JP2004086219A - Pressure roller, fixing device having the pressure roller and image forming device having the fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten the rising time of a fixing device which is provided with a fixing roller to be heated and a pressure roller to be pressed to this fixing roller and drives the rotation of the pressure roller and rotates the fixing roller following this pressure roller and makes a recording medium pass between the fixing roller and the pressure roller and brings a toner image on the recording medium into contact with the fixing roller to fix the toner image on the recording medium. <P>SOLUTION: The pressure roller 4 is constituted of a core shaft 5 sand a heat insulating layer 9 which is fixed to the roller 4 and the heat insulating layer 9 is formed of a rigid body in which many pores are formed. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a pressure roller, a fixing device having the pressure roller, and an image forming apparatus having the fixing device.

2. Description of the Related Art In an image forming apparatus configured as an electronic copying machine, a printer, a facsimile, or a multifunction peripheral having at least two functions thereof, for example, a toner image formed on a recording medium such as a transfer sheet or a resin sheet is fixed. A fixing device is used. As such a fixing device, a fixing device that allows a recording medium carrying a toner image to pass between a heated fixing member and a pressure roller and fixes the toner image on the recording medium has been widely used. I have.

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 fixing roller 3A having a hollow cylindrical shape, and a pressing roller 4A is pressed against the fixing roller 3A. Inside the fixing roller 3A, a heater 2A for heating the fixing roller is provided. During the printing operation of the image forming apparatus, the fixing roller 3A and the pressure roller 4A are pressed against each other, rotate in the directions indicated by the arrows, and the recording medium P carrying the unfixed toner image T passes between the two rollers. At this time, the toner image on the recording medium is pressed against 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 presses 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 fixing roller 3A is heated by the heater 2A, and the surface temperature becomes the fixing temperature suitable for fixing. Has started fixing operation. Further, during 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 before the printing operation is started, the fixing roller 3A and the pressure roller 4A are pre-rotated while It is conventionally known 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 have been taken such as making the thickness of 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. When the fixing roller 3A is heated by the heater 2A in order to raise the temperature of the fixing roller 3A, and the pressure roller 4A is in contact with the fixing roller 3A, the heat of the fixing roller 3A is pressurized. Since it is robbed by the roller 4A, it is not easy to raise the temperature of the fixing roller 3A 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 increased, the temperature of the fixing roller 3A is uniformly increased in the circumferential direction. With the start of the rotation, a large amount of heat of the fixing roller 3A is taken by the pressure roller 4A, so that the temperature of the fixing roller 3A sharply decreases. For this reason, the waiting time until the fixing roller 3A reaches the fixing temperature is lengthened, and there is inevitably a possibility of causing great inconvenience to the user.

In order to prevent the above-described problems, as shown in FIG. 9, a pressure roller 4A having a core shaft 5A made of a rigid body such as metal and a porous elastic body layer 6A made of a sponge laminated on its peripheral surface is used. A fixing device in which the fixing roller 3A is made of a rigid body has been proposed (see Japanese Patent Application Laid-Open No. 58-134672). When the pressure roller 4A having such a porous elastic layer is used, since the elastic layer is porous, its heat insulating property is enhanced, and the amount of heat taken by the pressure roller from the fixing roller is reduced. Can be reduced. Thereby, the waiting time until the fixing roller 3A reaches the fixing temperature can be shortened. In addition, when the pressure roller 4A comes into pressure contact with the fixing roller 3A, the elastic layer 6A of the pressure roller 4A is elastically deformed, thereby fixing the pressure roller 4A with the pressure roller 4A with a certain nip width N in the recording medium conveyance direction. Since the roller 3A is pressed, the necessary amount of heat is applied to the toner image T while the recording medium P passes therethrough, and 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 pressed by the fixing roller 3A made of a rigid body as shown in FIG. 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 that has exited the fixing roller 3A and the pressure roller 4A is easily wound around the peripheral surface of the fixing roller 3A as indicated by a symbol PA in FIG. 9 and indicated by a chain line. Usually, since a separation claw 30A for separating the recording medium from the fixing roller 3A 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 separation claw 30A. At this time, the toner image on the recording medium PA may be rubbed by the separation claw 30A, and a streaky trace may be formed on the toner image. Further, the amount of heat applied to the toner image on the recording medium from the fixing roller 3A differs greatly between the case where the recording medium is wound around the peripheral surface of the fixing roller 3A and the case where the recording medium is not wound. However, the amount of heat given from the fixing roller 3A increases. For this reason, a difference occurs in the glossiness of the toner image on the recording medium, and a toner image of uniform quality cannot be obtained. In particular, in the case of a color image forming apparatus, since the glossiness of the toner image has a relatively large effect on the image quality, this problem cannot be ignored.

