JP2007256333A - Induction heating fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating fixing device capable of surely restraining excessive temperature rise and shortening rising time even when an image is consecutively fixed on a small-size recording medium or when the driving of the device is stopped suddenly in a fixing stage of an electromagnetic induction heating system, and to provide an image forming apparatus. <P>SOLUTION: The induction heating fixing device is provided with a first exothermic member and a second exothermic member as an exothermic member, wherein the first exothermic member has a Curie point Tq1 higher than the fixing temperature of the induction heating fixing device and also the second exothermic member has a Curie point Tq2 higher than the Curie point Tq1. The induction heating fixing device has an exothermic member selection means to select either the first exothermic member or the second exothermic member so as to heat a fixing belt. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device used in an image forming apparatus such as a copying machine or a printer, and more particularly to an induction heating type fixing device and an image forming apparatus using such an induction heating type fixing device.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, an apparatus using an electromagnetic induction heating type fixing device is often used for the purpose of reducing the rise time of the apparatus and saving energy (for example, patents). Reference 1).

  In Patent Document 1, etc., an electromagnetic induction heating type fixing device has a heat generating member (heat generating roller in Reference 1) and a fixing auxiliary roller (fixing roller), and a fixing belt stretched between the heat generating member and the fixing auxiliary roller, An induction coil portion that faces the heat generating member via the fixing belt, a pressure roller that faces the fixing auxiliary roller via the fixing belt, and the like.

  The induction coil unit includes an induction coil unit (or an excitation coil) that extends in the width direction (a direction orthogonal to the conveyance direction of the recording medium), a core that faces the induction coil unit, and the like.

  The fixing belt is heated at a position facing the induction coil unit. The heated fixing belt heats and fixes the toner image on the recording medium conveyed to the positions of the auxiliary fixing roller and the pressure roller. Specifically, when a high-frequency alternating current is passed through the induction coil portion, a magnetic field is formed around the induction coil portion, and an eddy current is generated near the surface of the heating member. When an eddy current is generated in the heat generating member, Joule heat is generated by the electric resistance of the heat generating member itself. The fixing belt wound around the heat generating member is heated by the Joule heat.

  Such an electromagnetic induction heating type fixing device is known as being capable of raising the surface temperature (fixing temperature) of the fixing belt to a desired temperature with a small energy consumption and a short rise time.

  On the other hand, Patent Document 2 and the like disclose a technique using a fixing belt using an electromagnetic induction heating method and including a base layer and a heat generating layer. Here, the base layer of the fixing belt is formed so as to have a relative permeability of 2 or more. The heat generating layer of the fixing belt has a relative permeability of 2 or less, and is formed so that the layer thickness is smaller than the penetration depth when excited by electromagnetic induction. This technique aims to improve the heat generation efficiency of the fixing belt.

  Patent Document 3 and the like disclose a technique using a heat generating member (fixing member) made of a magnetic layer having a Curie point, which is a fixing device using an electromagnetic induction heating method. Here, the magnetic layer of the heat generating member is formed so that the amount of heat generated when the temperature becomes equal to or higher than the Curie point is ½ of the amount of heat generated when excited at the normal temperature. This technique is intended to suppress overheating of the fixing member.

  Patent Document 4 and the like disclose a fixing device that uses an electromagnetic induction heating method and adjusts the Curie point of the core portion (magnetic core) of the induction heating portion in the width direction. Specifically, the curie point of the core part at both ends in the width direction is formed to be smaller than the curie point at the center part in the width direction. This technique is intended to suppress the temperature rise that occurs at both ends in the width direction of the fixing belt when a small-size recording medium is passed.

  In the conventional fixing device described above, when a small-sized recording medium is continuously fixed, or when the device suddenly stops driving due to a paper jam or the like, a part or all of the fixing belt overheats. was there.

  Details are as follows.

  A general image forming apparatus is configured to form an image on several types of recording media having different sizes in the width direction. Here, the recording media having different sizes in the width direction include recording media of irregular sizes in addition to recording media of various regular sizes in the A and B rows of JIS dimensions. Even in the case of recording media of the same size (for example, A4 size), the transport direction is the short direction (the direction perpendicular to the longitudinal direction) when the longitudinal direction is the transport direction. In some cases, recording media having different sizes in the width direction are handled.

  When fixing such a recording medium having a different size in the width direction with the fixing device, the heat distribution in the width direction of the fixing belt fluctuates according to the width direction size of the recording medium, resulting in temperature unevenness. was there. For example, when fixing by passing a recording medium having a small size in the width direction, a lot of heat is taken away at the position of the fixing belt corresponding to the size in the width direction of the recording medium (the paper passing area). The fixing temperature is lower than at other positions (non-sheet passing area). Such a phenomenon becomes particularly prominent when a recording medium having a small size in the width direction is continuously fed.

  Therefore, when trying to control the fixing temperature in the entire width direction of the fixing belt with reference to the fixing temperature in the center portion in the width direction of the fixing belt, the fixing temperature in the center portion in the width direction of the fixing belt can be controlled to a desired temperature. The fixing temperature at both ends in the direction will rise (overheated). As described above, when a large recording medium in the width direction is fixed in a state where the fixing temperature at both ends in the width direction of the fixing belt is increased, a hot offset occurs on the recording medium corresponding to the temperature increase position. Furthermore, when the fixing temperature at both ends in the width direction exceeds the heat resistance temperature of the fixing belt, it is considered that the fixing belt is thermally damaged.

