JPH10240054A - Fixing device for toner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly perform the fixing of a toner image by arranging two pressure rollers by bringing them into contact on the upper and lower sides of a heating roller in a rotational direction at an area where they are brought into contact with a recording medium and setting the surface temperature of the nip part of the pressure roller on the upper side lower than that of the pressure roller positioned on the lower side. SOLUTION: A first pressure roller 26, a guide roller unit 32, a second pressure roller 38, a peeling pawl 41, a cleaning roller unit 44, an oil applying roller unit 48 and a thermistor 52 are disposed on the peripheral surface of a heat roller 24 in order from an upper side in the rotational direction. Then, the surface temperature of the nip part 38a of the second pressure roller 38 is set higher than that of the nip part 26a of the first pressure roller 26. Thus, the recording medium is heated at high temperature from a rear surface to the toner sticking surface of the recording medium, so that toner is infiltrated by nip pressure. Thus, an image having a high fixing ratio is formed even though a color image is fixed at high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic toner fixing device for use in a copying machine, a printer, a facsimile or the like.

[0002]

2. Description of the Related Art A latent image corresponding to each color component is formed on an image carrier, and the latent image is developed with a toner corresponding to each color component. Fixing an image on a recording medium at a practical speed requires a much larger heat source than a monotone fixing device, and always involves the risk of fire.

To solve such a problem, Japanese Patent Laid-Open Publication No. 58-2
No. 1262 or Japanese Patent Application Laid-Open No. 55-29822 discloses a device in which the peripheral speed on the downstream side is increased.
With one pressure roller or a pressure belt stretched between the two rollers, the recording medium fed onto the heating roller is brought into contact with the circumference thereof over a wide surface, and the toner is efficiently softened at a lower temperature. Although these are effective in softening the toner,
Not only is there a problem in that a large amount of superimposed toner is firmly fixed on the recording medium, but also a slight speed difference between the heating roller and the pressure roller causes disturbance of the toner image in surface contact. There are problems that can arise.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem.
By separately carrying the functions of melting the toner and fixing the toner to the recording medium on each of the two pressure rollers, a new and more reliable fixing of the toner image can be performed. To provide a simple fixing device.

[0005]

That is, the present invention provides a toner fixing device for achieving the above object.
Two pressure rollers are disposed in contact with the upper side and the lower side in the rotation direction of the heating roller in a region where the heating roller is in contact with the recording medium, and the surface temperature of the nip portion of the pressure roller located on the upper side is lowered. Is set to be lower than the surface temperature of the nip portion of the pressure roller located at.

[0006]

With this configuration, the nip portion of the upper pressure roller has a role of heating and melting the toner, and the nip portion of the lower pressure roller applies the melted toner to the recording medium. Thus, the high-duty fixing process can be performed more quickly and more reliably by having the function of firmly fixing the film by the action of pressure and pressure.

[0007]

Embodiments of the present invention will be described below.

FIG. 1 shows a fixing device according to an embodiment of the present invention.

First, an outline of a color image forming apparatus provided with a fixing device according to the present invention will be described with reference to FIG.

In the drawing, a charging roller 2, a laser beam scanning type latent image forming unit 3, a yellow drum,
Magenta, cyan, and black developing units 4, 5,
6, 7 and a cleaning unit 9 with the transfer unit 8 interposed therebetween.
Is formed, and a toner image corresponding to the recording information is formed by repeating each image forming process of yellow, magenta, cyan, and black every time the intermediate transfer belt 10 rotates.

On the other hand, the endless intermediate transfer belt 10 which comes into contact with and separates from the photosensitive drum 1 at the transfer section 8 is connected to a primary transfer roller 11.
The secondary transfer of the color toner image formed on the peripheral surface of the photosensitive drum 1 onto the recording medium S by the backup roller 12 is also performed. Reaches a secondary transfer unit 17 via a paper feed roller 15 and paper transport rollers 16 and 16, where the color image is transferred by a toner, and further subjected to a fixing process by a fixing unit 20, The paper is discharged to the paper discharge stacker 18 via the pair 19.

FIG. 1 shows the fixing unit 2 described above.
Next, a detailed configuration of this unit will be described. A casing (not shown) covering the fixing unit 20 is attached to a fulcrum pin 21 provided at an inner lower end of the apparatus main body. The developing unit 4 is configured so that it can be easily replaced when its life has expired, and is rotated toward the front side of the apparatus.
It is configured so as not to hinder the replacement of 5, 6, 7 and the like.

The fixing unit 20 has a heat roller 2 provided with a halogen lamp 23 as a heat source at an axial center thereof.
A recording medium 4 is arranged so as to be driven to rotate by a driving motor (not shown), and the recording medium S guided from the transfer unit 17 in a substantially horizontal state is fixed on the surface by attaching toner to the surface. , And is fed almost right above the discharge stacker 18.