Further, a fixing device in which a heated fixing member is formed of an endless fixing belt wound around a plurality of winding rollers, and a toner image is fixed through a recording medium between the fixing belt and the pressure roller is also known. As is well known, such a fixing device also has the same problems as described above.

The present invention has been made based on the above-described novel recognition, and a first object of the present invention is to provide a pressure roller for a fixing device which can eliminate the above-mentioned conventional disadvantages.

A second object of the present invention is to provide a fixing device in which the above-mentioned disadvantages are eliminated.

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

The present invention proposes, in order to achieve the first object, a pressure roller for a fixing device including a heat insulating layer formed of a rigid body having a large number of pores (claim 1).

In this case, it is advantageous that the heat insulating layer is constituted by at least one of a porous molded body, a porous ceramic, and a porous resin in which a large number of pores are formed between the bonded fibers. (Claim 2).

Further, in order to achieve the second object, the present invention includes a fixing member to be heated, and a pressure roller for pressing a recording medium against the fixing member, and a toner image carried on the recording medium. A fixing device that passes the recording medium between the fixing member and the pressure roller so that the toner image is fixed to the recording medium so that the recording medium contacts the fixing member. A fixing device having a heat insulating layer made of a rigid body is proposed (claim 3).

In this case, it is advantageous that the fixing member includes a fixing roller, and the fixing roller has an elastic layer that is elastically deformed by being pressed by the pressing roller (claim 4).

In the fixing device according to the fourth aspect, it is advantageous that the pressure roller is configured to be directly driven to rotate by a driving device without passing through the fixing roller. ).

Further, in the fixing device according to the fourth or fifth aspect, it is advantageous to include a heating unit that heats the fixing roller from the surface of the fixing roller (claim 6).

Further, in the fixing device according to claim 3, the fixing member includes an endless fixing belt wound around a plurality of winding rollers, and at least one of the plurality of winding rollers is It is advantageous to have an elastic layer which is elastically deformed by being pressed by the pressure roller via the fixing belt (claim 7).

Further, in the fixing device according to the seventh aspect, it is advantageous that the pressure roller is configured to be directly driven to rotate by a driving device without passing through the fixing belt (claim 8). ).

Further, in the fixing device according to any one of the third to eighth aspects, it is advantageous to include a heating unit that heats the pressure roller from the surface of the pressure roller (claim 9).

Further, in the fixing device according to any one of claims 3 to 9, the heat insulating layer includes a porous molded body, a porous ceramic, and a porous resin in which a number of pores are formed between the bonded fibers. Advantageously, it is constituted by at least one of the following (claim 10).

In order to achieve the third object, the present invention proposes an image forming apparatus including the fixing device according to any one of claims 3 to 10 (claim 11).

According to the first and second aspects of the invention, it is possible to provide a pressure roller capable of raising the temperature of the fixing member in a short time.

According to the third and tenth aspects of the present invention, the temperature of the fixing member can be raised in a short time, and the problem that the recording medium coming out from between the fixing member and the pressure roller is wound around the fixing member can be prevented. .

According to the fourth aspect of the invention, it is possible to more reliably prevent the recording medium coming out from between the fixing roller and the pressure roller from being wound around the fixing roller.

According to the fifth and eighth aspects of the present 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 invention of claim 6, although the fixing roller has the elastic layer, the temperature of the fixing roller can be raised in a short time.

