JP2002296937A - Belt fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a belt fixing device which does not cause image break due to the rubbing of an image because recording material is prevented from being dropped and it does not come into contact with a fixing belt even when the latter half part of transfer paper is separated from a paper feeding roller and set free. SOLUTION: A fixing nip part 69 is formed by the fixing belt 61 wound round a fixing roller 63 and a pressure roller 62 press-contacting with the roller 63 via the belt 61, and the roller 63 is formed in drum shape that its center part 63c is thick and its both ends 63a and 63b are thin with reference to its rotation center line 100, and the roller 62 is formed in drum shape that its center part 62c is thin and its both ends 62a and 62b are thick with reference to its rotation center line 101.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field 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, various printers, and a multifunction machine thereof, and more particularly to a fixing roller and a pressure roller constituting the belt fixing device. Related to various shapes.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. 6-3245886 discloses that
By forming the pressure roller in the shape of a drum and the fixing roller in the shape of a drum, the effects on recording materials such as wavy, streaks, reverse curls, and wrinkles, which tend to occur during transfer, are greatly improved. There has been proposed a fixing device in which image quality is improved without causing an increase in cost, a decrease in productivity, or the like. Japanese Patent Application Laid-Open No. 6-301306 discloses a configuration in which a roller having a narrow central portion and a thick end portion along the rotation axis direction is used as a pressure roller or a fixing roller, and a fixing roller is arranged along the rotation axis. There has been proposed a fixing device having a configuration in which the pressure roller is formed to have the same thickness, and the pressure roller has a shape in which the center portion is narrow along the rotation axis and the both ends are thick.

[0003]

The technique disclosed in the above-mentioned publication, in particular, Japanese Patent Laid-Open Publication No. Hei 6-3245886, has a construction in which the heat of a heating element is applied to a recording material through a heat-resistant film. Although there is a description that it may be used for a heat fixing device, a so-called belt fixing device, a new technical problem when used for a belt fixing device is not recognized. That is, in a belt fixing device, particularly a device using a method in which a fixing belt is brought close to or wound around a fixing nip formed by a fixing roller and a pressure roller, the width of the fixing nip is smaller than that of the conventional roller fixing. Although it has the advantage that it can be taken large and the size of the apparatus can be reduced, there is a serious problem that the recording material comes into contact with the fixing belt just before reaching the fixing nip and the image is rubbed, and the image is destroyed. . Particularly when the recording material is conveyed upward from below, if the trailing edge of the recording material is free through the roller having a re-feeding action, the recording material hangs down with its leading end being pinched by the fixing nip portion, Such a phenomenon occurs remarkably. The present invention is directed to a belt fixing method that does not cause the recording material to hang down, does not contact the fixing belt, and does not cause image destruction due to image rubbing, even when the rear end side of the recording material is free before entering the fixing device. It is an object to provide an apparatus and an image forming apparatus.

[0004]

In order to solve the above-mentioned problems, according to the first aspect, a rotatable fixing roller around which a fixing belt is wound, and a rotatable fixing roller at a position opposed to the fixing roller via the fixing belt. A pressure roller that forms a fixing nip portion between the fixing roller and the fixing belt by being pressed against the fixing roller, and the fixing roller is thick at the center and narrow at both ends with respect to the rotation center line. There has been proposed a belt fixing device having a drum shape and a pressure roller in which a pressure roller has a drum shape in which a center portion is narrower and both ends are thicker with respect to a rotation center line thereof.

A second aspect of the present invention proposes a belt fixing device having the configuration according to the first aspect, wherein the on-axis hardness of the fixing roller is larger than the on-axis hardness of the pressure roller. Claim 3
A belt fixing device having the configuration according to claim 1 or 2, wherein the amount of protrusion from the end of the fixing roller to the center of the fixing roller is larger than the amount of retraction from the end of the pressure roller to the center thereof. is suggesting. In claim 4, claims 1 and 2
Or a belt fixing device having the configuration described in 3, wherein the amount of protrusion from the end of the fixing roller to the center is at least twice the amount of retraction from the end of the pressure roller to the center. .

