JP3516445B2 - Fixing device and image forming apparatus having the fixing device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device having a pressure roller and an image forming apparatus having the fixing device.

[0002]

2. Description of the Related Art Electronic copying machines, printers, facsimiles,
Alternatively, in an image forming apparatus configured as a multi-function peripheral having at least two functions, a fixing device that fixes a toner image formed on a recording medium such as a transfer paper or a resin sheet is used. As such a fixing device, a fixing device which passes a recording medium carrying a toner image between a heating fixing member and a pressure roller and fixes the toner image on the recording medium has been widely adopted. There is.

FIG. 9 is a sectional view showing a conventional example of this type of fixing device. In the fixing device 1A illustrated here, the fixing member is configured as a hollow cylindrical fixing roller 3A, and the pressure roller 4A is in pressure contact with the fixing roller 3A. Inside the fixing roller 3A, a heater 2A that heats the fixing roller is installed. During the printing operation of the image forming apparatus, the fixing roller 3A and the pressure roller 4A are in pressure contact with each other and rotate in the respective arrow directions, and the recording medium P carrying the unfixed toner image T passes between the rollers. At this time, the toner image on the recording medium is brought into pressure contact with the surface of the fixing roller 3A, and the toner image is fixed on the recording medium P by the action of heat and pressure. The pressure roller 4A serves to press the recording medium P against the fixing roller 3A.

By the way, in the image forming apparatus having the fixing device as described above, when the main switch is turned on, the heater 2A heats the fixing roller 3A, and the surface temperature thereof becomes a fixing temperature suitable for fixing. Since then, the above-mentioned fixing operation is started. Further, during the standby with the main switch turned on, the temperature of the fixing roller 3A is kept at a standby temperature lower than the fixing temperature, and while the fixing roller 3A and the pressure roller 4A are pre-rotated before the start of the printing operation, It is well known in the art that the fixing roller 3A is heated by the heater 2A and the fixing operation is executed after the surface temperature of the fixing roller 3A reaches the fixing temperature. Thus, it is desirable that the waiting time until the temperature of the fixing roller 3A rises to the fixing temperature is as short as possible.

Therefore, conventionally, measures such as making the fixing roller 3A as thin as possible to reduce its heat capacity and shortening the waiting time until the temperature of the fixing roller 3A rises to the fixing temperature are taken. However, when the fixing roller 3A is being heated by the heater 2A to raise the temperature of the fixing roller 3A, the pressure roller 4 is applied to the fixing roller 3A.
If A is in contact with the fixing roller 3A,
Heat of the fixing roller 3A is removed by the pressure roller 4A.
It is not easy to raise the temperature of 1 to the fixing temperature in a short time. In particular, when the fixing roller 3A and the pressure roller 4A are pre-rotated as described above when the temperature of the fixing roller 3A is raised to raise the temperature of the fixing roller 3A uniformly in the circumferential direction, As the rotation of the fixing roller 3A is started, a large amount of heat is taken by the pressure roller 4A, so that the temperature of the fixing roller 3A rapidly decreases. For this reason, the waiting time until the fixing roller 3A reaches the fixing temperature becomes long, which inevitably causes a great inconvenience to the user.

In order to prevent the above-mentioned problems, as shown in FIG. 9, a pressure roller 4A in which a core shaft 5A made of a rigid body such as metal and a porous elastic layer 6A made of sponge are laminated on the peripheral surface thereof. And a fixing device in which the fixing roller 3A is made of a rigid body has been proposed (Japanese Patent Laid-Open No. 58-58-58).
(See Japanese Patent No. 134672). When the pressure roller 4A having such a porous elastic layer is used, the elastic layer is porous, so that the heat insulating property is improved and the amount of heat taken from the fixing roller to the pressure roller is increased. Can be reduced. As a result, the waiting time until the fixing roller 3A reaches the fixing temperature can be shortened. Moreover, the pressure roller 4
When A is pressed against the fixing roller 3A, the elastic layer 6A of the pressure roller 4A is elastically deformed, whereby the pressure roller 4 has a certain nip width N in the recording medium conveyance direction.
Since A and the fixing roller 3A are in pressure contact with each other, a necessary amount of heat is applied to the toner image T while the recording medium P passes therethrough,
The toner image T can be reliably fixed on the recording medium.

