JP2003091185A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a temperature difference in the width direction of a fixing member small and to efficiently heat the fixing member in a fixing device where an unfixed toner image carried on a recording medium is heated and melted by an electromagnetic induction heating device and fixed on the recording medium. SOLUTION: A pressure pad 3 and a pad supporting member 4 supporting the pad 3 are provided on the inside of a fixing belt 1, and the electromagnetic induction heating device is provided to be opposed to the belt 1. The pad supporting member 4 is a bar-like member having a nearly circular cross section, and its diameters at both ends are reduced so that the inner surface guide part 22 of a guide member 6 may be fit. A heat absorption part 23 consisting of heat-resistant resin is formed to be integrated with the guide part 22. The heat absorption part 23 abuts on the inner peripheral surface of the belt 1 at a part heated by a part 24 where the winding of an exciting coil 5b is folded and having high calorific power and takes away heat from the belt 1. Therefore, the temperature in the width direction of the belt 1 becomes nearly uniform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in image recording devices such as printers, copiers and facsimiles.
The unfixed toner image carried on the recording medium is heated and melted,
The present invention relates to a fixing device that fixes a recording medium.

[0002]

2. Description of the Related Art Generally, in a process of fixing a toner image in an image forming apparatus using powdery toner, a toner image is electrostatically transferred onto a recording medium and then the toner image is melted on the recording medium by a fixing device. The crimping method is widely adopted.

The above-mentioned fixing device comprises a fixing member and a pressure member pressed against the fixing member. A recording medium carrying an unfixed toner image is sandwiched between the fixing member and the pressure member. It is heated and pressed to fuse the toner image to the recording medium to form a fixed image. As the fixing member, a heating element such as a halogen lamp is arranged inside a cylindrical core metal, and an elastic layer and a release layer are provided on the surface of the core metal, and the fixing member is supported in a tension-free state, and is heat resistant. An endless film having a heating element and an internal pressure member is generally used.

When power is applied to the heating element, the surface of the fixing member is heated to a temperature suitable for heating and melting the toner image due to radiant heat or contact heat of the heating element. However, when a heating element such as a halogen lamp is used as a heating source, it takes time for the heat of the heating element to be transferred to the surface of the fixing member after power is applied to the heating element and the fixing member reaches a predetermined temperature. . For this reason, it takes a long time to warm up the fixing member when the apparatus is started or when returning from the standby state, and power consumption increases.

Under these circumstances, as a means for heating the fixing member, there is known one in which a conductive layer is provided on the fixing member and the conductive layer is heated by electromagnetic induction heating.
In electromagnetic induction heating, an exciting coil that generates a fluctuating magnetic field is arranged opposite to a conductive layer, and a magnetic flux that penetrates the conductive layer is generated to generate an eddy current in the conductive layer and generate heat. According to the electromagnetic induction heating, the conductive layer can be heated in a very short time, and the fixing member can be directly heated. Therefore, as compared with the case where a heating element such as a halogen lamp is used as a heating source, the warming up of the device can be performed efficiently. Further, the exciting coil can be arranged either inside or outside the fixing member so as to face the conductive layer, which increases the degree of freedom in design.

[0006]

However, since the exciting coil is wound around a magnetic core or a non-magnetic core material arranged in parallel with the width direction of the fixing member, the exciting coil is alternately arranged. When a current is applied, magnetic flux is concentrated at both ends of the exciting coil, and accordingly, the amount of heat generated near both side edges of the conductive layer increases. On the other hand, the conductive layer is made of a thin metal layer having a small heat capacity, and heat is difficult to transfer in the width direction. Distribution will occur.

If the temperature of the fixing member in the width direction is not uniform as described above, the toner image may not be heated well, and the fixed image may have uneven gloss or uneven color. Further, when an endless film is used as the fixing member, the coefficient of thermal expansion of the film varies depending on the temperature unevenness in the width direction, so that a difference in transport speed occurs between the central portion and both end portions of the film, and wrinkles occur in the circumferential direction. Will result in poor fixing.

