JP2001066921A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance fixing performance by uniformly heating a fixing roller. SOLUTION: This fixing device is constituted so that toner is fixed on a recording medium by electromagnetic induction heating and provided with the fixing roller 13 constituted of a magnetic body, a pressure roller pressed to the roller 13, the magnetic field generation means 17 disposed around the roller 13. Then, a rough surface 13a is formed at the surface of the roller 13 facing the magnetic generation means 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic method, such as a copying machine, a printer, and a facsimile, and more particularly to a fixing device for fixing a toner image transferred onto a recording medium by electromagnetic induction heating. .

[0002]

2. Description of the Related Art In the above-mentioned image forming apparatus, an electrostatic latent image is formed on an image carrier such as a photoreceptor, and the electrostatic latent image is developed into a toner image, and then the toner image is transferred onto a recording medium. Then, the toner image transferred onto the recording medium is fixed by a fixing device. Conventionally, various methods of fixing by electromagnetic induction heating have been proposed as the fixing device.
For example, Japanese Patent No. 2,616,433 proposes a method in which a magnetic field generating means is arranged in an arc shape along an outer periphery of a fixing roller except for a contact portion with a pressure roller.

[0003]

However, in the above-mentioned conventional fixing device, the gap between the fixing roller and the magnetic field generating means is set small in order to increase the heating efficiency. In addition, due to the bias of the gap between the fixing roller and the magnetic field generating means, there is a problem that a concentrated portion of the magnetic flux is generated on the fixing roller, and as a result, uneven heating is caused and uneven fixing is caused.

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a fixing device capable of improving a fixing performance by uniformly heating a fixing roller.

[0005]

For this purpose, the present invention provides a fixing device for fixing toner on a recording medium by electromagnetic induction heating, comprising: a fixing roller made of a magnetic material;
A pressure roller pressed by the fixing roller; and a magnetic field generating means disposed around the fixing roller, wherein a rough surface is formed on a surface of the fixing roller on the side of the magnetic field generating means. .

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram showing an example of an image forming apparatus to which the present invention is applied. This image forming apparatus is a color electrophotographic printer capable of forming a full-color image using four color toners. However, the present invention is not limited to this, and is applicable to all image forming apparatuses using the electrophotographic method. Applicable.

The photoreceptor 1 has a thin cylindrical conductive substrate and a photosensitive layer formed on the surface thereof, and is driven to rotate in a direction indicated by an arrow by driving means (not shown). Around the photosensitive member 1, a charging device 2 for uniformly charging the photosensitive member 1 along the rotation direction, an exposure device 3 for forming an electrostatic latent image on the photosensitive member 1, A rotary developing device 4 for developing an electrostatic latent image, an intermediate transfer drum 5 for transferring a monochromatic toner image formed on the photoconductor 1 and a primary transfer device 6 are provided. On the outer circumference of
A secondary transfer device 7 for transferring the four-color full-color image formed on the intermediate transfer drum 5 onto a recording medium (paper or the like) and a fixing device 9 for fixing the toner image transferred on the recording medium are provided. Has been established. Reference numeral 10 denotes a paper feed tray for storing a recording medium, and reference numeral 11 denotes a recording medium transport passage.

The rotary developing device 4 includes a yellow developing device 4.
A developing unit 4C for Y, cyan, a developing unit 4M for magenta, and a developing unit 4K for black are configured to be rotatable, and these developing units 4Y, 4C, 4M, and 4K
Only one developing roller of one developing unit can selectively contact the photosensitive member 1 for each rotation. Each developing device is provided with a toner container 12 (only one tank is shown in the drawing) in which respective toners are stored.

The operation of the image forming apparatus having the above configuration will be described. When an image forming signal is input from a computer (not shown), the photosensitive member 1, the developing roller of the developing device 4, and the intermediate transfer drum 5 are driven to rotate. First, the outer peripheral surface of the photoconductor 1 is uniformly charged by the charging device 2,
The outer peripheral surface of the uniformly charged photoreceptor 1 is selectively exposed according to image information of the first color (for example, yellow) by the exposing device 3 to form a yellow electrostatic latent image.

