JP2019200442A - Fixing device and image forming apparatus - Google Patents

Abstract

To solve the problem in which: an attachment on a rotating body to be a cause of a defective image cannot be effectively removed.SOLUTION: In a fixing device comprising two rotating bodies 21 and 31 that are in contact with each other to form a nip part N and passing a recording medium having an image formed thereon through the nip part N to perform fixation of the image, the rotating bodies 21 and 31 are formed, at least at the nip part N, to have their outer diameter increasing or decreasing in a curved manner from the center part to an end part in the axial direction; the recording medium is passed through the nip part N while a sheer force having a circumferential direction component with a magnitude of 15 N or more and 25 N or less is generated between the rotating bodies 21 and 31.SELECTED DRAWING: Figure 12

Description

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

  In an electrophotographic image forming apparatus such as a printer or a copying machine, a toner image is recorded by passing a recording medium such as a sheet on which a toner image is formed through a nip portion between two rotating members that are in contact with each other. A fixing device for fixing on a medium is used.

  Basically, the toner (toner image) on the recording medium is fixed on the recording medium by being melted by heat applied from one or both of the rotating bodies. However, due to insufficient heat amount, excessive heat amount, or electrical action, all the toner may not adhere to the recording medium and may remain slightly attached to one or both of the rotating members. When such toner is fixed on the rotating body, the releasability of the toner with respect to the rotating body (the fixing property of the toner with respect to the recording medium) decreases at that portion. As a result, in the subsequent fixing process, the toner image is not fixed to the recording medium at the portion where the toner is fixed, and is adhered to the rotating body, so that the toner image on the rotating body is rotated with the rotation of the rotating body. An offset image is generated that is transferred onto the recording medium at a circumferential pitch.

  In addition, some of the recording media used in recent years contain a large amount of filler such as calcium carbonate. When such a recording medium is used, the filler tends to adhere to the rotating body. So-called filming, in which toner and its components adhere to the film as a starting point, is likely to occur. For this reason, particularly when such a recording medium is used, the reduction in the releasability of the toner with respect to the rotating body tends to be remarkable.

  For example, in Patent Document 1 (Japanese Patent Laid-Open No. 2002-40860), the transfer speed difference between the surfaces of the fixing member and the pressure member is changed before the transfer material reaches the fixing nip. A method of attaching is proposed.

  As another method, Patent Document 2 (Japanese Patent Laid-Open No. 2009-37078) proposes a method of installing a cleaning web and a cleaning roller for removing toner adhering to the surface of a pressure member.

  In the method described in Patent Document 1, the toner adhering to the surface of the pressure member is transferred to the fixing member and removed by making a difference in the moving speed between the surfaces of the fixing member and the pressure member. I can do it. However, the toner removing force (peeling force) obtained by the speed difference between the fixing member and the pressure member is insufficient for removing the fixed toner containing a large amount of paper powder (toner filler or the like), for example. Further, in this method, since the toner is removed before the transfer material reaches the fixing nip, there is a restriction that the toner cannot be removed while the transfer material passes through the fixing nip.

  On the other hand, in the method described in Patent Document 2, since the cleaning web and the cleaning roller are installed, there are problems that the cost is increased and the apparatus size is increased. Further, there is a problem that the toner collected by the cleaning roller is accumulated and solidified to generate abnormal noise, or the toner accumulated in a predetermined amount or more on the cleaning roller is melted to contaminate the recording medium.

  In order to solve the above-described problems, the present invention includes two rotating bodies that contact each other to form a nip portion, and fix the image by passing a recording medium on which an image is formed through the nip portion. The rotating body is formed such that at least in the nip portion, the outer diameter increases or decreases in a curved shape from the central side to the end side in the axial direction. The recording medium is allowed to pass through the nip portion in a state where a shearing force with a direction component of 15 N or more and 25 N or less is generated.

  According to the present invention, the recording medium is passed through the nip portion in a state in which a shearing force is generated between the rotating bodies so that the circumferential component has a magnitude of 15 N or more and 25 N or less. Adherent removal force (shearing force) can be sufficiently generated between the rotating bodies. As a result, deposits adhering to the surface of the rotating body can be transferred to the recording medium and reliably removed. In addition, the recording medium is less likely to be wrinkled, and a good image can be obtained. Further, according to the present invention, at least in the nip portion, the outer diameter of the rotating body is formed so as to increase or decrease in a curved shape from the central side to the end side in the axial direction. It is possible to generate shearing forces of different sizes over the range. This makes it possible to remove deposits more effectively due to the difference between these shear forces. In addition, according to the present invention, the deposit can be transferred to the recording medium and removed, so there is no need to separately install a cleaning means for removing the deposit on the rotating body. Further, since the adhering substance removing effect is exhibited every time the recording medium passes through the nip portion, the adhering substance can be frequently removed, and the accumulation of the adhering substance on the rotating body can be effectively suppressed. .

