JP2014092610A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive fixing device that has reduced warm-up time and has a simple configuration, and an image forming apparatus including the fixing device.SOLUTION: A fixing device includes: a fixing member 40 that runs in a predetermined direction to heat a toner image; a pressing member 60 that presses the fixing member to form a nip part N; a magnetic flux generating unit 50 that generates a magnetic flux; a heating member 20 that has a temperature-sensitive magnetic material, and heats the fixing member with heat generated by the magnetic flux; and a magnetic shielding member 21 that is provided inside the heating member. The magnetic shielding member has a temperature-sensitive distance adjustment member 22 attached thereto; and the temperature-sensitive distance adjustment member moves the magnetic shielding member in a direction to approach the heating member in association with an increase in temperature of the heating member, and moves the magnetic shielding member in a direction to separate from the heating member in association with a decrease in temperature of the heating member.

Description

  The present invention relates to a fixing device installed in an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine thereof, and an image forming apparatus including the fixing device, and more particularly to a fixing device and an image forming apparatus using an electromagnetic induction heating method. About.

  In recent years, an induction heating method has been widely adopted in a fixing device used in an electrophotographic image forming apparatus. Here, as one of the technical problems in the fixing device, there is an excessive temperature rise of the fixing device in a region outside the paper width during paper passing. Therefore, in the fixing device using the induction heating method, as a countermeasure for suppressing this excessive temperature rise, a magnetic shunt material is provided between the heating element and the magnetic shielding member, so that the shunt material exceeds the Curie temperature. In addition, there is already known a technique in which the magnetic flux generated from the excitation device is shielded inside the magnetic shunt material and suppresses excessive heating of the heating element.

  However, in the fixing device using the induction heating method provided with the conventional magnetic shunt material, when the temperature of the magnetic shunt material becomes close to the Curie temperature during the warm-up, the magnetic flux shielded inside the shunt material increases. As a result, the heating efficiency of the fixing device decreases. Therefore, there has been a problem that the warm-up time becomes long.

  On the other hand, there is also known a fixing device in which the configuration inside the fixing device can be switched between warm-up and paper-feeding by a drive system and control (for example, Patent Document 1). In the fixing device described in Patent Document 1, in the induction heating type fixing device provided with a magnetic shunt material, the position of the magnetic shielding member inside (inside) the fixing device can be changed between warm-up and paper feeding. Therefore, at the time of warm-up, the distance between the magnetic shunt material and the magnetic shielding member can be increased, the magnetic flux shielded inside the magnetic shunt material can be reduced, and the warm-up time can be shortened. Further, when the paper is passed, the distance between the magnetic shunt material and the magnetic shield member is shortened by moving the magnetic shield member, the magnetic flux is shielded inside the magnetic shunt material, and the excessive heating of the heating element can be suppressed.

  However, in the fixing device described in Patent Document 1, a complicated drive system is required to move the magnetic shielding member. In addition, complicated control is required to change the position of the magnetic shielding member between warm-up and paper feeding. This increases the cost of the fixing device.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an inexpensive fixing device having a simple configuration with a shortened warm-up time and an image forming apparatus including the fixing device.

In order to solve the above-described problem, a fixing device according to a first aspect of the present invention includes:
A fixing member that travels in a predetermined direction and heats the toner image;
A pressing member that presses the fixing member to form a nip portion;
A magnetic flux generator for generating magnetic flux;
A heating member having a temperature-sensitive magnetic material and heating the fixing member with heat generated by magnetic flux;
In a fixing device comprising a magnetic shielding member provided inside the heating member,
A temperature sensitive distance adjusting member is attached to the magnetic shielding member,
The temperature sensitive distance adjusting member moves the magnetic shielding member in a direction approaching the heating member as the temperature of the heating member rises, and the heating unit adjusts the magnetic shielding member as the temperature of the heating member decreases. It moves to the direction away from a member, It is characterized by the above-mentioned.

  According to the present invention, it is possible to provide an inexpensive fixing device having a simple configuration with a shortened warm-up time and an image forming apparatus including the fixing device.

1 is a configuration diagram schematically showing an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing a fixing device of the image forming apparatus shown in FIG. 1. FIG. 2 is a cross-sectional view schematically showing a cross section in a longitudinal direction of a heating roller of the image forming apparatus shown in FIG. 1. FIG. 2 is a cross-sectional view schematically showing a cross section of a fixing belt of the image forming apparatus shown in FIG. 1. FIG. 2 is a perspective view schematically showing a part of an induction heating coil of the image forming apparatus shown in FIG. 1. FIG. 6A is an explanatory diagram for explaining magnetic flux generated in the fixing device of the image forming apparatus shown in FIG. 1, FIG. 6A is an explanatory diagram for explaining the flow of magnetic flux during warm-up, and FIG. It is explanatory drawing explaining the flow of the magnetic flux in the case of paper passing. FIG. 2 is an explanatory diagram for explaining a temperature change of a fixing belt when the image forming apparatus illustrated in FIG. 1 is warmed up. FIG. 2 is an explanatory diagram for explaining a temperature change of a fixing belt when a sheet is passed through the image forming apparatus illustrated in FIG. 1. FIG. 9 is a cross-sectional view schematically showing a part of a fixing device of an image forming apparatus according to a second embodiment of the present invention, and FIG. 9A is a cross-sectional view showing a part of the fixing device during warm-up. FIG. 9B is a cross-sectional view showing a part of the fixing device during paper feeding. FIG. 6 is a cross-sectional view schematically illustrating a part of a fixing device of an image forming apparatus according to a third embodiment of the present invention.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing a schematic configuration of a color copying machine which is an example of an electrophotographic image forming apparatus including a fixing device according to the present invention. The mechanism of the entire image forming apparatus of this color copying machine is basically the same as the conventional one, and a predetermined apparatus necessary for forming an image around the photosensitive member, such as a charging device, an exposure device, a developing device, etc. And an image information reading device for a document and a paper feeding unit. Since it is a well-known configuration and operation, only a brief description will be given below, but the contents are also included as long as it is recognized that the configuration and operation are well-known in terms of not being described.

