JP2004191857A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device and an image forming apparatus employing a belt system having a quick rise time and free from an abnormal image even in the case of an oilless fixation. <P>SOLUTION: The fixing device is provided with an endless fixing belt 11 trained over supporting bodies including a pressing member 30, and a pressure roller 14 facing the pressing member 30 across the fixing belt 11 so as to form a nip part (n), wherein the pressing member 30 is provided with a support shaft 42 for holding the pressing member 30 at each longitudinal end, and the pressing member 30 is freely rotated around the support shaft 42. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrophotographic fixing device and an image forming apparatus using the fixing device.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a fixing method using a belt has been known as a fixing device having a quick start-up. In this type of fixing device, a belt is stretched over at least one or more pressure members, and a nip portion is formed by a pressure member disposed to face the pressure member via the belt. Then, the sheet carrying the toner image is configured to be fixed by passing through the nip portion.
[0003]
[Patent Document] Japanese Patent No. 3282494
[Patent Document] Japanese Patent Application Laid-Open No. 9-160405
Japanese Patent No. 3282494 discloses a heat fixing roller having an elastic layer, and a nip in which a recording sheet which is in contact with an outer peripheral surface of the heat fixing roller and carries a toner image is sandwiched between the heat fixing roller and the heat fixing roller. There is disclosed a fixing device including an endless belt that forms a portion, and a pad-shaped pressure applying member that is in contact with the inner surface side of the belt and presses the belt along the surface of the heat fixing roll.
[0004]
Japanese Patent Application Laid-Open No. Hei 9-160405 discloses an endless fixing belt stretched over a first roller and a second roller, and a third roller abutting on the outside of the fixing belt. There is disclosed a fixing device having a pressing member having elasticity on a surface for pressing a third roller at a winding start position on a roller.
[0005]
In the fixing device described in Japanese Patent No. 3282494, the belt is pressed by a pad-shaped pressing member along the surface of the heat fixing roll, and the attachment of the pressing member is not described. Therefore, the attachment of the pressing member, which is conventionally generally used, will be described with reference to FIG.
[0006]
In FIG. 7, guide holes 115 as shown are provided on both side plates of the fixing device, and both ends of the pressing member 114 are slidably supported along the guide holes 115. The pressing member 114 is pressed at both ends by a compression spring 134 and presses against the pressing roller 117 via the fixing belt 119.
[0007]
In Japanese Patent Application Laid-Open No. Hei 9-160405, as shown in FIG. 10, a first nip portion between a first roller 111 and a second roller 112 with a pressing member opposed to a third roller 118 via a fixing belt 116 is provided. And a third nip portion of the second roller 112 facing the third roller 118 with the fixing belt 116 interposed therebetween.
[0008]
[Problems to be solved by the invention]
However, in the former fixing device shown in FIG. 7, since the pressing member 114 is slid along the guide hole 115, the size of the guide hole 115 is slightly larger than the guide portion of the pressing member 114. Further, when the pressing member 114 is pressed by such a device, since the sliding resistance between the belt 119 and the pressing member 114 is large, the pressing member 114 is tilted or vibrated by driving the fixing belt 119 as shown in FIG. As a result, the pressure applied to the pressure roller 117 becomes non-uniform due to rattling or the like, and an abnormal image such as uneven fixing is generated. Also, in the longitudinal direction of the pressing member 114, the pressing member 114 is loose in the direction of the arrow shown in FIG. 9 and the pressure is uneven, so that an abnormal image such as uneven fixing is generated. Further, when an elastic member is used as the pressing member 114, the sliding property and the abrasion resistance are not always excellent, so that there is a problem in the transportability and durability of the belt 119. In FIG. 8, the guide holes 115 of the side plate are omitted, and in FIG. 9, the fixing belt 119 and the guide holes 115 of the side plate are omitted.
[0009]
Further, in the latter fixing device described in Japanese Patent Application Laid-Open No. 9-160405, since there are a plurality of nip portions, the peripheral speed difference between the fixing belt 116 and the third roller 118 due to slip or distortion of the roller as shown in FIG. Occurs, and in the second nip portion where there is no member facing the third roller 118, a floating B occurs between the fixing belt 116 and the third roller 118. In this configuration, the toner melted in the first nip portion is offset to the fixing belt 116, and a floating B occurs between the fixing belt 116 and the third roller 118, so that the toner is again fixed on the sheet at a position shifted in the third nip portion. As a result, an abnormal image such as an image shift occurs.