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating a schematic configuration of a fixing device according to an exemplary embodiment. FIG. 2 is a diagram illustrating a schematic configuration of a drive system of a fixing device according to the present embodiment. (A) and (b) are diagrams showing the state of occurrence of an offset image depending on the presence or absence of fixed toner on the fixing roller. It is a figure which shows the shearing force which arises between a fixing roller and a pressure roller. (A) and (b) are figures which show the example of the sliding bearing which supports a pressure roller. FIG. 4 is a diagram illustrating a state where fixed toner is removed from a fixing roller. It is a figure which shows a mode that fixed toner is removed from a pressure roller. It is a figure which shows the relationship between the magnitude | size of the circumferential direction component of a shear force, and the incidence rate of the defect image resulting from a fixed toner. FIG. 3 is a diagram illustrating an outer peripheral shape of a fixing roller according to the present embodiment. FIG. 2 is an enlarged view showing a part of the outer periphery of a fixing roller. It is a figure which shows the state which made the pressure roller contact the fixing roller, and was pressurized. It is a figure which shows schematic structure of a torque measuring device. It is a figure which shows the outer periphery shape of the fixing roller which concerns on other embodiment. FIG. 2 is an enlarged view showing a part of the outer periphery of a fixing roller. It is a figure which shows the state which made the pressure roller contact the fixing roller, and was pressurized. It is a figure which shows the outer periphery shape of the fixing roller which concerns on another embodiment. It is a figure which shows the outer periphery shape of the fixing roller which concerns on another embodiment. It is a figure which shows schematic structure of the other fixing apparatus which can apply this invention. It is a figure which shows schematic structure of another fixing device which can apply this invention. (A)-(d) is a figure which shows the variation of the shape of a nip formation member. (A) (b) is a figure which shows embodiment which provided the cleaning means. It is a figure which shows the outer periphery shape of the fixing roller which concerns on a comparative example.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each of the drawings for explaining the embodiments of the present invention, constituent elements such as members and components having the same function or shape are described once by giving the same reference numerals as much as possible. Then, the explanation is omitted.

(Schematic configuration of a color printer as an image forming apparatus)
As shown in FIG. 1, the image forming apparatus 1 of the present embodiment is a tandem color printer. Four bottles 102Y, 102M, 102C, and 102K corresponding to the respective colors (yellow, magenta, cyan, and black) are detachably (replaceable) installed in the bottle housing unit 101 above the image forming apparatus main body. Yes.

  An intermediate transfer unit 85 is disposed below the bottle housing portion 101. Image forming units 4Y, 4M, 4C, and 4K corresponding to the respective colors (yellow, magenta, cyan, and black) are arranged in parallel so as to face the intermediate transfer belt 78 of the intermediate transfer unit 85. Photosensitive drums 5Y, 5M, 5C, and 5K are disposed in the image forming units 4Y, 4M, 4C, and 4K, respectively.

  Further, around each of the photosensitive drums 5Y, 5M, 5C, and 5K, a charging unit 75, a developing unit 76, a cleaning unit 77, a charge eliminating unit, and the like are disposed. Then, an image forming process (charging process, exposure process, developing process, transfer process, cleaning process) is performed on each of the photoconductive drums 5Y, 5M, 5C, and 5K. An image of each color is formed on 5K. The photosensitive drums 5Y, 5M, 5C, and 5K are rotationally driven clockwise in FIG. 1 by a drive motor.

  Then, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K are uniformly charged at the position of the charging unit 75 (a charging process). Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the irradiation position of the laser light L emitted from the exposure unit 3, and electrostatic latent images corresponding to the respective colors are formed by exposure scanning at this position. (It is an exposure process.)

  Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach a position facing the developing unit 76, and the electrostatic latent image is developed at this position to form toner images of each color (development process). .) Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach positions facing the intermediate transfer belt 78 and the primary transfer bias rollers 79Y, 79M, 79C, and 79K, and the photosensitive drums 5Y, 5M are located at this position. The toner images on 5C and 5K are transferred onto the intermediate transfer belt 78 (this is a primary transfer process).

  At this time, a small amount of untransferred toner remains on the photosensitive drums 5Y, 5M, 5C, and 5K. Thereafter, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach a position facing the cleaning unit 77. At this position, the untransferred toner remaining on the photosensitive drums 5Y, 5M, 5C, and 5K is mechanically collected by the cleaning blade of the cleaning unit 77 (this is a cleaning process).

  Finally, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach a position facing the charge eliminating unit, and the residual potential on the photoconductive drums 5Y, 5M, 5C, and 5K is removed at this position. Thus, a series of image forming processes performed on the photosensitive drums 5Y, 5M, 5C, and 5K is completed.

  Thereafter, the toner images of the respective colors formed on the respective photosensitive drums through the developing process are transferred onto the intermediate transfer belt 78 in an overlapping manner. In this way, a color image is formed on the intermediate transfer belt 78.

  Here, the intermediate transfer unit 85 includes an intermediate transfer belt 78, four primary transfer bias rollers 79Y, 79M, 79C, and 79K, a secondary transfer backup roller 82, a cleaning backup roller 83, a tension roller 84, and an intermediate transfer cleaning unit 80. , Etc.

  The intermediate transfer belt 78 is stretched and supported by the three rollers 82 to 84 and is endlessly moved in the counterclockwise direction in FIG. The four primary transfer bias rollers 79Y, 79M, 79C, and 79K sandwich the intermediate transfer belt 78 with the photosensitive drums 5Y, 5M, 5C, and 5K, respectively, thereby forming primary transfer nips.

  Then, a transfer bias reverse to the polarity of the toner is applied to the primary transfer bias rollers 79Y, 79M, 79C, and 79K. The intermediate transfer belt 78 travels in the direction of the arrow and sequentially passes through the primary transfer nips of the primary transfer bias rollers 79Y, 79M, 79C, and 79K. In this way, the toner images of the respective colors on the photosensitive drums 5Y, 5M, 5C, and 5K are primarily transferred while being superimposed on the intermediate transfer belt 78.

