JP2001125407A - Image heating device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the return operation of belt temperature from being unstable in a conventional belt system image heating device by which warming-up time can be shortened. SOLUTION: The device have a heating roller having magnetic permeability obtained by setting a Curie temperature to a specified value and movably stretching the belt, an electrically conductive member arranged inside the heating roller, and an energizing means energizing the belt from an outside through the belt; and the belt temperature can be controlled to be stable without spoiling a temperature rising speed by making the conductive member take a first position and a second position different from the first position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image heating apparatus for shortening a warm-up time, and more particularly, to an image heating apparatus suitable for an image forming apparatus such as an electrophotographic apparatus and an electrostatic recording apparatus which is suitable for fixing an unfixed image. The present invention relates to an apparatus and an image forming apparatus using the same.

[0002]

2. Description of the Related Art As an image heating device represented by a heat fixing device, a contact heating system such as a heat roller system and a belt system has been generally used.

[0003] In recent years, due to demands for shortening the warm-up time and saving energy, a belt system capable of setting a small heat capacity has attracted attention.

Japanese Patent Application Laid-Open No. Hei 6-318001 is an example of such a structure, and FIG. Endless rotating belt 1
01 is stretched between the fixing roller 102 and the heating roller 103, and the heating roller 103 is heated by the heating source H1 in the heating roller 103, thereby heating the belt 101 to a predetermined temperature.

In this conventional example, the use of a belt having a small heat capacity is intended to achieve fixing without offset with a configuration in which oil application is small.

An electromagnetic induction heating method which has a possibility of rapid heating and high-efficiency heating has attracted attention.
23861 is an example, and the structure is shown in FIG. An excitation coil 114 is disposed inside the heating roller, and an AC magnetic field is generated by the excitation coil 114 and a core 117 made of ferrite or the like, thereby generating an eddy current in the heating roller 112 to generate heat. The recording material 110 on which the unfixed toner image 111 is placed passes through the pressure contact portion between the heating roller 112 and the pressure roller 113 and is fixed.

[0007]

In general, the belt system including the above-mentioned prior art has an advantage that the heat capacity of the belt can be set small in order to shorten the warm-up time, and the belt itself is heated to a predetermined temperature in a short time. You can do so. However, on the other hand, the smaller the heat capacity is, the stronger the tendency that the belt temperature is liable to be greatly reduced by the heat taken by the recording material when the toner image is fixed. At this time, it is necessary to stably and uniformly return the lowered belt temperature to a temperature required until the belt temperature reaches the fixing section again for reliable fixing.

[0008] An even more important problem is that the temperature of the belt after passing through the fixing section decreases depending on the recording material at that time,
This largely depends on the temperature state of the members and the like used for the pressing means. Regardless of these temperature conditions, that is, even if the temperature of the belt drops significantly after passing through the fixing unit, when the belt is brought back to the fixing unit, the belt is always returned to a constant temperature optimal for fixing. Is necessary for stable fixing.

In order to return the belt uniformly and stably to a predetermined temperature, the structure of heat transfer from the heat generating portion to the belt and the structure of the heat generating portion itself are important. No special consideration was given to this point in the heating device.

In general, in the belt system including the above-mentioned conventional example, the heat capacity of the film is set to be small in order to shorten the warm-up time. However, there has been a problem of uneven temperature and partial overheating. . This becomes a more remarkable problem when a recording material having a narrow width in the depth direction in FIG. 12 of the image heating apparatus is continuously passed. In other words, the portion through which the recording material passes must be heated accordingly in order for heat to be deprived by the recording material, but the portion through which the recording material does not pass is similarly heated, because the heat capacity of the heating element is small. The temperature rises steadily. When the recording medium rises abnormally, hot offset occurs when a wide recording material is passed in that state.

Conversely, if the heat generation is limited to prevent hot offset, the portion of the recording material from which the heat has been removed may have a low temperature, resulting in cold offset or unfixed portions.

The present invention solves the problem associated with reducing the heat capacity of these conventional belt-type image heating apparatuses.

Further, since the heat roller is heated by induction heating as in the second conventional example, a heating element such as a heat roller is directly heated by electromagnetic induction. It is described that the heat conversion efficiency is higher and the heat roller surface can be quickly raised to the fixing temperature with less electric power.

However, in a configuration in which a normal metal roller is simply heated by electromagnetic induction as in the above-described conventional example, it is difficult to significantly reduce warm-up as compared with the conventional halogen lamp system. Improving efficiency by induction heating alone is not enough to make the temperature rise time faster,
It is necessary to reduce the heat capacity of the roller itself. If the heat capacity is reduced, temperature unevenness and partial excessive temperature rise become problems as in the case of the belt.