Means for correcting the temperature difference in the width direction of the endless film as described above have been proposed in JP-A-8-30126 and JP-A-8-286534.
In the fixing device described in Japanese Patent Application Laid-Open No. 8-30126, a pressure plate made of a material having good thermal conductivity is in contact with the inner peripheral surface of an endless fixing film having a conductive layer, and an electromagnetic wave is further inside. An induction heating device is arranged. When the conductive layer heats up by the electromagnetic induction heating device, the heat of the conductive layer is transferred to the pressure plate and is transferred in the axial direction of the pressure plate, so that the temperature of the conductive layer in the axial direction becomes substantially uniform. However, since the pressure plate uses a ceramic with a large heat capacity,
It takes a long time to warm up the fixing film to heat the fixing film to a temperature at which the toner image is heated and melted.

Further, in the fixing device described in Japanese Patent Application Laid-Open No. 8-286534, an electromagnetic induction heat-generating member and an exciting coil are arranged inside the fixing film, and the electromagnetic induction heat-generating member is located near the central portion. The heat capacity at both ends is large, and the temperature at both ends does not rise easily. Alternatively, the amount of heat generation at both ends is suppressed by increasing the gap between the electromagnetic induction heat generating member and the exciting coil at both ends or changing the magnetic permeability of the electromagnetic induction heat generating member. Therefore, the temperature distribution of the fixing member in the axial direction becomes substantially uniform. But,
These electromagnetic induction heat-generating members have a problem that the structure becomes complicated and high precision is required for manufacturing, so that the production cost becomes high.

The present invention has been made in view of the above circumstances, and an object thereof is to heat a fixing member heated by electromagnetic induction to an unfixed toner image carried on a recording medium to heat it. In a fixing device that melts and fixes to a recording medium, the temperature distribution in the width direction of the fixing member is reduced, and the fixing member is efficiently heated.

[0011]

In order to solve the above problems, the invention according to claim 1 has an endless peripheral surface,
A fixing belt having a conductive layer along the peripheral surface, a pad supported so as to contact the inner peripheral surface over substantially the entire width of the fixing belt, and an outer peripheral surface of the fixing belt that contacts the fixing belt. A pressure member that is pressed against the pad via a belt, and an eddy current that is disposed so as to face the fixing belt and that generates a fluctuating magnetic field in the conductive layer of the fixing belt A fixing device for fixing a toner image by passing a recording medium carrying an unfixed toner image between the fixing belt and the pressure member, and heating and pressing the toner image to fix the toner image. The inner peripheral surface of the fixing belt is abutted with a heat absorbing member that absorbs heat to correct temperature unevenness in the width direction of the fixing belt due to heating by the electromagnetic induction heating device. Fixing To provide a location.

The electromagnetic induction heating device causes the conductive layer of the fixing belt to generate heat so that the surface of the fixing belt has a temperature suitable for heating and melting the toner image. The recording medium carrying the unfixed toner image is fed between the heated fixing belt and the pressure member, the unfixed toner image is melted by the heat of the fixing belt, and the pressure contact between the pressure member and the pad is performed. It is pressed against the recording medium by force to form a fixed image. In heating by the electromagnetic induction heating device, temperature unevenness occurs in the width direction of the fixing belt due to distribution of magnetic flux generated, etc., but the heat absorbing member is in contact with the inner peripheral surface of the portion where the temperature of the fixing belt becomes high. The heat is absorbed by the heat absorbing member and the temperature is lowered. In this way, the fixing belt is encouraged to have a uniform temperature in the width direction, and the temperature difference in the width direction is reduced. For this reason, it is possible to prevent uneven heating of the toner image and wrinkles on the fixing belt due to uneven temperature of the fixing belt, and it is less likely that defective fixing will occur.

According to a second aspect of the present invention, in the fixing device according to the first aspect, the heat absorbing member is located downstream of the position where the electromagnetic induction heating device faces when the fixing belt moves circularly. It is assumed that the pad is in contact with the inner peripheral surface of the fixing belt on the upstream side of the position where the pad is in contact.