The heat roller 24 is made of a material having a hardness of 15 to 90 degrees and a surface roughness of about 0.2 μm, and when the fixing speed is set at 100 to 300 mm / sec, The roller is formed as a roller having a diameter of 20 to 80 mm, and further has a first pressing roller 26, a guide roller unit 3
2, a second pressure roller 38, a peeling claw 41, a cleaning roller unit 44, an oil application roller unit 48, and a thermistor 52 are provided. The guide roller unit 32, the second pressure roller 38, and the cleaning Roller unit 44 and oil application roller unit 48
Are supported by separate frames, respectively, so that they can be appropriately replaced with new ones when their life has expired.

The first pressure roller 26 can be used with the heat roller 24 so that the recording medium S is brought into pressure contact with the heat roller 24 so that the toner adhered thereon is heated and softened. The roller is formed as a large-diameter roller so as to make contact with as large a surface as possible, and receives a pressing force greater than that of the second pressing roller 38 on the lower side by a pressing roller spring 29 acting on the supported frame 28 to generate heat. The roller 24 is configured to be brought into pressure contact with the peripheral surface. Reference numeral 30 in the drawing denotes a paper guide provided on the upper edge of the frame 28.

On the other hand, a guide roller unit 32 composed of a heat insulating cover 33 as guide means for the recording medium and guide rollers 34 and 35, which also serves to keep the heat roller 24 and the recording medium S warm and guide the recording medium. The second pressure roller 38 disposed on the lower side of the first roller has a function of pressing the recording medium S against the heat roller 24 and fixing the toner to the surface thereof. Pressure roller 26
The curvature at the nip is larger than that at the nip, in other words,
The pressure roller 26 has a diameter smaller than that of the pressure roller 26, and is pressed against the peripheral surface of the heat roller 24 by a pressure roller spring 39.

Next, the operation of fixing a color toner image on the recording paper S by the above-described apparatus will be described.

A solid color image composed of yellow, cyan, magenta and black toners formed on the surface of the photosensitive drum 1 through an image forming process for each rotation is
The image is sequentially transferred onto the intermediate transfer belt 10 by the primary transfer unit 8,
Further, the image is transferred onto the recording paper S by the second transfer unit 17.

The recording paper S onto which the color solid image has been transferred in this manner is fed into the fixing unit 20 and further guided by the paper guide 30 to reach the heat roller 24, where the first recording paper S is transferred. Nip 26 of pressure roller 26
While being strongly pressed on the heat roller 24 by a, it receives a heating action.

For this reason, the toner on the recording paper S is softened by the heat of the heat roller 24, and then the second pressure is applied by the guide rollers 34 and 35 of the guide roller unit 32 and the bottom edge of the heat retaining cover 33. The toner is then sent to the roller 38, where the toner is further subjected to a pressing force, and is again heated by the heat roller 24, so that the multi-layered toner is mixed into a film while mixing into the recording paper. And it is fixed.

As described above, the first pressure roller 26 whose main role is to melt the toner, together with the second pressure roller 38 whose main purpose is fixing, is 15 to 90 in hardness and surface roughness. The pressure rollers 26 and 38 are formed of a material of about 0.2 to 10 μm and are rotated by being driven by a drive motor. These pressure rollers 26 and 38 are described below in order to exhibit their respective functions. It is molded and arranged under such conditions.

That is, the pressing load F1 acting on the first pressing roller 26 is set to 0.4 to 100 kgf, preferably 12 kgf, and the pressing load F2 of the second pressing roller 38 is set to 0.3 to 70 kgf. Preferably, it is larger than 6 kgf, so that the nip width of the first pressure roller 26 is increased, and the toner on the recording medium S is brought into contact with the heat roller 24 on a wide surface, thereby effectively heating and melting the toner. Do. The contact pressure P2 of the nip portion 28a of the second pressure roller 38 is set to 0.004 to 28 kgf of that of the first pressure roller 26.
/ Cm ² larger than 0.006 to 40 kgf / cm ² , the recording medium is strongly pressed against the surface of the heat roller 24 by the second pressure roller 38, and the toner which has adhered to the surface and has already been softened is strongly pressed. The pressure is applied between the fibers of the recording medium S to fix the fibers. The anchor effect provides a high fixing strength, and the multi-layered toner is compressed and deformed and mixed into a film to obtain a sufficient coloring property. it can.

The nip portion 2 of the first heating roller 26
The width N1 of the second pressure roller 38 is set to 1 to 25 mm, preferably 8 mm.
The width N2 of the first pressure roller 26 is set to be larger than that of the second pressure roller 38, that is, the outer diameter of the first pressure roller 26 is made larger than that of the second pressure roller 38, The material of the pressure roller 26 is made softer than that of the second pressure roller 38, so that the recording medium S is brought into contact with the heat roller 24 on a surface as wide as possible, so that the heating and melting of the toner is effectively prevented. Do it.

Further, the pressing load of the first pressing roller 26 is made larger than that of the second pressing roller 38, and the friction coefficient of the surface of the first pressing roller 26 is reduced by the second pressing force. By using a material larger than that of the pressure roller 38, the frictional force of the nip portion of the first pressure roller 26 is reduced to the second pressure.
By setting the pressure roller 38 larger than that of the pressure roller 38, strongly holding the recording medium at the nip portion of the first pressure roller 26, and causing the second pressure roller 38 to slip on this recording medium, At the same time, the toner is melted without causing disturbance of the toner image, and at the same time, even if the recording medium is a double one such as an envelope, the fixing process can be performed without causing wrinkles or curls on the recording medium.

