JP6857337B2 - Fixing device and image forming device - Google Patents

Description

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

In an electrophotographic image forming apparatus such as a printer or a copier, a toner image is recorded by passing a recording medium such as paper on which a toner image is formed through a nip portion between two rotating bodies in contact with each other. A fixing device for fixing to a medium is used.

Basically, the toner (toner image) on the recording medium is fixed on the recording medium by being melted by the heat given from one or both rotating bodies. However, due to insufficient heat, excessive heat, or electrical action, all the toner may not be fixed on the recording medium, but may slightly adhere to one or both of the rotating bodies and remain. When such toner adheres to the rotating body, the releasability of the toner to the rotating body (fixability of the toner to the recording medium) is lowered 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, but conversely adheres to the rotating body, so that the toner image on the rotating body is formed as the rotating body rotates. An offset image is generated that is transferred onto the recording medium at a circumferential pitch.

In addition, some recording media used in recent years contain a large amount of filler such as calcium carbonate, and 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. Therefore, particularly when such a recording medium is used, the releasability of the toner with respect to the rotating body tends to be significantly reduced.

In response to the above problems, for example, in Patent Document 1 (Japanese Unexamined Patent Publication No. 2002-40860), the moving speed difference between the surfaces of the fixing member and the pressure member is set before the transfer material reaches the fixing nip. A method to attach it has been proposed.

Further, as another method, Patent Document 2 (Japanese Unexamined Patent Publication 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 pressurizing member is transferred to the fixing member and removed by making a difference in moving speed between the surfaces of the fixing member and the pressurizing member. Can be done. However, the toner removing force (peeling force) obtained by the speed difference between the fixing member and the pressurizing member is insufficient for removing the fixed toner containing a large amount of paper dust (toner filler, etc.), 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 such as an increase in cost and an increase in the size of the apparatus. Further, there are problems that the toner collected by the cleaning roller accumulates and solidifies to generate an abnormal noise, and the toner accumulated in a predetermined amount or more in the cleaning roller dissolves to stain the recording medium.

In order to solve the above problems, the present invention includes two rotating bodies that come into contact with each other to form a nip portion, and the nip portion is passed through a recording medium on which an image is formed to fix the image. In the rotating body, at least in the nip portion, 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, and the circumferential body is formed between the rotating bodies. It is characterized in that a recording medium is passed through the nip portion in a state where a shearing force having a magnitude of 15 N or more and 25 N or less is generated in the direction component.

According to the present invention, a recording medium is passed through the nip portion in a state where a shearing force having a circumferential component size of 15 N or more and 25 N or less is generated between the rotating bodies to form a recording medium. A sufficient deposit removing force (shearing force) can be generated between each rotating body. As a result, the deposits adhering to the surface of the rotating body can be transferred to the recording medium and reliably removed. Moreover, wrinkles are less likely to occur on the recording medium, 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 portion side in the axial direction toward the end portion side in the axial direction. It is possible to generate shearing forces of different sizes. This makes it possible to remove deposits more effectively due to the difference between these shear forces. Further, according to the present invention, since the deposits can be transferred to the recording medium and removed, it is not necessary to separately install a cleaning means for removing the deposits on the rotating body. Further, since the effect of removing deposits is exhibited each time the recording medium passes through the nip portion, the deposits can be removed frequently, and the accumulation of deposits on the rotating body can be effectively suppressed. ..