However, when the pressure roller 4A has the elastic layer 6A as described above, the elastic layer 6A is compressed by the fixing roller 3A made of a rigid body as shown in FIG. Since it is deformed, the recording medium P that has passed between the fixing roller 3A and the pressure roller 4A moves along the peripheral surface of the fixing roller 3A as indicated by an arrow BA in FIG.
For this reason, the recording medium exiting the fixing roller 3A and the pressure roller 4A is easily wrapped around the peripheral surface of the fixing roller 3A as indicated by the reference numeral PA in FIG. 9 and indicated by the chain line. Normally, a separation claw 30 for separating the recording medium from the fixing roller 3A
Since A is provided, the recording medium PA wound around the fixing roller 3A is separated from the peripheral surface of the fixing roller 3A by the separating claw 30A. At this time, the toner image on the recording medium PA is separated by the separating claw 30A. The toner image may be rubbed and a streak-like mark may be formed on the toner image. In addition, when the recording medium is wound around the peripheral surface of the fixing roller 3A and when it is not wound, the fixing roller 3A is
The amount of heat given to the toner image on the recording medium from A is largely different, and the amount of heat given from the fixing roller 3A is larger in the former case. Therefore, the glossiness of the toner image on the recording medium becomes different, and it becomes impossible to obtain a toner image of uniform quality. Especially in the case of a color image forming apparatus,
This defect cannot be ignored because the glossiness of the toner image has a relatively large effect on the image quality.

Further, the fixing member to be heated is composed of an endless fixing belt wound around a plurality of winding rollers, and a recording medium is passed between the fixing belt and the pressure roller to fix the toner image. Although the apparatus is well known in the related art, such a fixing apparatus also has the same problem as described above.

[0009]

[0010]

SUMMARY OF THE INVENTION A first object of the present invention is to provide a fixing device which eliminates the above-mentioned drawbacks.

A second object of the present invention is to provide an image forming apparatus having the above fixing device.

[0012]

[0013]

[0014]

In order to achieve the first object, the present invention comprises a fixing member to be heated, and a pressure roller for pressing a recording medium against the fixing member,
In the fixing device for fixing the toner image on the recording medium by passing the recording medium between the fixing member and the pressure roller so that the toner image carried on the recording medium contacts the fixing member. The pressure roller includes a heat insulating layer formed of a rigid body having a large number of pores, the fixing member includes a fixing roller, and the fixing roller includes an elastic layer that is elastically deformed by being pressed by the pressure roller. A fixing device characterized by having is proposed (Claim 1).

[0015]

Further, in the fixing device according to the first aspect, it is advantageous that the pressure roller is configured to be directly rotated by a driving device without passing through the fixing roller. Claim 2).

Further, it is advantageous that the fixing device according to claim 1 or 2 further comprises a heating means for heating the fixing roller from the surface of the fixing roller (claim 3).

In order to achieve the first object, the present invention comprises a fixing member to be heated and a pressure roller for pressing the recording medium against the fixing member, and is carried on the recording medium. And a fixing device for fixing the toner image to the recording medium by passing the recording medium between the fixing member and the pressure roller so that the toner image comes into contact with the fixing member.
The pressure roller includes a heat insulating layer formed of a rigid body having a large number of pores, and the fixing member includes an endless fixing belt wound around a plurality of winding rollers. At least one of the rollers has an elastic layer that is elastically deformed by being pressed by the pressure roller via the fixing belt, and a fixing device is proposed (claim 4). .

Further, in the fixing device according to the fourth aspect, it is advantageous that the pressure roller is directly rotated by a driving device without passing through the fixing belt ( Claim 5).

Further, in the fixing device according to any one of claims 1 to 5, it is advantageous to provide a heating means for heating the pressure roller from the surface of the pressure roller (claim 6).

Further, in the fixing device according to any one of claims 1 to 6, the heat insulating layer is a porous molded body in which a large number of pores are formed between bonded fibers, a porous ceramics, and At least one of the porous resins
Advantageously, it is constituted by one (claim 7).

In order to achieve the above second object, the present invention proposes an image forming apparatus comprising the fixing device according to any one of claims 1 to 7 (claim 8).

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a vertical sectional view showing the outline of the image forming apparatus. In the main body 31 of the image forming apparatus, an image forming means 32 for forming a toner image on a recording medium, and an image forming means for recording the image. It has a feeding means 33 for feeding the medium and a fixing device 1 for fixing the toner image formed on the recording medium. First, the outline of the image forming means 32 will be clarified.

The image forming means 32 illustrated here has a drum-shaped photoconductor 35 which is an example of an image carrier. When the photoconductor 35 rotates clockwise, the surface of the photoconductor is charged by the charging device 36. It is charged to a predetermined polarity. The charged surface is irradiated with a light-modulated laser beam L emitted from a laser writing unit 37 which is an example of an exposure device, whereby an electrostatic latent image is formed on the surface of the photoconductor. This electrostatic latent image is visualized as a toner image by the developing device 38, and the toner image is transferred onto the recording medium P fed by the feeding means 33 by the action of the transfer device 39.
The transfer residual toner adhering to the surface of the photoconductor after the transfer of the toner image is removed by the cleaning device 40.

The feeding means 33 has a cassette 41 containing a recording medium P made of, for example, a resin sheet or transfer paper, and the uppermost recording medium P is fed out from the cassette 41 by the rotation of the feeding roller 42. The recording medium sent out is fed to the transfer position between the photoconductor 35 and the transfer device 39 by the rotation of the registration roller pair 43, where the toner image on the photoconductor 35 is recorded as described above. It is transferred onto the medium.

