JP3324377B2 - Fixing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device which is used in an image forming apparatus such as an electrophotographic copying machine, a printer and a facsimile and fixes a toner image on a recording medium.

[0002]

2. Description of the Related Art In an electrophotographic copying machine, a toner (developer) of a toner image (unfixed image) transferred onto a sheet such as recording paper or a transfer material as a recording medium to be conveyed is used.
Is fused by heat to fuse the sheet onto the sheet.

There are various types of this fixing device, such as a roller heating system and a film heating system disclosed in Japanese Patent Application Laid-Open No. 5-66688. However, energy saving (low power consumption) of the fixing device and user The improvement of operability (quick print) has been attracting much attention and has been emphasized.

As a fixing device meeting such a demand, there has been proposed an induction heating type fixing device in which electric-to-heat conversion efficiency is improved by utilizing high frequency induction. In this induction heating fixing device, an induced eddy current is induced in a metal body by a high-frequency magnetic field generated by flowing a high-frequency current through an induction coil, and the metal body itself is caused to generate Joule heat by a skin resistance of the metal body itself.

[0005]

In an induction heating fixing device, a metal body functions as a heating element, but quick printing can be realized by shortening the preheating time even by reducing the heat capacity of the heating element. Therefore, it is conceivable to reduce the thickness of the metal body.

However, as the thickness of the metal body is reduced, heat conduction in the longitudinal direction of the metal body hardly occurs.

For this reason, in a mode in which a sheet having a size smaller than the maximum sheet passing width frequently generated in a copying machine or the like is continuously passed, the temperature of the metal body in the non-sheet passing area is lower than the temperature regulation temperature. As a result, the temperature difference between the temperature in the paper passing area and the temperature in the non-paper passing area becomes extremely large. Due to such temperature unevenness in the longitudinal direction of the metal body, there is a possibility that the heat-resistant life of the peripheral member made of the resin material may be reduced, or the metal member may be thermally damaged. Further, when a large-sized sheet is passed immediately after the mode, there is a problem that a so-called high-temperature offset that causes partial unevenness in fixability occurs.

It is to be noted that the present invention is not limited to the induction heating type fixing device using a thin metal body that generates heat. In a fixing device using a film or the like, due to a rise in the temperature of the heated object in the non-sheet passing area, the temperature unevenness in the longitudinal direction of the thin-walled heated object becomes remarkable, and the above-described reduction in the heat-resistant life of the peripheral members and high temperature Problems such as offset generally occurred.

Therefore, in the fixing device, it is necessary to suppress the temperature unevenness in the longitudinal direction of the thin-walled heated body while responding to the request for the quick print. Further, the tendency of the temperature rise of the heated member in the non-sheet passing area greatly differs depending on the number of sheets continuously passed, the size of the sheet passed, and the like. It is also necessary to suppress the temperature unevenness of the thin-walled heated object in response to the change.

[0010]

[0011] The present invention solves the above-mentioned problems associated with the prior art.
In order to stabilize the fixing performance regardless of the paper feeding mode, the temperature unevenness in the longitudinal direction of the thin object to be heated is appropriately suppressed in accordance with the change in the use condition of the fixing device. and purpose thereof is to provide a fixing device capable of ensuring.

[0012]

[0013]

[0014]

[0015]

The invention of claim 1 to achieve the object above Symbol of SUMMARY OF THE INVENTION may, developer unfixed image formed on a recording medium conveyed, it melted by the recording by heat A fixing device for fusing on a medium, comprising: a heating source; a thin-walled heated body that is heated by the heating source and is movably provided along a conveyance direction of the recording medium; And a pressing member that slides in contact with the holding member and the object to be heated via the recording medium conveyance path, and presses against the holding member and the object to be heated. The holding member is provided with at least two nip portions for holding the recording medium in a switchable manner, and each of the nip portions is made of a material having good thermal conductivity along a longitudinal direction of the holding member. Providing a heat diffusing means; A fixing device comprising at different respective thermal conductivity of diffusing means.