  On the other hand, if it is attempted to control the fixing temperature in the entire width direction of the fixing belt based on the fixing temperature at both ends in the width direction of the fixing belt, the fixing temperature at both ends in the width direction of the fixing belt can be controlled to a desired temperature. However, the fixing temperature at the center in the width direction is lowered. As described above, when the recording medium is fixed in a state where the fixing temperature at the center portion in the width direction of the fixing belt is lowered, a cold offset occurs on the recording medium corresponding to the temperature lowered position.

  Further, when a paper jam (jam) occurs in the conveyance path in the image forming apparatus, the driving of the fixing device is suddenly stopped. In such a case, the portion of the fixing belt facing the induction heating unit instantaneously overheats in a short time until the energization to the induction heating unit is cut off. As a result, it is also conceivable that the structural members such as the fixing belt and the induction coil section of the induction heating section are thermally damaged.

  On the other hand, the technique disclosed in Patent Document 2 described above improves the heat generation efficiency of the fixing belt by optimizing the relative permeability and the layer thickness of the base layer and the heat generation layer of the fixing belt. Therefore, the effect of suppressing the excessive temperature increase of the fixing belt cannot be expected.

  In the technique disclosed in Patent Document 3 and the like, a predetermined Curie point is set in the magnetic layer of the fixing member. However, the heat generation amount when the temperature of the magnetic layer is equal to or higher than the Curie point is formed to be ½ of the heat generation amount when normally excited. Moreover, since the current flows through the entire thickness of the heating roller even when the temperature of the magnetic layer becomes equal to or higher than the Curie point, it is possible to reliably prevent the above-described overheating of the fixing belt. I cannot expect the effect to do.

  Moreover, the above-mentioned technologies such as Patent Document 4 adjust the Curie point of the core portion of the induction heating unit in the width direction. However, since the overheating of the fixing member heated by the induction heating unit occurs before the overheating of the core portion occurs, the effect of directly suppressing the overheating of the fixing belt cannot be expected. .

Further, when the temperature is in the vicinity of the desired fixing temperature at the Curie point, the amount of heat generated by the magnetic flux gradually decreases in the vicinity of the Curie point, so that the temperature does not rise easily when reaching the vicinity of the desired fixing temperature. This is a major problem for shortening the rise time described above, and at present, it is not possible to achieve both energy saving and prevention of excessive temperature rise by shortening the rise time.
Japanese Patent Laid-Open No. 2003-215556 JP 2003-7438 A JP 2000-35724 A JP 2000-162912 A

  The present invention has been made to solve the above-described problems. In a fixing process using an electromagnetic induction heating method, when a small-size recording medium is continuously fixed or when the apparatus suddenly stops driving. Even in such cases, it is an object to provide an induction heating type fixing device and an image forming apparatus in which excessive temperature rise is reliably suppressed and the rise time can be shortened (energy saving).

  In order to solve the above-described problem, the induction heating type fixing device of the present invention is the induction heating type fixing device provided with the fixing belt heated by the heat generating member. A first heating member having a Curie point Tq1 higher than the fixing temperature of the induction heating type fixing device, and the second heating member has a Curie point Tq1. An induction heating type fixing device having a higher Curie point Tq2 and having a heat generating member selecting means for selecting one of the first heat generating member and the second heat generating member to heat the fixing belt. .

  In addition, the induction heating type fixing device of the present invention is characterized in that at least one of the heat generating members is made of a magnetic shunt alloy.

  In order to solve the above-described problem, the induction heating type fixing device according to the present invention is the induction heating type fixing device according to claim 1 or 2, wherein both the first and second cylinders have a semicylindrical shape. The heating member and the second heating member are provided on a surface of one cylindrical base, and a heating cylinder is provided with the central axis of the cylindrical base being 180 ° rotationally symmetrical to each other. It is characterized by.

  An induction heating type fixing device according to the present invention is the induction heating type fixing device according to claim 3, wherein the heating cylinder rotates about the axis of the cylinder as a rotation axis. A cylindrical rotating means is provided as the heating member selecting means.

  An induction heating type fixing device according to the present invention is the induction heating type fixing device according to claim 3 or 4, wherein the inner surface of the fixing belt and the outer surface of the heating cylinder are as described in claim 5. And an induction coil portion for heating the heating member of the heating cylinder by electromagnetic induction is provided inside and outside the heating cylinder, and these induction coil portions Is arranged at a position sandwiching a contact portion between the cylindrical substrate and the fixing belt.

  The induction heating type fixing device of the present invention is the induction heating type fixing device according to any one of claims 3 to 5, wherein the surface of the heating cylinder is as defined in claim 6. It is characterized by being covered with a fluorine resin layer.

  The induction heating type fixing device according to the present invention is the induction heating type fixing device according to any one of claims 3 to 5, wherein the surface of the heating cylinder is as defined in claim 7. It is covered with a nickel layer.

