JP2002182500A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device by which the scattering of toner is prevented. SOLUTION: This fixing device is provided with a fixing belt 1 having a heat-generating substance generating heat by electromagnetic induction and an induction heating device 3 to heat the fixing belt 1 by the electromagnetic induction, and recording paper P to which toner T incorporating the heat generating substance generating the heat by the electromagnetic induction is stuck is moved by coming into contact with the fixing belt 1, so that the toner T is fixed on the recording paper P. The fixing belt 1 and the recording paper P start coming into contact with the magnetic path of the induction heating device 3 at the outside of the recording paper P on an upstream side in a moving direction, and are separated at outside on a downstream side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device in a dry electrophotographic apparatus (such as an image forming apparatus such as a copying machine and a laser printer).

[0002]

2. Description of the Related Art As a fixing device in a dry-type electrophotographic image forming apparatus, a fixing device in which a recording sheet with toner attached thereto is passed between a pair of pressure rollers to fix the toner on the recording sheet by pressure, 2. Description of the Related Art There is known an image forming apparatus in which a recording sheet with toner is passed between a heating roller and a pressure roller to fix the toner on the recording sheet by heat and pressure. Then, in such a fixing device, in order to obtain high-quality and stable printing without requiring warm-up, a toner containing non-ferrous conductor powder which generates heat by electromagnetic induction is used, and an induction heating unit is used on the recording paper. It has been proposed that the toner be directly induction heated.

For example, in a fixing device described in Japanese Patent Application Laid-Open No. Hei 7-28357, toner on a paper being conveyed is heated and melted by induction heating means, and is fixed on the paper.
Further, a pair of pressure rollers enhances the adhesion of the toner to the sheet.

In the fixing device described in Japanese Patent Application Laid-Open No. H11-344830, a sheet on which toner has been adhered is passed between a heating roller and a pressure roller, and is heated by induction heating means disposed in the heating roller. The heating roller and the toner on the paper are induction heated to fix the toner on the paper.

[0005]

However, the fixing device described in JP-A-7-28357 has a problem that sufficient fixing energy cannot be obtained by heating only the toner.

Further, the fixing device described in Japanese Patent Application Laid-Open No. 11-344830 has the following problem. First, since a roller system using a pair of a heating roller and a pressure roller is used, toner is scattered by magnetic force acting on the toner, and image quality is deteriorated. In addition, it is difficult to efficiently heat both the heating roller and the toner, whose physical properties are far apart, with a single induction heating unit. If two induction heating units for separately heating the heating roller and the toner are used, high efficiency can be achieved. However, not only the device becomes large and complicated, but also mutual magnetic interference (crosstalk) occurs between the two induction heating means. Further, in order to generate heat by electromagnetic induction, both the heating roller and the toner have a ferromagnetic material, and a magnetic force is generated between the two, so that the toner is liable to be scattered. The so-called offset that the toner melts too much and remains on the surface of the heating roller is more likely to occur than in the apparatus.

An object of the present invention is to provide a fixing device which can prevent toner from scattering.

[0008]

The fixing device according to the present invention includes an induction heating member having a heating substance that generates heat by electromagnetic induction, and an induction heating unit that heats the induction heating member by electromagnetic induction. In a fixing device in which the recording medium to which the toner containing the heat generating substance that generates heat by electromagnetic induction is attached and moves by contacting the induction heating member, the toner is fixed to the recording medium. The magnetic path of the induction heating means starts to contact outside on the upstream side in the moving direction of the recording medium, and is separated on the outside on the downstream side.

As the toner, for example, a styrene acrylic toner is used.

According to the fixing device of the present invention, since the induction heating member and the recording medium come into contact with or separate from each other outside the magnetic path where no magnetic force acts, scattering of toner due to the magnetic force can be prevented, and high image quality can be obtained. Printing can be obtained.

In the fixing device of the present invention, for example, the heat generating substance contained in the toner or the induction heating member is a soft magnetic material.

As the soft magnetic material, for example, soft ferrite is used. The saturation magnetic flux density of soft ferrite is 1.0T.

In this case, by using a soft magnetic material as the heat generating substance contained in the toner, the residual magnetic energy after passing through the magnetic path can be reduced, and the offset caused by the magnetic force can be prevented.