When the fixing belt passes by a circular movement through a position facing the electromagnetic induction heating device, the conductive layer generates heat and the temperature rises sharply. At this time, temperature unevenness occurs in the width direction of the fixing belt, but the high temperature portion of the fixing belt absorbs heat by the heat absorbing member, and the temperature decreases, and the temperature in the width direction of the fixing belt becomes substantially uniform. After that, the fixing belt is conveyed to the pressure contact portion between the pad and the pressure member, contacts the toner image on the recording medium, heats and melts the toner image, and the temperature decreases again. That is, after the fixing belt is heated, the temperature unevenness in the width direction is corrected, and the fixing belt is pressed against the toner image. Further, when the fixing belt is driven at the pressure contact portion between the pad and the pressure member, on the upstream side of this pressure contact portion,
The heat absorbing member, which is applied with a tensile force to the fixing belt and is in contact with the inner peripheral surface of the fixing belt, is in close contact with the inner peripheral surface of the fixing belt and absorbs heat well.

According to a third aspect of the present invention, in the fixing device according to the first aspect, a cylindrical curved surface is provided, and the cylindrical curved surface comprises:
The fixing belt has a pair of inner surface guide members that come into contact with the inner peripheral surfaces of both side edge portions of the fixing belt, and the heat absorbing member is provided so as to be integrated with the inner surface guide member, and is arranged in the width direction of the fixing belt. It shall be supported so as to project to the center side.

The fixing belt maintains the shape of the peripheral surface due to the rigidity of the fixing belt itself and the inner surface guide member which is in contact with the inner peripheral surface at both side edges of the fixing belt. Since the inner surface guide member is only in contact with the inner peripheral surfaces of both side edges of the fixing belt, heat is less likely to be taken away by other members at the central portion in the width direction of the fixing belt, and the fixing belt is heated by electromagnetic induction heating. The device efficiently heats up to a predetermined temperature. Then, when temperature unevenness occurs in the width direction of the fixing belt, the heat absorbing member supported so as to project from the inner surface guide member to the central portion side in the width direction of the fixing belt contacts the high temperature portion of the fixing belt. They come into contact with each other and absorb heat from the fixing belt to correct uneven temperature.

According to a fourth aspect of the present invention, in the fixing device according to the first aspect, the heat absorbing member is provided so as to be integrated with a pad supporting member that supports the pad.

The pad is supported by a pad supporting member so as to contact the inner peripheral surface over substantially the entire width of the fixing belt, and a pressing force is applied to the pad supporting member from the pressing member via the fixing belt and the pad. To work. It is desirable that the pad support member have rigidity to withstand this pressing force and be in non-contact with the fixing belt so that heat of the fixing belt is not transferred. The belt can be accurately brought into contact with the high temperature portion, and the temperature unevenness in the width direction of the fixing belt can be effectively corrected.

According to a fifth aspect of the present invention, in the fixing device according to the first aspect, a cylindrical curved surface is formed by cutting out a part in a circumferential direction, and the cylindrical curved surface is an inner circumference at both side edge portions of the fixing belt. A pair of inner surface guide members that are in contact with the surface, and the electromagnetic induction heating device heats a central portion side from a portion in contact with the inner surface guide member in the width direction of the fixing belt, The member is provided between the position where the pair of inner surface guide members are in contact with the fixing belt.

Since the fixing belt is heated by the electromagnetic induction heating device in a region where the inner guide member of the fixing belt is not in contact, the heat of the fixing belt is difficult to be transferred to the inner guide member, so that the fixing belt can be efficiently transferred. The temperature is raised to a predetermined temperature. The heat absorbing member is located between the positions where the pair of inner surface guide members are in contact with the fixing belt, that is,
It is provided in the heating range by the electromagnetic induction heating device, and temperature unevenness in the width direction of the fixing belt in this range is corrected.

According to a sixth aspect of the present invention, in the fixing device according to the first aspect, the circumferential length of the contact area of the heat absorbing member with the fixing belt changes in the width direction.

The amount of heat conduction from the fixing belt to the heat absorbing member is
Since the fixing belt, which is driven in the circumferential direction, is in contact with the heat absorbing member in time, the amount of heat conduction increases as the length of the heat absorbing member in the circumferential direction increases, and the temperature of the fixing belt further decreases. Therefore, according to the characteristics of the electromagnetic induction heating device, the circumferential length of the heat absorbing member abutting on the fixing belt is changed from both side edge portions of the fixing belt toward the central portion side, thereby fixing the fixing belt. The temperature in the width direction of the belt can be more accurately and substantially uniform.