It is a figure which shows the schematic structure of the image forming apparatus which concerns on one Embodiment of this invention. It is a figure which shows the schematic structure of the fixing device which concerns on this embodiment. It is a figure which shows the schematic structure of the drive system of the fixing device which concerns on this embodiment. (A) and (b) are diagrams showing a state in which an offset image is generated depending on the presence or absence of fixed toner on the fixing roller. It is a figure which shows the shearing force generated between a fixing roller and a pressure roller. (A) and (b) are diagrams showing an example of a slide bearing that supports a pressure roller. It is a figure which shows the state that the fixed toner is removed from a fixing roller. It is a figure which shows the state that the fixed toner is removed from a pressure roller. It is a figure which shows the relationship between the magnitude of the circumferential component of a shearing force, and the occurrence rate of a defective image due to sticking toner. It is a figure which shows the outer peripheral shape of the fixing roller which concerns on this embodiment. It is a figure which shows the part of the outer circumference of a fixing roller enlarged. It is a figure which shows the state which pressed the pressure roller by making contact with the fixing roller. It is a figure which shows the schematic structure of the torque measuring apparatus. It is a figure which shows the outer peripheral shape of the fixing roller which concerns on other embodiment. It is a figure which shows the part of the outer circumference of a fixing roller enlarged. It is a figure which shows the state which pressed the pressure roller by making contact with the fixing roller. It is a figure which shows the outer peripheral shape of the fixing roller which concerns on another embodiment. It is a figure which shows the outer peripheral shape of the fixing roller which concerns on still another embodiment. It is a figure which shows the schematic structure of the other fixing apparatus to which this invention is applied. It is a figure which shows the schematic structure of another fixing device to which this invention is applied. (A) to (d) are diagrams showing variations in the shape of the nip forming member. (A) and (b) are diagrams showing an embodiment provided with cleaning means. It is a figure which shows the outer peripheral 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 drawing for explaining the embodiment of the present invention, components such as members and components having the same function or shape are once described by giving the same reference numerals as much as possible. Then, the explanation is omitted.

(Rough configuration of a color printer as an image forming device)
As shown in FIG. 1, the image forming apparatus 1 of the present embodiment is a tandem color printer. Four toner bottles 102Y, 102M, 102C, and 102K corresponding to each color (yellow, magenta, cyan, and black) are detachably installed (replaceable) in the bottle accommodating portion 101 above the image forming apparatus main body. There is.

An intermediate transfer unit 85 is arranged below the bottle accommodating portion 101. Image-forming units 4Y, 4M, 4C, and 4K corresponding to each color (yellow, magenta, cyan, and black) are arranged side by side so as to face the intermediate transfer belt 78 of the intermediate transfer unit 85. Photoreceptor drums 5Y, 5M, 5C, and 5K are arranged in each image forming unit 4Y, 4M, 4C, and 4K, respectively.

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

Then, at the position of the charging portion 75, the surfaces of the photoconductor drums 5Y, 5M, 5C, and 5K are uniformly charged (the charging step). After that, the surfaces of the photoconductor drums 5Y, 5M, 5C, and 5K reach the irradiation position of the laser beam L emitted from the exposure unit 3, and the electrostatic latent image corresponding to each color is formed by the exposure scanning at this position. (It is an exposure process).

After that, the surfaces of the photoconductor 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 a toner image of each color (development step). It is.). After that, the surfaces of the photoconductor drums 5Y, 5M, 5C, and 5K reach the positions facing the intermediate transfer belt 78 and the primary transfer bias rollers 79Y, 79M, 79C, and 79K, and at this position, the photoconductor drums 5Y and 5M The toner images on 5, 5C and 5K are transferred onto the intermediate transfer belt 78 (this is the primary transfer step).

At this time, a small amount of untransferred toner remains on the photoconductor drums 5Y, 5M, 5C, and 5K. After that, the surfaces of the photoconductor drums 5Y, 5M, 5C, and 5K reach the positions facing the cleaning unit 77. At this position, the untransferred toner remaining on the photoconductor drums 5Y, 5M, 5C, and 5K is mechanically recovered by the cleaning blade of the cleaning unit 77 (cleaning step).

Finally, the surface of the photoconductor drums 5Y, 5M, 5C, and 5K reaches a position facing the static elimination portion, and the residual potential on the photoconductor drums 5Y, 5M, 5C, and 5K is removed at this position. In this way, a series of image forming processes performed on the photoconductor drums 5Y, 5M, 5C, and 5K are completed.