  An induction heating type fixing device according to the present invention is the induction heating type fixing device according to any one of claims 3 to 7, wherein the fixing belt is used for the heating. The cylinder, the supporting roller and the fixing auxiliary roller are stretched, and the fixing auxiliary roller is disposed so as to come into contact with the pressure roller that presses the conveyed recording medium via the fixing belt. It is characterized by that.

  According to a ninth aspect of the present invention, an image forming apparatus includes the induction heating type fixing device according to any one of the first to eighth aspects.

  According to the induction heating type fixing device of the present invention, the first heat generating member and the second heat generating member are provided as the heat generating members, and the first heat generating member is higher than the fixing temperature of the induction heating type fixing device. The second heat generating member has a Curie point Tq1, and the second heat generating member has a Curie point Tq2 higher than the Curie point Tq1, and one of the first heat generating member and the second heat generating member is selected and Since the heat generating member selection means for heating the fixing belt is provided, since the generation of Joule heat in the heat generating member is limited when the Curie point is reached, the heat generating member does not have a temperature higher than each Curie point. Even when a small-sized recording medium is continuously fixed, or when the device suddenly stops driving, excessive temperature rise is reliably prevented, resulting in long-life fixing. The location.

  Furthermore, according to the induction heating type fixing device according to claim 2, by using a magnetic conductive material such as nickel, iron, chromium, or an alloy thereof, a desired curie can be changed by changing a component ratio thereof. A heat generating member having a point can be obtained.

  Furthermore, according to the induction heating type fixing device of the third aspect, since the first heat generating member and the second heat generating member are unitized, it is easy to attach to the fixing device.

  Furthermore, according to the induction heating type fixing device according to claim 4, the heating member selecting means becomes a heating cylinder rotating means for rotating the heating cylinder about the axis of the cylinder. Since the heat generating member to be used can be changed simply by rotating it, the mechanism becomes extremely simple, and the heat generating member not in use can be prevented from coming into contact with the fixing belt, so there is no waste of energy and further space saving. Can be realized.

  According to the induction heating type fixing device of the fifth aspect, since the magnetic field is generated almost in parallel with the heat generating member, it can be heated efficiently. Moreover, even if it is a small induction coil, by using two, a heat generating member can be heated effectively, As a result, an induction heating type fixing device can be made compact.

  In addition, according to the induction heating type fixing device of the sixth aspect, the rust prevention effect of the heat generating member can be obtained, and the slidability between the surface of the cylindrical substrate and the fixing belt can be provided. When the cylindrical substrate and the fixing belt slide, the inner surface of the fixing belt is prevented from being damaged, and the life of the fixing belt can be extended.

  Furthermore, according to the induction heating type fixing device of the seventh aspect, the rust preventive effect of the heat generating member can be obtained, and the slidability between the cylindrical substrate surface and the fixing belt can be provided. When sliding between the cylindrical substrate and the fixing belt, scratches on the inner surface of the fixing belt can be prevented, the life of the fixing belt can be extended, and the hardness of the surface of the cylindrical substrate can be improved to generate heat. Surface wear of the member can be suppressed, and durability can be improved.

  Furthermore, according to the induction heating type fixing device according to the eighth aspect, the above-mentioned effect can be obtained with certainty even with a fixing device having a general structure.

  Furthermore, according to the induction heating type fixing device of the ninth aspect, it is possible to obtain a highly reliable fixing device having a short rise time and capable of suppressing an excessive temperature rise such as an end temperature rise with a simple configuration. .

  Furthermore, according to the image forming apparatus of the eighth aspect, it is possible to obtain a highly reliable image forming apparatus that has a short rise time and can suppress an excessive temperature rise such as an end temperature rise with a simple configuration.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

<Embodiment 1>
The first embodiment of the present invention will be described in detail with reference to FIGS.

  First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.

  With reference to FIG. 1, an operation during normal image formation in the image forming apparatus will be described. FIG. 1 shows a tandem type color image forming apparatus. A plurality of photosensitive drums 18BK, 18Y, 18M, and 18C are arranged on the transfer belt 8 in the image forming section. Although not shown, a charging unit, an exposure unit, a developing unit, a cleaning unit, and a charge eliminating unit are disposed on the outer periphery of each of the plurality of photosensitive drums 18BK, 18Y, 18M, and 18C.

  Then, a toner image of each color (black, yellow, magenta, cyan) is formed on each photosensitive drum 18BK, 18Y, 18M, 18C.

  The transfer unit includes a transfer belt 8 that transports the recording medium P, a bias roller 9 that faces each of the photosensitive drums 18BK, 18Y, 18M, and 18C via the transfer belt 8, and a cleaning roller 14 that cleans the surface of the transfer belt 8. , Etc.

  The transfer belt 8 sequentially conveys the recording medium P conveyed from the direction of the arrow to a position facing each of the photosensitive drums 18Y, 18M, 18C, and 18BK. At this time, the toner images of the respective colors are transferred onto the recording medium P by the transfer bias applied to the bias roller 9. Thus, a full-color toner image is formed on the recording medium P. Thereafter, the recording medium P on which a full-color toner image is formed is separated from the transfer belt 8 and conveyed toward the fixing device 20.