The recording medium on which the toner image is transferred continues to pass through the fixing device 1, and at this time, the toner image on the recording medium is fixed as described later. The recording medium that has passed through the fixing device 1 is discharged onto a tray 44 outside the machine.

FIG. 2 is an enlarged sectional view of the fixing device 1. The fixing device 1 shown here includes a fixing roller 3 which is an example of a fixing member, and a pressure roller 4 which is in pressure contact with the fixing roller 3 and extends substantially parallel to the fixing roller 3. . The pressure roller 4 includes a round rod-shaped core shaft 5 made of a rigid body such as metal or hard resin, a cylindrical heat insulating layer 9 fixed to the core shaft 5 by, for example, press fitting or bonding, and the heat insulating layer 9 thereof. The heat insulating layer 9 is concentrically fixed to the core shaft 5, and has a surface layer composed of a release layer 10 laminated on the surface. It is also possible to omit the release layer 10.

On the other hand, the fixing roller 3 includes a core shaft 11 made of a rigid body such as metal, a heat-resistant elastic layer 12 concentrically fixed to the core shaft 11, and an elastic layer 1 thereof.
2 and the release layer 13 laminated on the surface. The elastic layer 12 is made of, for example, non-foamed silicone rubber, or foamed molding of silicone rubber, and the release layers 13 and 10 of the fixing roller 3 and the pressure roller 4 are made of, for example, polytetrafluoroethylene or the like. It is made of a material such as a fluororesin having excellent release properties.

The heat insulating layer 9 of the pressure roller 4 is made of a rigid body having heat resistance and having a large number of pores, for example, a molded body made of a porous ceramic material. Ceramic materials have excellent heat resistance, high rigidity and high compressive strength, and exhibit high heat insulation due to the large number of pores. Moreover, the coefficient of thermal expansion is low and the coefficient of thermal expansion is much smaller than that of the elastic layer due to its high rigidity. When the volume ratio of all pores to the total volume of the heat insulating layer 9 made of a ceramic material is referred to as porosity, when the porosity is about 50%, the heat conductivity of the heat insulating layer 9 is about 0.3 W / mK. Becomes Porosity is 3
It can be set in the range of 0 to 70%.

The heat insulating layer 9 may be made of the above-mentioned ceramic material, or may be made of a porous molded body in which heat resistant fibers are mutually bonded by a binder and a large number of pores are formed between the fibers. . Such a porous molded body has the same characteristics as the molded body made of the ceramic material described above.

Japanese Unexamined Patent Publication (Kokai) No. 9-108601 discloses that "a fine interconnecting void having no binder present between fibers and a uniformly distributed pore group having a pore diameter of 0.05 to 2 mm and a total void ratio. It is described that a "porous" fibrous product having a content of 30 to 90% and glass fibers, for example, can be used as the fiber. After molding the material, it is dried and heated to produce a fibrous molded product. Although the method is described in detail, such a fibrous molded body can be used as a porous molded body forming the heat insulating layer 9.

Further, the heat insulating layer 9 may be made of a porous resin. For example, by packing resin granules in a molding die (not shown), heating and sintering it,
The cylindrical heat insulating layer 9 made of porous resin can be obtained. The pressure roller 4 can be manufactured by fixing the heat insulating layer 9 to the core shaft 5 by press fitting or bonding. The resin used includes polyimide, polyphenylene sulfide, polytetrafluoroethylene, etc.,
In particular, it is advantageous to sinter the polyimide granules to obtain a cylindrical porous resin molded body having a porosity of 60% and use this as the heat insulating layer 9.

The thermal conductivity of the solid resin is, for example, 0.
It is about 2 W / mK. Therefore, when the above-mentioned porous resin is used as the heat insulating layer 9, it is possible to obtain higher heat insulating properties than in the case where the porous ceramic is used as the heat insulating layer 9.

Further, the heat insulating layer 9 is formed by the above-mentioned porous molded body,
It can also be composed of a plurality of porous ceramics and porous resins. In short, the heat insulating layer 9 is made of at least one of a porous molded body in which a large number of pores are formed between the bonded fibers, a porous ceramics, and a porous resin.

The pressure roller 4 and the fixing roller 3 are rotatably supported by machine frames (not shown) of the fixing device 1 at the respective longitudinal end portions of the core shafts 5, 11 thereof. By the pressure means, the fixing roller 3 and the pressure roller 4 are pressed toward each other so that the surfaces of the rollers 3 and 4 are pressed against each other. At that time, since the pressure roller 4 has the heat insulating layer 9 having high rigidity and the fixing roller 3 has the elastic layer 12, both the rollers 3 and 4 are pressed against each other, so that The elastic layer 12 is elastically deformed to be compressed and deformed by the pressure roller 4, but the heat insulating layer 9 of the pressure roller 4 is hardly deformed.
By elastically deforming the elastic layer 12, both rollers 3,
4 presses each other with a nip width indicated by N.