In the fixing device of the present invention, for example, the induction heating member has a belt shape.

By forming the induction heating member in a belt shape, the contact nip width with the recording medium can be increased, and the induction heating member and the recording medium can be reliably contacted and separated outside the magnetic path. Become.

The contact nip width between the induction heating member and the recording medium is preferably 50 mm when the width of the magnetic path of the induction heating means (the width of the core when the induction heating means has a core) is 20 mm. .

In the above fixing device, for example, the optimum induction heating condition of the toner and the optimum induction heating condition of the induction heating member are equal or close to each other, and both are heated by a common induction heating means.

By bringing the optimum induction heating conditions of the toner and the induction heating member close to each other, high thermal efficiency can be obtained with a single induction heating means.

In the above-mentioned fixing device, for example, the induction heating member is made of a heat-resistant synthetic resin and a heat-generating substance of the same material as the heat-generating substance added to the toner.

By using the same heating material for the toner and the induction heating member, the optimum induction heating conditions for both can be made closer, and the efficiency of a single induction heating means can be improved.

In the above fixing device, for example, the particle size and content of the heat generating substance in the induction heating member are substantially equal to the particle size and content of the heat generating substance in the toner.

Preferably, the particle size of the heating substance is 0.3 μm.
m, the content is 15% by volume.

This makes it possible to make the optimal induction heating conditions of the toner and the induction heating member closer to each other.
The efficiency with a single induction heating means can be further improved.

In the fixing device of the present invention, for example, the induction heating means has a member for forming a magnetic path.

As a member for forming a magnetic path, for example, a ferrite core is used.

In this way, by forming an efficient magnetic path, the leakage magnetic flux can be reduced, the toner can be prevented from scattering due to the leakage magnetic flux, and the efficiency can be improved.

In the fixing device of the present invention, for example, the induction heating means has an air-core coil.

Using an air-core coil, this is
By driving at a high frequency of up to 200 KHz, the magnetic force acting on the induction heating member can be greatly reduced, and the vibration noise at the contact nip and the disturbance of the image due to this can be prevented.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a fixing device of a dry electrophotographic copying machine will be described below with reference to the drawings.

FIG. 1 schematically shows a fixing device in a dry electrophotographic copying machine.

The fixing device is a recording sheet (P) which is a recording medium.
And a fixing belt (1) constituting an induction heating member for heating the toner (T) on the surface thereof, and a pressing member for pressing the paper (P) against the belt (1) by pressing against the belt (1). A pressure roller (2) constituting pressure means and an induction heating device (3) constituting induction heating means for heating the toner (T) on the belt (1) and the paper (P) by electromagnetic induction. Have.

Toner (T) is adhered to the upper surface of the sheet (P) in a preceding image forming section (not shown).
Is moved from right to left in FIG. 1 between the belt (1) and the roller (2). In the following description, the front-back direction is paper (P)
The direction of movement of The rear side in the moving direction of the sheet (P) is defined as the upstream side, and the front side is defined as the downstream side.

As the toner (T), for example, a styrene acrylic toner is used. The glass transition temperature Tg of the styrene acrylic toner is 55 ° C. The toner (T) contains a filler that is a heat generating substance that generates heat by electromagnetic induction.

The belt (1) is stretched between a pair of front and rear rollers (4) and (5) extending in the left-right direction. One of the rollers (4) and (5) is a drive roller so that the belt (1)
, And the substantially horizontal portion below the belt (1) moves forward. The belt (1) is made of, for example, a heat-resistant synthetic resin such as a polyimide resin, and is added with a filler that is a heating substance that generates heat by electromagnetic induction.

The pressure roller (2) is disposed directly below the belt (1), and is rotated about an axis extending in the left-right direction in the direction of the arrow in FIG. The pressure roller (2) is made of, for example, rubber, and its upper portion is brought into contact with the substantially horizontal lower portion of the belt (1) in the front-rear direction for a certain length in the front-rear direction.

The heating device (3) is arranged inside the belt (1) and directly above the pressure roller (2). Heating equipment
(3) includes a core (6) that is a member for forming a magnetic path, and an induction heating coil (7) wound around the core, and a high-frequency current of 20 to 200 KHz is applied to the coil (7). By supplying and driving, a magnetic path is formed in a range substantially equal to the front-rear width of the core (6). Then, a magnetic field in which a magnetic force acts is formed in a space having the same width as the magnetic path. As the core (6), for example, a ferrite core is used.