The yellow developing unit 4Y is rotated with respect to the photosensitive member 1, and its developing roller comes into contact therewith, whereby a yellow electrostatic latent image toner image is formed on the photosensitive member 1. A primary transfer voltage having a polarity opposite to the charging polarity of the toner is applied to the primary transfer device 6, and the toner image formed on the photoconductor 1 is transferred onto the intermediate transfer drum 5. At this time, the secondary transfer device 7 is separated from the intermediate transfer drum 5. After the toner remaining on the photoreceptor 1 is removed by a photoreceptor cleaning device (not shown), the outer peripheral surface of the photoreceptor 1 is discharged by a discharging unit (not shown).

The above processing is repeated for the second, third and fourth colors of the image forming signal, and the latent image formation, development and transfer by one rotation of the photosensitive member 1 and the intermediate transfer drum 5 are repeated. Four color toner images corresponding to the contents of the image forming signals are superimposed and transferred on the intermediate transfer drum 5. Then, at the timing when this full-color image reaches the secondary transfer device 7, the recording medium is supplied from the transport passage 11 to the secondary transfer device 7. At this time, the secondary transfer device 7 is pressed against the intermediate transfer drum 5 and A secondary transfer voltage is applied, and the full-color toner image on the intermediate transfer drum 5 is transferred onto a recording medium. Then, the toner image transferred onto the recording medium is heated and pressed by the fixing device 9 and fixed.

2 to 6 show an embodiment of the fixing device according to the present invention, FIG. 2 is a sectional view of the fixing device, and FIG. FIG. 4 is a perspective view showing a state in which the case is removed, FIG. 4 is a side view showing a partially broken cross section viewed from the X direction in FIG. 2, FIG. 5 (A) is a plan view of the magnetic field generating means, and FIG. FIG. 5A is a side view, and FIG. 6 is a partially enlarged sectional view of the fixing roller. In the following description, the same configuration is denoted by the same reference numeral in each drawing, and the description may be omitted.

In FIG. 2, the fixing device 9 includes a cylindrical fixing roller 13 made of a magnetic material.
The pressure roller 14 is in contact with and pressed against 3. The pressure roller 14 includes a cylindrical rotating shaft 15 and an elastic layer 16 made of silicon rubber or the like on the outer periphery thereof.
4 rotates as shown by the arrow in the figure, the elastic layer 16
Is pressed by the fixing roller 13 to form a nip (pressing surface) N. On the outer periphery of the fixing roller 13,
The magnetic field generating means 17 is disposed at a predetermined gap from the fixing roller 13.

Fixing roller 13 and magnetic field generating means 17
Are housed in a case 21 made of a non-magnetic material.
The exciting coil 20 of the magnetic field generating means 17 is held by a coil holding member 19 made of an insulating material, and the coil holding member 19 is fixed to a case 21 by a mounting member 22. The case 21 is provided with a magnetic flux trapping member 23 made of ferrite or the like at a position facing the exciting coil 20 to prevent magnetic flux from leaking outside the case 21 and adversely affecting other electric circuits. A temperature sensor 24 is provided on the outer periphery of the fixing roller 13 on the upstream side in the rotation direction of the nip N,
Further, a peeling claw 25 for peeling the recording medium from the fixing roller 13 is provided on the downstream side. In addition, 26 is a recording medium conveyance guide, and 27 is a recording medium conveyance roller.

3 to 5, the fixing roller 13 and the pressure roller 14 are rotatably mounted on the case 21 by rotations 29 and 30, respectively. Fixing roller 13
The drive gear 31 is fixed to the rotating shaft 29 of the drive gear 3.
1 is driven to rotate by an electric motor (not shown). The coil holding member 19 of the magnetic field generating means 17
And two support members 19a and 19b arranged at a predetermined gap and at an interval from each other.
9a and 19b are connected by a plurality of connecting pieces 19c. Thereby, the ventilation path 3 is provided at the center of the coil holding member 19.
2 are formed. The exciting coil 20 is supported so that a loop is formed between the two supports 19a and 19b.