According to a seventh aspect of the present invention, in the fixing device according to the first aspect, the exciting coil of the electromagnetic induction heating device has windings arranged in parallel to the width direction of the fixing belt, and the parallel portion is formed. The heat absorbing member is provided at a position corresponding to the folded back portion of the exciting coil in the width direction of the fixing belt.

The exciting coil has windings arranged in parallel to the width direction of the fixing belt and is continuous so as to be folded back at both ends of the parallel portion. Therefore, when an alternating current is applied to the exciting coil, magnetic flux is concentrated at both ends of the exciting coil, and accordingly, the amount of heat generated near both side edges of the conductive layer of the fixing belt increases. In the fixing device, the heat absorbing member is provided at a position corresponding to the folded back portion of the exciting coil in the width direction of the fixing belt.
Even if the amount of heat generated at both side edges of the fixing belt is higher than that near the central portion, temperature unevenness does not easily occur in the width direction of the fixing belt.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a fixing device which is an embodiment according to claim 1, claim 2, claim 3, claim 5, claim 6 or claim 7. This fixing device includes a fixing belt 1 having an endless peripheral surface,
The pressure roll 2 that contacts the outer peripheral surface of the fixing belt 1.
A pressure pad 3 that is in contact with the back side of the fixing belt 1 and presses the fixing belt 1 against the pressure roll 2, a pad support member 4 that supports the pressure pad, and an outer peripheral surface of the fixing belt 1. The fixing belt 1 is provided along with an electromagnetic induction heating device 5 for heating the fixing belt 1, and guide members 6a and 6b which are in contact with inner peripheral surfaces of both side edges of the fixing belt 1.

Next, details of the structure of the fixing device will be described. The fixing belt 1 is composed of three layers including a base layer having sufficient strength, a conductive layer laminated on the base layer, and a top surface release layer. The base layer is
A highly heat-resistant resin such as polyester, polyethylene terephthalate, polyether sulfone, polyether ketone, polysulfone, polyimide, polyimide amide, or polyamide having a thickness of 10 to 100 μm is used.
The conductive layer is, for example, iron, nickel, cobalt, copper,
Chromium, aluminum, stainless steel, or an alloy mainly composed of them is formed to have a thickness of about 1 μm to 50 μm, and the material is selected so as to have a specific resistance value such that sufficient heat is obtained by electromagnetic induction. . The surface release layer is preferably a sheet or coat layer having a high release property, and examples thereof include PFA (tetrafluoroethylene perfluoroalkyl vinyl ether polymer), PTFE (polytetrafluoroethylene) silicon copolymer or A composite layer or the like can be used. If the surface release layer is too thin, the wear resistance will be poor, and if it is thick, the heat capacity will increase.
It is desirable that the thickness is about 1 μm to 50 μm. In this embodiment, the fixing belt 1 has a circular cross section with a diameter of 30 mm in a tension-free state and has a polyimide of 50 μm as a base layer so as to have rigidity such that buckling does not occur in the width direction. A layer in which 5 μm of copper is laminated as a conductive layer by means of plating or the like, and PFA is further laminated as a surface release layer is used.

The pressure roll 2 has a metal cylindrical core metal 2a as a core material, an elastic layer 2b of synthetic resin foam or rubber on the surface of the core metal 2a, and a surface release on the surface. Layer 2
and c. In this embodiment, a solid iron roll surface having a diameter of 22 mm has a thickness of 3 mm and a rubber strength of 60 ° (JI
SA) silicone rubber is provided and this is coated with PFA. The pressure roll 2 is rotationally driven by a drive motor (not shown), and the fixing belt 1 is driven to rotate accordingly.

