to rotate, and the outer peripheral surface of the sleeve is coated with a thin layer of magnetic toner having a negative electric charge to face the drum 1 surface. 4a is applied with the developing bias voltage V _DC whose absolute value is smaller than the dark potential V _{D of the} drum 1 and larger than the bright potential V _L.
The toner on the sleeve 4a is transferred only to the portion of the photosensitive drum 1 having the bright potential V _L , and the latent image is visualized (reversal development).

On the other hand, the recording material 15 as the second image carrier stacked and set on the paper feed tray 14 is fed out and fed one by one by the drive of the paper feed roller 13, and the conveyance guide 12a and the registration roller pair. 10 ・ 11, transfer guide 8 ・
Via the photosensitive drum 1 and the power source 1
8 is fed at a proper timing synchronized with the rotation of the photosensitive drum 1 to a nip portion (transfer portion) n with the transfer roller 5 as a transfer member to which a transfer bias is applied, and the surface of the fed transfer material 15 The toner images on the surface of the photosensitive drum 1 are sequentially transferred to the. The transfer roller 5 as a transfer member preferably has a resistance of about 10 ⁸ to 10 ⁹ Ωcm.

The recording material 15 that has passed through the transfer portion is the photosensitive drum 1.
After being separated from the surface, the transfer guide 12b introduces the transferred toner image to the fixing device 7, and the transferred toner image is fixed, and is output to the paper discharge tray 16 as an image formed product (print). After the separation of the recording material, the surface of the photosensitive drum 1 is cleaned by the cleaning device 6 to remove the residual toner such as toner remaining after transfer, and the surface is cleaned and repeatedly used for image formation.

This fixing device will be described in more detail using FIG. 1 as a stomach.

Reference numeral 17 is a film, which is made of polyimide,
Polyamideimide, PEEK, PES, PPS, PF
A, PTFE, FEP and other resins with a thickness of 10 μm to 100
A film base material with a thickness of μm is formed, and metal such as Ni, Cu, Cr, Fe, and Co is 1 μm by plating on it.
Formed to a thickness of ~ 100μm, PFA, PTF in the outermost layer
It is a mixture of a heat-resistant resin having good releasability such as E, FEP, and a silicone resin, or is coated alone.

Reference numeral 21 is a coil, which is wound around an iron core 22. Reference numeral 23 denotes a stay for supporting the coil and keeping the film 17 running, and is made of liquid crystal polymer, phenol resin, or the like, and a rubbing plate 23 is attached to a portion in contact with the film.

The sliding plate 25 is preferably made of glass or the like having a small friction resistance with the film 17, and it is preferable to apply grease or oil to the surface thereof. Alternatively, the core material 22 may have a smooth surface configuration.

Reference numeral 24 is a pressure roller, which is formed by winding silicone rubber, fluororubber or the like around the core metal.

In the nip between the film 17 and the pressure roller, a magnetic field is generated downstream from the center of the nip with respect to the rotation direction a of the film 17, and the recording material P is heated and pressed to melt the toner image T. Fix it.

With such a structure, the coil 21 has 10 k
A current is applied from an excitation circuit (not shown) at a frequency of Hz to 500 kHz, whereby the magnetic flux indicated by the arrow H is repeatedly generated and extinguished around the coil 21. This magnetic flux H
However, the core material 22 is configured so as to traverse the conductive layer of the film 17. Eddy currents are generated in the conductor so that as the fluctuating magnetic field traverses the conductor, it creates a magnetic field that impedes changes in the magnetic field. This eddy current is indicated by arrow A.

Due to the skin effect, this eddy current I almost concentrates and flows on the surface on the coil 21 side, and heat is generated by electric power proportional to the display resistance R _S in the film conductive layer. R _S is
Skin depth obtained from angular frequency ω, permeability μ, and specific resistance ρ

[0034]

[Outside 1] Is shown.

