JP3584132B2 - Image heating device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electromagnetic (magnetic) induction heating type heating device, and to an image forming apparatus such as an electrophotographic apparatus and an electrostatic recording device provided with the heating device as an image heating device.
[0002]
[Prior art]
For convenience, an image heating device (fixing device) provided in an image forming apparatus such as a copying machine or a printer for heating and fixing a toner image on a recording material will be described as an example.
[0003]
In an image forming apparatus, a recording material (transfer material sheet, electrofax sheet, electrostatic recording paper, OHP sheet, printing paper, format) is used in an appropriate image forming process means such as an electrophotographic process, an electrostatic recording process, and a magnetic recording process. As a fixing device for heating and fixing an unfixed image (toner image) of target image information formed and carried on a transfer method or a direct method on paper as a permanent fixed image on a recording material surface, a heat roller type device is widely used. Was used. Recently, a film heating type apparatus has been put into practical use. Also, an electromagnetic induction heating system has been proposed.
[0004]
Japanese Utility Model Laid-Open Publication No. 51-109739 discloses an induction heating fixing device in which current is induced in a fixing roller by magnetic flux to generate heat by Joule heat. This makes it possible to directly generate heat in the fixing roller by utilizing the generation of the induced current, and achieves a more efficient fixing process than a heat roller type fixing device using a halogen lamp as a heat source.
[0005]
However, since the energy of the alternating magnetic flux generated by the exciting coil as the magnetic field generating means is used to raise the temperature of the entire fixing roller, there is a disadvantage that heat dissipation is large, the density of the fixing energy with respect to the input energy is low, and the efficiency is poor.
[0006]
Therefore, in order to obtain the energy acting on the fixing at a high density, the excitation coil is moved closer to the fixing roller, which is a heating element, or the alternating magnetic flux distribution of the excitation coil is concentrated near the fixing nip, thereby achieving high-efficiency fixing. The device was devised.
[0007]
FIG. 13 shows a schematic configuration of an example of an electromagnetic induction heating type fixing device according to the background art of the present invention in which the alternating magnetic flux distribution of the exciting coil is concentrated on the fixing nip to improve the efficiency.
[0008]
Reference numeral 10 denotes a cylindrical fixing film having an electromagnetic induction heating layer (a conductor layer, a magnetic layer, and a resistor layer) and serving as an electromagnetic induction heating rotating body.
[0009]
Numeral 16 denotes a gutter-shaped film guide member having a substantially semicircular cross section, and the cylindrical fixing film 10 is loosely fitted outside the film guide member 16.
[0010]
Numeral 15 denotes a magnetic field generating means disposed inside the film guide member 16 and comprises an exciting coil 18 and an E-shaped magnetic core (core material) 17.
[0011]
Numeral 30 denotes an elastic pressure roller which forms a fixing nip portion N of a predetermined width with a predetermined pressing force on the lower surface of the film guide member 16 with the fixing film 10 interposed therebetween, and is pressed against each other. The magnetic core 17 of the magnetic field generating means 15 is disposed at a position corresponding to the fixing nip portion N.
[0012]
The pressure roller 30 is driven to rotate in the counterclockwise direction indicated by the arrow by the driving means M. A rotational force acts on the fixing film 10 by a frictional force between the pressing roller 30 and the outer surface of the fixing film 10 due to the rotational driving of the pressing roller 30, and the inner surface of the fixing film 10 is fixed at the fixing nip portion N. While closely sliding on the lower surface of the guide member 16, the film guide member 16 is rotated in a clockwise direction as indicated by an arrow at a peripheral speed substantially corresponding to the rotational peripheral speed of the pressure roller 30 (pressure roller drive method).
[0013]
The film guide member 16 serves to pressurize the fixing nip, support the exciting coil 18 and the magnetic core 17 as the magnetic field generating means 15, support the fixing film 10, and stabilize the conveyance of the film 10 during rotation. I do. The film guide member 16 is an insulating member that does not hinder the passage of magnetic flux, and is made of a material that can withstand a required load.
[0014]
The exciting coil 18 generates an alternating magnetic flux by an alternating current supplied from an exciting circuit (not shown). FIG. 14 schematically shows a state of generation of an alternating magnetic flux near the fixing nip portion N. The magnetic flux C represents a part of the generated alternating magnetic flux.
[0015]
The alternating magnetic flux (C) is intensively distributed in the fixing nip N by the E-shaped magnetic core 17 corresponding to the position of the fixing nip N, and the alternating magnetic flux (C) is distributed in the fixing film 10 in the fixing nip N. An eddy current is generated in the electromagnetic induction heating layer. This eddy current generates Joule heat in the electromagnetic induction heating layer due to the specific resistance of the electromagnetic induction heating layer. The heat value Q here is determined by the density of the magnetic flux passing through the electromagnetic induction heating layer, and has a distribution as shown in FIG. In the graph of FIG. 14, the horizontal axis represents the fixing nip center as 0, and the position of the fixing film is represented by an angle θ from the fixing nip center. The vertical axis represents the heat value Q in the electromagnetic induction heating layer of the fixing film 10.