[0010]
SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide a fixing device and an image forming apparatus which do not cause an abnormal image even in oilless fixing, particularly in a belt system having a short start-up time.
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides an endless belt member wound around a support including at least one pressing member, and a member that forms a nip portion facing the pressing member via the belt member. A pressure member, and a heating means for heating the belt member or the pressure member. The recording sheet carrying the toner image is conveyed to the nip portion, and the toner image is transferred by passing through the nip portion. In the fixing device for fixing the recording sheet by heating and melting, the pressing member has a fulcrum for holding the pressing member at both ends in a longitudinal direction thereof, and is rotatable about the fulcrum. Features.
[0012]
According to another aspect of the present invention, there is provided an endless belt member wound around a support including at least one pressing member and a fixing member; and the pressing member and the fixing member via the belt member. And a heating means for heating the belt member or the pressing member, wherein the pressing member in the nip portion moves in a traveling direction of the belt member from the fixing member. In a fixing device which is located on the upstream side, conveys a recording sheet carrying a toner image in the nip portion, and heats and melts the toner image by passing through the nip portion to fix the toner image on the recording sheet, the pressing member is A fulcrum for holding the pressing member at both ends in the longitudinal direction of the pressing member, wherein the pressing member is rotatable about the fulcrum, and a nip portion most downstream portion of the pressing member. It is characterized in that proximate to the nip portion most upstream portion of the fixing member.
[0013]
The present invention is effective when the fulcrum position of the pressing member is a position where the pressing member rotates in the clearance direction with respect to the pressing member when the belt member runs.
[0014]
Furthermore, the present invention is effective when the pressing member has a pressing body and a biasing unit that urges the pressing body in a direction of pressing the pressing member against the pressing member.
Furthermore, the present invention is effective when the pressing body has a rigid supporting member and an elastic layer provided on the pressing surface side of the supporting member.
[0015]
Furthermore, the present invention is effective when the fulcrum of the pressing member and the part facing the belt member are integrated.
Furthermore, the present invention is effective when a lubricating member that comes into contact with the belt member during running of the belt member is provided on the longitudinal side surface of the pressing member on the upstream side of the nip portion.
[0016]
Still further, in the present invention, a low friction member exists between the pressing member and the belt member, and a friction coefficient μ1 between the pressing member and the belt member is smaller than that of the belt member and the pressing member. It is effective if the coefficient of friction is smaller than μ2.
[0017]
Furthermore, the present invention is effective when the low friction member is a graphite sheet.
According to another aspect of the present invention, there is provided an image forming apparatus including the belt fixing device according to any one of claims 1 to 18.
[0018]
In the image forming apparatus of the present invention, it is effective to use a toner containing at least a binder resin, a colorant, and a wax.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a color image forming apparatus provided with a fixing device according to the present invention.
In FIG. 1, the image carrier of the image forming apparatus main body is a drum-shaped photoconductor 1Y, 1C, 1M, 1BK made of a photoconductive organic or inorganic material. In the color image forming apparatus to which the present invention is applied, a plurality of photoconductors 1Y, 1C, 1M, and 1BK are arranged along one running side of a transfer belt 20 wound around a plurality of rollers 21. To rotate.
[0020]
As a full-color image forming apparatus using an electrophotographic method, a color separation superposition transfer system is generally used. In this type of image forming apparatus, an image information light obtained by color-separating a document into three colors of blue, red and green is read by a document reading unit (29), and image processing is performed based on the intensity level of each color light. The four photoconductors 1A, 2A, 3A, and 4A based on the write image data to be developed in each color of yellow (Y), cyan (C), magenta (M), and black (BK) obtained by performing Optical writing is performed thereon, and the obtained electrostatic latent images are used as developing units 2Y, 2C containing yellow, cyan, magenta, and black developers provided for the respective photoconductors 1Y, 1C, 1M, 1BK. , 2M, 2BK. An example of a recording sheet in which each color toner image formed on each photoconductor by this development is electrostatically attracted to a transfer belt 20 that rotates while coming into contact with each photoconductor in sequence via a registration roller 27 from a paper supply unit. The transfer is performed by the transfer rollers 3Y, 3C, 3M, and 3BK, which are transfer members provided for the respective photoconductors, in an overlapping manner. After the transfer, the transfer paper is separated from the transfer belt 20 by the separation device 28 and fixed by the fixing device 10 to obtain a color image.
