JPH09244441A - Heat fixing device - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide a heat fixing device capable of eliminating a wait time by heating a fixing nip portion at a high speed. SOLUTION: The heating part and the conduction part 12 are connected to the exciting coil 1
3, a heating member 12a made of a ferromagnetic conductive member that is induction-heated by 3 and a heat transfer member 12b having high heat conductivity such as aluminum that transfers heat generated by the heating member 12a to the fixing nip portion via the fixing film 11. To do.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device provided in an image forming apparatus adopting an electrophotographic system, an electrostatic recording system or the like, and more specifically, a fixing member and a pressure member arranged in pressure contact with each other. The present invention relates to a heat fixing device composed of

[0002]

2. Description of the Related Art Conventionally, in a fixing device provided in an image forming apparatus which employs an electrophotographic system, an electrostatic recording system, etc., a transfer roller carrying an unfixed toner image is pressed against each other to rotate a fixing roller. A heat fixing device of a so-called heat roller type is widely used in which a permanent image is fixed on a transfer material by passing through a nip portion formed by a pressure roller and a pressure roller. An example of this heat roller type heat fixing device is shown in FIG.

In FIG. 11, reference numeral 40 denotes a fixing roller in which a halogen lamp 41 as a heating means is arranged inside an aluminum hollow cored bar 42, and the hollow cored bar 42 is energized by a power source (not shown). Sufficient heating is performed to melt the toner on the transfer material P from the inside. Further, in order to fix the toner on the transfer material P on the transfer material P without offsetting it, polytetrafluoroethylene (PTF) having excellent releasability is provided outside the hollow cored bar 42.
E), a releasable layer 43 such as perfluoroalkoxytetrafluoroethylene copolymer (PFA) is formed. The thermistor 44 is in contact with the surface of the fixing roller 40, detects the temperature of the surface of the fixing roller 40, and turns on the power supply to the halogen lamp so as to heat the toner image on the transfer material P at an appropriate temperature. / Off control.

On the other hand, reference numeral 50 denotes a pressure roller which presses the fixing roller 40 at both ends in the roller longitudinal direction by pressure springs (not shown) to nip and convey the transfer material P. The pressure roller 50 includes an elastic layer formed by molding silicone rubber on the outside of a core metal 51 or a sponge elastic layer 52 formed by foaming silicone rubber, and a fixing roller 40 on the outer layer.
The same release layer 53 of PTFE or PFA is formed. Therefore, due to the elasticity of the pressure roller 50, a sufficient nip width can be formed between both rollers. The toner image on the transfer material P nipped and conveyed in this nip portion can be fixed by heating from the fixing roller 40.

According to the conventional heat roller type heat fixing apparatus as described above, the fixing roller 40 does not suddenly lower the temperature in the nip even if heat is taken by the transfer material P. Had a heat capacity. As a result, when the print signal is sent to the main body of the image forming apparatus, the fixing roller 40 is warmed to a predetermined temperature during standby so that the printing operation can be started immediately. That is, when the fixing roller 40 is heated to a predetermined temperature during the standby without a printing operation and the print signal is received,
By the time the transfer material P reaches the fixing nip portion, the fixing roller 4
The toner image on the transfer material P was fixed by heating until 0 reached the temperature required for fixing.

[0006] Further, a method in which power is not supplied to the heating and fixing device during standby and power consumption is kept as low as possible, more specifically, a toner image on a transfer material is fixed through a film between a heater section and a pressure roller. The method is disclosed in Japanese Patent Laid-Open No. 4-44075. An example of this is shown in FIG. FIG.
In the above, the fixing member 60 heat-fixes the toner image on the transfer material by the following configuration. That is, a heating resistance portion 61 provided on a ceramic substrate and covered with a thin glass protective layer is held by a plastic stay holder 62 that also serves as a guide for the film 63, and the stay holder 62 is held. Further, a seamless thin film 63 is slidably disposed, and is configured to rotate following the rotation of the pressure roller 50 as a pressure member.

The base layer of the film 63 is made of polyimide, polyamide imide, PEEK or the like, and has high heat resistance, insulation and high elasticity. The base layer maintains mechanical strength such as tear strength. There is. Further, a conductive primer is formed as a thin layer having a thickness of about 2 to 6 μm on the outer layer. In addition, PFA, PTFE, FE on the surface
A fluororesin such as P is coated with a thickness of about 10 μm as a release layer for preventing offset.

In the conventional example of FIG. 12 using such a thin fixing film 63, the heat capacity of the fixing member is much lower than that of the heat fixing device using the fixing roller 40. Therefore, in fixing the toner image on the transfer material, the heat from the heater can be efficiently applied to the transfer material, and only the fixing nip portion is heated by making the thickness of the film 63 as thin as 20 to 70 μm. By doing so, quick start heat fixing is achieved. Furthermore, since the heat capacity of the fixing member is kept low, it is not necessary to warm the fixing member even during standby, and power consumption is kept low.

[0009]

However, in the heat fixing device using the fixing roller 40 shown in FIG. 11, first, in order to keep the fixing roller 40 warm to a predetermined temperature during standby, power is not always supplied. However, the power consumption may increase. Further, it takes time depending on the heat capacity of the fixing roller 40 after the power of the image forming apparatus main body is turned on until the temperature reaches a predetermined temperature. For example, even a thin fixing roller which has recently been used has a minimum value. About 30 seconds was in a wait state, which sometimes required a so-called wait time. Therefore, in order to reduce the power consumption during standby as much as possible, it may be necessary to wait until the fixing roller reaches a predetermined temperature each time printing is performed, even if the power is turned off during non-printing.

Next, in the case of the heat fixing device for realizing quick start heat fixing by the fixing member 60 having a small heat capacity as shown in FIG. 12, the standby state as described above is unnecessary, while the ceramic is used. Heat is applied to the transfer material through the film 63 by the heater portion 61 made of a linear heating element, and therefore the glass protective layer of the heater portion 61 and the thickness of the film 63 must be suppressed as much as possible. That is, it is necessary to keep the heat transfer to the fixing nip portion well by realizing the heat fixing by quick start by suppressing the respective thicknesses.

However, since the glass protective layer having poor thermal conductivity is required to have sufficient withstand voltage performance between the heating element to which an alternating voltage is applied and the film 63, it may be difficult to form an extremely thin layer. It was Therefore, in a high-speed electrophotographic apparatus in which the transfer material onto which the toner image has been transferred is fast, the speed at which the amount of heat generated by the heating element is applied to the transfer material through the glass protective layer having poor heat conduction and the film 63 is in time. In some cases, fixing failure may occur, and it may be difficult for the heat fixing device having the configuration shown in FIG. 12 to achieve a high-speed electrophotographic device.

