JP2000235329A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the surface temp. unevenness on a fixing roller both end parts at the time of starting a fixing roller and to restrain the progress of heat deterioration of respective member on the fixing device and to avoid hot offsetting of toner on the fixing roller surface on the non-paper passing area by preventing the both end part from becoming abnormally high temp. SOLUTION: Induction heating means provided with a magnetic body core 8 and an exciting coil 7 is arranged with the sectional plane E type magnetic body core 8 and the exciting coil 7 over the rotary shaft direction inside the fixing roller 1, and to arrange them on both end part only outside the fixing roller 7. In such a manner, the fixing device is made possible to independently control the surface temp. on the fixing roller 1 in the center part and both end parts of the fixing roller 1 by controlling means, and to normally maintain the temp. distribution on the surface of the fixing roller 1 uniformly with regard to the rotary shaft direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for fusing and fixing a toner image formed on a transfer material in an image forming apparatus.

[0002]

2. Description of the Related Art An image forming apparatus using an electrophotographic method is:
Normally, a transfer material and a toner made of a resin, a magnetic material, a colorant, and the like, which are electrostatically carried on the transfer material, are pressed and rotated at a pressure contact portion (nip portion) of a fixing roller and a pressure roller which are pressed and rotated with each other. It has a fixing device that performs fusing and fixing by applying heat and pressure while nipping and conveying.

In such a fixing device, as a means for heating, a method has been proposed in which an eddy current is generated in a conductive layer provided on the fixing roller by a magnetic field generated by an exciting coil to generate heat by Joule heat.

In this method, the heat generation source can be placed very close to the toner, so that the temperature of the surface of the fixing roller is more suitable for fixing when the fixing device is started, as compared with the conventional heat roller method using a halogen lamp. The feature is that the time required to reach the temperature can be shortened. Another feature is that the heat transfer path from the heat generation source to the toner is short and simple, so that the heat efficiency is high.

[0005]

However, in the case of the above-described prior art, the following problems have occurred.

In order to take advantage of the fact that the time required for the surface temperature of the fixing roller to reach an appropriate temperature for fixing when starting the fixing device can be shortened, the heat capacity of the fixing roller should be as small as possible. When the fixing roller is used, it becomes difficult to transfer heat in the rotation axis direction,
For example, when a large number of small-sized transfer materials are continuously fixed, a large temperature difference may occur between the portion of the fixing roller surface where the transfer material does not contact and the portion where the transfer material does not contact.

Further, if the temperature is adjusted at the paper passing portion of the fixing roller, the temperature of the non-paper passing portion greatly exceeds the temperature suitable for fixing, and the thermal deterioration of each member of the fixing device proceeds, or the temperature of the non-paper passing portion becomes large. There is a disadvantage that hot offset of toner to the surface of the fixing roller occurs.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art. It is an object of the present invention to reduce surface temperature unevenness at both ends of a fixing roller at the time of starting a fixing device. A fixing device and a fixing device capable of preventing both ends from being abnormally high in temperature and thereby preventing thermal progression of each member of the fixing device and hot offset of toner to the fixing roller surface in a non-sheet passing portion. An image forming apparatus provided with:

[0009]

According to the present invention, an eddy current is generated in a conductive layer provided on a fixing rotating member by an induction heating means having a magnetic core and an exciting coil. In the fixing device of the electromagnetic induction heating type in which heat is generated by heating, the induction heating means is provided inside and outside the fixing rotating member, respectively.

[0010] It is also preferable that one of the induction heating means provided inside and outside the fixing rotating member is provided only at both ends of the fixing rotating member. .

Further, one of the induction heating means provided inside and outside the fixing rotating member is provided only at both ends of the fixing rotating member, and the other induction heating means is provided. Is preferably disposed over the entire rotation axis direction of the fixing rotation member.

In addition, the amount of electric power supplied to each excitation coil of the induction heating means disposed inside and outside the fixing rotating member is individually controlled in accordance with the axial heat generation distribution of the fixing rotating member. It is also preferable to provide control means.

The image forming apparatus includes an image forming means for forming a toner image on a transfer material, and the above-described fixing device for passing the transfer material on which the toner image is formed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the illustrated embodiments.