The problem of the temperature unevenness becomes more remarkable when a recording material having a width smaller than the width of the heat roller is continuously passed, and electric power is supplied to maintain the temperature of the central portion where heat is taken by the recording material. Continued addition may cause an abnormal temperature rise in places where heat absorption at both ends is small. This leads to damage to the bearings and the like at both ends, resulting in partial unevenness of the fixed image and deteriorating the image quality.

The present invention also solves the problem associated with reducing the heat capacity of these conventional roller-type image heating devices.

[0017]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a belt, pressing means for pressing the belt to form a nip on the surface side of the belt, and controlling the Curie temperature to a predetermined value. A heating roller having a magnetic permeability set to a value and movably suspending the belt, a conductive member installed in the heating roller, and from outside through the belt,
An image heating device comprising: an exciting unit that excites the heat generating roller; and the conductive member takes a first position and a second position different from the first position. This is an image forming apparatus using this.

The present invention also provides a heating roller having a magnetic permeability with a Curie temperature set to a predetermined value, a pressing member for pressing the heating roller to form a nip, and a conductive member provided in the heating roller. A member, and exciting means for exciting the heat generating roller from outside the heat generating roller, and the conductive member takes a first position and a second position different from the first position. And an image forming apparatus using the same.

The present invention also provides an image heating apparatus having switching means for switching the conductive member between a first position and a second position, and an image forming apparatus using the same.

According to the invention, there is provided an image heating apparatus wherein the conductive member is located at a first position close to the exciting means and is located at a second position far from the exciting means. This is the image forming apparatus used.

According to the present invention, there is provided an image heating apparatus wherein the conductive member is at the first position during a normal operation, and an image forming apparatus using the image heating apparatus.

According to the present invention, there is provided an image heating apparatus and an image forming apparatus using the same, wherein the conductive member has a substantially semicircular cross section having an arc portion having a substantially equal distance from the inner surface of the heat generating roller. is there.

Also, in the present invention, the arc portion of the conductive member opposes the exciting means at a first position and does not oppose it at a second position, and an image heating apparatus using the image heating device. It is a forming device.

According to the present invention, there is provided an image heating apparatus characterized in that the length of the conductive member in the width direction is substantially equal to or less than the excitation width of the heat generating roller by the excitation means, and an image using the image heating apparatus. It is a forming device.

In the present invention, the conductive member is formed at a position opposing the recording material, outside the minimum width of the recording material, and substantially equal to or less than the excitation range of the heat generating roller. And an image forming apparatus using the same.

[0026]

FIG. 12 is a sectional view of an image forming apparatus using an image heating device according to an embodiment of the present invention as a fixing device. The configuration and operation of this device will be described below.

Reference numeral 1 denotes an electrophotographic photosensitive member (hereinafter, photosensitive drum). The surface of the photosensitive drum 1 is uniformly charged to a predetermined negative dark potential V0 by the charger 2 while being rotationally driven at a predetermined peripheral speed in the direction of the arrow.

Reference numeral 3 denotes a laser beam scanner which outputs a laser beam modulated in accordance with a time-series electric digital pixel signal of image information input from an image reading device (not shown) or a host device such as a computer. The surface of the photosensitive drum 1, which is uniformly charged as described above, is scanned and exposed by this laser beam, and the exposed portion has a small absolute value of potential and becomes a bright potential VL, and an electrostatic latent image is formed on the surface of the photosensitive drum 1. It is formed.

Next, the latent image is reversely developed with a negatively charged powder toner by a developing device 4 to be visualized.

The developing device 4 has a developing roller 4a which is driven to rotate.
A thin layer of toner having a negative charge is formed on the outer peripheral surface of the roller to oppose the surface of the photosensitive drum 1, and the absolute value of the developing roller 4a is
Is applied, the toner on the developing roller 4a transfers to only the portion of the photosensitive drum 1 where the light potential VL is applied, and the latent image is visualized. Is done.

On the other hand, a recording material 15 is fed one by one from a paper feeding unit 10 and passes through registration roller pairs 11 and 12 to a nip portion between the photosensitive drum 1 and a transfer roller 13 which is in contact with the photosensitive drum 1. It is sent at an appropriate timing synchronized with the rotation of the photosensitive drum 1. The toner image on the photosensitive drum 1 is sequentially transferred to the recording material 15 by the action of the transfer roller 13 to which the transfer bias is applied. The recording material 15 that has passed through the transfer section is separated from the photosensitive drum 1 and introduced into a fixing device 16, where the transfer toner image is fixed. The recording material 15 to which the image has been fixed and fixed is output to the paper discharge tray 17.

After the separation of the recording material, the surface of the photosensitive drum 1 is cleaned by the cleaning device 5 to remove the residual toner such as toner remaining after transfer, and is repeatedly used for the next image formation.

Next, an image heating apparatus according to an embodiment of the present invention will be described in detail.

