JP3813458B2 - Belt fixing device and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a belt fixing device used in an image forming apparatus such as a copying machine, a facsimile machine, various printers, and a combination of these, and relates to suitable shapes of a fixing roller and a pressure roller constituting the belt fixing device.
[0002]
[Prior art]
In Japanese Patent Laid-Open No. 6-3245886, a pressure roller is formed in a drum shape and a fixing roller is formed in a drum shape, so that recording materials such as undulations, streaks, reverse curls, and wrinkles that tend to occur during transfer are disclosed. There has been proposed a fixing device that prevents the influence and enhances the image quality without causing significant device improvement, cost increase, and productivity deterioration.
Japanese Patent Laid-Open No. 6-301306 discloses a configuration in which a roller having a narrow central portion along the rotation axis direction and a thick end portion is used as a pressure roller or a fixing roller, and the fixing roller along the rotation axis. There has been proposed a fixing device having a configuration in which the thickness is the same, and the pressure roller has a shape with a narrow central portion and thick both ends along the rotation axis.
[0003]
[Problems to be solved by the invention]
The technology disclosed in the above publication, particularly Japanese Patent Application Laid-Open No. 6-3245886, applies the proposed technology to a heat fixing apparatus, a so-called belt fixing apparatus, configured to apply heat from a heating element to a recording material through a heat-resistant film. Although there is a description that it may be used, a new technical problem when used in a belt fixing device is not recognized. That is, the width of the fixing nip portion is larger than that of the conventional roller fixing in the belt fixing device, particularly in the case of using a method in which the fixing belt is approached or wound before the fixing nip portion formed by the fixing roller and the pressure roller. While it has the advantage that it can be taken large and the apparatus can be downsized, there is a serious problem that the image is rubbed by contact with the fixing belt before the recording material reaches the fixing nip portion, and the image is destroyed. . In particular, when the recording material is transported from the bottom to the top, if the trailing edge of the recording material passes through the roller having a feeding action and becomes free, the recording material hangs down with its leading edge held by the fixing nip portion, Such a phenomenon occurs remarkably.
The present invention provides belt fixing in which the recording material does not hang down, does not come into contact with the fixing belt, and does not cause image destruction due to image rubbing even when the trailing edge of the recording material becomes free before entering the fixing device. An object is to provide an apparatus and an image forming apparatus.
[0004]
[Means for Solving the Problems]
In order to solve the above problem, in claim 1, A fixing belt wrapped around a rotatable fixing roller and a heating roller And a pressure roller that is rotatably provided at a position facing the fixing roller via the fixing belt, and forms a fixing nip portion between the fixing belt by being in pressure contact with the fixing roller, and transports paper more than the fixing nip portion. Direction upstream And between the heating roller and the fixing roller The fixing roller has a support roller around which the fixing belt is wound, and the fixing roller has a drum shape with a thick central portion and thin end portions with respect to the rotation center line, and the pressure roller has a rotation center line. On the other hand, a belt fixing device having a drum shape with a narrow central portion and thick end portions has been proposed.
[0005]
A second aspect of the present invention comprises the configuration according to the first aspect. ,Pressurization The axial hardness of the roller Fixing We have proposed a belt fixing device that is larger than the on-axis hardness of the roller. According to a third aspect of the invention, there is provided a belt having the configuration according to the first or second aspect, wherein a protruding amount from the end portion of the fixing roller to the central portion of the fixing roller is larger than a retracting amount from the end portion of the pressure roller to the central portion. A fixing device is proposed. According to a fourth aspect of the present invention, the amount of protrusion from the end portion of the fixing roller to the central portion is more than twice the amount of retraction from the end portion of the pressure roller to the central portion. A belt fixing device is proposed.
[0006]
According to a fifth aspect of the present invention, there is provided a belt fixing device having the configuration according to any one of the first to fourth aspects, wherein the amount of retraction from the end portion of the pressure roller to the central portion is 0.06 mm to 0.15 mm. Yes.