Further, in this structure, since the main purpose is to transfer the heat from the heat generating portion only in the direction of the pressure roller 50, it is difficult to improve the heat transfer in the longitudinal direction in the heat fixing device in terms of the structure. There was a case. Therefore, when a transfer material having a small size in the longitudinal direction is conveyed, heat transfer from the heating element fixes the toner image on the transfer material, and directly heats the pressure roller 50 in the non-conveyance area of the transfer material. It will be. Therefore, a temperature difference occurs in the longitudinal direction of the pressure roller 50,
In the system in which the pressure roller 50 is driven to convey the transfer material, the conveying force is partially different. As a result, the thin film 63 that is driven to rotate is twisted, and in the worst case, a film whose thickness is suppressed as much as possible to satisfy the fixing property may be damaged due to buckling.

Further, the heat resistance of the temperature rising portion must be fully taken into consideration, and the cost of the member may be increased.

Further, since the heat flow in the longitudinal direction is small,
Since the resistance value distribution of the heating portion of the ceramic linear heating element directly affects the fixing property of the transfer material, there are cases where a strict uniformity of the resistance value distribution is required.

Further, since the temperature distribution in the fixing nip portion is uniform from the upstream side to the downstream side in the transfer material conveying direction, the transfer material is separated from the fixing film in a state where the toner is sufficiently melted, and the high temperature offset is caused. May have occurred.

Further, in the fixing device, the film 63 having a small heat capacity is rapidly heated in the fixing nip portion and the toner image on the rolling material is fixed by the heat transfer, so that the heat generated by the heater 61 as a heat source is generated. The part is designed to fit within the fixing nip. If the heat generating portion of the heater 61 to be applied is not inside the fixing nip and protrudes outside the nip, heat is radiated from the heat generating portion in the protruding portion to the pressure roller 50 and the like to the heat generating portion in the nip. In some cases, the ceramics were small and were abnormally heated, and in the worst case, the ceramic might break. Therefore, it is an essential condition that the heat generating portion of the heater 61 be contained in the fixing nip.

For this reason, the transfer material is not heated until immediately before the nip portion, but is heated as soon as it enters the fixing nip. At this time, steam is released from the transfer material that has entered the fixing nip portion due to heating, but this steam cannot flow into the fixing nip portion and is flowed to the upstream side of the fixing nip. As a result, when the water vapor generated from the transfer material blows off the toner image on the transfer material that has not reached the fixing nip portion to the upstream side (below the image on the transfer material) and deteriorates the image quality, so-called tailing occurs. was there.

Further, when the printing ratio of the toner image on the transfer material is high, the transfer material is rapidly cooled by the temperature of the atmosphere when discharged from the fixing nip portion, so that the solidification speed of the toner at that time is increased. Due to the difference, image deterioration such as uneven gloss may occur.

Therefore, it is an object of the first invention of the present application to provide a heat fixing device capable of eliminating the wait time by heating the fixing nip portion at a high speed.

In addition to the above object, the second invention of the present application eliminates buckling of the film even when a small-sized transfer material is conveyed by improving heat transfer in the longitudinal direction. It is an object of the present invention to provide a heat fixing device that can be used.

Further, in addition to the above objects, the third invention of the present application provides a heat fixing device capable of preventing the occurrence of a high temperature offset due to the toner being separated from the film in a molten state. Especially.

The fourth object of the present invention is to:
In the first to third inventions described above, it is an object of the present invention to provide a heating and fixing device capable of achieving more uniform temperature in the longitudinal direction.

Further, the fifth and sixth inventions of the present application
Another object of the present invention is to provide a heat fixing device capable of preventing the so-called tailing phenomenon in addition to the above object.

A seventh invention according to the present application is to provide a heat fixing device capable of further reliably preventing high temperature offset in the fifth invention or the sixth invention.

Further, an eighth invention according to the present application is to provide a heating fixing device capable of preventing overheating of a heating member outside the fixing nip in the fifth invention to the seventh invention. .

[0026]

According to the first invention of the present application, the above object is to provide a heating means, a fixing film arranged so as to rub against a part of the heating means, and A transfer member on which an unfixed image is formed, including a pressure member arranged so as to be in pressure contact with the heating means via a fixing film,
In a heat fixing device for fixing the unfixed image as a permanent image on a transfer material by passing through the pressure contact portion, the heating means includes an exciting coil and a ferromagnetic heating member that is electromagnetically induction-heated by the exciting coil. And a heat transfer member for transmitting the heat generated by the ferromagnetic heating member to the pressure contact portion,
This is achieved when the magnetic permeability of the ferromagnetic heating member is larger than that of the heat transfer member.

According to the second aspect of the present invention,
In the first aspect of the invention described above, the heat conductivity of the heat transfer member is higher than that of the ferromagnetic heating member.

Further, according to a third invention of the present application, in the above-mentioned object, in the first invention or the second invention, the volume ratio of the ferromagnetic heating member and the heat transfer member is the transfer material conveying direction. This is achieved by having a distribution at.

According to the fourth invention of the present application,
The above object is any one of the first to third inventions, wherein the volume ratio of the ferromagnetic heating member and the heat transfer member is
This is achieved by having a distribution in the longitudinal direction of the ferromagnetic heating member and the heat transfer member.

Further, according to a fifth invention of the present application, in the above-mentioned object, in any one of the first invention to the fourth invention, the width of the ferromagnetic heating member in the transfer material conveying direction is This is achieved by making the width larger than the width of the pressure contact portion between the heating means and the pressure member.

According to the sixth invention of the present application,
The above object is achieved in any one of the first to fourth inventions, in which the width of the heat transfer member in the transfer material conveying direction is larger than the width of the pressure contact portion between the heating unit and the pressure member. .

Further, according to a seventh invention of the present application, in the above-mentioned fifth invention or sixth invention, the above-mentioned object is to form a distribution of heat conductivity or heat capacity in the transfer material conveying direction. It is achieved by

According to the eighth invention of the present application,
The above object is achieved in any one of the fifth to seventh inventions, in that the contact position between the exciting coil and the ferromagnetic heating member is outside the pressure contact portion between the heating means and the pressure member. It

That is, in the first invention of the present application, the thin layer ferromagnetic heating member having a small heat capacity is induction-heated, and the heat transfer from the heating member to the fixing nip portion is excellent in heat conductivity. Since the fixing is carried out by the member, the fixing nip portion is heated at a high speed to eliminate the need for preheating during standby, thereby eliminating the wait time.

Further, in the second invention according to the present application, since the heat transfer member of the first invention is excellent in heat conductivity, it produces a heat flow in the longitudinal direction, and the transfer material of a small size. Even when the sheet is conveyed, it has a function to flow the heat in the non-conveying zone to the conveying zone, and makes the temperature distribution in the longitudinal direction of the pressing member uniform, so that the conveying force of the pressing member becomes uniform, and Does not twist.