As shown in FIG. 3, the core shaft 5 of the pressure roller 4 is
A pressure roller gear 14 is fixed to the pressure roller gear 14, and a drive gear 15 rotatably supported on the image forming apparatus main body side is meshed with the pressure roller gear 14, and the rotation thereof is performed by the operation of a drive motor (not shown). It is transmitted to the pressure roller 4 via the gears 15 and 14, and the pressure roller 4 is rotationally driven counterclockwise in FIG. In addition, the fixing roller 3
The fixing roller gear 16 is fixed to the core shaft 11 of the fixing roller gear 16, the fixing roller gear 16 meshes with the pressure roller gear 14, and the rotation of the pressure roller gear 14 is transmitted to the fixing roller gear 16, which causes the fixing roller 3 to rotate in the clockwise direction in FIG. Is driven to rotate. The fixing roller gear 16 is not provided, and the rotation of the pressure roller 4 is brought into contact with the surface of the fixing roller 3 by pressure.
The fixing roller 3 can also be driven to rotate. In any case, the pressure roller 4 is directly driven to rotate by the driving device including the driving motor and the gears 14 and 15 without the interposition of the fixing roller 3. The pressure roller 4 and the fixing roller 3 are rotated by rotationally driving the pressure roller 4 by the driving device.

On the other hand, the fixing roller 3 is constituted so that the surface of the fixing roller 3 is heated by the heating means 17. The heating means 17 shown as an example in FIG.
The fixing roller 3 is rotatably supported by the machine frame of the fixing device 1 and
It is composed of a heating cylinder 18 which is pressed against the surface of the rotating body and is driven to rotate, and a heater 19 accommodated therein.
To the surface of the fixing roller 3 via
Heating the surface of.

The surface of the fixing roller 3 is in contact with a temperature detecting means composed of a thermistor 20, and based on the result of the temperature detection of the surface of the fixing roller by the thermistor 20,
ON / OFF of energization of the heater 19 is controlled. As a result, during the fixing operation, the temperature of the surface of the fixing roller is controlled to be a fixing temperature within a predetermined range suitable for fixing the toner image.

Although the toner image is transferred onto the recording medium P as described above, the recording medium P carrying the unfixed toner image T is guided by the entrance guide plate 21 as shown in FIG. , An arrow A is attached to the pressure contact portion between the fixing roller 3 and the pressure roller 4 which rotate in the directions indicated by the arrows in FIG.
It is sent as shown in. At this time, the toner image T contacts the surface of the fixing roller 3, and the toner image T is fixed on the recording medium P by the heat transmitted from the fixing roller 3 and the pressure received from the fixing roller 3 and the pressure roller 4. . The recording medium P is passed between the fixing roller 3 and the pressure roller 4 so that the toner image T carried on the recording medium P contacts the surface of the fixing roller 3, and the toner image is fixed on the recording medium. Of. The recording medium P that has passed through the fixing device 1 is, as described above, ejected from the main body of the image forming apparatus by the discharge tray 44 (FIG. 1).
Discharged on top.

As described above, the fixing device 1 of the present example includes the fixing roller 3 which is an example of a heated fixing member, and the pressure roller 4 for pressing the recording medium P against the fixing member. The recording medium P is passed between the fixing member and the pressure roller 4 so that the toner image T carried on the recording medium P contacts the fixing member, and the toner image T is fixed on the recording medium P. Is configured. Also in the case of this fixing device 1, after the main switch (not shown) of the image forming apparatus is turned on, the fixing device 3 is heated by the heating means 17 at the start-up, and the surface temperature thereof becomes the fixing temperature.
Perform the fixing operation. Similarly, with the main switch turned on, the fixing roller 3 is kept at a standby temperature lower than the fixing temperature, the fixing roller 3 is heated by the heating means 17 before the start of the printing operation, and the temperature becomes the fixing temperature. And then start the fixing operation. When the temperature of the fixing roller 3 is raised, it is usual to rotate the fixing roller 3 and the pressure roller 4 in the direction shown by the arrow in FIG. 2 to uniformly raise the temperature of the fixing roller 3 in the circumferential direction.

Since the pressure roller 4 is provided with the heat insulating layer 9 made of a rigid body in which a large number of pores are formed, when the temperature of the fixing roller 3 is raised to the fixing temperature as described above, the pressure roller 4 is used. The heat insulating layer 9 has a high heat insulating property due to the action of the pores thereof, and the amount of heat taken from the fixing roller 3 to the pressure roller 4 is higher than that of a conventional fixing device having a pressure roller without such a heat insulating layer. Can be significantly reduced. The pressure roller 4 is supplied with heat from the fixing roller 3, and the temperature of the release layer 10 rises. However, since the heat insulating layer 9 exists, the temperatures of the heat insulating layer 9 and the core shaft 5 do not rise so much, and the fixing roller 3 It is possible to suppress the temperature drop.