The pressure pad 3 is made of an elastic material and forms a nip portion between the pressure pad 3 and the pressure roll 2 with the fixing belt 1 interposed therebetween. In this embodiment, this elastic body is made of silicone rubber having a thickness of 3 mm and a rubber strength of 30 ° (JIS-A), and the contact surface with the fixing belt 1 is along the peripheral surface of the pressure roll 2. It has a curved shape. Therefore, the recording paper P fed into the nip portion between the pressure roll 2 and the fixing belt 1 is
The shape of the fixing belt 1, that is, the shape of the fixing belt 1 advances along the circumferential surface of the pressure roll 2, but the shape of the fixing belt 1 changes abruptly at the exit of the nip portion. To be done.

The elastic body is adhered to a supporting member having rigidity. As the supporting member, for example, a metal such as stainless steel or aluminum or a resin having high heat resistance can be used. However, if the support member is placed in a place affected by the magnetic flux from the electromagnetic induction heating device,
By using a synthetic resin, aluminum with low magnetism, non-magnetic stainless steel, or the like, it is possible to prevent the heating efficiency of the fixing belt 1 from decreasing.

Between the pressure pad 3 and the fixing belt 1, a sheet-like member having high wear resistance and slidability is provided in order to improve the slidability of the fixing belt 1 and further lubricated. Apply the material. In this embodiment, a glass fiber sheet impregnated with a fluororesin is used as the sheet-shaped member, and silicone oil is used as the lubricant. As a result, when the pressure roll 2 is rotated, the drive torque of the conventional pressure roll (which does not use the sheet-shaped member and the lubricant) was about 6 kg / cm, whereas it was about 3 kg / cm.
The fixing belt 1 is smoothly rotated by the rotation of the pressure roller 2.

Both ends of the pad supporting member 4 are fixedly supported by the frame of the fixing device main body, and as shown in FIG. 2, they are rod-shaped members having a substantially circular cross section. The both ends have a reduced diameter, and the guide members 6a and 6b are fitted in these parts. The pressure pad 3
Is adhered along the axis between these two guide members, and when a pressure contact force is applied from the pressure roll 2 via the fixing belt 1, the pad support member 4 causes the pressure pad 3 to move.
It is designed to receive this pressure contact force on the back surface of. The pad support member 4 is made of glass-containing PPS (polyphenylene sulfide), phenol, polyimide, so as not to be heated by the influence of magnetic flux by the electromagnetic induction heating device 5.
A heat resistant resin such as a liquid crystal polymer or heat resistant glass can be used as a material. In this embodiment, glass-containing PP
S is used. Further, the pad supporting member 4 has an outer peripheral surface of the pad supporting member 4 and an inner peripheral surface of the fixing belt 1 so that heat is not transferred from the fixing belt 1 and the slidability of the fixing belt 1 is not affected. Is non-contact.

The electromagnetic induction heating device 5 comprises the fixing belt 1
Along the outer peripheral surface, the gap with this outer peripheral surface is 0.5 m.
The exciting coil 5b, which is arranged so as to be m to 2 mm, is supported by the coil supporting member 5a, and the exciting coil 5b.
The exciting circuit 5c for supplying an alternating current to b constitutes the main part. In the present embodiment, as the exciting coil 5b, a litz wire in which 16 copper wires having a diameter of 0.5 mm which are insulated from each other are bundled is used, and continuous litz wires are arranged in parallel to the width direction of the fixing belt 1. , Both ends of the parallel part are folded back. The coil support member 5a is preferably made of a heat-resistant non-magnetic material, for example, heat-resistant glass or heat-resistant resin such as polycarbonate.

When an alternating current is supplied from the exciting circuit 5c to the exciting coil 5b, magnetic flux is repeatedly generated and extinguished around the exciting coil 5b. Then, this magnetic flux is applied to the fixing belt 1.
When the conductive layer is crossed, an eddy current is generated in the conductive layer so as to generate a magnetic field that prevents the change of the magnetic field, and heat is generated in proportion to the skin resistance of the conductive layer. As a result, the fixing belt 1 is heated to a predetermined temperature.

The guide members 6a and 6b are made of heat-resistant resin, and as shown in FIG. 3, have an edge guide portion 21 and an inner surface guide portion 22, and are rectangular so as to be integrated with the inner surface guide portion 22. The heat absorbing part 23 is provided. As shown in FIG. 2, the inner surface guide portion 22 is fitted to the reduced diameter portion 4 a provided at the end portion of the pad support member 4, and the edge guide portion 21 comes close to or abuts on the edge of the fixing belt 1. To be done. As a result, the fixing belt 1 is restricted from moving in the width direction by the edge guide portion 21, and meandering when the fixing belt 1 orbits along with the driving of the pressure roller 2 is prevented.