  The recording medium P that has reached the fixing device 20 is fed between a fixing belt 22 and a pressure roller 30 described later with reference to FIG. 2, and receives heat from the fixing belt 22 as a fixing member and the pressure roller 30. The toner image is fixed by the pressure received from the toner. The recording medium P on which the toner image is fixed is sent from between the fixing belt 22 and the pressure roller 30, and then is discharged from the image forming apparatus main body 1 as an output image and placed on a paper discharge tray. . Thus, a series of image forming processes is completed.

  Next, the configuration and operation (fixing process) of the fixing device 20 in the image forming apparatus main body 1 will be described in detail with reference to FIG.

  As shown in FIG. 2, the fixing device 20 mainly includes a fixing auxiliary roller 21, a fixing belt 22, a support roller 23, an induction heating unit 24, a pressure roller 30, a thermistor 38, a guide plate 35, a separation plate 36, and a surface. Both of them are composed of a heating cylindrical body 33 composed of a cylindrical base body 33a provided with a first heat generating member layer 33b and a second heat generating member layer 33c which are both semicylindrical in shape.

  Here, the fixing auxiliary roller 21 is formed by forming an elastic layer such as silicone rubber on the surface of a cored bar made of stainless steel or the like. The elastic layer of the fixing auxiliary roller 21 has a thickness of 3 to 10 mm and an Asker hardness of 10 to 50 degrees. The fixing auxiliary roller 21 is rotationally driven counterclockwise in FIG. 2 by a driving unit (not shown).

  As shown in FIG. 3, the heating cylinder 33 has a semi-cylindrical first heating member 33b made of a magnetic conductive material on the side surface of a (one) cylindrical base 33a made of a nonmagnetic material. And the layer composed of the second heat generating member 33c on the side surface of the cylindrical substrate 33a, with the central axis of the cylindrical substrate being 180 ° rotationally symmetrical center (so as to face each other in the axial direction). It is arranged and formed.

  Two concave storage portions are provided on the side surface of the cylindrical substrate 33a so that the surface of the cylindrical body 33a is not uneven when the heating cylinder 33 is formed. The heat generating members 33b and 33c are respectively provided in the storage portions. It is stored.

  The cylindrical substrate 33a is a hollow cylindrical tube having no magnetism, and in this example, the wall thickness t is 0.6 to 3 mm.

  As shown in FIG. 2, the fixing belt 22 rotating in the counterclockwise direction rotates while sliding on the surface of the heating cylinder 33 arranged in contact with the inside thereof. The heating cylinder 33 is illustrated with its axis as the center so that either the surface of the heating cylinder 33 on the first heat generating member 33b side or the surface of the second heat generating member 33c side is in contact with each other. Rotating means (in this example, a stepping motor) that can be rotated, and as the heat generating member selecting means, a stepping motor (not shown) and its stepping motor are controlled to rotate the heating cylinder 33 at 180 ° C. A heating cylinder rotating means composed of a heating portion is provided. For example, when a sheet passing signal is received from a sheet passing control section or the like from a resting state, the heating cylinder 33 is rotated as necessary to form a second heating member. A temperature rise end signal notifying that the temperature of the fixing belt 22 has been sufficiently heated from a fixing belt temperature detecting means (such as a thermistor) that starts the temperature increase of the fixing belt 22 by 3c and detects the temperature of the fixing belt 22 is provided. When it comes, the heating cylinder 33 is rotated as necessary to start heating the fixing belt 22 by the first heat generating member 33b.

  In this example, the induction heating unit 24 that heats the first heat generating member 33b or the second heat generating member 33c on the cylindrical base 33a by electromagnetic induction sandwiches the cylindrical base 33a and the fixing belt 22 as shown in FIG. Thus, the linear induction coil part 25a of the induction heating part 24 is arranged inside the cylindrical base 33a, and the other linear induction coil part 25b of the induction heating part 24 is arranged outside the cylindrical base 33a. .

  The linear induction coil portions 25a and 25b of the induction heating unit 24 may be provided independently of each other, or are continuous by a portion not shown in the figure such as a “U” shape or an “O” shape. Also good. In this example, the induction heating unit 24 is formed in a U-shape by the induction coil units 25a and 25b of the linear induction heating unit 24 and a connecting portion that connects between the induction coil units 25a and 25b.

  That is, as shown in FIG. 3, the induction coil portions 25 a and 25 b are excitation coils arranged so as to sandwich the fixing belt 22 and the heating cylinder 33. In other words, the fixing belt 22 and a part of the heating cylinder 33 are sandwiched in the space of the U-shaped induction heating unit 24.

  As shown in FIG. 3, the induction coil portions 25 a and 25 b extend in parallel to the axis of the heating cylinder 33. One end of the induction coil portions 25a and 25b in the width direction is connected to each other by a connecting portion, and the other end is connected to the high frequency power source portion 40. Then, an alternating current of 10 k to 1 MHz (preferably 10 k to 300 kHz) is applied between the induction coil units 25a and 25b from the high frequency power supply unit 40.

  In the first embodiment, the induction heating unit 24 is formed by one excitation coil. However, a plurality of U-shaped coil units may be installed so as to sandwich the cylindrical base 33a and the fixing belt 22. Alternatively, one excitation coil may be installed by being wound a plurality of times in a spiral shape so as to sandwich the cylindrical substrate 33a and the fixing belt 22. The state of the magnetic flux at this time is schematically shown in FIG.