FIG. 1 is a sectional view of a fixing device as an image heating device according to a first embodiment of the present invention.

The thin belt 20 is an endless belt whose base material 21 is made of a polyimide resin and has a diameter of 50 mm and a thickness of 5 mm.
As shown in FIG. 2, the surface is coated with a release layer 22 of fluorocarbon resin having a thickness of 5 μm in order to impart a release property. As the material of the base material 21, a very thin metal such as nickel or the like manufactured by electroforming can be used in addition to heat-resistant polyimide or fluororesin. The release layer 22 on the surface may be coated with a resin or rubber having good releasability, such as PTFE, PFA, FEP, silicone rubber, and fluororubber, alone or in combination. For fixing a monochrome image, it is sufficient to secure only the releasability, but when used for fixing a color image, it is desirable to impart elasticity, in which case it is necessary to form a somewhat thick rubber layer .

Numeral 23 denotes an exciting coil as exciting means, which uses a litz wire bundled with thin wires and has a sectional shape formed so as to cover the belt 20 as shown in FIG. Is installed. The core 24 may be made of a material having a high magnetic permeability such as permalloy. FIG. 3 is a view of the structure of the core material 24 and the exciting coil 23 as viewed from the front side of the belt. The exciting coil 23 is formed along the center core material 24 over substantially the entire length of the heat generating roller as shown in FIG. The core material on the back surface exists only in part and is configured to capture magnetic flux leaking to the outside. An alternating current of 30 kHz is applied to the exciting coil 23 from the exciting circuit 25.

Returning to FIG. 1 again, the belt 20 has a low heat conductive fixing roller 43 having a diameter of 20 mm and made of a resilient foamed silicone rubber having a low hardness (JISA 30 degrees), and an alloy described later. It is suspended with a predetermined tension between the heating roller 44 having a diameter of 20 mm and is rotatable in the direction of arrow B. The heat generating roller 44 is made of a magnetic material having a high magnetic permeability made of an alloy of iron, nickel and chromium having a thickness of 0.4 mm, and its Curie temperature is adjusted to 220 degrees by the amount of chromium mixed in the material. Manufactured. Inside the heating roller 44,
An arc portion 45 with a 0.5 mm gap from the heat generating roller 44
A conductive member 45 made of aluminum having a substantially semicircular cross section and having higher conductivity than the heat generating roller 44 is provided. The conductive member 45 has an axial length substantially the same as or slightly shorter than the excitation range of the excitation coil 23, and is rotatably supported by a shaft 46.
3 is fixed at a predetermined position, and the phase can be switched by the switching means 53.

As shown in FIG. 4, the heat generating roller 44 and the conductive member 45 are supported at both ends by flanges 47 and 48 made of heat-resistant resin having a small heat conductivity such as bakelite. The generated heat is not easily transmitted to the conductive member 45. Heating roller 44
Is rotationally driven by a driving unit of the apparatus main body (not shown).

In FIG. 1, the pressure roller 49 has a hardness JI.
The nip is formed by pressing the fixing roller 43 through the belt 20 as shown in FIG. The pressure roller 49 was supported rotatably around the metal shaft 50 in that state. Pressure roller 4
The material 9 may be made of another heat-resistant resin or rubber such as fluoro rubber or fluoro resin. The surface of the pressure roller 49 is made of PFA, PTF, or the like in order to enhance wear resistance and releasability.
A resin or rubber such as E or FEP may be coated alone or as a mixture. In order to prevent heat dissipation, the pressure roller 49
Is preferably made of a material having low thermal conductivity.

In this embodiment, due to the configuration of the heat-generating roller portion, this portion has a self-temperature control characteristic.
The operation will be described below with reference to FIGS.

The conductive member 45 is fixed at a phase in which an arc portion 45 a having a distance substantially equal to that of the heating roller 44 is opposed to the exciting coil 23. Here, an operation in which the image forming apparatus outputs an image on a recording material is referred to as a normal operation, and an operation in which the image forming apparatus warms up to a state in which the image forming apparatus can operate normally is referred to as an unusual operation. As a warm-up operation from a normal temperature (non-normal operation), first, a heating roller 44, a fixing roller 43, a pressure roller 49,
When the excitation coil 23 is driven by the excitation circuit 25 with an alternating current having a frequency of 25 to 30 kHz while the belt 20 is moved, and heating is started, in FIG. Since the portion 44a is at a temperature lower than the Curie point, and the magnetic flux generated by the magnetic field generated by the exciting coil 23 is magnetized by the heat generating roller 44, it is almost generated through the heat generating roller 44 as shown by arrows D and D 'in the figure. Repeated extinction, the induced current generated thereby flows almost only on the surface of the heat generating roller 44 due to the skin effect, and Joule heat is generated at that portion.