Electric power P generated in the conductive layer 19 of the film
Can be expressed as Pα · R _S ∫ | _{If f} | ² ds ( _If is the current flowing in the film).

Therefore, the power can be increased and the amount of heat generation can be increased by increasing R _S or increasing I _f .

To increase R _S , the frequency ω may be increased or a material having a high magnetic permeability μ and a high material resistivity ρ may be used.

From now on, the non-magnetic metal is added to the conductive layer 19
It is presumed that it is difficult to heat when used for
When the thickness t of 9 is smaller than the display thickness δ,

[0039]

[Outside 2] Therefore, heating is possible.

The skin thickness is from 10 kHz to 500 kHz depending on the material and temperature frequency, and is generally several μm to several hundreds μm at room temperature to 200 ° C. When the thickness of the conductive layer is actually set to 1 μm or less, most of the electromagnetic energy cannot be absorbed by the conductive layer 19, resulting in poor energy efficiency. There is also a problem that the magnetic field generated in the vertical direction heats other metal parts. On the other hand, in the conductive layer 19 exceeding 100 μm, the rigidity of the film becomes too high, and
There is a problem that heat is transferred by heat conduction in the conductive layer, and it becomes difficult for the release layer 20 to warm up. In addition, manufacturing time and cost are increased. Therefore, the thickness of the conductive layer is preferably 1 to 100 μm.

The current applied to the coil 21 is 10
Absorption from the kHz or higher to the conductive layer is improved, 500 kHz
Up to z can be made with a commercially available device, but more preferably 20 kH
If it is z or more, the sound at the time of energization is also in the audible range or more, and if it is 200 kHz or less without causing the user discomfort, the loss generated in the excitation circuit is small and the radiation noise to the surroundings does not become large.

In this embodiment, as shown in FIG. 2, a coil that is long in the film axial direction is used to generate a magnetic flux H that passes vertically through the film surface, so that the film is located downstream of the center of the nip in the direction of film rotation. The heat was generated uniformly in the axial direction.

In this embodiment, in the nip between the film and the pressure roller, a magnetic field is generated downstream from the center of the nip with respect to the rotation direction arrow a of the film to heat the film for fixing. . Therefore, the unfixed image of the magnetic toner is pressed and held on the upstream side of the nip where the influence of the magnetic field is small, and then passes through the heat generating portion where the magnetic field is generated and is fixed, so that the image may be disturbed by the influence of the magnetic field. Disappear.

Reference numeral 26 is a thermistor attached to the surface of the pressure roller, which detects the temperature of the pressure roller and controls the current applied to the coil 21.

For example, when the pressure roller 24 is cold, it is energized with a full wave, but as it gets warmer, the heating amount can be adjusted by gradually turning it off and thinning the energization even at the ON timing.

The thermistor may be separately attached to the back of the sliding plate 25 or the core 22. Further, the safety element 27 for preventing runaway does not normally warm up even if a low operating temperature is used, so that it does not spontaneously disconnect. In addition, since the operating temperature is low at the time of an abnormality, the energization is stopped quickly, so that it is faster than before. It's safe.

Although the film base material 18 and the conductive layer 19 are separate layers in this example, the film base material itself may be the conductive layer.

Further, in the present invention, the film base material has only to act as a heat insulating material in terms of heat, and the range of choices is wider than the conventional film fixing system using a film as a heat conductor.

As described above, since heat is generated directly near the surface layer of the film, there is an advantage that heating can be performed rapidly regardless of the heat conductivity and heat capacity of the film substrate. Further, since the rigidity of the film is improved for speeding up because it does not depend on the thickness of the film, even if the base material of the film is made thick, it can be quickly heated to the fixing temperature.

Further, since the film base material is a resin, it has a good heat insulating property, and it can be insulated from a coil having a large heat capacity such as a coil inside the film. Therefore, even if continuous printing is performed, heat loss is small and energy efficiency is high. Good, heat is not transmitted to the coil in the film, and the performance of the coil does not deteriorate.