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 to the center of the pressure roller is 0.06 mm to 0.15 mm. is suggesting.

A sixth aspect of the present invention proposes 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 provided the fixing belt according to any one of the first to sixth aspects, wherein a polyimide resin is used as a base material of the fixing belt, and a thickness of the fixing belt is set to 150.
A belt fixing device having a thickness of μm or less has been proposed. Claim 8 provides the configuration 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.
m is proposed. In a ninth aspect, there is proposed a belt fixing device having the configuration according to the eighth aspect, wherein the fixing belt has a multilayer structure, and a surface layer or an intermediate layer thereof is formed of an elastic layer.

According to a tenth aspect, in an image forming apparatus for fixing an image formed with a developer to a recording material by a fixing device, the belt fixing device according to any one of the first to ninth aspects is used as a fixing device. Proposed image forming apparatus.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an electrophotographic color printer (hereinafter, referred to as a color printer) as 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 is a photoconductor unit 1 having a photoconductor belt 11 as an image carrier.
0, a writing optical unit 20, a developing unit 30, an intermediate transfer unit 40, a secondary transfer unit 50, a fixing unit 60, a double-sided printing reversing unit 70, and the like. In a color printer, Black: black (hereinafter, referred to as Bk), Cyan: cyan (hereinafter, referred to as C), Mage
nta: Magenta (hereinafter referred to as M), Yellow:
A yellow (hereinafter, referred to as Y) color image is sequentially visualized on the photoreceptor belt 11, and these are superimposed to form a final four-color full-color image.
The image is fixed thereon by the fixing unit 60.

The photoreceptor belt 11 rotates clockwise as indicated by arrow A (hereinafter referred to as "A direction").
A photoconductor cleaning device 12, a charging roller 13 as a charging member, a selected developing device of the developing unit 30, an intermediate transfer belt 41 of the intermediate transfer unit 40, and the like are arranged. The photoreceptor belt 11 is stretched between a driving roller 14, a primary transfer opposing 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 seam is used for the photoreceptor 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 an image is formed avoiding the joint.

The writing optical unit 20 converts 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 emission drive control unit (not shown), a polygon mirror 22, three reflection mirrors 23a, 23b, and 23c.

The developing unit 30 includes a Bk developing device 31K,
C developing device 31C, M developing device 31M, Y developing device 31Y,
Each developing unit is constituted by a contacting / separating mechanism (not shown) for moving the developing unit in the left-right direction in the drawing to make contact with / separate from the photosensitive belt 11. Developing units 31K, 31C, 31M, and 31Y are developer sleeves 32K, 32C, and 32M, respectively, each of which rotates with a developer carried thereon to develop an electrostatic latent image on the surface of the photoreceptor belt 11. , 32Y, developer paddles 33K, 33C, 33M, and 33Y serving as stirring members that rotate to draw up and agitate the developer, and developer storage cases 34K, 34C, and 34 that store the developer.
M, 34Y and the like.

These developer storage cases 34K, 34C,
34M and 34Y contain a one-component developer composed of toner of each color as a developer. In this embodiment, a developing device 31K containing black toner, a C developing device 31C containing cyan toner, an M developing device 31M containing magenta toner, and a Y developing device 31Y containing yellow toner are arranged in this order from the lower side of the printer main body 1A. Are arranged. The toner in the developing units 31K, 31C, 31M, and 31Y is charged to a predetermined polarity. Developing sleeves 32K, 32C,
A developing bias is applied to 32M and 32Y by a developing bias power supply (not shown), whereby the developing sleeves 32K, 32C, 32M and 32Y are biased to a predetermined potential with respect to the photosensitive belt 11. The contact / separation mechanism is driven by driving means such as a motor (not shown) from developing devices 31K and 31K.
When an electromagnetic clutch (not shown) for transmitting the drive to C, 31M, and 31Y is turned on, the driving force moves the developer accommodating cases 34K, 34C, 34M, and 34Y to the photosensitive belt 11 side (the right side in the drawing). It is made to let. At the time of development, the developing devices 31K, 31C, 31M, 31
Any one selected from Y moves and comes into contact with the photoreceptor belt 11. On the other hand, when the electromagnetic clutch (not shown) is turned off to cancel the drive transmission, the photosensitive belt 11
Is moved in the direction away from the photoreceptor belt 11 (left side in the figure).