As a result, the waiting time until the fixing roller 3 of the fixing device 1 reaches the fixing temperature can be effectively shortened. Therefore, with the main switch of the image forming apparatus turned on, when the image forming apparatus is on standby, power supply to the heater 19 of the heating unit 17 may be turned off so that the fixing roller 3 is not preheated. it can.
Even with this configuration, it is possible to raise the temperature of the fixing roller 3 to the fixing temperature in a short time after the energization of the heater 19 is started before the printing operation is started. This is the same in the case of an example described later in which a fixing belt is used as the fixing member. With this configuration, the energy consumed by the image forming apparatus can be further reduced.

Since the heat insulating layer 9 is made of a rigid body instead of an elastic body, the recording medium P passing between the fixing roller 3 and the pressure roller 4 is removed from the fixing roller 3 as shown by an arrow B in FIG. It is transported in a direction away from it. Therefore, it is possible to prevent the problem that the recording medium P winds around the surface of the fixing roller 3. For this reason, it is possible to prevent the problem that the toner image on the recording medium has a stripe-shaped mark due to the separation claw and the glossiness of the toner image varies as in the related art. In the case of a fixing device for a color image forming apparatus, it is possible to obtain a toner image of uniform quality by preventing the glossiness of the toner image from varying. Further, the recording medium P is the fixing roller 3
Since it is possible to prevent the recording medium P from wrapping around, the recording medium P does not contact the fixing roller 3 for an excessively long time. For this reason, it is possible to prevent hot offset in which toner adheres to the fixing roller 3 without applying the offset prevention liquid to the fixing roller 3. Thereby, the cost of the fixing device 1 can be further reduced. Of course, if the offset prevention liquid is applied to the fixing roller 3, the hot offset prevention effect can be more surely enhanced.
Further, in the fixing device 1 of this example, since the release layers 13 and 10 are provided on the surfaces of the fixing roller 3 and the pressure roller 4, respectively, this also causes a problem that the toner is transferred to these surfaces. Can be prevented.

In the case of the fixing device shown in FIG. 2,
In addition to the configuration described above, the fixing roller 3 has the elastic body layer 12 that is elastically deformed by being pressed by the pressure roller 4, so that the elastic body layer 12 is pressed by the pressure roller 4 to a large extent. It is compressed and deformed, whereby the recording medium P ejected from between the fixing roller 3 and the pressure roller 4 can be more reliably directed in the direction away from the fixing roller 3, and the above-mentioned effect is further ensured. be able to.

Further, in the fixing device 1 of this embodiment, as described above, the pressure roller 4 is directly driven to rotate by the driving device without the fixing roller 3 interposed therebetween. Even with this configuration, the recording medium P can be conveyed at a constant and correct speed. A configuration related to this will be described below in comparison with a conventional example.

In the case of the conventional fixing device shown in FIG. 9, the elastic layer 6A of the pressure roller 4A is elastically deformed, so that the pressure contact portion of the fixing roller 3A and the pressure roller 4A is the highest in the recording medium conveyance direction. The radius R1 of the pressure roller in the upstream portion NU and the most downstream portion NL and the radius R2 of the pressure roller in the intermediate portion NC are slightly different, and R1> R2.

Therefore, when the pressure roller 4A is driven by the driving device and the fixing roller 3A is driven to rotate by the rotation of the pressure roller 4A, even if the angular velocity of the pressure roller 4A is constant, The recording medium conveying speed at the most upstream side portion NU and the most downstream side portion NL of the pressure contact portion between the pressure roller 4A and the fixing roller 3A, and the intermediate portion N
A difference occurs in the recording medium conveyance speed in C, which disturbs the toner image on the recording medium and may deteriorate the image quality. The elastic layer 6A undergoes large thermal expansion due to temperature rise, and such thermal expansion also causes fluctuations in the transport speed of the recording medium.

On the other hand, in the case of the fixing device 1 of the present example shown in FIG. 2, when the recording medium P passes between the fixing roller 3 and the pressure roller 4 as described above, both rollers 3, 4 are Since they are pressed against each other with a predetermined nip width N, a sufficient amount of heat can be applied to the toner image on the recording medium passing therethrough to securely fix the toner image on the recording medium P.
At that time, the pressure roller 4 includes the fixing roller 3 and the pressure roller 4.
The elastic body layer 12 of the fixing roller 3 is elastically deformed at the pressure contact portion of No. 2 and the predetermined nip width N is secured. Therefore, the speed of the surface of the pressure roller 4 which is rotationally driven by the driving device is substantially equal in the entire area of the pressure contact portion between the rollers 3 and 4. The uppermost stream side part NU of the press contact part
The radius R of the pressure roller 4 is substantially equal in both the downstream portion NL and the intermediate portion NC thereof, and the surface speed of the pressure roller 4 rotating at a constant angular velocity is uniform over the entire circumference. Become. Moreover, since the heat insulating layer 9 of the fixing roller 3 is made of a rigid body, the thermal expansion amount is extremely smaller than that of the elastic layer of the conventional fixing roller. Therefore, the conveyance speed of the recording medium P nipped and conveyed by the fixing roller 3 and the pressure roller 4 can be kept constant. Therefore, the toner image can be fixed while the recording medium is conveyed in a stable state, and the problem that the toner image on the recording medium is disturbed can be prevented.