According to the seventh aspect of the invention, it is possible to more reliably prevent the recording medium coming out from between the fixing belt and the pressure roller from being wound around the fixing belt.

According to the ninth aspect of the present invention, the temperature of the fixing member can be increased in a shorter time, and the surface temperature of the pressure roller can be reduced in a short time even though the pressure roller has a heat insulating layer. Can be raised.

According to the eleventh aspect, it is possible to provide an image forming apparatus having the above effects.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a vertical sectional view schematically showing an image forming apparatus. In an image forming apparatus main body 31, an image forming means 32 for forming a toner image on a recording medium and a recording medium supplied to the image forming means are supplied. The fixing device 1 includes a feeding unit 33 for feeding and a fixing device 1 for fixing a toner image formed on a recording medium. First, the outline of the image forming means 32 will be described.

The image forming means 32 illustrated here has a drum-shaped photoconductor 35 as an example of an image carrier, and when the photoconductor 35 rotates clockwise, the surface of the photoconductor has a predetermined polarity by a charging device 36. Is charged. 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 operation of the transfer device 39. The transfer residual toner adhering to the photoreceptor surface 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 a transfer sheet, and the top recording medium P is sent from the cassette 41 by the rotation of the feeding roller 42, and the feeding is performed. The recording medium thus fed is fed to a transfer position between the photoconductor 35 and the transfer device 39 by the rotation of the pair of registration rollers 43, where the toner image on the photoconductor 35 is transferred onto the recording medium as described above. Transcribed.

The recording medium onto which the toner image has been 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 apparatus.

FIG. 2 is an enlarged sectional view of the fixing device 1. The fixing device 1 shown here has 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 a metal or a hard resin, a cylindrical heat insulating layer 9 fixed to the core shaft 5 by, for example, press-fitting or bonding, and a heat insulating layer 9. A heat insulating layer 9 is fixed concentrically to the core shaft 5. The release layer 10 can be omitted.

On the other hand, the fixing roller 3 is composed of a core shaft 11 made of a rigid body such as a metal, an elastic layer 12 having heat resistance fixed concentrically to the core shaft 11, and laminated on the surface of the elastic layer 12. And a release layer 13 provided. The elastic layer 12 is made of, for example, non-foamed silicone rubber or a foamed 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 another material. It is made of a material having excellent releasability such as fluororesin.

The heat insulating layer 9 of the pressure roller 4 is made of a rigid body having heat resistance and 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 insulating properties due to their large number of pores. Moreover, due to its low thermal conductivity and its high rigidity, it has a much lower coefficient of thermal expansion than the elastic layer. If 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 thermal conductivity of the heat insulating layer 9 is about 0.3 W / mK. It becomes. The porosity can be set in a range of about 30 to 70%.

In addition to the heat insulating layer 9 being made of the above-mentioned ceramic material, the heat insulating layer 9 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 also has the same characteristics as the molded body made of the ceramic material described above.

Japanese Patent Application Laid-Open No. 9-108601 describes that “a fine pore group having no communicating agent between fibers and a pore group having a pore diameter of 0.05 to 2 mm uniformly distributed, and a total porosity of 30 to It is described that a fibrous molded article of "90% porous" and, for example, glass fiber can be used as the fiber, and a method of producing a fibrous molded article by molding, drying, and heating the material is described in detail. Although described, such a fibrous formed body can be used as a porous formed body constituting the heat insulating layer 9.

Furthermore, the heat insulating layer 9 may be made of a porous resin. For example, a cylindrical heat insulating layer 9 made of a porous resin can be obtained by filling a resin mold in a molding die (not shown) and heating and sintering it. The pressure roller 4 can be manufactured by fixing the heat insulating layer 9 to the core shaft 5 by press fitting or bonding. Examples of the resin to be used include polyimide, polyphenylene sulfide, and polytetrafluoroethylene. In particular, the polyimide particles are sintered to obtain a cylindrical porous resin molded body having a porosity of 60%. It is advantageous to use as

The thermal conductivity of the solid resin is, for example, about 0.2 W / mK. Therefore, when the above-described porous resin is used as the heat insulating layer 9, the heat insulation is higher than when the porous ceramic is used as the heat insulating layer 9. Character can be obtained.