[0021]
In the example shown in the figure, each color-separated image information is optically color-separated by a document reading section 29 provided at the upper part of the color image forming apparatus main body, read by three CCDs 25, and subjected to arithmetic processing based on the output signals. The optical writing is performed by the laser writing devices 4Y, 4C, 4M, and 4BK provided for the photoconductors 1Y, 1C, 1M, and 1BK based on the respective color data obtained as described above.
[0022]
The photoconductors 1Y, 1C, 1M, and 1BK are negatively charged by the charging devices 5Y, 5C, 5M, and 5BK, respectively, and the portions on which optical writing has been performed are reversely developed with negatively charged toner. As the charging device, a device such as a corotron or a scorotron which generates charges by corona discharge and scatters them on the surface of the image carrier is used. In the arrangement of the developing devices, 2Y, 2C, 2M, and 2BK are respectively used for yellow, cyan, magenta, and black toners from the paper supply side, and the overlapping transfer is sequentially performed by the positive corona in this order. The transfer belt 20 is made of a dielectric material such as polyester film, and is positively charged by the transfer rollers 3Y, 3C, 3M, and 3BK. Therefore, after the transfer paper is separated, the transfer belt 20 is neutralized by the neutralization device 26. The static eliminator 26 performs a negative AC corona discharge from both sides of the transfer belt 20 with a charger to neutralize the charge accumulated on the transfer belt 20 (static elimination) to initialize the transfer belt 20. The transfer belt 20 is cleaned by a cleaning unit 22 to remove residual toner.
[0023]
The separation device 28 performs a negative AC corona discharge with a charger from the upper surface of the transfer paper to neutralize (discharge) the accumulated charge of the transfer paper, and causes toner dust due to peeling discharge when the transfer paper is separated from the transfer belt 20. To prevent
[0024]
As shown in FIG. 2, the fixing device 10 includes a pressing member 30, a heating roller 12 for applying tension, and a support roller 13 disposed before and after the pressing member 30, and an endless belt that rotates in the direction of the arrow. A fixing belt 11 as a member is wound. The pressing member 30 presses the pressing roller 14 via the fixing belt 11 as described later in detail. A halogen heater 15 is provided inside the heating roller 12, and a halogen heater 16 is provided inside the pressure roller 14, and heats the fixing belt 11 and the pressure roller 14. Then, the paper P having the toner image on its surface passes through the nip portion n of the pressing member 30 and the pressure roller 14 so that the toner image is fixed.
[0025]
As shown in FIGS. 2 and 3, the pressing member 30 of the present embodiment includes a holder 31 as a rigid support member made of aluminum or the like, and a pressing roller 14 via the fixing belt 11 of the holder 31. And a low-friction member sheet 33 that covers the elastic layer 32. Since the holder 31 is supported by the support shaft 42 provided on the side plates 40 and 41 of the fixing device, the pressing member 30 is rotatable about the support shaft 42. That is, the pressing member 30 is rotatably mounted on the support shaft 42 at both ends in a direction orthogonal to a paper passing direction (a running direction of the fixing belt 11) which is a longitudinal direction thereof. Further, the pressing member 30 is provided with a compression spring 34 as pressing force urging means for pressing the elastic layer 32 toward the pressing roller 14 via the holder 31 near both ends thereof. In this embodiment, the holder 31 and the elastic layer 32 covered with the low-friction member sheet 33 constitute a pressing member of the pressing member 30. Further, the pressing force urging means is not limited to the compression spring 34, but may be a torsion spring, an elastic rubber, a weight, or the like. However, a compression spring is preferable in terms of assemblability.
