JP2005173030A - Fixing device and image forming apparatus with same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device which secures fixability and releasability of a recording medium and is made small-sized and saves power and to provide an image forming apparatus with the same. <P>SOLUTION: A fixing device 10 is provided with a pressure roll 21 and a release roll which are pressed to a heat roll 11. The pressure roll 21 is arranged upstream from the release roll in a transport direction of a recording paper. Outside diameters of the pressure roll 11, the pressure roll 21, and the release roll 31 are made smaller in this order. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fixing device that fixes an unfixed developer on a recording medium and an image forming apparatus including the fixing device.

  In general, the amount of toner used when forming a toner image on a recording sheet in an electrophotographic image forming apparatus is larger in color printing than in monochrome printing. Therefore, in color printing, in order to satisfactorily fix the toner image on the recording paper, the toner releasability from the fixing roller of the fixing device used in the color image forming apparatus and the releasability of the recording paper are improved. Alternatively, it is required to improve the melting performance of the color toner.

  For example, Patent Document 1 discloses that a recording paper is improved in a belt nip type fixing device having a fixing roll that forms a nip portion in contact with an endless belt that is rotatably stretched on a support roll. The structure to perform is disclosed. In the fixing device described in Patent Document 1, a pressure roll that is in pressure contact with the fixing roller via an endless belt is provided at the outlet of the nip portion. Because of this pressure roll, micro slip occurs at the interface between the toner on the recording paper and the fixing roll at the exit of the nip portion, so that the recording paper can be peeled off without using a peeling device during color printing. Is possible.

  Patent Documents 2 and 3 disclose a fixing device having a plurality of nip portions formed by contact between a fixing roller (heating roller) and a pressure roller. In the fixing device, by providing a plurality of nip portions, the recording material can be sufficiently supplied with the amount of heat necessary for fixing without reducing the heat treatment speed of the recording material. Thus, even in color printing, the toner image is melted and fixed on the recording paper, and a fixed image is formed satisfactorily.

  Further, in the fixing device described in Patent Document 2, after the recording paper passes through the first nip portion on the upstream side with respect to the conveyance direction of the recording paper, the recording paper enters the second nip portion on the downstream side. In order to prevent jamming, the hardness of each roller forming the plurality of nip portions is made different. That is, in the fixing device described in Patent Document 2, when pressure is applied between rollers having different hardnesses, a roller having low hardness is deformed to follow a roller having high hardness. Therefore, when each roller is rotated with the low hardness roller deformed and the recording paper is passed between the rollers, the recording paper is conveyed following the high hardness roller. In the above-mentioned patent document 2, paying attention to this property, setting the hardness of each roller allows the recording paper that has passed through the first nip portion to surely enter the second nip portion, thereby reducing the occurrence of jamming. doing.

  Further, in the fixing device described in Patent Document 3, the surface pressure in the upstream nip portion is lower than the surface pressure in the downstream nip portion with respect to the conveyance direction of the recording paper. Therefore, the pressure applied to the recording material is reduced in the early stage of the heat treatment, and the pressure applied to the recording material is increased in the later stage of the heat treatment, so that the toner image is suppressed and the toner image is improved. Has been established.

Further, a fixing device including a plurality of nip portions is also described in Patent Document 4. In the fixing device described in Patent Document 4, in order to perform recording without generating wrinkles even on a support such as an envelope formed by stacking a plurality of sheets, As a plurality of pressure rollers, an auxiliary pressure roller and a main pressure roller are provided. First, the support is wound around the fixing roller by the auxiliary pressure roller, and further, the support is conveyed between the fixing roller and the main pressure roller by controlling the rotation speed of the auxiliary pressure roller. It is like that. As described above, by providing the auxiliary pressure roller, the adhesion between the support and the fixing roller is improved, and the fixing property of the toner image is improved.
Japanese Patent No. 3084692 (Registered July 7, 2000) JP 2001-42676 A (published February 16, 2001) Japanese Patent Laid-Open No. 2001-92296 (released on April 6, 2001) Japanese Patent Publication No. 5-63795 (announced on September 13, 1993)

  Incidentally, in recent years, power saving and downsizing of image forming apparatuses are required, and power saving and downsizing are also required for fixing devices provided in the image forming apparatus. Therefore, with respect to the fixing device, while ensuring good fixing performance of the toner image on the recording paper, which has been realized in the above-mentioned Patent Documents 1 to 4, further power saving and downsizing of the fixing device. It is desirable to achieve In particular, full-color printing using an image forming apparatus equipped with a fixing device has been actively performed in recent years, and not only monochrome printing but also image forming apparatuses that perform full-color printing have achieved power saving and downsizing. It has been demanded. In order to meet such a demand, it is considered that there is room for further improvement with respect to the fixing devices described in Patent Documents 1 to 4.

  For example, in order to realize power saving of the fixing device, the fixing roller is thinned to reduce the heat capacity of the fixing roller. When the thickness of the fixing roller is reduced, the pressure roller is brought into pressure contact with the fixing roller, so that the shape of the fixing roller is easily deformed. Therefore, it is necessary to control the nip pressure when the pressure roller is in pressure contact with the fixing roller so that the fixing device is not destroyed due to the deformation of the fixing roller.

  However, when the amount of toner to be fixed on the recording paper is large as in full-color printing, if a thin fixing roller is used, sufficient nip pressure cannot be ensured and good fixing performance of the toner image can be ensured. It becomes difficult. Therefore, conventionally, the thinned fixing roller has not been suitable for full-color printing.

  The present invention has been made to solve the above-described conventional problems, and its purpose is to shorten the warm-up time, reduce the amount of power required for the warm-up, and reduce the size of the fixing device. An object of the present invention is to provide a fixing device capable of performing fixing processing suitably and satisfactorily for both full-color printing and monochrome printing even when a thinned heating roller is used, and an image forming apparatus provided with the fixing device.

  In order to achieve the above object, the fixing device according to the present invention includes at least two pressure rollers that form a nip portion by being pressed against a heating roller having a heat source. The first pressure roller of the two pressure rollers mainly has a fixing function of melting the unfixed developer on the recording medium by the heat amount of the heating roller and fixing it on the recording medium. The second pressure roller, which is the other pressure roller, mainly transports the recording medium on which the developer is fixed by being conveyed between the first pressure roller and the heating roller. It has a peeling function for peeling from the heating roller. As described above, by using the fixing device including the first pressure roller having the fixing function and the second pressure roller having the peeling function, a preferable and favorable fixing process can be realized.

In other words, in order to solve the above-described problem, the fixing device according to the present invention has at least two pressure rollers that form a nip portion in pressure contact with a heating roller having a heat source. In the fixing device that rotates and conveys the recording medium to the nip portion and fixes the developer on the recording medium, the pressure roller is at least in contact with the heating roller to contact the first nip. A first pressure roller that takes in a recording medium conveyed from the outside into the first nip portion, and a second nip portion by pressing against the heating roller. And a second pressure roller for separating the recording medium that has passed through the second nip portion from the heating roller. The first pressure roller is located above the conveying direction of the recording medium. Than the second pressure roller, disposed upstream, and the heating roller, and the first pressure roller, between the second pressure roller,
(Outer diameter of heating roller)> (Outer diameter of first pressure roller)> (Outer diameter of second pressure roller)
It is characterized by the relationship.

  Further, the fixing device according to the present invention is the above fixing device, wherein the heating roller is provided on a side of the heating roller having a thickness of 3 mm or less in a hollow cylinder having thermal conductivity and having a thickness of 1 mm or less. An elastic layer is formed.

  In the fixing device according to the present invention, in the fixing device described above, the pressure load of the first pressure roller in pressure contact with the heating roller is the pressure load of the second pressure roller in pressure contact with the heating roller. It is characterized by being smaller than.

  In the fixing device according to the present invention, the nip width of the first nip portion is larger than the nip width of the second nip portion in the fixing device.

  Further, the fixing device according to the present invention is the above fixing device, wherein the first pressure roller is an elastic material formed on the surface of a cylindrical rotating body with the same material as the heating roller side elastic layer. It is preferable to have a first pressure roller side elastic layer which is a layer having

  The fixing device according to the present invention is the above-described fixing device, wherein the second pressure roller is an elastic layer formed on a cylindrical cored bar with the same material as the heating roller-side elastic layer. It is preferable to have the second pressure roller side elastic layer.

  Further, in the fixing device according to the present invention, in the fixing device, the surface hardness of the first pressure roller is smaller than the surface hardness of the heating roller, and the surface hardness of the second pressure roller is It is characterized by being larger than the surface hardness of the heating roller.