  Thereafter, the intermediate transfer belt 78 onto which the toner images of the respective colors are transferred in an overlapping manner reaches a position facing the secondary transfer roller 89. At this position, the secondary transfer backup roller 82 sandwiches the intermediate transfer belt 78 between the secondary transfer roller 89 and forms a secondary transfer nip. The four color toner images formed on the intermediate transfer belt 78 are transferred onto the recording medium P conveyed to the position of the secondary transfer nip.

  At this time, untransferred toner that has not been transferred to the recording medium P remains on the intermediate transfer belt 78. Thereafter, the intermediate transfer belt 78 reaches the position of the intermediate transfer cleaning unit 80. At this position, the untransferred toner on the intermediate transfer belt 78 is collected.

  Thus, a series of transfer processes performed on the intermediate transfer belt 78 is completed. The above is the description of the configuration and operation of the image forming unit. Here, the recording medium P transported to the position of the secondary transfer nip is transported from the paper feed unit 12 disposed below the apparatus main body via the paper feed roller 97, the timing roller pair 98, and the like. Is.

  Specifically, a plurality of recording media P such as transfer paper are stored in the paper supply unit 12 in an overlapping manner. When the paper feed roller 97 is driven to rotate counterclockwise in FIG. 1, the uppermost recording medium P is fed toward the timing roller pair 98. The recording medium P transported to the timing roller pair 98 temporarily stops at the position of the roller nip of the timing roller pair 98 that has stopped rotating.

  Then, the timing roller pair 98 is rotationally driven in synchronization with the color image on the intermediate transfer belt 78, and the recording medium P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the recording medium P.

  Thereafter, the recording medium P on which the color image is transferred at the position of the secondary transfer nip is conveyed to the position of the fixing device 20. At this position, the color image transferred onto the surface of the intermediate transfer belt 78 by the heat and pressure from the fixing roller 21 as the fixing rotator and the pressure roller 31 as the pressure rotator is placed on the recording medium P. It is fixed.

  Thereafter, the recording medium P is discharged out of the apparatus through a pair of paper discharge rollers 99. The recording medium P discharged out of the apparatus by the discharge roller pair 99 is sequentially stacked on the stack unit 100 as an output image. Thus, a series of image forming processes in the image forming apparatus 1 is completed.

(Configuration of fixing device)
Next, the basic configuration of the above-described fixing device 20 will be described.
As shown in FIG. 2, the fixing device 20 includes two rotating bodies, that is, a fixing roller 21 and a pressure roller 31 that form a nip portion N in contact with each other. Inside the fixing roller 21, a halogen heater 24 is disposed as a heating unit that heats the fixing roller 21. Further, the fixing roller 21 and the pressure roller 31 are configured to be rotatable in the direction of the arrow in the figure by a rotation driving means such as a motor.

  As shown in FIG. 3, in the present embodiment, a gear portion 21 a is provided continuously at one end portion of the fixing roller 21 in the circumferential direction, and the gear portion 21 a is provided with a rotation driving means 40 such as a motor. The drive gear 41 is engaged and connected. For this reason, when the rotation driving means 40 is driven, a driving force is applied to the fixing roller 21 via the gear portion 21a, and the fixing roller 21 is rotationally driven. On the other hand, the pressure roller 31 is rotatably supported by a bearing, and the fixing roller 21 is driven to rotate together with the rotation of the fixing roller 21.

  The fixing roller 21 is a cylindrical member in which the periphery of the heat conductive substrate is covered with a covering layer having releasability. As the heat conductive substrate, a carbon steel material or aluminum material having a required mechanical strength and good heat conductivity is mainly used. The outer (outer peripheral surface) coating layer is formed of a material having good releasability from the toner, high thermal conductivity, and high durability. For example, those coated with a fluororesin (PFA) tube, those coated with a fluororesin (PFA or PTFE) paint, or those formed with a silicone rubber layer or a fluororubber layer are used as the coating layer.

  The pressure roller 31 is a cylindrical member that includes a cored bar, an elastic layer formed on the outer side (outer periphery) of the cored bar, and a covering layer that covers the elastic layer. For example, STKM or the like is used as the core metal, and silicone rubber, fluorine rubber, or a foam thereof is used as the elastic layer. The covering layer is formed of, for example, a tube of heat-resistant fluororesin such as PFA or PTFA rich in releasability. The pressure roller 31 is urged toward the fixing roller 21 by an urging mechanism using a spring or the like.

  A claw-shaped separation member 23 having a sharp tip is disposed opposite to the fixing roller 21 on the downstream side in the recording medium conveyance direction from the nip portion N (upper side in FIG. 2). In the present embodiment, four separation members 23 are arranged in the axial direction of the fixing roller 21. However, the number of separating members 23 is not limited to four as long as it is plural.

  As a material of the separation member 23, a material having good release properties and slidability such as PFA, PEK, and PEEK is mainly used. Further, the surface of the separating member 23 may be coated with a material having good mold release and sliding properties such as PFA and Teflon (registered trademark).