The contact nip width of the pressure roller (2) with respect to the belt (1) is substantially equal to or slightly larger than the front-rear width of the core (6). The paper (P) and the toner (T) on the upper surface of the paper (P) contact almost the entire lower part of the belt (1) which is substantially horizontal, and contact the belt (1) at the contact nip portion of the pressure roller (2). Pressed. Then, the paper (P) is belted almost immediately below the center of the rear roller (5) and on the upstream side outside the magnetic path.
The contact with the belt (1) is started, and the belt is separated from the belt (1) on the downstream side outside the magnetic path almost immediately below the center of the front roller (4). For example, the front and rear width A of the core (6) is about 20 mm,
The contact nip width B of the belt (1) with respect to (P) is about 50 mm.

In the above-mentioned fixing device, the heating substance added to the belt (1) and the toner (T) generates heat due to a change in the magnetic flux of the heating device (3), and the heating material contacts the belt (1) and the belt (1). The toner (T) on the running paper (P) is heated. As a result, the toner (T) is melted and fixed on the paper (P) by heat and pressure. Then, the sheet (P) on which the fixing has been completed is discharged through a discharge roller or the like (not shown). At this time,
Since the belt (1) and the paper (P) come into contact with and separate from each other outside the magnetic path (magnetic field) where no magnetic force acts, it is possible to prevent toner from being scattered by the magnetic force.

Preferably, the optimum induction heating condition of the toner (T) and the optimum induction heating condition of the belt (1) are equal or close to each other. Therefore, it is preferable to use the same material for the filler of the toner (T) and the filler of the belt (1). For example, soft magnetic materials such as soft ferrite are suitable for these fillers. Further, preferably, the particle size and content of the filler in the belt (1), the toner
It is almost equal to those in (T). For example, the particle size of these fillers is 0.3 μm, and the content is 15% by volume.

In the above embodiment, the heating device (3) is provided with the core (6).
However, an air-core coil may be used. When an air-core coil is used for the heating device (3), the magnetic force acting on the belt (1) can be significantly reduced by driving the coil at a high frequency of, for example, 20 to 200 KHz. Image disturbance due to this can be prevented.

The overall configuration of the fixing device and the configuration of each part are as follows.
The present invention is not limited to the above-mentioned crouching form, but can be appropriately rebelled.

[Brief description of the drawings]

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

[Explanation of symbols]

 (1) Fusing roller (2) Pressure roller (3) Induction heating device (6) Core (7) Induction heating coil

Continued on the front page F term (reference) 2H005 AA02 CB04 FB01 2H033 AA01 AA09 AA30 BA11 BA12 BA25 BA27 BA58 BB28 BE06 3K059 AB19 AD21 AD23 CD75

Claims (8)

[Claims] 1. An induction heating member having a heating substance which generates heat by electromagnetic induction, and an induction heating means for heating the induction heating member by electromagnetic induction, wherein a toner containing a heating substance which generates heat by electromagnetic induction is attached. In a fixing device in which toner is fixed to a recording medium by moving the recording medium in contact with the induction heating member, the induction heating member and the recording medium are moved relative to a magnetic path of the induction heating means. A fixing device that starts contacting on the outer side on the upstream side in the direction and is separated on the outer side on the downstream side in the direction. 2. The fixing device according to claim 1, wherein the heat generating substance contained in the toner or the induction heating member is a soft magnetic material. 3. The fixing device according to claim 1, wherein the induction heating member has a belt shape. 4. An optimum induction heating condition of the toner and an optimum induction heating condition of the induction heating member are equal to or close to each other;
4. The fixing device according to claim 3, wherein both are heated by a common induction heating means. 5. The fixing device according to claim 4, wherein the induction heating member is made of a heat-resistant synthetic resin and a heat-generating substance of the same material as the heat-generating substance added to the toner. 6. The fixing device according to claim 5, wherein the particle size and content of the heat generating substance in the induction heating member are substantially equal to the particle size and content of the heat generating substance in the toner. 7. The fixing device according to claim 1, wherein the induction heating means has a member for forming a magnetic path. 8. The fixing device according to claim 1, wherein the induction heating means includes an air-core coil.