  The fixing device according to the present invention is characterized in that, in the fixing device, the rotation speed V2 of the second pressure roller is equal to or higher than the rotation speed V1 of the first pressure roller. .

Further, in the fixing device according to the present invention, in the fixing device, the rotation speed V2 of the second pressure roller is higher than the rotation speed V1 of the first pressure roller.
V1 × 1.0 ≦ V2 ≦ V1 × 1.1
It is characterized by satisfying the relationship.

  An image forming apparatus according to the present invention includes any one of the above-described fixing devices in order to solve the above-described problem.

  The image forming apparatus according to the present invention further includes a discharge mechanism for discharging the recording medium in the image forming apparatus, and the recording medium conveyed from the fixing device is discharged to a position where the discharge mechanism is disposed. As described above, it is preferable that the pressure load of the second pressure roller in pressure contact with the heating roller is set.

  The image forming apparatus according to the present invention may be capable of selecting a monochrome printing mode or a full-color printing mode in the image forming apparatus described above.

As described above, the fixing device according to the present invention includes the heating roller, the first pressure roller for taking the recording medium into the fixing device from the outside and conveying it, and the second pressure for peeling the recording medium. What is a pressure roller?
(Outer diameter of heating roller)> (Outer diameter of first pressure roller)> (Outer diameter of second pressure roller)
Meet the relationship. Therefore, since the first pressure roller and the second pressure roller are downsized as compared with the heating roller, the first pressure roller and the second pressure roller are arranged close to each other. Can do. As a result, the deflection of the recording medium between the first nip portion and the second nip portion can be prevented, and the occurrence of jam can be reduced. Further, by preventing the deflection of the recording medium, it is possible to prevent the positional deviation of the developer fixed on the recording medium when passing through the first nip portion and the second nip portion. Furthermore, since the first pressure roller and the second pressure roller are downsized, the fixing device can be downsized.

  Further, the outer diameter of the first pressure roller is formed smaller than the outer diameter of the heating roller and larger than the outer diameter of the second pressure roller. Therefore, it is easy to capture the recording medium conveyed to the fixing device at the first nip portion and take it into the first nip portion. Furthermore, since the outer diameter of the second pressure roller is the smallest among the three rollers described above, the nip width of the second nip portion is narrowed. Therefore, the second pressure roller can concentrate the pressure load and press-contact the heating roller, so that the recording medium can be suitably peeled even with a small pressure load.

  Further, by reducing the outer diameters of the first pressure roller and the second pressure roller, the time required for warming up to heat each roller of the fixing device from room temperature to a predetermined fixing temperature ( Hereinafter, it is described as warm-up time) and electric energy can be reduced. Therefore, the fixing device of the present invention has an effect that the warm-up can be performed at a high speed and the size and power can be further reduced as compared with the conventional fixing device.

  Further, in the fixing device according to the present invention, the heating roller further includes a heating roller side elastic layer having a thickness of 1 mm or less on a hollow cylinder having a heat conductivity of 3 mm or less. As a result, it is possible to reduce the thickness of the heating roller. Thereby, the heat capacity of the cylinder and the heating roller side elastic layer (hereinafter referred to as a heat storage unit) in which heat generated from the heat source of the heating roller is accumulated can be reduced. Moreover, since the heat storage part is thinned, the heat radiation amount can be reduced. As a result, there is an effect that it is possible to reduce the power consumption of the fixing device by reducing the warm-up time of the heating roller and the amount of power required for the warm-up.

  Furthermore, since the second pressure roller is downsized, the nip width of the second nip portion is narrow. Therefore, it is possible to concentrate the pressure load of the second pressure roller on a narrow nip width and press the heating roller, so even if the pressure load applied to the second pressure roller is small, The recording medium can be suitably peeled off. Therefore, even when a thin heating roller is pressed against a hollow cylinder, the pressure load applied to the heating roller from the second pressure roller is small, so that the shape or deformation of the heating roller is prevented. There is no cause.

  Further, in the fixing device according to the present invention, the pressure load of the first pressure roller in pressure contact with the heating roller is smaller than the pressure load of the second pressure roller in pressure contact with the heating roller. Accordingly, even when the recording medium passes through the first nip portion in a state where a sufficient amount of heat is not given to the developer, the pressure load at the first nip portion is reduced, so that the developer It is possible to prevent sticking to the heating roller. In addition, since the pressure load at the second nip portion is increased, the developer can be sufficiently flattened and fixed on the recording medium.

  Further, in the fixing device according to the present invention, the nip width of the first nip portion is larger than the nip width of the second nip portion. Therefore, first, the recording medium can be brought into contact with the heating roller at the first nip portion. Then, the recording medium is conveyed between the first nip portion and the second nip portion while being in contact with the heating roller. Accordingly, since the recording medium can be heated between the first nip portion and the second nip portion, the developer can be sufficiently melted by giving a larger amount of heat to the developer. . Further, since the nip width of the second nip portion is narrow, as described above, the recording medium that has passed through the second nip portion can be peeled off from the heating roller.

  Further, in the fixing device according to the present invention, the first pressure roller is an elastic layer formed of the same material as the heating roller side elastic layer on the surface of the cylindrical rotating body. It is preferable to have a certain first pressure roller side elastic layer. Further, in the fixing device according to the present invention, the second pressure roller is a second pressure roller that is an elastic layer formed of the same material as the heating roller side elastic layer on a cylindrical cored bar. It is preferable to have a pressure roller side elastic layer.

  Thereby, since the surface hardness becomes the same, the first nip portion and the second nip portion can be formed in a planar shape with a sufficient nip width. Therefore, the recording medium can be conveyed without curling at the first nip portion or the second nip portion. In addition, since the first pressure roller side elastic layer and the second pressure roller side elastic layer are provided, the recording medium is peeled off even when printing on the back surface of the recording medium is performed during double-sided printing. Can be performed satisfactorily.

  Further, in the fixing device according to the present invention, in the fixing device, the surface hardness of the first pressure roller is smaller than the surface hardness of the heating roller, and the surface hardness of the second pressure roller is It is larger than the surface hardness of the heating roller. Thereby, since the recording medium is conveyed along the higher surface hardness, the recording medium that has passed through the first nip portion can be conveyed along the heating roller. Therefore, the developer can be sufficiently melted by supplying a larger amount of heat from the heating roller to the recording medium conveyed between the first nip portion and the second nip portion. In addition, it is possible to prevent the recording medium that has passed through the first nip portion from hitting the second pressure roller and causing a paper jam, and to reliably convey the recording medium to the second nip portion. Further, since the recording medium that has passed through the second nip portion is conveyed along the second pressure roller, the recording medium is conveyed in a direction away from the heating roller. Therefore, there is an effect that the peelability of the recording medium can be improved.

Further, in the fixing device according to the present invention, the rotation speed V2 of the second pressure roller is equal to or higher than the rotation speed V1 of the first pressure roller. Specifically, the rotation speed V2 of the second pressure roller is higher than the rotation speed V1 of the first pressure roller.
V1 × 1.0 ≦ V2 ≦ V1 × 1.1
Meet the relationship. Thereby, even if the recording medium conveyed through the first nip portion is heated and expanded, it is possible to prevent the recording medium from sagging between the first nip portion and the second nip portion. . Further, since the second nip portion is reliably conveyed while the recording medium is in contact with the heating roller, the conveyance state of the recording medium can be kept constant. Therefore, if the fixing device of the present invention is used, the developer can be satisfactorily fixed on the recording medium.

  In addition, as described above, the image forming apparatus according to the present invention includes each of the fixing devices described above. Therefore, the image forming apparatus can be reduced in size and power consumption while ensuring good fixing performance of the toner image on the recording medium. There is an effect that it is possible to provide an image forming apparatus that realizes the above.

  The image forming apparatus according to the present invention further includes a second pressure roller that is in pressure contact with the heating roller so that the recording medium conveyed from the fixing device is discharged to the position where the discharge mechanism is disposed. Pressure load is set. The fixing device can adjust the discharge direction of the recording medium discharged from the second nip portion by controlling the pressure load of the second pressure roller. Therefore, even when the arrangement of each part in the image forming apparatus is limited, by adjusting the pressure load of the second pressure roller according to the arrangement of the discharge mechanism, the second nip part can be adjusted. There is an effect that the recording medium to be discharged can be reliably conveyed to the discharge mechanism.

