JP2011141432A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of image failure due to the occurrence of wrinkling in a transfer section, because the slack amount, in an intermediate transfer belt on a driving roller and a first transfer roller, becomes greater when adopting a composition making an interval between the driving roller and the first transfer roller narrower than the interval between a hanging roller and the driving roller. <P>SOLUTION: The first transfer roller has each of the diameters in end sections greater than the diameter in a central section in the axial direction of the first transfer roller, and an inclined section, which inclines toward the central section from the end sections of the first transfer roller, is provided in the first transfer roller. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a transfer technique for transferring a toner image formed on an image carrier onto a recording material using an electrophotographic technique such as a copying machine or a laser beam printer.

  A toner image formed on an image carrier such as a photosensitive drum is transferred to an intermediate transfer belt stretched by a plurality of rollers (stretching roller, first transfer roller, driving roller, etc.), and then the recording material is transferred from the intermediate transfer belt. An image forming apparatus having a transfer portion for transferring a toner image is employed. The transfer unit that transfers the toner image onto the recording material contacts the inner surface of the intermediate transfer belt, contacts the inner transfer roller that stretches the intermediate transfer belt, and the outer surface of the intermediate transfer belt. And a second transfer roller that presses one transfer roller.

  As an example of such an image forming apparatus, there is a configuration as described in Patent Document 1. In this configuration, a configuration is adopted in which a driving roller that transmits a driving force to the intermediate transfer belt is disposed downstream of the image carrier and upstream of the transfer unit in the moving direction of the intermediate transfer belt. By disposing the drive roller on the downstream side of the image carrier, the tension of the belt surface facing the image carrier can be increased, and the transfer of the toner image from the image carrier to the intermediate transfer belt can be stabilized. it can. On the other hand, since the roller forming the transfer portion is not a driving roller, there is an advantage that the degree of freedom of the configuration of the driving roller can be increased in order to improve the transmission of driving force from the driving roller to the intermediate transfer belt.

JP2008-176298

  On the other hand, the belt surface on the downstream side of the drive roller tends to sag in the moving direction of the intermediate transfer belt. If the configuration in which the distance between the driving roller and the transfer inner roller is narrower than the distance between the tension roller and the driving roller, the amount of sag of the belt between the driving roller and the transfer inner roller increases. Further, since the intermediate transfer belt is sandwiched and conveyed between the outer transfer roller and the inner transfer roller, the transfer portion is likely to be wrinkled toward the center. As a result, there arises a problem that image defects due to wrinkles occur.

  Therefore, according to the present invention, a driving roller is provided on the upstream side of the transfer unit in the moving direction of the intermediate transfer belt, and even if the amount of sag of the intermediate transfer belt at the transfer unit is large, the intermediate transfer belt is shifted toward the center. An object of the present invention is to provide a configuration that reduces the tendency to become easy.

  An image carrier, a rotatable intermediate transfer belt carrying a toner image transferred from the image carrier, a first transfer roller contacting an inner surface of the intermediate transfer belt, and an outer surface of the intermediate transfer belt; A second transfer roller that presses the first transfer roller via the intermediate transfer belt, and a transfer unit that forms a transfer portion that transfers a toner image formed on the intermediate transfer belt to a recording material; A tension roller that is in contact with an inner surface of the transfer belt and stretches the intermediate transfer belt; and a driving roller that transmits a driving force for rotating the intermediate transfer belt to the intermediate transfer belt, The transfer roller is disposed downstream of the drive roller and upstream of the stretching roller in the moving direction of the intermediate transfer belt, and the first transfer roller is located adjacent to the drive roller. In the image forming apparatus, a diameter of an end portion of the first transfer roller is larger than a diameter of a central portion, and the first transfer roller is configured to extend from the end portion of the first transfer roller in the axial direction of the first transfer roller. It has the inclination part which inclines toward the center part of a 1st transfer roller, It is characterized by the above-mentioned.

  According to the present invention, the driving roller is provided on the upstream side of the transfer portion in the moving direction of the intermediate transfer belt, and image deterioration can be reduced even if the amount of sag of the intermediate transfer belt at the transfer portion is large.