In the fixing device configured as described above, when at least two nip portions provided on the holding member are selectively switched, the heat diffusing means having different thermal conductivity faces the nip position. When the conditions of use of the fixing device change, the tendency of the temperature of the heated object in the non-sheet passing area is different. However, by selectively facing the desired heat diffusion unit to the nip position, the thin heated object is heated. Temperature unevenness in the longitudinal direction of the fixing device can be suitably suppressed in accordance with a change in the use condition of the fixing device. As a result, the heat-resistant life of the peripheral member made of the resin material is not shortened or suffers thermal damage.Furthermore, immediately after the mode in which a recording medium having a smaller size than the maximum paper passing width is continuously passed. Even when a large-sized recording medium is passed, partial unevenness in the fixability does not occur.

Further, the switching between the at least two nip portions is performed based on whether or not preheating of the object to be heated is completed.

Until the preheating of the object to be heated is completed, if the heat diffusing means having the smaller thermal conductivity faces the nip position, the rapid heating of the object to be heated is not hindered. When the preheating is completed, the heat diffusing means having the higher thermal conductivity is switched to the nip position, and in response to a change in the use condition of the fixing device such as whether or not the preheating of the object to be heated is completed, a non- The temperature rise in the paper passing area can be reduced, and the temperature unevenness in the longitudinal direction of the object to be heated can be suitably suppressed, and stable fixing performance can be obtained.

Further, the switching between the at least two nip portions is performed based on whether or not a predetermined number of sheets are continuously passed.

When the continuous paper passing operation is performed, the temperature unevenness in the longitudinal direction of the object to be heated tends to increase. When the number of continuous paper passing exceeds a preset number, by switching the heat diffusing means having the higher thermal conductivity to the nip position, the continuous paper passing operation changes in the use condition of the fixing device. Correspondingly, the temperature rise in the non-sheet passing area can be reduced, and the temperature unevenness in the longitudinal direction of the heated object can be suitably suppressed, and stable fixing performance can be obtained.

Further, the switching between the at least two nip portions is performed based on the size of the recording medium.

When a recording medium having a size larger than a predetermined size is passed, the heat diffusing means having a smaller thermal conductivity faces the nip position, and when a recording medium having a size smaller than the predetermined size is passed, the thermal conductivity becomes smaller. If the larger heat diffusion means faces the nip position, the temperature rise in the non-sheet passing area is reduced in response to a change in the use condition of the fixing device that the size of the recording medium to be passed is different. Temperature unevenness in the longitudinal direction of the object to be heated can be suitably suppressed, and stable fixing performance can be obtained.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. << Embodiment 1 >> FIG. 1 is a sectional view schematically showing an induction heating type fixing device according to Embodiment 1 of the present invention.

As shown in FIG. 1, the induction heating fixing device comprises:
A coil assembly 10 for melting a developer of an unfixed image formed on a conveyed recording medium by heat and fusing the developer on the recording medium, and generating a high-frequency magnetic field
A metal sleeve 11 (corresponding to a heat-generating metal body) which is heated by the coil assembly 10 and is movable along the transport direction of the recording medium 14, and a fixed holder with which the metal sleeve 11 is in sliding contact. And a pressure roller 13 (corresponding to a pressing member) which faces the holder 12 and the metal sleeve 11 and presses them against the holder 12 and the metal sleeve 11 via the conveyance path of the recording medium 14. The pressure roller 13 is rotatably provided in the direction of arrow a in FIG. 1, and the metal sleeve 11 is sandwiched between the pressure roller 13 and the holder 12, and is rotated by the rotation of the pressure roller 13.