[0007]
According to a sixth aspect of the present invention, there is proposed a belt fixing device having the configuration according to any one of the first to fifth aspects, wherein the fixing roller is a sponge roller.
According to a seventh aspect of the present invention, there is proposed a belt fixing device having the configuration according to any one of the first to sixth aspects, using a polyimide resin as a base material of the fixing belt and having a thickness of 150 μm or less.
According to an eighth aspect of the present invention, there is proposed a belt fixing apparatus having the configuration according to any one of the first to seventh aspects, wherein the fixing belt has an elastic layer, and the thickness of the elastic layer is 50 μm or more.
According to a ninth aspect of the present invention, there is proposed a belt fixing device having the configuration according to the eighth aspect, wherein the fixing belt has a multilayer structure, and the surface layer or intermediate layer thereof is formed of an elastic layer.
[0008]
The image forming apparatus using the belt fixing device according to any one of claims 1 to 9 as a fixing device in an image forming device that fixes an image formed with a developer onto a recording material by a fixing device. A device is proposed.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an electrophotographic color printer (hereinafter referred to as a color printer) which is an example of an image forming apparatus to which the present invention is applied will be described with reference to the drawings.
In FIG. 1, a color printer denoted by reference numeral 1 includes a photoreceptor unit 10 having a photoreceptor belt 11 as an image carrier, a writing optical unit 20, a developing unit 30, an intermediate transfer unit 40, a secondary transfer unit 50, and a fixing unit. 60, a double-sided printing reversal unit 70, and the like. In a color printer, black: black (hereinafter referred to as “Bk”), Cyan: cyan (hereinafter referred to as “C”), magenta: magenta (hereinafter referred to as “M”), yellow: yellow (hereinafter referred to as “Y”) is used as a photosensitive belt. 11 are sequentially visualized, and these are superposed to form a final four-color full-color image, which is fixed on a sheet P as a recording material by a fixing unit 60.
[0010]
The photosensitive belt 11 rotates in a clockwise direction indicated by an arrow A (hereinafter referred to as “A direction”), and around the photosensitive belt cleaning device 12, a charging roller 13 as a charging member, and a developing unit 30 are selected. A developing device, an intermediate transfer belt 41 of the intermediate transfer unit 40, and the like are disposed. The photosensitive belt 11 is stretched between a driving roller 14, a primary transfer counter roller 15, and a stretching roller 16, and is rotated in a direction A by a driving motor (not shown). When a belt having a joint is used as the photosensitive belt 11, a joint mark is provided in a non-image forming area at the end of the belt, and detection is performed by a sensor (not shown) so that image formation is performed while avoiding the joint. .
[0011]
The writing optical unit 20 converts the color image data into an optical signal, performs optical writing corresponding to each color image, and forms an electrostatic latent image on the photosensitive belt 11. The writing optical unit 20 includes a semiconductor laser 21 as a light source, a laser light emission drive control unit (not shown), a polygon mirror 22, three reflection mirrors 23a, 23b, and 23c.
[0012]
The developing unit 30 includes a Bk developing unit 31K, a C developing unit 31C, an M developing unit 31M, and a Y developing unit 31Y. It consists of an approach / separation mechanism. The developing units 31K, 31C, 31M, and 31Y are developing sleeves 32K, 32C, and 32M as developer carrying members that rotate by carrying a developer on the surface for developing the electrostatic latent image on the surface of the photoreceptor belt 11, respectively. , 32Y, developer paddles 33K, 33C, 33M, and 33Y as stirring members that rotate to pump up and stir the developer, and developer storage cases 34K, 34C, 34M, and 34Y that store the developer Has been.