[0016]
The electromagnetically induced heat of the fixing film 10 is generated intensively in the fixing nip N where the alternating magnetic flux is intensively distributed, and the fixing nip N is heated with high efficiency.
[0017]
The temperature of the fixing nip N is controlled such that a predetermined temperature is maintained by controlling the current supply to the exciting coil 18 by a temperature control system including a temperature detection unit (not shown).
[0018]
Thus, the pressure roller 30 is driven to rotate, and accordingly, the cylindrical fixing film 10 rotates around the film guide member 16, and the power is supplied from the excitation circuit to the excitation coil 18 as described above. The recording material P on which the unfixed toner image t formed from the image forming means (not shown) is fixed in a state where the electromagnetic induction heat is generated and the fixing nip N rises to a predetermined temperature and the temperature is adjusted. The image surface is introduced between the fixing film 10 and the pressure roller 30 in the nip portion N with the image surface facing upward, that is, opposed to the fixing film surface. The fixing nip N is conveyed while being held together with the film 10. In the process of nipping and transporting the recording material P together with the fixing film 10 through the fixing nip N, the unfixed toner image t on the recording material P is heated and fixed by heating by the electromagnetic induction heat of the fixing film 10. After passing through the fixing nip N, the recording material P is separated from the outer surface of the rotary fixing film 10 and is discharged and conveyed.
[0019]
[Problems to be solved by the invention]
However, regarding the above-described electromagnetic induction type fixing device as shown in FIG. 13, when the toner layer to be fixed is thick such as a high-speed printer / copier or a full-color image, the pressing force at the fixing nip must be set high. but only the rigidity of the mold member will deflect the mold member, there is a problem that that can not be that applying sufficient pressure to the central portion of the nip.
[0020]
[Means for Solving the Problems]
Means for Solving the Problems The present invention is directed to a magnetic field generating means, a rotating body that generates electromagnetic induction by the action of a magnetic field of the magnetic field generating means, and the rotating body which is fixed so as not to rotate inside the rotating body. A supporting member made of a resin for loosely supporting the rotating member, and a pressing member forming a nip portion with the supporting member with the rotating member interposed therebetween, wherein the rotating member of the nip portion and the pressing member the recording material is sandwiched transported between, for holding the pressure from the at image heating apparatus for heating an image on a recording material by rotating body heat, said pressure member through said rotating body and said support member metal Alternatively , there is provided a pressure holding member made of an alloy , and the magnetic field generating means is provided at a place other than between the support member and the pressure holding member.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
(First embodiment)
(1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus of this example is an electrophotographic color printer.
[0022]
Reference numeral 101 denotes a photosensitive drum (image carrier) made of an organic photosensitive member or an amorphous silicon photosensitive member, and is rotated at a predetermined process speed (peripheral speed) in a counterclockwise direction indicated by an arrow.
[0023]
The photosensitive drum 101 undergoes a uniform charging process of a predetermined polarity and potential by a charging device 102 such as a charging roller during the rotation process.
[0024]
Next, the charged surface is subjected to a scanning exposure process of target image information by a laser beam 103 output from a laser optical box (laser scanner) 110. The laser optical box 110 outputs a laser beam 103 modulated (on / off) in accordance with a time-series electric digital pixel signal of target image information from an image signal generating device such as an image reading device (not shown) to output a rotating photoconductor. An electrostatic latent image corresponding to the target image information scanned and exposed on the surface of the drum 101 is formed. A mirror 109 deflects the output laser light from the laser optical box 110 to the exposure position of the photosensitive drum 101.
[0025]
In the case of full-color image formation, scanning exposure / latent image formation is performed on a first color-separated component image of a target full-color image, for example, a yellow component image, and the latent image is developed by the yellow developing unit 104 of the four-color color developing device 104. Is developed as a yellow toner image by the operation of the container 104Y. The yellow toner image is transferred onto the surface of the intermediate transfer drum 105 at a primary transfer portion T1 which is a contact portion (or a close portion) between the photosensitive drum 101 and the intermediate transfer drum 105. After the transfer of the toner image to the surface of the intermediate transfer drum 105, the surface of the rotary photoconductor drum 101 is cleaned by the cleaner 107 after removing the adhered residue such as untransferred toner.
[0026]
The process cycle of charging, scanning exposure, development, primary transfer, and cleaning as described above is performed by the second color separation component image of the target full-color image (for example, the magenta component image, the magenta developing device 104M is activated), and the third color. The color separation component images (for example, the cyan component image and the cyan developing device 104C are activated) and the fourth color separation component image (for example, the black component image and the black developing device 104BK are activated) are sequentially executed for the color separation component images, and the intermediate transfer member The four toner images of a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image are sequentially transferred onto the surface of the drum 105 in a superimposed manner, and a color toner image corresponding to a target full-color image is synthesized and formed.
[0027]
The intermediate transfer drum 105 has a medium-resistance elastic layer and a high-resistance surface layer on a metal drum, and contacts at or near the photosensitive drum 101 at an almost same peripheral speed as the photosensitive drum 101. Is rotated clockwise to apply a bias potential to the metal drum of the intermediate transfer drum 105 to transfer the toner image on the photosensitive drum 101 side to the surface of the intermediate transfer drum 105 by a potential difference from the photosensitive drum 101. .
