JP2016024307A - Fixation device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixation device capable of preventing the deterioration in image quality, which is caused by wax attached to a fixation belt, at low cost and without excessively increasing the size of the device.SOLUTION: A fixation device 200 comprises: a fixation belt 209 that is provided rotationally; a pressure member 210 that presses an outer peripheral side of the fixation belt 209 to form a fixation nip part N; and heating means 208h that heats the fixation belt 209. The fixation device 200 sandwiches and conveys a recording medium P having an unfixed image formed thereon, and fixes the image on the recording medium P at the fixation nip part N. The fixation device 200 further comprises a curvature changing member 101 that is provided in the vicinity of the way out of the recording medium P at the fixation nip part N and in contact with an inner peripheral side of the fixation belt 209, and causes the curvature of the fixation belt 209 to decrease at the contact position. The curvature changing member 101 is provided independently from the member forming the fixation nip part N.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fixing device and an image forming apparatus.

In an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a combination of these, an image is fixed using a fixing device and output as a recorded image. In such an image forming apparatus, charging, writing, development, transfer, cleaning, static elimination, etc. are repeated to form toner images on an image carrier in sequence, and the toner images are sequentially transferred to a recording medium such as a sheet or an OHP film. An electrophotographic method for fixing and outputting a recorded image is widely used.
In this electrophotographic image forming apparatus, the recording medium after the toner image has been transferred is passed between a heated fixing member and a pressure member, and the toner image on the recording medium is fixed while being conveyed. A fixing method using a pressure type fixing device has become the mainstream in recent years.

  As a heat-pressure type fixing device, for example, a recording medium on which an unfixed toner image is formed is passed through a nip formed by a fixing belt having a heating roller on its inner periphery and a pressure roller. In some cases, the toner image is fixed on the recording medium. At this time, since the toner becomes sticky when melted, problems such as toner offset and winding of the recording medium around the fixing belt occur. In general, these problems can be solved by providing a release layer composed of a material such as a fluororesin on the surface of the fixing belt, or by adding WAX as a release agent to the toner. I have been trying.

However, in the toner containing WAX, when the image is separated from the fixing belt at the exit of the nip portion, the WAX exuded from the toner adheres to the fixing belt, and the WAX attached to the fixing belt deteriorates the image quality. cause.
That is, since the releasability is partially enhanced at the location where the wax is attached on the fixing belt, the image fixed at that location on the second round of the fixing belt has a high glossiness with respect to the surroundings. There is a problem in that the glossiness is different among the images on the recording medium, and the image quality is deteriorated.
Further, as described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2002-244331), a portion where WAX is attached to the fixing belt is not non-image portion in the second rotation of the fixing belt. There is a problem in that WAX adheres to the image portion and the trace of the image portion at the time of previous fixing is projected. With regard to such a problem, particularly in the case of a transparent recording medium such as an OHP film, a decrease in transparency due to WAX transferred from the fixing belt is more clearly observed.

As a means for solving such a problem, Patent Document 1 discloses a method of collecting WAX by pressing a roller against the surface of a fixing belt.
However, in the method of pressing the roller, the collected WAX is reattached to the fixing belt. If the WAX is further removed from the roller against this reattachment, the cost can be increased by providing another member. This leads to an increase in the size of the fixing device.

  The present invention has been made in view of the above-described problems in the prior art, and is intended to reduce the image quality caused by WAX adhering to the fixing belt at a low cost and excessively enlarge the apparatus. It is an object of the present invention to provide a fixing device that can be prevented without any problems.

  In order to solve the above problems, a fixing device according to the present invention includes a fixing belt that is rotatably provided, a pressure member that presses an outer peripheral side of the fixing belt to form a fixing nip portion, and the fixing belt. And a heating device that heats the recording medium on which an unfixed image is formed at the fixing nip portion, and fixes the image on the recording medium. And a curvature changing member that is provided in contact with the inner peripheral side of the fixing belt and that reduces the curvature of the fixing belt at the contact position, and the curvature changing member includes the fixing nip. It is characterized by being provided independently of the member forming the part.