[0013]
In these developer storage cases 34K, 34C, 34M, and 34Y, single-component developers made of toner of respective colors are stored as developers. In this embodiment, the developing device 31K containing black toner, the C developing device 31C containing cyan toner, the M developing device 31M containing magenta toner, and the Y developing device 31Y containing yellow toner are arranged in this order from the lower side of the printer main body 1A. It is arranged. The toner in the developing devices 31K, 31C, 31M, and 31Y is charged with a predetermined polarity. A developing bias is applied to the developing sleeves 32K, 32C, 32M, and 32Y by a developing bias power source (not shown), whereby the developing sleeves 32K, 32C, 32M, and 32Y are biased to a predetermined potential with respect to the photosensitive belt 11. . When the electromagnetic clutch (not shown) for transmitting the drive from the driving means such as a motor (not shown) to the developing devices 31K, 31C, 31M, 31Y is turned on, the contact / separation mechanism is driven by the developer containing cases 34K, 34C, 34M and 34Y are moved to the photosensitive belt 11 side (right side in the figure). At the time of development, any one selected from the developing devices 31K, 31C, 31M, and 31Y moves and contacts the photosensitive belt 11. On the other hand, when the electromagnetic clutch (not shown) is turned off to cancel the drive transmission, the developing device that has been in contact with the photosensitive belt 11 moves in a direction away from the photosensitive belt 11 (left side in the figure).
[0014]
In the standby state of the color printer, the developing unit 30 has all the developing devices 31K, 31C, 31M, and 31Y set at positions separated from the photosensitive belt 11, and when the printing operation is started, the color image data is displayed. Based on this, optical writing with a laser beam and formation of an electrostatic latent image start (hereinafter, an electrostatic latent image based on Bk image data is referred to as a Bk electrostatic latent image; the same applies to C, M, and Y). In the color printer, before the leading edge of the electrostatic latent image reaches the Bk developing position to enable development from the leading edge of the Bk electrostatic latent image, the rotation of the Bk developing sleeve 32K is started, The image is developed with Bk toner. Thereafter, the developing operation of the Bk electrostatic latent image area is continued. When the rear end portion of the Bk electrostatic latent image passes the Bk developing position, the Bk developing unit 31K is separated from the photosensitive belt 11 and immediately proceeds to the next. The developing device of the color is in contact with the photosensitive belt 11. This is completed at least before the leading edge of the electrostatic latent image based on the next image data reaches the developing position.
[0015]
The intermediate transfer unit 40 includes an intermediate transfer belt 41, a belt cleaning device 42, a position detection sensor 43, and the like. The intermediate transfer belt 41 is stretched around a drive roller 44, a primary transfer roller 45, a secondary transfer counter roller 46, a cleaning counter roller 47, and a tension roller 48, and is counterclockwise as indicated by an arrow B by a drive motor (not shown). Rotational drive control is performed. The non-image forming area at the end of the intermediate transfer belt 41 is provided with a plurality of position detection marks (not shown), and one of these position detection marks (for position detection at the start of the image forming operation). The position detection mark 43) that first passes through the sensor 43 is detected by the position detection sensor 43, and image formation is started at this detection timing. The belt cleaning device 42 includes a cleaning brush 42a, a brush contact / separation mechanism (not shown), and the like. The belt cleaning device 42 uses a brush contact / separation mechanism while transferring the Bk image of the first color to the intermediate transfer belt 41 and transferring the images of the second, third, and fourth colors to the intermediate transfer belt 41. The cleaning brush 42a is separated from the surface of the intermediate transfer belt 41, and operates so that the cleaning brush 42a contacts the surface of the intermediate transfer belt 41 during cleaning. The toner cleaned from the surface of the intermediate transfer belt 41 is stored in a waste toner tank 49 provided inside the intermediate transfer unit 40.
[0016]
A sheet P is stored in a cassette 80 disposed in the lower portion of the printer main body 1A, and is fed and conveyed in the direction of the registration roller pair 82 by sheet feeding rollers 81a, 81b, and 81c. On the right side of the color printer 1, a manual feed tray 83 for manual paper feed such as OHP paper or thick paper as a recording material is provided.
