JP2006113238A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus mounted with a fixing device designed such that a transfer material is restrained from being wrapped round an external pressure roller or a fixing belt and, as a result, a curl is corrected and steadily recovered by preventing the curl from becoming large during transfer and eliminating the need to add a curl correcting means such as a decurler. <P>SOLUTION: The image forming apparatus includes a belt fixing device which has an endless fixing belt wound around a support pressure roller and a heating roller with a space in-between and the external pressure roller disposed opposite to the support pressure roller via the fixing belt, and which fixes an unfixed image on the transfer material while holding the transfer material between the external pressure roller and the fixing belt. The image forming apparatus is provided with a separating auxiliary means having a separation pawl disposed close to or in contact with the surface of the external pressure roller. A stable curled state is retained by a relational expression of time and a distance between the tip position of separation claw on the upstream side in the transfer material conveyance direction and the position of an exit on the downstream end of an area where the external pressure roller and the fixing belt hold the transfer material in a nipped state in the direction of the transfer material conveyance. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is equipped with a fixing device in which curling generated on the transfer material during fixing is suppressed, and winding around the external pressure roller or fixing belt is suppressed so that the fixed transfer material is stably recovered. The present invention relates to an image forming apparatus.

  As shown in Patent Document 1 and Patent Document 2, when fixing is performed by passing a transfer material between a nipped fixing roller and a pressure roller, curling is generated along the nip, which is provided downstream of the fixing unit. Attempts have been made to correct with decals. In addition, in order to obtain satisfactory performance in the POD market that is capable of high-speed heat-fixing processing, supports color images, and also supports various types of transfer materials used, Taking advantage of the flexibility of the fixing belt, an external pressure roller presses the fixing belt to form a wide nip.

In any case, since the paper as the transfer material is heated and pressed by the fixing belt and the external pressure roller for a considerable time during which the nip is applied, the paper as the transfer material after fixing is largely curled. There was a bug that would This is particularly true for thick paper used in POD.
JP-A-5-72937 Japanese Patent Laid-Open No. 10-231061

  The present invention solves the problems of the prior art as described above, prevents the curling during transfer from becoming large, and without providing a curling correction means such as a decurler, the transfer material can be an external pressure roller or a fixing belt. It is an object of the present invention to provide an image forming apparatus equipped with a fixing device that is restrained from being wound around the sheet, and consequently curls are corrected and stably recovered.

  This object is achieved by any one of the following technical means (1) to (3).

  (1) An endless fixing belt wound between a supporting pressure roller and a heating roller, and an external pressure roller provided through the fixing belt so as to face the supporting pressure roller. An image forming apparatus having a belt fixing device that fixes a non-fixed image on a transfer material by sandwiching a transfer material between a pressure roller and the fixing belt, and is arranged close to or in contact with the surface of the external pressure roller. Separation assisting means having a separation claw is provided, and the leading end position of the separation claw on the upstream side in the transfer material conveyance direction, the external pressure roller and the fixing belt nip the transfer material between them. An image forming apparatus characterized in that a relationship as shown in the following equation is provided between an exit position at a downstream end portion in the transfer material conveyance direction of an area.

−180t + 5.8 <h <−180t + 11.5
h = r (1-cos θ), t = rθ / L
here,
r: Roller radius (mm)
θ: The external pressure from the leading end of the separation claw upstream in the transfer material conveyance direction to the outlet of the transfer material conveyance direction downstream end in the region where the external pressure roller and the fixing belt sandwich the transfer material. Angle measured around the rotation axis of the roller (radians)
L: Transfer material conveyance speed (mm / s)
(2) In the image forming apparatus described in (1), the separation assisting unit includes an adjusting unit that changes the position of the separation claw in accordance with a change in the conveyance speed of the transfer material. apparatus.

  (3) The position change of the separation claw by the adjustment means is performed by the adjustment means rotating the separation auxiliary means around the rotation axis of the external pressure roller and fixing it to an appropriate position. The image forming apparatus according to item (2).

  A separation claw provided on the pressure roller is brought into contact with or brought close to a position corresponding to the linear velocity. If it is too close, it curls to the opposite side of the peripheral surface of the pressure roller, and if it is too far, it curls to the side along the pressure roller. When changing the linear velocity, it is necessary and desirable to change the nail position accordingly.