  A support roller 23 is disposed between the fixing cylinder 21 and the upstream side of the heating cylinder 33 with respect to the rotation direction of the fixing belt 22. The support roller 23 has a heat insulating layer (in the present invention, a felt-like non-woven fabric made of aramid fibers is bonded) formed on the surface thereof, and an urging force (not shown) in the normal direction of the rotating fixing belt 22. Since the member is biased from both sides of the shaft, the fixing belt 22 is rotated with a constant tension tension.

  Here, as a material of the heat generating members 33b and 33c, a magnetic conductive material such as nickel, iron, chromium, or an alloy thereof can be used.

  Here, the fixing temperature of the fixing device is generally 150 to 190 ° C. In the present invention, the fixing temperature is usually determined from this range. Here, the Curie point Tq1 of the first heat generating member 33b depends on the heat capacity and the rotation speed of the fixing belt 22 that is rotationally driven, but is 10 to 30 ° C. from the fixing temperature (160 ° C. (target value) in this example). High is desirable. Specifically, the temperature Tq1 is a temperature at which the temperature of the fixing unit where the fixing is performed is maintained at a predetermined fixing temperature, and is 190 ° C. (target value; actually, about 192 ° C.) in this example.

  On the other hand, the Curie point Tq2 of the second heat generating member 33c needs to be higher than the temperature Tq1, and further depends on the heat capacity and the rotational speed of the fixing belt 22 that is rotationally driven, but is 80 to 130 ° C. above the fixing temperature. It is desirable to be high (270 ° C. in this example).

  A material having a Curie point at such a temperature can be obtained by changing the compounding ratio in a magnetic conductive material such as nickel, iron, chromium, or an alloy thereof. The heat generating member 33b uses a magnetic shunt alloy having a Curie point of 190 ° C., and the second heat generating member 33c uses a magnetic shunt alloy having a Curie point of 270 ° C.

  Here, in the fixing step of fixing the toner image on the recording medium P in the fixing step, the cylindrical substrate 33a (heating cylinder 33) is maintained so that the nip portion (fixing portion) where the fixing is performed is maintained at the fixing temperature. The heating cylinder 33 is rotated or rotated so that the surface on which the first heat generating member 33 b is disposed is in sliding contact with the inner surface of the fixing belt 22, and is heated by the induction heating unit 24. . The temperature of the first heat generating member 33b at this time is Tq1 that is the Curie point temperature.

  Here, when the small-sized recording medium P is continuously fixed, only the sheet passing area of the small-sized recording medium P dissipates heat (heat is transferred to the recording medium P). Then, the fixing belt 22 whose temperature has been lowered is supplied to the contact position with the heating cylinder 33. As a result, the first heat generating member 33b of the heating cylinder 33 is also partially from its Curie point temperature Tq1. The temperature also decreases. At that time, only the region where the temperature has decreased is heated by the induction heating unit 24, and the Curie point temperature is maintained in a region where the temperature does not decrease, that is, other than the portion corresponding to the paper passing region, and the magnetic flux generated by the induction heating unit 24 is concentrated. Thus, no heat is generated.

  On the other hand, the nip portion (fixing portion) where the fixing is performed, such as the start of a fixing operation from a standby state (in recent years, energy conservation has been promoted and the standby state is left at room temperature) has changed from a normal temperature (low temperature) state to a predetermined temperature ( When the temperature is raised to the (fixing temperature), it is required to shorten the time for raising the temperature to a predetermined temperature as much as possible. Therefore, the heating cylinder 33 is arranged such that the surface of the cylindrical base body 33a (heating cylinder 33) on which the second heat generating member 33c is disposed is in sliding contact with the inner surface of the fixing belt 22. Rotate. At this time, as a result of heating by the induction heating unit 24, the second heat generating member 33c reaches its Curie point temperature Tq2, and the nip portion where the fixing is performed is rapidly heated to a predetermined temperature, thereby shortening the rise time ( Raising the temperature from this normal temperature state to a predetermined temperature at the time of fixing is referred to as a temperature raising step).

  Here, the heat generation characteristics near the Curie point of the magnetic shunt alloy used in the present invention will be described in a model manner with reference to FIG.

  FIG. 4 is a model graph showing the relationship between the magnetic flux density applied to the magnetic shunt alloy and the temperature. The magnetic flux density is remarkably lowered at the Curie point Tc ° C. in the figure, and the characteristic that induction heat generation does not generate heat due to the decrease of the magnetic flux density is shown. In addition, the magnetic flux density gradually decreases as the temperature approaches the Curie point Tc, but it can be seen that the temperature rise rate gradually decreases as the temperature approaches the Curie point Tc.

  As described above, in the present invention, it is sufficient that the fixing device has a heat generation characteristic that compensates for the temperature drop due to the sheet passing when the fixing is performed. Therefore, the temperature of the fixing unit is set to a predetermined temperature. In order to maintain the (fixing temperature), a temperature that is higher than the predetermined temperature and not much higher than the predetermined fixing, and that has a Curie point at a temperature Tq1 at which the fixing temperature of the fixing unit that performs fixing can be maintained. The first heating member 33b is used for heating, and the second heating member 33c having a Curie point Tq2 higher than the temperature Tq1 is used in the temperature raising step for the purpose of shortening the rise time.