[0026]
In the pressing member 30 configured as described above, the support shaft 42 is provided on the upstream side of the fixing nip portion, that is, on the right side in FIG. 2, and this is the rotation that the pressing member 30 receives by the fixing belt 11 running clockwise. Since the action is in the direction of escaping from the pressing roller 14, the pressing member 30 is uniformly pressed by the compression spring 34. Conversely, if the support shaft 42 is on the downstream side of the fixing nip portion n, the rotation effect received by the traveling of the fixing belt 11 will be in the direction of biting into the pressure roller 14, and the pressing member 30 will be inclined due to the inclination and the like. This is because pressure may occur.
[0027]
Further, since the pressing member 30 is provided with the elastic layer 32, a uniform load can be applied to the toner image, and a high-quality fixed image can be obtained. Further, by using the low friction member sheet 33, the friction coefficient μ1 between the pressing member 30 and the fixing belt 11 can be made smaller than the friction coefficient μ2 between the fixing belt 11 and the pressure roller 14. When μ1 <μ2, the running property of the fixing belt 11 can be improved.
[0028]
In the fixing device shown in FIG. 2, the holder 31 is made of aluminum, the elastic layer 32 is made of a liquid silicone rubber having a thickness of 3 mm, and the low friction member sheet 33 is made of a graphite sheet. It was desired that the low friction member sheet 33 was not unevenly worn due to the fact that the low friction member sheet 33 did not bite into the pressure roller 14 side.
[0029]
In addition, as the low friction member sheet 33, a PTFE sheet, a resin sheet containing glass fiber, or the like can be used in addition to the graphite sheet. Here, the case where the graphite sheet is used as the low friction member sheet 33 will be described. The graphite sheet is a material having low sliding resistance and extremely high thermal conductivity in the crystal direction. Therefore, when the crystal plane of the graphite sheet and the inner surface of the fixing belt 11 are aligned and the crystal direction is oriented in the longitudinal direction of the fixing belt 11, the temperature distribution in the longitudinal direction of the fixing belt 11 can be made uniform, and the nip portion n This is also effective in reducing the temperature unevenness and particularly the rise in the temperature at the end.
[0030]
Further, the pressing member 30 is formed such that a fulcrum where the support shaft 42 is pivotally supported and the elastic layer 32 covered with the sheet 33 which is a portion of the pressing member 30 facing the fixing belt 11 are not separate bodies but integrated. The looseness of the pressing member 30 can be further reduced, and abnormal images such as uneven fixing can be reliably prevented.
[0031]
When the pressing member 30 is formed of heat-resistant rubber or an elastic body such as a leaf spring having an R-shaped surface facing the pressure roller 14, it is assumed that the elastic layer 32 is not provided on the surface facing the pressure roller 14. Also, a uniform load can be applied to the toner image, and a high-quality fixed image can be obtained.
[0032]
The fixing belt 11 uses an endless belt-shaped base made of a heat-resistant resin or metal for the base. As the material of the heat-resistant resin, polyimide, polyamideide, polyetherketone (PEEK) or the like is used, and as the material of the metal belt, nickel, aluminum, iron, or the like is used. The thickness of the fixing belt 11 is desirably as thin as 100 μm or less. The surface of the fixing belt 11 needs to be releasable because it comes into pressure contact with paper and a toner image, and preferably has excellent heat resistance and durability. Therefore, the surface layer of the fixing belt 11 is configured to be covered with a heat-resistant release layer (such as a fluorine-based resin or a high-release silicone rubber). The fluororesin as the heat-resistant release layer is coated on the surface of the base by spraying or the like, and is heated and fused to form a surface release layer.
[0033]
As another configuration of the fixing belt 11, an elastic layer such as silicone rubber is provided on a base made of a heat-resistant resin such as polyimide, and a release layer such as a fluororesin or a PFA tube is provided on the elastic layer. , OHP transparency, and a better fixed image in uniform fixing can be obtained. As a specific example, 90 μm thick polyimide was used as the base of the fixing belt 11, a 200 μm thick silicone rubber was formed thereon, and a 30 μm thick PFA tube was further coated thereon.