1 is a schematic front view of an image forming apparatus according to an embodiment of the present invention. It is a front schematic diagram of a secondary transfer part according to an embodiment of the present invention. FIG. 3 is a schematic front view showing wrinkles on the intermediate transfer belt according to the embodiment of the invention. FIG. 5 is a measurement schematic diagram for measuring a level difference of a wrinkle on an intermediate transfer belt according to an embodiment of the present invention. It is a shape figure of the 1st transfer roller concerning an embodiment of the invention.

(Example)
<About image forming apparatus>
An image forming apparatus according to the present invention will be described with reference to FIG.

  The image forming apparatus shown in FIG. 1 is a color image forming apparatus using an electrophotographic system. The image forming apparatus shown in FIG. 1 is a cross-sectional view of a so-called intermediate transfer tandem type image forming apparatus in which four color image forming portions are arranged side by side on an intermediate transfer belt.

  First, the image forming units 1Y, 1M, 1C, and 1K will be described. In this embodiment, an image forming unit 1Y that forms a yellow image, an image forming unit 1M that forms a magenta image, an image forming unit 1C that forms a cyan image, and a black image are formed. The image forming unit 1K is provided with four image forming units. Next, each image forming unit will be described.

  Reference numerals 2a, 2b, 2c, and 2d denote photosensitive drums as image carriers that can rotate in the direction of arrow B, respectively. Reference numerals 3a, 3b, 3c, and 3d denote charging devices for charging the respective photosensitive drums. Reference numeral 7 denotes an exposure apparatus that performs image exposure of each photosensitive drum based on input image information. Reference numerals 4a, 4b, 4c and 4d denote developing devices for forming toner images on the respective photosensitive drums. Reference numerals 6a, 6b, 6c and 6d denote cleaning devices for removing toner remaining on the photosensitive drum after the transfer process.

  The intermediate transfer belt 8 is stretched by a stretching roller 11, a driving roller 59, and a first transfer roller 10, and is rotated in the arrow A direction. The tension roller 11 is a roller that applies tension to the intermediate transfer belt so that the tension of the intermediate transfer belt is constant. The driving roller 59 is a roller that transmits driving force to the intermediate transfer belt. The first transfer roller 10 is a roller that forms the secondary transfer portion 34.

  Inside the intermediate transfer belt 8, primary transfer rollers 5a, 5b, 5c for forming primary transfer portions (32a to 32d) for transferring the toner images formed on the respective photosensitive drums to the intermediate transfer belt 8. 5d. With this configuration, four color toner images are superimposed and transferred onto the intermediate transfer belt and conveyed to the secondary transfer unit 34.

  The recording material P conveyed from the paper feed cassette 17 is conveyed to the secondary transfer unit 34 by the registration roller 19. The secondary transfer unit 34 is in contact with the first transfer roller 10 provided on the inner surface of the intermediate transfer belt 8 and the outer surface of the intermediate transfer belt 8, and presses the first transfer roller 10 via the intermediate transfer belt 8. The transfer roller 12 is formed. The toner is transferred to the recording material by applying a voltage having a polarity opposite to the normal charging polarity of the toner from the power source to the second transfer roller 12.

  The toner image formed on the intermediate transfer belt 8 is sent from the registration roller 19 to the secondary transfer unit 34 at a preset timing, and then transferred onto the recording material P conveyed to the secondary transfer unit 34. Is done. Thereafter, the recording material P is conveyed to the fixing device 16. The fixing device 16 includes a fixing roller 16a and a pressure roller 16b, and applies a predetermined pressure and heat by the fixing roller 16a and the pressure roller 16b to melt and fix the toner image on the recording material P. Then, the paper is discharged out of the image forming apparatus by the paper discharge roller 21.

  The toner remaining on the intermediate transfer belt 8 without being transferred to the recording material P by the secondary transfer unit 34 is cleaned by the intermediate transfer belt cleaning device 13.