  A color copying machine (hereinafter simply referred to as a copying machine) 1 forms a tandem image forming unit by arranging four image forming units of yellow, cyan, magenta, and black side by side at the center of the apparatus main body. In the tandem image forming unit, image forming means as individual toner image forming means are arranged. In each of the image forming means, drum-shaped photoconductors 111Y, 111M, 111C, and 111BK as latent image carriers (hereinafter, Y, M, C, and yellow indicating yellow, cyan, magenta, and black are shown for simplification of display). A charging device 112, a developing device 113, a photosensitive member cleaning device 115, and the like are provided around (BK is omitted).

  An optical writing unit 102 as a latent image forming unit is provided below the tandem image forming unit. The optical writing unit 102 irradiates the surface of each photoconductor 111 with laser light based on image data from the document reading unit 104 at the top of the copier to form an electrostatic latent image for each color. The document reading unit 104 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like. The document reading unit 104 irradiates the document D arranged on the contact glass 105, converts image data into an electrical signal, and performs optical writing. Transmit to unit 102.

  An intermediate transfer belt 117 having an endless belt shape is provided as an intermediate transfer member immediately above the tandem image forming unit. The intermediate transfer belt 117 is wound around a plurality of support rollers, and a drive motor (not shown) serving as a drive source is disposed on a rotation shaft of a drive roller (for example, a transfer roller disposed in the secondary transfer unit) among the support rollers. Are connected. A belt cleaning device 116 is provided upstream of the tandem image forming unit of the intermediate transfer belt 117. When the drive motor is driven, the intermediate transfer belt 117 rotates counterclockwise in the figure and the followable support roller rotates. A primary transfer device (not shown) for transferring the toner image formed on the photoreceptor 111 onto the intermediate transfer belt 117 is provided inside the intermediate transfer belt 117.

  A secondary transfer roller 106 as a secondary transfer device is provided downstream of the primary transfer device in the driving direction of the intermediate transfer belt 117. A transfer support roller 118 is disposed on the opposite side of the secondary transfer roller 106 and the intermediate transfer belt 117, and functions as a pressing member.

  Further, the copying machine 1 includes a paper feeding cassette 107, a paper feeding roller 108, a registration roller (positioning roller), and the like at the lower part thereof. Further, a fixing device 10 for fixing an image on the recording medium P and a paper discharge roller 109 are provided downstream of the secondary transfer roller 106 in the traveling direction of the recording medium P to which the toner image is transferred by the secondary transfer roller 106. ing.

  Next, the operation of the copying machine will be described. The photosensitive member 111 is rotated by individual image forming means, and the surface of the photosensitive member 111 is uniformly charged by the charging device 112 as the photosensitive member rotates. Next, an electrostatic latent image is formed on the photoreceptor 111 by irradiating the writing light from the optical writing unit 102. Thereafter, toner is attached by the developing device 113 to make the electrostatic latent image visible, and a single color image of yellow, magenta, cyan, and black is formed on each photosensitive drum 111, respectively. Further, the driving roller is rotated by a driving motor (not shown), the other supporting rollers are driven to rotate, the intermediate transfer belt 117 is rotated and conveyed, and the visible image is transferred onto the intermediate transfer belt 117 by the primary transfer device. Transfer sequentially. As a result, a composite color image is formed on the intermediate transfer belt 117. Further, the surface of the photoconductor 111 after image transfer is cleaned by removing residual toner by the photoconductor cleaning device 115 to prepare for the image formation again.

  In accordance with the image formation timing, the leading edge of the recording medium P is fed from the paper feed cassette 107 by the paper feed roller 108, conveyed to the registration rollers, and temporarily stops. Then, the sheet is conveyed between the transfer support roller (secondary transfer counter roller) 118 and the intermediate transfer belt 117 while taking timing with the image forming operation. Here, the intermediate transfer belt 117 and the transfer support roller 118 form a so-called secondary transfer nip across the recording medium P, and the secondary transfer roller 106 transfers the toner image on the intermediate transfer belt 117 onto the recording medium P. Secondary transfer. After the secondary transfer, the recording medium P is separated from the intermediate transfer belt 117 and the transfer support roller 118 by a separating member (not shown), and then discharged to the outside through the paper discharge roller 109. On the other hand, the intermediate transfer belt 117 after image transfer is removed by the belt cleaning device 116 to remove residual toner remaining on the intermediate transfer belt 117 after image transfer, and is prepared for re-image formation by the tandem image forming unit.