Since the thermal efficiency is improved, the temperature rise in the apparatus can be suppressed and the influence on the image forming portion of the electrophotographic apparatus can be reduced.

The conductive layer 19 of the film 17 in the above embodiment
Was formed by plating, but it may be formed by vacuum vapor deposition, sputtering or the like, whereby a material such as aluminum or a metal oxide alloy that cannot be attached by plating can be formed as a layer.

For example, when a material having a high magnetic permeability such as iron, cobalt, or nickel is attached, the electromagnetic energy generated by the coil 21 can be easily absorbed, the heating can be efficiently performed, and the magnetism leaked to the outside of the nip is reduced, so that it is not fixed yet. The effect on the image can also be reduced. Also, it is better to choose one of these with high resistivity.

Further, the conductive layer 19 may be made of not only metal but also conductive and highly magnetically permeable particles or whiskers dispersed in the adhesive.

For example, manganese, titanium, chromium, iron,
Particles of copper, cobalt, nickel or the like, particles of such ferrite or oxide as these alloys, or whiskers may be mixed with conductive particles such as carbon and dispersed in an adhesive to form the conductive layer 19.

Another embodiment will be described.

In this embodiment, the conductive layer 19 of the film 17 is used.
In order to increase the heat generation and to reduce the influence of the magnetic field other than the heat generating part, a material such as ferrite permalloy having a high magnetic permeability and a low residual magnetic flux density was used as the core material 22 of the coil.

In order to increase the heat generation of the conductive layer 19 of the film 17, the eddy current I _f in the conductive layer 19 may be increased. For that purpose, the number of windings of the coil 21 is increased to increase the magnetic flux generated, or the core material 22 of the coil 21 may be made of ferrite permalloy having a high magnetic permeability and a low residual magnetic flux density. If a material having a low residual magnetic flux density is used for the core material 22, it is possible to prevent conversion loss due to the core material 22 itself generating heat due to the eddy current generated in the core material 22. Further, when a material having a high magnetic permeability is used, it serves as a path for magnetic flux, and leakage to the outside is reduced. Therefore, the core material 2
By using such a material for 2, even if the heat generation of the conductive layer 19 is increased, efficient heating can be performed, and moreover,
It is possible to suppress the leakage of magnetic flux to areas other than the heat generating section as much as possible, and reduce the influence on the unfixed image.

[0059]

As described above, in the fixing device which generates heat by electromagnetic induction, the magnetic field is generated downstream of the film in the nip direction of the film in the nip direction to heat the film to fix the toner. It is possible to reduce the influence of the magnetic field on the received image.

Further, the amount of heat generated can be efficiently increased and the leakage of the magnetic field to the outside of the nip can be reduced by the materials of the conductive layer of the film and the core material of the coil.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of an embodiment of the present invention.

FIG. 2 is a diagram of a coil used in an embodiment of the present invention.

FIG. 3 is a diagram showing an electrophotographic apparatus using an embodiment of the present invention.

[Explanation of symbols]

 1 Photosensitive Drum 2 Primary Charger 3 Laser Optical Box 4 Developing Device 5 Transfer Roller 6 Cleaner 7 Fixing Device 17 Film 18 Film Base Material 19 Conductive Layer 20 Release Layer 21 Coil 22 Core Material 23 Stay 24 Pressure Roller 25 Sliding Plate 26 Thermistor 27 Safety element

Claims (1)

[Claims] 1. A film having a fixedly supported exciting coil, a conductive layer that moves in a magnetic field generated by the exciting coil, and an object to be heated which is adhered and pressed to the film to generate in the conductive layer of the film. In an image forming apparatus that has a heating device for heating an object to be heated with an eddy current and forms an image with magnetic toner, a magnetic field is generated in the contact surface between the film and the object to be heated on the downstream side in the rotation direction of the film. A heating device for an image forming apparatus, which heats an object to be heated.