  Further, the image forming apparatus according to the present invention may be capable of further selecting a monochrome printing mode or a full color printing mode. The fixing device of the present invention can fix the developer suitably and satisfactorily in any case where the amount of developer to be fixed on the recording medium is small or large. Therefore, the fixing device can be suitably used for both the monochrome printing mode in which the amount of developer used is small and the full color printing mode in which the amount of developer used is large. Therefore, there is an effect that it can be suitably used for an image forming apparatus that performs image forming processing in both the monochrome printing mode and the full-color printing mode.

  One embodiment of the present invention will be described with reference to FIGS. 1 to 7 as follows.

  FIG. 1 is a schematic cross-sectional view of a fixing device 10 according to the present embodiment. The fixing device 10 is provided in, for example, an electrophotographic printer (image forming apparatus), and melts an unfixed toner image made of unfixed toner (developer) on a recording paper (recording medium) on the recording paper Secure to. That is, the fixing device 10 includes a cylindrical heating roller 11, a cylindrical pressure roller (first pressure roller) 21, and a cylindrical peeling roller (second pressure roller) 31. The recording sheet is sandwiched and conveyed between these rollers to fix the toner image on the recording sheet by heating and pressing.

  As described above, the fixing device 10 includes the pressure roller 21 and the peeling roller 31 that are in pressure contact with the heating roller 11. Therefore, in the fixing device 10, as shown in FIG. 1, first, at a nip portion (first nip portion; hereinafter referred to as a first nip portion) where the heating roller 11 and the pressure roller 21 contact each other. Then, the recording paper is brought into contact with the surface of the heating roller 11. Subsequently, the recording paper is in contact with the surface of the heating roller 11 and a nip portion (second nip portion; hereinafter referred to as a second nip portion) where the heating roller 11 and the peeling roller 31 are in contact with each other along the rotation direction of the heating roller 11. 2 nip portion).

  In other words, in the fixing device 10, it is apparent that heat is transferred from the heating roller 11 to the second nip portion along the rotation direction of the heating roller 11 from the first nip portion. Nip portion (hereinafter referred to as a pseudo nip portion). Therefore, as will be described later, even when the heating roller 11 having a reduced thickness is used, a sufficient nip width is ensured without increasing the nip pressure of each of the pressure roller 21 and the peeling roller 31, Good fixing performance can be secured.

  In the second nip portion, since the recording paper is peeled off by the peeling roller 31, even if the recording paper is conveyed along the heating roller 11 between the first nip portion and the second nip portion, Good recording sheet peeling performance can be ensured.

  The fixing device 10 includes three rollers, but may be configured to include four or more rollers. When four or more rollers are provided, there is one peeling roller and three or more pressure rollers. As described above, when there are three or more pressure rollers, the contact time and the contact distance between the recording paper and the heating roller can be increased. Therefore, even when the recording paper is conveyed at high speed, The unfixed toner image can be reliably melted by heating. Hereinafter, each part of the fixing device 10 will be described in detail.

  The heating roller 11 is a heat source for melting the toner on the recording paper, and fixes the toner image on the recording paper by the pressing force of the heating roller 11, the pressure roller 21 and the peeling roller 31. The heating roller 11 receives a driving force from a driving source (not shown) and is rotationally driven in the direction of the arrow in FIG.

  The heating roller 11 has, for example, a heating side elastic layer (heating roller side elastic layer) 13 formed of silicon rubber on the outside of a metal cylinder (hereinafter, metal cylinder) 12 such as aluminum or iron. A roller having an outer diameter φ of about 40 mm, for example, is formed by forming a release layer (not shown) on the surface of the heating-side elastic layer 13. The aluminum cylinder is hollow, and a heater 14 as a heat source is provided inside. The metal cylinder 12 and the heating side elastic layer 13 of the heating roller 11 are heated by the heater 14.

  The metal cylinder 12 of the heating roller 11 serves as a heat storage unit for accumulating heat generated from the heater 14. The thickness of the metal cylinder 12 is preferably 3 mm or less in order to reduce the heat capacity and heat dissipation of the metal cylinder 12. Specifically, when the metal cylinder 12 is made of aluminum, it is formed in a thin shape of about 1 mm to 3 mm, and when the metal cylinder 12 is made of iron, it is 0.25 mm to 1.mm. It is preferably formed in a thin shape of about 0 mm. Thus, since the said heating roller 11 is equipped with the thin metal cylinder 12, the heat capacity and heat dissipation of a thermal storage part can be made small. As a result, the warm-up time of the heating roller 11 required for heating the heating roller 11 from room temperature to a predetermined fixing temperature can be shortened, and the amount of power required for warm-up can be reduced. Furthermore, it is possible to easily keep the temperature of the heating roller constant.

  The heating-side elastic layer 13 may be made of a material other than silicon rubber. Specifically, the heating-side elastic layer 13 is made of fluorine rubber having a hardness of about 26 (the hardness specified by an ASKER-C type hardness meter). What is necessary is just to be formed with the elastic material. The heating-side elastic layer 13 is preferably excellent in thermal conductivity in order to suitably perform heat-pressure fixing of the toner image on the recording paper. Here, the heating-side elastic layer 13 preferably has a thickness of 3 mm or less, and more preferably 1 mm or less.

  That is, when the heating-side elastic layer 13 increases in thickness, the heating-side elastic layer 13 has an inner surface side that is a joint portion with the metal cylinder 12 and an outer peripheral side that is the outer surface of the heating-side elastic layer 13. And the temperature difference becomes large. Such a large temperature difference between the inner surface side and the outer peripheral side of the heating side elastic layer 13 is not preferable from the viewpoint of the durability of the heating side elastic layer 13, so that the metal cylinder 12 is further heated to It is necessary to increase the temperature. However, when the temperature of the metal cylinder 12 is increased, the temperature of the heating side elastic layer 13 is increased, leading to deterioration due to the heat history of the heating side elastic layer 13 and an increase in hardness. Further, the amount of heat transferred from the metal cylinder 12 to the heating-side elastic layer 13 increases, the speed at which the surface temperature of the heating roller 11 increases, and the warm-up time increases. Therefore, as described above, the heating-side elastic layer 13 preferably has a thickness of 3 mm or less, and more preferably 1 mm or less.

  In order to improve the durability of the heating side elastic layer 13, the change in hardness due to heating of the heating side elastic layer 13, and the warm-up time of the fixing device, the hardness of the heating side elastic layer 13 is improved. Is preferably about 26 (the hardness specified by the ASKER-C type hardness tester). Thereby, deterioration due to the heat history of the heating side elastic layer 13 and an increase in warm-up time can be prevented, the toner can be sufficiently heated, and the toner image can be fixed satisfactorily.

  Further, since the heating roller 11 is elastically deformed following the unevenness of the toner image on the recording paper, the toner can be sufficiently melted even when the toners of the respective colors are overlapped as in color printing or the like. . Therefore, the fixing onto the recording paper can be performed satisfactorily. Furthermore, by providing the heating-side elastic layer 13, the heating roller side is recessed at the nip portion, so that the ease of peeling of the molten toner from the surface of the heating roller 11 can be improved.

  Further, since the heating roller 11 is in direct contact with the toner on the recording paper, a release layer is provided to improve the releasability from the toner and prevent the toner from adhering to the heating roller 11. . The release layer is preferably formed of a material having releasability and heat resistance. For example, a fluorine resin such as PFA (perfluoroalkoxytetrafluoroethylene copolymer) or polytetrafluoroethylene (PTFE) is used. Use it. The thickness of the release layer is preferably 10 μm to 50 μm in order to improve the release property, durability, and thermal conductivity. In the present embodiment, the heating-side elastic layer 13 is covered with a PFA tube having a thickness of 30 μm.

  Furthermore, the heater 14 only needs to be able to heat the metal cylinder 12 and the heating-side elastic layer 13 of the heating roller 11, and for example, a halogen lamp, a ceramic heater, or the like may be used.

  The pressure roller 21 is pressed against the heating roller 11 and presses the recording paper on which an unfixed toner image formed between the pressure roller 21 and the heating roller 11 is formed, thereby recording the recording paper. The toner image is fixed on the top. The pressure roller 21 is in pressure contact with the heating roller 11 with a predetermined pressing force (pressure load) by a pressure spring (not shown), and is rotated in accordance with the rotation of the heating roller 11 in this pressure contact state. 1 rotates in the direction of the arrow.

  The pressure roller 21 is made of, for example, a metal core such as stainless steel or iron, which is a cylindrical metal core (hereinafter referred to as a pressure side metal core) 22, and rubber or sponge on the surface of the pressure side metal core 22. A pressure-side elastic layer (first pressure roller-side elastic layer) 23 is provided, and the surface of the pressure-side elastic layer 23 is covered with a release layer (not shown).