[0034]
The pressure roller 14 has a heat-resistant elastic layer made of fluorine-based rubber, silicone rubber, or the like, and a surface release layer made of a fluorine-based resin, formed around the core of iron or aluminum. In the present embodiment, the thickness of the elastic layer of the pressure roller 14 is about 0.5 to 2 mm, and its surface hardness is AskerC 70 to 90 Hs. A halogen heater 16 is provided in the pressure roller 14 in order to accelerate the temperature rise of the pressure roller 14, but the halogen heater 16 may not be provided. In addition, the pressure roller 14 is driven by a driving unit (not shown), and the fixing belt 11 is caused to run by the driving unit. However, the fixing belt 11 may be driven by driving one of the support rollers 13.
[0035]
The heating roller 12 is a thin metal roller having an outer diameter of φ20 to φ30 made of iron or aluminum and having a thickness of 0.3 to 1 mm, and includes a halogen heater 15 therein. The fixing belt 11 is controlled by a temperature control element (not shown) so as to have a constant temperature, and plays a role of heating the fixing belt 11 to a required temperature. The heating roller 12 also serves as a tension roller, and the fixing belt 11 is stretched by a tension spring 17 in the direction of the arrow in the figure. The heat source may be provided not inside the heating roller 12 but outside the roller or directly outside the belt so as to directly heat the fixing belt. Further, the heat source is not limited to the halogen heater, and induction heating or the like may be used.
[0036]
When a toner containing a binder resin, a colorant, and a wax is used as a toner, a color fixed image can be obtained even in an oilless fixing device. Further, the heat source may be provided outside the roller instead of inside the roller. In the embodiment of FIG. 2, the fixing belt 11 side is the first surface of the sheet, but the pressure roller 14 side may be used as the first surface of the sheet.
[0037]
FIG. 4 is an explanatory diagram showing another embodiment of the fixing device according to the present invention.
In FIG. 4, the fixing device 10 includes a pressing member 30, a fixing roller 18, a heating roller 12 for applying tension, and a fixing belt 11 wound around a supporting roller 13. A halogen heater 15 is provided inside the heating roller 12, and a halogen heater 16 is provided inside the pressure roller 14, and heats the fixing belt 11 and the pressure roller 14.
[0038]
The pressing member 30 and the fixing roller 18 press the pressing roller 14 via the fixing belt 11. With this configuration, in the fixing device 10, the pressing member 30 facing the pressing roller 14 via the fixing belt 11 is used. 30, a second nip n2 of only the fixing belt 11 between the pressing member 30 and the fixing roller 18, and a fixing roller 18 opposed to the pressure roller 14 via the fixing belt 11. A third nip n3 is formed. Then, the sheet P carrying the toner image on its surface passes through the first, second, and third nip portions n1, n2, and n3, thereby fixing the toner image.
[0039]
The pressing member 30 is rotatably held about a support shaft 42 attached to both side plates (not shown), similarly to the pressing member 30 described in the embodiment of FIG. The pressing member 30 is pressed on both sides by the compression springs 34 to form a nip n1 with the pressing roller 14 via the fixing belt 11. By forming the pressing member 30 in such a form, the holder 31 of the pressing member 30 can have a downstream end in a plate shape or a thinner shape than the fulcrum portion, and the downstream end of the pressing member 30 is close to the fixing roller 18. be able to. As a result, the width of the second nip portion n2 can be made extremely small, so that even in a fixing device having a wide nip, an abnormal image such as an image shift caused by the floating B in the second nip portion n2 shown in FIG. can do.
[0040]
In the pressing member 30 of this embodiment, a 3 mm-thick liquid silicone rubber is provided as an elastic layer 32 on the lower surface of a thin aluminum plate-shaped holder 31, and a graphite sheet is used as a low friction member sheet 33 thereon. Further, as another configuration of the pressing member 30, if the holder 31 is a SUS plate spring having an R-shaped surface facing the pressure roller 14 and the elastic layer 32 is not provided, the downstream end of the pressing member 30 is Since it can be closer to the fixing roller 18, the second nip portion n2 can be further reduced, and an abnormal image such as an image shift caused by the floating B at the second nip portion n2 can be reliably eliminated.