Further, in the case of the fixing device 1 shown in FIG. 2, since the fixing roller 3 has the elastic layer 12, its thickness becomes large and its heat capacity also becomes large. Therefore, if the fixing roller is heated from the inside as in the conventional case, it takes a considerably long time to raise the temperature of the fixing roller 3 to the fixing temperature when the fixing device is started up.

On the other hand, in the fixing device 1 of the present embodiment, since the heating means 17 for heating the fixing roller 3 from the surface of the fixing roller 3 is provided, even if the heat capacity of the fixing roller 3 is large, the heat treatment can be performed. The surface can be raised to the fixing temperature in a short time.

In the fixing device 1 shown in FIG. 4, the fixing member is composed of an endless fixing belt 8 wound around a plurality of winding rollers 3B and 7. Here, if necessary, one winding roller 3B will be referred to as a first roller and the other winding roller 7 will be referred to as a second roller, and the first roller 3B and the second roller 3B will be referred to. 7
Are spaced from each other and extend in parallel with each other, and the pressure roller 4 is in pressure contact with the endless fixing belt 8 wound around the first and second rollers 3B and 7. In the illustrated example, the pressure roller 4 is in pressure contact with the first roller 3B via the fixing belt 8.

The structures of the first roller 3B and the pressure roller 4 are substantially the same as those of the fixing roller and the pressure roller described above with reference to FIGS. 2 and 3. That is, the pressure roller 4 shown in FIG. 4 also has a heat insulating layer 9 having heat resistance and rigidity and having a large number of pores,
The roller 3B also has an elastic layer 12 that is elastically deformed by being pressed by the pressure roller 4 via the fixing belt 8. Other configurations are the same as those of the fixing roller and the pressure roller shown in FIGS. 2 and 3. Therefore, the same reference numerals as those given to the respective portions of the fixing roller and the pressure roller in FIG. 2 are shown in FIG. The first roller 3B and the pressure roller 4 are attached to respective parts, and further description of the first roller 3B and the pressure roller 4 shown in FIG. 4 will be omitted. However, the first roller 3
Since B does not come into direct contact with the recording medium P, the release layer 13 as the surface layer of the first roller 3B can be omitted. Further, it is desirable to provide a release layer for preventing the adhesion of the toner on the surface of the fixing belt 8 which comes into contact with the recording medium P.

The second roller 7 is formed in a cylindrical shape, and each end of the second roller 7 is rotatably supported by the machine frame of the fixing device 1. Further, as shown in FIG. 5, each end of the second roller 7 is pressed by the compression spring 22 in a direction away from the first roller 3B, whereby the first roller 3B and the second roller 3B are separated from each other.
A predetermined tension can be applied to the fixing belt 8 stretched around the roller 7. The heater 23 is arranged inside the second roller 7, and the second roller 7 is heated by the heater 23, and the heat is transmitted to the fixing belt 8 to be fixed.
Is heated. The endless fixing belt 8 is the second roller 7
That is, the second roller 7 is heated by, and is configured as a heating roller. Further, a temperature detecting means composed of a thermistor 24 is in contact with the surface of the fixing belt 8, and ON / OFF of energization to the heater 23 is controlled based on the temperature detection result, and the temperature of the fixing belt 8 during the fixing operation is a toner image. The fixing temperature is maintained in a range suitable for fixing.

Also, in the fixing device 1 shown in FIG. 4, the fixing device 1 shown in FIGS.
The pressure roller 4 is configured as a drive roller that is directly rotated by the drive device without passing through the fixing belt 8 (see FIG. 3), and the first roller 3B is driven by the rotation of the pressure roller 4. Rotates, and the fixing belt 8 has an arrow C.
The second roller 7 rotates in the clockwise direction in FIG. By rotating the pressure roller 4, the pressure roller 4 and the first roller 3B are rotated, and the fixing belt 8 is run.

As in the case of the fixing device shown in FIG. 1, the first roller 3B and the pressure roller 4 are not shown in the direction in which the rollers 3 and 4 approach each other via the fixing belt 8. The elastic layer 12 of the first roller 3B is elastically deformed by the pressure means, and the fixing belt 8 and the pressure roller 4 are pressed against each other with a predetermined nip width N. At this time, the pressure roller 4 is hardly deformed.

The recording medium P on which the toner image T has been transferred as described above is guided by the entrance guide plate 21 while being guided by the first roller 3B and the pressure roller 4 as shown by an arrow A.
Enter in between. The recording medium P so that the toner image T carried on the recording medium P contacts the surface of the fixing belt 8.
Passes between the first roller 3B and the pressure roller 4, and at this time, the recording medium P is pressed against the fixing belt 8 by the pressure roller 4 and the heat transferred from the fixing belt 8
By the pressure received from the roller 3B and the pressure roller 4 of
The toner image is fixed on the recording medium P. The recording medium P that has passed through the fixing device 1 is ejected outside the main body of the image forming apparatus.