Then, the toner images of each color formed on each photoconductor drum through the developing process are superimposed and transferred on the intermediate transfer belt 78. 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, 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 three rollers 82 to 84, and is endlessly moved counterclockwise in FIG. 1 by the rotational drive of one roller 82. Each of the four primary transfer bias rollers 79Y, 79M, 79C, and 79K forms a primary transfer nip by sandwiching the intermediate transfer belt 78 between the photoconductor drums 5Y, 5M, 5C, and 5K, respectively.

Then, a transfer bias opposite to the polarity of the toner is applied to the primary transfer bias rollers 79Y, 79M, 79C, 79K. Then, 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, respectively. In this way, the toner images of each color on the photoconductor drums 5Y, 5M, 5C, and 5K are superimposed on the intermediate transfer belt 78 and first-order transferred.

After that, the intermediate transfer belt 78 on which the toner images of each color are superimposed and transferred reaches a position facing the secondary transfer roller 89. At this position, the secondary transfer backup roller 82 sandwiches the intermediate transfer belt 78 with the secondary transfer roller 89 to form a secondary transfer nip. Then, 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. After that, the intermediate transfer belt 78 reaches the position of the intermediate transfer cleaning unit 80. Then, at this position, the untransferred toner on the intermediate transfer belt 78 is collected.

In this way, a series of transfer processes performed on the intermediate transfer belt 78 is completed. The above is a description of the configuration and operation of the image forming unit. Here, the recording medium P conveyed to the position of the secondary transfer nip is conveyed from the paper feeding unit 12 arranged below the main body of the apparatus via the paper feeding roller 97, the timing roller pair 98, and the like. It is a thing.

Specifically, a plurality of recording media P such as transfer paper are stacked and stored in the paper feed unit 12. Then, when the paper feed roller 97 is rotationally driven counterclockwise in FIG. 1, the top recording medium P is fed between the timing rollers and the rollers 98. The recording medium P conveyed to the timing roller vs. 98 temporarily stops at the position of the roller nip of the timing roller vs. 98 where the rotational drive is stopped.

Then, the timing roller pair 98 is rotationally driven in time 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, the desired color image is transferred onto the recording medium P.

After that, 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. Then, at this position, the color image transferred to the surface of the intermediate transfer belt 78 by the heat and pressure of the fixing roller 21 as the fixing rotating body and the pressure roller 31 as the pressure rotating body is transferred onto the recording medium P. Be fixed.

After that, the recording medium P is discharged to the outside of the apparatus via the paper ejection roller vs. 99 rollers. The recording medium P discharged to the outside of the device by the paper ejection roller pair 99 is sequentially stacked on the stack unit 100 as an output image. In this way, a series of image forming processes in the image forming apparatus 1 is completed.

(Structure of fixing device)
Next, the basic configuration of the fixing device 20 described above will be described.
As shown in FIG. 2, the fixing device 20 has two rotating bodies, that is, a fixing roller 21 and a pressure roller 31 that come into contact with each other to form a nip portion N. Inside the fixing roller 21, a halogen heater 24 is provided as a heating means for heating the fixing roller 21. Further, the fixing roller 21 and the pressurizing 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 21a is continuously provided at one end of the fixing roller 21 in the circumferential direction, and the gear portion 21a is provided on the rotation driving means 40 such as a motor. The drive gears 41 are engaged and connected to each other. Therefore, 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 when the fixing roller 21 is rotationally driven, the pressurizing roller 31 is driven to rotate together with the pressurizing roller 31.

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

The pressure roller 31 is a cylindrical member composed of a core metal, an elastic layer formed on the outer side (outer circumference) of the core metal, and a coating layer covering the elastic layer. For example, STKM or the like is used as the core metal, and silicone rubber, fluororubber, or a foam thereof is used as the elastic layer. The coating layer is formed of, for example, a tube of a heat-resistant fluororesin such as PFA or PTFA, which is highly releasable. The pressurizing roller 31 is urged toward the fixing roller 21 by an urging mechanism using a spring or the like.

On the downstream side (upper side in FIG. 2) of the nip portion N in the recording medium transport direction, a claw-shaped separating member 23 having a sharp tip is arranged so as to face the fixing roller 21. In the present embodiment, four separating members 23 are arranged along the axial direction of the fixing roller 21. However, the number of the separating members 23 may be a plurality, and is not limited to four.