Further, in the third invention according to the present application, the volume ratio of the heating member and the heat transfer member having different heat capacities or heat conductivities in the transfer material conveying direction of the first invention or the second invention is fixed. There is a distribution in the nip, and in particular, the volume ratio is distributed so that the heat capacity on the upstream side is smaller than that on the downstream side in the transfer material conveying direction, or the heat transfer member of high heat conductivity on the upstream side compared to the downstream side By increasing the volume ratio, the temperature is set to be lower on the downstream side in the fixing nip than on the upstream side in the transfer material conveying direction. As a result, the toner image on the transfer material, which is sufficiently melted on the upstream side of the fixing nip, is conveyed to the downstream side of the nip where the temperature is slightly low, is cooled, and then is conveyed to the outside of the fixing nip. The toner image is reliably fixed on the transfer material on the downstream side of the nip without being liquefied and causing high temperature offset.

In the fourth invention of the present application, the volume ratio in the longitudinal direction of the heating member and the heat transfer member according to any one of the first to third inventions is made to have a distribution, and particularly the generated magnetic field is generated. The heat capacity of the portion corresponding to the end of the strong excitation coil is increased, or the volume ratio of the heating member and the heat transfer member is set so that the thermal conductivity becomes smaller than that in the longitudinal center. A uniform temperature distribution can be obtained in all directions.

Further, in the fifth invention of the present application, the width of the heating member according to any one of the first to fourth inventions is formed so as to be wider than the width of the fixing nip portion. The temperature of the atmosphere immediately before the nip is raised to eliminate a sharp temperature difference between immediately before the fixing nip and upstream of the fixing nip portion. As a result, the transfer material conveyed immediately before the fixing nip is given radiant heat from the heating member immediately before the fixing nip via the fixing film. As a result, the toner image on the transfer material is slightly melted, so that it is possible to prevent the water vapor generated from the transfer material in the fixing nip portion from blowing off the toner image immediately before the fixing nip. On the other hand, by providing the protruding portion of the heat transfer member on the downstream side from the fixing nip portion, it is possible to warm the atmosphere temperature on the downstream side of the fixing nip portion, and thereby the toner on the transfer material which is heat-fixed in the fixing nip portion. The image is not cooled rapidly, and the toner image is solidified by cooling at a slow speed, thus preventing image deterioration such as uneven gloss.

In the sixth invention according to the present application, the heat transfer member according to any one of the first to fourth inventions is formed so as to be wider than the fixing nip portion. The temperature of the atmosphere immediately before the fixing nip is increased to eliminate a sharp temperature difference between immediately before the fixing nip and upstream of the fixing nip portion. As a result, the transfer material conveyed immediately before the fixing nip is given radiant heat from the heating member immediately before the fixing nip via the fixing film. As a result, the toner image on the transfer material is slightly melted, so that it is possible to prevent the water vapor generated from the transfer material in the fixing nip portion from blowing off the toner image immediately before the fixing nip. On the other hand, by providing the protruding portion of the heat transfer member on the downstream side from the fixing nip portion, it is possible to warm the atmosphere temperature on the downstream side of the fixing nip portion, and thereby the toner on the transfer material which is heat-fixed in the fixing nip portion. The image is not cooled rapidly, and the toner image is solidified by cooling at a slow speed, thus preventing image deterioration such as uneven gloss. In addition, the start-up time (wait time) is shortened by suppressing the heat capacity of the heating member as small as possible.

Further, according to the seventh invention of the present application, the upstream side and the downstream side of the heat transfer member in the fixing nip portion in any one of the fifth invention and the sixth invention have thermal conductivity. By configuring with different members, it is possible to have a temperature distribution in the conveyance direction within the fixing nip, and especially if it is configured so that the downstream side has a lower temperature setting than the upstream side, high temperature offset is easy. Prevent.

Further, in the eighth invention of the present application, the contact position between the exciting core and the heating member in any one of the fifth invention to the seventh invention is located outside the fixing nip. The heating member protruding before and after the fixing nip as compared with the inside of the fixing nip portion is prevented from being overheated during continuous heating and fixing by appropriately radiating heat from the heating member outside the fixing nip to the exciting core. This prevents an abnormal temperature rise in the protruding portion of the heating member from the fixing nip, and prevents the toner image on the transfer material from being melted again by the heating member having a higher heat than that in the fixing nip before and after the fixing nip, particularly immediately after the fixing nip. To prevent. Further, a heat insulating member is provided only at the heating member contacting position on the upstream side of the exciting core provided outside the fixing nip, in particular, the heat escape to the upstream side of the exciting core is reduced, and the preheating effect immediately before the fixing nip is effectively made. Use it to prevent tailing.

[0042]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) An embodiment according to the present invention will be shown below. First, FIG. 1 is a block diagram of an image forming apparatus according to the present invention.

In FIG. 1, 1 is a photosensitive drum, and O
A photosensitive material such as PC, amorphous Se, or amorphous Si is formed on a cylindrical substrate such as aluminum or nickel. The photosensitive drum 1 is rotationally driven in the direction of the arrow, and first, the surface thereof is a charging roller 2 as a charging device.
Are uniformly charged by. Next, turn on according to the image information
Scanning exposure is performed by the laser beam 3 controlled to be ON / OFF, and an electrostatic latent image is formed. This electrostatic latent image is developed and visualized by the developing device 4. As a development method, a jumping development method, a two-component development method, an FEED development method, or the like is used, and a combination of image exposure and reversal development is often used.

The visualized toner image is transferred from the photosensitive drum 1 onto the transfer material P conveyed at a predetermined timing by the transfer roller 5 as a transfer device. At this time, the transfer material P is nipped and conveyed between the photosensitive drum 1 and the transfer roller 5 with a constant pressure. Transfer material P on which this toner image is transferred
Is transported to the fixing device 6 and fixed as a permanent image. On the other hand, the transfer residual toner remaining on the photosensitive drum 1 is removed from the surface of the photosensitive drum 1 by the cleaning device 7.

Next, the structure of the heat fixing device 6 according to the present invention used in the image forming apparatus as described above will be described with reference to FIG. In FIG. 2, 10 is a fixing member, which is composed of the following components. First, 11 is a fixing film having a small heat capacity, and polyimide, polyamide imide, PEE having heat resistance and high elasticity with a thickness of 100 μm or less to enable quick start.
KFA, PPS, PPS, PFA, PTFE, FEP, etc. as a release layer with a primer layer sandwiched between base layers.
It is a film coated with a fluororesin layer such as E or FEP. Here, the base layer, the surface layer, or the primer layer of the fixing film 11 may contain conductive powder such as carbon black. Further, a film having sufficient strength and excellent durability to form a heat fixing device having a long life is required to have a thickness of 20 μm or more. Therefore, the thickness of the fixing film 11 is optimally 20 μm or more and 100 μm or less.