[0041]
The fixing roller 18 has an outer diameter of φ20 to φ30, and has an elastic layer made of a heat-resistant elastic body, for example, a foamed silicone rubber or a liquid silicone rubber, in order to obtain a nip width around an iron core. The thickness of the elastic layer is about 3 to 6 mm. The surface hardness of the fixing roller 18 is about Asker C 30 to 50 Hs. The pressure roller 14 is driven by a driving unit (not shown), but the fixing roller 18 may be rotationally driven. In the fixing device of the present embodiment, the other components, the fixing bell 11, the heating roller 12, and the pressure roller 14 are the same as those of the fixing device of the embodiment of FIG. In the present embodiment, the fixing belt 11 side is used as the first surface of the sheet, but the pressure roller 14 side may be used as the first surface of the sheet.
[0042]
FIG. 5 is an explanatory view showing still another embodiment of the fixing device according to the present invention.
5, the fixing device 50 includes a pressing member 60, a heating roller 52 for applying tension, and a support roller 53 wound around the pressing member 60, and an endless pressing belt 54 that rotates in the direction of the arrow. It is stretched. The pressing member 60 presses the fixing roller 51 via the pressing belt 54. A halogen heater 56 is provided inside the fixing roller 51 to heat the pressure belt 54 and the fixing roller 51. Further, a halogen heater 55 may be provided inside the heating roller 52. Then, the paper having the toner image carried on its surface passes through the nip n between the pressing member 60 and the fixing roller 51, so that the toner image is fixed. In this embodiment, the fixing roller 51 is driven by a driving unit (not shown).
[0043]
As in the embodiment shown in FIGS. 2 and 4, the pressing member 60 is rotatably held about a support shaft 62, and is pressed on both sides by a compression spring 64, and is in contact with the fixing roller 51 via a pressing belt 54. A nip n is formed.
[0044]
A fulcrum, which is the support shaft 68, is arranged at a position where the pressing member 60 rotates in the escape direction when the pressing belt 54 is driven. The structure of the pressing member 60 of the present embodiment is similar to that of the embodiment of FIG. 2, in which an aluminum holder 61 having a rotation fulcrum and a liquid silicone rubber having a thickness of 3 mm as an elastic layer 62 are provided thereon to reduce friction. As the member sheet 63, a graphite sheet was used.
[0045]
In the present embodiment, a wall surface in the longitudinal direction of the upper side of the nip portion n is provided in the holder 61, and a graphite member 65 is attached as a lubricating member in the longitudinal direction of the wall surface. The graphite member 65 contacts the inner surface of the pressure belt 54 and improves the lubricity of the inner surface of the pressure belt 54. In the present apparatus, since the back tension is applied to the pressure belt 54 before the entrance of the nip n, when the lubricating member is attached to the entrance of the nip n in this manner, the ability of applying the lubricating member to the inner surface of the pressure belt 54 is high. Become. As a result, the friction coefficient between the pressing member 60 and the pressing belt 54 can be reliably reduced, the transportability of the pressing belt 54 can be improved, and the durability of the pressing belt 54 and the pressing member 60 can be improved.
[0046]
The fixing roller 51 was provided with a 2 mm silicone rubber layer on the outer periphery of an aluminum core, and a 30 μm thick PFA tube was coated thereon as a release layer. The other configuration of the fixing device used in the present embodiment is the same as the configuration of the fixing device of the embodiment shown in FIG. Furthermore, in the present embodiment, the fixing roller 51 side is the first surface of the sheet, but the pressure belt 54 side may be the first surface of the sheet.
[0047]
The fixing device of the embodiment described above is used in an image forming apparatus employing an electrophotographic process including charging, exposure, development, transfer, and fixing. As shown in FIG. It is apparent that the present invention can be applied to a modified example of electrophotography in which the image is transferred not from the transfer belt 81 to the recording sheet but from the intermediate transfer belt 81 to the fixing belt 11.
[0048]
In the secondary transfer portion, a conventionally known desired potential difference (including superimposition of AC, pulse, etc.) is provided as necessary to control the moving direction of the image. The roller 19 is provided on the secondary transfer member 80 via the intermediate transfer belt 81 and the fixing belt 11. Here, a bias for transferring to the fixing belt 11 may be applied to the roller 19. The other configuration of the fixing device includes a pressing member 30, a pressure roller 14, a heating roller 12, and the like, which are the same as the configuration of the fixing device 10 of the embodiment shown in FIG. In the fixing section, a potential difference may be provided as a means for preventing the offset.