As the material of the separating member 23, a material having good releasability 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 releasability and slidability such as PFA or Teflon (registered trademark).

Each separating member 23 is provided with abutting direction urging 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. It is possible. By this contact direction urging means, each separating member 23 is urged in a direction of contacting the fixing roller 21.

Further, a thermistor 25 as a temperature detecting means, a thermostat for preventing an abnormal temperature, and the like are arranged around the fixing roller 21. Then, the surface temperature of the fixing roller 21 is controlled to be maintained within a predetermined temperature range by the detection signal from the thermistor 25.

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

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 defect caused by the fixing toner as described above.

As described above, in the present embodiment, the pressurizing roller 31 is driven to rotate when the fixing roller 21 is rotationally driven, but the pressurizing roller 31 rotates not a little due to the frictional force generated between the rotating shaft of the pressurizing roller 31 and the bearing. It takes a load. Therefore, as shown in FIG. 5, a shearing force F as shown by an arrow in the figure is generated between the rotationally driven fixing roller 21 and the drivenly rotating pressure roller 31.

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

Generally, the slide bearing includes a U-shaped slide bearing 42 as shown in FIG. 6 (a) and a cylindrical slide bearing 42 as shown in FIG. 6 (b), and any of them may be used. Good. Further, as the material of the slide 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 passed through the nip portion N in a state where a shearing force F having a circumferential component size of 15 N or more and 25 N is generated between the fixing roller 21 and the pressure roller 31. Then, 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 to fix the toner 203 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 to the outside of the apparatus together with the recording medium P. Since the amount of fixed toner transferred onto the recording medium P is very small, it does not deteriorate the image quality.

Further, as shown in FIG. 8 (a), when there is a fixed toner 203 on the surface of the pressure roller 31, the recording medium P is passed through the nip portion N, so that as shown in FIG. 8 (b). The fixed 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 to the outside of the apparatus together with the recording medium P. In the present embodiment, since the pressurizing roller 31 is driven to rotate, the shearing force F1 generated between the surface of the fixing roller 21 and the recording medium P, and the surface of the pressurizing roller 31 and the recording medium P The shear forces F2 generated between them have the same value.

Hereinafter, the reason for setting the magnitude of the circumferential component of the shearing force F in the range of 15 N or more and 25 N or less will be described below.

FIG. 9 shows the test results of investigating the relationship between the magnitude of the circumferential component of the shearing force and the occurrence rate of defective images due to the fixed toner.
In FIG. 9, the 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, respectively, and the broken lines B1 and B2 indicate that the toner is fixed to the fixing roller, respectively. The incidence of defective images due to this is shown. When the shearing force is A1, the defective image generation rate is B1, and when the shearing force is A2, the defective image generation rate is B2. The horizontal axis of FIG. 9 indicates the cumulative number of sheets (cumulative number of sheets to be passed) through which the recording medium has passed 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, the occurrence rate of defective images was always 0% as shown by the broken line B1. On the other hand, in the case of A2 having a shearing force of less than 15 N, as shown by the broken line B2, the occurrence rate of defective images increased as the number of sheets to be passed increased. This is because in the case of A2, since the shearing force is small, a sufficient effect of removing the fixed toner cannot be obtained, and the fixed toner accumulates on the fixing roller as the number of sheets to be passed increases, which causes a defective image such as an offset image. It is probable that it was done. 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 effect of removing the fixed toner, the accumulation of the fixed toner on the fixing roller was suppressed and a defective image did not occur.

By setting the magnitude of the circumferential component of the shearing force to 15 N or more in this way, a sufficient effect of removing the fixed toner can be obtained, and the accumulation of the fixed toner on the fixing roller can be highly suppressed. It becomes. On the contrary, when the magnitude of the circumferential component of the shearing force is less than 15N, it becomes difficult to obtain the effect of removing the fixed toner. Further, the reason why the magnitude of the circumferential component of the shearing force is set to 25 N or less is that if it exceeds 25 N, wrinkles are likely to occur on the recording medium. Therefore, by setting the magnitude of the circumferential component of the shearing force to 25 N or less, wrinkles are less likely to occur on the recording medium, and a good image can be obtained.