Next, 12 is a heating portion and a heat transfer portion provided inside the fixing film 11, which heat the nip portion for melting and fixing the toner image of the transfer material. As shown in FIG. 3, the heating unit and the heat transfer unit 12 are composed of a heating member 12a and a heat transfer member 12b. In FIG. 3, the heating member 12a is a ferromagnetic conductive material that is induction-heated by an exciting coil 13. Fe, Co, Ni, Cu,
It is desirable to be formed of a metal such as Cr, an alloy thereof, or a resin layer containing the powdery substance of the ferromagnetic conductive member as described above. As the thickness of the heating member 12a, the heat capacity is suppressed, and the workability is 10 μm or more 2
It is desirable to be formed with a thickness of 00 μm or less. Further, 12b is a heat transfer member for transmitting the heat generated by the heating member 12a to the fixing nip portion via the fixing film, and is formed of a member having high heat conductivity such as aluminum, gold, silver, or copper. The heat transfer member 12b is also formed as thin as possible in order to suppress the heat capacity as much as possible, and has a sufficient mechanical strength against pressure to form a sufficient fixing nip between the fixing film 11 and the pressure member. In order to add, the total thickness with the heating member 12a is preferably 0.2 mm or more and 4 mm or less.

Here, the heating member 12a is mainly used for heating,
Since the heat transfer member 12b mainly contributes to heat conduction, the magnetic permeability and thermal conductivity of the heating member 12a are set to μ0 and κ0, and the magnetic permeability and thermal conductivity of the heat transfer member 12b are set to μ1 and κ1. At this time, the following relationships are desirable.

(1) Permeability Relationship .mu.0> .mu.1 (2) Thermal Conductivity Relationship .kappa.0 <.kappa.1 Further, the surface of the heat transfer member 12b which rubs against the fixing film 11 has a lubricant such as heat resistant grease. There is a small amount. This allows the fixing film 11 to rotate smoothly.

On the other hand, the exciting coil 13 for heating the heating member 12a by induction heating is a coil in which a conductor 13b is wound around a core 13a made of a ferromagnetic material such as ferrite.
A conductor (13b) wound around the core 13a is energized by a power source (not shown) from the end in the longitudinal direction. Here, the core 13a is generally used for a switching power supply, and typical shapes thereof include an I type, an E type, a U type and the like.
(FIG. 3 shows a U-shaped core, and other shapes can be used instead.) Here, between the core portion 13a of the exciting coil 13 and the heating member 12a, a glass layer having a high heat insulating effect, polyimide, polyamide imide, You may provide layers, such as PFA and PTFE. By providing this layer, the ferrite core 13a of the exciting coil 13 is heated by heat transfer and the reduction of the magnetic flux is prevented, so that more efficient induction heating is possible. The winding 13 wound around the ferrite core 13a
It is not necessary to worry about the withstand voltage by using a resin b covered with a tube of resin such as polyvinyl chloride or an elastomer having an excellent withstand voltage.
Therefore, the conductive heating member 12 is provided below the exciting coil 13.
There is no problem in arranging a, and there is no problem such as causing dielectric breakdown even if the conductive fixing film 11 is hung around the outside.

Next, in FIG. 2, reference numeral 20 denotes a pressure member, which has an elastic layer 22 formed by foaming heat resistant rubber such as silicone rubber or fluororubber or silicone rubber on the outside of the cored bar 21. PFA, PTFE, FEP on top
A releasable layer such as the above may be formed. The pressure member 20 is sufficiently pressed in the direction of the fixing member 10 by pressure members (not shown) from both ends in the longitudinal direction so as to form a nip portion necessary for heat fixing, and The rotation is driven in the direction of the arrow by the rotation driving (not shown) from the portion through the cored bar 21. As a result, the fixing film 11 is rotated outside the heating section and the heat transfer section 12 in the direction of the arrow in the figure.

When a high frequency current is applied to the conducting wire 13b of the exciting coil 13 shown in FIGS. 2 and 3 with the above-mentioned structure, an alternating magnetic field is generated in accordance with the applied current, and the heating member 12a which is a ferromagnetic conductive member has the above-mentioned structure. Eddy currents flow as if to hinder the change of the magnetic field. This eddy current is a conductive heating member 12a
Joule heat is generated by electric power proportional to the skin resistance of the sheet, and the toner image on the transfer material conveyed to the fixing nip portion via the heat transfer member 12b and the fixing film 11 is heated and fixed.

Next, in the present embodiment as described above,
By changing the materials and thicknesses of the heating member 12a and the heat transfer member 12b, measurement of the temperature rising rate on the surface of the heat transfer member, that is, the fixing nip side in contact with the fixing film 11, and the toner image on the transfer material after a lapse of a fixed time The experiment for confirming the fixing property will be described.

In this experiment, the heat fixing device according to the present invention was constructed as an example as follows. First, as the base layer of the fixing film 11, a mixture of polyimide and carbon black was used and was formed to have a thickness of 50 μm. The surface layer of the fixing film 11 was coated with a conductive primer and then coated with high resistance PFA to a thickness of 10 μm, and the surface resistivity of the surface of the fixing film 11 at this time was 10 ¹⁵ Ω or more.

Further, the pressure roller 20 as a pressure member has a core metal having an outer diameter of 17 mm and a conductive silicone rubber having a thickness of 4 mm, and a high resistance PFA tube having a thickness of 50 μm is formed on the outer layer thereof.
I used a cover. Here, the rotation speed of the pressure roller was constant, and the transfer material conveyance speed was set to 100 mm / s.

As a conventional example, a heat fixing device having the conventional linear heating element made of ceramic shown in FIG. 12 was used.

Further, as Comparative Example 1, instead of the heating member and the heat transfer member of the embodiment, the heating member and the heat transfer member were integrally formed of Fe, and as Comparative Example 2, the heating member of the embodiment. In place of the heat transfer member, the heating member and the heat transfer member integrally formed of Al were used.

Then, the heating rate of the heater was measured and the fixing property was confirmed. The comparison results are shown in the table below. In the table, ∘ indicates a problem-free level, Δ indicates an acceptable level, and x indicates poorness (the same applies to the tables below). Also,
The temperature rising rate of the glass protective layer or the surface of the heat transfer member in contact with the fixing film was measured as the time from room temperature of 25 ° C to the constant temperature of 175 ° C.

[0059]

[Table 1]

[0060]

[Table 2]

[0061]

[Table 3]

From the above results, the following can be seen. That is, from the results of Table 1, the embodiment in which the heating plate is heated by induction heating is better in supplying the amount of heat to the fixing nip portion than in the case where the ceramic heater according to the conventional example is used. It is advantageous for an electrophotographic apparatus in which the time from the print signal to the transfer material reaching the fixing nip is short, that is, the print time is short.

When Comparative Example 1 is compared with the Examples, in Comparative Example 1, Fe of the ferromagnetic member also serves as the heating member and the heat transfer member, the heat capacity is larger than that of the Examples, and the thermal conductivity is higher. Because of the low heat generation amount, it takes time for the surface temperature on the fixing nip side to reach the target temperature even if the heat generation amount is the same as that of the embodiment. Therefore, it becomes unsuitable for a high-speed electrophotographic apparatus using the above ceramic heater as in the conventional case.