[0017]
The secondary transfer unit 50 includes a swing mechanism (not shown) provided with a clutch or the like for bringing the secondary transfer roller 51 and the secondary transfer roller 51 into and out of contact with the intermediate transfer belt 41. The secondary transfer roller 51 is moved from the separated position to the contact position by the swing mechanism in accordance with the timing when the paper P reaches the transfer position. In the secondary transfer unit 50, the sheet P and the intermediate transfer belt 41 are fixed at a transfer portion formed between the secondary transfer roller 51 and the intermediate transfer belt 41 by the secondary transfer roller 51 and the secondary transfer counter roller 46. It comes to contact with the pressure of. The secondary transfer roller 51 maintains the positional accuracy of the parallelism with the secondary transfer counter roller 46 by a positioning member (not shown) provided in the intermediate transfer unit 40. The contact pressure of the secondary transfer roller 51 with respect to the intermediate transfer belt 41 is fixed by a positioning roller (not shown) provided on the secondary transfer roller 51. At the same time as the secondary transfer roller 51 is brought into contact with the intermediate transfer belt 41, a transfer bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 51. By receiving this bias application, the intermediate transfer is performed. The superimposed toner images on the belt 41 are collectively transferred onto the paper P.
[0018]
In the above configuration, each unit is provided so as to be detachable from the printer main body 1A. For example, in FIG. 1, when removing the intermediate transfer unit 40, the intermediate transfer unit 40 can be easily removed by opening a front cover (not shown) and sliding the intermediate transfer unit 40 from the back side of the apparatus to the front side.
[0019]
In the color printer 1 configured as described above, when the image forming cycle is started, first, the photosensitive belt 11 is rotated in the direction of arrow A and the intermediate transfer belt 41 is rotated in the direction of arrow B by a drive motor (not shown). A position detection mark (not shown) provided on the intermediate transfer belt 41 is detected by a position detection sensor 43, and Bk toner image formation and C toner image formation are performed on the photosensitive belt 11 in accordance with the detection timing of the position detection mark. M toner image formation and Y toner image formation are performed, and finally a toner image is formed on the intermediate transfer belt 41 in the order of Bk, C, M, and Y. At this time, the bias applied to the primary transfer roller 45 generally increases the voltage sequentially, but this is changed according to the resistance characteristics of the intermediate transfer belt 41 and the like.
[0020]
Bk toner image formation is performed as follows. The charging roller 13 uniformly charges the photosensitive belt 11 by an applied voltage of a power source (not shown). The laser beam LD for writing is exposed based on the Bk color image signal. When this exposure is performed, in the exposed portion of the photosensitive belt 11 which is initially uniformly charged, the charge proportional to the exposure light amount disappears, and a Bk electrostatic latent image is formed. Then, when the Bk toner carried on the Bk developing sleeve 32K comes into contact with the Bk electrostatic latent image, the toner does not adhere to the remaining portion of the photosensitive belt 11, and the portion without the charge, that is, the exposure. Bk toner is attracted to the portion thus formed, and a Bk toner image similar to the electrostatic latent image is formed. The Bk toner image formed on the photoreceptor belt 11 contacts the intermediate transfer belt 41 at the primary transfer position. At the primary transfer position, a nip is formed between the intermediate transfer belt 41 and the photosensitive belt 11 by the primary transfer roller 45 and the primary transfer counter roller 15, and the Bk toner image is transferred to the primary transfer roller 45. A Bk toner image is transferred to the intermediate transfer belt 41 by applying a reverse polarity bias.
[0021]
Some untransferred residual toner on the photoreceptor belt 11 is cleaned by the photoreceptor cleaning device 12 in preparation for reuse of the photoreceptor belt 11. The toner collected here is stored in a waste toner tank (not shown) via a collection pipe.