  Each separation member 23 is provided with a contact direction biasing means. For example, a tension coil spring can be used as the contact direction urging means, but other urging means may be used as the contact direction urging means depending on various conditions such as installation space and manufacturing cost. Is possible. By this abutting direction urging means, each separating member 23 is urged in a direction to abut against the fixing roller 21.

  Around the fixing roller 21, a thermistor 25 as temperature detecting means, a thermostat for preventing abnormal temperature, and the like are disposed. The surface temperature of the fixing roller 21 is controlled by the detection signal from the thermistor 25 so as to be maintained within a predetermined temperature range.

(Fixing device cleaning)
Normally, as shown in FIG. 4A, when the unfixed image pattern 201 passes through the nip portion N without the fixing toner 203 {see FIG. 4B} as the cause of the stain on the fixing roller 21. Since sufficient fixability is ensured, no offset image is generated. However, when the fixing toner 203 is fixed on the fixing roller 21 as shown in FIG. 4B, the fixing property of the fixing portion is lowered. For this reason, the unfixed toner that has passed over the fixed toner 203 is not sufficiently fixed on the recording medium P, resulting in a so-called fixing failure in which an offset image 202 is generated on the recording medium P at the circumferential pitch of the fixing roller 21.

  Therefore, in the fixing device 20 according to the embodiment of the present invention, the following measures are taken in order to prevent the fixing failure caused by the above-described fixed toner.

  As described above, in the present embodiment, the pressure roller 31 is driven and rotated by the rotation of the fixing roller 21, but is not less rotated by the frictional force generated between the rotation shaft of the pressure roller 31 and the bearing. Load is applied. For this reason, as shown in FIG. 5, a shearing force F as shown by an arrow in the figure is generated between the fixing roller 21 that is rotationally driven and the pressure roller 31 that is driven to rotate.

  As described above, the shearing force F is generated between the fixing roller 21 and the pressure roller 31. In the present invention, the magnitude of the circumferential direction (roller rotating direction) component of the shearing force F is 15 N or more. It is set to be 25N or less. In the present embodiment, a sliding bearing that is more likely to generate a rotational load than a rolling bearing is used as a bearing that supports the pressure roller 31 so that the circumferential component of the shearing force F is in the above range.

  Generally, there are U-shaped plain bearings 42 as shown in FIG. 6A and cylindrical plain bearings 42 as shown in FIG. 6B. Good. Moreover, as a material of the sliding bearing 42, it is preferable to use TFE {fluororesin (tetrafluoroethylene)}, PI (polyimide), PAI (polyamideimide), PPS (polyphenylene sulfide), or the like.

  As described above, the recording medium P is allowed to pass through the nip portion N in a state where the shearing force F is generated between the fixing roller 21 and the pressure roller 31 so that the circumferential component has a magnitude of 15N to 25N. Thus, the fixed toner adhering to the surface of the fixing roller 21 or the pressure roller 31 can be scraped off by the recording medium P.

  For example, as shown in FIG. 7A, when the fixing toner 203 is present on the surface of the fixing roller 21, the recording medium P is passed through the nip portion N, thereby fixing as shown in FIG. 7B. The fixed toner 203 is scraped off by the shearing force F1 generated between the surface of the roller 21 and the recording medium P. Then, as shown in FIG. 7C, the scraped fixed toner 203 is transferred onto the recording medium P and discharged together with the recording medium P to the outside of the apparatus. Note that since the amount of the fixed toner transferred onto the recording medium P is very small, the image quality is not deteriorated.

  Further, as shown in FIG. 8A, when the fixing toner 203 is present on the surface of the pressure roller 31, the recording medium P is passed through the nip portion N, as shown in FIG. The fixing toner 203 is scraped off by the shearing force F2 generated between the surface of the pressure roller 31 and the recording medium P. Then, as shown in FIG. 8C, the scraped fixed toner 203 is transferred onto the recording medium P and discharged together with the recording medium P to the outside of the apparatus. In this embodiment, since the pressure roller 31 is driven and rotated by the fixing roller 21, the shearing force F <b> 1 generated between the surface of the fixing roller 21 and the recording medium P and the surface of the pressure roller 31 and the recording medium P are The shearing force F2 generated between them is the same value.

  Hereinafter, the reason why the magnitude of the circumferential component of the shearing force F is set in the range of 15N to 25N will be described below.

FIG. 9 shows the test results of examining the relationship between the magnitude of the circumferential component of the shear force and the occurrence rate of defective images caused by the fixed toner.
In FIG. 9, solid lines A1 and A2 indicate the magnitudes of the circumferential components of the shearing force generated between the fixing roller and the pressure roller, and broken lines B1 and B2 indicate that the toner is fixed to the fixing roller. The rate of occurrence of defective images is shown. When the shearing force is A1, the defective image occurrence rate is B1, and when the shearing force is A2, the defective image occurrence rate is B2. In addition, the horizontal axis of FIG. 9 indicates the cumulative number of sheets (cumulative sheet passing number) that has passed the recording medium through the nip portion.

  From the results shown in FIG. 9, in the case of A1 in which the shearing force is in the range of 15N to 25N, as shown by the broken line B1, the incidence of defective images was always 0%. On the other hand, in the case of A2 where the shearing force was less than 15 N, as shown by the broken line B2, the incidence of defective images increased as the number of sheets passed increased. In the case of A2, since the shearing force is small, a sufficient fixing toner removal effect cannot be obtained, and the fixing toner accumulates on the fixing roller as the number of passing sheets increases, and this causes a defective image such as an offset image. It is thought that. On the other hand, in the case of A1 having a shearing force of 15 N or more, it is considered that as a result of obtaining a sufficient fixed toner removal effect, accumulation of fixed toner on the fixing roller is suppressed, and no defective image is generated.