  According to the present invention, it is possible to provide a fixing device that can prevent a reduction in image quality caused by WAX adhering to the fixing belt at a low cost and without excessively increasing the size of the device.

1 is a schematic diagram illustrating a configuration in an embodiment of an image forming apparatus according to the present invention. 1 is a schematic diagram illustrating a configuration in an embodiment of a fixing device according to the present invention. 6 is a graph showing the relationship of the image quality with respect to the distance from the leading end of the fixing nip portion N of the nip shape changing member 101 to the inflection point X. FIG. 6 is a schematic diagram illustrating a configuration of another embodiment of a fixing device according to the present invention. FIG. 10 is a schematic diagram showing a configuration of still another embodiment of the fixing device according to the present invention. FIG. 4 is a perspective view of the vicinity of a nip shape changing member 101 in FIG. 3.

The fixing device according to the present invention heats the fixing belt 209 that is rotatably provided, a pressure member 210 that presses the outer peripheral side of the fixing belt 209 to form a fixing nip portion N, and the fixing belt 209. A fixing device 200 that includes a heating unit 208h and sandwiches and conveys the recording medium P on which an unfixed image is formed at the fixing nip N to fix the image on the recording medium P. The fixing nip N A curvature changing member 101 provided near the outlet of the recording medium P and in contact with the inner peripheral side of the fixing belt 209 and reducing the curvature of the fixing belt 209 at the contact position. The curvature changing member 101 is provided independently of the member forming the fixing nip portion N.
In the present invention, the adhesion of WAX onto the fixing belt 209 can be suppressed by reducing the speed (separation speed) at which the image is separated from the fixing belt 209 at the exit of the fixing nip N. By reducing the separation speed, the WAX can easily feel the difference in surface properties between the fixing belt 209 and the image, and the amount of the WAX attached to the fixing belt 209 having a release layer having the property that the WAX does not easily adhere is reduced.

Next, the fixing device according to the present invention will be described in more detail with reference to the drawings.
Although the embodiments described below are preferred embodiments of the present invention, various technically preferable limitations are attached thereto, but the scope of the present invention is intended to limit the present invention in the following description. Unless otherwise described, the present invention is not limited to these embodiments.

FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus according to an embodiment of the present invention.
An image forming apparatus 200 shown in FIG. 1 includes an image forming unit 220A positioned at the center of the apparatus main body, a paper feeding unit 200B positioned below the image forming unit 220A, and an image (not shown) positioned above the image forming unit 220A. A high-speed machine having a reading unit.

  An intermediate transfer belt 213 having a transfer surface extending in the horizontal direction is disposed in the image forming unit 220A, and an image having a color complementary to the color separation color is formed on the upper surface of the intermediate transfer fixing belt 213. A configuration is provided. That is, the photoconductors 205Y, 205M, 205C, and 205K as image carriers that can carry images of toners of complementary colors (yellow (Y), magenta (M), cyan (C), and black (K)). Are juxtaposed along the transfer surface of the intermediate transfer belt 213.

  Each of the photoconductors 205Y, 205M, 205C, and 205K is composed of a drum that can rotate in the same direction (counterclockwise direction). Around the drums, charging devices 202Y, 202M, 202C, and 202K are arranged in the rotation process. An optical writing device 201, a developing device 203Y, 203M, 203C, and 203K, a primary transfer device 204Y, 204M, 204C, and 204K, and a cleaning device that perform a forming process are arranged. Each developing device 203Y, 203M, 203C, 203K contains a respective color toner.

  The intermediate transfer belt 213 is configured to be able to move in the same direction at a position facing the photoconductors 205Y, 205M, 205C, and 205K by being wound around a driving roller and a driven roller. In addition, a secondary transfer roller 215 is provided at a position facing a roller 214 that is one of the driven rollers.

  On the other hand, the paper P as a recording medium stacked in the paper feed tray 220 is taken out by the pick roll 221, and the transport roll 222 moves the transport path R 1 in the direction toward the registration roller 223 and the secondary transfer roller 215. Be transported.