(Embodiment 1) FIG. 1 (a) is a drawing that best illustrates the features of the present invention. FIG. 1 (b) is a schematic cross-sectional view of a fixing device according to a first embodiment of the present invention. () Is a perspective view.

The fixing roller 1 serving as a fixing rotating member is an iron core metal cylinder having an outer diameter of 32 [mm] and a thickness of 0.5 [mm].
[Μm] or a layer of PFA 10 to 50 [μm] may be provided.

Further, as another material of the fixing roller 1, a material having a relatively high magnetic permeability μ and an appropriate resistivity ρ, such as a magnetic material (magnetic metal) such as a magnetic stainless steel, may be used.

The pressure roller 2 has a 5 mm thick Si rubber layer on the outer periphery of an iron core having an outer diameter of 20 mm, and improves the surface releasability similarly to the fixing roller 1. For example, PTFE 10 to 100 [μm], PFA 10 to 1
00 [μm] may be provided, and the total outer diameter is about 30 [m].
m].

The fixing roller 1 and the pressure roller 2 are rotatably supported so that only the fixing roller 1 is driven. The pressure roller 2 is in pressure contact with the surface of the fixing roller 1 and is arranged so as to be driven to rotate by frictional force at a pressure contact portion (nip portion).

The pressure roller 2 is pressed in the direction of the rotation axis of the fixing roller 1 by a mechanism (not shown) using a spring or the like.

In the present embodiment, the pressure roller 2 is about 30
In this case, the width (nip width) of the pressure contact portion is about 4 [mm]. However, the nip width may be changed by changing the load depending on circumstances.

The transport guide 3 is arranged at a position where the transfer material 5 transported while carrying the unfixed toner image 4 formed by the image forming means is guided to a nip portion between the fixing roller 1 and the pressure roller 2. Is done.

The separation claw 6 is disposed in contact with the surface of the fixing roller 1, and is provided after the transfer material 5 has passed through the nip.
If it sticks to the, it is forcibly separated to prevent jam.

The exciting coil 7 is wound around the center projection of the magnetic core 8 having an E-shaped cross section in the axial direction. In the present embodiment, the number of windings is six.

The coil wire has an outer diameter of 0.15 to 0.50.
It uses a 20 to 150 litz insulated conductor wire of [mm] and is connected to a high-frequency converter (not shown), an alternating current of 10 to 100 [kHz] is applied, and up to about 2000 [W]. Power is supplied.
Further, in consideration of the case where the temperature of the exciting coil 7 rises, a heat-resistant material is used for the insulating coating.

The magnetic field induced by the alternating current flowing through the exciting coil 7 causes an eddy current to flow near the inner surface of the conductive fixing roller 1 to generate Joule heat. In order to increase the heat generation, it is preferable to increase the current amplitude of the alternating current.

The magnetic core 8 having an E-shaped cross section is preferably a magnetic core having a high magnetic permeability and a low loss, and is used for increasing the efficiency of the magnetic circuit and for shielding the magnetic field. The magnetic core is not limited to the E type, but may be, for example, a T type.

The temperature sensor 9 is arranged so as to contact the surface of the portion of the fixing roller 1 which locally generates heat, and supplies power to the exciting coil 7 by control means (not shown) based on a detection signal of the temperature sensor 9. Is automatically controlled so that the surface temperature of the fixing roller 1 becomes a predetermined constant temperature.

In the present embodiment, the magnetic core 8 and the exciting coil 7 having an E-shaped cross section are arranged inside the fixing roller 1 over the entire rotation axis direction, and are arranged only at both ends outside. Have been.

FIG. 3 shows the fixing roller 1 when the fixing device is started.
FIG. 4 is a diagram showing the surface temperature of the fixing roller 1 when heating is performed.

At the time of startup, according to only the excitation coil 7 arranged inside the fixing roller 1 over the entire rotation axis direction,
As shown by the curve 10, the surface temperature of the fixing roller 1 tends to be lower at both ends than at the center in the rotation axis direction.

Therefore, when the fixing device is started, not only the internal excitation coil 7 but also the excitation coils 7 arranged at both outer ends of the fixing roller 1 are used by a control means (not shown).
The fixing roller 1 is heated as shown by a curve 11.

As a result, the temperature gradient in the direction of the rotation axis is represented by the curve 12, and the temperature unevenness at the center and both ends of the fixing roller 1 when the fixing device is started can be eliminated.