  Thus, by setting the magnitude of the circumferential component of the shearing force to 15 N or more, a sufficient removal effect of the fixed toner can be obtained, and accumulation of the fixed toner on the fixing roller can be highly suppressed. It becomes. On the other hand, when the magnitude of the circumferential component of the shearing force is less than 15 N, it is difficult to obtain the fixed toner removing effect. Also, the reason why the circumferential component of the shearing force is 25 N or less is that when it exceeds 25 N, wrinkles are likely to occur on the recording medium. For this reason, when the magnitude of the circumferential component of the shearing force is 25 N or less, the recording medium is less likely to be wrinkled, and a good image can be obtained.

  In FIG. 9, in the case of A2 where a defective image is generated, in the initial state where the cumulative number of sheets passed is small (less than about 500 sheets), the shearing force is 15 N or more and A1 where no defective image is generated. Although it was almost the same, after that, the shear force decreased rapidly. In this case, different materials were used as the slide bearings for supporting the pressure roller in the case of A1 and in the case of A2, but since both were new in the initial state, the characteristics of the rotational load due to the difference in material This is probably because there was not much difference in (effect on shearing force). That is, since the surface of the plain bearing was covered with the skin layer in the new state, the difference due to the difference in the material of each plain bearing did not appear clearly, and then the skin layer was shaved and the characteristics of the material itself appeared. It is considered that a difference occurred in the shearing force. From this, in a fixing device using a new or equivalent sliding bearing, it is difficult to determine whether the shearing force is 15 N or more in the initial state, and at least the cumulative number of sheets to be passed is 1000 sheets. It can be said that it is better to judge in the above state.

  Further, in the present embodiment, in addition to setting the shearing force F between the rollers 21 and 31 within a predetermined range as described above, in order to more effectively remove the fixed toner, the outer side of the fixing roller 21 is removed. The diameter is changed in the axial direction.

  Specifically, as shown in FIG. 10, the outer diameter of the fixing roller 21 is formed so as to increase in a curved shape from the axial center to the end. Further, the increasing rate of the outer diameter of the fixing roller 21 is made to increase from the central side to the end side in the axial direction. The rate of increase in outer diameter here is the amount of increase in outer diameter per predetermined length in the axial direction. That is, the increase rate of the outer diameter increases toward the end side as shown in FIG. 11 in the sections C1 to Cn divided by a predetermined length in the axial direction of the fixing roller 21. It means that the increase amount D1 to Dn of the outer diameter with respect to the section adjacent to the side gradually increases from the central part side toward the end part side (D1 <D2 <D3 <... <Dn).

  The actual increase rate of the outer diameter of the fixing roller 21 is not as great as shown in FIGS. 10 and 11, but in FIGS. 10 and 11 and the drawings used in the following description, the outer diameter of the fixing roller 21 is increased. The outer diameter shape is exaggerated to make it easy to understand the change.

FIG. 12 is a diagram illustrating a state in which the pressure roller 31 is brought into contact with the fixing roller 21 according to the present embodiment and is pressed.
The pressure roller 31 according to the present embodiment is formed so that the outer diameter does not change in the axial direction (same size), but since it is an elastic roller having an elastic layer, the fixing roller 21 is a hard roller. It is elastically deformed by touching. For this reason, the pressure roller 31 has an outer peripheral surface deformed in accordance with the shape of the fixing roller 21 at least in the nip portion N, and the outer diameter of the pressure roller 31 is opposite from the central side in the axial direction to the end side. It decreases in a curved line toward.

  As described above, when the pressure roller 31 is pressed against the fixing roller 21 and both the rollers 21 and 31 are rotated in this state, the shearing force Fa˜ between the both rollers 21 and 31 as indicated by the arrows in FIG. Fc is generated. These shearing forces Fa to Fc are generated so as to incline toward the end in the axial direction with respect to the recording medium transport direction E, and further increase gradually toward the end (Fa <Fb <Fc). In FIG. 10, the shearing force generated in the axial direction is represented by six arrows (two sets of Fa to Fc) for convenience. Actually, however, the shearing force has a different magnitude at each position in the axial direction. Occurs.

  In the present embodiment, the direction in which each of the shearing forces Fa to Fc is generated is inclined in the direction toward the end with respect to the recording medium conveyance direction E. This is because the peripheral speed difference of the fixing roller 21 is generated between the central portion side and the end portion side. In the present embodiment, the shear forces Fa to Fc gradually increase toward the end side because the rate of increase in the outer diameter of the fixing roller 21 increases from the central side in the axial direction toward the end side. Due to

  On the other hand, as shown in FIG. 23, unlike the present embodiment, when the rate of increase in the outer diameter of the fixing roller 21 is constant (the outer diameter increases linearly), shearing occurs at each position in the axial direction. The magnitudes of the forces Fa to Fc are the same and do not change.