In Comparative Example 2, a member having a high thermal conductivity such as Al and a heat capacity smaller than that of Fe is used as the heating member and the heat transfer member. In this case, the magnetic permeability of Al is low. Therefore, the heat generation amount is small, and the heating of the fixing nip becomes slower than in the conventional example using the ceramic heater.

From the above, in the embodiment in which a member having high magnetic permeability is used as the heating member and a member having high thermal conductivity is used on the fixing nip side, the time for heating the fixing nip portion to a predetermined temperature is shortened. This is advantageous for increasing the speed of the electrophotographic apparatus.

From the results shown in Table 2, it is desirable that the heating member has a thickness of 5 μm or more, preferably 10 μm or more in order to effectively utilize the alternating magnetic field generated by the exciting coil for high-efficiency heating. However, in order to suppress the heat capacity of the heating member, 250 μm or less, preferably 200 μm
It is desirable to form the heating member with the following thickness.

Further, from the results shown in Table 3, it can be seen that when the thickness of the heat transfer member is as thin as possible, the fixing nip portion can be rapidly heated. Although depending on the thickness of the heating member, it is desirable that the thickness of the heat transfer member be 4 mm or less, preferably 3.5 mm or less in order to suppress the heat capacity. However, the heating part and heat transfer part are pressed against the pressure roller to form a sufficient fixing nip necessary for fixing, and the mechanical strength that can withstand this pressing is satisfied. Must be present. Therefore, the total thickness of the heating member and the heat transfer member is at least 0.2 mm or more, preferably 0.
It is desirable that it is 3 mm or more.

As described above, in this embodiment, the heating member made of a ferromagnetic material is rapidly heated by induction heating, and the heat is transferred to the fixing nip portion by the heat transfer member having high thermal conductivity. The part can be heated to the target temperature. Therefore, there is no wait time, and high-speed heat fixing of the electrophotographic apparatus is possible. Further, since the electrophotographic apparatus main body can perform sufficient heating until the transfer material reaches the fixing nip portion after receiving the print signal, the printing time can be shortened.

In addition to the above effects, the following effects are obtained in this embodiment as compared with the conventional example. That is, compared with the heating of the fixing nip portion by the conventional ceramic heater, in the heat fixing device using the heating member and the heat transfer member by the induction heating of the present embodiment, the heat transfer member is a member having high thermal conductivity, Since the flow of heat in the direction of relaxing the heat distribution in the longitudinal direction is generated, the resistance value distribution of the heat generating portion of the conventional ceramic heater is severe, whereas the temperature of the fixing nip portion of the fixing nip portion is simple with a simple configuration. Uniformity can be achieved.
Further, since there is a heat flow in the longitudinal direction, it has an effect of loosening the temperature difference between the transport area and the non-transport area when transporting a small size, and it is possible to prevent the fixing film from twisting. As a result, it becomes possible to shift the heat resistant grade of various fixing members to the low temperature side, and the cost of the members can be reduced.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. It should be noted that description of the common points with the first embodiment is omitted, and the same reference numerals are given to the common points.

In this embodiment, the heating member and the heat transfer member are formed in the fixing nip so as to have a temperature distribution in the transfer material conveying direction.

The structure of the heat fixing device in this embodiment will be described with reference to FIGS. 4 (a) and 4 (b). In the figure,
The volume ratio of the heating member 12a and the heat transfer member 12b has a distribution in the transfer material conveying direction in the fixing nip, and particularly in the vicinity of the central portion in the transfer material conveying direction, that is, in the upstream side and the downstream side as compared with the vicinity of the fixing nip portion center. Heating member 12a
The volume ratio of the heat transfer member 12b is increased and the volume ratio of the heat transfer member 12b is decreased. However, since the alternating magnetic field generated by the exciting coil 13 is used more effectively for heating the heating member and the amount of heat generated on the surface of the heating member 12a is made uniform in the nip, the thickness d of the thinnest portion of the heating member 12a is As shown in the first embodiment, it is formed so as to have a thickness of 10 μm or more.

As described above, in the fixing nip portion, the volume of the heat transfer member 12a corresponding to the center of the nip is larger than that of the upstream and downstream ends, so that the heat quantity uniformly generated on the surface of the heating member 12a is concentrated in the central portion of the fixing nip. Flow to. Due to the uneven heat amount, the temperature distribution in the fixing nip portion is higher near the center than at the upstream and downstream ends.

Alternatively, as shown in FIG. 4B, the heating member 12a and the heat transfer member are arranged so that the volume ratio of the portion corresponding to the downstream side of the fixing nip occupied by the heating member 12a becomes larger than that of the upstream side and the central portion. A curved shape may be added to the member 12b in the transfer material conveying direction.

As described above, in the present embodiment, the volume ratio of the heating member 12a to the heat transfer member 12b is set so that the temperature distribution at least on the downstream side in the fixing nip portion is lower than that in the central portion. As a result, the toner image on the transfer material is sufficiently melted on the upstream side and the central portion of the fixing nip, and heat is applied to the transfer material at a slightly lower temperature on the downstream side immediately before the transfer material is carried out from the fixing nip. Since the toner image on the transfer material is slightly cooled and then conveyed outside the fixing nip, it is possible to avoid an abnormally heated state, and to prevent the toner image on the transfer material from occurring without causing problems such as high temperature offset. It becomes possible to fix it.

(Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIGS. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, the shapes of the heating member and the heat transfer member are slightly different from those of the first embodiment, and a uniform temperature distribution is provided in the longitudinal direction.

The shapes of the heating member and the heat transfer member in this embodiment will be described with reference to FIG. In the figure heating member 1
The shape of 2a is formed so that the heat capacity is larger at both end portions than in the central portion in the longitudinal direction. That is, the volume ratio of the heating member 12a and the heat transfer member 12b is distributed, and the volume ratio of the heating member 12a having a larger heat capacity is larger at both end portions than in the central portion in the longitudinal direction. On the contrary, the heat transfer member 12b having high thermal conductivity is set to have a smaller volume at both end portions than in the central portion in the longitudinal direction.
As a result, in the fixing nip portion, it is more difficult for the both end portions to warm up than the central portion in the longitudinal direction.

In general, when the exciting coil 13 as described in the first embodiment is used, the magnetic flux density is higher at B at both end portions than at A at the central portion. This is the excitation coil 13
This is an effect of the folded portion of the winding at the end portion, which may result in an uneven temperature distribution in the longitudinal direction. The present embodiment is a method for solving such a problem by providing a distribution in the volume ratio of the heating member 12a and the heat transfer member 12b, which can be dealt with by the heat capacity or heat conductivity distribution in the longitudinal direction. It is possible to easily make the temperature distribution uniform.