  Next, the configuration of the fixing device 10 will be described below with reference to FIG.

  The fixing device 10 includes a heating roller (supporting roller) 20 as a heating member that also serves as a heating element by including a heat generating layer, an aluminum member 21 as a magnetic shielding member, and an expansion member as a temperature sensitive distance adjusting member. A silicone rubber 22, a core metal 23 as an expanding portion supporting member, a fixing roller 30, a fixing belt 40 as a fixing member spanned between the heating roller 20 and the fixing roller 30, and a fixing belt 40 on the heating roller 20. And a pressure roller (pressing member) 60 that contacts the fixing roller 30 via the fixing belt 40 to form a nip portion N.

  The heating roller 20 uses a magnetic shunt alloy of a temperature-sensitive magnetic material having a cylindrical shape and a Curie temperature of about 160 to 220 ° C. At this time, the magnetic shunt alloy is used as a heat generating layer. In addition, you may form Cu about 3-15 micrometers in thickness as a heat generating layer in the magnetic shunt alloy surface layer. By forming Cu on the surface of the magnetic shunt alloy, the heat generation efficiency of the heat generation layer can be further increased. Furthermore, it is also suitable to apply Ni plating to the Cu surface layer for the purpose of rust prevention.

  Inside the heating roller 20, two semi-cylindrical (arch-shaped) two aluminum members 21 are arranged so as to face each other. Further, the central axis of the heating roller 20 and the central axes of the two aluminum members 21 are arranged so as to coincide with each other. The thickness of the aluminum member 21 is desirably about 0.6 to 2.0 mm.

  In addition, a silicone rubber 22 is provided inside the aluminum member 21, and a cored bar 23 is provided inside thereof. The silicone rubber 22 has a thickness of 5 to 10 mm, and the core metal 23 is preferably made of a metal such as carbon steel and has a cylindrical shape with a diameter of about 5 to 10 mm.

  Further, as shown in FIG. 6A, the semi-cylindrical aluminum member 21 is an aggregate of aluminum member pieces 21a divided into a plurality in the longitudinal direction of the aluminum member 21 and in a direction perpendicular to the longitudinal direction. Yes. Therefore, when the silicone rubber 22 having a larger linear expansion coefficient than aluminum expands due to heat, the aluminum member 21 is dispersed in units of the aluminum member pieces 21a as shown in FIG. 6B. As a result, the aluminum member 21 attached to the silicone rubber 22 does not drop off or the base material of the aluminum member 21 is not destroyed. Moreover, each aluminum member piece 21a is temporarily fixed, for example with an adhesive agent etc., and the one aluminum member 21 is formed. Therefore, workability when attaching the aluminum member 21 to the silicone rubber 22 is improved. Needless to say, the method of temporarily fixing the aluminum member pieces 21a is not limited to the adhesive.

  The silicone rubber 22 may be another expanded body, and preferably has heat resistance and a high coefficient of thermal expansion. Further, instead of the silicone rubber 22, foamed rubber may be used. By using foam rubber, a larger amount of thermal expansion is expected. In addition, since the foamed rubber can have a smaller heat capacity depending on the expansion ratio, it can be expected to exhibit a greater effect for shortening the warm-up time of the fixing device 10 and reducing the power consumption.

Since the silicone rubber 22 has a thermal expansion coefficient of about 5 × 10 ⁻⁴ [/ ° C.], for example, when the temperature rises by about 100 ° C. during paper feeding, the silicone rubber 22 expands by about 0.3 to 0.5 mm. Accordingly, the distance between the heating roller 20 and the aluminum member 21 can be shortened. Furthermore, by providing the cored bar 23 inside the silicone rubber 22, expansion of the silicone rubber 22 toward the cored bar 23 (inside the silicone rubber) is suppressed. Therefore, the distance between the heating roller 20 and the aluminum member 21 can be shortened by about 0.6 to 1.0 mm.

  In this embodiment, the cored bar 23 is employed to promote the expansion of the silicone rubber 22 in one direction. However, the present invention is not limited to this mode, and a fixing member such as a stop spring is provided to support the silicone rubber 22. May be provided. Further, the distance between the heating roller 20 and the aluminum member 21 may be adjusted only by the expansion of the aluminum member 21 without providing the silicone rubber 22 and the cored bar 23.

  Next, the heating roller 20 and the inner members 21 to 25 of the heating roller 20 will be described below with reference to FIG. The heating roller 20 and the aluminum member 21 are supported by a flange member 24 which is a support member made of a heat resistant resin. The aluminum member 21 is provided with a square C-shaped depression (gap) 24 a in the flange member 24 so that the aluminum member 21 can move in a direction approaching the heating roller 20. Further, since both the aluminum member 21 and the silicone rubber 22 are not fixed to the flange member 24, the aluminum member 21 and the silicone rubber 22 can freely move in the direction approaching the heating roller 20 (the outer peripheral direction of the aluminum member 21). Therefore, when the heating roller 20 is heated, the aluminum member 21 and the silicone rubber 22 are thermally expanded, and the aluminum member 21 moves in a direction approaching the heating roller 20. As a result, the distance between the aluminum member 21 and the heating roller 20 can be shortened. When the heating of the heating roller 20 is finished, the aluminum member 21 and the silicone rubber 22 contract and the aluminum member 21 can move in a direction away from the heating roller 20.