  In the present embodiment, paper (paper) is used as a recording medium. However, the present invention is not limited to this, and a material other than paper such as an OHP film may be used as the recording medium. .

  In image formation in the image forming apparatus 200 of the present embodiment, the surface of the photoreceptor 205Y is uniformly charged by the charging device 202Y, and an electrostatic latent image is formed on the photoreceptor 205Y based on image information from the image reading unit. Is formed. The electrostatic latent image is visualized as a toner image by a developing device 203Y containing yellow toner, and the toner image is primarily transferred onto a transfer belt 213 by a primary transfer device 204Y to which a predetermined bias is applied. . The other photoconductors 205M, 205C, and 205K also form similar images only with different toner colors, and the toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 213 by the electrostatic force and superimposed.

Next, the toner image primarily transferred from the photoconductors 205Y, 205M, 205C, and 205K onto the intermediate transfer belt 213 is transferred to the paper P conveyed by the roller 214 and the secondary transfer roller 215.
The sheet P onto which the toner image has been transferred is further conveyed to the fixing device 206 and is fixed at a fixing nip N between the fixing belt 209 and the pressure roller 210. Next, the paper P discharged from the fixing nip N is sent out to the stacker 216 along the discharge path.

The fixing device 206 rotates at a position facing the fixing roller 207 via the fixing belt 209, a fixing roller 207 that is a counter member, a heating roller 208, a fixing belt 209 that is stretched over the fixing roller 209, and a fixed tension. And a pressure roller 210 that is a pressure member that freely press-contacts to form the fixing nip portion N.
Here, the fixing belt 209 is an endless belt, and has a two-layered structure in which an elastic layer such as a silicon rubber layer is formed on a base material such as nickel, stainless steel, or polyimide.
The heating roller 208 is an aluminum or iron hollow roller, and has heating means including a heater 208 h such as a halogen heater inside, and heats the fixing belt 209. In addition, a heating means is not restricted to this, For example, what is used well-known, such as an IH heating member, can be used.

The configuration of the fixing device 206 will be described in detail below.
The image forming apparatus according to the present invention includes the fixing device according to the present invention, which will be described in detail below, so that an image with high image quality that does not cause a gloss difference due to adhesion of WAX to the fixing belt 209 can be obtained. It is done.

<First Embodiment of Fixing Device>
Next, the configuration of an embodiment of the fixing device according to the present invention will be described with reference to FIG. FIG. 2 is a schematic diagram showing the configuration of the fixing device according to the embodiment of the present invention, and is an enlarged view of the exit portion of the fixing nip portion N of the fixing device 206 shown in FIG.
In the present embodiment, as shown in FIG. 2, the nip shape changing member 101 is brought into contact with the inner side of the fixing belt 209, while being not in contact with the fixing roller 207 so as not to prevent the rotation of the fixing roller 207. Arrange so that

At this time, since the nip shape changing member 101 exists on the inner peripheral side of the fixing belt 209, the angle (separation angle) formed between the paper P and the fixing belt 209 is θ ₁ near the exit of the fixing nip portion N, and the nip shape This is smaller than θ ₂ when the changing member 101 does not exist. By reducing the separation angle, the speed at which the paper P is separated from the fixing belt 209 (separation speed) is reduced, and the adhesion of WAX to the fixing belt 209 is suppressed.
As described above, by disposing the nip shape changing member 101 inside the fixing belt 209, it is possible to reduce the speed at which the recording medium P is separated from the fixing belt 209, and to suppress the adhesion of WAX to the fixing belt 209. It becomes. Further, in the present invention, since the WAX adhesion to the fixing belt 209 can be suppressed only by providing the nip shape changing member 101, the cost is low.

On the other hand, even if the nip shape changing member 101 exists, the separation angle is θ ₃ at a position away from the exit portion of the fixing nip portion N and is larger than θ ₂ , and separation is performed at this location. On the contrary, the separation speed becomes faster. Therefore, it is necessary to separate angle fixing belt 209 and the sheet P at a point theta ₁ is completely is completely separated.
For this reason, it is necessary to set a longer distance from the front end of the fixing nip portion N of the nip shape changing member 101 to the inflection point X.