  The pressure-side elastic layer 23 has a hardness of about 26 (hardness specified by an ASKER-C type hardness meter), a rubber material such as silicon rubber, and a foaming sponge such as a silicon-based sponge formed by foaming silicon rubber. May be formed. The pressure-side elastic layer 23 is preferably formed of an elastic material having the above-described hardness and the same material as the heating-side elastic layer 13.

  The outer diameter of the pressure roller 21 is preferably as small as possible in order to reduce the size of the fixing device. Here, especially when the amount of toner on the recording paper is large as in color printing, it is necessary to transfer heat over a wide range in order to melt the toner. Further, by sufficiently securing the fixing temperature and the fixing time, the gloss of the surface of the recording paper on which the toner image is fixed can be improved. In addition, in order to capture the leading end portion of a recording sheet conveyed (from outside) via a transfer roller of a printer, which will be described later, and take it into the first nip where the heating roller 11 and the pressure roller 21 come into contact with each other. In addition, a predetermined outer diameter is required. In other words, it is necessary to secure an outer diameter of a predetermined size so that the leading end portion of the recording paper conveyed does not hit the pressure roller 21 and cause a paper jam (jam) or the like.

  The nip width of the first nip portion can be ensured by providing the pressure roller 21 with the pressure side elastic layer 23. That is, the heating roller 11 and the pressure roller 21 are in pressure contact with each other, and the pressure-side elastic layer 23 is elastically deformed, so that a conveyance force for conveying the recording paper can be secured. Accordingly, in consideration of the nip width secured by the pressure-side elastic layer 23 and the reliable capture of the leading end portion of the recording paper, the outer diameter φ of the pressure roller 21 is smaller than that of the heating roller 11, and the peeling roller It is preferably larger than 31, and usually preferably about 10 mm to 25 mm. More specifically, the pressure roller 21 may be formed by providing a pressure side elastic layer 23 having a thickness of 2 mm on a pressure side core metal 22 having an outer diameter of 14 mm, for example.

  A first nip portion formed by the pressure contact between the heating roller 11 and the pressure roller 21 by using the pressure roller 21 configured as described above and pressing the pressure roller 21 against the heating roller 11 with a pressure of 5 kg · f. Thus, a nip width of about 3 mm can be secured.

  FIG. 2 is a schematic cross-sectional view of the fixing device 10 when a backup member 33 that contacts the peeling roller 31 is provided. The peeling roller 31 is pressed against the heating roller 11 with a predetermined pressing force (pressing load) by the backup member 33 shown in FIG. The backup member 33 is provided in order to prevent the deflection generated in the rotation axis direction of the peeling roller 31 and to uniformize the pressure contact force of the peeling roller 31 against the heating roller 11 in the rotation axis direction of the peeling roller 31. ing. In the state where the peeling roller 31 is in pressure contact with the heating roller 11 by the backup member, it receives a drive from a drive source such as a gear (not shown) and rotates in the direction of the arrow in FIG.

  Thus, when the separation roller 31 passes between the separation roller 31 and the heating roller 11, the separation roller 31 is thrown so that the melted unfixed toner image enters the unevenness of the surface of the recording sheet, thereby recording the recording sheet. The toner image is flattened and fixed completely. Further, the peeling roller 31 peels the recording paper conveyed through the second nip portion where the heating roller 11 and the peeling roller 31 are in contact with each other without being wound around the heating roller 11.

  The peeling roller 31 is made of, for example, a cylindrical cored bar made of metal (columnar cored bar; hereinafter referred to as a peeling side cored bar) 32 or an elastic material made of the same material as the heating side elastic layer 13. The surface of the peeling-side cored bar 32 may be covered with a peeling-side elastic layer (second pressure roller-side elastic layer) (not shown) formed in this way. Here, the release-side elastic layer is preferably formed of the same elastic material as that of the heating-side elastic layer 13 or is formed of an elastic material such as rubber harder than the heating-side elastic layer 13. Thereby, the peeling performance of the recording paper can be improved.

  That is, if the peeling side elastic layer is formed of the same elastic material as that of the heating side elastic layer 13, the peeling side elastic layer and the heating side elastic layer 13 are elastically deformed at the second nip portion. Therefore, the second nip portion is linear in the cross section orthogonal to the central axes of the heating roller 11, the pressure roller 21, and the peeling roller 31 shown in FIG. Therefore, since the recording paper passes linearly through the second nip portion, it can be easily peeled off from the heating roller 11 and the peeling roller 31.

  If the peeling-side elastic layer is formed of an elastic material harder than the heating-side elastic layer 13, the peeling roller 31 dents the surface of the heating roller 11 at the second nip portion. The heating side elastic layer 13 is elastically deformed. Accordingly, the recording paper that has passed through the second nip portion is conveyed along the peeling roller 31, and thus the recording paper can be suitably peeled off.

  The outer diameter of the peeling roller 31 is smaller than that of the heating roller 11 and the pressure roller 21, for example, 15 mm or less, more preferably 8 mm to 10 mm, and preferably 8 mm or more. Therefore, since the nip width in the second nip portion can be reduced to about 1 mm to 2 mm, the load from the peeling roller 31 to the heating roller 11 can be concentrated. As a result, it is possible to secure a pressure for completely fixing the melted unfixed toner image and a pressure for peeling the recording paper. Further, since the peeling roller 31 having a small outer diameter is provided, the fixing device can be downsized.

  In order to shorten the warm-up time of the fixing device 10 and reduce the amount of power required for the warm-up, the peeling-side cored bar 32 may be hollow to reduce the heat capacity of the peeling roller 31.

  In the fixing device 10 including the heating roller 11, the pressure roller 21, and the peeling roller 31 having the above-described configuration, the pressure roller 21 and the peeling roller 31 are disposed so as to be in pressure contact with the heating roller 11 as illustrated in FIG. 1. The Further, the rollers are arranged so that the central axes of the heating roller 11, the pressure roller 21, and the peeling roller 31 are parallel to each other. In the fixing device 10, the pressure roller 21 is disposed on the upstream side with respect to the recording sheet conveyance direction, and the peeling roller 31 is disposed on the downstream side. More preferably, it is preferable that the pressure roller 21 is disposed on the most upstream side and the peeling roller 31 is disposed on the most downstream side with respect to the conveyance direction of the recording paper.

Further, it is preferable that the pressure roller 21 and the peeling roller 31 are arranged so as not to contact each other and to be close to each other so that the recording paper can be suitably conveyed from the first nip portion to the second nip portion. Specifically, it is desirable that the closest distance between the outer periphery of the pressure roller 21 and the outer periphery of the peeling roller 31 is 1 mm or less. Furthermore, the outer diameter of each roller of the heating roller 11, the pressure roller 21, and the peeling roller 31 includes
(Outer diameter of heating roller 11)> (Outer diameter of pressure roller 21)> (Outer diameter of peeling roller 31)
There is a relationship. That is, the heating roller 11, the pressure roller 21, and the peeling roller 31 become smaller in this order.

  As described above, in the fixing device 10, each roller satisfies the above relationship, and the interval between the pressure roller 21 and the peeling roller 31 is made as small as possible so that the pressure roller 21 and the peeling roller 31 are connected. They are placed close together. Accordingly, the pressure roller 21 fixes the unfixed toner image satisfactorily, and the peeling roller 31 peels the recording paper satisfactorily, so that jamming in the fixing device 10 can be prevented.

  Note that the arrangement positions of the pressure roller 21 and the peeling roller 31 vary depending on the outer diameters of these rollers. FIG. 3 is a cross-sectional view showing the arrangement position of the pressure roller 21 when the diameter of the peeling roller 31 is changed. As shown in FIG. 3, as the outer diameter of the peeling roller 31 increases to 31, 31 ', 31 ", the arrangement position of the pressure roller 21 changes to 21, 21, 21". Accordingly, when the outer diameter of the peeling roller 31 is increased, a straight line connecting the center of the heating roller 11 and the center of the peeling roller 31, and the center of the heating roller 11 and the center of the pressure roller 21 in the cross-sectional view shown in FIG. Are formed in the order of θ, θ ′, and θ ″. That is, the distance between the central axis of the pressure roller 21 and the central axis of the peeling roller 31 on the outer periphery of the heating roller 11 is increased. This tendency is the same when the outer diameter of the pressure roller 21 is changed.