(4) The heat insulating layer 9 may be made of a plurality of the above-described porous molded bodies, porous ceramics, and porous resins. In short, the heat insulating layer 9 is formed of at least one of a porous formed body having a large number of pores formed between the bonded fibers, a porous ceramic, and a porous resin.

The pressing roller 4 and the fixing roller 3 are rotatably supported at respective longitudinal ends of the core shafts 5 and 11 by a machine frame (not shown) of the fixing device 1. The fixing roller 3 and the pressing roller 4 are pressed in a direction approaching each other, whereby the surfaces of the rollers 3 and 4 are pressed against each other. At this time, the pressure roller 4 has the heat insulating layer 9 having high rigidity, and the fixing roller 3 has the elastic layer 12. The elastic layer 12 is elastically deformed to be compressed and deformed by being pressed by the pressure roller 4, but the heat insulating layer 9 of the pressure roller 4 hardly deforms. When the elastic layer 12 is elastically deformed, the rollers 3 and 4 are pressed against each other with a nip width indicated by N.

As shown in FIG. 3, a pressure roller gear 14 is fixed to the core shaft 5 of the pressure roller 4, and a driving gear 15 rotatably supported on the image forming apparatus main body side meshes with the pressure roller gear 14. By the operation of a drive motor (not shown), the rotation is transmitted to the pressure roller 4 via the gears 15 and 14, and the pressure roller 4 is driven to rotate counterclockwise in FIG. Further, a fixing roller gear 16 is also fixed to the core shaft 11 of the fixing roller 3, and the fixing roller gear 16 meshes with the pressing roller gear 14, and the rotation of the pressing roller gear 14 is transmitted to the fixing roller gear 16, whereby the fixing roller 3 is rotated. It is driven to rotate clockwise in FIG. Without providing the fixing roller gear 16, the rotation of the pressure roller 4 may be transmitted to the fixing roller 3 pressed against the surface thereof, and the fixing roller 3 may be driven to rotate. In either 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 intervention of the fixing roller 3. The pressure roller 4 and the fixing roller 3 are rotated by driving and rotating the pressure roller 4 by the driving device.

On the other hand, the fixing roller 3 is configured to be heated from the surface of the fixing roller 3 by the heating unit 17. The heating means 17 shown as an example in FIG. 1 is rotatably supported by the machine frame of the fixing device 1, and is rotated by being pressed against the surface of the fixing roller 3, and a heater 19 accommodated therein. The heater 19 generates heat by energizing the heater 19, and transfers the heat to the surface of the fixing roller 3 via the heating cylinder 18 to heat the surface of the fixing roller 3.

{Circle around (4)} The surface of the fixing roller 3 is brought into contact with a temperature detecting means composed of a thermistor 20, and on / off of energization to the heater 19 is controlled based on the result of temperature detection of the fixing roller surface by the thermistor 20. Thus, 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.

As described above, the toner image is transferred onto the recording medium P. As shown in FIG. 2, while the recording medium P carrying the unfixed toner image T is guided by the entrance guide plate 21 as shown in FIG. As shown by an arrow A, the sheet is fed into a pressure contact portion between the fixing roller 3 and the pressure roller 4 which rotates in the directions indicated by the arrows. 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 to fix the toner image on the recording medium. It is. The recording medium P that has passed through the fixing device 1 is discharged onto a discharge tray 44 (FIG. 1) outside the image forming apparatus main body as described above.