[0028]
The color toner image synthesized and formed on the surface of the rotary intermediate transfer drum 105 is transferred to the secondary transfer portion T2 at a secondary transfer portion T2 which is a contact nip portion between the rotary intermediate transfer drum 105 and the transfer roller 106. Is transferred onto the surface of the recording material P sent at a predetermined timing from a paper supply unit (not shown). The transfer roller 106 sequentially and collectively transfers the combined color toner images from the surface of the intermediate transfer drum 105 to the recording material P by supplying charges of the opposite polarity to the toner from the rear surface of the recording material P.
[0029]
The recording material P that has passed through the secondary transfer portion T2 is separated from the surface of the intermediate transfer drum 105, introduced into the image heating device (fixing device) 100, and subjected to the heat-fixing process of the unfixed toner image to form a color image formed product. And is discharged to a discharge tray (not shown) outside the apparatus. The fixing device 100 will be described in detail in the following section (2).
[0030]
After the transfer of the color toner image to the recording material P, the rotating intermediate transfer drum 105 is cleaned by the cleaner 108 by removing the residual toner such as untransferred toner and paper dust. The cleaner 108 is normally kept in a non-contact state with the intermediate transfer drum 105, and is brought into contact with the intermediate transfer drum 105 in the process of performing the secondary transfer of the color toner image from the intermediate transfer drum 105 to the recording material P. Will be retained.
[0031]
Also, the transfer roller 106 is always kept in a non-contact state with the intermediate transfer drum 105, and the recording material is applied to the intermediate transfer drum 105 during the secondary transfer of the color toner image from the intermediate transfer drum 105 to the recording material P. It is kept in contact via P.
[0032]
A print mode for a monochrome image such as a black and white image can also be executed. Also, a double-sided image print mode or a multiple image print mode can be executed.
[0033]
In the case of the double-sided image print mode, the recording material P on which the first-side image has been printed out of the image heating device 100 is turned upside down via a recirculation transport mechanism (not shown), and is again sent to the secondary transfer unit T2. After receiving the toner image transfer on the two surfaces, the toner image is again introduced into the image heating device 100 and subjected to the fixing process of the toner image on the two surfaces, whereby a two-sided image print is output.
[0034]
In the case of the multiple image print mode, the recording material P on which the first image has been printed out of the image heating device 100 is sent again to the secondary transfer unit T2 without being turned over via a recirculation transport mechanism (not shown). The second transfer of the toner image to the surface on which the first image has been printed is received, and the multi-image print is output by being introduced again into the image heating device 100 and undergoing the second toner image fixing process.
[0035]
In this example, the toner contains a low softening substance.
[0036]
(2) Fixing device 100
FIG. 2 is a cross-sectional side view of a main part of the fixing device 100 of this embodiment, FIG. 3 is a frontal view of the main part, and FIG. 4 is a longitudinal front view of the main part.
[0037]
Similar to the fixing device of FIG. 13, the present example apparatus 100 is an apparatus of a pressure roller driving system and an electromagnetic induction heating system using a cylindrical electromagnetic induction heating film as a rotating body. The same reference numerals are given to the same constituent members and portions as those in the apparatus of FIG. 13, and the description will not be repeated.
[0038]
The magnetic cores 17a, 17b, and 17c are members having a high magnetic permeability, and are preferably made of a material used for a transformer core such as ferrite or permalloy, and more preferably, ferrite that has a small loss even at 100 kHz or more.
[0039]
The fixing member 16b of the fixing film is an upper film guide member on which the magnetic cores 17a, 17b, and 17c and the exciting coil 18 are disposed, and has a substantially semi-circular cross section having a cross section disposed over the supporting member 16a. A mold film guide member. The film guide member 16a and the upper film guide member 16b form a substantially cylindrical body.
[0040]
Outside the assembly of the film guide member 16a and the upper film guide member 16b, a fixing film 10, which is a cylindrical electromagnetic induction heating film, is loosely fitted.
[0041]
Reference numeral 22 denotes a pressing rigid stay, which is a horizontally long pressing force holding member disposed in contact with the upper surface flat portion of the film guide 16a.
[0042]
Reference numeral 19 denotes an insulating member for insulating the magnetic core 18 from the rigid pressing stay 22.
[0043]
Reference numerals 23a and 23b denote flange members which regulate and hold the ends of the fixing film 10 and are fixedly attached to the right and left ends of the assembly of the film guide member 16a and the upper film guide member 16b.
[0044]
The pressure roller 30 as a pressure member includes a core metal 30a and a heat-resistant / elastic material layer 30b made of silicone rubber, fluoro rubber, fluoro resin, or the like, which is formed and coated concentrically around the core metal in a roller shape. , And both ends of the cored bar 30a are rotatably supported by bearings between chassis-side sheet metal (not shown) of the apparatus.