In the standby state of the color printer, the developing unit 30 is connected to any of the developing units 31K, 31C, 31M,
31Y is also set at a position separated from the photoreceptor belt 11, and when a printing operation is started, light writing by a laser beam based on color image data and formation of an electrostatic latent image are started (hereinafter referred to as Bk image data). The electrostatic latent image is called a Bk electrostatic latent image, and the same applies to C, M, and Y). In the color printer, before the front end of the electrostatic latent image arrives at the Bk development position to enable development from the front end of the Bk electrostatic latent image,
The rotation of the Bk developing sleeve 32K is started to develop the Bk electrostatic latent image with the Bk toner. Thereafter, the developing operation of the Bk electrostatic latent image area is continued.
At the point in time when the developer passes the developing position, the Bk developing device 31K separates from the photosensitive belt 11, and the developing device of the next color immediately contacts the photosensitive belt 11. This is completed at least before the leading end of the electrostatic latent image based on the next image data reaches the developing position.

The intermediate transfer unit 40 comprises an intermediate transfer belt 41, a belt cleaning device 42, a position detecting sensor 43 and the like. The intermediate transfer belt 41 includes a driving roller 44, a primary transfer roller 45, and a secondary transfer facing roller 4.
6, is stretched around the cleaning opposing roller 47 and the tension roller 48, and is rotationally controlled in a counterclockwise direction indicated by an arrow B by a drive motor (not shown). A plurality of position detection marks (not shown) are provided in the non-image forming area at the end of the intermediate transfer belt 41, and one of these position detection marks (the position detection The position detection mark 43 that has passed the sensor 43 first) 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. In the belt cleaning device 42, while the first color Bk image is being transferred to the intermediate transfer belt 41, and while the second, third, and fourth color images are being transferred to the intermediate transfer belt 41, the brush contact / separation mechanism is used. Cleaning brush 42 from the surface of intermediate transfer belt 41
a, so that the cleaning brush 42a is brought into contact with 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.

Paper P is stored in a cassette 80 disposed at the lower portion of the printer main body 1A.
Paper is fed and conveyed in the direction of the pair of registration rollers 82 by 1a, 81b and 81c. On the right side of the color printer 1, a manual feed tray 83 for manually feeding OHP paper or thick paper as a recording material is provided.

The secondary transfer unit 50 is constituted by a swing mechanism (not shown) having a clutch and 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 used for the sheet P
Is moved from the separated position to the contact position by the swing mechanism in accordance with the timing at which the image reaches the transfer position. In the secondary transfer unit 50, the sheet P and the intermediate transfer belt 41 are fixed at a transfer section formed between the secondary transfer roller 51 and the intermediate transfer belt 41 by the secondary transfer roller 51 and the secondary transfer opposing roller 46. It comes in contact with the pressure of. The secondary transfer roller 51 is moved by a positioning member (not shown) provided in the intermediate transfer unit 40 to the secondary transfer opposing roller 46.
And the positional accuracy of the parallelism is maintained. The contact pressure of the secondary transfer roller 51 with respect to the intermediate transfer belt 41 is made constant by a positioning roller (not shown) provided on the secondary transfer roller 51. The secondary transfer roller 51 is moved to the intermediate transfer belt 4
1 and a transfer bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 51 at the same time. P is transferred to P at once.