As described above, the fixing device 1 of the present embodiment includes the fixing roller 3 as an example of a fixing member to be heated, 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 pressing roller 4 so that the toner image T is fixed on the recording medium P so that the toner image T carried on the recording medium P contacts the fixing member. ing. In the case of the fixing device 1 as well, at the time of startup immediately after a main switch (not shown) of the image forming apparatus is turned on, the fixing roller 3 is heated by the heating unit 17 and the fixing operation is performed after the surface temperature of the fixing roller 3 reaches the fixing temperature. I do. Similarly, with the main switch turned on, the fixing roller 3 is maintained at a standby temperature lower than the fixing temperature, and the heating means 17 heats the fixing roller 3 before the start of the printing operation, and the temperature becomes the fixing temperature. After that, the fixing operation is started. When the temperature of the fixing roller 3 is raised, it is usual that the fixing roller 3 and the pressure roller 4 are rotated in the direction indicated 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 has the heat insulating layer 9 made of a rigid body having a large number of pores, when the temperature of the fixing roller 3 is raised to the fixing temperature as described above, the heat insulating layer 9 of the pressure roller 4 is used. 9 shows high heat insulating properties due to the action of the pores, and greatly reduces the amount of heat taken by the pressure roller 4 from the fixing roller 3 as compared with a conventional fixing device having a pressure roller without such a heat insulating layer. Can be reduced. The pressure roller 4 is supplied with heat from the fixing roller 3, and the temperature of the release layer 10 increases. However, since the heat insulating layer 9 is provided, the temperatures of the heat insulating layer 9 and the core shaft 5 do not increase so much. Temperature drop can be suppressed.

(4) Accordingly, the waiting time until the fixing roller 3 of the fixing device 1 reaches the fixing temperature can be effectively reduced. Therefore, when the main switch of the image forming apparatus is turned on and the image forming apparatus is on standby, the power supply to the heater 19 of the heating unit 17 is turned off, and the fixing roller 3 is not preheated. it can. Even with such a configuration, the temperature of the fixing roller 3 can be raised 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 using a fixing belt as a 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, not an elastic body, the recording medium P passing between the fixing roller 3 and the pressure roller 4 is moved away from the fixing roller 3 as shown by an arrow B in FIG. Conveyed. Therefore, it is possible to prevent the recording medium P from being wound around the surface of the fixing roller 3. Therefore, it is possible to prevent the toner image on the recording medium from having a streak-like trace due to the separation claw and a problem that 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 uniform quality toner image by preventing a variation in glossiness of the toner image. In addition, since the recording medium P can be prevented from winding around the fixing roller 3, the recording medium P does not contact the fixing roller 3 for an excessively long time. Therefore, it is possible to prevent hot offset in which toner adheres to the fixing roller without applying the anti-offset liquid to the fixing roller 3. Thereby, the cost of the fixing device 1 can be further reduced. Of course, if the anti-offset liquid is applied to the fixing roller 3, the effect of preventing hot offset can be more reliably improved. Further, in the fixing device 1 of this embodiment, 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.

Further, in the case of the fixing device shown in FIG. 2, since the fixing roller 3 has the elastic layer 12 that is elastically deformed by being pressed by the pressure roller 4, The body layer 12 is pressed by the pressure roller 4 and greatly deformed by compression, whereby the recording medium P coming out from between the fixing roller 3 and the pressure roller 4 is more reliably directed in a direction away from the fixing roller 3. Therefore, the above-described effect can be further ensured.

Further, in the fixing device 1 according to the present embodiment, as described above, the pressure roller 4 is configured to be directly rotated and driven by the driving device without the intervention of the fixing roller 3. However, the recording medium P can be conveyed at a constant 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, since the elastic layer 6A of the pressure roller 4A is elastically deformed, the most upstream portion of the pressure contact portion between the fixing roller 3A and the pressure roller 4A in the recording medium transport direction. The radius R1 of the pressure roller in the NU and the most downstream portion NL is slightly different from the radius R2 of the pressure roller in the intermediate portion NC, 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 pressure roller The recording medium transport speed at the most upstream portion NU and the most downstream portion NL of the press-contact portion between the fixing roller 4A and the fixing roller 3A differs from the recording medium transport speed at the intermediate portion NC. And the image quality may be degraded. The elastic layer 6A undergoes a large thermal expansion due to a rise in temperature, and such thermal expansion also causes a change in the transport speed of the recording medium.