In particular, the second pressure roller 38 greatly contributes to the permeation and fixation of the melted toner by the recording medium without fail. This will be described below.

First, the nip 3 of the second pressure roller 38
8a is applied to the nip 2 of the first pressure roller 26.
By setting the surface temperature of the recording medium 6a higher, the recording medium can be heated at a high temperature from the back side with respect to the toner adhering surface of the recording medium to allow the toner to penetrate under the nip pressure. This means that the toner can be sufficiently penetrated in accordance with the pressure of the second pressure roller 38 without cooling and solidifying the melted toner during the permeation, so that a sufficient anchor effect can be provided. Therefore, even if a color image is fixed at a high speed, an image having a high fixing rate can be formed. On the other hand, when forming a matte color image with a low surface gloss using a toner that is not so excellent as a heat melting property, a higher fixing temperature is required, so that a fixing device that forms a matte image does not increase in size. Fast and reliable fixing is possible.

Next, by setting the heat capacity of the second pressure roller 38 to be smaller than the heat capacity of the first pressure roller 26, heat is received from the heat roller 24 in a space between sheets where no recording medium exists. The temperature can be raised immediately, and an image having a high fixing rate can be formed as described above.

Further, by setting the thermal conductivity of the second pressure roller 38 to be smaller than the thermal conductivity of the first pressure roller 26, the saturation temperature after the temperature rise due to the heat received from the heat roller 24 can be reduced. As a result, an image having a high fixing rate can be formed as described above.

Further, by setting the outer diameter of the second pressing roller 38 to be smaller than the outer diameter of the first pressing roller 26, the second pressing roller can be reduced in diameter and downsized. The temperature can be raised instantaneously even in a short space between sheets,
The speed of the image forming apparatus can be further increased. It is also advantageous for separating the curvature of the recording medium.

At the same time as providing the above conditions, the paper feed speed of the first pressure roller 26 is made smaller than the paper feed speed of the second pressure roller 38 or the paper discharge roller 19, whereby the recording medium Can be performed while the toner image is kept in close contact with the peripheral surface of the heat roller 24 while suppressing the disturbance of the toner image. Similarly, in the conveyance path of the recording medium from the secondary transfer unit to the paper discharge roller,
By increasing the speed toward the downstream, it is possible to prevent paper wrinkles and prevent image disturbance due to slippage.
On the other hand, in this transport path, it is desirable that the gripping force with the recording medium be reduced toward the downstream from the fixing unit to prevent slipping at the fixing unit and eliminate image disturbance.

[0031]

As described above, according to the present invention, two pressure rollers are provided on the peripheral surface of the heating roller in the area where the pressure roller contacts the recording medium, and the nip of the pressure roller located on the upper side is provided. Surface temperature of the nip portion of the pressure roller located on the lower side, so that high-duty fixing such as forming a solid image using multi-color toner can be shortened. It can be performed more efficiently with time, and it is possible to ensure the penetration of the toner into the recording medium and the fixing of the toner.

Further, by setting the heat capacity of the lower pressure roller to be smaller than the heat capacity of the upper pressure roller, heat can be received from the heat roller and the temperature can be raised immediately, and an image having a high fixing rate can be obtained. Can be formed.

Further, by setting the thermal conductivity of the lower pressure roller to be smaller than the thermal conductivity of the upper pressure roller, the saturation temperature after the temperature rise can be increased. Thus, an image having a high fixing rate can be formed.

Furthermore, by setting the outer diameter of the lower pressure roller to be smaller than the outer diameter of the upper pressure roller, both miniaturization and high speed can be achieved.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram illustrating an example of an image forming apparatus including the above device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor drum 10 transfer belt 20 fixing unit 24 heat roller 26 first pressure roller 33 heat insulation cover 38 second pressure roller

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazutoshi Fujisawa 3-3-5 Yamato, Suwa-shi, Nagano Seiko Epson Corporation (72) Inventor Hiroshi Tanaka 3-3-5 Yamato, Suwa-shi, Nagano Seikoー Epson Corporation

Claims (4)

[Claims] 1. A nip portion of the pressure roller located on the upper side, wherein two pressure rollers are disposed in contact with the upper side and the lower side in the rotation direction of the heating roller in a region in contact with the recording medium. A toner fixing device, wherein the temperature is set lower than the surface temperature of a nip portion of the pressure roller located on the lower side. 2. The toner fixing device according to claim 1, wherein the heat capacity of the pressure roller located on the upper side is set to be larger than the heat capacity of the pressure roller located on the lower side. 3. The toner according to claim 1, wherein the thermal conductivity of the upper pressure roller is set to be smaller than the thermal conductivity of the lower pressure roller. Fixing device. 4. The toner fixing device according to claim 2, wherein an outer diameter of the pressure roller located on the upper side is set to be larger than an outer diameter of the pressure roller located on the lower side. .