The magnetic field generating means 17 has an exciting coil 20 held in a loop on a coil holding member 19.
The magnetic field generating means 17 is wound substantially in parallel with the outer peripheral surface of the fixing roller 13 and along the outer periphery of a rectangle or an ellipse which is long in the axial direction of the fixing roller 13. As a result, the lines of magnetic force that intersect perpendicularly with the coil forming surface are caught almost perpendicularly to the surface of the fixing roller 13, generating an eddy current orbiting around the surface of the fixing roller 13 and generating heat. A uniform temperature rise over a wide range of directions can be realized.

The exciting coil 20 is formed by twisting a plurality of coated thin wires so that each coil is hardly affected by magnetic loss. While enabling
By using a stranded wire, the rigidity of the wire is increased and the coil can be easily formed.

Each turn of the exciting coil 20 is formed as a single layer in the radial direction of the fixing roller 13 so as to be located in the same plane. If the coil lines wound multiple times overlap in the radial direction of the fixing roller, the magnetic force of the coil closer to the roller cancels the magnetic line of the far side, but each turn of the coil is entirely on the roller surface. , The rollers receive the lines of magnetic force generated by all of them, so that the heat generation efficiency can be increased. Also, in each round of the exciting coil 20, the coils are wound tightly without gaps,
This is equivalent to forming a coil having a thick wire, and efficient heat generation is possible. In addition, there is no portion where the lines of magnetic force cancel each other out, and uniform heat generation on the roller surface facing the coil can be realized.

Further, since the ventilation path 32 can be formed at the center of the magnetic field generating means 17, the exciting coil 20 is cooled,
A decrease in heat generation due to a rise in coil temperature can be prevented. Further, the coil holding member 19, the case 21, the transport guide 26 and the like are all made of a non-magnetic material. If there is a magnetic material other than the fixing roller 13 around the magnetic field generating means 17, the magnetic force concentrates on the magnetic material and the temperature becomes partially high. However, by forming the member adjacent to the magnetic field generating means 17 with a non-magnetic material, In addition, abnormal concentration of magnetic force can be prevented, and the fixing roller 13 can be efficiently heated with uniform heating without heating other members.

Next, the features of the present invention will be described with reference to FIG. FIG. 6 is a partially enlarged sectional view of the fixing roller. Due to the manufacturing tolerance of the surface of the fixing roller 13 and the bias of the gap between the fixing roller and the magnetic field generating means, a concentrated portion of the magnetic flux is generated on the fixing roller 13, and as a result, uneven heating occurs.
Uneven fixing occurs. Therefore, as shown in FIG. 6A, a rough surface 13a composed of minute projections is formed on the surface of the fixing roller 13 on the magnetic field generating means 17 side. The height of the protrusion is 50 to 50 mm for the thickness of the fixing roller 13 of 1 to 2 mm.
It is about 100 μm. A well-known method such as a method of applying a polishing brush is used as a method of forming a rough surface, but a blast method in which spherical abrasive grains are sprayed is preferable for forming projections uniformly. With this configuration, the magnetic flux generated by the magnetic field generating means 17 is concentrated on the protrusions, and the fine protrusions are uniformly formed on the roller surface. Therefore, uniform heating can be realized as a whole, and the rough surface 13a is formed on the fixing surface. Therefore, the contact area at the time of fixing is increased by the fine projections, so that the fixing property is improved and the thermal efficiency is also increased.

FIGS. 6B and 6C show a modification, in which a release layer 13b made of a fluororesin is formed on the surface of the fine projections on the rough surface 13a. According to the present example, the releasability of the toner can be ensured. FIG.
In the example of (B), since the release layer 13b also has an uneven surface, the effect of increasing the contact area is maintained.