On the other hand, in the case of the fixing device 1 of the present embodiment shown in FIG. 2, when the recording medium P passes between the fixing roller 3 and the pressure roller 4 as described above, the rollers 3 and 4 Since the pressure contact is performed with the width N, a sufficient amount of heat is applied to the toner image on the recording medium passing therethrough, and the toner image can be reliably fixed on the recording medium P. The roller 4 hardly deforms at the pressure contact portion between the fixing roller 3 and the pressure roller 4, and the elastic layer 12 of the fixing roller 3 elastically deforms to secure a predetermined nip width N. Accordingly, the speed of the surface of the pressure roller 4 driven to rotate by the driving device becomes substantially equal in the entire area of the pressure contact portion between the rollers 3 and 4. In the most upstream portion NU, the most downstream portion NL, and the intermediate portion NC of the press contact portion, the radius R of the pressure roller 4 is substantially equal, and the surface of the pressure roller 4 rotating at a constant angular velocity is substantially equal. The speed becomes uniform over the entire circumference. Moreover, since the heat insulating layer 9 of the fixing roller 3 is made of a rigid body, the amount of thermal expansion is extremely small as compared with the elastic layer of the conventional fixing roller. Therefore, the conveyance speed of the recording medium P conveyed while being nipped between 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.

In addition, in the case of the fixing device 1 shown in FIG. 2, since the fixing roller 3 has the elastic layer 12, its thickness is increased and its heat capacity is also increased. Therefore, assuming that the fixing roller is heated from the inside as in the related art, it takes a considerably long time to raise the temperature of the fixing roller 3 to the fixing temperature when starting up the fixing device.

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 treatment surface is short. The temperature can be raised to the fixing temperature over time.

(4) The fixing device 1 shown in FIG. 4 includes an endless fixing belt 8 whose fixing member is wound around a plurality of winding rollers 3B and 7. Here, as necessary, one winding roller 3B is referred to as a first roller, and the other winding roller 7 is referred to as a second roller. The pressure roller 4 is spaced apart from each other and extends in parallel with each other, and the pressure roller 4 is in pressure contact with an 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 configurations of the first roller 3B and the pressure roller 4 are not substantially different from the fixing roller and the pressure roller described above with reference to FIGS. That is, the pressure roller 4 shown in FIG. 4 also has heat resistance and rigidity, and also has a heat insulating layer 9 in which a large number of pores are formed, and the first roller 3B is also applied via the fixing belt 8. The elastic body layer 12 is elastically deformed by being pressed by the pressure roller 4. 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 in FIG. The first roller 3B and the pressure roller 4 are attached to the respective portions of the first roller 3B and the pressure roller 4, and further description of the first roller 3B and the pressure roller 4 shown in FIG. However, since the first roller 3B does not directly contact the recording medium P, the release layer 13 as a surface layer of the first roller 3B can be omitted. Further, it is desirable to provide a release layer for preventing toner from adhering to the surface of the fixing belt 8 that contacts the recording medium P.

The second roller 7 is formed in a cylindrical shape, and each end thereof is rotatably supported by the frame of the fixing device 1. Each end of the second roller 7 is pressed by a compression spring 22 in a direction away from the first roller 3B as shown in FIG. 5, whereby the first roller 3B and the second roller 7 are pressed. A predetermined tension can be applied to the fixing belt 8 stretched on the fixing belt 8. The heater 23 is disposed inside the second roller 7, whereby the second roller 7 is heated, and the heat is transmitted to the fixing belt 8 to heat the fixing belt 8. The endless fixing belt 8 is heated by the second roller 7, and the second roller 7 is configured as a heating roller. The surface of the fixing belt 8 is brought into contact with a temperature detecting means composed of a thermistor 24. On / off of the power supply to the heater 23 is controlled based on a result of the temperature detection. Is maintained at a fixing temperature in a range suitable for fixing.

Also, in the fixing device 1 shown in FIG. 4, the pressure roller 4 is directly rotated by the driving device without the intervention of the fixing belt 8, just like the fixing device shown in FIGS. (See FIG. 3), the first roller 3B rotates in accordance with the rotation of the pressure roller 4, and the fixing belt 8 travels in the direction of arrow C. The second roller 7 rotates clockwise in FIG. By driving the pressure roller 4 to rotate, 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 connected via a fixing belt 8 by a pressure unit (not shown) so that these rollers 3 and 4 approach each other. At this time, the elastic layer 12 of the first roller 3B is elastically deformed, 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 hardly deforms.