In order to confirm the above, the temperature distribution on the surface of the heat transfer member 12b was measured. FIG. 6 shows the result. As shown in FIG. 6, as a comparative example, a heating member 1 made of a uniform material in the longitudinal direction and having a uniform heat capacity and thermal conductivity distribution.
The temperature distribution was measured also when 2a and the heat transfer member 12b were used. In addition, in Example 3 used for confirmation here, the heating member 12a and the heat transfer member 12b correspond to the present embodiment and are shown in FIG. 5 using a Ni plate and an Al plate. In addition, a member having a distribution in heat capacity and thermal conductivity by changing the volume ratio in the longitudinal direction of the heating member, and the same Ni plate and Al plate as a comparative example, with a uniform volume in the longitudinal direction. The formed member was used. Further, a high-frequency alternating current of 100 kHz was applied to the winding of the exciting coil 13.

From FIG. 6, it is understood that the comparative example in which the heating member and the heat transfer member having a uniform heat capacity and heat conductivity in the longitudinal direction have higher temperatures at both end portions than at the central portion.
In comparison with this, the heating member and the heat transfer member of the present embodiment are provided with a distribution of heat capacity and heat conductivity in the longitudinal direction so that both ends have a larger heat capacity or a lower heat conductivity than the central part. When formed, the temperature distribution has a substantially uniform temperature distribution from the left end to the right end.

From the above, by providing an appropriate distribution in the heat capacity or heat conductivity of the heating member 12a and the heat transfer member 12b in the longitudinal direction of the heating member, the resistance value distribution of the heat generating portion of the conventional ceramic heater is severe. On the other hand, the temperature of the fixing nip portion can be made uniform with a simple configuration. As a result, the fixing property of the toner image on the transfer material can be made uniform.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described with reference to FIG. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the present embodiment, the width of the heating member and the heat transfer member is set to be larger than the width of the fixing nip portion, and the effect of preheating the toner image on the transfer material is added on the upstream side of the fixing nip, and the downstream side of the fixing nip. On the side, it prevents the occurrence of uneven gloss due to rapid cooling.

The relationship between the heating member, the heat transfer member and the fixing nip in this embodiment will be described with reference to FIG. In FIG. 7, the heating member 12a and the heat transfer member 12b are formed with a width wider than the fixing nip width N, and at least the heat transfer member 12b projects outside the fixing nip on the upstream and downstream sides of the fixing nip.

Here, as shown in the first embodiment, the heat transfer member 12b is formed of a member having high thermal conductivity, so that the protrusion of the heat transfer member 12b can be easily extended to the upstream and downstream ends of the fixing nip. Can transfer heat to. Therefore, in this embodiment, the atmosphere immediately before and immediately after the fixing nip can be sufficiently warmed from this protruding portion through the fixing film. Therefore, when the transfer material is conveyed, the temperature of the atmosphere immediately before the fixing nip is increased, so that the toner image on the transfer material is slightly melted, and the toner itself becomes viscous. As a result, even if the water vapor generated by heating the transfer material in the fixing nip portion flows just before the fixing nip as if the toner on the upstream side of the fixing nip is blown off, the toner image on the transfer material is not covered by the toner. It is not blown off to the upstream side due to ties, and does not cause image deterioration such as tailing. Further, since the transfer material discharged from the fixing nip after being heated in the fixing nip portion is not rapidly cooled, image deterioration such as gloss unevenness occurs even when the printing rate of the toner image on the transfer material is high. It can be fixed without causing Here, the same effect can be obtained even if the heat transfer member 12b has an upstream or downstream side of the fixing nip which is inclined or curved in a direction away from the pressure roller.

In order to confirm the effects of the tailing prevention and the gloss unevenness prevention, the protrusion amount L from the fixing nip portion of the heat transfer member 12b was shaken to confirm the tailing prevention and gloss unevenness prevention effects. Further, if the protrusion amount L of the heat transfer member 12b is too large, the heat capacity of the heat transfer member 12b cannot be ignored, and there is a possibility that the fixability will be affected.
The fixability was evaluated at the same time. The evaluation results are shown below.

[0088]

[Table 4]

From the above results, it is possible to prevent tailing by projecting the heat transfer member 12a to the upstream side of the fixing nip and preheating the toner image on the transfer material to make it slightly melted. Since the transfer material after fixing is not rapidly cooled, problems such as uneven gloss can be solved.
Here, the amount of protrusion of the heat transfer member that is effective in preventing tailing and uneven gloss is 1 mm or more, preferably 2 mm or more. However, since the increase in the amount of protrusion of the heat transfer member is accompanied by the increase in the heat capacity of the heat transfer member, the amount of protrusion of the heat transfer member is preferably 12 mm or less in order to sufficiently heat the fixing nip portion and prevent defective fixing. Is preferably 10 mm or less.

As described above, in the present embodiment, by making the width of the heat transfer member larger than the width of the fixing nip, it is possible to prevent tailing and uneven gloss.

(Fifth Embodiment) Next, a fifth embodiment of the present invention will be described with reference to FIG. The same parts as those of the first and fourth embodiments are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, a plurality of members are used as the heat transfer member, and each heat transfer member has a preheating effect and a high temperature offset preventing effect.

The heat transfer member in this embodiment will be described with reference to FIG. In the figure, the heat transfer member is made of at least two materials, and as shown in the fourth embodiment, the heat transfer member 12b including the protrusion on the upstream side of the fixing nip.
Is made of a material having a high heat conductivity and a small heat capacity, such as Al. On the other hand, the downstream side of the fixing nip is composed of a heat transfer member 12c made of a member having a larger heat capacity or a smaller heat conductivity than the heat transfer member 12b. As the heat transfer member 12c, a member having a larger heat capacity than Al, such as Cu, or a member having smaller thermal conductivity than Al, such as Fe, stainless steel, Su, and Ni, is suitable.

As described above, according to the present embodiment, as shown in the fourth embodiment, the heat transfer member 12b having the protruding portion on the upstream side of the fixing nip has a high thermal conductivity to warm the ambient temperature immediately before the fixing nip. There is an effect of preheating, and it is possible to prevent tailing of the toner image on the transfer material. Further, in this embodiment, since the heat transfer member 12c having a large heat capacity or a small heat conductivity is used on the downstream side of the fixing nip, the temperature distribution on the downstream side in the fixing nip is lower than that on the upstream side and the central portion of the fixing nip. Has become. Therefore, the second
As described in the second embodiment, the toner image on the transfer material is slightly cooled immediately before passing through the fixing nip to prevent high temperature offset.

(Sixth Embodiment) Next, a sixth embodiment of the present invention will be described with reference to FIG. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the present embodiment, a U-shaped exciting core arranged over the fixing nip is used, and the contact position between the exciting core and the heating member is formed outside the fixing nip.

In FIG. 9, each member is the same as the member used in the first embodiment. Here, the U-shaped exciting core 13a
The contact position with the heating member 12a is outside the fixing nip N. That is, the inner width T of the U-shaped core 13a is configured to be larger than the fixing nip width N.