[0045]
Above the pressure roller 30, the film guide member 16a, the magnetic cores 17a, 17b, and 17c, the exciting coil 18, the upper film guide member 16b, the rigid stay for press 22, the insulating member 19, the fixing film 10, and the flange A heating unit composed of members 23a and 23b is disposed with the semicircular bottom surface of the film guide member 16a facing downward, and between the both ends of the rigid stay for press 22 and the spring receiving members 29a and 29b on the apparatus chassis side. The pressurizing springs 25a and 25b are respectively contracted to apply a pressing force to the pressurizing rigid stay 22. As a result, the lower surface of the film guide member 16a and the upper surface of the pressure roller 30 are pressed against each other with the fixing film 10 interposed therebetween, thereby forming a fixing nip portion N having a predetermined width. The lower surface of the pressing rigid stay 22 is located at a position corresponding to the fixing nip portion N with the bottom plate portion of the film guide member 16a interposed therebetween.
[0046]
The pressure roller 30 is driven to rotate in the counterclockwise direction indicated by the arrow by the driving means M. A rotational force acts on the fixing film 10 by a frictional force between the pressing roller 30 and the outer surface of the fixing film 10 due to the rotational driving of the pressing roller 30, and the inner surface of the fixing film 10 is fixed at the fixing nip portion N. The outer periphery of the film guide member 16a and the upper film guide member 16b is rotated in a clockwise direction indicated by an arrow at a peripheral speed substantially corresponding to the rotational peripheral speed of the pressure roller 30 while sliding in close contact with the lower surface of the guide member 16a. Become.
[0047]
In this case, in order to reduce the mutual sliding friction force between the lower surface of the film guide member 16a and the inner surface of the fixing film 10 in the fixing nip portion N, the lower surface of the film guide 16a of the fixing nip portion N and the inner surface of the fixing film 10 are reduced. A lubricant such as heat-resistant grease may be interposed therebetween, or the lower surface of the film guide member 16a may be covered with a lubricant.
[0048]
A fixing device such as a high-speed printer or a color printer requires a higher pressing force than a low-speed device. For example, a pressure of 15 N or more may be required for a printer of 20 ppm (prints per minute) or more, and a pressure of 30 N or more may be required for a full color printer.
[0049]
Here, as Comparative Example 1, FIG. 5B shows a nip shape when a high pressing force is applied to only the film guide 16 as shown in FIG. If nip central portion has a fixing nip width N ₁ necessary for obtaining a good fixing property, a sufficient fixing in the narrower becomes poor fixing region nip width than N ₁ of the fixing nip central portion by insufficient rigidity of the film guide 16 Sex was not obtained.
[0050]
As a comparative example 2, when a pressing rigid stay 22 is disposed on a magnetic core 17 via an insulating member 19 as shown in FIG. 15 and a high pressing force is applied, as shown in FIG. A nip width (> N ₁ ) was obtained. However, the magnetic core 17 has the property of being hard but brittle, and there is a possibility that the core will crack if an excessive load is applied. In addition, the excitation coil 18 must maintain insulation between turns of the coil, and if an excessive load is applied thereto, the insulation coating of the coil may be damaged and dielectric breakdown may occur. In Comparative Example 2, the magnetic core was not able to withstand the high pressing force, and the magnetic core was broken, thereby damaging the insulating coating of the exciting coil.
[0051]
Therefore, in the present invention, the magnetic core and the exciting coil are not arranged between the pressing position of the pressing rigid stay 22 and the fixing nip. In the present embodiment, the excitation coil and the magnetic core are disposed above the pressing stay 22, and only the film guide 16 a and the fixing film 10 are provided between the pressing position of the pressing stay 22 and the fixing nip. Configuration.
[0052]
According to the above configuration, a stable fixing nip as shown in FIG. 5A could be obtained without applying a load to the magnetic cores 17a, 17b, 17c and the exciting coil 18 as the magnetic field generating means. In the present embodiment, a stable fixing nip was obtained in which the nip width at the central portion was not reduced even when a total pressing force of 40 N was applied, and there was almost no change with time due to durability.
[0053]
Further, in the configuration of the present invention, since no load is applied to the magnetic cores 17a, 17b, 17c and the exciting coil 18, there is no restriction on the shape of the core coil, and the heat generation efficiency can be improved.
[0054]
As the Young's modulus E of the pressurizing rigid stay 22, a metal or alloy with E ≧ 7 × 10 ¹⁰ is preferable. In the case of E <7 × ¹⁰ 10 is cause crooked pressurizing rigid stay 22 not completely bear the increased pressure, can not be secured nip width N ₁ necessary for good fixing.
[0055]
The pressurizing rigid stay 22 is preferably made of a nonmagnetic metal or alloy. When the pressurizing rigid stay 22 is a magnetic metal, the stay itself generates heat by absorbing a part of the magnetic field generated by the exciting coil 18, and the heat generation efficiency of the fixing film 10 is reduced. If the pressurizing rigid stay 22 is a non-magnetic metal or alloy, an effect of shielding the magnetic field can be obtained, and a decrease in the heat generation efficiency of the fixing film 10 can be prevented.
[0056]
In the present embodiment, non-magnetic stainless steel SUS304 having a thickness of 2 mm is used by bending it into a U-shape.