The operation of the present invention having the above configuration will be described. When an alternating current is applied to the exciting coil 20 by an exciting circuit (not shown), the exciting coil 20
3, an eddy current flows through the magnetic fixing roller 13 placed in the AC magnetic field by electromagnetic induction, and Joule heat is generated by the current and the resistance of the metal itself. 13 itself heats up and its temperature is raised. When the temperature of the fixing roller 13 is increased while the rotation of the fixing roller 13 is performed, and the temperature of the fixing roller 13 is detected to be increased to a predetermined temperature by the output of the temperature sensor 24, the surface temperature of the fixing roller 13 is set to the predetermined temperature. It is controlled to maintain. When the recording medium is moved to the fixing roller 13, the recording medium is guided between the fixing roller 13 and the pressure roller 14, and is heated and pressed by the two rollers. Be established.

FIG. 7 shows another embodiment of the fixing device of the present invention. FIG. 7A is a cross-sectional view of the fixing device, and FIG. 7 (C) is a side view of FIG. 7 (B). Note that the same components as those of the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted.

In this embodiment, as shown in FIG. 7A, the magnetic field generating means 17 is provided inside the fixing roller 13 along the inner peripheral surface thereof. Magnetic field generating means 17
The excitation coil 20 is held by a coil holding member 33 attached to a fixed shaft 29. FIG. 7 (B),
In (C), a pair of coil holding members 33 are fixed on both sides of the fixed shaft 29 by screws 34. The coil holding member 33 includes a mounting portion 33a, a mounting hole 33b formed in the mounting portion 33a, and coil holding portions 33c and 33d formed bifurcated from the mounting portion 33a. The excitation coil 20 is fixed by screws 34, and the coil holding portions 33c and 33d hold the excitation coil 20 in a loop shape as in FIG.

In the present embodiment, a rough surface 13a composed of minute projections described with reference to FIG. 6A is formed on the inner peripheral surface of the fixing roller 13 (on the side of the magnetic field generating means 17). In this case, since the inner peripheral surface does not serve as a fixing surface, FIG.
It is not necessary to provide the release layers (B) and (C).

Although the embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications can be made. For example, in the above-described embodiment, the fixing roller 13 and the pressure roller 14 are arranged in a substantially horizontal direction, and the conveyance direction Y of the recording medium is set to be substantially vertical from the bottom to the top. 13 and the pressure roller 14 are arranged substantially vertically, and
May be substantially horizontal.

[0027]

As is apparent from the above description, according to the present invention, since the fine projections are uniformly formed on the surface of the fixing roller, uniform heating can be realized as a whole.
Further, if the rough surface is used as the fixing surface, the contact area in the fixing can be increased by the fine projections, so that the fixing property can be improved and the thermal efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram illustrating an example of an image forming apparatus to which the present invention is applied.

FIG. 2 is a sectional view showing one embodiment of a fixing device of the present invention.

FIG. 3 is a perspective view showing a state where a case is removed in FIG. 2;

FIG. 4 is a side view showing a partially broken section viewed from the X direction in FIG. 2;

5 (A) is a plan view of a magnetic field generating means, FIG.
FIG. 5B is a side view of FIG.

FIG. 6 is a partially enlarged cross-sectional view of the fixing roller of FIG. 2 showing a feature of the present invention.

7 shows another embodiment of the fixing device of the present invention, and FIG.
7A is a cross-sectional view of the fixing device, FIG. 7B is a front view showing a state where the magnetic field generating means is mounted, and FIG. 7C is a side view of FIG. 7B.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 13 ... Fixing roller 13a ... Rough surface 13b ... Release layer 14 ... Pressure roller 17 ... Magnetic field generating means

Claims (4)

[Claims] A fixing device for fixing toner on a recording medium by electromagnetic induction heating, wherein a fixing roller made of a magnetic material, a pressure roller pressed by the fixing roller, and a fixing roller are provided around the fixing roller. And a magnetic field generating means having a rough surface formed on the surface of the fixing roller on the side of the magnetic field generating means. 2. The fixing device according to claim 1, wherein said rough surface is formed by a blast method of spraying spherical abrasive grains. A magnetic field generating means provided on an outer periphery of the fixing roller;
The fixing device according to claim 1, wherein the rough surface is a fixing surface. 4. The fixing device according to claim 3, wherein a release layer is provided on the rough surface.