  Even when the fixing roller 21 shown in FIG. 23 is used, when the recording medium P passes through the nip portion N, these shearing forces Fa to Fc are generated, so that the fixing toner is supplied from the fixing roller 21 or the pressure roller 31. It is considered that the effect of removing can be obtained to some extent. However, in this case, when the shear forces Fa to Fc at the respective positions in the axial direction are compared, they have the same magnitude, and there is no difference between the shear forces Fa to Fc. Is considered difficult to obtain.

  On the other hand, in this embodiment, as shown in FIG. 10, when the shearing forces Fa to Fc change in the axial direction and the shearing forces Fa to Fc at each position in the axial direction are compared, the shearing forces Fa There is a difference between. Due to the difference between the shearing forces, the fixed toner can be effectively removed. Therefore, compared with the example shown in FIG. 23, a higher fixed toner removing effect can be obtained. In this embodiment, since the shearing force increases toward the end portion side, a high fixing toner removing effect can be obtained particularly on the end portion side.

  In the present embodiment, the outer diameter is changed in a curved shape over the entire axial direction of the fixing roller 21, but the range in which the outer diameter is changed is not necessarily the entire axial direction, but only a part. Good. However, in order to effectively remove the fixed toner by the recording medium and prevent an offset image, the outer diameter of the fixing roller 21 changes at least over the range of the recording medium passage width Wp (see FIG. 10). Preferably it is.

  Here, when the radius of the fixing roller 21 is R and the torque (rotational torque) generated in the fixing roller 21 is Tr, the value Fr of the circumferential component of the shearing force generated between the fixing roller 21 and the pressure roller 31 is Can be represented by the following formula 1.

  Fr = Tr / R Formula 1

  As described above, the value Fr of the circumferential component of the shearing force can be obtained from the values of the radius R of the fixing roller 21 and the torque Tr, but the fixing roller 21 according to the present embodiment has a radius R extending in the axial direction. Different. Therefore, when calculating the value Fr of the circumferential component of the shearing force, the average radius is simply used as the radius R of the fixing roller 21.

  The torque Tr generated in the fixing roller 21 is the total torque generated in the fixing roller 21. The total torque of the fixing roller 21 can be measured by, for example, a torque measuring device 50 as shown in FIG.

  A torque measuring device 50 shown in FIG. 13 includes a torque converter 51, a motor 52, a signal conditioner 53, a computer 54, and a fixed base 55. A torque converter 51 and a motor 52 are installed on the fixed base 55, and a computer 54 is connected to the torque converter 51 via a signal conditioner 53. A drive gear 56 is provided at the tip of the rotating shaft of the motor 52 that passes through the torque converter 51.

  In order to measure the total torque of the fixing roller 21, first, the fixing roller 21 is fixed to the fixing base 55 together with the fixing device 20, and a gear portion 21 a provided at one end portion in the axial direction of the fixing roller 21 is connected to the drive gear 56. To do. In this state, the motor 52 is driven, and the total torque generated at the fixing roller 21 at that time is measured by the torque converter 51. Then, the measurement data is converted into a predetermined signal by the signal conditioner 53 and input to the computer 54 to calculate the total torque.

  By inputting the total torque value Tr of the fixing roller 21 and the average radius value R of the fixing roller 21 obtained in the above-described manner into the above equation 1, shearing between the fixing roller 21 and the pressure roller 31 occurs. It is possible to calculate the value Fr of the circumferential component of the force. And the magnitude | size of a torque, a roller radius, etc. should just be adjusted so that the value Fr of the circumferential direction component of the obtained shear force may become the range of 15N or more and 25N or less. In this embodiment, the total torque of the fixing roller 21 that is a driving roller is calculated. However, when the pressure roller 31 is a driving roller, the total torque of the pressure roller 31 is calculated in the same manner, The value Fr of the circumferential component of the shearing force may be calculated using this value and the average radius (at the nip portion N) of the pressure roller 31.

  The configuration of another embodiment of the present invention will be described below. Note that, in the configuration of the embodiment described below, portions having the same functions as those of the above embodiment are denoted by the same reference numerals, and redundant description is omitted.

  In the embodiment shown in FIG. 14, as in the above-described embodiment, the outer diameter of the fixing roller 21 is formed so as to increase in a curve from the central side to the end side in the axial direction. The rate of increase in diameter is different. In the embodiment shown in FIG. 14, unlike the above-described embodiment, the increasing rate of the outer diameter of the fixing roller 21 decreases from the central side to the end side in the axial direction. That is, as shown in FIG. 15, in each of the sections C1 to Cn divided by a predetermined length in the axial direction of the fixing roller 21, the outer diameter of the end side section with respect to the adjacent central section is set. The increase amounts D1 to Dn are gradually decreased from the central side toward the end side (D1> D2> D3>...> Dn).

FIG. 16 is a view showing a state where the pressure roller 31 is brought into contact with the fixing roller 21 shown in FIG.
Also in this embodiment, since the pressure roller 31 is an elastic roller, when it is pressed against the fixing roller 21, it is elastically deformed following the shape of the fixing roller 21 at least at the nip portion N.

  In the present embodiment, when the fixing roller 21 is rotated with the pressure roller 31 being pressed, shearing forces Fa to Fc as indicated by arrows in FIG. These shear forces Fa to Fc are generated so as to incline toward the axial end with respect to the recording medium conveyance direction E, as in the above-described embodiment. However, in the present embodiment, unlike the above-described embodiment, the increase rate of the outer diameter of the fixing roller 21 is decreased from the central side to the end side in the axial direction. Thus, the shear forces Fa to Fc gradually decrease toward the end side (Fa> Fb> Fc).