In FIG. 9, in the case of A2 in which a defective image is generated, in the initial state where the cumulative number of sheets to be passed is small (a state of less than about 500 sheets), the shearing force is 15 N or more, and the case of A1 in which no defective image is generated is used. It was about the same, but then the shear force dropped sharply. This is because different materials were used for the slide bearings that support the pressurizing rollers in the case of A1 and the case of A2, but since they were all new in the initial state, the characteristics of the rotational load due to the difference in materials. It is probable that there was not much difference in (effect on shearing force). That is, in the new state, the surface of the slide bearing was covered with the skin layer, so that the difference due to the difference in the material of each slide bearing did not appear clearly, and then the skin layer was scraped off and the characteristics of the material itself appeared. , It is probable that there was a difference in shearing force. From this, it is difficult to determine whether or not the shearing force is 15 N or more in a fixing device using a new or equivalent slide bearing in the initial state, and at least the cumulative number of sheets to be passed is 1000. 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 both rollers 21 and 31 within a predetermined range as described above, in order to remove the fixed toner more effectively, the outside of the fixing roller 21 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 central portion side in the axial direction to the end portion side. Further, the rate of increase in the outer diameter of the fixing roller 21 is increased from the central portion side in the axial direction toward the end portion side. The increase rate of the outer diameter referred to here is the amount of increase in the outer diameter per predetermined length in the axial direction. That is, as shown in FIG. 11, the rate of increase in the outer diameter increases toward the end side in the central portion of each section C1 to Cn divided by a predetermined length in the axial direction of the fixing roller 21. This means that the amount of increase in outer diameter D1 to Dn with respect to the section adjacent to the side gradually increases from the central portion side to the end portion side (D1 <D2 <D3 << ... <Dn).

Although the actual rate of increase in the outer diameter of the fixing roller 21 is not as large as shown in FIGS. 10 and 11, in FIGS. 10 and 11, and in each drawing used in the following description, the outer diameter of the fixing roller 21 is increased. The outer diameter shape is exaggerated so that the change in can be easily understood.

FIG. 12 is a diagram showing a state in which the pressurizing roller 31 is brought into contact with the fixing roller 21 according to the present embodiment to pressurize.
The pressure roller 31 according to the present embodiment is formed so that the outer diameter does not change (with the same size) in the axial direction, but since it is an elastic roller having an elastic layer, the fixing roller 21 is a hard roller. Elastically deforms when it comes into contact with. Therefore, at least in the nip portion N, the outer peripheral surface of the pressure roller 31 is deformed according to the shape of the fixing roller 21, and the outer diameter is from the central portion side to the end side in the axial direction, contrary to the fixing roller 21. It decreases in a curve toward.

As described above, when the pressurizing roller 31 is pressed against the fixing roller 21 and both rollers 21 and 31 are rotated in that state, the shearing force Fa ~ as shown by the arrow in FIG. Fc occurs. These shearing forces Fa to Fc are generated so as to be inclined toward the end side in the axial direction with respect to the recording medium transport direction E, and further increase gradually toward the end side (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, but in reality, the shearing force of a different magnitude is shown at each position in the axial direction. Occurs.

In the present embodiment, the direction in which the shearing forces Fa to Fc are generated is the direction in which the shearing forces Fa to Fc are inclined toward the end side with respect to the recording medium transport direction E so that the outer diameter of the fixing roller 21 is set to the end side in the axial direction. This is because the peripheral speed difference of the fixing roller 21 is generated between the central portion side and the end portion side by increasing the size toward the central portion. Further, in the present embodiment, the shearing 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 portion side in the axial direction toward the end portion side. It is caused by doing.