The outer peripheral surface of the inner surface guide portion 22 is in contact with the inner peripheral surface of the end portion of the fixing belt 1 and stretches the end portion of the fixing belt in the circumferential direction. The fixing belt 1 maintains the shape of the peripheral surface due to the inner surface guide portion 22 and the rigidity of the fixing belt 1 itself, and slides along the outer peripheral surface of the inner surface guide portion 22. Since the inner surface guide portion 22 comes into contact with the fixing belt 1 to absorb heat, it is desirable that the number of contact portions with the fixing belt 1 is small. Further, heating the area in contact with the inner surface guide portion 22 by the electromagnetic induction heating device 5
Since the power consumption is lost, the exciting coil 5b is arranged at a position facing the central portion side of the portion where the pair of inner surface guide portions 22a and 22b contact the fixing belt 1, as shown in FIG.

The heat absorbing portion 23 is in contact with the inner peripheral surface of the fixing belt 1 on the downstream side of the position where the electromagnetic induction heating device 5 faces and on the upstream side of the nip portion, and heat from the fixing belt 1 is absorbed. Transmitted. As shown in FIG. 4, the heat absorbing parts 23a, 23
b extends from the inner surface guide portion 22 to the central portion side in the width direction of the fixing belt 1, and corresponds to the portions 24a and 24b where the winding of the exciting coil 5b is folded back in the width direction of the fixing belt 1. It is provided in.
The shape of the heat absorbing portion 23 is adjusted in consideration of the temperature distribution of the fixing belt 1 so that a desired amount of heat is transferred from the fixing belt 1 to the heat absorbing portion 23. May vary depending on the position from the side edge portion of the fixing belt 1 toward the central portion side.

Next, the operation of the fixing device will be described. A toner image T of four color toners of yellow, magenta, cyan, and black is transferred onto the recording paper P by a transfer device (not shown). These toners are composed of a thermoplastic resin binder containing a color pigment. The pressure roll 2 is rotated by a drive motor (not shown), and the fixing belt 1 is driven by the pressure roll 2 to rotate,
When passing through the heating area facing the electromagnetic induction heating device 5, the toner image T is heated to a temperature suitable for melting and heating. The recording paper P carrying the toner image T is fed to the nip portion where the fixing belt 1 and the pressure roll 2 are in contact with each other.
The toner image T is heated and melted by the fixing belt 1, and at the same time, is pressed onto the recording paper P by the pressure contact force between the pressure roll 2 and the pressure pad 3. Since the shape of the fixing belt 1 changes rapidly at the exit of the nip portion, the recording paper P is separated from the fixing belt 1 due to the rigidity of the recording paper itself, and a fixed image is formed.

Since the exciting coil 5b included in the electromagnetic induction heating device 5 is folded back at both ends of the portion arranged in parallel with the width direction of the fixing belt 1, the exciting coil 5b.
When an alternating current is applied to the magnetic flux, magnetic flux is concentrated and generated at both ends of the exciting coil 5b. Along with this, the fixing belt 1
A large amount of heat is generated in the vicinity of both side edges of the conductive layer included in, that is, a portion corresponding to the position where the magnetic flux is concentrated. Guide members 6a and 6b supporting both side edges of the fixing belt 1 are in contact with the inner peripheral surface near both side edges of the fixing belt 1, and a heat absorbing portion continuously provided with the guide members 6a and 6b. Two
3a and 23b are in contact with the portion of the fixing belt 1 where the heat generation amount is large. The heat absorbing portion 23 is made of a heat resistant resin having a large heat capacity, heat is transferred from the fixing belt 1 to the heat absorbing portions 23a and 23b, and the temperature of the portion of the fixing belt 1 where the heat generation amount is large is lowered. Therefore, the temperature of the fixing belt 1 in the width direction becomes substantially uniform.