In the above configuration, each of the above units is provided so as to be easily detachable from the printer main body 1A. For example, in FIG.
In order to remove 0, the front cover (not shown) is opened, and the intermediate transfer unit 40 can be easily removed by sliding the intermediate transfer unit 40 from the back side to the front side.

In the color printer 1 having the above configuration, when the image forming cycle is started, first, the photosensitive belt 11
Is in the direction of arrow A, the intermediate transfer belt 41 is in the direction of arrow B,
It is rotated 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 a Bk toner image and a C toner image are formed on the photoreceptor belt 11 according to the detection timing of the position detection mark. , M toner image formation, and Y toner image formation, 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 in sequence, but this is changed according to the resistance characteristics of the intermediate transfer belt 41 and the like.

The Bk toner image is formed as follows. The charging roller 13 uniformly charges the photoreceptor belt 11 by an applied voltage of a power supply (not shown). Then, the laser light LD for writing performs exposure based on the Bk color image signal. When this exposure is carried out, the exposed portion of the photoreceptor belt 11 which is initially uniformly charged loses the charge proportional to the amount of exposure light, 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 a portion of the photoreceptor belt 11 where the charge remains, and a portion having no charge, that is, exposure The Bk toner is adsorbed to the portion thus formed, and a Bk toner image similar to the electrostatic latent image is formed.
Then, the Bk toner image formed on the photosensitive 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 opposing roller 15, and the primary transfer roller 45 has a Bk toner image and The Bk toner image is transferred to the intermediate transfer belt 41 by applying a reverse polarity bias.

A small amount of untransferred residual toner on the photoreceptor belt 11 is cleaned by the photoreceptor cleaning device 12 in preparation for reusing the photoreceptor belt 11. The collected toner is stored in a waste toner tank (not shown) via a collection pipe.

On the photosensitive belt 11 side, the process proceeds to the C image forming step after the Bk image forming step, and the position detecting sensor 4
In accordance with the detection timing of No. 3, writing by the laser light LD based on the C image data is performed, and a C electrostatic latent image is formed. Then, after the trailing end of the previous Bk electrostatic latent image has passed and before the leading end of the C electrostatic latent image has arrived, the Bk developing device retreats from the developing position, and the C developing device C moves to the developing position. And 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 of the C electrostatic latent image passes, the C developing device C is retracted from the developing position as in the case of the Bk developing device B. Then, the next M developing device M is moved to the developing position. This is also completed before the leading end of the next M electrostatic latent image reaches the developing position. The M and Y image forming processes are the same as the processes of Bk and C described above, since the operations of forming and developing the electrostatic latent image are the same as those of the processes of Bk and C described above. The intermediate transfer belt 41 includes the photosensitive belt 1
The toner images of Bk, C, M, and Y which are sequentially formed on the same color are sequentially aligned on the same surface to form a four-color toner image. In the next secondary transfer process, the four-color toner image is formed. Are collectively transferred to transfer paper.

When the image forming operation is started, the paper P
Is fed from either the cassette 80 or the manual feed tray 83 and is waiting at the nip of the pair of registration rollers 82. Then, the intermediate transfer belt 41 is attached to the secondary transfer roller 51.
When the top of the four-color superimposed toner image approaches, the registration roller pair 82 is driven such that the top of the paper P coincides with the top of this toner image, and the registration between the paper P and the toner image is performed. . Then, the sheet P is superimposed on 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
Transcribed above.

The sheet P on which the four-color superimposed toner image is collectively transferred from the intermediate transfer belt 41 is conveyed to a fixing unit 60, and the toner is transferred to a fixing nip 69 between a fixing belt 61 controlled at a predetermined temperature and a pressing roller 62. The image is fused and fixed by heat and pressure, sent out of the printer main body 1A (in the direction of arrow C), and stacked face-down on a paper discharge tray 84 formed on the upper part of the printer main body 1A to copy a full-color image. obtain.