  Even when the fixing roller 21 shown in FIG. 14 is used, since the shearing forces Fa to Fc change in the axial direction, the fixing toner can be effectively removed by the difference between the shearing forces in the axial direction. . In this embodiment, since the shearing force increases toward the central portion, a high fixed toner removing effect can be obtained particularly on the central portion.

  Further, as another embodiment different from the above, a fixing roller 21 as shown in FIGS. 17 and 18 may be used. In the fixing roller 21 shown in FIG. 17, the outer diameter decreases from the central portion side in the axial direction toward the end portion, and the decreasing rate of the outer diameter increases from the central portion side in the axial direction toward the end portion. It is formed as follows. On the other hand, in the fixing roller 21 shown in FIG. 18, the outer diameter decreases from the central portion side in the axial direction toward the end portion side. It is formed so as to become smaller.

  When the fixing roller 21 shown in FIG. 17 is used, the shearing forces Fa to Fc generated between the fixing roller 21 and the pressure roller 31 gradually increase toward the end side (Fa <Fb <Fc). On the other hand, when the fixing roller 21 shown in FIG. 18 is used, the shearing forces Fa to Fc generated between the fixing roller 21 and the pressure roller 31 gradually decrease toward the end side (Fa> Fb> Fc). . As described above, the fixing roller 21 shown in FIG. 17 and the fixing roller 21 shown in FIG. 18 differ depending on whether the side where the shearing forces Fa to Fc are increased is the center side or the end side. Also in the roller, the shearing forces Fa to Fc change in the axial direction. Therefore, even when the fixing roller 21 shown in FIG. 17 or FIG. 18 is used, the fixed toner can be effectively removed by the difference between the shearing forces in the axial direction.

  However, the fixing roller 21 shown in FIGS. 17 and 18 is generated such that the shearing forces Fa to Fc are inclined toward the central portion in the axial direction with respect to the recording medium conveyance direction E. For this reason, considering the ease of occurrence of wrinkles on the recording medium P, the fixing roller 21 shown in FIGS. 10 and 14 is preferable to the fixing roller 21 shown in FIGS. 17 and 18 (wrinkles occur). Hateful.). In particular, in the case of the fixing roller 21 shown in FIG. 10, since the shearing forces Fa to Fc increase toward the end side, wrinkles are hardly generated.

  Further, the configuration of the fixing roller 21 as described above can be applied to, for example, the fixing device 20 as shown in FIG. 19 in addition to the fixing device 20 as shown in FIG. A fixing device 20 shown in FIG. 19 includes a fixing roller 21, a heating roller 22 having a halogen heater 24 inside, an endless fixing belt 27 stretched around the fixing roller 21, and the fixing roller 21 via the fixing belt 27. A pressure roller 31 in contact therewith. By applying the shape of the fixing roller 21 shown in any of FIGS. 10, 14, 17, and 18 to the fixing roller 21 provided in the fixing device 20, the above-described shearing force is generated and effectively applied. The fixed toner can be removed. That is, by making the fixing roller 21 into the shape of the fixing roller 21 in any of FIGS. 10, 14, 17, and 18, the fixing belt 27 and the pressure roller 31 that are in contact with each other at least have a nip portion N. , The outer diameter is formed so as to increase or decrease in a curved shape from the central portion side to the end portion side in the axial direction. As a result, a shearing force whose size varies in the axial direction can be generated between the fixing belt 27 and the pressure roller 31, so that the fixed toner is effectively removed by the difference between the shearing forces. can do.

  Furthermore, the configuration of the present invention is also applicable to a fixing device 20 as shown in FIG. The fixing device 20 shown in FIG. 20 does not have a fixing roller, and forms a nip portion N by bringing the fixing belt 27 into contact with the pressure roller 31 by a fixed nip forming member 26. In such a fixing device 20, the surface of the nip forming member 26 that contacts the fixing belt 27 is formed in any one of the shapes shown in FIGS. 21A to 21D, so that the fixing belt 27, the pressure roller 31, Can be formed so as to increase or decrease in a curved shape from the central portion side in the axial direction toward the end portion at least in the nip portion N. The shape of the nip forming member 26 shown in FIGS. 21A to 21D corresponds to the shape of the fixing roller 21 shown in FIGS. 10, 14, 17, and 18 in this order.

  Further, in order to more reliably prevent the occurrence of fixed toner, a cleaning roller 43 as a cleaning unit may be disposed in contact with the surface of the fixing roller 21 as in the embodiment shown in FIG. . Alternatively, the cleaning roller 43 may be disposed in contact with the surface of the pressure roller 31 as shown in FIG. In this case, the fixing toner 203 on the fixing roller 21 or the pressure roller 31 is removed by the recording medium P passing through the nip portion N, and the fixing toner 203 is also removed by the cleaning roller 43. As a result, the fixed toner 203 can be removed more reliably, and the occurrence of defective images can be prevented to a higher degree.

  As described above, even when the cleaning roller 43 is provided, the amount of the fixed toner 203 removed and collected by the cleaning roller 43 is reduced by the amount of the fixed toner 203 being removed by the recording medium P. For this reason, the fixing toner 203 collected by the cleaning roller 43 is solidified to generate abnormal noise, or the fixing toner 203 accumulated in a predetermined amount or more on the cleaning roller 43 is melted to contaminate the recording medium. Is less likely to occur.