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 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 removed from the fixing roller 21 or the pressure roller 31. It is considered that the effect of removing is obtained to some extent. However, in this case, when the shearing forces Fa to Fc at each position in the axial direction are compared, they have the same magnitude and there is no difference between the shearing forces Fa to Fc, so that a high adhesive toner removing effect is achieved. Is considered difficult to obtain.

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

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

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 expressed by the following equation 1.

Fr = Tr / R ... Equation 1

As described above, the value Fr of the circumferential component of the shearing force can be obtained from the value of the radius R of the fixing roller 21 and the torque Tr, but the fixing roller 21 according to the present embodiment has the radius R extending in the axial direction. Is different. Therefore, in 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, the torque measuring device 50 as shown in FIG.

The 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 fixing 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. Further, a drive gear 56 is provided at the tip of the rotation shaft of the motor 52 through which the torque converter 51 is inserted.

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 the gear portion 21a provided at one end 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 in 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 value Tr of the total torque of the fixing roller 21 and the value R of the average radius of the fixing roller 21 obtained in this manner into the above equation 1, the shearing generated between the fixing roller 21 and the pressure roller 31 It is possible to calculate the value Fr of the circumferential component of the force. Then, the magnitude of the torque, the roller radius, and the like may be adjusted so that the value Fr of the obtained circumferential component of the shearing force is in the range of 15 N or more and 25 N or less. In the present embodiment, the total torque of the fixing roller 21 which is the drive roller is calculated, but when the pressure roller 31 is the drive roller, the total torque of the pressure roller 31 is calculated in the same manner. Using this value and the average radius (at the nip portion N) of the pressurizing roller 31, the value Fr of the circumferential component of the shearing force may be calculated.

Hereinafter, configurations of other embodiments of the present invention will be described. Of the configurations of the embodiments described below, the parts having the same functions as those of the above-described embodiments are designated by the same reference numerals and duplicate description will be 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 curved shape from the central portion side to the end portion side in the axial direction. The rate of increase in diameter is different. In the embodiment shown in FIG. 14, unlike the above embodiment, the rate of increase in the outer diameter of the fixing roller 21 decreases from the central portion side to the end portion side in the axial direction. That is, as shown in FIG. 15, in each of the compartments C1 to Cn divided by a predetermined length in the axial direction of the fixing roller 21, the outer diameter of the compartment on the end side with respect to the compartment on the central portion side adjacent to each other. The amount of increase D1 to Dn gradually decreases from the central portion side to the end portion side (D1> D2> D3> ...> Dn).

FIG. 16 is a diagram showing a state in which the pressurizing roller 31 is brought into contact with the fixing roller 21 shown in FIG. 14 to pressurize.
In the case of this embodiment as well, since the pressure roller 31 is an elastic roller, when it is pressed against the fixing roller 21, at least the nip portion N is elastically deformed according to the shape of the fixing roller 21.

In the present embodiment, when the pressurizing roller 31 is rotated while the fixing roller 21 is pressurized, shearing forces Fa to Fc as shown by arrows in FIG. 14 are generated between the roller 21 and 31. These shearing forces Fa to Fc are generated so as to be inclined toward the end side in the axial direction with respect to the recording medium transport direction E, as in the above-described embodiment. However, in the present embodiment, unlike the above-described embodiment, the rate of increase in the outer diameter of the fixing roller 21 is reduced from the central portion side in the axial direction toward the end portion side, which is caused by this. Then, the shearing 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 fixed toner can be effectively removed by the difference between the shearing forces in the axial direction. .. Further, in the present embodiment, since the shearing force increases toward the central portion side, a high adhesive toner removing effect can be obtained particularly on the central portion side.

Further, as an embodiment different from the above, the fixing roller 21 as shown in FIGS. 17 and 18 may be used. The outer diameter of the fixing roller 21 shown in FIG. 17 decreases from the central portion side in the axial direction toward the end portion side, and the reduction rate of the outer diameter increases from the central portion side in the axial direction toward the end portion side. It is formed like this. On the other hand, the outer diameter of the fixing roller 21 shown in FIG. 18 decreases from the central portion side in the axial direction toward the end portion side, but the reduction rate of the outer diameter decreases from the central portion side in the axial direction to the end portion side. It is formed so as to become smaller toward it.