  Therefore, it is preferable to set the arrangement positions of the pressure roller 21 and the peeling roller 21 so that the leading end portion of the recording paper that has passed through the first nip portion is conveyed to the second nip portion. Hereinafter, the arrangement positions of the pressure roller 21 and the peeling roller 21 will be described in more detail with reference to FIGS. 4 to 6.

  4A, 4B, and 5A, 5B are schematic cross-sectional views for explaining the movement of the recording paper in the arrangement of the heating roller 11, the pressure roller 21, and the peeling roller 31, respectively. Show. 6A to 6C are schematic sectional views for explaining the arrangement of the heating roller 11, the pressure roller 21, and the peeling roller 31. Each of FIGS. 4 to 6 shows a cross section of the heating roller 11, the pressure roller 21, and the peeling roller 31, which are arranged so that the central axes are parallel to each other, perpendicular to the central axes. .

  As shown in FIGS. 4A and 4B and FIGS. 5A and 5B, the arrangement of the heating roller 11, the pressure roller 21, and the peeling roller 31 after passing through the first nip portion. The conveyance direction of the recording paper 41 changes. That is, as will be described in detail later, as shown in FIGS. 4A and 4B, the leading end portion of the recording paper 41 comes into contact with the outer peripheral surface of the peeling roller 31 closer to the second nip portion. The recording paper 41 is conveyed to the section.

  On the other hand, as shown in FIGS. 5A and 5B, when the leading end portion of the recording paper 41 contacts the outer peripheral surface of the peeling roller 31 far from the second nip portion, the recording paper 41 is conveyed to the second nip portion. It becomes difficult to be done. That is, as shown in FIG. 5A, even if the leading end portion of the recording paper 41 that has passed through the first nip portion comes into contact with the peeling roller 31, it is not conveyed to the second nip portion. As shown to b), it will be conveyed to the position which does not contact with the heating roller 11, and will cause a jam.

  Therefore, in the fixing device 10, in the cross section shown in FIG. 6A, the center of the heating roller 11 (crossing portion of + in the drawing) and the center of the pressure roller 21 (crossing portion of + in the drawing). A straight line n (indicated by an arrow n in FIG. 6A) that is orthogonal to the straight line m connecting the two and passes through the first nip portion is in contact with a region (contact region) within a predetermined range of the outer periphery of the peeling roller 31. Thus, the arrangement positions of the pressure roller 21 and the peeling roller 31 are set. Here, the straight line n corresponds to the conveyance direction of the recording paper.

  More specifically, as shown in FIG. 6A, on the outer peripheral surface of the peeling roller 31, the outer periphery of the peeling roller 31 in the region between the point x and the point y1 (hereinafter referred to as the xy1 region). The pressure roller 21 and the peeling roller 31 are arranged so that the straight line n that is the recording sheet conveyance direction is in contact with the area (indicated by the double arrow in FIG. 6A). Here, the point x is the end of the second nip portion on the upstream side with respect to the conveyance direction of the recording sheet on the outer peripheral surface of the peeling roller 31, that is, the end of the second nip portion on the pressure roller 21 side. Part. The point y1 is perpendicular to a straight line p connecting the center of the heating roller 11 and the center of the peeling roller 31 (the crossing portion of + in the drawing), and a straight line q1 passing through the center of the peeling roller 31 is It is a position that intersects the outer peripheral surface of the peeling roller 31 on the pressure roller 21 side.

  The point y1 is a position closest to the pressure roller 21 side in the outer periphery of the peeling roller 31. For this reason, the point y1 is considered to be a boundary for conveying the recording sheet upstream or downstream of the point y1 with respect to the rotation direction of the peeling roller 31. Therefore, in order to convey the recording sheet more reliably downstream from the point y1, the pressure roller 21 and the peeling roller are set against the heating roller 11 so that the arrow n contacts the xy1 region. 31 is preferably arranged.

  By disposing the pressure roller 21 and the peeling roller 31 so as to satisfy the above relationship, the leading end portion of the recording paper that has passed through the first nip portion shown in FIG. 4A is brought into contact with the xy1 region. Can be made. As a result, as shown in FIGS. 4A and 4B, the recording paper 41 is conveyed by the pressure roller 21 and the peeling roller 31 is driven to rotate, so that the recording paper 41 is reliably moved to the second nip portion. Can be transported. That is, as the recording paper 41 is conveyed, a sliding phenomenon occurs in which the leading end portion of the recording paper 41 slides on the surface of the peeling roller 31 toward the second nip portion. Further, when the peeling roller 31 is rotated, the leading end portion of the recording paper 41 in contact with the xy1 region is conveyed to the second nip portion side. Therefore, as shown in FIG. 4B, the recording paper 41 is conveyed to the second nip portion due to the slip phenomenon and the rotation of the peeling roller 31.

  Of the arrangements in which the straight line n is in contact with the xy1 region of the peeling roller 31 shown in FIG. 6A, a particularly preferred arrangement of the pressure roller 21 and the peeling roller 31 is shown in FIG. 6B. That is, in order to more suitably transport the recording sheet from the first nip portion to the second nip portion, as shown in FIG. 6B, in a region between the point x described above and a point y2 described later. The pressure roller 21 and the peeling roller 31 are arranged so that the straight line n is in contact with an outer peripheral surface of the peeling roller 31 (hereinafter referred to as an xy2 region; a region indicated by a double arrow in FIG. 6B). It is preferable to set the arrangement position. Here, the point y2 indicates that the straight line q2 obtained by extending the straight line n toward the peeling roller 31 passes through the center of the peeling roller 31, and the straight line q2 is the outer periphery of the peeling roller 31 on the pressure roller 21 side. It is the position that intersects the plane. That is, the straight line n and the straight line q2 are the same straight line.

  As described above, when the leading end portion of the recording sheet comes into contact with the xy2 region, the recording sheet is easily conveyed to the second nip portion due to the slip phenomenon. On the other hand, when the recording sheet abuts against the area other than the xy2 area in the xy1 area, the recording sheet is moved to the second nip portion by the sliding phenomenon and the rotation of the peeling roller 31 as described above. Be transported. In this case, it is preferable that the rotation speed of the peeling roller 31 is substantially the same as the recording paper conveyance speed or faster than the recording paper conveyance speed. Here, the conveyance speed of the recording paper is substantially determined by the rotation speed of the pressure roller 21.

  On the other hand, as shown in FIG. 6C, when the straight line n that is the conveyance direction of the recording paper is in contact with a region on the peeling roller 31 other than the xy1 region, the first nip portion is formed. It becomes difficult to transport the leading end portion of the recording paper 41 that has passed to the second nip portion (FIGS. 5A and 5B). That is, when the pressure roller 21 and the peeling roller 31 are arranged so that the straight line n is in contact with an area other than the xy1 area of the peeling roller 31 (FIG. 6C), the above-described sliding phenomenon occurs. Even if the peeling roller 31 is rotated, the recording paper 41 that has passed through the first nip portion is not conveyed to the second nip portion as shown in FIGS.

  Therefore, when the recording paper 41 comes into contact with an area other than the x-y1 area of the peeling roller 31 (FIG. 5A), it is not conveyed to the second nip portion as shown in FIG. 5B. For example, it passes through between the peeling roller 31 and the pressure roller 21. As described above, when the recording paper 41 is conveyed to a position other than the second nip portion, a jam is caused. Therefore, it is not preferable to arrange the pressure roller 21 and the peeling roller 31 so that the straight line n shown in FIG. 6C is in contact with a region on the peeling roller 31 other than the xy1 region.

  As described above, in the fixing device 10, the arrangement positions of the pressure roller 21 and the peeling roller 31 are controlled so that the recording paper comes into contact with the xy1 region of the surface of the peeling roller 31. As a result, even if the recording paper is not conveyed in close contact with the heating roller 11 between the first nip portion and the second nip portion and may come into contact with the surface of the peeling roller 31, the occurrence of jamming is reduced. can do.

  Further, the pressure load of the pressure roller 21 in pressure contact with the heating roller 11 is smaller than the pressure load of the peeling roller 31 in pressure contact with the heating roller 11. Specifically, the pressure load of the pressure roller 21 in pressure contact with the heating roller 11 is, for example, about 5 kg · f, and the pressure load of the peeling roller 31 in pressure contact with the heating roller 11 is, for example, about 15 kg · f. It has become. Therefore, the sufficiently melted toner can be flattened and fixed on the recording paper through the first nip portion and between the first nip portion and the second nip portion. In addition, since the pressure load at the second nip portion is sufficiently secured, the recording paper can be suitably peeled off.