Here, in FIG. 8, the curve μ shows the relationship between the magnetic permeability and the temperature of the magnetic material made of an alloy of iron, nickel and chromium used for the heat generating roller 44. In this figure,
The horizontal axis represents the temperature of the material of the heat roller, and the vertical axis represents the magnetic permeability. When the temperature of the heating roller 44 is low, the magnetic permeability shows a high value, the magnetic flux generated by the exciting coil 23 passes through the inside of the heating roller 44 as described above, and the induced current is mostly concentrated on the surface thereof, and heat is generated by Joule heat. The temperature of the roller 44 rises rapidly. The point Tk in the figure represents the Curie temperature, above which the magnetic permeability is almost the same as in air. That is, the magnetic flux generated by the exciting coil 23 is
4 and diverges to the conductive member 45 as well, and the induced current flows overwhelmingly in the conductive member 45 having high conductivity.

In FIG. 6, the heat generating portion 4 of the heat generating roller 44 is provided.
Since the magnetic permeability decreases when the temperature of 4a approaches the Curie temperature, the magnetic flux diverges toward the internal conductive member 45 as shown by arrows E and E 'in the figure, and the induced current is reduced by the conductive member having high conductivity. Since the current flows predominantly in the chamber 45, the conductivity is high, that is, the resistance is low. Therefore, if the current is limited to a constant value, heat generation is significantly reduced, and the temperature is stabilized. According to the calculation, the depth of the portion where the current due to the skin effect flows is about 0.3 mm when the frequency of the exciting current is 30 kHz. If the thickness of the heating roller 44 is equal to or greater than the skin depth, almost all current is generated in the heating roller 44 at low temperatures. As the current frequency is increased, the skin depth becomes smaller, and a thinner heating roller can be used. However, if the frequency of the exciting current is too high, the cost increases and the noise emitted to the outside increases.

The magnetic permeability is about 140 as shown by the curve μ in FIG.
Although the same value is shown up to the degree, the curve goes down from here to the Curie point Tk by drawing a gradual curve. That is, the magnetic permeability gradually decreases, and accordingly, the amount of the magnetic flux transmitted through the heating roller 44 also gradually increases, so that the magnetic flux passing through the conductive member 45 increases, and the induced current generated in the conductive member 45 increases. . As a result, the temperature rise rate of the heating roller gradually decreases from around 140 degrees, and the temperature stabilizes at around 190 degrees.

FIG. 9 shows the heating time of the heating roller 44,
The horizontal axis represents the temperature rise time, and the vertical axis represents the temperature of the heat generating roller. In FIG. 9, the curve A represents the temperature rise time when the arc portion 45a of the conductive member 45 and the exciting coil 23 are in a phase opposing each other as described above. The speed becomes slow and is stable around 190 degrees.

Here, the conductive member 45 is connected as shown in FIG.
When an arc portion 45a having a substantially constant distance from the heat roller 44 is fixed at a position not facing the excitation coil 23 and the excitation coil 23 is energized, when the temperature of the heat roller 44 is low, the magnetic fluxes are indicated by arrows D and D 'in the figure. Even if the temperature rises and the magnetic permeability decreases, the distance between the conductive member 45 and the arc portion 45a of the conductive member 45 is long, that is, the magnetic field is out of the range of the magnetic field generated by the exciting coil 23. Therefore, almost no magnetic flux passes through the conductive member 45 as indicated by arrows E and E 'in the figure, so that the induced current hardly flows through the heat generating roller 44, and the heating rate hardly changes. A curve B in FIG. 9 shows a case where the arc portion 45a of the conductive member 45 does not face the exciting coil 23. In this embodiment, the heating roller 4
4 rose to 190 degrees and continued to rise thereafter.

Here, when energization is started from a state in which energization to the excitation coil 23 is not performed (during non-normal operation), the conductive member 45 is moved to the second position, that is, the arc portion 45a is opposed to the excitation coil 23. The heating roller 4
4 is near the Curie temperature. In this case, when the temperature reaches around 190 ° C. (during normal operation), the temperature rises when the arc portion 45 a of the conductive member 45 is switched to the first position, that is, the position facing the exciting coil 23. When the warming time was represented, it became like the curve C of FIG. In this embodiment, with the above setting, the heat generating roller rose to 190 degrees in about 15 seconds, and after a slight overshoot, stable temperature control was realized at about 190 degrees.

As described above, the arc portion 45a of the conductive member 45
Starts at a phase (second position) in which the heating roller 4 is not opposed to the exciting coil 23, and
When the surface temperature of No. 4 rises to near the Curie temperature (during normal operation), when the arc portion 45a of the conductive member 45 is switched to the phase (first position) facing the exciting coil 23,
The heating time is almost the same as the case without self-temperature control,
The effect of self-temperature control such that the steady temperature is stabilized can be obtained.