  As described above, according to the fixing device according to the present invention, the shearing force is generated between the rotating bodies such as the fixing roller and the pressure roller so that the size of the circumferential component is 15N or more and 25N or less. In this state, by allowing the recording medium to pass through the nip portion, a deposit removal force (shearing force) can be sufficiently generated between the recording medium and each rotating body. That is, it is possible to generate a larger deposit removing force than the configuration in which a moving speed difference is provided between the fixing member and the pressure member without using a recording medium as in Patent Document 1. As a result, in the fixing device according to the present invention, it is possible to reliably remove deposits such as fixed toner on the rotating body. In addition, the recording medium is less likely to be wrinkled, and a good image can be obtained.

  Furthermore, according to the fixing device of the present invention, at least at the nip portion, the outer diameter of the rotating body is formed so as to increase or decrease in a curved shape from the central portion side to the end portion side in the axial direction. Thus, shearing forces of different sizes can be generated in the axial direction. Thereby, deposits can be more effectively removed by the difference between these shear forces.

  Further, according to the fixing device of the present invention, the deposit on the rotating body can be transferred to the recording medium and removed, so that the cleaning means (such as a cleaning web and a cleaning roller) described in Patent Document 2 above can be removed. ) Need not be installed separately. For this reason, an increase in cost and an increase in size of the apparatus can be avoided.

  Note that, as in the embodiment shown in FIG. 22, a cleaning unit that removes the fixed toner on the fixing roller or the pressure roller may be separately provided as necessary. In this case, even if the cleaning unit is provided, the amount of the fixed toner removed and collected by the cleaning unit can be reduced by the amount that the fixed toner is removed by the recording medium. For this reason, it is possible to make it difficult to cause problems such as generation of abnormal noise due to solidification of the fixed toner collected by the cleaning unit and contamination of the recording medium due to dissolution of the fixed toner from the cleaning unit.

  Further, in the fixing device according to the present invention, the deposit removal effect is exhibited every time the recording medium passes through the nip portion. For this reason, compared with the configuration in which toner removal is not performed during paper passing as described in Patent Document 1 above, it is possible to frequently remove deposits and effectively deposit deposits on a rotating body. Can be suppressed.

  In particular, the effects of the present invention as described above can be expected to be significant when a recording medium containing a large amount of filler such as calcium carbonate is used. In addition, a great effect can be expected when a toner to which silica particles containing silicone oil are externally added is used. In this type of toner, for example, 2 parts of hydrophobic silica RY50 (manufactured by Aerosil) containing or coated with silicone oil on the surface is added to 100 parts of pulverized toner or polymerized toner, and the peripheral speed is 40 m / min with a 20 L Henschel mixer. for 5 minutes, and then sieved with a sieve having an opening of 75 microns.

  As mentioned above, although this invention was demonstrated, this invention is not limited to the above-mentioned embodiment, Of course, a various change can be added in the range which does not deviate from the summary of this invention. The image forming apparatus provided with the fixing device according to the present invention is not limited to the color image forming apparatus as shown in FIG. 1 but may be a monochrome image forming apparatus. Further, the image forming apparatus to which the present invention can be applied includes a printer, a copying machine, a facsimile, or a complex machine thereof.

20 Fixing device 21 Fixing roller (rotating body)
31 Pressure roller (rotating body)
E Recording medium conveyance direction N Nip part P Recording medium

Japanese Patent Laid-Open No. 2002-40860 JP 2009-37078 A

Claims (10)

Comprising two rotating bodies that contact each other to form a nip,
In the fixing device for fixing the image by passing the recording medium on which the image is formed through the nip portion,
The rotating body is formed such that at least in the nip portion, the outer diameter increases or decreases in a curved shape from the axial central portion side toward the end portion side,
A fixing device, wherein a recording medium is passed through the nip portion in a state where a shearing force is generated between the rotating bodies so that a circumferential component has a magnitude of 15 N or more and 25 N or less. One of the two rotating bodies is a hard roller, and the other is an elastic roller that elastically deforms by contacting the hard roller,
The fixing device according to claim 1, wherein an outer diameter of the hard roller is formed so as to increase in a curved shape from a central portion side to an end portion side in the axial direction.   The fixing device according to claim 2, wherein an increasing rate of an outer diameter of the hard roller increases from a central portion side to an end portion side in the axial direction.   The fixing device according to claim 2, wherein an increase rate of an outer diameter of the hard roller decreases from a central portion side to an end portion side in the axial direction.   5. The fixing device according to claim 1, wherein a shearing force generated between the rotating bodies is generated so as to be inclined toward an axial end with respect to a recording medium conveyance direction.   6. The fixing device according to claim 1, wherein a shearing force generated between the rotating bodies increases from an axially central portion side toward an end portion side.   The fixing device according to claim 1, wherein a shearing force generated between the rotating bodies decreases from an axially central portion side toward an end portion side.   The value of the circumferential component of the shearing force generated between the rotating bodies is a value obtained by dividing the total torque generated in the rotating bodies by the average radius of the rotating bodies. The fixing device according to Item 1.   9. One of the two rotating bodies is a driving rotating body that rotates by being applied with a driving force, and the other is a driven rotating body that is driven to rotate together with the driving roller. The fixing device according to Item. An image forming apparatus comprising the fixing device according to claim 1.