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 are different depending on whether the side where the shearing force Fa to Fc is increased is the central portion side or the end portion side. Also in the roller, the shear 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 rollers 21 shown in FIGS. 17 and 18 are generated so that the shearing forces Fa to Fc are inclined toward the central portion in the axial direction with respect to the recording medium transport direction E. Therefore, considering the susceptibility of wrinkles to the recording medium P, the fixing rollers 21 shown in FIGS. 10 and 14 are preferable to the fixing rollers 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 less likely to occur.

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. The fixing device 20 shown in FIG. 19 is attached to a fixing roller 21 via a fixing roller 21, a heating roller 22 having a halogen heater 24 inside, an endless fixing belt 27 stretched therein, and a fixing belt 27. It is provided with a pressure roller 31 that comes into contact with the pressure roller 31. By applying the shape of the fixing roller 21 of any one of FIGS. 10, 14, 17, and 18 to the fixing roller 21 included in the fixing device 20, the above-mentioned shearing force is generated effectively. Adhering toner can be removed. That is, by making the fixing roller 21 into the shape of the fixing roller 21 of any one of FIGS. 10, 14, 17, and 18, the fixing belt 27 and the pressure roller 31 that are in contact with each other are at least nip portion N. The outer diameter is formed so as to increase or decrease in a curved shape from the central portion side in the axial direction toward the end portion side. As a result, a shearing force whose size changes in the axial direction can be generated between the fixing belt 27 and the pressure roller 31, so that the adhesive toner can be effectively removed by the difference between the shearing forces. can do.

Further, the configuration of the present invention is also applicable to the 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 fixing belt 27 and the pressure roller 31 are formed by forming the surface of the nip forming member 26 in contact with the fixing belt 27 into any of the shapes shown in FIGS. 21 (a) to 21 (d). The outer diameter of the nip portion N can be 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 at least in the nip portion N. The shape of the nip forming member 26 shown in FIGS. 21 (a) to 21 (d) corresponds to the shape of the fixing roller 21 shown in FIGS. 10, 14, 17, and 18, in that order.

Further, in order to more reliably prevent the generation of fixed toner, the cleaning roller 43 as a cleaning means may be placed in contact with the surface of the fixing roller 21 as in the embodiment shown in FIG. 22 (a). .. Alternatively, as shown in FIG. 3B, the cleaning roller 43 may be arranged in contact with the surface of the pressure roller 31. In this case, the fixed 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 fixed 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.

Further, even when the cleaning roller 43 is provided in this way, the amount of the fixed toner 203 removed and recovered by the cleaning roller 43 is reduced by the amount that the fixed toner 203 is removed by the recording medium P. For this reason, the fixed toner 203 collected by the cleaning roller 43 solidifies to generate an abnormal noise, and the fixed toner 203 accumulated in the cleaning roller 43 in a predetermined amount or more melts out to stain the recording medium. Is less likely to occur.

As described above, according to the fixing device according to the present invention, a shearing force having a circumferential component size of 15 N or more and 25 N or less is generated between rotating bodies such as a fixing roller and a pressure roller. By passing the recording medium through the nip portion in this state, a sufficient deposit removing force (shearing force) can be 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 the 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, the fixing device according to the present invention can reliably remove deposits such as fixed toner on the rotating body. Moreover, wrinkles are less likely to occur on the recording medium, and a good image can be obtained.

Further, according to the fixing device 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 portion side to the end portion side in the axial direction. Therefore, shear forces of different sizes can be generated in the axial direction. Thereby, the difference between these shearing forces can more effectively remove the deposits.

Further, according to the fixing device according to the present invention, the deposits on the rotating body can be transferred to the recording medium and removed, so that the cleaning means (cleaning web, cleaning roller, etc.) as described in Patent Document 2 above can be used. ) Does not need to be installed separately. Therefore, it is possible to avoid an increase in cost and an increase in size of the device.