  The flange member 24 is fixed to the metal core 23 by a metal bearing 25, and the inner members 21 to 25 are configured to be driven integrally with the heating roller 20. Therefore, it becomes an easy design with a very simple configuration.

  The distance between the heating roller 20 and the aluminum member 21 is desirably 1.0 to 3.0 mm at room temperature. This is a design in which the distance between the heating roller and the aluminum member of the fixing device by the conventional induction heating is larger.

  As shown in FIG. 2, the fixing roller 30 is an elastic member in which a metal cored bar 32 such as stainless steel or carbon steel and a heat-resistant silicone rubber covering the cored bar 32 are solid or foamed. 33. The pressure roller 60 presses the fixing roller 30 through the fixing belt 40 to form a contact portion (fixing nip portion N) having a predetermined width. The outer diameter of the fixing roller 30 is about 30 to 40 mm, the thickness of the elastic member 33 is about 3 to 10 mm, and the hardness of the elastic member 33 is about 10 to 50 ° (JIS-A).

  As shown in FIG. 4, the fixing belt 40 has an elastic layer 42 and a release layer 43 laminated on a base material 41. The substrate 41 has characteristics such as mechanical strength when the fixing belt 40 is stretched between the heating roller 20 and the fixing roller 30, flexibility, and heat resistance that can withstand use at a fixing temperature. In the present embodiment, an insulating heat-resistant resin material, polyimide, polyimide amide, PEEK, PES, PPS, fluorine resin, or the like is suitable for the base material 41 for inductively heating the heating roller 20. In addition, the thickness of the base material 41 is desirably 30 to 200 μm from the relationship between heat capacity and strength.

  The elastic layer 42 is formed for the purpose of giving flexibility to the surface of the fixing belt in order to obtain a uniform image without uneven glossiness, the rubber hardness is 5 to 50 ° (JIS-A), and the thickness is 50 to 500 μm. Is desirable. In order to satisfy heat resistance at the fixing temperature, silicone rubber, fluorosilicone rubber or the like is used as the material.

  The release layer 43 is made of tetrafluoroethylene resin (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin (PFA), and tetrafluoroethylene / hexafluoropropylene copolymer (FEP). Or the like, or a mixture of these resins or a heat-resistant resin in which these fluorine resins are dispersed.

  Here, when the release layer 43 made of the above-described material covers the elastic layer 42, it is possible to improve the release property of the toner and to prevent the paper dust from sticking without using silicone oil or the like, and so-called oil-less can be achieved. . However, since these resins having releasability generally do not have elasticity like rubber materials, if the release layer 43 is formed thick on the elastic layer, the flexibility of the surface of the fixing belt is impaired and gloss unevenness is generated. . Therefore, in order to achieve both releasability and flexibility, the film thickness of the release layer 43 is 5 to 50 μm, preferably 10 to 30 μm.

  If necessary, a primer layer may be provided between the respective layers, and a layer for improving durability during sliding may be provided on the inner peripheral surface of the base material 41. It is also preferable to provide the base material 41 with a heat generating layer. For example, it is possible to form a Cu layer of 3 to 15 μm on a base material made of polyimide or the like and use it as a heat generating layer.

  As shown in FIG. 2, the induction heating coil 50 includes a case 55, a coil 51, and magnetic cores 52, 53, and 54. The arch core 52 is arranged so that the coil 51 is sandwiched between the arch core 52 and the pressure roller 60 so as to surround substantially half of the outer peripheral surface of the heating roller opposite to the fixing roller 30. The side core 54 extends from the circumferential end of the arch core 52 toward the heating roller 20. The center core 53 extends from the center in the circumferential direction of the arch core 52 toward the heating roller 20.

  The magnetic cores 52, 53, and 54 form a magnetic path that concentrates the magnetic flux generated from the coil 51 on the heating roller 20. A plurality of arch cores 52 are installed in the longitudinal direction of the heating roller 20 at appropriate intervals so that the temperature distribution in the longitudinal direction of the heating roller 20 is uniform. The magnetic cores 52, 53, and 54 are preferably soft magnetic materials having a small coercive force and a large magnetic permeability and a high electrical resistivity. As the material of the magnetic cores 52, 53, 54, Mn—Zn ferrite, Ni—Zn ferrite, or the like is used. In addition to ferrite, materials such as permalloy may be used.

  The coil 51 is formed by twisting about 90 lead wires having an insulation coating of about 0.15 m to form a litz wire and winding the litz wire five times. The litz wire is provided with a fusion layer on the surface thereof, and the fusion layer is solidified by heating in an electric heating or thermostatic bath, and the shape of the wound coil 51 can be maintained. In addition, a litz wire can be given a shape by press-molding a wound coil 51 by using a litz wire that does not have a fusion layer on its surface. Further, since the litz wire requires heat resistance equal to or higher than the fixing temperature, a resin having both heat resistance and insulation properties, such as polyamideimide and polyimide, is used for the insulation coating material of the strand. In addition, the coil 51 is not limited to this aspect, About 50-500 conducting wires with an insulation coating are twisted about 50 to 500 to form a litz wire. It may be wound 15 times.