When a large amount of small-size transfer material is continuously fixed, and both ends of the fixing roller 1 which is a non-sheet passing portion greatly exceed a temperature suitable for fixing, control means (not shown) is used. By stopping the heating by the excitation coils 7 at both ends of the fixing roller 1, it is possible to prevent a temperature rise at both ends of the fixing roller 1.

As described above, in the present embodiment, the magnetic core 8 and the exciting coil 7 are disposed over the entire rotation axis direction inside the fixing roller 1, and at both ends outside the fixing roller 1. By disposing only the fixing roller 1, the temperature of the surface of the fixing roller 1 is controlled by control means (not shown).
Can be controlled separately at the center and both ends of the
Can be kept uniform in the direction of the rotation axis.

(Second Embodiment) FIG. 2 is a schematic sectional view of a fixing device according to a second embodiment of the present invention.

In the second embodiment, the magnetic core 8 and the exciting coil 7 having an E-shaped cross section are disposed only at both ends inside the fixing roller 1, and are disposed over the whole in the rotation axis direction outside. Have been.

In the present embodiment, as in the first embodiment, the temperature distribution on the surface of the fixing roller 1 can always be kept uniform in the rotation axis direction.

[0039]

As described above, according to the present invention,
Since the induction heating means is provided inside and outside the fixing rotating member, it is possible to efficiently heat the fixing rotating member in the rotation axis direction.

Further, since the temperature of the surface of the fixing rotating member can be individually controlled at the center and both ends of the fixing rotating member, the temperature distribution on the surface of the fixing rotating member is always uniform in the rotation axis direction. Therefore, it is possible to provide a fixing device and an image forming apparatus with improved fixability.

Further, it is possible to eliminate uneven surface temperatures at both ends of the fixing rotating member when the fixing device is started, and to make the surface temperature of the fixing rotating member uniform in the direction of the rotation axis.

Further, when a large amount of a small-sized transfer material is continuously fixed, and both ends of the fixing rotating member, which is a non-sheet passing portion, greatly exceed a temperature suitable for fixing. And a fixing device and an image forming apparatus capable of preventing the progress of thermal deterioration of each member of the fixing device and the hot offset of toner to the surface of the fixing rotating member in a non-sheet passing portion. Can be provided.

[Brief description of the drawings]

FIG. 1A is a sectional configuration diagram of a fixing device according to a first embodiment of the present invention, and FIG. 1B is a perspective view.

FIG. 2 is a perspective view of a fixing device according to a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a surface temperature distribution of a fixing roller of the fixing device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Fixing roller (fixing rotating member) 2 Pressure roller 3 Conveyance guide 4 Toner image 5 Transfer material 6 Separation claw 7 Excitation coil 8 Magnetic material core 9 Temperature sensor 10 Fixing roller by induction heating means arranged inside the whole in the axial direction 1. Curve representing the surface temperature gradient in the axial direction 11; Curve representing the axial gradient of the surface temperature of the fixing roller 1 by the induction heating means disposed at both external ends 12 Induction heating means disposed inside and outside Curve representing the axial gradient of the surface temperature of the fixing roller 1 due to

Claims (5)

[Claims] 1. An electromagnetic induction heating type fixing device in which an induction heating means having a magnetic core and an excitation coil generates an eddy current in a conductive layer provided on a fixing rotating member to generate heat, wherein the induction heating means comprises: A fixing device provided inside and outside the fixing rotating member. 2. The method according to claim 1, wherein one of the induction heating units provided inside and outside the fixing rotating member is provided only at both ends of the fixing rotating member. The fixing device according to claim 1. 3. An induction heating means provided inside and outside the fixing rotating member, one of which is provided only at both ends of the fixing rotating member, and the other induction heating means. The fixing device according to claim 1, wherein the fixing device is disposed over the entire rotation axis direction of the fixing rotation member. 4. An amount of power supply to each excitation coil of induction heating means disposed inside and outside the fixing rotating member is individually controlled according to an axial heat generation distribution of the fixing rotating member. The fixing device according to claim 1, further comprising a control unit. 5. An image forming means for forming a toner image on a transfer material, and the fixing device according to claim 1, which passes the transfer material on which the toner image is formed. Characteristic image forming apparatus.