[0049]
As a means for generating a potential difference, there are known methods such as bias application, grounding, and static elimination, and current control and voltage control can be used. It is also effective to use a Zener diode or the like to maintain a constant potential difference.
[0050]
Regarding the transfer of the present embodiment, since the secondary transfer is always performed on a fixed partner member, that is, the fixing belt 11, which is a transfer fixing member, it is easy to stably obtain high image quality. Further, since a part of the toner T is softened by heat and the scattering of the image at the time of transfer is prevented, the image quality becomes high. Since the heat transfer to the intermediate transfer belt 81 in the secondary transfer portion is performed only to the surface layer via the toner with respect to the fixing and heat in the present embodiment, the temperature rise of the intermediate transfer belt 81 is minimized. Therefore, a problem due to a rise in the temperature of the intermediate transfer belt 81 hardly occurs. Further, the toner heating time can be set sufficiently, and the recording sheet can be heated for the same amount of time as in the related art.
[0051]
Furthermore, it should be noted that the heating time of the toner and the heating time of the recording medium can each be set while keeping the heating time of the intermediate transfer belt 81 at a minimum. Therefore, the toner heating time, which is important for image quality such as gloss, and the recording medium heating time, which is important for adhesion to the recording medium, can be set freely, and environmental performance such as energy saving by not heating the recording medium wastefully is achieved for the first time. Is done.
[0052]
Although only a four-color tandem embodiment is described, it is obvious that the same can be applied to color, monochrome, and two colors using one image carrier as long as an intermediate transfer member is used.
[0053]
In the fixing device of the present invention, when a toner containing at least a binder resin, a colorant, and a wax is used, the color image can be fixed without the recording sheet being wound around the belt member even in the oilless fixing device. Can be. By using such a fixing device of the present invention, an image forming apparatus of oilless fixing can be provided.
[0054]
【The invention's effect】
According to the configuration of the first aspect, the pressing member has a fulcrum for holding the pressing member at both ends in the longitudinal direction, and is rotatable around the fulcrum. In a fixing device having a short start-up time, the pressure applied by the pressing member can be stabilized, and an abnormal image can be prevented.
[0055]
According to the configuration of the second aspect, the pressing member has fulcrums at both ends in the longitudinal direction for holding the pressing member, and is rotatable around the fulcrum. Since the downstream portion is close to the most upstream portion of the nip portion of the fixing member, in a fixing device having a wide nip width using the pressing member and the fixing member, the nip width between the most downstream portion of the pressing member and the most upstream portion of the fixing member is reduced. It is possible to make the image narrower and prevent an abnormal image.
[0056]
According to the configuration of claim 3, since the fulcrum position of the pressing member is the position where the pressing member rotates in the clearance direction with respect to the pressing member when the belt member runs, the pressing member is pressed when the belt member runs. It is possible to prevent digging into the.
[0057]
According to the configuration of claim 4, since the pressing member has the pressing body and the urging means for urging the pressing body in the direction of pressing the pressing member against the pressing member, the pressing member is uniform with respect to the pressing member. , And uneven fixing can be prevented.
[0058]
According to the configuration of claim 5, since the pressing member has the rigid supporting member and the elastic layer provided on the pressing surface side of the supporting member, the pressing member can apply uniform pressure to the pressing member. A high-quality fixed image can be obtained.
[0059]
According to the configuration of claim 6, since the fulcrum portion of the pressing member and the portion facing the belt member are integrated, it is possible to eliminate rattling of the pressing member and prevent occurrence of an abnormal image.
[0060]
According to the configuration of claim 7, the lubricating member that comes into contact with the belt member when the belt member travels is provided on the longitudinal side surface on the upstream side of the nip portion of the pressing member. , And the durability of the belt and the pressing member can be increased.
[0061]
According to the configuration of claim 8, the low friction member exists between the pressing member and the belt member, and the friction coefficient μ1 between the pressing member and the belt member is determined by the friction coefficient between the belt member and the pressing member. Since the coefficient is smaller than the coefficient μ2, the sliding resistance between the pressing member and the belt member can be reduced, the transportability of the belt can be enhanced, and the partial pressing of the pressing member can be prevented to prevent the uneven wear of the low friction member.