  According to the first aspect of the present invention, the degree of curling of the transfer material to be wound around the external heating roller or the fixing belt is reduced, and stable fixing and recovery of the transfer material can be easily performed. According to the second and third aspects of the present invention, the position of the separation assisting unit is adjusted in accordance with the change in the transfer material conveyance speed, and a stable mechanism that does not cause curling or wrapping caused thereby. Image forming apparatus can be obtained.

  Embodiments of the present invention will be described below. The description in this column does not limit the technical scope of the claims or the meaning of terms. In addition, the following assertive description in the embodiment of the present invention shows the best mode, and does not limit the meaning or technical scope of the terms of the present invention.

  FIG. 1 is a schematic configuration diagram showing a color image forming apparatus as an embodiment of the image forming apparatus of the present invention.

  This image forming apparatus 100 is called a tandem full-color image forming apparatus. A plurality of image forming units 10Y, 10M, 10C, and 10K, and an endless belt-shaped intermediate transfer unit 7 as an intermediate transfer unit. And a sheet feeding / conveying means 21 and a belt fixing device 24. A document image reading device SC is disposed on the upper part of the main body A of the image forming apparatus.

  The image forming unit 10Y that forms a yellow image includes a drum-shaped photoconductor 1Y, a charging device 2Y disposed around the photoconductor 1Y, an image exposure unit 3Y, a developing unit 4Y, and a primary transfer unit as a primary transfer unit. It has a roller 5Y and a cleaning means 6Y. The image forming unit 10M that forms a magenta image includes a drum-shaped photoconductor 1M, a charging device 2M disposed around the photoconductor 1M, an image exposure unit 3M, a developing unit 4M, and a primary transfer as a primary transfer unit. It has a roller 5M and a cleaning means 6M. The image forming unit 10C for forming a cyan image includes a drum-shaped photoreceptor 1C, a charging device 2C disposed around the photoreceptor 1C, an image exposure unit 3C, a developing unit 4C, and a primary transfer unit as a primary transfer unit. It has a roller 5C and a cleaning means 6C. The image forming unit 10K that forms a black image includes a drum-shaped photoconductor 1K, a charging device 2K disposed around the photoconductor 1K, an image exposure unit 3K, a developing device 4K, and a primary transfer roller 5K as a primary transfer unit. And a cleaning means 6K.

  An endless belt-like intermediate transfer body unit 7 as an intermediate transfer body unit is wound around a plurality of rollers and is rotatably supported, and is an endless belt-like intermediate transfer body 70 as a semiconductive endless belt-like intermediate transfer body. Have

  The images of the respective colors formed by the image forming units 10Y, 10M, 10C, and 10K are sequentially transferred and synthesized on the rotating endless belt-shaped intermediate transfer body 70 by the primary transfer rollers 5Y, 5M, 5C, and 5K. A color image is formed. A transfer material P such as a sheet as a recording medium accommodated in the sheet feeding cassette 20 is fed by a sheet feeding means 21, passes through a plurality of intermediate rollers 22 A, 22 B, 22 C, 22 D, and a registration roller 23, and is subjected to secondary transfer. The image is conveyed to a secondary transfer roller 5A as a means, and the color image is collectively transferred onto the transfer material P. The transfer material P onto which the color image has been transferred is fixed by the belt fixing device 24, is sandwiched between the discharge rollers 25, and is placed on the discharge tray 26 outside the apparatus.

  On the other hand, after the color image is transferred to the transfer material P by the secondary transfer roller 5A as the secondary transfer means, the residual toner is removed by the cleaning means 6A from the endless belt-shaped intermediate transfer body 70 from which the transfer material P is separated by curvature. The

  During the image forming process, the primary transfer roller 5K is always in pressure contact with the photoreceptor 1K. The other primary transfer rollers 5Y, 5M, and 5C are pressed against the corresponding photoreceptors 1Y, 1M, and 1C, respectively, only during color image formation.

  The secondary transfer roller 5A comes into pressure contact with the endless belt-shaped intermediate transfer body 70 only when the transfer material P passes through the secondary transfer roller 5A.

  Further, the housing 8 can be pulled out from the apparatus main body A through the support rails 82L and 82R.