The fixing device constructed as described above is
To which the toner image has been transferred by the image forming apparatus
1 was projected from the direction of arrow F with the surface of the toner 35 facing upward as shown in FIG. 1 to fix the toner on the recording material 15.

According to the above embodiment, since the heat generating roller itself has the self-temperature control characteristic, the temperature of the heat generating portion does not become abnormally high. You can do it. The conductive member has substantially the same length as the exciting width of the exciting coil, and acts on a partial temperature difference in the depth direction of FIG. Therefore, even if the recording material having a small width is continuously passed, the portion where the recording material does not pass does not become abnormally high in temperature, and hot offset does not occur even after passing through the wide recording material. .

Further, since the material and thickness of the heat roller can be set independently of the belt, an optimum material and thickness can be selected for self-temperature control, and the heat capacity of the belt is different from that. Since it can be set, the optimal value can be selected.

On the other hand, since the fixing roller itself has a low thermal conductivity and is made of a foam, the presence of internal voids makes it difficult for the heat generated by the belt to escape, thereby improving the efficiency.

In this embodiment, in order to achieve the object of shortening the warm-up time, the heat capacity of the belt is set as small as possible, and the heat capacity of the heat roller is also set small by reducing the thickness of the heat generating roller. When the thickness of the heat generating roller is reduced as in the present embodiment in order to speed up the rise and the heat capacity of the heat roller reaches a level equivalent to the heat capacity of the belt, the amount of heat stored in the heat generating roller becomes very small. Even if heat is stored in the heat generating roller, the temperature usually drops immediately. In other words, in a method in which heat is applied to the heat-generating roller once at a place other than the contact portion with the belt to thereby heat the belt, it is necessary to heat the heat-generating roller itself to a considerably high temperature in order to apply sufficient heat to the belt. There is. Furthermore, the belt that is cooled when passing through the nip may be cooled to a significantly different temperature depending on the temperature of the pressure roller and the fixing roller and the temperature of the recording material at that time. Therefore, in the above-described method, the temperature of the heat generating roller must be set to a significantly different temperature accordingly.

In the present embodiment, however, heat is generated at the portion of the heat generating roller that is in contact with the belt, so that the heat required for the belt is immediately transmitted, so that the temperature of the heat generating roller does not need to be raised more than necessary. Also, since there is almost no heat generation at the position of the heating roller past the contact portion with the belt, the temperature of this portion is controlled to be kept constant, so that the temperature of the belt entering the nip portion is always kept constant. Thus, stable fixing can be performed regardless of the temperature state of the pressure roller and the like.

In this embodiment, since the heat capacity of the belt is small, when the belt starts to contact the recording material, the recording material begins to lose heat, and when the belt passes through the nip, the temperature drops considerably. Will not be hot offset.

In this embodiment, the belt is made of resin.
If metal is used instead, some heat will be generated in this belt, but if the thickness is extremely small, most of the magnetic flux described above will pass through this and reach the heat roller, so similar self-temperature control etc. Function can be performed.

In the present embodiment, the heat generating portion is located inside the belt, while the exciting coil and the core material can be installed outside the belt. Therefore, the temperature of the exciting coil and the like is hardly increased due to the temperature of the heat generating portion. Can be kept stable.

In the present embodiment, the heat generating roller 44 and the conductive roller 45 are thermally separated from each other. However, even if they are brought into close contact with each other, the self-temperature control characteristic can be similarly obtained.
In this case, the heat capacity of the heat generating roller part is slightly increased, and the warm-up time is correspondingly long.

Next, an image heating apparatus according to a second embodiment will be described with reference to FIG.

In the second embodiment, portions having the same configuration and the same function as those of the fixing device of the first embodiment are given the same reference numerals, and detailed description thereof will be omitted.

Reference numeral 44 denotes an exothermic roller having a thickness of 0.4 mm.
nickel. It is made of a magnetic material made of a chromium alloy, and is manufactured so as to have a Curie point of 250 degrees. The heat generating roller 44 has a diameter of 30 mm, and its surface is coated with a 15 μm-thick release layer of a fluororesin in order to impart release properties. PTF as the release layer on the surface
A resin or rubber having good releasability such as E, PFE, FEP, silicone rubber, and fluoro rubber may be coated alone or in combination. As a fixing device for a monochrome image, only the releasability may be secured, but when used as a fixing device for a color image, it is desirable to impart elasticity, in which case it is necessary to form a somewhat thick rubber layer. There is.

Reference numeral 23 denotes an exciting coil as exciting means, which uses a litz wire bundled with thin wires and has a sectional shape formed so as to cover the heat generating roller 44 as shown in FIG. A core member 24 made of ferrite is provided. As in the first embodiment, the exciting coil 23 is formed over the substantially entire length of the heat generating roller 24 along the central core member 24, and the core member 24 on the back surface exists only in a part and removes magnetic flux leaking to the outside. It is configured to supplement. Similarly, an alternating current of 25 to 30 KHz is applied to the exciting coil 23 from the exciting circuit 25.