[0057]
Reference numeral 16e (FIG. 6) denotes a plurality of lower film guide circumferential ribs formed on the side surface of the upper film guide member 16b at intervals along the length of the film guide member. The convex rib portion 16e functions to reduce the contact sliding resistance between the side surface of the film guide member 16b and the inner surface of the fixing film 10, thereby reducing the rotational load of the fixing film 10. Such a convex rib portion can be formed and provided on the film guide member 16a in a similar shape.
[0058]
The excitation coil 18 in the upper film guide member 16b is connected to an excitation circuit 27 (FIG. 6) at the power supply portions 18a and 18b. The excitation circuit 27 can generate a high frequency of 20 kHz to 500 kHz by a switching power supply.
[0059]
The exciting coil 18 in the upper film guide member 16b generates an alternating magnetic flux by an alternating current (high-frequency current) supplied from the exciting circuit 27.
[0060]
FIG. 7 schematically shows a state of generation of an alternating magnetic flux near the fixing nip portion N. The magnetic flux C represents a part of the generated alternating magnetic flux.
[0061]
The alternating magnetic flux (C) guided to the magnetic cores 17a, 17b, and 17c is intensively distributed between the magnetic cores 17a and 17b and between 17a and 17c, and is distributed to the electromagnetic induction heating layer 1 of the fixing film 10. Generates eddy currents. This eddy current generates Joule heat (eddy current loss) in the electromagnetic induction heating layer 1 due to the specific resistance of the electromagnetic induction heating layer 1. The heat value Q here is determined by the density of the magnetic flux passing through the electromagnetic induction heating layer 1, and shows a distribution as shown in the graph of FIG. The graph of FIG. 7 shows the position of the fixing film 10 by the angle θ from the center of the fixing nip, with the center of the fixing nip being 0 on the horizontal axis. The vertical axis represents the heat value Q in the electromagnetic induction heating layer 1 of the fixing film 10. Here, the heating area H is defined as an area where the heating value is Q / e or more, where Q is the maximum heating value.
[0062]
The temperature of the fixing nip N is controlled such that a predetermined temperature is maintained by controlling the current supply to the exciting coil 18 by a temperature control system including a temperature detection unit (not shown). Reference numeral 26 denotes a temperature sensor such as a thermistor for detecting the temperature of the fixing film 10. In this example, the temperature sensor 26 is brought into contact with the fixing film 10 immediately after the fixing nip, and based on the temperature information, the fixing nip N The temperature is controlled.
[0063]
Thus, the pressure roller 30 is driven to rotate, and accordingly, the cylindrical fixing film 10 rotates around the film guide member 16a and the upper film guide member 16b, and the excitation circuit 27 excites the inside of the upper film guide member. In a state where the fixing film 10 is heated by the electromagnetic induction heating of the fixing film 10 to a predetermined temperature by the power supply to the coil 18 as described above, the unfixed toner image conveyed from the image forming means unit. The recording material P on which the t is formed is introduced between the fixing film 10 and the pressure roller 30 in the fixing nip portion N with the image surface facing upward, that is, opposed to the fixing film surface. The fixing nip N is conveyed together with the fixing film 10 in close contact with the outer surface of the fixing film 10. In the process of nipping and transporting the recording material P together with the fixing film 10 through the fixing nip N, the unfixed toner image t on the recording material P is heated and fixed by heating by the electromagnetic induction heat of the fixing film 10. After passing through the fixing nip N, the recording material P is separated from the outer surface of the rotary fixing film 10 and is discharged and conveyed. After passing through the fixing nip, the heat-fixed toner image on the recording material is cooled and becomes a permanent fixed image.
[0064]
As shown in FIG. 3, the length L _R of length L _F and a pressure roller of the fixing film 10 is in the L _F> L _R to be prevented that damage the pressure roller at the film edge .
[0065]
The flange members 23a and 23b receive the ends of the fixing film 10 when the fixing film 10 rotates, and play a role of restricting the shifting of the fixing film along the length of the film guide member. The flange members 23a and 23b may be configured to rotate following the fixing film 10.
[0066]
In this example, since a toner containing a low softening substance was used in the toner t, an oil applying mechanism for preventing offset was not provided in the fixing device, but when a toner containing no low softening substance was used, An oil application mechanism may be provided. Also, when a toner containing a low softening substance is used, oil application or cooling separation may be performed.
[0067]
A) Excitation coil 18
The exciting coil 18 is formed by bundling a plurality of copper thin wires (bundled wires), each of which is individually insulated and coated, as a conducting wire (electric wire) constituting a coil (wire loop), and winding the winding a plurality of times to excite. Forming a coil. In this example, the exciting coil 18 is formed by winding 12 turns.
[0068]
As the insulating coating, a coating having heat resistance is preferably used in consideration of heat conduction due to heat generation of the fixing film 10. In this embodiment, a coating with polyimide is used, and the heat resistance temperature is 220 ° C.
[0069]
Here, the density may be improved by applying pressure from outside the excitation coil 18.
[0070]
In order for the magnetic field generated by the exciting coil 18 and the magnetic cores 17a, 17b, 17c to be efficiently absorbed by the heat generating layer of the fixing film 10, the heat generating layer 1 of the fixing coil 10 and the exciting coil 18 and the magnetic cores 17a, 17b, 17c are required. It is better to be as close as possible.