  When the fixing device 10 having the above-described configuration performs heat and pressure fixing of an unfixed toner image on a recording sheet, it is performed as follows. That is, when a recording sheet on which an unfixed toner image is formed is conveyed so that the unfixed toner and the heating roller 11 are in contact with each other through a transfer roller of a printer, which will be described later, a drive source (not shown) The heating roller 11, the pressure roller 21, and the peeling roller 31 are rotationally driven in the direction of the arrow in FIG. As a result, the recording paper is conveyed through the first nip portion and the toner is melted, and then the toner melted at the second nip portion is completely fixed on the recording paper. Thereafter, the recording sheet is peeled off from the heating roller 11 and discharged from the fixing device 10, and the fixing process is completed. Hereinafter, the fixing process will be described in detail.

  That is, when the recording paper on which the unfixed toner image is formed is conveyed, the heating roller 11, the pressure roller 21, and the peeling roller 31 are rotationally driven. At this time, the rotation speed (circumferential speed) of the heating roller 11 may be set in accordance with the process speed of the image forming apparatus.

  For example, as in the present embodiment, when the pressure roller 21 is driven to rotate as the heating roller 11 rotates, and the peeling roller 31 is driven by a driving source different from the driving source of the heating roller 11, or When the heating roller 11, the pressure roller 21, and the peeling roller 31 are driven by different driving sources, the rotation speed V1 of the pressure roller 21 should be equal to or less than the rotation speed V2 of the peeling roller 31. Is preferred. That is, it is preferable that the rotation of the pressure roller 21 is the same as or slower than the rotation of the peeling roller 31.

When the rotational speed V2 of the peeling roller 31 is slower than the rotational speed V1 of the pressure roller 21, the rotational speed V2 of the peeling roller 31 is set to the rotational speed V1 of the pressure roller 21,
V1 × 1.0 ≦ V2 ≦ V1 × 1.1
It is preferable to set so that it is in the range.

  This is because the recording sheet conveyed through the first nip portion is heated and expanded, and there is a possibility that the recording sheet conveyed between the first nip portion and the second nip portion may sag. . The sagging of the recording paper generated between the first nip portion and the second nip portion causes a fixing deviation of the toner image on the recording paper. Therefore, by setting the rotation speeds of the pressure roller 21 and the peeling roller 31 so as to satisfy the above formula, the slack of the recording paper is prevented and good fixing performance without fixing deviation is ensured.

  When the rotation speeds of the pressure roller 21 and the peeling roller 31 are the same, the pressure roller 21 and the peeling roller 31 may be rotated by the heating roller 11.

  When the heating roller 11, the pressure roller 21, and the peeling roller 31 are rotationally driven at the rotation speed described above, the leading end portion of the recording paper fed from the transfer unit is formed between the heating roller 11 and the pressure roller 21. The first nip portion that is the contact portion is reached. At this time, since the pressure roller 21 is formed with an outer diameter of about 18 mm, the leading end portion of the recording paper is suitably captured by the first nip portion.

  When the recording paper is captured in the first nip portion, the recording paper is conveyed by the rotation of the heating roller 11 and the pressure roller 21. At this time, each roller of the fixing device 10 is heated to the fixing temperature by the heater 14 in the heating roller 11. Subsequently, the recording sheet that has passed through the first nip portion is conveyed to a second nip portion that is a contact portion between the heating roller 11 and the peeling roller 31 as the heating roller 11 and the pressure roller 21 rotate.

  At this time, it is preferable that the recording sheet is conveyed in a state of being close to the heating roller 11 between the first nip portion and the second nip portion. That is, as described above, during the period from the first nip portion to the second nip portion along the rotation direction of the heating roller 11, the pseudo nip portion that receives heat from the heating roller 11 and Become. Therefore, the toner on the recording paper is completely melted at the pseudo nip portion, and good fixing performance can be obtained.

  Therefore, as described above, even when the heating roller 11 having a reduced thickness is used, a sufficient nip width is obtained after the pressure roller 21 and the peeling roller 31 are pressed against the heating roller 11 without increasing the nip pressure. Can be secured. Therefore, the fixing device 10 using the heat roller 11 having a reduced thickness can be preferably used even when full-color printing is performed.

  Further, as described with reference to FIGS. 6A and 6B, since the arrangement positions of the pressure roller 21 and the peeling roller 31 are set, the leading end portion of the recording paper that has passed through the first nip portion is determined. Thus, it can be more reliably conveyed to the second nip portion.

  Further, since the rotational speed V1 of the pressure roller 21 and the rotational speed V2 of the peeling roller 31 are set so as to satisfy the relationship of the above formula, recording is performed between the first nip portion and the second nip portion. The sheet can be conveyed without causing the sheet to bend. The deflection of the recording paper that occurs between the first nip and the second nip causes the occurrence of a jam, the deviation of the fixing position of the toner image on the recording paper, and the like, so that the deflection of the recording paper is prevented. As a result, the fixing performance of the fixing device 10 can be improved.

  When the recording paper reaches the second nip portion, the unfixed toner melted on the recording paper is fixed at the second nip portion. Since the second nip portion has a small nip width as described above, the load applied from the peeling roller 31 to the heating roller 11 can be concentrated. Therefore, in the second nip portion, the toner melted in the first nip portion is pressed and hardened so as to be flat with a pressure higher than the pressure in the first nip portion, and is fixed on the recording paper. . Further, since a high pressing force is applied to the recording paper, the gloss of the recording paper surface can be obtained.

  The recording sheet on which the toner image is fixed as described above is peeled off from the heating roller 11 and the peeling roller 31 after passing through the second nip portion. In the second nip portion, by concentrating the load on a narrow nip width, a pressing force necessary for peeling the recording paper can be obtained, so that the recording paper can be peeled off suitably. The releasability of the recording paper and the paper output direction (discharge direction) can be controlled by the load generated in the second nip portion. Specifically, the larger the load at the second nip portion, the more the recording paper is discharged in the direction away from the heating roller 11, and the peelability is improved. In this way, by controlling the load at the second nip portion, it is possible to control the paper output direction of the recording paper from the fixing device 10, so that the position of the paper discharge mechanism (discharge mechanism) of the printer, which will be described later, is set. Accordingly, the paper output direction can be adjusted.

  In this way, after the recording paper on which the toner image is fixed is peeled off at the second nip portion, the toner melted by natural cooling is completely cured and sent out in the direction of a paper discharge mechanism of the printer described later.

  As described above, in the fixing device 10 of the present embodiment, the heat roller 11 is thinned to reduce the heat capacity of the heat roller 11. Further, the outer diameters of the pressure roller 21 and the peeling roller 31 are made smaller than the outer diameter of the heating roller 11. For this reason, in the fixing device 10 of the present embodiment, the heating roller 11 is reduced in rigidity by being thinned. However, while ensuring a sufficient load and peelability in the second nip portion, Sufficient nip width is secured.

  That is, the nip width of the second nip portion is reduced, and the pressure applied when the peeling roller 31 is pressed against the heating roller 11 is reduced to concentrate the load between the heating roller 11 and the peeling roller 31. ing. As a result, the toner image is fixed on the recording paper and the releasability of the recording paper from the heating roller 11 is sufficiently secured even when the applied pressure is large enough not to cause deformation or destruction of the heating roller 11. be able to.

  In addition, since the heating roller 11 is provided with the heating side elastic layer 13 and the pressure roller 21 is provided with the pressure side elastic layer 23, the nip width in the first nip portion can be increased. Thereby, the unfixed toner on the recording paper can be sufficiently melted.

  Further, by reducing the outer diameters of the pressure roller 21 and the peeling roller 31, the pressure roller 21 and the peeling roller 31 can be disposed close to each other. In addition, the heat capacities of the pressure roller 21 and the peeling roller 31 can be reduced. Thereby, the downsizing of the fixing device 10 can be realized. Further, in the fixing device 10, it is possible to reduce the time and electric energy required for warm-up and to realize power saving of the fixing device 10 as compared with the fixing device in which the outer diameters of the respective rollers are the same. is there.

  The surface hardness of the heating roller 11 may be set to be higher than the surface hardness of the pressure roller 21 and lower than the surface hardness of the peeling roller 31. With this configuration, as shown in FIG. 1, in the first nip portion, the heating roller 11 presses the pressure-side elastic layer 23 of the pressure roller 21 so that the surface of the pressure roller 21 is depressed. . Moreover, in the 2nd nip part, when the peeling roller 31 presses the heating side elastic layer 13 of the heating roller 11, it will be in the state where the surface of the heating roller 11 became depressed. As described above, when the surface hardness of the peeling roller 31 is higher than the surface hardness of the heating roller 11, the recording paper is conveyed along the surface of the peeling roller 31.

