JP2000039788A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a fixing device the temperature drop of which is restrained even when thick transfer paper is made to consecutively pass and which has excellent fixing performance by using the sintered product of rear earth transition metal alloy for a magnetic substance core. SOLUTION: An energizing coil 8 is provided with the magnetic substance core 9 including the rear earth transition metal alloy, For example, the coil 8 has the core 9 whose cross-sectional shape is E-shape and is connected to a high-frequency converter. Since the high frequency power of 100 to 2000 (kW) is supplied to the coil 8, wiring is performed by using several thin wires to which heat resistant coating is applied in a litz wire state. The AC current of 10 to 100 (kHz) is applied to the coil 8 by the high frequency converter. Magnetic flux induced by the AC current passes inside the core 9 without leaking to the outside, flows to the outside of the magnetic substance from an E-shaped projection part and passes through the conductive layer of a fixing roller 1. As a result, an eddy current is generated and the conductive layer itself generates Joule heat.

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:
The image forming apparatus includes a transfer device that forms an image of a toner including a resin, a magnetic material, a colorant, and the like as a toner image, and further fixes the toner image on a transfer material as a recording medium, and a fixing device that fixes the toner image on the transfer material.

Here, the fixing device has two rollers, a fixing roller and a pressure roller, which are pressed against each other and can rotate, and
The transfer material to which the toner image has been fixed by the transfer device at the preceding stage is heated and pressed while the pressure contact portion (nip portion) of the two rollers is nipped and conveyed to fuse and fix the transfer material.

In such a fixing device, as a means for heating, for example, there is a heat roller method using a Halongen lamp or a heating method by electromagnetic induction using an exciting coil.

Here, the latter induction heating method is a method in which an eddy current is generated in a conductive layer provided on the inner surface of a fixing roller by an excitation coil using a ferrite magnetic core, and the eddy current is used to heat the conductive layer. In this method, since the heat generation source can be placed very close to the toner, the time required for the surface temperature of the fixing roller to reach a predetermined temperature from the start is very short, and the toner An advantage is that the heat transfer path is short and simple, so that the heat efficiency is high.

However, even in this induction heating type fixing device, when thick transfer paper or the like is continuously passed, the amount of heat taken by the transfer paper is large, so that the surface temperature is lowered and the fixability is remarkably deteriorated. Such a problem has come to the surface.

Further, since such a fixing device has a limited available electric power, it is necessary to generate heat efficiently. For this purpose, it is preferable to concentrate the magnetic flux in a narrow region. For example, a structure in which an excitation coil is wound around a central projection of a magnetic core having an E-shaped cross section is preferably used. However, conventional ferrite magnetic cores have poor formability, and as the shape of the magnetic core becomes more complicated as in the above-described E-shape, the production yield decreases and the production cost increases. The problem has become apparent. To solve this problem, a method has been proposed in which ferrite powder is mixed with an organic polymer binder in advance, molded into a desired shape, and then sintered. However, this method causes a decrease in the magnetic flux density due to a decrease in the content of the ferrite component, resulting in deterioration of the fixing property.

As described above, in the fixing device of the induction heating system, the fixing property is deteriorated when the thick transfer material is continuously passed, and the shape of the magnetic core is reduced when the power is saved while maintaining the high magnetic flux density. Due to problems such as design limitations, there is a limit in applying this method to an electrophotographic apparatus.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a fixing device which suppresses a temperature decrease of the fixing device even when thick transfer paper is continuously passed, and has a good fixing property. I do.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a fixing roller and a pressure roller which are in pressure contact with each other on their surfaces and can rotate freely, and an eddy current is generated in a conductive layer provided on the fixing roller. The present invention relates to a fixing device having an excitation coil for heating a magnetic material, wherein the excitation coil has a magnetic core containing a rare-earth transition metal alloy.

The inventor of the present application has made intensive studies on the material of the magnetic core of the exciting coil, and as a result, by using a magnetic core containing a rare-earth transition metal alloy instead of a ferrite magnetic core, the object of the present invention is as follows. It became possible to solve.