  The wound coil 51 is adhered to the case 55 using a silicone adhesive or the like. Since the case 55 requires heat resistance equal to or higher than the fixing temperature, PET, liquid crystal polymer, or the like, which is a resin having high heat resistance, is used.

  Next, the configuration of the induction heating coil 50 of the present embodiment will be described in more detail below with reference to FIG. The coil 51 is formed by bundling 90 insulated copper wires having an outer diameter of 0.15 mm to form a wire bundle, and circulating the wire bundle. And it arrange | positions over the whole surface of the convex side of case 55 shape | molded so that the heating roller 20 which is a heat generating member may be covered. The coil 51 is formed in a spiral shape around the center core 53 as an axis, and is formed along the outer peripheral surface of the heating roller 20.

  As shown in FIG. 2, the pressure roller 60 includes a release layer 61, an elastic layer 62 with high heat resistance, and a cored bar 63 made of a metal cylindrical member. Then, the fixing roller 30 is pressed via the fixing belt 40 to form a fixing nip portion N. The outer diameter of the pressure roller 60 is about 30 to 40 mm.

  The elastic layer 62 has a thickness of about 0.3 to 5 mm and a hardness of about 20 to 50 ° (Asker hardness). The elastic layer 62 is made of silicone rubber because it requires heat resistance. Furthermore, in order to improve the releasability at the time of double-sided printing, a release layer 61 made of a fluororesin is formed on the elastic layer by about 10 to 100 μm.

  By making the pressure roller 60 harder than the fixing roller 30, the pressure roller 60 bites into the fixing roller 30 (and the fixing belt 40). Therefore, the recording paper (recording medium) P has a curvature that cannot be along the surface of the fixing belt 40 at the exit of the nip portion due to this biting shape, and the releasability of the recording paper P can be improved.

  Next, the operation of the fixing device of this embodiment will be described. The temperature of the inner members 21 and 22 during continuous paper passing is about 100 to 120 ° C., and the temperature of the inner members 21 and 22 during warm-up is about 25 to 50 ° C. The fixing belt 40 rotates in the arrow R direction as shown in FIG. The heating roller 20 is heated by the induction heating coil 50.

  Specifically, by flowing a high-frequency alternating current of 10 kHz to 1 MHz to the induction heating coil 50, the direction of the magnetic field lines is alternately switched in both directions in the loop of the induction heating coil 50, and an alternating magnetic field is formed. The alternating magnetic field generates an eddy current in the heating roller 20 to generate Joule heat, and the heating roller 20 is induction-heated.

  Then, the fixing belt 40 is heated by the heat generated from the heating roller 20, and the conveyed recording paper P and the fixing belt 40 come into contact with each other at the nip portion N to heat and melt the toner image T on the recording paper.

  In the present embodiment, the inner members 21 and 22 of the heating roller 20 thermally expand according to the temperature and change their shapes. And the variation | change_quantity is about 0.6-1.0 mm per 100 degreeC temperature rise as mentioned above. And the distance between the heating roller 20 and the aluminum member 21 becomes short, so that the temperature of the inner members 21 and 22 is high.

  Here, the distance between the heating roller 20 and the aluminum member 21 during continuous paper feeding of the fixing device 10 is approximately the same as that of the conventional fixing device by induction heating using a magnetic shunt alloy, 0.4-2. About 0 mm. As a result, the inner members 21 and 22 are not in thermal expansion when the fixing device 10 is warmed up compared to when the paper is passed, and the distance between the heating roller 20 and the aluminum member 21 is 0. It becomes about 6-1.0 mm wide and becomes about 1.0-3.0 mm.

  That is, when warming up, the heating roller 20 and the aluminum member 21 are separated from each other as compared with the conventional fixing device. For this reason, the warm-up time of the fixing device 10 is shortened. Specifically, when warming up, as shown in FIG. 6A, the distance between the heating roller 20 and the aluminum member 21 is sufficiently large. Therefore, until the magnetic shunt alloy of the heating roller 20 reaches near the Curie temperature, most of the magnetic flux A generated by the induction heating coil 50 does not pass through the inside of the heating roller 20, and most of the input power is consumed by the heating roller 20. Is done. Further, since the distance between the heating roller 20 and the aluminum member 21 is sufficiently large, there is an effect that heat is not easily transmitted to the aluminum member 21, and further shortening of the warm-up time is expected.

  On the other hand, in the case of continuous paper passing, as shown in FIG. 6B, the magnetic flux B passes through the magnetic shunt alloy of the heating roller 20 in the portion where the excessive temperature rise has occurred in the non-sheet passing portion, and the heating roller 20 Is shielded by the aluminum member 21 inside. For this reason, it is possible to suppress overheating of the fixing device to the same extent as before.

  Next, the temperature change during the warm-up of the fixing belt surface and the paper passing in the present embodiment will be described below with reference to FIGS.