  Further, the peelability of the recording paper changes depending on the outer diameter of the peeling roller 31. Therefore, when the surface hardness of the peeling roller 31 is higher than the surface hardness of the heating roller 11, the recording paper that has passed through the second nip portion is separated from the surface of the heating roller 11 as the outer diameter of the peeling roller 31 is smaller. The paper is discharged in the direction and conveyed. Therefore, the smaller the outer diameter of the peeling roller 31, the higher the peelability from the heating roller 11.

  Next, a printer (image forming apparatus) 40 provided with the fixing device 10 will be described. FIG. 7 is a schematic sectional view of the printer 40 of the present embodiment. The printer 40 forms a multi-color or single-color image on a predetermined recording sheet based on, for example, image data transmitted from each terminal device on a network (not shown). Therefore, the printer 40 can select a full color printing mode or a monochrome printing mode.

  The printer 40, together with the fixing device 10 already described, includes an exposure unit 1, an image forming station P (Pa / Pb / Pc / Pd), an intermediate transfer belt unit 7, a transfer roller 6, a paper feed tray 8, a paper discharge tray ( A paper discharge mechanism / discharge mechanism) 9 is provided.

  Since the printer is capable of full-color printing and monochrome printing, the four image stations Pa, Pb, and Black correspond to each color of black (K), cyan (C), magenta (M), and yellow (Y). Pc and Pd are juxtaposed. That is, the image forming station Pa performs image formation using black (K) toner, the image forming station Pb performs image formation using cyan (C) toner, and the image forming station Pc includes magenta ( The image formation is performed using the toner M), and the image formation station Pd performs the image formation using the yellow (Y) toner.

  The image forming stations Pa to Pd have substantially the same configuration, and each includes a developing device 2 (2a, 2b, 2c, and 2d), a photosensitive drum 3 (3a, 3b, 3c, and 3d), and a cleaner unit. 4 (4a, 4b, 4c, 4d) and a charger 5 (5a, 5b, 5c, 5d) are provided. In the above and below, “a” to “d” assigned to each member number correspond to “a” to “d” assigned to each image forming station P.

  The exposure unit 1 exposes the surfaces of the photosensitive drums 3a to 3d charged by the charger 5 from below according to the image data input to the printer 40, and electrostatic latent images are formed on the surfaces of the photosensitive drums 3a to 3d. Form an image. As shown in FIG. 7, the exposure unit 1 is a laser scanning unit (LSU) including a laser irradiation unit and a reflection mirror, for example. As the exposure unit 1, for example, an EL writing head or an LED writing head in which light emitting elements are arranged in an array can be used instead of the LSU.

  The chargers 5a to 5d provided in the image forming stations Pa to Pd uniformly charge the surfaces of the photosensitive drums 3a to 3d to a predetermined potential. As shown in FIG. 7, the chargers 5 a to 5 d may be, for example, a contact type roller type or a brush type, or may be a non-contact type charger type. Further, the developing devices 2a to 2d visualize the electrostatic latent images formed on the surfaces of the photosensitive drums 3a to 3d with toners of respective colors. The cleaner units 4a to 4d remove and remove toner remaining on the surfaces of the photosensitive drums 3a to 3d after the development processing in the developing units 2a to 2d and the transfer of the images formed on the photosensitive drums 3a to 3d. to recover.

  The intermediate transfer belt unit 7 includes an intermediate transfer belt 70, an intermediate transfer belt driving roller 71, an intermediate transfer belt driven roller 72, an intermediate transfer belt tension mechanism 73, intermediate transfer rollers 74 (74a, 74b, 74c, 74d), and an intermediate transfer belt. A cleaning unit 75 is provided.

  The intermediate transfer belt 70 is formed endlessly with a film having a thickness of about 100 μm to 150 μm. The intermediate transfer belt 70 is provided so as to be in contact with the photosensitive drums 3a to 3d, and the toner images of the respective colors formed on the photosensitive drums 3a to 3d are sequentially transferred. When the toner images of each color are superimposed on the intermediate transfer belt 70, a color toner image (multicolor toner image) is formed. The toner image formed on the intermediate transfer belt 70 is transferred onto a recording sheet by a transfer roller 6 described later.

  The intermediate transfer belt driving roller 71, the intermediate transfer belt driven roller 72, the intermediate transfer belt tension mechanism 73, and the intermediate transfer rollers 74a to 74d stretch the intermediate transfer belt 70, and in the direction of arrow A in FIG. The belt 70 is driven to rotate.

  The intermediate transfer rollers 74 a to 74 d are provided for each of the image forming stations Pa to Pd, and are rotatably supported by the intermediate transfer roller mounting portion of the intermediate transfer belt tension mechanism 73. The intermediate transfer rollers 74a to 74d are provided so as to face the photosensitive drums 3a to 3d via the intermediate transfer belt 70, and transfer the toner images formed on the surfaces of the photosensitive drums 3a to 3d to the intermediate transfer rollers 70a to 74d. A transfer bias for transferring onto the belt 7 is applied.

  Therefore, the intermediate transfer rollers 74a to 74d are based on a metal shaft such as stainless steel having a diameter of 8 to 10 mm, and the surface of the metal shaft is made of conductive material such as EPDM (ethylene-propylene-methylene copolymer) or urethane foam. It is covered with an elastic material. The transfer bias is applied to the intermediate transfer rollers 74a to 74d by applying a high-voltage transfer bias (a high voltage having a polarity (+) opposite to the toner charge polarity (-)) to transfer the toner image. Is uniformly applied to the intermediate transfer belt 70 by the conductive elastic material. In this embodiment, the roller-shaped intermediate transfer rollers 74a to 74d are used, but the same function can be obtained by using a brush-shaped transfer electrode.

  Further, the intermediate transfer belt cleaning unit 75 removes toner adhered to the intermediate transfer belt 70 by contact with the photosensitive drums 3a to 3d or toner remaining on the intermediate transfer belt 70 without being transferred onto the recording paper. Remove and collect. This prevents toner color mixing in the next printing step. The intermediate transfer belt cleaning unit 75 is provided with, for example, a cleaning blade that contacts the intermediate belt 70. By providing the cleaning blade at a position facing the intermediate transfer belt driven roller 72 with the intermediate transfer belt 70 interposed therebetween, it is possible to suitably remove toner.

  The transfer roller 6 transfers the toner image formed on the intermediate transfer belt 70 onto a recording sheet. The transfer roller 6 is disposed so as to be in pressure contact with the intermediate transfer belt 70 at a position where the recording paper and the intermediate transfer belt 70 are in contact with each other. Further, the transfer roller 6 is provided to face the intermediate transfer belt driving roller 71 with the intermediate transfer belt 70 interposed therebetween. Therefore, one of the transfer roller 6 and the intermediate transfer belt drive roller 71 is formed of a hard material such as metal so that the transfer roller 6 is pressed against the intermediate transfer belt 70 with a predetermined pressure, and the other is elastic rubber. It is preferable that the elastic roller is made of a soft material such as a foaming resin. A voltage for transferring the toner image formed on the intermediate transfer belt 70 onto the recording paper is applied to the transfer roller 6 (a high voltage having a polarity (+) opposite to the toner charging polarity (−)). .

  The paper feed tray 8 is a tray for storing recording paper used for image formation, and is provided below the image forming stations Pa to Pd and the exposure unit 1 of the printer 40.

  Further, the printer 40 is provided with a manual paper feed tray 8 ′ used when the user prints a small number of sheets. One end of the manual paper feed tray 8 ′ is attached to a side portion of the printer 40, and is attached to the side portion so as to be rotatable. For this reason, when the manual feed tray 8 ′ is not used, as shown by the broken line in FIG. 7, the recording paper is placed on the side of the printer 40 along the side of the printer 40. A compact design has been achieved. On the other hand, when the recording paper is manually supplied to the printer 40, the manual paper feed tray 8 ′ is moved so that the above-described placement surface is separated from the side portion of the printer 40, and the recording paper is placed on the placement surface. Can be placed.

  The paper discharge tray 9 is provided on the top of the printer 40 and is a tray for placing printed recording paper face down.

  In the printer 40 having the above-described configuration, the print processing operation is performed as follows. That is, when image data is input from the outside to the printer 40, the recording paper stored in the paper feed tray 8 is separated one by one by the pickup roller 81 provided at the end of the paper feed tray 8. The sheet is sent out to the sheet conveyance path S (the chain line in the figure). Thereafter, the recording paper is conveyed to the registration roller 99 by the conveyance roller 91, and the conveyance of the recording paper is temporarily stopped with the leading edge of the recording paper reaching the registration roller 99.