  In addition, as the fixing belt 22, a belt generally used in a fixing device can be used as it is.

  The fixing belt is, for example, an endless belt having a multilayer structure in which an elastic layer and a release layer are sequentially formed on a base material. The base material is made of an insulating heat-resistant resin material, and for example, polyimide, polyamideimide, PEEK, PES, PPS, fluorine resin, or the like can be used. The layer thickness of the substrate is preferably 30 to 200 μm from the viewpoint of heat capacity and strength.

  The elastic layer of the fixing belt is preferably made of, for example, silicone rubber, fluorosilicone rubber or the like, and is formed to have a layer thickness of 50 to 500 μm and an Asker hardness of 5 to 50 degrees. Thereby, a uniform image quality without glossy spots can be obtained in the output image.

  For example, the release layer of the fixing belt may be a so-called fluorine-based material such as tetrafluoroethylene resin (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin (PFA), tetrafluoroethylene / hexafluoride. A fluororesin such as a propylene copolymer (FEP), a mixture of these resins, or a resin in which these resins are dispersed in a heat resistant resin can be used. The release layer has a thickness of 5 to 50 μm (preferably 10 to 30 μm). Thereby, the toner releasability on the fixing belt is ensured, and the flexibility of the fixing belt is ensured. A primer layer or the like can be provided between the layers of the fixing belt.

  As the pressure roller 30, a common pressure roller for the fixing device can be used.

  For example, an elastic layer made of fluorine rubber, silicone rubber or the like is formed on a cylindrical member made of aluminum, copper or the like. The elastic layer of the pressure roller has a thickness of 1 to 5 mm and an Asker hardness of 20 to 50 degrees.

  As shown in FIG. 2, the pressure roller 30 is in pressure contact with the auxiliary fixing roller 21 via the fixing belt 22. Then, the recording medium P is conveyed to a contact portion (a fixing nip portion) between the fixing belt 22 and the pressure roller 30.

  A guide plate 35 for guiding the conveyance of the recording medium P is disposed on the entrance side of the contact portion (fixing portion) between the fixing belt 22 and the pressure roller 30.

  A separation plate 36 that guides the conveyance of the recording medium P and promotes the separation of the recording medium P from the fixing belt 22 is disposed on the exit side of the contact portion between the fixing belt 22 and the pressure roller 30. Yes.

  A thermistor 38, which is a thermosensitive element with high thermal response, is in contact with the outer peripheral surface of the fixing belt 22 and upstream of the fixing nip portion. The surface temperature on the fixing belt 22 is detected by the thermistor 38. The thermistor 38 detects, for example, that the fixing belt 22 has reached a temperature sufficient for fixing in a temperature raising step, and generates heat. The heat generating member that heats the fixing belt 22 is switched to the first heat generating member 33b by the member selecting means. Here, the contact position of the thermistor 38 to the fixing belt 22 is optimized as needed. Further, although the contact-type temperature sensitive element is used in the first embodiment, a non-contact element may be used, and in this case, scratches on the surface of the fixing belt 22 are prevented in advance.

  The fixing device 20 configured as described above operates as follows.

  By the rotation driving of the auxiliary fixing roller 21, the fixing belt 22 rotates in the arrow direction in FIG. 2A, the support roller 23 also rotates counterclockwise, and the pressure roller 30 also rotates in the arrow direction. The fixing belt 22 is heated between the induction coil portions 25a and 25b.

  Specifically, the high-frequency alternating current of 10 kHz to 1 MHz is supplied from the high-frequency power supply unit 40 to the coil unit 25 so that the lines of magnetic force are alternately switched between the induction coil unit 25a and the induction coil unit 25b. . By forming the alternating magnetic field in this way, when the temperature of the first heat generating member 33b (or the second heat generating member 33c) of the heating cylinder 33 is equal to or lower than the Curie point Tq1 (or Tq2), An eddy current is generated in one heating member 33b (or the second heating member 33c) and is heated by Joule heat. Thus, the fixing belt 22 is heated by the heat received from the first heat generating member 33b (or the second heat generating member 33c) that has generated heat.

  In the temperature raising step, the second heat generating member 33c of the heating cylinder 33 is heated by the induction coil portions 25a and 25b, the heat is transmitted to the fixing belt 22, and the fixing belt 22 is rapidly heated and rotated. Therefore, the temperature rise is continued until it is confirmed by the thermistor 38 that the temperature of the fixing belt 22 has reached or reached the fixing temperature.

  Thereafter, the heating member for heating the fixing belt 22 is switched to the first heating member 33b by the heating member selection means, and the fixing belt 22 heats and fixes the toner image T on the recording medium P conveyed to the fixing unit. To do.

  Specifically, the recording medium P carrying the toner image T through the image forming process described above is fed between the fixing belt 22 and the pressure roller 30 while being guided by the guide plate 35. The toner image T is fixed to the recording medium P by the heat received from the fixing belt 22 and the pressure received from the pressure roller 30, and the recording medium P is sent from between the fixing belt 22 and the pressure roller 30.