The recording medium 14 to which the unfixed toner image has been transferred, that is, the sheet, is conveyed from the left as shown by the arrow b in FIG. 1 and is sent toward the nip 23 that holds the sheet 14 therebetween. The sheet 14 is conveyed through the nip 23 while the heat of the heated metal sleeve 11 and the pressure applied from the pressure roller 13 are applied. Thus, the unfixed toner is fixed, and a fixed toner image is formed on the sheet 14. The sheet 14 that has passed through the nip 23 is separated from the metal sleeve 11 by a separation claw 15 whose leading end abuts on the surface of the metal sleeve 11, and is conveyed rightward in FIG. The sheet 14 is conveyed by a discharge roller (not shown) and discharged onto a discharge tray.

The metal sleeve 11 is a thin hollow metal conductor having flexibility, for example, nickel, iron, SU
It is formed of a conductive magnetic material such as S430. The outer peripheral surface of the metal sleeve 11 is coated with a fluororesin to form a heat-resistant release layer. The thickness of the metal sleeve 11 is 20 μm to 60 μm.

Inside the metal sleeve 11, a coil assembly 10 for generating a high-frequency magnetic field is provided to induce an induced current (eddy current) in the metal sleeve 11 to generate Joule heat. This coil assembly 1
0 is held inside the holder 12. Holder 12
Are fixed to a fixing unit frame (not shown) and are non-rotating.

The coil assembly 10 includes a core 16 made of a magnetic material, a bobbin 17 having a through hole for inserting the core 16, and a metal sleeve formed by winding a copper wire around the bobbin 17. 11 has an induction coil 18 (corresponding to a heating source) for inducing an induced current for heating. The bobbin 17 functions as an insulating part that insulates the core 16 from the induction coil 18. The coil assembly 10 is housed in the holder 12 formed separately from the bobbin 17 so as not to be exposed to the outside.

[0029] Holder 12, bobbin 17 and separation claw 15
Is made of heat-resistant insulating engineering plastic.

The pressure roller 13 is composed of a shaft core 19 and a silicon rubber layer 20 formed around the shaft core 19, which is a surface-releasable heat-resistant rubber layer.

Above the metal sleeve 11, a temperature sensor 21 for detecting the temperature of the metal sleeve 11 is provided. The temperature sensor 21 is in pressure contact with the surface of the metal sleeve 11 so as to face the induction coil 18 with the metal sleeve 11 interposed therebetween. The temperature sensor 21 is composed of, for example, a thermistor, and while the temperature of the metal sleeve 11 is detected by the thermistor, energization to the induction coil 18 is controlled so that the temperature of the metal sleeve 11 becomes an optimum temperature.

Above the metal sleeve 11, a thermostat 22 is provided as a safety mechanism in the event of abnormal temperature rise. The thermostat 22 is in contact with the surface of the metal sleeve 11, and when a predetermined temperature is reached, the contact is opened to cut off the power supply to the induction coil 18,
The temperature of the metal sleeve 11 is prevented from being higher than a predetermined temperature.

The holder 12 of the first embodiment has, in particular,
At the position of the nip portion 23, a heat diffusion means 24 made of a material having good thermal conductivity and non-magnetic properties is provided along the longitudinal direction (axial direction) of the holder 12.

The heat diffusion means 24 has an arc-shaped cross section, and its arc surface is smoothly connected to the outer peripheral surface of the holder 12 so as not to hinder the smooth sliding of the metal sleeve 11.
The heat diffusion means 24 is preferably a relatively long form having the same length as the dimension along the longitudinal direction of the holder 12, but a relatively short form is preferable as long as good heat transfer in the longitudinal direction can be realized. A plurality of holders 12 may be arranged along the longitudinal direction. In the case of the latter configuration, the holder 12 may be arranged “dense” near both ends in the axial direction, and may be arranged “rough” at the center in the axial direction.

Materials having good thermal conductivity and non-magnetic properties include those having a relative magnetic permeability of approximately 1 and a thermal conductivity of approximately 200.
A material of W / (mk) or more (at 200 ° C.) is suitable, and the thermal diffusion means 24 is specifically formed of aluminum, silver, copper, or an alloy thereof.
Further, ceramics having improved thermal conductivity can also be used.
The material of the thermal diffusion means 24 is selected and the cross-sectional area is determined so that the thermal conductivity has a predetermined value.