The recording medium P onto which the toner image T has been transferred as described above enters the space between the first roller 3B and the pressure roller 4 while being guided by the entrance guide plate 21, as shown by the arrow A. The recording medium P passes between the first roller 3B and the pressure roller 4 so that the toner image T carried on the recording medium P comes into contact with the surface of the fixing belt 8, and at this time, the recording medium P The toner image is fixed on the recording medium P by being pressed against the fixing belt 8 by the pressure roller 4 and transmitted by the fixing belt 8 and the pressure received from the first roller 3B and the pressure roller 4. The recording medium P that has passed through the fixing device 1 is discharged out of the image forming apparatus main body.

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 formed of a rigid body having a large number of pores, it can be used when the fixing device is started up. When the fixing belt 8 is heated by the second roller 7 before the start of the printing operation, when the fixing belt 8 and the pressure roller 4 start rotating, heat of the fixing belt 8 is applied to the pressure roller 4 in a large amount. You will not be robbed. 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 layer 12 that is elastically deformed by being pressed by the pressure roller 4 via the fixing belt 8. The recording medium that has exited the pressure contact portion between the fixing belt 8 and the pressure roller 4 is conveyed in a direction away from the fixing belt 8 (in the direction of arrow B), thereby preventing the recording medium P from winding around the fixing belt 8. . In addition, since the elastic layer 12 of the first roller 3B pressed against the pressure roller 4 via the fixing belt 8 is elastically deformed and the pressure roller 4 hardly deforms, it rotates at a constant angular velocity. The surface speed of the pressure roller 4 at the pressure contact portion between the driven pressure roller 4 and the fixing belt 8 is constant over the entire surface. In addition, the thermal expansion of the heat insulating layer 9 of the pressure roller 4 is extremely small. Thus, the conveying speed of the recording medium P passing through the 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, so that the fixing belt 8 can be fixed by the second roller 7 in a fixing temperature suitable for fixing a toner image in a very short time. Can be heated up to.

By forming the fixing belt 8 thin as described above and reducing its heat capacity, the fixing belt 8 can be instantaneously heated by the second roller 7. At the pressure contact portion with the pressure roller 4, the heat of the fixing belt 8 is taken by the recording medium P passing through the pressure contact portion and the toner image carried thereon, and the temperature of the fixing belt 8 is rapidly lowered. Hot offset in which the toner on P transfers to the surface of the fixing belt 8 can be more effectively prevented. As described above, by reducing the heat capacity of the fixing belt 8, the fixing belt 8 can be heated instantaneously, and its self-cooling property can prevent hot offset. On the other hand, the fixing belt 8 is pressed against the pressure roller 4. The unit must have a heat capacity necessary to melt and fix the toner on the recording medium passing therethrough. The thickness of the fixing belt 8, that is, the heat capacity thereof, must be set so that such a requirement can be satisfied at the same time.

In order to satisfy the above-mentioned requirements, for example, as shown in a schematic enlarged view in FIG. 6, when the fixing belt 8 is constituted by the base 25 and the release layer 26 integrally laminated thereon, Alternatively, when polyimide is used, its thickness is about 30 to 150 μm, when silicone rubber is used for the release layer 26, its thickness is about 50 to 300 μm, and a fluororesin is used for the release layer 26. When used, its thickness is preferably about 10 to 50 μm. Alternatively, a release layer 26 having a good thermal response by forming a thin fluororesin on silicone rubber may be used.

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 have great strength and rigidity. Need to be. On the other hand, a large external force such as that applied to the first roller 3B or the pressure roller 4 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 used. Therefore, the second roller 7 is not required to have much rigidity and strength, and the second roller 7 can be reduced in size and thickness. By using the thin second roller 7 and reducing the heat capacity of the second roller 7, the second roller 7 can be heated to a predetermined temperature in a short time, and the waiting time can also be reduced. .