[0071]
Therefore, in this example, as shown in FIG. 2, the shape of the exciting coil 18 is made to follow the curved surface of the heat generating layer. In this embodiment, the distance between the heat generated by the fixing film 10 and the exciting coil 18 is set to be approximately 1 mm.
[0072]
As the material of the film guide members 16a and 16b, a material having excellent insulation properties and good heat resistance in order to secure insulation from the fixing film 10 is preferable. For example, a phenol resin, a fluorine resin, a polyimide resin, a polyamide resin, a polyamide imide resin, a PEEK resin, a PES resin, a PPS resin, a PFA resin, a PTFE resin, a FEP resin, an LCP resin, or the like may be selected.
[0073]
The shorter the distance between the magnetic cores 17a, 17b, 17c and the exciting coil 18 and the heat generating layer of the fixing film is, the higher the magnetic flux absorption efficiency is. However, when the distance exceeds 5 mm, the efficiency is reduced. It is preferable to set the thickness to 5 mm or less because it is significantly reduced. If the distance is within 5 mm, the distance between the heating layer of the fixing film 10 and the exciting coil 18 does not need to be constant.
[0074]
With respect to the lead wires 18a and 18b of the exciting coil 18 from the film guide member 16a, portions outside the film guide member 16a are covered with insulating coating outside the bundle.
[0075]
B) Fixing film 10
FIG. 8 is a schematic diagram of the layer structure of the fixing film 10 in this example. The fixing film 10 of the present embodiment includes a heating layer 1 made of a metal film or the like serving as a base layer of an electromagnetic induction heating fixing film, an elastic layer 2 laminated on its outer surface, and a release layer 3 laminated on its outer surface. It has a composite structure. A primer layer (not shown) may be provided between each layer for adhesion between the heat generating layer 1 and the elastic layer 2 and adhesion between the elastic layer 2 and the release layer 3. In the cylindrical fixing film 10, the heat generating layer 1 is on the inner side, and the release layer 3 is on the outer side. As described above, when the alternating magnetic flux acts on the heat generating layer 1, an eddy current is generated in the heat generating layer 1, and the heat generating layer 1 generates heat. The heat heats the fixing film 10 via the elastic layer 2 and the release layer 3, and heats a recording material as a material to be passed through the fixing nip N to heat and fix the toner image.
[0076]
a. Heating layer 1
The heat generating layer 1 may be made of a non-magnetic metal, but is preferably made of a ferromagnetic metal such as nickel, iron, ferromagnetic SUS, or a nickel-cobalt alloy.
[0077]
The thickness is preferably larger than the skin depth represented by the following formula and 200 μm or less. The skin depth σ [m] is σ = 503 × (ρ / fμ) ^{1/2 with} the frequency f [Hz] of the excitation circuit, the magnetic permeability μ, and the specific resistance ρ [Ωm].
It is expressed as
[0078]
This indicates the depth of absorption of electromagnetic waves used in electromagnetic induction. At depths below this, the intensity of electromagnetic waves is less than 1 / e, and conversely, most energy is absorbed up to this depth. (FIG. 10).
[0079]
The thickness of the heat generating layer 1 is preferably 1 to 100 μm. If the thickness of the heat generating layer 1 is smaller than 1 μm, most of the electromagnetic energy cannot be absorbed, so that the efficiency is deteriorated. On the other hand, if the heat generating layer exceeds 100 μm, the rigidity becomes too high, and the flexibility deteriorates, which is not practical for use as a rotating body. Therefore, the thickness of the heat generating layer 1 is preferably 1 to 100 μm.
[0080]
b. Elastic layer 2
The elastic layer 2 is a material having good heat resistance and good thermal conductivity, such as silicone rubber, fluorine rubber, or fluorosilicone rubber.
[0081]
The thickness of the elastic layer 2 is preferably from 10 to 500 μm. The elastic layer 2 has a thickness necessary to guarantee the quality of a fixed image.
[0082]
When a color image is printed, a solid image is formed over a large area on the recording material P, particularly 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, uneven heating will occur, and uneven gloss will occur in the image in portions where the amount of heat transfer is large and small. The glossiness is high in a portion having a large amount of heat transfer, and low in a portion having a small amount of heat transfer. If the thickness of the elastic layer 2 is 10 μm or less, the elastic layer 2 cannot follow the unevenness of the recording material or the toner layer, resulting in uneven image gloss. 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 thickness of the elastic layer 2 is preferably 50 to 500 μm.
[0083]
If the hardness of the elastic layer 2 is too high, the elastic layer 2 cannot follow the irregularities of the recording material or the toner layer, resulting in uneven image gloss. Therefore, the hardness of the elastic layer 2 is preferably 60 ° (JIS-A) or less, more preferably 45 ° (JIS-A) or less.
[0084]
Regarding the thermal conductivity λ of the elastic layer 2, λ = 6 × 10 ⁻⁴ to 2 × 10 ⁻³ [cal / cm · sec · deg. ] Is good.