The heating roller 44 is provided inside the heating roller 44.
A conductive member 45 made of aluminum having a substantially semicircular cross section having a circular arc portion 45 a with a gap of 0.5 mm and having a higher conductivity than the heat generating roller 44 is provided. The conductive member 45 is rotatably supported by a shaft 46, the phase with the exciting coil 23 is fixed at a predetermined position, and the phase can be switched by a switching unit 53.

In FIG. 11, the length in the width direction of the conductive member 45 corresponds to the position where the non-recording material 15 passes, and is substantially the same as the length of the central core material 24 from outside the minimum width of the recording material 15. The shaft 46 is formed at both ends.

The heat-generating roller 44 and the conductive member 45 are supported at both ends by flanges 47 and 48 made of heat-resistant resin such as bakelite, which has a small heat conductivity. The heat generated by the heat-generating roller 44 is hardly transmitted to the conductive member 45. Has become.

The heat generating roller 44 is rotatably supported by a bearing 51, and is driven to rotate by driving means (not shown) of the apparatus main body.

Referring again to FIG. 10, the pressure roller 49 is made of silicon rubber having a low hardness (JISA 30 degrees), and presses against the heat generation roller 44 to form a nip.
The pressure roller 49 was rotatably supported around a metal shaft 50 by being driven. The material of the pressure roller 44 may be made of another heat-resistant resin or rubber such as fluorine rubber or fluorine resin, or may be made of a foam. Further, PFA, PTF and the like are provided on the surface of the pressure roller 49 in order to enhance abrasion resistance and mold release properties.
A resin such as E or FEP or a rubber may be coated alone or as a mixture.

Reference numeral 52 denotes a temperature detecting sensor which is a heating roller 44.
The heating roller 44 is disposed substantially at the center in the axial direction so as to detect the surface temperature of the heating roller 44. This temperature sensor 52
Is output to the excitation circuit 23 to control the power supplied to the excitation coil.

Also in this embodiment, similar to the first embodiment, the above-mentioned heat generating portion has a self-temperature control characteristic in this portion. The operation will be described below.

The conductive member 45 rotates the heat generating roller 44 by driving means (not shown) in a state where the arc portion 45 a is fixed at a phase (second position) not opposed to the exciting coil 23, and the frequency 25 is fixed by the exciting circuit 25. When the excitation coil 23 is driven by an alternating current of 30 kHz to start heating (non-normal operation), the heating portion 44a of the heating roller 44 facing the excitation coil 23 in FIG. 5 is at a temperature below the Curie point, The magnetic flux generated by the exciting coil 23 almost passes through the inside of the heat roller 44 as shown by arrows D and D 'in the figure, and the temperature of the heat roller 44 is raised. In this case, the conductive member 45 is located far from the exciting coil 23 and is almost out of the range of the magnetic field. Regardless of the shape of the conductive member 45 in the width direction, the magnetic flux almost penetrates through the heating roller 44. I do. When the temperature of the heat generating roller 44 is increased and it is detected from the output of the temperature sensor 52 that the temperature has been increased to a predetermined temperature (190 degrees in the present embodiment), the excitation circuit 25 detects the surface temperature of the heat generating roller 44 thereafter. The output is controlled to maintain a predetermined temperature, and the surface temperature of the heat generating roller 44 is maintained at the predetermined temperature. Until the temperature sensor 52 detects a predetermined temperature, even if the temperature of the heat generating roller rises, the magnetic flux is generated because the distance between the arc portion 45a of the conductive member 45 and the exciting coil 23 is long as shown in FIG. The magnetic field generated by the coil 23 is almost out of the range, and there is almost no magnetic flux passing through the conductive member 45 as indicated by arrows E and E 'in FIG. The temperature of the heat generating roller 44 is substantially uniformly increased over the excitation width. When the temperature sensor 52 detects a predetermined temperature, a normal operation state is set, and the arc portion 45a of the conductive member 45 is moved to a position (first position) facing the exciting coil 23 by the switching means 53. Can be switched.

The fixing device constructed as described above is
As shown in FIG. 10, the recording material 15 having the minimum width onto which the toner image has been transferred by the image forming apparatus shown in FIG. The above toner was fixed.

The surface temperature of the heating roller 44 at the portion where the recording material 15 has passed decreases, the temperature is detected by the temperature sensor 52, and power is supplied by the excitation circuit 25 to recover the decrease. Then, a strong magnetic flux flows at both ends of the heating roller 44 other than the portion where the recording material 15 has passed, in order to increase the temperature. As shown by arrows E and E ′ in FIG. 15 diverges to the conductive member 45 formed outside the position corresponding to the position 15, and the induced current flows predominantly in the conductive member 45 having high conductivity. The temperature was remarkably reduced, the temperature was stabilized, and in the case of the present example, it was almost stabilized at 220 degrees.