As can be seen from the above description, also in the fixing device 1 shown in FIG. 4, since the pressure roller 4 has a heat insulating layer made of a rigid body in which a large number of pores are formed, the fixing device 1 stands. When the fixing belt 8 is heated by the second roller 7 at the time of raising or before starting the printing operation, when the fixing belt 8 and the pressure roller 4 start to rotate, the heat of the fixing belt 8 is applied. It won't be robbed in large numbers. Therefore, the fixing belt 8 can be raised to the fixing temperature in a short time. Moreover, the heat insulating layer 9 of the pressure roller 4 is made of a rigid body, and in particular, the first roller 3B has the elastic body layer 12 that is elastically deformed by being pressed by the pressure roller 4 via the fixing belt 8. Fixing belt 8 and pressure roller 4
The recording medium that has come out of the pressure contact portion with is conveyed in the direction away from the fixing belt 8 (direction of arrow B), and thus the problem that the recording medium P winds around the fixing belt 8 can be prevented. In addition, the first roller that is in pressure contact with the pressure roller 4 via the fixing belt 8
The elastic layer 12 of the roller 3B is elastically deformed, and the pressure roller 4 is hardly deformed. Therefore, in the pressure contact portion between the pressure roller 4 and the fixing belt 8 which are rotationally driven at a constant angular velocity. The surface speed of the pressure roller 4 is constant over the entire surface. Moreover, the thermal expansion amount of the heat insulating layer 9 of the pressure roller 4 is extremely small. As a result, the conveyance speed of the recording medium P passing through this pressure contact portion is kept constant, and the toner image on the recording medium is not disturbed.

Further, as the fixing belt 8, a belt having a small thickness and therefore a small heat capacity can be used,
As a result, the fixing belt 8 can be heated by the second roller 7 to a fixing temperature suitable for fixing the toner image in an extremely short time.

The fixing belt 8 is formed thin as described above,
By reducing the heat capacity of the fixing belt 8,
Can be instantly heated by the second roller 7, but at the time of the fixing operation, the heat of the fixing belt 8 passes through the pressure contact portion at the pressure contact portion between the fixing belt 8 and the pressure roller 4. Since the temperature of the fixing belt 8 is drastically reduced by being taken away by the toner image carried on the fixing belt 8 or the toner image carried on the fixing belt 8, hot offset in which the toner on the recording medium P is transferred to the surface of the fixing belt 8 can be more effectively prevented. it can. As described above, by reducing the heat capacity of the fixing belt 8, it can be heated instantaneously, and hot offset can be prevented by its self-cooling property. On the other hand, the fixing belt 8 is pressed against the pressure roller 4. In part, it must have the heat capacity necessary to melt and fix the toner on the recording medium passing through it. The thickness of the fixing belt 8, that is, its heat capacity should be set so that such requirements can be satisfied at the same time.

To meet the above requirements, for example, FIG.
When the fixing belt 8 is composed of the base 25 and the release layer 26 integrally laminated on the base 25, as shown in FIG. Is about 30 to 150 μm,
When silicone rubber is used as the release layer 26, the thickness thereof is about 50 to 300 μm.
When a fluororesin is used as the material, its thickness is preferably about 10 to 50 μm. Further, it is also possible to use the release layer 26 in which the fluororesin is thinly formed on the silicone rubber to improve the thermal response.

Since the first roller 3B and the pressure roller 4 need to be pressed against each other with a large pressure so as to secure a predetermined nip width N, the first roller 3B and the pressure roller 4 are in contact with each other.
Must have great strength and rigidity. On the other hand, a large external force that the first roller 3B and the pressure roller 4 receive does not act on the second roller 7, and the pressure applied by each compression spring 22 to each end thereof is, for example, 1 kgf.
A small pressure of about (9.8 N) to 3 kgf (29.4 N) may be sufficient. For this reason, the second roller 7 is not required to have so much rigidity or strength, and the second roller 7 can be made small and thin. In this way, by using the thin second roller 7 and reducing its heat capacity,
The second roller 7 can be heated to a predetermined temperature in a short time, and the waiting time can also be shortened.

Further, as shown in FIG. 7, the pressure roller 4 interposes the fixing belt 8 and the first and second rollers 3B and 7B.
It is also possible to provide an elastic layer on the second roller 7 when it is in pressure contact with and to elastically deform it by the pressure roller 4. At least one roller of the plurality of winding rollers that stretches the fixing belt 8 may be configured to be elastically deformed by being pressed by the pressure roller via the fixing belt 8. At that time, instead of or in addition to heating the fixing belt 8 by the second roller 7, the fixing belt may be heated by a heating unit which is in contact with or separate from the fixing belt 8.