[0085]
The thermal conductivity λ is 6 × 10 ⁻⁴ [cal / cm · sec · deg. ], The thermal resistance is large, and the temperature rise in the surface layer (release layer 3) of the fixing film becomes slow.
[0086]
Thermal conductivity λ is 2 × 10 ⁻³ [cal / cm · sec · deg. ], The hardness becomes too high or the compression set deteriorates.
[0087]
Therefore, the thermal conductivity λ is 6 × 10 ⁻⁴ to 2 × 10 ⁻³ [cal / cm · sec · deg. ] Is good. More preferably, 8 × 10 ^{−4 to} 1.5 × 10 ⁻³ [cal / cm · sec · deg. ] Is good.
[0088]
c. Release layer 3
The release layer 3 can be made of a material having good releasability and heat resistance, such as fluororesin, silicone resin, fluorosilicone rubber, fluororubber, silicone rubber, PFA, PTFE, and FEP.
[0089]
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 a portion having poor releasability is formed due to coating unevenness of the coating film and durability is insufficient. 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-based release layer, the hardness becomes too high, and the effect of the elastic layer 2 is lost.
[0090]
Further, as shown in FIG. 9, in the layer structure of the fixing film 10, a heat insulating layer 4 may be provided on the free surface side of the heat generating layer 1 (the side opposite to the elastic layer 2 side of the heat generating layer 1).
[0091]
As the heat insulating layer 4, a heat-resistant resin such as a fluororesin, a polyimide resin, a polyamide resin, a polyamideimide resin, a PEEK resin, a PES resin, a PPS resin, a PFA resin, a PTFE resin, and a FEP resin is preferable.
[0092]
Further, the thickness of the heat insulating layer 4 is preferably from 10 to 1000 μm. 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 the thickness exceeds 1000 μm, the distance between the heat generating layer 1 and the magnetic cores 17a, 17b, 17c and the exciting coil 18 increases, and the magnetic flux cannot be sufficiently absorbed by the heat generating layer 1.
[0093]
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 efficiency of heat supply to the recording material P is improved as compared with the case where the heat insulating layer 4 is not provided. Therefore, power consumption can be reduced.
[0094]
As described above, according to the present embodiment, a stable magnetic field can be generated by applying no stress to the coil core as the magnetic field generating means. Further, since no stress is applied, it is advantageous in durability.
[0095]
By using a metal or an alloy for the pressing force holding member, it becomes strong against bending, and a stable fixing nip can be formed.
[0096]
Further, by using a non-magnetic metal for the pressing force holding member, heat generation due to the magnetic field generated by the magnetic field generating means can be prevented, and the heat generation efficiency is improved.
[0097]
(Second embodiment)
In this example, as shown in FIG. 11, a thermo switch 40 as a temperature detecting element is provided at a position of the fixing film 10 opposite to the heat generating region H to cut off power supply to the exciting coil 18 at the time of runaway. I have. Further, the magnetic cores 17a, 17b, and 17c and the exciting coil 18 were disposed at a position rotated by about 90 ° upstream of the fixing nip. Thereby, the heat generation region H can be made closer to the fixing nip. Except for this, the configuration is the same as that of the first embodiment, and the same reference numerals are given to the same components and portions as those of the apparatus of FIG.
[0098]
FIG. 12 is a circuit diagram of the safety circuit used in this example. The thermo switch 40, which is a temperature detecting element, is connected in series with the +24 VDC power supply and the relay switch 41. When the thermo switch 40 is turned off, power supply to the relay switch 41 is cut off, the relay switch 41 operates, and the excitation circuit 27 When the power supply to the excitation coil 18 is cut off, the power supply to the excitation coil 18 is cut off. The thermoswitch 40 was set to an OFF temperature of 220 ° C.
[0099]
Further, the thermoswitch 40 is disposed in a non-contact manner on the outer surface of the fixing film 10 so as to face the heat generating area H of the fixing film 10. The distance between the thermoswitch 40 and the fixing film 10 was approximately 2 mm. Thereby, the fixing film 10 is not damaged by the contact of the thermoswitch 40, and the deterioration of the fixed image due to the durability can be prevented.
[0100]
According to this example, when the fixing device goes out of control due to a device failure, unlike the configuration in which heat is generated in the fixing nip N as shown in FIG. Even when the power supply is continued and the fixing film 10 continues to generate heat, the paper is not directly heated because no heat is generated in the fixing nip portion N where the paper is sandwiched. Further, since the thermoswitch 40 is disposed in the heat generation region H where the amount of generated heat is large, the thermoswitch 40 senses 220 ° C., and when the thermoswitch is turned off, the relay switch 41 switches to the exciting coil 18. Is cut off.
[0101]
According to this example, since the firing temperature of the paper was around 400 ° C., the heat generation of the fixing film could be stopped without firing the paper.
[0102]
In this example, a thermoswitch is used as the temperature detection element, but a temperature fuse may be used.
[0103]
As described above, according to the present embodiment, in addition to the effects of the above-described embodiment, a temperature detecting element such as a thermoswitch or a temperature fuse is provided as a safety device outside the rotating body in a heating region of the rotating body of electromagnetic induction heating. By arranging the temperature detecting element in a non-contact manner, the surface of the rotating body is not damaged, so that it is possible to safely cut off the power supply when the heating device runs away without deteriorating the fixed image.