As in the embodiment shown in FIG. 22, a cleaning means for removing the fixed toner on the fixing roller or the pressure roller may be separately provided, if necessary. In this case, even if the cleaning means is provided, the amount of the fixed toner removed / recovered by the cleaning means can be reduced by the amount that the fixed toner is removed by the recording medium. Therefore, it is possible to prevent problems such as abnormal noise due to solidification of the fixed toner collected by the cleaning means and stains on the recording medium due to the fixed toner melting out from the cleaning means.

Further, in the fixing device according to the present invention, the effect of removing deposits is exhibited every time the recording medium passes through the nip portion. Therefore, as compared with the configuration in which the toner is not removed during paper passing as described in Patent Document 1, the deposits can be removed more frequently, and the deposits on the rotating body can be effectively deposited. It can be suppressed.

In particular, the above-mentioned effects of the present invention can be expected to be great when a recording medium containing a large amount of a filler such as calcium carbonate is used. Further, a great effect can be expected when a toner in which silica particles containing silicone oil are externally added is used. For this type of toner, for example, 2 parts of hydrophobic silica RY50 (manufactured by Aerosil) whose surface contains or is coated with silicone oil is added to 100 parts of crushed toner or polymerized toner, and a peripheral speed of 40 m / m with a 20 L Henschel mixer. It is obtained by mixing for sec and 5 minutes, and then sieving with a sieve having a mesh size of 75 microns.

Although the present invention has been described above, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the gist of the present invention. The image forming apparatus provided with the fixing apparatus according to the present invention is not limited to the color image forming apparatus as shown in FIG. 1, and 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, a multifunction device thereof, and the like.

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

JP-A-2002-40860 JP-A-2009-37078

Claims (10)

It has two rotating bodies that come into contact with each other to form a nip.
In a fixing device that fixes an image by passing a recording medium on which an image is formed through the nip portion.
One of the two rotating bodies is a hard roller, and the other is an elastic roller that elastically deforms when it comes into contact with the hard roller.
A fixing device characterized in that the circumferential component of the shearing force generated between the hard roller and the elastic roller is 15 N or more and 25 N or less. The fixing device according to claim 1, wherein the shearing force generated between the hard roller and the elastic roller is generated so as to be inclined toward the end side in the axial direction with respect to the recording medium transport direction. The fixing device according to claim 1 or 2, wherein the shearing force generated between the hard roller and the elastic roller increases from the central portion side in the axial direction toward the end portion side. The fixing device according to claim 1 or 2 , wherein the shearing force generated between the hard roller and the elastic roller decreases from the central portion side in the axial direction toward the end portion side. When there is no member other than the elastic roller that comes into contact with the surface of the hard roller, the value of the circumferential component of the shearing force generated between the hard roller and the elastic roller is the value, and the total torque generated in the hard roller is the value. The fixing device according to any one of claims 1 to 4 , wherein the value is obtained by dividing by the average radius of the hard roller. When there is no member other than the hard roller that comes into contact with the surface of the elastic roller , the value of the circumferential component of the shearing force generated between the hard roller and the elastic roller is used as the value of the circumferential component of the shearing force, and the total torque generated by the elastic roller is used as the value. The fixing device according to any one of claims 1 to 4 , wherein the value is obtained by dividing by the average radius of the elastic roller. One of said rigid roller and said resilient roller, a driven rotary member driving force to rotate is applied and the other of claims 1 to a driven rotating body that is driven to rotate together with the drive rotor 6 The fixing device according to any one item. Any of claims 1 to 7, wherein the shearing force generated between the hard roller and the elastic roller is 15 N or more and 25 N or less in a state where the cumulative number of recording media passing through the nip portion is 1000. The fixing device according to item 1. Claim 1 in which the shearing force generated between the hard roller and the elastic roller is 15 N or more and 25 N or less in a state where the cumulative number of recording media passing through the nip portion is 1000 or more and 10000 or less. The fixing device according to any one of 8 to 8. An image forming apparatus comprising the fixing apparatus according to any one of claims 1 to 9.

Images