Next, the operation will be described.

When a high-frequency current is applied to the induction coil 18, the heat diffusion means 24 is made of a material having non-magnetic characteristics, so that the induction current is hardly generated and hardly generates heat. An electric current is induced to generate heat. Since the heat diffusion means 24 is in contact with the metal sleeve 11 which is a heating element, the heat of the metal sleeve 11 is taken by the heat diffusion means 24.
However, the induction heating method has a high heat generation efficiency, and the metal sleeve 11 is formed to be thin to reduce the heat capacity, so that the temperature of the metal sleeve 11 rises at a high speed. For this reason,
The advantage of the induction heating fixing device that the preheating time and the power consumption are reduced is not substantially impaired.

Further, since the heat diffusing means 24 which is in contact with the metal sleeve 11 is made of a material having good heat conductivity, the heat conduction in the longitudinal direction of the metal sleeve 11 is improved, and the heat of the metal sleeve 11 is reduced in the longitudinal direction. It is easy to be transmitted to. For this reason, even in a mode in which a sheet 14 having a size smaller than the maximum sheet passing width is continuously passed, heat in the non-sheet passing area is conducted to the sheet passing area through the heat diffusion means 24 and the metal sleeve 1
The temperature difference between the temperature in the one sheet passing area and the temperature in the non-sheet passing area becomes smaller. In this way, the temperature rise in the non-sheet passing area is reduced, and the temperature unevenness in the longitudinal direction of the metal sleeve 11 is suppressed. As a result, the heat resistance life of the peripheral members such as the separation claw 15 made of a resin material is reduced or the thermal resistance is reduced. No damage is caused, and even when a large-sized sheet 14 is passed immediately after the mode,
High-temperature offset can be prevented without causing partial unevenness in fixability.

As described above, according to the first embodiment, it is possible to suppress the temperature unevenness in the longitudinal direction of the metal sleeve 11 that generates heat, and to realize stable fixing performance in any paper passing mode. .

Second Embodiment FIGS. 2A and 2B are cross-sectional views schematically showing a fixing device according to a second embodiment of the present invention. Are denoted by the same reference numerals, and description thereof will be omitted. 2, the separation claw 15, the temperature sensor 21, and the thermostat 22 are not shown.

The second embodiment is an induction heating fixing device using a metal sleeve 11 as in the first embodiment. However, the second embodiment is different from the first embodiment in that a plurality of nip portions 31 and 32 are provided in a holder 30. This is different from the first mode.

As shown in FIG. 2, the induction heating fixing apparatus according to the second embodiment also includes a coil assembly 10, a metal sleeve 11 (corresponding to a heated object), and a metal sleeve 11 sliding. A contacting holder 30 (corresponding to a holding member), a pressing roller 13 (corresponding to a pressing member),
Having.

The holder 30 according to the second embodiment has, in particular,
The two nip portions 31 and 32 are provided so as to be switchable, and are provided on each of the nip portions 31 and 32 along the longitudinal direction of the holder 12.
First and second heat diffusion means 33 and 34 made of a material having good thermal conductivity are provided. Further, the thermal conductivity of the first thermal diffusion means 33 and the thermal conductivity of the second thermal diffusion means 34 are different.

Since the fixing device of the second embodiment is of the induction heating type, the heat diffusion means 33 and 34 are formed of a material having further non-magnetic characteristics. The configuration and specific materials of the first and second heat diffusion units 33 and 34 are the same as those of the first embodiment, and thus the description thereof is omitted.

In order to make the thermal conductivity of the first and second heat diffusing means 33 and 34 different, each of the heat diffusing means 33 and 34 is formed of a material having a different thermal conductivity. The material of the means 33 is aluminum, and the material of the second heat diffusion means 34 is copper. Since copper has a higher thermal conductivity than aluminum, the second heat diffusion means 3
4 has higher thermal conductivity than the first heat diffusion means 33.