  The housing 8 includes image forming units 10Y, 10M, 10C, and 10K and an endless belt-shaped intermediate transfer body unit 7.

  The image forming units 10Y, 10M, 10C, and 10K are arranged in tandem in the vertical direction. An endless belt-shaped intermediate transfer body unit 7 is disposed on the left side of the photoreceptors 1Y, 1M, 1C, and 1K in the figure. The endless belt-shaped intermediate transfer body unit 7 includes an endless belt-shaped intermediate transfer body 70 that can be rotated by winding rollers 71, 72, 73, 74, 76, and 77, primary transfer rollers 5Y, 5M, 5C, and 5K, and cleaning. Means 6A.

  The image forming units 10Y, 10M, 10C, and 10K and the endless belt-shaped intermediate transfer body unit 7 are integrally pulled out from the main body A by the drawer operation of the housing 8.

  In this way, a toner image is formed on the photoreceptors 1Y, 1M, 1C, and 1K by charging, exposure, and development, and the toner images of the respective colors are primarily transferred and superimposed on the endless belt-shaped intermediate transfer body 70, which are collectively collected. Then, the toner image is secondarily transferred to the transfer material P, and fixed and fixed by pressure and heating by the belt fixing device 24. The photoreceptors 1Y, 1M, 1C, and 1K after the toner image is transferred to the endless belt-shaped intermediate transfer body 70 are the residual toners remaining on the photoreceptors at the time of transfer by the cleaning units 6Y, 6M, 6C, and 6K. After cleaning, the charging, exposure and development cycle described above is entered, and the next image formation is performed.

  Next, the belt fixing device 24, which is a feature of the present invention, will be described in detail with reference to the front view of the belt fixing device in FIG. 2 in addition to FIG.

  The belt fixing device 24 winds an endless fixing belt 242 formed by molding a metal base or a heat-resistant resin base and silicon rubber into a belt shape between a heating roller 241 having a built-in heater and a supporting pressure roller 243, and fixing the belt. By supporting and conveying the belt 242, the fixing belt 242 and the transfer material P are sandwiched in a nip shape between the support pressure roller 243 and the external pressure roller 246 opposite to the support pressure roller 243, and the transfer material P is added. The fixing belt 242 is supported and conveyed by driving rotation of the external pressure roller 246 and / or the support pressure roller 243. Further, an external heating roller 247 can be provided on the external pressure roller 246 in order to cope with a large heat supply amount necessary for high productivity as required. If necessary, a cleaning roller 244 may be provided to remove dirt attached to the fixing belt 242 when a jam occurs.

  The heating roller 241 is provided with two halogen lamps 245 having different light distributions as shown in FIG. 2 in order to cope with sheets of different sizes of transfer materials. Of course, a halogen lamp 245 may be further added to cope with higher productivity.

  Now, the transfer material P is heated and pressed at the nip portion and discharged from the nip outlet, but on the downstream side of the nip outlet, the separation claw of the separation auxiliary means 250 that contacts the surface of the external pressure roller 246. 250A is installed, and is applied to the external pressure roller 246 with a predetermined force (in this embodiment, 2 N / m. Generally, 10 N / m or less is suitable for minimizing scratches on the roller). It touches. Without this separation claw 250A, the paper as the transfer material P deformed along the fixing nip shape winds around the external pressure roller 246 and causes paper jams.

  The inventor has found through experiments that the curling method changes depending on the distance from the exit of the end of the nip downstream side of the transfer material P to the separation pawl 250A.

  In the belt fixing device 24 to which the present invention is applied, in order to reliably separate the transfer material P from the fixing belt 242 at the main pressure nip, the configuration is such that an upward convex nip is formed. Is discharged from the outlet at the downstream end of the fixing nip in an upwardly convex state. Qualitatively, when the paper is bent upward by the separation claw 250A immediately after coming out of the upward convex nip, the paper is deformed while being flexible by heating, and becomes downward convex. After discharging from the nip outlet, the upward convex nip is extended. In this way, if it is peeled off after being cooled to some extent along the external pressure roller, it is thought that it will be convex upward in the form of leaving its shape. This experimental result is considered to indicate that there is an appropriate value between the distance and time from the nip outlet to the tip position of the separation claw 250A, the amount of bending of the transfer material P at that time, and the cooling state at that time. It is done. In other words, it is necessary to peel off in an appropriate cooling state (≈cooling time) after discharging from the nip outlet.