As a result, the heat generated in the heating member 12a by the induction heating outside the fixing nip N flows to the exciting core 13a, and the heating member 12a outside the fixing nip N is not overheated. Particularly, when the transfer material is conveyed while the heating member 12a immediately before the fixing nip is overheated by the continuous heat fixing, the toner image fixed on the transfer material is reheated in the fixing nip, and this heat causes the toner There is a possibility that the image may be melted and the toner image on the transfer material may be stripped off due to rubbing against the transport system of the image forming apparatus after the fixing device. Therefore, it is necessary to radiate to some extent the overheating of the heating member 12a immediately after the fixing nip. Therefore, in the present embodiment, the above problems can be prevented by appropriately radiating the excessive heating of the heating member 12a outside the fixing nip to the exciting core 13a.

The above effect was confirmed by shaking the inner width T of the exciting core 12a with respect to the fixing nip N. As a confirmation method, a temperature rise temperature of a protruding portion from the fixing nip on the downstream side of the heating member 12a when 100 transfer materials are continuously conveyed is measured, and a CR rubber (non A conveyance system was constituted by a rubber roller formed from the toner image carrying side) and a roller formed from POM (toner image carrying side), and the image deterioration of the toner image on the transfer material due to being peeled off by the rollers was evaluated. The width of the fixing nip N was fixed at 5 mm, and the power consumption of the heating and fixing device was 500 W. Further, the width of the heating member in the transfer material conveying direction is fixed at 12 mm, and the exciting core 13a and the heating member 12 are
The contact area with a was set similarly. The evaluation results are shown below. In the table, ◯ represents a level without problems, Δ represents an acceptable level, and x represents a poor level.

[0100]

[Table 5]

From the above results, when the inner width T of the U-shaped exciting core 13a is equal to or larger than the fixing nip width N,
Since the heat generated by the heating member 12a escapes to the exciting core 13a side, the temperature rise of the heating member outside the fixing nip becomes small,
It can be seen that the image deterioration is not caused. Therefore, by setting the width T inside the exciting core 13a to be equal to the width of the fixing nip N, preferably 1 mm wider, the heating member is overheated for proper heat dissipation from the heating member outside the fixing nip to the exciting core. As a result, image deterioration due to remelting of the toner image on the transfer material can be prevented.

As described above, in the present embodiment, the contact area between the exciting core and the heating member is set outside the fixing nip, so that the fixing nip is appropriately released from the heating member outside the fixing nip to the exciting core. Suppresses the temperature rise of the outside heating member,
Heat fixing without image deterioration is possible.

(Seventh Embodiment) Next, a seventh embodiment of the present invention will be described with reference to FIG. The same parts as those of the first and sixth embodiments are designated by the same reference numerals and the description thereof will be omitted.

In the present embodiment, a heat insulating member having a large heat insulating property is provided between the heating member on the upstream side of the U-shaped exciting core arranged on the upstream and downstream sides of the fixing nip.

In FIG. 10, each member is the same as the member used in the first embodiment. U-shaped excitation core 1
The contact position of 3a with the heating member 12a is configured to be outside the fixing nip N, and the exciting core 13 on the upstream side thereof is arranged.
A heat insulating member 14 is provided between a and the heating member 12a.
Here, the heat insulating member 14 is a porous material such as heat-resistant silicone sponge, foam glass, or foam concrete, or powdery heat insulating material such as pearlite, alumina powder, carbon balun, cotton such as glass fiber, silica, cotton, or the like. Insulation material is good.

As described above, in the present embodiment, almost no heat flows from the heating member 12a to the exciting core 13a in the upstream of the fixing nip, and thus the heat transfer member 1 protruding toward the upstream of the fixing nip.
The atmosphere immediately before the fixing nip is warmed from 2b. Also,
Since the heat radiation to the exciting core 13a is very small, it is possible to sufficiently warm the atmospheric temperature immediately before the fixing nip even if the amount of protrusion of the heat transfer member 12b to the upstream side of the fixing nip is small. Therefore, when the transfer material is conveyed,
Since the temperature of the atmosphere immediately before the fixing nip is sufficiently raised, the toner image on the transfer material is slightly melted, and the toner itself becomes viscous. As a result, even if the water vapor generated by heating the transfer material in the fixing nip portion flows just before the fixing nip as if the toner on the upstream side of the fixing nip is blown off, the toner image on the transfer material is not covered by the toner. Without being blown off to the upstream side due to ties,
Does not cause image deterioration such as tailing.

[0107]

As described above, the first embodiment according to the present application is described.
According to the invention, the transfer material on which the unfixed image is formed is passed through the nip maintained at a predetermined temperature between the fixing member and the pressure member, so that the unfixed image is transferred onto the transfer material. In a heat fixing device for fixing as a permanent image, a ferromagnetic thin layer heating member which is induction-heated by an exciting coil and a heat transfer member having a small heat capacity and excellent thermal conductivity are provided, and the magnetic permeability of the heating member is transferred to the above-mentioned transfer member. Since it is larger than the heat member, the thin layer ferromagnetic heating member with a small heat capacity is induction-heated, and the heat transfer member with excellent heat conductivity conducts heat transfer from the heating member to the fixing nip part. Since it is possible to heat the part at high speed and there is no need to preheat during standby, the wait time can be eliminated. Further, this makes it possible to sufficiently cope with the speedup of the main body of the image forming apparatus, and in particular, it takes a short time to transfer the transfer material to the fixing nip portion after the print signal is received by the image forming apparatus. This can be an advantageous heating method for a device having a short length.

According to the second aspect of the present invention,
In the first aspect of the invention, since the heat transfer member has excellent thermal conductivity, it produces a heat flow in the longitudinal direction, and even when a small-sized transfer material is transferred, heat in the non-transfer area is transferred. It has a function of flowing into the transport area, and therefore does not cause problems such as buckling of the fixing film, and high durability is not required.

Further, according to the third invention of the present application, in the first or second invention, the transfer material conveyance of the heating member and the heat transfer member having different heat capacities or heat conductivities in the fixing nip. The volume ratio in the direction can be easily changed, and an arbitrary temperature gradient can be provided in the fixing nip. In particular, the volume ratio is distributed so that the heat capacity on the upstream side is smaller than that on the downstream side in the transfer material conveying direction, or the volume ratio of the heat transfer member having high thermal conductivity on the upstream side is increased compared to the downstream side, thereby fixing The temperature is set to be lower on the downstream side than on the upstream side in the transfer material conveying direction in the nip. As a result, the toner image on the transfer material, which is sufficiently melted on the upstream side of the fixing nip, is conveyed to the downstream side of the nip where the temperature is slightly low, is cooled, and then is conveyed to the outside of the fixing nip. The toner image is reliably fixed on the transfer material on the downstream side of the nip without being liquefied and causing high temperature offset. Further, the characteristics that contribute to the heat generation distribution in the longitudinal direction are alleviated, and the fixing property of the transfer material can be made uniform.