The number of switchable nip portions is 2
The number is not limited to three, and three or four may be provided.
Further, since the thermal conductivity is affected by both the thermal conductivity and the cross-sectional area, when the same material is used, the cross-sectional areas of the heat diffusing means 33 and 34 should be different as shown in FIG. The thermal conductivity can also be varied depending on the temperature.

The holder 30 does not rotate during normal printing, but is rotatable only when the two nip portions 31 and 32 are selectively switched. As conceptually shown in FIG. 4, a groove 35 is formed at an end of the holder 30, and a claw 36 that engages with the groove 35 is swingably provided on the apparatus main body. When the claw portion 36 is engaged with the groove portion 35, the holder 30 is in a non-rotational state, and when the claw portion 36 swings and is disengaged from the groove portion 35, the holder 30 is in a rotation-free state. When the pressure roller 13 is driven to rotate while the holder 30 is in a rotation-free state, the holder 30 is driven to rotate together with the metal sleeve 11. When it is detected that the holder 30 has rotated by a predetermined angle based on the amount of rotation of the pressure roller 13 and the like, the claw portion 36 is swung to be engaged with the groove portion 35. Thereby, the nip portions 31 and 32 of the holder 30 are selectively switched, and the holder 30 is held in a non-rotating state. If the holder 30 is configured to rotate in accordance with the rotation of the pressure roller 13 as described above,
There is no need to separately provide a driving means for rotating the holder 30, and there is no increase in cost.

The magnetic flux density passing through the metal sleeve 11 is the largest at the portion facing the induction coil 18, and since this portion generates heat locally, the heat generation portion and the nip portion at least partially overlap. As in the induction coil 18
The direction of is determined. Therefore, the nip portion 31,
Even when rotating holder 30 to switch 32, coil assembly 10 is held in a non-rotating state.

Next, the operation will be described.

In the second embodiment, two nip portions 31,
32 is performed based on whether or not the preheating (warm-up) of the metal sleeve 11 has been completed.

FIG. 5 is a timing chart for explaining the switching operation of the nip portion in the second embodiment. Until the warm-up of the metal sleeve 11 is completed, as shown in FIG. The first heat diffusion means 33 having a smaller degree is located at a nip position facing the pressure roller 13.

When a high-frequency current is applied to the induction coil 18 in this state, the first heat diffusion means 33 is made of a material having non-magnetic properties, so that the induction current is hardly generated and hardly generates heat, while the metal sleeve 11 is made of a magnetic metal. , A high-frequency induction current is induced to generate heat. The temperature of the metal sleeve 11, which is a heating element, rises at a high speed.

When the metal sleeve 11 generates heat to a predetermined temperature, the pawl 36 is swung and the groove 35 of the holder 30 is rotated.
Is released, and the holder 30 is set in a rotation-free state. Next, the pressure roller 13 is rotationally driven to rotate the holder 30.
Is driven and rotated together with the metal sleeve 11. When the second heat diffusing means 34 having the higher thermal conductivity reaches the nip position facing the pressure roller 13, the rotation of the pressure roller 13 is stopped, and the claw 36 is swung to engage the groove 35. Combine. As a result, the holder 30 has its nip portions 31, 3
2 is switched and held in a non-rotating state, and FIG.
As shown in (B), the second thermal diffusion means 34 faces the nip position.

The second heat diffusing means 34 includes the first heat diffusing means 33
Since the heat conductivity is higher than that of the metal sleeve 11, heat conduction in the longitudinal direction of the metal sleeve 11 is improved, and heat of the metal sleeve 11 is easily transmitted in the longitudinal direction. Therefore, the heat in the non-sheet passing area is
The sheet 1 is transmitted to the sheet passing area through the heat diffusion means 34 and has a smaller size than the maximum sheet passing width as in the first embodiment.
4, even in the mode of continuously passing paper through the metal sleeve 1
1 can suppress the temperature non-uniformity in the longitudinal direction, prevent the peripheral members from being degraded in the heat resistance life or suffering thermal damage, and furthermore, when the large-sized sheet 14 is passed immediately after the mode. However, partial unevenness does not occur in the fixing property.