It is also possible to provide a heating means for directly heating the pressure roller 4 shown in FIGS. 2, 4 and 7, and by doing so, it is possible to further increase the time required for the fixing belt 8 to reach the fixing temperature. It can be further shortened. At that time, since the pressure roller 4 has a heat insulating layer, if a heating means is provided inside the heat roller, it is difficult to raise the surface temperature of the pressure roller 4. Therefore, as shown in FIGS. 2 and 4, when the heating means for the pressure roller 4 is provided, it is desirable to use the heating means 29 for heating the pressure roller 4 from the surface of the pressure roller 4. Thereby, the surface temperature of the pressure roller 4 can be raised in a short time. Illustrated heating means 2
9 comprises a heater 29a and a sleeve 29b.

Further, the present invention, as shown in FIG.
Also, the fixing member and the pressure roller are separated from each other when the pressure roller 4 is brought into pressure contact with the portion of the fixing belt 8 that is not in contact with the second rollers 3B and 7, and when the image forming apparatus is powered off. The present invention can be widely applied to a fixing device to be placed and a fixing device that heats the fixing member by a heat source provided in the fixing member itself.

[0066]

[0067]

According to the inventions of claims 1 and 7, the temperature of the fixing member can be raised in a short time, and the recording medium ejected from between the fixing member and the pressure roller is wound around the fixing member. It is possible to prevent problems that occur.

[0068]

According to the second and fifth aspects of the invention, the recording medium can be conveyed at a constant speed, and the disturbance of the toner image on the recording medium can be prevented.

According to the third aspect of the invention, although the fixing roller has the elastic layer, the temperature of the fixing roller can be raised in a short time.

According to the fourth aspect of the invention, it is possible to more reliably prevent the problem that the recording medium, which comes out between the fixing belt and the pressure roller, is wound around the fixing belt.

According to the invention of claim 6, the temperature of the fixing member can be raised in a shorter time, and the pressure roller has a heat insulating layer, but the surface temperature of the pressure roller is high. Can be raised in a short time.

According to the invention of claim 8, it is possible to provide an image forming apparatus having the above effect.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an image forming apparatus.

FIG. 2 is a cross-sectional view of a fixing device.

FIG. 3 is a vertical cross-sectional view of a fixing roller and a pressure roller of the fixing device shown in FIG.

FIG. 4 is a cross-sectional view of another fixing device.

FIG. 5 is a diagram showing how the heating roller shown in FIG. 4 is pressed by a compression spring.

FIG. 6 is an enlarged cross-sectional view of a fixing belt.

FIG. 7 is a schematic view of still another fixing device.

FIG. 8 is a schematic view of yet another fixing device.

FIG. 9 is a cross-sectional view of a conventional fixing device.

[Explanation of symbols]

1 fixing device 3 fixing roller 3B winding roller 4 pressure roller 7 Rolling roller 8 fixing belt 9 Thermal insulation layer 12 Elastic layer P recording medium T toner image

─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-55-164859 (JP, A) JP-A-59-102266 (JP, A) JP-A-5-27620 (JP, A) Actual development Sho-58- 23351 (JP, U) Actual development Sho 59-141359 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 13/20 G03G 15/20

Claims (8)

(57) [Claims] 1. A fixing member, which is heated, and a pressure roller for pressing a recording medium against the fixing member, wherein the toner image carried on the recording medium contacts the fixing member. In a fixing device for fixing a toner image on a recording medium by passing a recording medium between a fixing member and a pressure roller, the pressure roller includes a heat insulating layer made of a rigid body having a large number of pores. The fixing device comprises a fixing roller, and the fixing roller has an elastic layer that is elastically deformed by being pressed by the pressure roller. 2. The pressure roller is driven by a driving device.
The fixing device according to claim 1, wherein the fixing device is directly rotationally driven without passing through the fixing roller. 3. The fixing device according to claim 1, further comprising heating means for heating the fixing roller from the surface thereof. 4. A fixing member to be heated, and a pressure roller for pressing a recording medium against the fixing member, wherein the toner image carried on the recording medium comes into contact with the fixing member. In a fixing device for fixing a toner image on a recording medium by passing a recording medium between a fixing member and a pressure roller, the pressure roller includes a heat insulating layer made of a rigid body having a large number of pores. The fixing member comprises an endless fixing belt wound around a plurality of winding rollers, and at least one roller of the plurality of winding rollers is pressed by the pressure roller via the fixing belt. A fixing device having an elastic layer that is elastically deformed by being deformed. 5. The pressure roller is driven by a drive device.
The fixing device according to claim 4, wherein the fixing device is directly driven to rotate without passing through the fixing belt. 6. The fixing device according to claim 1, further comprising a heating unit that heats the pressure roller from the surface of the pressure roller. 7. The heat insulating layer is made of at least one of a porous molded body having a large number of pores formed between bonded fibers, a porous ceramics, and a porous resin. 7. The fixing device according to any one of 1 to 6. 8. An image forming apparatus comprising the fixing device according to claim 1.