  On the other hand, when the recording paper placed on the manual paper feed tray 8 ′ is transported, the recording paper is separated and fed one by one by the pickup roller 82 and sent to the paper transport path S. . Thereafter, the sheet is conveyed by a plurality of conveyance rollers 96, 95, and 94 and conveyed to the registration roller 99.

  In parallel with the feeding of the recording paper from the paper feed tray 8 or the manual paper feed tray 8 ', the image forming stations Pa to Pd start forming a toner image based on the input image data. That is, when image data is input to the printer 40, the surfaces of the photosensitive drums 3a to 3d are charged by the chargers 5a to 5d. Thereafter, electrostatic latent images are formed on the surfaces of the photosensitive drums 3a to 3d by the exposure unit 1 in accordance with the input image data. In order to develop the electrostatic latent image, toner is supplied from the developing devices 2a to 2d to form a toner image. Subsequently, the toner images formed on the photosensitive drums 3a to 3d are sequentially transferred onto the intermediate transfer belt 70 by the intermediate transfer rollers 74a to 74d, and the toner images of the respective colors are overlapped to form a multicolor toner image. In the case of monochrome printing, only a black (K) toner image is formed on the intermediate transfer belt 70.

  When the toner image is formed on the intermediate transfer belt 70 in this way, the conveyance of the recording paper from the registration roller 99 is started at the timing aligned with the leading end of the toner image. As the recording paper passes between the transfer roller 6 and the intermediate transfer belt 70, the toner image is transferred onto the recording paper. Thereafter, after the toner image on the recording paper is melted and fixed and printed by the fixing device 10, the paper discharge roller (paper discharge mechanism / discharge mechanism) 92 and the paper discharge roller (paper discharge mechanism / discharge mechanism) 93 are printed. As a result, the paper is discharged onto the paper discharge tray 9.

  As described above, the output direction of the recording paper discharged from the fixing device 10 can be controlled by the pressure load between the peeling roller 31 and the heating roller 11. That is, the separation roller 31 that is in pressure contact with the heating roller 11 so that the recording paper conveyed from the fixing device 10 is discharged to the arrangement positions of the paper discharge mechanisms such as the paper discharge rollers 92 and 93 and the paper discharge tray 9. Pressurized load is set. For this reason, in the printer 40, the pressure load between the peeling roller 31 and the heating roller 11 is controlled so that the recording paper is discharged in the direction of the paper discharge roller 92. Thereby, the recording paper discharged from the fixing device 10 can be reliably conveyed to the paper discharge roller 92.

  When double-sided printing is requested, after passing through the fixing device 10, the trailing edge of the recording paper is held by the paper discharge roller 93. With the trailing edge of the recording paper held, the paper discharge roller 93 rotates reversely to be guided to the transport rollers 97 and 98 and reach the registration roller 99 again. Thereafter, as described above, in accordance with the rotation timing of the intermediate transfer belt 70 to which the toner image has been transferred, the recording paper is conveyed and printing is performed on the surface opposite to the previously printed surface. .

  In this embodiment, a printer is described as an example. However, an image is formed by an electrophotographic method such as a copier, a fax machine, or a digital multifunction machine having a printer function, a copy function, a fax function, or the like. The fixing device 10 can be similarly applied to various image forming apparatuses.

  The fixing device of the present invention is used in an image forming apparatus such as a printer, a copying machine, a fax machine, or a digital multi-function machine having these functions, which uses toner to form an image by electrophotography. it can. Since the fixing device can sufficiently secure the fixing property of the toner image on the recording paper and the releasability of the recording paper, it can cope with both monochrome printing and color printing. Further, since the heating roller is thinned and the outer diameters of the pressure roller and the peeling roller are reduced, it is possible to achieve downsizing and power saving of the fixing device, and an image forming apparatus including the fixing device. Can be reduced in size and power consumption.

1 is a schematic cross-sectional view illustrating an embodiment of a fixing device according to the present invention. It is a schematic sectional drawing which shows the structure at the time of providing a backup member in the peeling roller of the said fixing apparatus. FIG. 4 is a schematic cross-sectional view showing the arrangement position of the pressure roller when the outer diameter of the peeling roller is changed in the fixing device. (A) and (b) are schematic sectional views for explaining the movement of the recording paper when the pressure roller and the peeling roller are arranged close to each other in the fixing device. (A) and (b) are schematic sectional views for explaining the movement of the recording paper when the pressure roller and the peeling roller are arranged apart from each other in the fixing device. (A)-(c) is a schematic sectional drawing explaining each arrangement | positioning of a pressure roller and a peeling roller in the said fixing device. It is a schematic sectional drawing which shows one Embodiment of the printer in this invention provided with the said fixing device.

Explanation of symbols

9 Paper discharge tray (paper discharge mechanism, discharge mechanism)
10 Fixing Device 11 Heating Roller 12 Cylinder (Metal Cylinder)
13 Heating side elastic layer (heating roller side elastic layer)
14 Heater (heat source)
21 Pressure roller (first pressure roller)
22 Core (pressurized side core)
23 Pressure-side elastic layer (first pressure roller-side elastic layer)
31 Peeling roller (second pressure roller)
32 Core (peeling side, cylindrical core)
33 Backup member 40 Printer (image forming apparatus)
41 Recording paper (recording medium)
92 Paper discharge roller (paper discharge mechanism, discharge mechanism)
93 Paper discharge roller (paper discharge mechanism, discharge mechanism)
m virtual plane n virtual plane p virtual plane q1 virtual plane q2 virtual plane x second nip upstream end y1 virtual straight line y2 virtual straight line

Claims (12)

It has at least two pressure rollers that form a nip portion in pressure contact with a heating roller having a heat source. When the heating roller and the pressure roller rotate, the recording medium is conveyed to the nip portion, and the recording is performed. In a fixing device for fixing a developer on a medium,
The pressure roller includes at least a first pressure roller that forms a first nip portion by being pressed against the heating roller, and that takes in a recording medium conveyed from the outside into the first nip portion. A second nip portion is formed by pressure contact with the heating roller, and a second pressure roller for peeling the recording medium that has passed through the second nip portion from the heating roller,
The first pressure roller is arranged on the upstream side of the second pressure roller with respect to the conveyance direction of the recording medium,
Between the heating roller, the first pressure roller, and the second pressure roller,
(Outer diameter of heating roller)> (Outer diameter of first pressure roller)> (Outer diameter of second pressure roller)
A fixing device characterized by the following relationship:   2. The heating roller according to claim 1, wherein a heating roller side elastic layer having a thickness of 1 mm or less is formed on a hollow cylinder having a thermal conductivity of a thickness of 3 mm or less. Fixing device.   3. The fixing according to claim 1, wherein a pressure load of the first pressure roller in pressure contact with the heating roller is smaller than a pressure load of the second pressure roller in pressure contact with the heating roller. apparatus.   4. The fixing device according to claim 1, wherein the nip width of the first nip portion is larger than the nip width of the second nip portion.   The first pressure roller has a first pressure roller side elastic layer, which is an elastic layer formed of the same material as the heating roller side elastic layer, on the surface of a cylindrical rotating body. The fixing device according to claim 3, wherein the fixing device is provided.   The second pressure roller has a second pressure roller side elastic layer which is an elastic layer formed of the same material as the heating roller side elastic layer on a cylindrical cored bar. The fixing device according to claim 3, wherein the fixing device is characterized in that: The surface hardness of the first pressure roller is smaller than the surface hardness of the heating roller,
The fixing device according to claim 1, wherein a surface hardness of the second pressure roller is larger than a surface hardness of the heating roller.   The fixing device according to claim 1, wherein a rotation speed V2 of the second pressure roller is equal to or higher than a rotation speed V1 of the first pressure roller. The rotation speed V2 of the second pressure roller is higher than the rotation speed V1 of the first pressure roller.
V1 × 1.0 ≦ V2 ≦ V1 × 1.1
The fixing device according to claim 1, wherein the relationship is satisfied.   An image forming apparatus comprising the fixing device according to claim 1. Equipped with a discharge mechanism for discharging the recording medium,
The pressure load of the second pressure roller that is in pressure contact with the heating roller is set so that the recording medium conveyed from the fixing device is discharged at the position of the discharge mechanism. The image forming apparatus according to claim 10.   12. The image forming apparatus according to claim 10, wherein a monochrome printing mode or a full color printing mode can be selected.

Images