As described above, according to the second embodiment, the first thermal diffusion means 33 having the smaller thermal conductivity faces the nip position until the warm-up is completed. High-speed heating is not hindered. When the warm-up is completed, the second heat diffusion means 34 having the larger thermal conductivity is switched to the nip position. The temperature rise in the sheet passing area can be reduced, and the temperature unevenness in the longitudinal direction of the metal sleeve 11 can be suitably suppressed, and stable fixing performance can be obtained in any sheet passing mode.

<< Embodiment 3 >> Embodiment 3 to be described below and Embodiment 4 to be described later are described in Embodiment 2.
On the other hand, the timing at which the two nip portions 31 and 32 are switched is modified, and the configuration of the fixing device is the same as that of the second embodiment.

In the third embodiment, two nip portions 31,
The switching of 32 is performed based on whether or not a predetermined number of sheets have been continuously passed. Therefore, the switching operation is performed based on a signal from a continuous print counter that counts the number of sheets continuously passed. The continuous print counter may be provided on the fixing device side, or may be provided on the image forming device side such as a printer incorporating the fixing device.

FIG. 6 is a timing chart for explaining the switching operation of the nip portion in the third embodiment. Initially, the first heat diffusion means 33 having a smaller thermal conductivity is used.
Is located at the nip position.

When the warm-up of the metal sleeve 11 is completed and a continuous printing operation is performed, the number of sheets is counted by a continuous print counter. During the continuous printing, the voltage applied to the induction coil 18 remains high, so that the temperature unevenness in the longitudinal direction of the metal sleeve 11 tends to increase.

When the number of continuous prints exceeds a preset number, the swing of the claw 36 and the holder 3
The nip portions 31 and 32 are switched by the driven rotation of 0,
The second thermal diffusion means 34 having the larger thermal conductivity is made to face the nip position.

The second heat diffusing means 34 is the first heat diffusing means 33
Since the heat conductivity is higher than that of the metal sleeve 11, heat conduction in the longitudinal direction of the metal sleeve 11 is improved, and heat of the metal sleeve 11 is easily transmitted in the longitudinal direction. Therefore, the heat in the non-sheet passing area is
The sheet 1 is transmitted to the sheet passing area through the heat diffusion means 34 and has a smaller size than the maximum sheet passing width as in the first embodiment.
4, even in the mode of continuously passing paper through the metal sleeve 1
1 can suppress the temperature non-uniformity in the longitudinal direction, prevent the peripheral members from being degraded in the heat resistance life or suffering thermal damage, and furthermore, when the large-sized sheet 14 is passed immediately after the mode. However, partial unevenness does not occur in the fixing property.

After the continuous printing operation is completed, the state in which the second heat diffusion means 34 faces the nip position is continued for a predetermined time in order to remove the temperature unevenness in the longitudinal direction of the metal sleeve 11.

As described above, according to the third embodiment, the second heat diffusing means 34 having the larger thermal conductivity is switched to the nip position if continuous printing operation for a predetermined number or more is performed. In response to a change in the use condition of the fixing device, that is, a paper passing operation, the temperature rise in the non-paper passing area can be reduced, and the temperature unevenness in the longitudinal direction of the metal sleeve 11 can be suitably suppressed. Fixing performance is obtained.

Fourth Embodiment In the fourth embodiment, switching between the two nip portions 31 and 32 is performed based on the size of the sheet 14. The signal regarding the sheet size is supplied from the image forming apparatus side.

FIGS. 7A, 7B and 7C are graphs showing the temperature distribution in the longitudinal direction of the metal sleeve 11 when the first heat diffusion means 33 made of aluminum is made to face the nip position. These are temperature distributions when sheets of A3 size, A4 size, and A5 size are continuously passed. FIGS. 8A, 8B and 8C are graphs showing the temperature distribution in the longitudinal direction of the metal sleeve 11 when the second thermal diffusion means 34 made of copper is made to face the nip position. Size, A4 size and A5
This is a temperature distribution when a sheet of a size is continuously passed.
The horizontal axis of each graph represents the distance (mm) from the central position in the longitudinal direction of the metal sleeve, and the vertical axis represents the temperature control temperature (for example, 150 mm).
２００200 ° C.).