FIG. 3 is a graph showing the relationship of the image quality with respect to the distance from the front end of the fixing nip portion N of the nip shape changing member 101 to the inflection point X.
As is apparent from FIG. 3, in order to achieve the desired image quality, the length of the nip shape changing member (the distance from the tip on the exit side of the fixing nip portion N to the inflection point X) is a predetermined length. It is preferable to have. On the other hand, if the length of the nip shape changing member 101 is too long, the circumferential length of the fixing belt 209 is increased, leading to an increase in the size of the fixing device, which is not preferable.

  As described above, changing the nip shape by inserting a member inside the fixing belt is performed in JP 2011-090340 A and the like. However, in Japanese Patent Application Laid-Open No. 2011-090340, the separation performance between the fixing belt and the recording medium is improved by increasing the curvature of the fixing belt at the nip exit portion by inserting a member. On the other hand, the present invention is based on a technical idea that is completely opposite to the conventional technique. By inserting the nip shape changing member 101 on the inner peripheral side of the fixing belt 209, the curvature is reduced, and the image quality is improved. It is intended to suppress the decrease.

<Second Embodiment of Fixing Device>
Next, another embodiment of the fixing device according to the present invention will be described.
FIG. 4 is a schematic view showing a configuration of another embodiment of the fixing device according to the present invention, and is a view showing an operation mechanism of the nip shape changing member 101.
In the operation mechanism of the nip shape changing member 101 in the present embodiment, the support rod 102 with the cam 103 attached is arranged closer to the fixing roller 207 than the nip shape changing member 101, and the nip shape changing member 101 depends on the operating conditions of the fixing device. This is done by extruding the top surface. A support rod 102 and a cam 103 rotated by a drive motor (not shown) push out the arm 104, and a spring member 105 provided between the arm 104 and the nip shape changing member 101 pushes the upper surface of the nip shape changing member 101. The cam 102 is attached at three positions on the front, center, and rear (three positions in the direction perpendicular to the paper surface), and the cam 102 is extruded uniformly in the axial direction. The exit side of the fixing nip portion N of the nip shape changing member 101 is fixed to the frame (not shown) of the fixing device at the side surface, and the upper surface of the nip shape changing member 101 is pushed out, so that the exit side of the fixing nip portion N rotate as a fulcrum, it is possible to change the separation angle theta _1.

As described above, the change of the separation angle is executed according to the operating condition of the fixing device, and this operating condition is, for example, the rotation speed of the fixing roller 207 in the present embodiment. In this embodiment, the fixing roller 207 is rotationally driven, and the fixing belt 209 is driven along with the rotation. Therefore, the faster the rotational speed of the fixing roller 207, the fixing belt 209 since the faster rate at which the sheet P is separated, WAX attaching the separation speed by reducing the theta ₁ for inhibiting the fixing belt 209 It is necessary to prevent the rise.

Here, in the present embodiment, the WAX adhesion to the fixing belt 209 is suppressed by adopting an arrangement configuration that takes the separation angle shown in Table 1 below by the operation mechanism with respect to a rotational speed of 100 to 300 mm / sec. And confirmed that good image quality was maintained. Examples of operating conditions other than the rotation speed include a fixing temperature that affects the amount of WAX exuded from the toner.
By providing the operation mechanism of the nip shape changing member 101 using the cam 102 in this way, it becomes possible to create a separation angle that suppresses the adhesion of WAX to the fixing belt 209 for each operation condition of the fixing device 200.

  As is apparent from Table 1 above, by setting the separation angle to a predetermined value with respect to the rotation speed of the fixing roller 207, it is possible to reduce the adhesion of WAX to the fixing belt 209. However, as the separation angle is reduced, the separation between the toner on the recording medium P and the fixing belt 209 decreases. Therefore, it is preferable to use the maximum value of the values described in Table 1 for the separation angle. Further, as the separation angle becomes smaller, the distance until the toner on the recording medium P is separated from the fixing belt 209 becomes longer. Therefore, it is desirable to change the length of the nip shape changing member 101 according to the separation angle as shown in Table 1.