  The surface of the fixing belt 22 that has passed through the contact position (fixing portion) with the pressure roller 30 then reaches again between the induction coil portion 25a and the induction coil portion 25b. Such a series of operations is continuously repeated to complete the fixing step in the image forming process.

  In such a fixing step, when the temperature of the first heat generating member 33b reaches the Curie point Tq1, the generation of eddy currents in the vicinity of the surface is limited to decrease the magnetic flux density, that is, to lose magnetism. As a result, the amount of Joule heat generated decreases, and even when the fixing belt 22 stops rotating due to jamming or the like, excessive temperature rise is suppressed.

<Embodiment 2>
A second embodiment of the present invention will be described in detail.

  In the second embodiment, in the fixing device 20 described above, the surface of the heating cylinder 33 (see FIG. 2) is covered and integrated with a heat-shrinkable tube 33d made of a fluororesin, as schematically shown in FIG. It is what has been made. The heat-shrinkable tube 33d made of a fluororesin has a thickness of 20 μm, but can be appropriately selected within a range of 15 to 30 μm. Alternatively, the heating cylinder 33 and the adhesive layer may be integrated. Other configurations are the same as those of the first embodiment.

<Embodiment 3>
The third embodiment will be described in detail with reference to FIG.

  In the fixing device 20 of the third embodiment, as schematically shown in FIG. 6A, the side surface of the cylindrical base 33a constituting the heating cylinder 33 is set to 1 at 180 ° C. with respect to the central axis. Two groove-shaped notches 33e parallel to the central axis are provided, both of which are bent using the notches 33e, and the ends are greatly bent. A semi-cylindrical first heating member 33b and a second heating member 33c, both of which are made by press-fitting a semi-cylindrical first heating member 33b and a second heating member 33c made of a material, A heating cylinder 33 is used which is arranged on the surface of one cylindrical base with the central axes of the cylindrical bases being 180 ° rotationally symmetric.

  Here, the nickel plating layer 33f (20 μm) is formed on the surface of the heat generating members 33b and 33c in contact with the back surface of the fixing belt 22 (the side surface of the heating cylinder 33 is formed) as shown in FIG. 6B. Is formed, and it has rust prevention and slidability. Other configurations are the same as those of the first embodiment. The nickel plating layer is determined in consideration of durability, easy implementation conditions and the like, for example, 5 to 30 μm.

  In the first to third embodiments, the induction coil section for heating the heat generating member of the cylindrical base body by electromagnetic induction is disposed inside and outside the heating cylinder body with the cylindrical base body and the fixing belt interposed therebetween. However, the present invention is not limited to this, and the present invention is not limited to this. Even if the induction coil portion is only outside the cylindrical substrate, an example is shown in FIG. ) Alternatively, it may be disposed only inside the cylindrical substrate.

  The fixing device shown in FIG. 7 differs from the fixing device 20 of FIG. 2 only in the arrangement of the induction coil section. Due to the difference in the arrangement of the induction coil portions, the direction of the magnetic flux in the case of the first embodiment is a heating member that heats the fixing belt 22 of the heating cylinder 33 as schematically shown in FIG. In contrast to being substantially parallel to the layers, the arrangement as shown in FIG. 8 is perpendicular to the heat generating member layer. For this reason, the heating of the fixing belt 22 is partial heating, and the efficiency during heating is lowered.

  Hereinafter, experimental examples for confirming the effects described in the above embodiments will be described.

  In the evaluation of the present invention, the image forming apparatus 1 schematically shown in FIG. 1 is used to measure the rise time in the medium speed machine fixing conditions of a linear speed of 154 mm / second and a fixing temperature of 160 ° C., and A4 size cardboard ( Ricoh 90k paper) was evaluated for the edge temperature rise when 200 sheets were continuously fed by vertical conveyance. The end temperature rise needs to be 200 ° C. or less in the hot offset region of the fixing temperature, and the smaller the difference from the fixing temperature 160 ° C. that is the control value, the better. In Examples 1 to 3, the fixing belt was heated by switching to the second heat generating member in the temperature raising step, and the fixing belt was heated by switching to the first heating member at the time of fixing.

  The temperature measurement points were measured at five locations at equal intervals with respect to the entire area of the fixing belt in the axial direction.

  For the temperature measurement, a contact-type temperature sensor (E-type thermocouple) is brought into contact with the fixing belt 22 so that both ends of the fixing belt width direction center and two intermediate portions between the center and both ends are measured. The measurement was performed for each temperature, and from these results, the maximum value (basically both ends of the fixing belt outside the paper passing area) and the temperature difference between the maximum value and the minimum value were calculated.

  Further, as an endurance test, A4 size plain paper (T6200 manufactured by Ricoh Co., Ltd.) was continuously fed by horizontal conveyance, and the presence or absence of abnormal images was examined based on the guaranteed number of 100,000 sheets of product (image fixing device).

  The results are shown in Table 1. According to the present invention, the temperature can be raised quickly in the temperature raising process. As a result, the rise time is short, and at the same time, energy saving is possible. It can be seen that a long life is achieved and the temperature difference in the belt width direction is sufficiently small.