That is, in the induction heating type fixing device, the magnetic flux density can be improved by using a magnetic core containing a rare earth transition metal alloy which has never been used before, and as a result, the organic polymer binder is improved. The upper limit margin of the addition amount is increased, and the moldability can be improved at the same time.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A rare earth transition metal alloy is an alloy of a rare earth transition metal and another metal and has good magnetic properties.
When used as the core of the excitation coil, the alloy needs to be an alloy that efficiently generates an eddy current as compared with the conventional excitation coil of a ferrite core. For example, such an alloy includes an alloy of a rare earth 4f transition metal and an iron group 3d transition element. Specifically, Sm, Nd, Pr and Co
And SmCo ₅ , Sm ₂ (Co
_0.59 X _0.41 ) ₁₇ (where X is Mn, Ni, Fe, C
u, Ti, Zr, or Hf). Nd, Fe and B, or Nd, F
A ternary alloy such as e and Si or an alloy using Pr instead of Nd may also be used. In particular, Nd ₂ Fe ₁₄ B, which is an Nd—Fe—B-based alloy, has very good magnetic properties and can be suitably used. Further, it is possible to add a small amount of an additive to these rare earth transition metal alloys for the purpose of improving magnetic properties.

Next, a method of manufacturing the magnetic core will be described. When forming and sintering a rare-earth transition metal alloy to produce a magnetic core, similarly to the case of producing a ferrite magnetic core, by a commonly used method, molding and sintering,
A magnetic core can be manufactured. That is, the powder of the rare-earth transition metal alloy is formed into a powder and further sintered.
This powder molding may be performed in a magnetic field. The sintering temperature varies depending on the type of the rare earth transition metal alloy, but is, for example, about 500 ° C. to 600 ° C.

The shape of the exciting coil may be complicated depending on the design of the electrophotographic apparatus, and in some cases, better formability may be required. In such a case, a magnetic core having a complicated shape can be produced by mixing an organic polymer binder with a rare earth transmetal alloy powder and molding the mixture. When the amount of the organic polymer binder added increases, the magnetic flux density decreases. Therefore, it is preferable to suppress the amount of addition to such an extent that the magnetic flux density is equal to or higher than that of the ferrite magnetic core. For example, a substantially 100% ferrite magnetic core and substantially 10%
When the magnetic material core made of 0% SmCo ₅ is compared, the latter magnetic flux density shows about 2.5 times the magnetic flux density of the former. ,
The latter magnetic material core can contain about 60% by weight of an organic polymer binder. As a result, a magnetic core having a complicated shape can be manufactured with high yield.

In this case, the magnetic core is prepared by adding a required amount of an organic polymer binder to a rare earth transition metal alloy powder and using a method such as injection molding or extrusion molding. The magnetic core can be manufactured by molding into a shape. This molding may be performed in a magnetic field. The forming temperature varies depending on the type of the rare-earth transition metal alloy and the type of the organic metal binder, but is, for example, about 150 ° C. to 200 ° C.

(Embodiment 1) Next, a fixing device using the above-described coil will be described with reference to the drawings. FIG. 1 schematically shows a cross section of a fixing device according to an embodiment of the present invention.

The fixing roller 1 has an outer diameter of 40 (m
m), an iron core cylinder having a thickness of 0.7 (mm), made of PTFE10 to 50 to improve the surface release property.
(Μm) or a layer of PFAl0 to 50 (μm). Further, as another material that can be used for the fixing roller, a material having a relatively high magnetic permeability μ and an appropriate resistivity ρ, such as a magnetic material (magnetic metal) such as magnetic stainless steel, may be used. Further, even among non-magnetic materials, a conductive material such as a metal can be used as a thin film on the surface of the roll.

The pressure roller 2 has, for example, an outer diameter of 20 (mm).
PTFE10 to 50 in order to enhance the surface releasability similarly to the Si rubber layer having a thickness of 5 (mm)
(Μm) or a layer of PFAl0 to 50 (μm). In this case, the outer diameter is about 30 (mm).

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 rotation axis direction of the fixing roller 1 by a mechanism (not shown) using a spring or the like. The pressure roller 2 is loaded with a load of about 30 (kg weight), and in this case, the width (nip width) of the press contact portion is about 6 (mm). It is also possible to change the nip width by changing the load.

The temperature sensor 3 is disposed so as to be in contact with the surface of the fixing roller 1. The power supply to the exciting coil 8 is increased or decreased based on the detection signal of the temperature sensor 3 so that the surface temperature of the fixing roller 1 is reduced. The temperature is automatically controlled to a predetermined constant temperature.

The transport guide 4 is arranged at a position for guiding the transfer material 6 transported while carrying the unfixed toner image 5 to a nip portion between the fixing roller 1 and the pressure roller 2. The separation claw 7 is disposed in contact with the surface of the fixing roller 1 and is for forcibly separating the transfer material 6 to prevent a jam when the transfer material 6 sticks to the fixing roller 1 after passing through the nip portion. is there.

In this drawing, the exciting coil 8 has a sectional shape of E.
Since it has a magnetic core and is connected to the high-frequency converter 10 and is supplied with high-frequency power of 100 to 2000 (kW), it is formed by winding several litz-shaped thin wires coated with heat resistance. ing.