The temperature of the portion where the recording material 15 of the heating roller 44 passes decreases, and the magnetic permeability becomes larger than that of both ends, and the heating roller 44 does not face the conductive member 45. Therefore, arrows D and D 'in FIG. As described above, the magnetic flux almost penetrates through the heat roller 44, the induced current flows through the heat roller 44, the surface temperature recovers, and the output of the temperature sensor 52 causes a predetermined temperature (190 degrees in the present embodiment). When the recovery is detected, the output of the excitation circuit 25 is controlled so that the surface temperature of the heat roller 44 is maintained at a predetermined temperature, and the surface temperature of the heat roller 44 is maintained at the predetermined temperature.

In this embodiment, warm-up is started (non-normal operation) at a phase (second position) in which the arc portion of the conductive member does not face the exciting coil, and the temperature of the heat generating roller reaches a predetermined temperature. Is detected, and the conductive member is switched to the phase (first position) facing the exciting coil (during normal operation). Safety is ensured.

In this embodiment, since the conductive member is formed over the excitation range of the heating roller from the outside of the minimum width of the recording material, almost all of the magnetic flux is always applied to the heating roller where the recording material has passed. Passes through, so that more magnetic flux passes through the heat generating roller than when the conductive member is formed over the entire width, the amount of heat generation also increases, and when the recording material passes continuously, the recording material passes. Even when the speed is high, the temperature of the heat generating roller can be recovered, and it is possible to cope with a higher speed range.

In this embodiment, the heat generating roller itself has a self-temperature control characteristic and acts also on a partial temperature difference in the depth direction in FIG. Even if the recording material having a small width continuously passes, the portion through which the recording material does not pass does not become abnormally high in temperature, and the heat capacity of the heat generating roller is configured to be small. In this case, the temperature of the heat generating roller drops quickly, and hot offset does not occur even after passing through a wide recording material.

Further, since there is almost no heat generation at a position passing through the exciting coil opposite to the exciting coil, the temperature of the heating roller entering the nip is controlled by controlling the temperature of this portion to be kept constant. The temperature can be kept constant, and stable fixing can be performed irrespective of the temperature state of the pressure roller and the like.

In this embodiment, the exciting coil and the core material are installed outside the heat generating roller, and the exciting coil and the like are hardly heated by the influence of the temperature of the heat generating portion, and the heat generation amount is stably maintained. Can be.

In the first and second embodiments, a conductive member is provided inside the heat roller and an exciting coil is provided outside. However, an exciting coil may be provided inside the heat roller and a conductive member may be provided outside. It is possible to obtain a similar effect.

In the first and second embodiments, aluminum is used as the conductive member. However, other highly conductive metals such as copper can be used. The same effect can be obtained with other alloys that can set the Curie temperature for the heat generating roller.

In the first and second embodiments, the temperature of the heat generating roller is set as an object for detecting the timing of switching the position of the conductive member. Even if there is no problem, it is sufficient to adopt an optimal target in the configuration.

Further, in the first and second embodiments, the conductive member has a substantially semicircular cross section having an arc portion having a substantially equal distance from the inner surface of the heat generating roller. However, it is possible to obtain a similar effect.

In the first and second embodiments, the position (phase) of the conductive member and the exciting coil is switched between facing and non-facing depending on the first position and the second position. The same effect can be obtained by switching between when the distance is increased and when the distance is increased.

Further, in the first and second embodiments, the whole conductive member having a substantially semicircular cross section is made of a metal having high conductivity. However, only the part facing and separating from the heat roller needs to be conductive. The same effect can be obtained even if the other parts are made of another material, for example, a synthetic resin.

In the first and second embodiments, the image heating apparatus for a monochrome image is described. However, by changing the surface of the belt or the surface of the roller, the image heating apparatus for a color image can be sufficiently obtained. Can be used.

[0086]

As described above, according to the present invention, the heat capacity of the belt as the object to be heated and the heat roller as the heat generating element can be set very small. Up time can be extremely small. Further, even if the heat capacity of the heat generating roller is set to be small, the temperature of the heat generating roller can be set low due to heat generated at the belt contact portion.

By setting the thickness of the heat generating roller larger than the skin depth, uniform heat generation without unevenness can be achieved.

Further, the self-temperature control provides stable temperature control and causes a hot offset or heat generation without excessively increasing the temperature of a portion where the recording material does not pass even if the recording material having a narrow width passes continuously. The amount does not become unstable and damage to the exciting coil and the like due to heat can be prevented.