When the first heat diffusion means 33 made of aluminum is positioned at the nip position, as shown in FIGS. 7A and 7B, sheets A3 and A4 are continuously passed. Sometimes, the temperature difference between the temperature in the paper passing area of the metal sleeve 11 and the temperature in the non-paper passing area is
The temperature is suppressed to 20 ° C. or less, which is practically acceptable. However, as shown in FIG.
When the paper is continuously passed, the temperature difference exceeds 20 ° C., and it can be seen that the temperature unevenness in the longitudinal direction of the metal sleeve 11 becomes remarkable.

On the other hand, when the second thermal diffusion means 34 made of copper whose thermal conductivity is larger than that of the first thermal diffusion means 33 faces the nip position, as shown in FIGS. 8A to 8C. , A3
The temperature of the metal sleeve 11 in the paper passing area and the temperature in the non-paper passing area of the metal sleeve 11 not only when the A4 size sheet 14 and the A4 size sheet 14 are continuously passed, but also when the A5 size sheet 14 is continuously passed. It is understood that the temperature difference can be suppressed to 20 ° C. or less that is practically allowable.

As a result, in the fourth embodiment, when the sheets 14 of the A3 size and the A4 size are passed, the first heat diffusion means 33 having the smaller thermal conductivity is located at the nip position, and the small size is used. When a certain A5 size sheet 14 is passed, the nip portions 31 and 32 are switched by the swinging of the claw portion 36 and the driven rotation of the holder 30 so that the second heat diffusion means 34 having the larger thermal conductivity is moved to the nip position. It is located in.

The second heat diffusing means 34 is the first heat diffusing means 33
The heat of the metal sleeve 11 is easily transmitted in the longitudinal direction, and even in the mode of continuously passing the A5 size sheet 14, the heat of the non-sheet passing area becomes the second heat.
The heat is transmitted to the paper passing area through the heat diffusion means 34, and the temperature unevenness in the longitudinal direction of the metal sleeve 11 is practically allowed.
° C or lower. For this reason, the heat resistance life of the peripheral members is not reduced or thermal damage is not caused. Further, even when the A14 sheet and the A4 size sheet 14 are passed immediately after the mode, a part of the fixing property is not improved. No unevenness occurs.

During the warm-up of the metal sleeve 11, in order to achieve a high-speed temperature rise, as in the second embodiment, the first heat diffusion means 33 having a smaller thermal conductivity is used.
Is preferably located at the nip position. After the warm-up of the metal sleeve 11 is completed, the nip portions 31 and 32 are switched based on the size of the sheet 14 as described above, and the first heat diffusion unit 33 or the second heat diffusion unit 34 is switched.
Is selectively located at the nip position.

When a continuous printing operation is performed, even if the sheets 14 are A3 size and A4 size, as in the third embodiment, the second heat diffusing means having the larger thermal conductivity is used. 34 may be located at the nip position.

As described above, according to the fourth embodiment, the nip portion 3 is adjusted according to the size of the sheet 14 to be passed.
1 and 32, the temperature rise in the non-sheet-passing area is reduced to reduce the temperature unevenness in the longitudinal direction of the metal sleeve 11 in response to a change in the use condition of the fixing device that the size of the sheet 14 to be passed is different. , And stable fixing performance can be obtained in any paper passing mode.

In the second to fourth embodiments, the case of the induction heating type fixing device using the induction coil 18 as a heating source has been described. However, the heating method is not limited to the induction heating, but is freely movable. A heating method using an electric heater or a halogen lamp as a heating source may be used as long as it can heat a thin and thin object to be heated. Further, the object to be heated is not limited to the shape of the metal sleeve 11, but may take various forms such as a belt shape and the like which are movable.