In this embodiment, the process speed (peripheral speed) of the pressure roll 2 is 140 mm / s, and the fixing belt 1 is driven by the pressure roll 2 to move at 140 mm / s. When 900 W of effective power is supplied from the exciting circuit 5c of the electromagnetic induction heating device 5 to the exciting coil 5b, the fixing belt 1 reaches a temperature at which fixing is possible in about 3 seconds. As for the temperature of the fixing belt 1 at the entrance of the nip portion, assuming that the length of the heat absorbing portion in the circumferential direction is 5 mm, as shown in FIG. 5, the temperature of the central portion of the fixing belt 1 and the positions corresponding to both ends of the exciting coil 5b. Was 200 ° C.

On the other hand, when the guide member was not provided with a heat absorbing portion, when the temperature of the central portion of the fixing belt was 200 ° C., it was 220 ° C. at the positions corresponding to both ends of the exciting coil. Further, when a heat absorbing portion of 7 mm is provided in the circumferential direction, the contact area between the fixing belt and the heat absorbing portion is large, so that the temperature at the position corresponding to both ends of the exciting coil is 190 ° C. and is 3 m.
Since the contact area is small in the heat absorption part of m, it becomes 210 ° C,
In either case, temperature unevenness occurred in the width direction of the fixing belt.

FIG. 6 is a schematic configuration diagram showing a fixing device according to an embodiment of the present invention. In this fixing device, the pad support member 34 is provided with heat absorbing portions 34a and 34b, and a convex portion is provided near a position where the guide members 36a and 36b are fitted to each other.
Is to be contacted with. The fixing belt 31, the pressure roll 32, the pressure pad 33, and the electromagnetic induction heating device 35 are the same as those of the fixing device shown in FIG. Further, the guide members 36a and 36b are the same as those shown in FIG.
As shown in (b) and FIG. 7, the pad support member 34 is fitted to both ends of the fixing belt 31, and abutted on the inner peripheral surfaces of both side edges of the fixing belt 31, and the edge guide portions are provided on both side edges of the fixing belt 31. The fixing belt 31 is abutted against the portion to prevent meandering when the fixing belt 31 goes around.

The pad supporting member 34 is a rod-shaped member having a substantially circular cross section, and as shown in FIG. 8, the heat absorbing portion 34a.
Are integrally formed so as to project from the peripheral surface of the pad support member 34. The top of the convex portion is a curved surface along the inner peripheral surface of the fixing belt 31, and almost the entire curved surface is in contact with the inner peripheral surface of the fixing belt 31. The heat absorbing portion 34a is provided on the downstream side of the position where the electromagnetic induction heating device 35 faces and on the upstream side of the nip portion.
In the width direction of the fixing belt 31, it is provided at a position corresponding to the folded back portion of the exciting coil 35b arranged in parallel with the width direction of the fixing belt 31.

In the present embodiment, the fixing belt 31 has the highest temperature at the portions where the central portions of the heat absorbing portions 34a and 34b in the width direction of the fixing belt 31 contact. Endotherm 3
4a and 34b are long in the width direction of the fixing belt 31, and the length in the circumferential direction is 2 m at both ends in the width direction.
m, 5 mm in the central part. This is because the amount of heat generated at the portion where the magnetic flux due to the exciting coil is concentrated has a mountain-shaped peak, and the amount of heat absorption corresponds to this peak shape. The highest temperature portion of the fixing belt 31 is the heat absorbing portion 34.
The contact time with a and 34b becomes maximum. As a result, the fixing belt 31 has a substantially uniform temperature in the width direction.

By providing a ferromagnetic material such as ferrite inside the exciting coil, the magnetic flux can efficiently penetrate through the conductive layer of the fixing belt. However, the magnetic flux can be penetrated to the end portion of the ferromagnetic material. The magnetic flux concentrates, which causes a problem that the amount of heat generated by the conductive layer facing the end of the ferromagnetic material increases. The present embodiment is also effective in such a case,
By providing a heat absorbing portion at a position corresponding to the end portion of the ferromagnetic body in the width direction of the fixing belt, the fixing belt has a substantially uniform temperature in the width direction.