  First, the temperature change on the surface of the fixing belt during warm-up will be described. As shown in FIG. 7, the set fixing temperature on the surface of the fixing belt of the fixing device 10 is 170 ° C., and the Curie temperature of the magnetic shunt alloy is 200 ° C. Here, what is indicated by (a) in FIG. 7 shows the temperature change of the surface of the fixing belt of the conventional fixing device using the magnetic shunt alloy. As for the temperature of the fixing belt surface of the conventional fixing device, the temperature increasing rate becomes slow (the temperature increasing becomes gentle) as it approaches the fixing set temperature, and the warm-up time is 30 seconds. This is considered to be because the heating efficiency decreases as described above as the belt surface temperature approaches the Curie temperature.

  Also, what is shown in FIG. 7B is a temperature change on the surface of the fixing belt of the fixing device 10 according to the present embodiment. The temperature of the fixing belt surface of the fixing device 10 according to the present embodiment does not slow down even near the fixing set temperature (the change in temperature rising speed is small), and the warm-up time is 5 seconds shorter than (a). It was 25 seconds. Therefore, the temperature of the surface layer of the fixing belt 40 of the present embodiment is quickly raised as compared with the conventional one, and the start-up characteristics of the fixing device 10 are very good. The rising characteristic means a warm-up time until the fixing belt 40 reaches a temperature necessary for fixing the toner image T. The shorter the warm-up time, the easier it is for the user to use the image forming apparatus. As the warm-up time is shortened, the image forming apparatus 1 of the present embodiment is also expected to reduce power consumption.

  On the other hand, the temperature change of the non-sheet passing portion on the surface of the fixing belt during the sheet passing will be described below with reference to FIG. 8A shows the temperature change of the non-sheet passing portion of the fixing belt surface in the conventional fixing device using the magnetic shunt alloy, and is shown in FIG. 8B. The figure shows the temperature change of the non-sheet passing portion on the surface of the fixing belt in the fixing device 10 of this embodiment. The temperature change of the non-sheet passing portion on the surface of the fixing belt according to the present embodiment reduces the effect of shielding the magnetic flux of the magnetic shunt alloy by the configuration of the fixing device 10. Therefore, (b) has a faster temperature increase rate than (a). Furthermore, (b) increases the effect of the magnetic shunt alloy shielding magnetic flux as the inner member expands after a certain amount of time has passed since the paper was passed. Therefore, in (b), the temperature rise stops at 200 ° C., which is the Curie temperature, as in (a). Therefore, the fixing device 10 according to the present embodiment can also have a function of suppressing the excessive temperature rise of the fixing device as much as or more than the conventional fixing device using the magnetic shunt alloy.

  Next, the operation of the image forming apparatus 1 according to this embodiment will be described. A temperature sensitive distance adjusting member is provided that changes the distance between the heating roller 20 and the aluminum member 21 without using a drive system as the temperature of the heating roller 20 rises. Then, during warm-up when the temperature inside the heating roller is low, the distance between the heating roller 20 and the aluminum member 21 can be adjusted and lengthened as compared with the conventional fixing device. Therefore, the effect of the aluminum member 21 shielding the magnetic flux during the warm-up is reduced, the heating roller 20 can be heated more efficiently, and the warm-up time can be shortened.

  On the other hand, when the paper is passed, the temperature sensitive distance adjusting member can adjust the distance between the heating roller 20 and the aluminum member 21 to be shorter than the conventional fixing device as the temperature inside the heating roller rises. Therefore, the effect that the aluminum member 21 shields the magnetic flux increases, and the excessive temperature rise of the heating roller 20 can be suppressed. In addition, since the drive system is not used in the present invention, complicated control is not required, and cost can be reduced with a simple configuration as compared with the conventional invention.

  Further, by providing the flange member 24 with the gap 24a, the distance between the heating roller 20 and the aluminum member 21 can be easily adjusted. Therefore, it is possible to efficiently suppress the excessive temperature rise of the heating roller 20 when the paper is passed, and it is possible to efficiently heat the heating roller 20 when warming up.

  Further, by providing the expansion member, the amount of thermal expansion of the expansion member is small during warm-up when the temperature of the heating roller 20 is lower than the fixing target temperature, and the heating roller 20 and the aluminum member 21 are smaller than those of the conventional fixing device. Can be extended. Therefore, the effect of shielding the magnetic flux of the aluminum member 21 is reduced, and the heating roller 20 can be heated more efficiently. As a result, the warm-up time can be shortened.

  On the other hand, when the temperature of the heating roller 20 passes through the vicinity of the fixing target temperature, the amount of thermal expansion of the expansion member is large, and between the heating roller 20 and the aluminum member 21 is equal to or higher than that of the conventional fixing device. Distance can be shortened. Therefore, the effect of shielding the magnetic flux of the aluminum member 21 is increased, and the excessive temperature rise of the heating roller 20 can be suppressed.

  When the expansion member is the silicone rubber 22, thermal expansion and contraction are facilitated. Therefore, during the warm-up, the amount of expansion of the silicone rubber 22 due to heat is small, and the heating roller 20 and the aluminum member 21 are separated from the conventional fixing device, and the effect of shielding the magnetic flux of the aluminum member 21 is reduced. Thus, the heating roller 20 can be heated more efficiently. As a result, the warm-up time can be shortened.