[0022]
On the photosensitive belt 11 side, the process proceeds to the C image forming process after the Bk image forming process, and writing with the laser light LD is performed by the C image data in accordance with the detection timing of the position detecting sensor 43, and the C electrostatic latent image is obtained. Is formed. Then, after the rear end portion of the previous Bk electrostatic latent image passes and before the front end portion of the C electrostatic latent image arrives, the Bk developing unit is retracted from the developing position, and the C developing unit C is moved to the developing position. The C electrostatic latent image is developed with C toner. Thereafter, the development of the C electrostatic latent image area is continued, but when the rear end portion of the C electrostatic latent image passes, the C developing device C is retracted from the developing position as in the case of the previous Bk developing device B. Then, the next M developing device M is moved to the developing position. This is also completed before the leading edge of the next M electrostatic latent image reaches the developing position. The M and Y image forming steps are the same as the Bk and C steps described above, and the description thereof is omitted. On the intermediate transfer belt 41, Bk, C, M, and Y toner images sequentially formed on the photosensitive belt 11 are sequentially aligned on the same surface to form a four-color superimposed toner image. In the transfer process, the four color toner images are collectively transferred onto the transfer paper.
[0023]
At the time when the image forming operation is started, the paper P is fed from either the cassette 80 or the manual feed tray 83 and waits at the nip portion of the pair of registration rollers 82. Then, when the leading edge of the four-color superimposed toner image on the intermediate transfer belt 41 approaches the secondary transfer roller 51, the registration roller pair 82 is driven so that the leading edge of the paper P exactly coincides with the leading edge of the toner image. The alignment between the paper P and the toner image is performed. Then, the paper P is overlapped with the toner image on the intermediate transfer belt 41 and passes through the secondary transfer position. At this time, the paper P is charged by the transfer bias by the secondary transfer roller 51, and most of the toner image is transferred onto the paper P.
[0024]
The sheet P onto which the four-color superimposed toner images have been collectively transferred from the intermediate transfer belt 41 is conveyed to the fixing unit 60, where the toner image is heated by the fixing nip portion 69 of the fixing belt 61 and the pressure roller 62 controlled to a predetermined temperature. Are melted and fixed by the pressure, sent out of the printer main body 1A (in the direction of arrow C), and stacked on the paper discharge tray 84 formed on the upper portion of the printer main body 1A so as to obtain a full color image.
[0025]
When performing duplex printing, the paper P that has passed through the fixing unit 60 is guided in the direction of arrow D by the duplex switching claw 85 and sent to the duplex printing reversal unit 70. After the trailing edge of the paper passes through the reverse switching claw 71, the reverse roller pair 72 stops and the paper P also stops. Then, the reverse roller pair 72 starts reverse rotation after a certain blank time, and the paper P starts to switch back. At this time, the reverse switching claw 71 is switched, and the paper P is guided in the direction of arrow E and sent to the registration roller pair 82. The paper P sent to the registration roller pair 82 stands by at the nip of the registration roller pair 82 in a state where the paper P is reversed. Then, the registration roller pair 82 is driven at a predetermined timing, the paper P is sent to the secondary transfer position, and the four-color superimposed toner image is collectively transferred from the intermediate transfer belt 41, and then the toner image is melted by the fixing unit 60. It is fixed and sent out of the printer body 1A.
[0026]
The surface of the photoconductor belt 11 after the primary transfer is cleaned by the photoconductor cleaning device 12 and is uniformly discharged by a discharge lamp (not shown). Further, the surface of the intermediate transfer belt 41 after the toner image is transferred to the paper P is cleaned by pressing the cleaning brush 42a of the belt cleaning device 42 with a contact / separation mechanism (not shown). The toner cleaned from the intermediate transfer belt 41 is stored in a waste toner tank 49. After the images are collectively transferred, the toner image is melted and fixed by the fixing unit 60 and sent out of the printer main body 1A.