[0045]

As described above, in the fixing device according to the present invention, the inner peripheral surface of the portion where the temperature of the fixing belt becomes high with respect to the temperature difference generated in the width direction of the fixing belt due to the characteristics of the electromagnetic induction heating device. The heat-absorbing portion abutted against absorbs heat, and the temperature difference is corrected. Therefore, it is possible to prevent uneven heating of the toner image and wrinkles on the fixing belt due to uneven temperature of the fixing belt, and it is possible to obtain a good image without defective fixing.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram illustrating a fixing device that is an embodiment of the present invention.

2A and 2B are a cross-sectional view and a schematic perspective view of a main part of the fixing device shown in FIG.

3A and 3B are a front view and a side view of a guide member included in the fixing device illustrated in FIG.

FIG. 4 is a schematic diagram showing a relationship between a coil configuration and a heat absorbing portion of the fixing device shown in FIG.

5 is a diagram showing a temperature distribution in the width direction of the fixing belt in the fixing device shown in FIG.

FIG. 6 is a schematic configuration diagram showing a fixing device according to another embodiment of the present invention.

7A and 7B are a front view and a side view of a guide member included in the fixing device illustrated in FIG.

8 is a schematic perspective view showing a heat absorbing portion of the fixing device shown in FIG.

[Explanation of symbols]

1,31 fixing belt 2, 32 pressure roll 3, 33 pressure pad 4, 34 Pad support member 5,35 Electromagnetic induction heating device 6,36 guide member 21 Edge guide part 22 Inner surface guide 23 Heat absorption part

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H033 AA03 BA11 BA25 BA27 BA29                       BB03 BB05 BB06 BB13 BB14                       BB23 BB28 BE06                 3K059 AB04 AD05 AD07 AD39 CD52

Claims (7)

[Claims] 1. A fixing belt having an endless peripheral surface and having a conductive layer along the peripheral surface, and a pad supported over almost the entire width of the fixing belt so as to contact the inner peripheral surface. A pressing member that is in contact with the outer peripheral surface of the fixing belt and is pressed by the pad via the fixing belt; and a fixing member that is arranged so as to face the fixing belt and forms a fluctuating magnetic field. And an electromagnetic induction heating device that heats the conductive layer by an eddy current generated in the conductive layer, passing a recording medium carrying an unfixed toner image between the fixing belt and the pressing member. A fixing device that heats and pressurizes a toner image to correct the temperature unevenness in the widthwise direction of the fixing belt due to heating by the electromagnetic induction heating device on the inner peripheral surface of the fixing belt. The heat absorbing member that absorbs heat is Fixing apparatus characterized by being. 2. The fixing belt is provided on the downstream side of a position where the electromagnetic induction heating device faces the upstream side of a position where the pad is abutted when the fixing belt moves around. The fixing device according to claim 1, wherein the fixing device is in contact with the inner peripheral surface of the fixing device. 3. A cylindrical curved surface is provided, and the cylindrical curved surface has a pair of inner surface guide members that are in contact with inner peripheral surfaces at both side edge portions of the fixing belt, and the heat absorbing member is the inner surface guide member. The fixing device according to claim 1, wherein the fixing device is integrally provided and is supported so as to project toward a central portion side in the width direction of the fixing belt. 4. The fixing device according to claim 1, wherein the heat absorbing member is provided so as to be integrated with a pad supporting member that supports the pad. 5. A cylindrical curved surface, which is partially cut away in the circumferential direction, has a pair of inner surface guide members that are in contact with inner peripheral surfaces of both side edges of the fixing belt. The electromagnetic induction heating device heats a central portion side of a portion in contact with the inner surface guide member in the width direction of the fixing belt, and the heat absorbing member includes a pair of the inner surface guide members that contact the fixing belt. The fixing device according to claim 1, wherein the fixing device is provided between the contacting positions. 6. The fixing device according to claim 1, wherein the heat absorbing member has a circumferential length of a contact region with the fixing belt that varies in the width direction. 7. An exciting coil included in the electromagnetic induction heating device has windings arranged in parallel to a width direction of the fixing belt and continuous so as to be folded back at both ends of the parallel portion. The fixing device according to claim 1, wherein is provided at a position corresponding to a folded-back portion of the exciting coil in a width direction of the fixing belt.