  On the other hand, when the paper is passed, the amount of expansion of the silicone rubber 22 due to heat is large, and the heating roller 20 and the aluminum member 21 are closer to each other than the conventional fixing device, so that the excessive temperature rise of the heating roller 20 can be efficiently suppressed. . Moreover, since the silicone rubber 22 has physical properties with good heat resistance, durability of the fixing device is improved.

  Moreover, by having the metal core 23 inside the expansion member, the thermal expansion in the direction perpendicular to the axial line of the silicone rubber 22 expands in the direction in which the outer periphery of the silicone rubber 22 spreads (on the heating roller 20 side). Therefore, during the warm-up, the amount of expansion due to heat is small, and the heating roller 20 and the aluminum member 21 are separated from the conventional fixing device, and the effect of the aluminum member 21 shielding the magnetic flux is reduced. Can be heated more efficiently. As a result, the warm-up time can be further shortened.

  On the other hand, when passing paper, the amount of expansion due to heat is large compared to the case where the metal core 23 is not provided inside the silicone rubber 22, and the excessive temperature rise of the heating roller 20 can be more efficiently suppressed. .

  Further, by mounting the fixing device as described above on the image forming apparatus, an inexpensive image forming apparatus with a simple configuration with a shortened warm-up time can be obtained.

  Next, a second embodiment of the present invention will be described below with reference to FIG. In addition, about the structure equivalent to 1st Embodiment mentioned above, a corresponding code | symbol is attached | subjected and detailed description is abbreviate | omitted.

  This embodiment uses a different configuration for the member inside the heating roller 20 compared to the first embodiment described above. Specifically, a shape memory alloy (shape memory member) 226 is used instead of the silicone rubber 22 as the temperature sensitive distance adjusting member.

  The shape memory alloy 226 is an alloy such as NiTi, and is a material that maintains a certain shape when a certain shape memory temperature Tr is reached. In the present embodiment, the Tr of the shape memory alloy 226 is desirably about 100 to 120 ° C.

  In this embodiment, the shape memory alloy 226 is fixed to the aluminum member 21 and the cored bar 23 at room temperature, which is equal to or lower than Tr, as shown in FIG. 8a. A linear shape is formed by the drag from the aluminum member 21 and the cored bar 23. At this time, it is desirable to provide a spring or the like (not shown) between the aluminum member 21 and the shape memory alloy 226 so that the drag is applied so that the shape memory alloy 226 is linear. Further, similarly to the first embodiment, the aluminum member 21 is provided with a gap (not shown) so that it can move in a direction approaching the heating roller 20.

  Here, when continuous paper passing is performed and the temperature of the shape memory alloy 226 exceeds Tr, the shape memory alloy 226 is deformed into a shape memorized as shown in FIG. 8b. As a result, the aluminum member 21 connected to the shape memory alloy 226 approaches the heating roller 20. Therefore, as in the first embodiment, the distance between the heating roller 20 and the aluminum member 21 is large as shown in FIG. 8a when warming up, and both of them as shown in FIG. 8b when passing paper. It can be set as the structure where the distance between approaches. Therefore, also in the present embodiment, it is possible to reduce the warm-up time of the fixing device 10 while having the performance of suppressing the excessive temperature rise during the sheet passing more than before. That is, by providing the shape memory member instead of the silicone rubber, the same effects as when the silicone rubber is provided can be exhibited.

  Next, a third embodiment of the present invention will be described below with reference to FIG. In addition, about the structure equivalent to 1st Embodiment mentioned above, a corresponding code | symbol is attached | subjected and detailed description is abbreviate | omitted.

  The fixing device 310 of the image forming apparatus according to the present embodiment is different from the other embodiments in that roller fixing is used instead of belt fixing. Other configurations are the same as those in the first embodiment.

  First, the configuration of roller fixing will be described below with reference to FIG. The fixing device 310 includes an induction heating coil 50, a fixing roller 380 as a heat generating member / fixing member, a pressure roller 60, and the like. Here, the fixing roller 380 as a fixing member has an outer diameter of about 30 to 40 mm, and an elastic layer 382, a heat generating layer 383, a release layer (not shown), and the like are laminated on the cored bar 381. It is configured. The fixing roller 380 rotates in the direction of the arrow R in FIG. 9, is heated by induction heating, and heats and melts the toner image T on the conveyed recording paper.

  The release layer is formed on the outermost layer of the fixing roller 380. The release layer is made of fluorine resin such as tetrafluoroethylene resin (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), etc. , A mixture of these resins, or a dispersion of these resins in a heat resistant resin. The release layer has a thickness of 5 to 50 μm, preferably 10 to 30 μm. Thereby, the toner releasability on the fixing roller 380 is ensured, and the flexibility of the fixing roller 380 is ensured.

  The heat generating layer 383 uses a magnetic shunt alloy having a Curie temperature of about 160 to 220 ° C. At this time, you may form Cu about 3-15 micrometers in thickness. By forming Cu, the heat generation efficiency of the heat generating layer 383 can be further increased. In this case, it is also suitable to apply Ni plating to the Cu surface layer for the purpose of rust prevention.