[0027]
The fixing unit 60 according to the present invention will be described in detail with reference to FIG. FIG. 2 is a diagram showing an internal configuration of the fixing unit 60 schematically described in FIG. The fixing unit 60 is a so-called belt fixing device, and includes a fixing belt 61, a pressure roller 62, a fixing roller 63 serving as a driving roller, a heating roller 64 serving as a driven roller, and a support roller 65. The fixing belt 61 is wound around a fixing roller 63, a heating roller 64, and a support roller 65, which are rotatably supported by a frame or the like (not shown). The pressure roller 62 is disposed at a position facing the fixing roller 63 via the fixing belt 61, and is rotatably supported by a frame or the like (not shown). The fixing roller 63 and the pressure roller 62 are in pressure contact with each other via the fixing belt 61 so that an appropriate fixing nip portion 69 is formed. Inside the pressure roller 62 and the heating roller 64, halogen heaters 66 and 67 are provided as heat sources, respectively. The halogen heater 66 controls the pressure roller 62, and the halogen heater 67 controls the fixing belt 61 so as to reach a predetermined temperature.
[0028]
A sheet P having an unfixed toner image T is conveyed from below in the figure along a guide plate 68 disposed in front of the fixing nip 69 to the fixing belt 61 controlled to a predetermined temperature. The toner image is melted and fixed at the fixing nip portion 69 of the pressure roller 62, and sent out of the printer main body 1A as shown in FIG.
[0029]
In the fixing unit 60, the sheet P is conveyed to the fixing unit 60, enters the fixing nip portion 69 formed between the fixing belt 61 controlled to a predetermined temperature and the pressure roller 62, and starts fixing. The rear end P <b> 1 is disengaged from the secondary transfer unit 50 that applies a conveying force to the paper P. Then, as shown in FIG. 3, the rear end P1 of the paper P hangs down by its own weight, and the surface P2 on which the unfixed toner image T is transferred contacts the fixing belt 61 located on the opposite side, The unfixed toner image T is rubbed and the image is destroyed. Therefore, the toner image T needs to be separated from the fixing belt 61.
[0030]
The shapes of the pressure roller 62 and the fixing roller 63, which are characteristic portions of the fixing unit 60, will be described with reference to FIG. The fixing roller 63 has a thick central portion 63c with respect to the rotation center line 100 of the rotary shaft 630 provided so as to be rotatable integrally with the roller, and both end portions 6 of the fixing roller 63. 3 a, 6 3 b is formed in a thin drum shape. The pressure roller 62 has a central portion 6 along a rotation center line 101 of a rotation shaft 620 provided so as to be integrally rotatable with the roller. 2 C is thin and both end portions 62a and 62b are formed in a thick drum shape. The paper P sandwiched between the drum-shaped fixing roller 63 and the drum-shaped pressure roller 62 is given a curl effect by the R shape generated by the drum shape and the drum shape. Koshi will be given. Therefore, the phenomenon that the trailing edge P1 of the sheet P becomes free and hangs down is eliminated, and contact with the fixing belt 61 can be avoided.
[0031]
Example 1
Next, the experiment was attempted by setting the axial hardness of the fixing roller 63 to 40 ° (Asker C) and the axial hardness of the pressure roller 62 to be greater than 78 ° (Asker C). By doing so, the shape of the paper P in the fixing nip portion 69 is closer to the shape of the pressure roller 62, the curling effect is increased, and the destruction of the toner image T due to further paper rubbing can be prevented. It turns out that you can.
[0032]
(Example 2)
The amount of protrusion Y from the ends 63a, 63b of the drum-shaped fixing roller 63 to the central portion 63c is 0.3 mm, and the amount of retraction from the ends 62a, 62b of the drum-shaped pressure roller 62 to the central portion 62c (knob) Amount) X was set to 0.12 mm, and an experiment was attempted with a retraction amount X larger than that. By doing so, the shape of the paper P in the fixing nip portion 69 is closer to the shape of the pressure roller 62 even for a small-sized paper P, the curling effect is increased, and toner caused by further rubbing on the paper surface It has been found that the destruction of the image T can be prevented.