[0062]
According to the configuration of claim 9, since the low friction member is a graphite sheet, the sliding resistance is small, and the graphite sheet, which is a high heat conductive material, is used as a sliding member between the pressing member and the belt member, thereby reducing the pressing member. The sliding resistance between the belt member and the belt member can be reduced, and the nip temperature unevenness can be reduced.
[0063]
According to the tenth aspect, since the belt fixing device according to any one of the first to ninth aspects is provided, an image forming apparatus used for oil-less fixing in which paper is prevented from being wound around a belt member is provided. Can be provided.
[0064]
According to the configuration of the eleventh aspect, since the toner containing at least the binder resin, the colorant, and the wax is used, it is possible to provide an oilless fixing image forming apparatus without winding around the belt member.
[Brief description of the drawings]
FIG. 1 is a configuration diagram schematically showing an image forming apparatus provided with a fixing device according to the present invention.
FIG. 2 is an explanatory diagram showing one embodiment of a fixing device according to the present invention.
FIG. 3 is an explanatory side view of the fixing device shown in FIG. 2;
FIG. 4 is an explanatory view showing another embodiment of the fixing device according to the present invention.
FIG. 5 is an explanatory view showing still another embodiment of the fixing device according to the present invention.
FIG. 6 is an explanatory view showing still another embodiment according to the present invention.
FIG. 7 is an explanatory diagram showing a conventional fixing device.
FIG. 8 is an explanatory diagram showing a problem of the fixing device of FIG. 7;
FIG. 9 is an explanatory diagram showing another problem in the fixing device of FIG. 7;
FIG. 10 is an explanatory diagram showing another conventional fixing device.
[Explanation of symbols]
10 Fixing device
11 Fixing belt
14 Pressure roller
30 pressing member
31 Holder
32 elastic layer
33 Low friction member sheet
34 compression spring
42 Support shaft

Claims (11)

An endless belt member wound around a support including at least one pressing member, and a pressing member that faces the pressing member via the belt member to form a nip portion; A fixing device having heating means for heating a pressing member, conveying a recording sheet carrying a toner image in the nip portion, and heating and melting the toner image by passing through the nip portion to fix the toner image on the recording sheet. At
The fixing device is characterized in that the pressing member has fulcrums at both ends in the longitudinal direction for holding the pressing member, and is rotatable about the fulcrum. An endless belt member wound around a support including at least one pressing member and a fixing member, and a pressing member forming a nip portion facing the pressing member and the fixing member via the belt member. A heating unit that heats the belt member or the pressing member, wherein the pressing member in the nip portion is located upstream of the fixing member in the traveling direction of the belt member, and forms a toner image on the nip portion. A fixing device that conveys the held recording sheet and heats and melts the toner image by passing through the nip portion and fixes the toner image on the recording sheet,
The pressing member has a fulcrum for holding the pressing member at both ends in the longitudinal direction thereof, and is rotatable about the fulcrum. A fixing device, which is located close to the most upstream portion of the nip portion. The fixing device according to claim 1, wherein a fulcrum position of the pressing member is a position where the pressing member rotates in a clearance direction with respect to the pressing member when the belt member runs. The fixing device according to claim 1, wherein the pressing member includes a pressing member, and a pressing unit configured to press the pressing member in a direction of pressing the pressing member against the pressing member. 5. apparatus. The fixing device according to claim 4, wherein the pressing body includes a rigid supporting member and an elastic layer provided on a pressing surface side of the supporting member. The fixing device according to claim 1, wherein a fulcrum of the pressing member and a portion facing the belt member are integrated. The lubrication member which contacts the belt member at the time of running the belt member is provided on a longitudinal side surface of the nip portion upstream side of the pressing member, the lubrication member according to any one of claims 1 to 4, 6. Fixing device. A low friction member exists between the pressing member and the belt member, and a friction coefficient μ1 between the pressing member and the belt member is smaller than a friction coefficient μ2 between the belt member and the pressing member. The fixing device according to claim 1, wherein the fixing device is small. The fixing device according to claim 8, wherein the low friction member is a graphite sheet. An image forming apparatus comprising the belt fixing device according to claim 1. The image forming apparatus according to claim 10, wherein a toner containing at least a binder resin, a colorant, and a wax is used.

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