<Third Embodiment of Fixing Device>
Next, still another embodiment of the fixing device according to the present invention will be described.
FIG. 5 is a schematic diagram showing the configuration of still another embodiment of the fixing device according to the present invention.
As shown in FIG. 5, when the present invention the effects of the present invention should be changed only separation angle theta _1, the nip shape changing member 101 in the fixing device according to the present embodiment, as shown in the drawing the plate-like Take shape.

<Perspective view of fixing device>
FIG. 6 is a perspective view of the vicinity of the nip shape changing member 101 of FIG. By providing the width of the nip shape changing member 101 in the axial direction of the fixing belt 209 wider than the width of the paper P that can be passed, WAX adhesion to the fixing belt 209 can be prevented over the entire surface of the recording medium P. In the present invention, by providing the nip shape changing member 101 over the entire length of the recording medium P in at least the sheet passing range, it is possible to prevent the WAX from adhering to the fixing belt 209 over the entire surface of the recording medium P.

  Further, a sliding layer 106 is added to the surface of the nip shape changing member 101 in order to prevent wear of the nip shape changing member 101 and the fixing belt as the fixing belt 209 rotates. As a material of the sliding layer 106, for example, a fluororesin excellent in heat resistance is preferable. By providing the sliding layer 106, it is possible to suppress the adhesion of WAX to the fixing belt 209 without hindering the operation of the fixing device 200.

  As described above, in the present invention, the nip shape changing member 101 and the fixing device 200 having the nip shape changing member 101 operating mechanism (such as the cam 103) cause the WAX to adhere to the fixing belt 209 regardless of the operating conditions of the fixing device 200. And image quality can be kept good.

  Although the present invention has been described with the belt fixing system shown in the drawings, the present invention is not limited to the embodiments shown in the drawings, and other embodiments, additions, modifications, deletions, etc. It can be changed within the range that can be conceived by a trader, and any embodiment is included in the scope of the present invention as long as the effects and effects of the present invention are exhibited.

100 Tension roller 101 Nip shape changing member 102 Support rod 103 Cam 104 Arm 105 Spring member 106 Sliding layer 200 Image forming device 220A Image forming unit 200B Paper feeding unit 201 Writing devices 202Y, 202C, 202M, 202K Charging devices 203Y, 203C, 203M, 203K Developing devices 204Y, 204C, 204M, 204K Primary transfer devices 205Y, 205C, 205M, 205K Photoconductor 206 Fixing device 207 Fixing roller 208 Heating roller 208h Halogen heater 209 Fixing belt 210 Pressure roller 213 Intermediate transfer belt 214 Roller ( Driven roller)
215 Secondary transfer roller 216 Stacker 220 Paper feed tray 221 Pick roller 222 Conveying roller N Fixing nip P Paper (recording medium)
T Toner X Inflection point R1 of nip shape changing member

JP 2002-244331 A

Claims (6)

A fixing belt provided rotatably,
A pressure member that pressurizes the outer peripheral side of the fixing belt to form a fixing nip;
Heating means for heating the fixing belt,
A fixing device that sandwiches and conveys a recording medium on which an unfixed image is formed at the fixing nip portion and fixes the image on the recording medium,
A curvature changing member provided near the exit of the recording medium in the fixing nip portion and in contact with the inner peripheral side of the fixing belt, and for reducing the curvature of the fixing belt at the contact position;
The fixing device, wherein the curvature changing member is provided independently of a member forming the fixing nip portion.   The fixing device according to claim 1, wherein the curvature changing member changes a contact angle with the fixing belt according to an operation condition of the fixing device.   The fixing device according to claim 2, wherein the operating condition is a rotation speed of the fixing belt.   4. The fixing device according to claim 1, wherein the curvature changing member is disposed over at least the entire length of a sheet passing range of the fixing belt. 5.   The fixing device according to claim 1, wherein the curvature changing member includes a sliding layer that suppresses sliding on a surface layer of a surface in contact with the fixing belt.   An image forming apparatus comprising the fixing device according to claim 1.