Further, according to the fourth invention of the present application,
In any one of the first to third inventions, the volume ratio in the longitudinal direction of the heating member and the heat transfer member having different heat capacities or thermal conductivities in the fixing nip can be easily changed. It is possible to easily give an arbitrary temperature distribution simply by changing. In particular, the heat capacity of the portion corresponding to the end portion of the exciting coil where the generated magnetic field is strong is increased, or the volume ratio of the heating member and the heat transfer member is set so that the thermal conductivity becomes smaller than that in the longitudinal center portion. Inside, a uniform temperature distribution is obtained over the longitudinal direction.

Further, according to the fifth invention of the present application, in any one of the first invention to the fourth invention, the width of the heating member is formed to be wider than the width of the fixing nip portion. As a result, the temperature of the atmosphere immediately before the fixing nip can be increased and a sharp temperature difference between immediately before the fixing nip and upstream of the fixing nip portion can be eliminated. As a result, the transfer material conveyed immediately before the fixing nip is given radiant heat from the heating member immediately before the fixing nip via the fixing film. As a result, the toner image on the transfer material is slightly melted, so that it is possible to prevent the occurrence of tailing in which the water vapor generated from the transfer material in the fixing nip portion blows off the toner image immediately before the fixing nip. On the other hand, by providing the protruding portion of the heat transfer member on the downstream side from the fixing nip portion, it is possible to warm the atmosphere temperature on the downstream side of the fixing nip portion, and thereby the toner on the transfer material which is heat-fixed in the fixing nip portion. The image is not cooled rapidly, and the toner image is solidified by cooling at a slow speed, so that image deterioration such as uneven gloss can be prevented.

According to the sixth invention of the present application,
In any one of the first to fourth inventions, by forming the width of the heat transfer member to be wider than the width of the fixing nip portion, the temperature of the atmosphere immediately before the fixing nip is increased and the temperature immediately before the fixing nip is increased. It is possible to eliminate a sharp temperature difference between the fixing nip portion and the fixing nip portion. As a result, the transfer material conveyed immediately before the fixing nip is given radiant heat from the heating member immediately before the fixing nip via the fixing film. As a result, the toner image on the transfer material is slightly melted, so that it is possible to prevent the occurrence of tailing in which the water vapor generated from the transfer material in the fixing nip portion blows off the toner image immediately before the fixing nip. On the other hand, by providing the protruding portion of the heat transfer member on the downstream side from the fixing nip portion, it is possible to warm the ambient temperature on the downstream side of the fixing nip portion, and thereby the toner on the transfer material which is heat-fixed in the fixing nip portion. The image is not cooled rapidly, and the toner image is solidified by cooling at a slow speed, so that image deterioration such as uneven gloss can be prevented. Further, the startup time (wait time) can be shortened by suppressing the heat capacity of the heating member as small as possible.

Further, according to the seventh invention of the present application, in the fifth invention or the sixth invention, the heat transfer member in the fixing nip portion has different heat conductivity between the upstream side and the downstream side. With this configuration, it is possible to have a temperature distribution in the conveyance direction within the fixing nip, and particularly when the temperature is set lower on the downstream side than on the upstream side, high temperature offset can be easily prevented. It becomes possible.

Further, according to the eighth invention of the present application,
In any one of the fifth to seventh inventions, the contact position between the exciting core and the heating member is set to a position outside the fixing nip, and fixing is performed during continuous heat fixing as compared with inside the fixing nip portion. The heating member protruding before and after the nip is prevented from being overheated by appropriately radiating heat from the heating member outside the fixing nip to the exciting core. This prevents an abnormal temperature rise in the protruding portion of the heating member from the fixing nip, and prevents the toner image on the transfer material from being melted again by the heating member having a higher heat than that in the fixing nip before and after the fixing nip, particularly immediately after the fixing nip. To prevent. Further, a heat insulating member is provided only at the heating member contacting position on the upstream side of the exciting core provided outside the fixing nip, in particular, the heat escape to the upstream side of the exciting core is reduced, and the preheating effect immediately before the fixing nip is effectively made. Use it to prevent tailing.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a heat fixing device in the device of FIG.

FIG. 3 is an enlarged view of a heating unit in the apparatus shown in FIG.

FIG. 4 is an enlarged view of a heating means according to a second embodiment of the present invention.

FIG. 5 is an enlarged view of a heating means according to a third embodiment of the present invention.

FIG. 6 is a diagram showing a temperature distribution of a heating unit in an example and a comparative example in the third exemplary embodiment of the present invention.

FIG. 7 is an enlarged view of a heating means according to a fourth embodiment of the present invention.

FIG. 8 is an enlarged view of a heating means according to a fifth embodiment of the present invention.

FIG. 9 is an enlarged view of a heating unit according to a sixth embodiment of the present invention.

FIG. 10 is an enlarged view of a heating means according to a seventh embodiment of the present invention.

FIG. 11 is a configuration diagram of a heat fixing device according to a conventional example.

FIG. 12 is a configuration diagram of a heat fixing device according to a conventional example.

[Explanation of symbols]

 11 Fixing Film 12a Heating Member (Ferromagnetic Heating Member) 12b, 12c Heat Transfer Member 13 Excitation Coil 20 Pressure Roller (Pressure Member) P Transfer Material

Front page continuation (72) Inventor Yuko Ogama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Masahiro Goto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yozo Hotta 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (8)

[Claims] 1. A heating unit, a fixing film arranged so as to rub against a part of the heating unit, and a pressure member arranged so as to come into pressure contact with the heating unit through the fixing film. And a heating member for fixing the unfixed image as a permanent image on the transfer material by passing the transfer material on which the unfixed image is formed through the pressure contact portion. A ferromagnetic heating member that is heated by electromagnetic induction by the exciting coil, and a heat transfer member that transfers heat generated by the ferromagnetic heating member to the press contact portion, and the magnetic permeability of the ferromagnetic heating member is the heat transfer coefficient. A heat fixing device characterized by being larger than the member. 2. The heat fixing device according to claim 1, wherein the heat conductivity of the heat transfer member is higher than that of the ferromagnetic heating member. 3. The volume ratio of the ferromagnetic heating member and the heat transfer member is
2. A distribution is provided in the transfer material conveying direction.
Alternatively, the heat fixing device according to claim 2. 4. The volume ratio between the ferromagnetic heating member and the heat transfer member is
The heat fixing device according to any one of claims 1 to 3, wherein the ferromagnetic heating member and the heat transfer member have a distribution in a longitudinal direction. 5. The heating according to claim 1, wherein the width of the ferromagnetic heating member in the transfer material conveyance direction is larger than the width of the pressure contact portion between the heating means and the pressing member. Fixing device. 6. The heat fixing according to claim 1, wherein the width of the heat transfer member in the transfer material conveyance direction is larger than the width of the pressure contact portion between the heating unit and the pressure member. apparatus. 7. The heat fixing device according to claim 5, wherein a distribution of heat conductivity or heat capacity is formed in the transfer material conveying direction. 8. The heating according to claim 5, wherein a contact position between the exciting coil and the ferromagnetic heating member is outside the pressure contact portion between the heating means and the pressure member. Fixing device.