When performing double-sided printing, the fixing unit 6
The paper P passing through 0 is guided in the direction of arrow D by the double-side switching claw 85 and sent to the double-sided printing reversing unit 70. After the trailing edge of the sheet has passed the reversing switching claw 71, the reversing roller pair 7
2 stops, and the paper P also stops. Then, the reversing roller pair 72 starts reverse rotation after a certain blank time, and the paper P
Begins switchback. At this time, the reversing switching claw 71 is switched, and the sheet P is guided in the direction of arrow E and sent to the registration roller pair 82. The sheet P sent to the registration roller pair 82 is turned upside down with the registration roller pair 82
Wait at the nip. Then, the registration roller pair 82 is driven at a predetermined timing, and the sheet P is sent to the secondary transfer position, where the four-color superimposed toner image is collectively transferred from the intermediate transfer belt 41, and then the toner image is fused by the fixing unit 60. The image is fixed and sent out of the printer main body 1A.

The surface of the photoreceptor belt 11 after the primary transfer is
The photosensitive member is cleaned by the photoreceptor cleaning device 12 and is uniformly discharged by a discharge lamp (not shown). The surface of the intermediate transfer belt 41 after the transfer of the toner image onto the sheet P is
Cleaning brush 42 of belt cleaning device 42
The cleaning is performed by pressing a 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 fused and fixed by the fixing unit 60 and sent out of the printer main body 1A.

FIG. 2 shows a fixing unit 6 according to the present invention.
0 will be described in detail. FIG. 2 is a diagram showing the 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, and a fixing roller 6 serving as a driving roller.
3. Heating roller 64 and supporting roller 65 which are driven rollers
It has. The fixing belt 61 includes a fixing roller 63 rotatably supported by a frame or the like (not shown).
It is wound around the heating roller 64 and the support roller 65 and stretched. 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 (not shown) or the like. 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. Halogen heaters 66 and 67 are provided as heat sources inside the pressure roller 62 and the heating roller 64, respectively. The halogen heater 66 controls the heating of the pressure roller 62, and the halogen heater 67 controls the heating of the fixing belt 61 such that the fixing belt 61 has a predetermined temperature.

A sheet P having an unfixed toner image T is conveyed from below to a fixing unit 60 along a guide plate 68 disposed in front of a fixing nip 69, and the fixing belt is controlled to a predetermined temperature. The toner image is fused and fixed in the fixing nip portion 69 of the pressing roller 61 and the pressing roller 62, and is sent out of the printer main body 1A as shown in FIG.

In the fixing unit 60, after the sheet P is conveyed to the fixing unit 60 and enters the fixing nip 69 formed between the fixing belt 61 and the pressure roller 62 controlled at a predetermined temperature, the fixing is started. , Trailing edge P of paper P
1 is a secondary transfer unit 5 for applying a conveying force to the paper P
Deviates from 0. Then, the rear end P1 of the paper P hangs down by its own weight as shown in FIG. 3, 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.

The shapes of the pressure roller 62 and the fixing roller 63, which are characteristic parts of the fixing unit 60, will be described with reference to FIG. The fixing roller 63 has a center portion 63c that is thicker with respect to a rotation center line 100 of a rotation shaft 630 that is provided so as to be integrally rotatable with the roller, and has both end portions 62a and 62c.
2b is formed in a thin drum shape. Pressure roller 62
Is a rotating shaft 62 provided so as to be able to rotate integrally with this roller.
Along the 0 rotation center line 101, the central portion 63c is formed in a thin drum shape with both ends 62a, 62b being thick. The paper P sandwiched between the drum-shaped fixing roller 63 and the drum-shaped pressure roller 62 is given a curling effect by the R shape generated by the drum shape and the drum shape. Kosi will be given. Therefore, the phenomenon that the trailing edge P1 of the sheet P is free and hangs down is eliminated, and the contact with the fixing belt 61 can be avoided.