As shown in FIG. 7, when the pressure roller 4 is in pressure contact with the first and second rollers 3B and 7 via the fixing belt 8, the elastic layer is also applied to the second roller 7. It can be provided and elastically deformed by the pressure roller 4. At least one of the plurality of winding rollers that stretches the fixing belt 8 may be configured to be elastically deformed by being pressed by the pressing roller via the fixing belt 8. In this case, instead of or together with the heating of the fixing belt 8 by the second roller 7, the fixing belt can be heated by a heating unit that is in contact with or separated from the fixing belt 8.

Further, a heating means for directly heating the pressure roller 4 shown in FIGS. 2, 4 and 7 can be provided. In this case, the time for the fixing belt 8 to rise to the fixing temperature can be further shortened. be able to. At this time, since the pressure roller 4 has a heat insulating layer, it is difficult to increase the surface temperature of the pressure roller 4 if a heating unit is provided inside 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 increased in a short time. The illustrated heating means 29 includes a heater 29a and a sleeve 29b.

Further, as shown in FIG. 8, the present invention relates to a fixing device for pressing the pressure roller 4 against a portion of the fixing belt 8 which is not in contact with the first and second rollers 3B and 7, and a power supply of the image forming apparatus. The present invention can be widely applied to a fixing device in which the fixing member is separated from the pressure roller when the fixing member is turned off, a fixing device in which the fixing member is heated by a heat source provided in the fixing member itself, and the like.

FIG. 2 is a schematic diagram of an image forming apparatus. FIG. 3 is a cross-sectional view of the fixing device. FIG. 3 is a longitudinal sectional view of a fixing roller and a pressure roller of the fixing device shown in FIG. 2. FIG. 10 is a cross-sectional view of another fixing device. FIG. 5 is a diagram illustrating a state in which the heating roller illustrated in FIG. 4 is pressed by a compression spring. FIG. 3 is an enlarged sectional view of a fixing belt. FIG. 11 is a schematic diagram of still another fixing device. FIG. 10 is a schematic view of still another fixing device. FIG. 9 is a cross-sectional view of a conventional fixing device.

Explanation of reference numerals

REFERENCE SIGNS LIST 1 fixing device 3 fixing roller 3B wrapping roller 4 pressure roller 7 wrapping roller 8 fixing belt 9 heat insulating layer 12 elastic layer P recording medium T toner image

Claims (11)

A pressure roller for a fixing device, comprising a heat insulating layer made of a rigid body having a large number of pores. The heat insulating layer according to claim 1, wherein the heat insulating layer is made of at least one of a porous molded body, a porous ceramic, and a porous resin in which a number of pores are formed between the bonded fibers. Pressure roller. A fixing member to be heated; and a pressure roller for pressing a recording medium against the fixing member. The recording medium is fixed to the fixing member so that a toner image carried on the recording medium contacts the fixing member. And a fixing device for fixing the toner image to the recording medium by passing between the pressure roller and the pressure roller, wherein the pressure roller includes a heat insulating layer made of a rigid body having a large number of pores. Fixing device. The fixing device according to claim 3, wherein the fixing member includes a fixing roller, and the fixing roller has an elastic layer that is elastically deformed by being pressed by the pressure roller. The fixing device according to claim 4, wherein the pressure roller is directly driven to rotate by a driving device without passing through the fixing roller. The fixing device according to claim 4, further comprising a heating unit configured to heat the fixing roller from a surface of the fixing roller. The fixing member includes an endless fixing belt wound around a plurality of winding rollers, and at least one of the plurality of winding rollers is pressed by the pressure roller via the fixing belt. The fixing device according to claim 3, further comprising an elastic body layer that is elastically deformed by being applied. The fixing device according to claim 7, wherein the pressure roller is directly driven to rotate by a driving device without passing through the fixing belt. The fixing device according to claim 3, further comprising a heating unit configured to heat the pressure roller from a surface of the pressure roller. 10. The heat insulating layer according to claim 3, wherein the heat insulating layer is formed of at least one of a porous molded body, a porous ceramic, and a porous resin having a large number of pores formed between the bonded fibers. A fixing device according to any one of the above. An image forming apparatus comprising the fixing device according to claim 3.

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