An alternating current of 10 to 100 (kHz) is applied to the exciting coil 8 by a high-frequency converter (not shown). The magnetic flux induced by the alternating current passes through the inside of the E-shaped magnetic core 9 without leaking to the outside, flows from the E-shaped protrusion to the outside of the magnetic body, penetrates the conductive layer of the fixing roller 1, and as a result, an eddy current is generated. Then, the conductive layer itself generates Joule heat. By shaping the magnetic core into such an E-shape, the magnetic flux can be concentrated and a strong eddy current can flow at a high density.

In this embodiment, an E-type magnetic core formed by the above-described method was used without using an organic polymer binder, using an Sm-Co alloy as a rare earth transition metal alloy. As a result, the magnetic flux density penetrating through the fixing roll 1 is almost equal to 2.times. When the magnetic core made of ferrite is used.
That is, the fixing roller was able to efficiently generate heat.

Further, as a rare earth transition metal alloy, Sm-
Even if a Nd-Fe-B-based alloy is used instead of a Co-based alloy,
A magnetic flux density approximately 2.5 times that of the ferrite magnetic core was obtained, and the same effect was confirmed.

(Embodiment 2) In this embodiment, fixing is performed in exactly the same manner as in Embodiment 1, except that a mixture of a rare earth transition metal alloy powder and an organic polymer binder is used as the material of the magnetic core 9. The device was made.

By using the organic polymer binder as described above, the moldability of the magnetic core is improved, and the yield at the time of molding the core is improved as compared with the magnetic core of the conventional ferrite sintered body. Accuracy is also improved. As the accuracy after molding is improved, the distance between the magnetic core and the fixing roller, which is a heat generating portion, becomes uniform, and the effect of reducing temperature unevenness of the fixing roller also occurs. In this embodiment, the Sm-Co alloy is used as the rare earth transition metal alloy. However, since the magnetic flux density of this magnetic material is 2.5 times that of ferrite, the magnetic material and the organic polymer binder Mixing ratio of 2: 3
As a result, a magnetic core was produced. As a result, it was confirmed that those having this mixing ratio exhibited good moldability and could be produced with good yield. As for the magnetic flux density penetrating the fixing roll 1, almost the same magnetic flux density of the ferrite magnetic core was obtained. In the present embodiment, the amount of the organic polymer binder is added on the basis of the amount of the magnetic flux density equivalent to that of the ferrite magnetic core. It is also possible to aim.

As a rare earth transition metal alloy, Nd-
The same effect can be obtained by using an Fe-B alloy.

[0030]

According to the present invention, by using a sintered molded article of a rare earth transition metal alloy for the magnetic core, heat can be generated with higher efficiency, and the present invention can be applied to a higher-speed fixing device. further,
By using a molded product obtained by adding an organic polymer binder to a rare earth transition metal alloy powder and using a molded product, a magnetic core for electromagnetic induction heating excellent in moldability and shape stability can be obtained without reducing thermal efficiency.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a fixing device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing roller 2 Pressure roller 3 Temperature sensor 4 Transport guide 5 Unfixed toner image 6 Transfer material 7 Separation claw 8 Excitation coil 9 Magnetic core

[Procedure amendment]

[Submission date] July 29, 1998 (1998.7.2
9)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction contents]

In this case, the magnetic core is prepared by adding a required amount of an organic polymer binder to a rare earth transition metal alloy powder and using a method such as injection molding or extrusion molding. The magnetic core can be manufactured by molding into a shape. This molding may be performed in a magnetic field. The forming temperature varies depending on the type of the rare earth transition metal alloy and the type of the organic polymer binder, but is, for example, about 150 ° C. to 200 ° C.

Claims (5)

[Claims] A fixing roller and a pressure roller which are in pressure contact with each other on their surfaces and can rotate freely, and an exciting coil for generating an eddy current in a conductive layer provided on the fixing roller to heat the fixing roller. The fixing device according to claim 1, wherein the exciting coil has a magnetic core including a rare earth transition metal alloy. 2. The fixing device according to claim 1, wherein the magnetic core is a molded and sintered product of a rare earth transition metal alloy. 3. The fixing device according to claim 1, wherein the magnetic core is a molded product obtained by mixing and molding a rare earth transition metal alloy powder and an organic polymer binder. 4. The rare earth transition metal alloy according to claim 1, wherein the rare earth transition metal alloy is Sm—Co.
The fixing device according to claim 1, wherein the fixing device is a system alloy. 5. The rare earth transition metal is Nd—Fe—B.
The fixing device according to claim 1, wherein the fixing device is a system alloy.