  In the belt fixing device 24 of the image forming apparatus 100, the inventor is an endless belt having an inner diameter of 80 mm, in which a base is coated with a PI of 70 μm, a 200 μm Si rubber layer, and a 30 μm PFA release layer. The support pressure roller 243 is a 45 mm outer diameter roller in which a 6 mm Si rubber inner layer and a 4 mm Si sponge outer layer are lined on an iron core, and the heating roller 241 is an aluminum pipe having an outer diameter of 50 mm and a wall thickness of 2 mm. The outer pressure roller 246 is a roller in which a 3 mm Si rubber layer and a 30 μm PFA release layer are lined and coated on an aluminum pipe, and the external heating roller 247 has an outer diameter. 25mm, 2mm thick aluminum pipe coated with 20μm PFA release layer Ri, the cleaning roller 244 and the experiment was set to be the aluminum roller having an outer diameter of 20 mm.

In this experiment, Oji Paper's electrophotographic coated paper POD 100 g / m ² (A4 size) having the largest curl amount in the preliminary experiment was used.

  The fixing load (nip load) is 900 N / 370 mm width, the fixing belt set temperature is 195 ° C., the external pressure roller set temperature is 170 ° C., the external heating roller set temperature is 210 ° C., and the fixing belt tension is 50 N. The laboratory environmental conditions were 25 ° C. and 30-50% RH.

  In this way, the present inventor changes the diameter of the external pressure roller to several values, changes the tip position of the separation claw 250A and the transfer speed of the transfer material P in various ways, and curls the paper as the transfer material P. Was measured. In this measurement method, the paper after fixing is placed on a flat surface in a downward convex state, and the heights of the four corners are measured. The paper of the upward convex curl is represented by inverting the polarity of the measured value. Then, the height t from the nip exit to the separation claw 250A is the vertical axis, and the time t from when the paper as the transfer material P leaves the nip until it is peeled off at the position of the separation claw 250A FIG. 4 is a graph in which the curl amount of the transfer material P corresponding to each of h and t is measured with r = rθ / L as the horizontal axis, and the curl state is plotted in a graph. That is, it is a diagram showing the distribution state of the curl of the transfer material in the relational area between the distance from the nip to the position of the separation claw and time. The table shows the results obtained by measuring the curl state of the transfer material P by changing the radius of the external pressure roller corresponding to h and t, the linear velocity thereof, and the tip position of the separation claw 250A. Is shown in Table 1.

  Where r: radius of external pressure roller (mm), θ: angle (unit radians) measured from the nip outlet to the tip of separation claw 250A around the rotation axis of external pressure roller 246, L: linear velocity (mm) / S).

  In addition, the curled state was evaluated as “◯” when the measured value of the curl amount of the A4-sized transfer material P was less than 10 mm, “10 mm or more”, “upwardly convex” ×× 10 mm or more, and “downward” as Δ. This is because a paper jam (jam) may occur in the conveyance path after fixing when the curl amount exceeds 10 mm regardless of whether it is upward or downward.

FIG. 4 is a graph in which the curl amount is measured for each value when h and t are changed, and the three curl states classified according to the measured values shown in Table 1 are plotted. As a result, the lower convex curl exceeds 10 mm below the line A represented by the equation h = −180t + 5.8, and the upward convex curl above the line B represented by the equation h = −180t + 11.5. It was found that the paper discharge path and the reverse path after fixing curl easily.
Therefore,
−180t + 5.8 <h <−180t + 11.5
By selecting the set value so as to satisfy the above, the curl amount can be suppressed to a range that does not cause a practical problem (a range represented by a circle in FIG. 4 and Table 1).

  In the example, as shown in Table 1 and FIG. 4, for example, by setting r = 25 mm, θ = 22 degrees (22π / 180 radians), and L = 300 mm / s, the curl amount is good within 5 mm. Got.