[0074]

[0075]

Effects of the Invention According to the fixing device according to claim 1, since it is possible to face the selective thermal diffusion means having a different thermal conductivity to the nip position, the longitudinal direction of the thin object to be heated to be heated Temperature unevenness can be suppressed appropriately in response to changes in the use conditions of the fixing device, the heat resistance life of the peripheral members is not reduced and thermal damage is not caused, and stable fixing performance regardless of the paper feeding mode Can be secured.

According to the fixing device of the second aspect, it is preferable to reduce the temperature unevenness in the longitudinal direction of the object to be heated in response to a change in the use condition of the fixing device such as whether or not the preheating of the object to be heated is completed. And stable fixing performance can be obtained.

According to the fixing device of the third aspect , it is possible to appropriately suppress the temperature unevenness in the longitudinal direction of the object to be heated in response to a change in the use condition of the fixing device such as a continuous paper passing operation,
Stable fixing performance can be obtained.

According to the fixing device of the fourth aspect , it is possible to appropriately reduce the temperature unevenness in the longitudinal direction of the object to be heated in response to a change in the use condition of the fixing device that the size of the recording medium to be passed is different. It can be suppressed and stable fixing performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view schematically showing an induction heating type fixing device according to Embodiment 1 of the present invention.

FIGS. 2A and 2B show Embodiment 2 of the present invention.
1 is a cross-sectional view schematically showing a fixing device according to the first embodiment.

FIG. 3 is a cross-sectional view showing an example of a configuration in which the thermal conductivity of a thermal diffusion unit is made different.

FIG. 4 is a perspective view showing a main part of a holder according to a second embodiment.

FIG. 5 is a timing chart for explaining a switching operation of a nip portion in a second embodiment.

FIG. 6 is a timing chart for explaining a nip portion switching operation according to a third embodiment;

FIGS. 7A, 7B, and 7C show the temperature distribution in the longitudinal direction of the metal sleeve when the first heat diffusion unit made of aluminum according to the fourth embodiment faces the nip position. It is a graph, A3 size, A
This is a temperature distribution when sheets of 4 size and A5 size are continuously passed.

FIGS. 8A, 8B, and 8C are graphs showing a temperature distribution in a longitudinal direction of a metal sleeve in a case where a copper second heat diffusion unit according to a fourth embodiment faces a nip position. Are temperature distributions when sheets of A3 size, A4 size and A5 size are continuously passed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Metal sleeve (thin-wall metal body, thin-walled heated body) 12, 30 ... Holder (holding member) 13 ... Pressure roller (pressure member) 14 ... Sheet (recording medium) 18 ... Induction coil (heating source) 23, 31, 32: nip portion 24, 33, 34: heat diffusion means

Claims (4)

(57) [Claims] An unfixed recording medium formed on a conveyed recording medium;
The developer of the image is melted by heat and
A fixing device for fusing , comprising: a heating source; and heating of the heating source and conveyance of the recording medium.
A thin-walled heated body movably provided in a direction, a holding member with which the heated body is in sliding contact, and the holding member and the holding member via a recording medium conveyance path.
Opposed to the object to be heated, the holding member and the object to be heated
A pressurizing member that presses the recording medium , wherein the holding member sandwiches the recording medium.
Three nip portions are provided to be switchable , and each of the nip portions is provided in the longitudinal direction of the holding member.
Along with heat diffusion made of material with good thermal conductivity properties
A fixing device provided with a heat-diffusing means having different thermal conductivities . 2. The switching of said at least two nips.
Based on whether the preheating of the object to be heated has been completed or not.
The fixing device according to claim 1, wherein the fixing is performed. 3. The fixing device according to claim 1 , wherein the switching of the at least two nip portions is performed based on whether a predetermined number of sheets have been continuously passed. Wherein switching of said at least two nip, the fixing device according to claim 1, characterized in that based on the size of the recording medium.