[0104]
In the present invention,
1) The fixing film 10 with heat generated by electromagnetic induction may have a configuration in which the elastic layer 2 is omitted in the case of heat fixing such as a monochrome or one-pass multicolor image. The heat generating layer 1 may be formed by mixing a metal filler into a resin. The heating layer may be a single layer member.
[0105]
2) The device configuration of the fixing device 100 as a heating device is not limited to the pressure roller driving method of the embodiment.
[0106]
For example, as shown in FIG. 16, an endless belt-shaped fixing film 10 of electromagnetic induction heat is suspended and stretched between a film guide 16, a driving roller 31, and a tension roller 32. It is also possible to adopt a configuration in which the fixing unit 10 and the pressing roller 30 serving as a pressing member are pressed against each other with the fixing film 10 interposed therebetween to form a fixing nip portion N, and the fixing film 10 is rotationally driven by the driving roller 31. In this case, the pressure roller 30 is a driven rotation roller.
[0107]
3) The pressing member 30 is not limited to the roller body, but may be another type of member such as a rotating belt type.
[0108]
Further, in order to supply thermal energy to the recording material also from the pressing member 30 side, a heat generating means such as electromagnetic induction heating is provided on the pressing member 30 side so as to heat and control the temperature to a predetermined temperature. You can also.
[0109]
4) The heating device of the present invention is not limited to the image heating and fixing device of the embodiment, but an image heating device that heats a recording material bearing an image to improve surface properties such as gloss, an image heating device that is assumed to be worn, In addition, it can be widely used as a means / apparatus for heat-treating a material to be heated, such as a device for heating and drying a material to be heated, a heating laminating device, and the like.
[0110]
【The invention's effect】
As described above, according to the present invention, in the heating device of the electromagnetic induction heating type, a high pressurizing force is provided by disposing the pressurizing stay at a position where no stress is applied to the coil core as the magnetic field generating means. In addition, a stable fixing nip can be obtained, and a good fixed image can be obtained.
[0111]
In addition, by disposing a temperature detecting element, which is a safety element, in a non-contact manner in the heat generating area outside the fixing film, the fixing film is not damaged, so that the fixed image can be prevented from deteriorating and the apparatus can be prevented from deteriorating. Heating of the fixing film can be stopped safely during runaway.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus used in a first embodiment; FIG. 2 is a cross-sectional side view of a main part of a fixing device as a heating device; FIG. 3 is a front model of a main part of FIG. FIG. 4 is a front cross-sectional view of a main part of FIG. 2; FIG. 5 is a view showing a nip shape; FIG. 6 is a perspective view of a film guide member, an exciting coil, and a magnetic core; FIG. FIG. 8 is a diagram showing the relationship between heat generation values.
FIG. 9 is a schematic diagram of a layer structure of a fixing film having electromagnetic induction heat generation (part 2).
FIG. 10 is a graph showing the relationship between the depth of the heating layer and the electromagnetic wave intensity. FIG. 11 is a schematic cross-sectional view of the configuration according to the second embodiment. FIG. 12 is a safety circuit diagram according to the second embodiment. FIG. 14 is a schematic diagram of an example of a heating device (fixing device) of an electromagnetic induction heating system as a background art of the invention. FIG. 14 is a diagram showing a relationship between a magnetic flux and a heating value of a fixing film. FIG. 16 is a schematic view of another example of the configuration of the fixing device.
REFERENCE SIGNS LIST 1 heat generating layer 2 elastic layer 3 release layer 4 heat insulating layer 10 fixing film 16 film guides 17a to 17c magnetic core 18 exciting coil 22 pressurizing rigid stays 23a and 23b fixing / holding flange members 25a and 25b Pressure spring member 26 Temperature detection element (thermistor)
30 Pressure roller 40 as pressure member Temperature detecting element (thermo switch)
41 relay switch

Claims (5)

A magnetic field generating means, a rotating body that generates electromagnetic induction by the action of the magnetic field of the magnetic field generating means, and a resin support member fixed so as not to rotate inside the rotating body and loosely supporting the rotating body. A pressurizing member that forms the nip portion with the support member sandwiching the rotating body therebetween , and conveys the recording material between the rotary body and the pressurizing member of the nip portion and conveys the recording material. In an image heating device that heats an image on a recording material by body heat ,
Between the rotating body and said have a metal or alloy pressure holding member for holding the pressure from the through supporting member and the pressure member, the said magnetic field generating means and the support member and the pressure holding member An image heating device provided in a place other than the above. 2. The image heating apparatus according to claim 1, wherein said rotator is an endless film. 2. The image heating apparatus according to claim 1 , wherein a Young's modulus E of the pressing force holding member satisfies E ≧ 7 × 10 ¹⁰ . An apparatus according to claim 1 or 3, wherein the pressure holding member is made of a nonmagnetic metal or alloy. One of the image heating apparatus according to claim 1 to 4, characterized in that arranged the temperature sensing element in a non-contact from the outside of the rotating body to the heating zone of the rotating body.

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