  When the linear velocity is changed corresponding to the glossiness change or the paper thickness change, it is desirable to change the position of the separation claw 250A according to the linear velocity. As shown in the front sectional view of FIG. 3, the position of the separation claw 250A is changed by changing the frame 251 of the separation auxiliary means 250 having the separation claw 250A around the rotation shaft 246S of the external pressure roller 246 to the branch frame 254. At the same time, by rotating the spring 255 against the bias of the spring 255 and adjusting the adjusting screw 258 of the adjusting means 257, the mechanism can be realized with a highly accurate and simplified mechanism. The separation claw is biased by the spring 253 in the frame 251 and rotates around the pin 251A so as to lightly contact the external pressure roller surface with a predetermined pressing force. Further, in the case where the contact is stopped without contacting, the object can be achieved by turning the eccentric pin 252 to an appropriate position. Of course, if a known motor or a driving device comprising its control circuit is added to the adjusting means 257, it can be automatically adjusted by a command from the control unit of the image forming apparatus 100.

  The paper as the transfer material P holding the toner image conveyed to the fixing area by a paper feed guide or the like and the fixing belt 242 are sandwiched between the external pressure roller 246 and the supporting pressure roller 243 wound around the fixing belt. And pressurized. In this way, the main pressure nip formed between the pressure rollers is pressed and heated. As described above, the toner is fixed to the paper by the heat of the fixing belt 242 and the pressure by the pressure rollers 243 and 246. Since the rubber is brought into contact with the toner layer through rubber or a very thin releasable layer, the rubber deforms and follows the unevenness of the paper or toner layer, uniformly contacts, and has no uneven gloss. Uniform fixing is performed, and the toner image has an appropriate gloss. After fixing, the paper separated from the external pressure roller with the assistance of the separation claw is discharged and placed in a substantially flat shape by setting the appropriate position.

  In this embodiment, the claw is brought into contact with the external pressure roller, but it goes without saying that the same setting is effective even when the rollers are arranged close to each other in order to avoid scratches on the roller surface.

  According to the present invention, an image forming apparatus including a fixing device that achieves both separation performance and paper flatness is provided.

1 is a schematic configuration diagram illustrating a color image forming apparatus as an embodiment of an image forming apparatus of the present invention. It is a front sectional view showing an example of a belt fixing device used in the present invention. It is a front sectional view showing a separation claw and its position adjusting means in the separation auxiliary means of the belt fixing device used in the present invention. FIG. 6 is a diagram showing a distribution state of the magnitude of curl of a transfer material in an area related to a distance and a time from a nip to a position of a separation claw.

Explanation of symbols

1Y, 1M, 1C, 1K Photoconductor 24 Belt fixing device 100 Image forming device 241 Heating roller 242 Fixing belt 243 Supporting pressure roller 244 Cleaning roller 245 Halogen lamp 246 External pressure roller 246S Rotating shaft 247 External heating roller 250 Separation assisting means 250A Separation claw 251 Frame 252 Eccentric pin 253, 255 Spring 254 Branch frame P Transfer material

Claims (3)

An endless fixing belt wound between a supporting pressure roller and a heating roller, and an external pressure roller provided through the fixing belt so as to face the supporting pressure roller, An image forming apparatus having a belt fixing device that fixes a non-fixed image on a transfer material by sandwiching a transfer material between the fixing belts, and is disposed close to or in contact with the surface of the external pressure roller. Separation assisting means having a separation claw is disposed, and the transfer of the separation claw on the upstream end position in the transfer material conveyance direction, and the region where the external pressure roller and the fixing belt nip the transfer material and nip the transfer material An image forming apparatus characterized in that a relationship as shown in the following equation is provided between the outlet position at the downstream end portion in the material conveying direction.
−180t + 5.8 <h <−180t + 11.5
h = r (1-cos θ), t = rθ / L
here,
r: Roller radius (mm)
θ: The external pressure from the leading end of the separation claw upstream in the transfer material conveyance direction to the outlet of the transfer material conveyance direction downstream end in the region where the external pressure roller and the fixing belt sandwich the transfer material. Angle measured around the rotation axis of the roller (radians)
L: Transfer material conveyance speed (mm / s) The image forming apparatus according to claim 1, wherein the separation assisting unit includes an adjusting unit that changes a position of the separation claw according to a change in a conveyance speed of the transfer material. 3. The position change of the separation claw by the adjustment means is performed by the adjustment means rotating the separation auxiliary means around an axis of rotation of the external pressure roller and fixing it to an appropriate position. The image forming apparatus described in 1.

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