Also, the increase in warm-up time due to the decrease in the amount of heat generated near the Curie point due to self-temperature control can be achieved by switching the phase of the conductive member to allow the induced current to flow through the conductive member, or by concentrating on the heat generating roller. By switching to the case where the temperature control is performed, it is possible to obtain a warm-up time substantially equal to that in a case where the temperature is suppressed to a minimum and the self-temperature control is not performed.

Further, since the exciting means and the core material can be installed outside the belt, a stable heating value can be obtained without exposing the exciting means and the core material to a high temperature.

[Brief description of the drawings]

FIG. 1 is a sectional view of an image heating apparatus according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a belt used in the image heating apparatus according to the first embodiment of the present invention.

FIG. 3 is a front view showing an excitation coil and a core material used in the image heating apparatuses according to the first and second embodiments of the present invention.

FIG. 4 is a cross-sectional view of a heating roller used in the image heating apparatus according to the first embodiment of the present invention.

FIG. 5 is a view for explaining the flow of magnetic flux passing through a heating roller used in the image heating apparatus according to the first and second embodiments of the present invention when the conductive member is at a second position and in a low temperature state.

FIG. 6 is a diagram illustrating a flow of a magnetic flux passing through a heat roller used in the image heating apparatus according to the first and second embodiments of the present invention when the conductive member is at a second position and in a high temperature state.

FIG. 7 is a view showing the first embodiment of the present invention when the conductive member is at the first position;
For explaining the flow of magnetic flux passing through a heat generating roller used in the image heating apparatus of the second embodiment and FIG.

FIG. 8 is a diagram illustrating the relationship between the magnetic permeability and the temperature of the heat generating roller used in the image heating apparatus according to the first embodiment of the present invention.

FIG. 9 is a diagram illustrating a heating time of a heat generating roller used in the first embodiment of the present invention.

FIG. 10 is a sectional view of an image heating apparatus according to a second embodiment of the present invention.

FIG. 11 is a sectional view of a heat roller of an image heating apparatus used in a second embodiment of the present invention.

FIG. 12 is a sectional view of an image forming apparatus using the image heating apparatus according to the first and second embodiments of the present invention.

FIG. 13 is a cross-sectional view of a first conventional image heating apparatus.

FIG. 14 is a cross-sectional view of a second conventional image heating apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 16 Fixing device 20 Belt 23 Excitation coil 24 Core material 43 Fixing roller 44 Heating roller 45 Conductive member 49 Pressure roller 53 Switching means 15 Recording material

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Terada 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Terms (reference) 2H033 BA11 BB01 BB18 BB28 BE06 3K059 AA08 AB00 AB19 AB20 AB28 AC34 AC37 AC73 AD05 AD07 AD15 AD34 BD17 CD19 CD66 CD73 CD77

Claims (10)

[Claims] 1. A belt, a pressure means for pressing the belt to form a nip on the surface side of the belt, and a magnetically permeable material having a Curie temperature set to a predetermined value, the belt being movably suspended. A heat generating roller, a conductive member installed in the heat generating roller, and an exciting unit for exciting the heat generating roller from outside through the belt, and the conductive member has a first position An image heating apparatus, which takes a second position different from the first position. 2. A heating roller having a magnetic permeability in which a Curie temperature is set to a predetermined value, a pressing member for pressing the heating roller to form a nip, and a conductive member disposed in the heating roller. Exciting means for exciting the heat roller from outside the heat roller, and wherein the conductive member takes a first position and a second position different from the first position. Image heating device. 3. An image heating apparatus according to claim 1, wherein said conductive member has a switching means for switching between a first position and a second position. 4. The image heating apparatus according to claim 1, wherein the conductive member is located at a position closer to the exciting means in a first position, and is located far from the exciting means in a second position. apparatus. 5. The image heating apparatus according to claim 1, wherein the conductive member is at a first position during a normal operation. 6. The image heating apparatus according to claim 1, wherein the conductive member has a substantially semicircular cross section having an arc portion having a substantially equal distance from the inner surface of the heat generating roller. 7. The image heating apparatus according to claim 6, wherein the arc portion of the conductive member faces the exciting unit at a first position and does not face the exciting unit at a second position. 8. The image heating apparatus according to claim 1, wherein the length of the conductive member in the width direction is substantially equal to or less than the excitation width of the heat generating roller. 9. A conductive member is provided at a position corresponding to a recording material.
9. The image heating apparatus according to claim 1, wherein the recording material is formed outside the minimum width of the recording material and substantially equal to or less than the excitation range of the heat generating roller. 10. An image forming apparatus comprising: an image forming means for forming and carrying an unfixed image on a recording material; and a heat fixing device for thermally fixing the unfixed image to the recording material. An image forming apparatus, which is the image heating apparatus according to any one of 1 to 9.