Example 1 Next, an experiment was conducted by setting the axial hardness of the fixing roller 63 to 40 ° (Asker C) and increasing the axial hardness of the pressure roller 62 to more than 78 ° (Asker C). . By doing so, the shape of the paper P in the fixing nip portion 69 becomes closer to the shape of the pressure roller 62, the curl effect increases, and the destruction of the toner image T due to further rubbing of the paper surface can be prevented. It turns out that it can be done.

(Embodiment 2) The protrusion Y from the ends 63a and 63b of the drum-shaped fixing roller 63 to the center 63c is 0.3 mm, and the end 62 of the drum-shaped pressure roller 62 is formed.
An experiment was conducted by setting the amount of retraction (amount of knob) X from the a and 62b to the center portion 62c to 0.12 mm and making the amount larger than the amount of retraction X. By doing so, the shape of the paper P in the fixing nip portion 69 becomes closer to the shape of the pressure roller 62 even if the paper P is a small size, the curl effect is increased, and the toner is further rubbed by the paper surface. It has been found that the destruction of the image T can be prevented.

(Example 3) An experiment was conducted by setting the protrusion amount (taiko amount) Y of the fixing roller 63 to twice or more the retraction amount X of the pressure roller 62. By doing so, the shape of the sheet P in the fixing nip portion 69 becomes closer to the shape of the pressure roller 62 even if the sheet P is of a small size, and the destruction of the toner image T due to further rubbing of the sheet surface is prevented. It turns out that it can be prevented.

Example 4 An experiment was conducted by setting the amount of retraction X from the end diameter of the pressure roller 62 to 0.06 to 0.15 mm. It has been found that by setting the retraction amount X in this way, the destruction of the toner image T due to the rubbing of the paper surface can be further prevented.

Example 5 The fixing roller 63 was formed by 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 to prevent the rubbing of the image, and the heat insulation effect saves energy and shortens the rise time. became.

(Embodiment 6) FIG. 5 is a partially enlarged 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 a material of a base 61c, and the thickness thereof is 150 μm.
It was as follows. 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 portion 69 cannot be formed. This follows the shape of the pressure roller 62, so that destruction of the toner image T due to rubbing of the paper surface with the belt can be prevented. Surface layer 61a or intermediate layer 62b of fixing belt 61
Was composed of an elastic layer, and the layer thickness was set to 50 μm or more. By configuring the fixing belt 61 in this manner, the surface of the fixing belt 61 more closely conforms to the shape of the pressure roller 62, so that rubbing of an image can be prevented.

(Embodiment 7) An optimal 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 the base material, layer thickness of 90 μm Upper layer of the base material is composed of silicon (Si) rubber, layer thickness of 150 μm Pressure roller: 40 mm in diameter, surface layer of solid rubber of 1.5 mm thickness Configuration Knob amount X = 0.12 μm Roller hardness 78 ° (Asker C) Fixing roller: composed of sponge rubber having a diameter of 30 mm and a surface layer of 6 mm thick Tyco amount Y = 0.3 μm Roller hardness 40 ° (Asker C)

[0038]

According to the present invention, the fixing roller is formed in a drum shape having a central portion that is thicker with respect to the rotation center line and both end portions are thinner. Since both end portions are formed in a thick drum shape, when the recording material is positioned between the fixing belt and the pressure roller, the recording material is shaped like the drum shape and the drum shape to give a stiffness. For this reason, even if the trailing end of the recording material becomes free, the recording material does not violently or sag, so that the recording material does not come into contact with the fixing belt before fixing, and image rubbing can be prevented.

According to the present invention, by making the hardness of the fixing roller lower than that of the pressure roller, the recording material in the fixing nip portion becomes closer to the shape of the pressure roller, and the recording material is transferred to the fixing belt before fixing. Can be prevented.

According to the present invention, even when a small-sized recording material is used, recording can be performed in the fixing nip by making the protrusion amount, which is the amount of the fixing roller, larger than the retraction amount, which is the pinch amount of the pressure roller. The material approaches the shape of the pressure roller, and it is possible to prevent the image material from rubbing due to the contact of the recording material with the fixing belt before fixing.