  In the above, the heating member 33 used for heating the fixing belt is switched by rotating the heating cylinder 33 by 180 ° C. so that the second heating member and the first heating member are used during the temperature raising step and the fixing, respectively. However, when the temperature raising process and fixing were performed using the second heat generating member without switching, the temperature rising was sufficiently fast as 17.3 seconds, but overheating occurred during fixing, and it could not be continued. On the other hand, it was found that when the temperature raising step and the fixing were performed using the first heat generating member, 30 to 33 seconds were required for the temperature raising step, which was not practical.

  Here, using the induction heating type fixing device shown in model in FIG. 7 in which the magnetic field generated by the induction coil is perpendicular to the heat generating member, the surface is provided with a layer made of the heat generating member having a Curie point of 190 ° C. The heating step and fixing were performed using a heating cylinder (Comparative Example 1) and a heating cylinder (Comparative Example 2) provided with a layer made of a heat generating member having a Curie point of 285 ° C., respectively. The results are also shown in Table 1 as Comparative Examples 1 and 2.

  From these results, it can be seen that the heating process takes too much time in Comparative Example 1, and overheating occurs during fixing in Comparative Example 2.

  In addition, this invention is not limited to said each embodiment, As long as the effect of this invention is acquired, a modification, improvement, etc. can be performed.

  In the induction heating type fixing device and the image forming apparatus of the present invention, even when a small-size recording medium is continuously fixed in the electromagnetic induction heating type fixing process or when the apparatus is suddenly stopped. Since overheating is reliably suppressed and the rise time can be shortened (energy saving), it can be suitably applied to the field of image forming apparatuses such as copying machines and printers.

FIG. 3 is a model diagram illustrating the configuration and operation of the entire image forming apparatus. FIG. 3 is a model diagram illustrating a configuration / operation of a fixing device. FIG. 5 is a model perspective view that schematically shows the relationship between the configuration of the heating cylinder 33 and the induction heating unit 24; It is the model graph which showed the relationship between the magnetic flux density applied to a magnetic shunt alloy, and temperature. FIG. 6 is a model cross-sectional view showing a heating cylinder in the second embodiment. (A) It is model sectional drawing which showed the cylindrical body for a heating in this Embodiment 3. FIG. (B) It is an expanded model sectional view near the surface of the cylinder for heating of (a). It is a model figure which shows the fixing device by which the induction coil part was distribute | arranged only outside the cylindrical base | substrate.

Explanation of symbols

1. Image forming device body (device body)
7 Transfer section
8 Transfer belt 9 Bias roller 10 Paper discharge unit (tray)
14 Transfer section cleaning roller 18 Photosensitive drum 20 Fixing device 21 Fixing auxiliary roller 22 Fixing belt 23 Support roller 24 Induction heating section 25 Coil section 30 Pressure roller 33 Heating cylinder 33a Cylindrical base body 33b First heating member 33c First 2 heat generating member 33d heat shrinkable tube 33e made of fluororesin 33 notch 33f nickel plating layer 38 thermistor (temperature sensing element)
40 High frequency power supply

Claims (9)

In an induction heating type fixing device provided with a fixing belt heated by a heat generating member,
As the heat generating member, a first heat generating member and a second heat generating member are provided, and the first heat generating member has a Curie point Tq1 higher than the fixing temperature of the induction heating type fixing device, and the second heat generating member. The heat generating member has a Curie point Tq2 higher than the Curie point Tq1, and
An induction heating type fixing device comprising heating member selecting means for selecting one of the first heating member and the second heating member and heating the fixing belt.   The induction heating type fixing device according to claim 1, wherein at least one of the heat generating members is made of a magnetic shunt alloy.   The first heat generating member and the second heat generating member, both of which are semi-cylindrical, are arranged on the surface of one cylindrical base, with the central axis of the cylindrical base being mutually centered at 180 ° rotational symmetry. The induction heating type fixing device according to claim 1, further comprising a heating cylinder.   4. The induction heating type fixing device according to claim 3, further comprising: a heating cylinder rotating unit that rotates the heating cylinder about the axis of the cylinder as the rotation axis. The inner surface of the fixing belt and the outer surface of the heating cylinder are in contact with each other; and
Induction coil portions for heating the heating member of the heating cylinder by electromagnetic induction are provided inside and outside the heating cylinder, and these induction coil portions include the cylindrical base, the fixing belt, and the like. 5. The induction heating type fixing device according to claim 3, wherein the induction heating type fixing device is disposed at a position sandwiching the contact portion.   The induction heating type fixing device according to any one of claims 3 to 5, wherein a surface of the heating cylinder is covered with a fluorine resin layer.   6. The induction heating type fixing device according to claim 3, wherein a surface of the heating cylinder is covered with a nickel layer.   The fixing belt is stretched between the heating cylinder, a support roller, and a fixing auxiliary roller, and the fixing auxiliary roller contacts the pressure roller that presses the conveyed recording medium via the fixing belt. The induction heating type fixing device according to any one of claims 3 to 7, wherein the induction heating type fixing device is disposed so as to be in contact with each other.   An image forming apparatus comprising the induction heating type fixing device according to any one of claims 1 to 8.

Images