[0033]
Example 3
An experiment was attempted by setting the protrusion amount (the amount of the lever) Y of the fixing roller 63 to be not less than twice the retraction amount X of the pressure roller 62. By doing so, the shape of the paper P in the fixing nip 69 is closer to the shape of the pressure roller 62 even for a small-sized paper P, and the toner image T is further destroyed by rubbing the paper surface. It has been found that it can be prevented.
[0034]
Example 4
An experiment was attempted with the amount of retraction X from the end diameter of the pressure roller 62 set to 0.06 to 0.15 mm. It has been found that the toner image T can be further prevented from being destroyed by rubbing on the paper surface by making the amount of retraction X in this way.
[0035]
(Example 5)
The fixing roller 63 was formed with a sponge roller. As a result, the shape of the paper P in the fixing nip portion 69 is closer to the shape of the pressure roller 62 and prevents image rubbing, and the heat insulation effect saves energy and shortens the rise time. became.
[0036]
(Example 6)
FIG. 5 is a partial enlarged cross-sectional view of the fixing belt 61. In this example, the fixing belt 61 has a multilayer structure, a polyimide resin (hereinafter referred to as “PI”) is used as the material of the base 61 c, and the thickness thereof is 150 μm or less. As a result, if the fixing belt 61 sandwiched between the fixing roller 63 and the pressure roller 62 is hard, the desired shape of the fixing nip 69 cannot be formed. However, the fixing belt 61 can be added by using the above-described material and layer thickness. The shape of the pressure roller 62 is followed, and the destruction of the toner image T due to paper rubbing against the belt can be prevented.
The surface layer 61a or the intermediate layer 62b of the fixing belt 61 is composed of an elastic layer, and the layer thickness is set to 50 μm or more. By configuring the fixing belt 61 in this manner, the surface of the fixing belt 61 is more in line with the shape of the pressure roller 62, and image rubbing can be further prevented.
[0037]
(Example 7)
The optimum configuration of the fixing belt 61, the pressure roller 62, and the fixing roller 63 in the present invention will be described.
Fixing belt: Multi-layer structure, using PI for base material, layer thickness 90μm
The upper layer of the base material is composed of silicon (Si) rubber, layer thickness 150μm
Pressure roller: Consists of solid rubber with a diameter of 40 mm and a surface layer of 1.5 mm
Knob amount X = 0.12 μm Roller hardness 78 ° (Asker C)
Fixing roller: Consist of 30 mm diameter and 6 mm thick sponge rubber
Tyco Y = 0.3μm Roller hardness 40 ° (Asker C)
[0038]
【The invention's effect】
According to the present invention, the fixing roller has a drum shape with a thick central portion and thin end portions with respect to the rotation center line, and the pressure roller has a thin drum portion with a thin central portion and both end portions with respect to the rotation center line. Since the recording material is formed in a shape, when the recording material is positioned between the fixing belt and the pressure roller, the drum shape and the shape along the drum shape are provided, and the stiffness is given. For this reason, even if the trailing edge of the recording material becomes free, the recording material does not move or hang down, so that the recording material does not come into contact with the fixing belt before fixing, and image rubbing can be prevented.
[0039]
According to the present invention, the hardness of the fixing roller is made lower than that of the pressure roller, so that the recording material in the fixing nip portion becomes closer to the shape of the pressure roller, and the recording material comes into contact with the fixing belt before fixing. Image rubbing can be prevented.
[0040]
According to the present invention, by increasing the protrusion amount that is the amount of the fixing roller to be larger than the retraction amount that is the amount of the pressing roller, the recording material is added in the fixing nip even when a small size recording material is used. It becomes close to the shape of a pressure roller, and image rubbing due to contact of the recording material with the fixing belt before fixing can be prevented.
[0041]
According to the present invention, by using a sponge roller as the fixing roller, the fixing roller is easily deformed, and while eliminating image rubbing due to contact of the recording material with the fixing belt before fixing, energy saving is achieved by its heat insulating effect. In addition, the rise time can be shortened.