According to the present invention, by using a sponge roller for the fixing roller, the fixing roller is easily deformed, so that the image rubbing caused by the contact of the recording material with the fixing belt before the fixing is eliminated, and the heat insulating effect is obtained. As a result, energy can be saved and the rise time can be reduced.

If the fixing belt sandwiched between the fixing roller and the pressure roller is hard, the shape of the fixing nip is not as intended. However, as in the present invention, the belt base is made of a polyimide resin having a layer thickness of 150 μm or less. Since the image also follows the shape of the pressure roller, it is possible to more reliably prevent image rubbing due to contact of the recording material with the fixing belt before fixing.

According to the present invention, by forming the surface or the intermediate layer of the fixing belt as an elastic layer having a thickness of 50 μm or more, the surface of the fixing belt more easily follows the shape of the pressure roller. Image rubbing due to the contact of the recording material with the fixing belt can be more reliably prevented.

According to the present invention, by defining the amount of retraction of the pressure roller, it is possible to more reliably prevent image rubbing due to contact of the recording material with the fixing belt before fixing.

According to the present invention, in the belt fixing device, the image rubbing due to the contact of the recording material with the fixing belt before fixing is prevented, so that the image quality can be improved.

[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 illustrating a configuration of a belt fixing device that is a main part of the present invention.

FIG. 3 is an enlarged view illustrating 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 illustrating a configuration of a fixing belt according to the present invention.

[Explanation of symbols]

 Reference Signs List 60 belt fixing device 61 fixing belt 61c substrate of fixing belt 61a surface layer (elastic layer) of fixing belt 61b intermediate layer of fixing belt (elastic placement) 62 pressure rollers 62a, 62b both ends 62c central part 63 fixing rollers 63a, 63b both ends Part 63c Central part 100, 101 Center of rotation X Retracted amount Y Projected amount

Claims (10)

[Claims] A fixing roller that is rotatable around a fixing belt, and is rotatably provided at a position facing the fixing roller via the fixing belt; And a pressure roller forming a fixing nip portion between the fixing roller and the pressing roller, wherein the fixing roller has a drum shape in which a center part is thick and both ends are thin with respect to a rotation center line thereof, and A belt fixing device, wherein the roller has a drum shape in which a center portion is thinner and both ends are thicker with respect to a rotation center line thereof. 2. The belt fixing device according to claim 1, wherein the axial hardness of the fixing roller is greater than the axial hardness of the pressure roller. 3. The belt fixing device according to claim 1, wherein the fixing roller has an amount of protrusion from an end to a center thereof.
The belt fixing device according to claim 1, wherein the amount of the pressure roller is larger than the amount of retraction from the end to the center. 4. The belt fixing device according to claim 1, wherein the fixing roller has an amount of protrusion from an end to a center thereof.
2. The belt fixing device according to claim 1, wherein an amount of retraction of the pressure roller from an end portion to a center portion is twice or more. 5. The belt fixing device according to claim 1, wherein an amount of retraction of the pressure roller from an end portion to a center portion is equal to 0.
A belt fixing device having a thickness of from 06 mm to 0.15 mm. 6. The belt fixing device according to claim 1, wherein the fixing roller is a sponge roller. 7. The belt fixing device according to claim 1, wherein the fixing belt has a base, the base material is a polyimide resin, and the thickness is 150 μm or less. A belt fixing device. 8. The belt fixing device according to claim 1, wherein the fixing belt has an elastic layer, and the thickness of the elastic layer is 5
A belt fixing device having a thickness of 0 μm or more. 9. The belt fixing device according to claim 8, wherein the fixing belt has a multilayer structure, and the elastic layer forms a surface layer or an intermediate layer of the belt. 10. An image forming apparatus for fixing an image formed with a developer to a recording material by a fixing device, wherein the belt fixing device according to claim 1 is used as the fixing device. Characteristic image forming apparatus.