  For the elastic layer 382, an elastic body such as fluorine rubber, silicone rubber, or fluorosilicone rubber can be used. By providing the fixing roller 380 with the elastic layer 382, the width of the nip region can be increased by allowing the fixing roller 380 to bend. Further, the roller hardness can be made smaller than that of the pressure roller 60 to improve the paper discharge performance and the recording material separation performance. Further, the elastic layer 382 is made of sponge rubber so that the heat generated by the heat generating layer 383 can be insulated and acts to quickly heat the elastic layer 382 or the release layer on the surface side of the fixing roller. Therefore, the surface of the fixing roller quickly reaches the temperature required for fixing, and even if the recording paper P is deprived of heat, the supply of heat can catch up. As a result, a good nip region can be formed, and heat generation of the heat generation layer can be insulated and heat transfer to the inside of the fixing roller can be suppressed.

  In the present embodiment, foamed silicone rubber having a thickness of 9 mm is used for the elastic layer 382. Therefore, the heat of the heat generating layer 383 arranged on the surface layer of the fixing roller 380 does not easily flow into the fixing roller, and efficient heating can be performed.

  The core metal layer 381 is made of aluminum in this embodiment. The aluminum cored bar layer 381 had an outer diameter of 22 mm and a thickness of 2.0 mm. The cored bar layer 381 is set to 2.0 mm because it needs to have rigidity capable of withstanding the load applied to the fixing roller 380 in order to form the nip region. The cored bar layer 381 is not limited to this mode, and may be a material having rigidity capable of withstanding a load applied to the fixing roller 380 for forming the nip region, and may be a metal such as iron. In addition, a material that does not affect induction heating can be used by forming the cored bar layer 381 from a nonmagnetic and insulating material such as ceramic.

  As shown in FIG. 9, the inner member of the fixing roller 380 has an aluminum member 21, and a silicone rubber 22 and a core metal 23 are provided on the inner side. Therefore, at the time of warm-up, the aluminum member 21 and the heat generating layer 381 of the fixing roller 380 are separated from the conventional fixing device, and the effect of the aluminum member 21 shielding the magnetic flux is reduced, and the heat generating layer 383 of the fixing roller 380 is reduced. Can be heated more efficiently. As a result, the warm-up time can be shortened. Even if the fixing method is roller fixing instead of belt fixing, it can be efficiently fixed with a simple configuration.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this.

  It should be noted that the materials and dimensions of each component introduced in the above-described embodiment are merely examples, and it is needless to say that various materials and dimensions can be selected within a range where the effects of the present invention can be exhibited.

1 Copying machine (an example of an image forming device)
DESCRIPTION OF SYMBOLS 10 Fixing device 20 Heating roller 21a Aluminum member piece 21 Aluminum member (an example of a magnetic shielding member)
22 Silicone rubber (example of temperature sensitive distance adjusting member, example of expansion member)
23 Core (an example of an inflatable part support member)
24 Flange member (an example of a support member)
24a hollow (gap)
25 Bearing 30 Fixing roller 32 Core metal 33 Elastic member 40 Fixing belt (an example of a fixing member)
41 Substrate 42 Elastic layer 43 Release layer 50 Induction heating coil (an example of a magnetic flux generator)
51 Coil 52 Arch core 53 Center core 54 Side core 55 Case 60 Pressure roller (an example of a pressing member)
61 Release layer 62 Heat-resistant layer 63 Core metal 226 Shape memory alloy (an example of a temperature sensitive distance adjusting member, an example of a shape memory member)
310 fixing device 380 fixing roller (an example of a fixing member)
381 Core metal 382 Elastic layer 383 Heat generation layer N Nip part P Recording paper (an example of recording medium)
T Toner image

Japanese Patent Laid-Open No. 2007-156065 JP 2008-46531 A JP 2008-257155 A

Claims (9)

A fixing member that travels in a predetermined direction and heats the toner image;
A pressing member that presses the fixing member to form a nip portion;
A magnetic flux generator for generating magnetic flux;
A heating member having a temperature-sensitive magnetic material and heating the fixing member with heat generated by magnetic flux;
In a fixing device comprising a magnetic shielding member provided inside the heating member,
A temperature sensitive distance adjusting member is attached to the magnetic shielding member,
The temperature sensitive distance adjusting member moves the magnetic shielding member in a direction approaching the heating member as the temperature of the heating member rises, and the heating unit adjusts the magnetic shielding member as the temperature of the heating member decreases. A fixing device which is moved in a direction away from a member.   The fixing device according to claim 1, wherein a gap is provided in the support member so that the support member supporting the magnetic shielding member can move in a direction approaching the heating member and a direction away from the heating member.   The fixing device according to claim 1, wherein the temperature sensitive distance adjusting member is an expansion member.   The fixing device according to claim 3, wherein the expansion member is made of silicone rubber.   The fixing device according to claim 3, wherein an expansion portion support member is provided inside the expansion member.   The fixing device according to claim 1, wherein the temperature sensitive distance adjusting member is a shape memory member.   The fixing device according to claim 1, wherein the fixing member is a fixing belt, and the fixing belt is stretched over at least a heating roller and a fixing roller.   The fixing device according to claim 1, wherein the fixing member is a fixing roller.   An image forming apparatus comprising the fixing device according to claim 1.

Images