[0042]
If the fixing belt sandwiched between the fixing roller and the pressure roller is hard, the shape of the fixing nip portion is not as intended. However, as in the present invention, by using a polyimide resin with a layer thickness of 150 μm or less, the belt is also pressed. Since it follows the shape of the roller, image rubbing due to contact of the recording material with the fixing belt before fixing can be more reliably prevented.
[0043]
According to the present invention, the surface of the fixing belt or the intermediate layer is made of an elastic layer having a thickness of 50 μm or more, so that the surface of the fixing belt more easily follows the shape of the pressure roller. Image rubbing due to contact with the fixing belt can be more reliably prevented.
[0044]
According to the present invention, it is possible to more reliably prevent image rubbing due to contact of the recording material with the fixing belt before fixing by regulating the retracting amount of the pressure roller.
[0045]
According to the present invention, in the belt fixing device, image rubbing due to contact of the recording material with the fixing belt before fixing is prevented, so that high image quality can be achieved.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram illustrating an example of an image forming apparatus to which the present invention is applied.
FIG. 2 is an enlarged view showing a configuration of a belt fixing device as a main part of the present invention.
FIG. 3 is an enlarged view showing a state of a recording material during a fixing operation in the belt fixing device.
FIG. 4 is an enlarged view of the shape of the fixing roller and the pressure roller and the state of the recording material at the time of fixing as viewed from the recording material discharge side.
FIG. 5 is a partially enlarged cross-sectional view showing a configuration of a fixing belt according to the present invention.
[Explanation of symbols]
60 Belt fixing device
61 Fusing belt
61c Base of fixing belt
61a Surface layer (elastic layer) of fixing belt
61b Intermediate layer of fixing belt (elastic placement)
62 Pressure roller
62a, 62b both ends
62c center
63 Fixing roller
63a, 63b both ends
63c center
100, 101 center line of rotation
X Retraction amount
Y protrusion amount

Claims (10)

A fixing belt that is rotatable, a fixing belt wound around a heating roller, and a fixing belt that is rotatably provided at a position facing the fixing roller via the fixing belt. In a belt fixing device having a pressure roller that forms a fixing nip portion therebetween,
A support roller that is disposed upstream of the fixing nip portion in the sheet conveying direction and between the heating roller and the fixing roller and around which the fixing belt is wound;
The fixing roller has a drum shape that is thick at the center and thin at both ends with respect to the rotation center line, and the pressure roller has a drum shape that is thin at the center and thick at both ends with respect to the rotation center line. A belt fixing device. The belt fixing device according to claim 1.
The belt fixing device, wherein the pressure roller has an on-axis hardness larger than that of the fixing roller. The belt fixing device according to claim 1 or 2,
The belt fixing device, wherein the fixing roller has an amount of protrusion from the end portion to the center portion larger than a retraction amount from the end portion of the pressure roller to the center portion. In the belt fixing device according to claim 1, 2, or 3,
The belt fixing device according to claim 1, wherein the fixing roller has an amount of protrusion from the end portion to the central portion that is at least twice the amount of retraction from the end portion of the pressure roller to the central portion. In the belt fixing device according to any one of claims 1 to 4,
The belt fixing device, wherein the amount of retraction from the end of the pressure roller to the center is 0.06 mm to 0.15 mm. The belt fixing device according to any one of claims 1 to 5,
The belt fixing device, wherein the fixing roller is a sponge roller. The belt fixing device according to any one of claims 1 to 6,
The fixing belt has a base, the base is made of polyimide resin, and the thickness thereof is 150 μm or less. The belt fixing device according to any one of claims 1 to 7,
The fixing belt has an elastic layer, and the thickness of the elastic layer is 50 μm or more. The belt fixing device according to claim 8.
The belt fixing apparatus, wherein the fixing belt has a multilayer structure, and the elastic layer constitutes a surface layer or an intermediate layer of the belt. In an image forming apparatus for fixing an image formed with a developer to a recording material by a fixing device,
An image forming apparatus using the belt fixing device according to claim 1 as the fixing device.

Images