<Each roller that stretches the intermediate transfer belt>
The intermediate transfer belt 8 will be described in detail with reference to FIGS.
First, the shape of each roller that stretches the intermediate transfer belt 8 will be described.
The shape of the first transfer roller 10 is a shape in which an inclined portion 202 is provided in the axial direction. (Details will be described in “First transfer roller”.) The shape of the second transfer roller 12 is a straight shape in the axial direction. The shape of the tension roller 11 and the shape of the drive roller 59 are straight in the axial direction. In this embodiment, the primary transfer rollers 5a, 5b, 5c, and 5d are straight in the axial direction.

Next, the arrangement of the rollers that stretch the intermediate transfer belt 8 will be described.
The rollers for stretching the intermediate transfer belt 8 are arranged such that a driving roller 59 is disposed obliquely downward with respect to the horizontal plane with respect to the stretching roller 11 and is substantially vertically upward from the driving roller 59 with respect to the bottom surface of the image forming apparatus. The first transfer roller 10 is disposed. In this embodiment, the bottom surface of the image forming apparatus is parallel to the horizontal plane. In the present embodiment, the term “substantially perpendicular” refers to a straight line connecting the rotation center of the drive roller 59 and the rotation center of the first transfer roller 10 and a vertical line (a line perpendicular to the bottom surface of the image forming apparatus). Is in the range of 0 ° to 15 °.
That is, the first transfer roller is disposed downstream of the drive roller and upstream of the stretching roller in the moving direction of the intermediate transfer belt 8.

  Further, the interval between the driving roller 59 and the first transfer roller 10 is arranged to be narrower than the interval between the stretching roller 11 and the driving roller 59. The reason why each roller is arranged in this way will be described.

  The intermediate transfer belt 8 stretched between the stretching roller 11 in which the image forming unit is disposed and the driving roller 59 is arranged such that the driving roller 59 is positioned obliquely below the horizontal surface with respect to the stretching roller 11. Inclined. Further, the drive roller 59 and the first transfer roller 10 are arranged so that the secondary transfer surface 8c is as short as possible. As a result, the illustrated image forming apparatus can be miniaturized in the height direction and the width direction. Further, in this embodiment, the intermediate transfer belt 8 between the stretching roller 11 and the driving roller 59 is inclined to further reduce the size.

  Next, the drive roller 59 and the first transfer roller 10 that form the secondary transfer surface 8c will be described. The drive roller 59 is disposed below the first transfer roller 10 in a substantially vertical direction with respect to the bottom surface of the image forming apparatus. Thus, the recording material conveyance path from the registration roller 19 to the secondary transfer surface 8c can be formed substantially linearly. In order to prevent the recording material P from electrostatically sticking to the intermediate transfer belt 8 toward the first transfer roller 10 when the recording material P is conveyed from the secondary transfer unit 34 to the fixing device 16, driving is performed. The maximum diameter of the first transfer roller 10 is made smaller than the maximum diameter of the roller 59. The maximum diameter of the first transfer roller 10 is the maximum diameter of the first transfer roller 10 so as to form a later-described inclined portion. Thereby, the separation property of the recording material from the secondary transfer portion 34 is improved. Specifically, the greater the curvature of the first transfer roller 10, the higher the separation of the recording material P. Furthermore, by making the diameter of the drive roller 59 larger than that of the first transfer roller 10, the contact area between the intermediate transfer belt 8 and the drive roller 59 can be increased, and the drive transmission to the intermediate transfer belt 8 can be kept good. It becomes.

<Problems of wrinkles on the secondary transfer surface>
However, when the first transfer roller 10 has a straight shape in the axial direction of the first transfer roller 10, there is a problem that uneven wrinkles are generated on the secondary transfer surface 8c in the axial direction. The wrinkles generated on the intermediate transfer belt 8 will be described with reference to FIGS.

  In the configuration in which the driving roller 59 is provided upstream of the first transfer roller 10, wrinkles are generated on the intermediate transfer belt 8 upstream of the secondary transfer unit 34, as shown in FIG. 3. In FIG. 3, the wrinkles are portions indicated by dotted lines. The level difference of the wrinkles is determined by the thickness of the intermediate transfer belt 8 and the tension pressure of the intermediate transfer belt 8. The tension pressure on the intermediate transfer belt 8 is determined by the strength of the intermediate transfer belt 8 and the conveyance stability of the intermediate transfer belt 8. The intermediate transfer belt 8 used in this example was evaluated by changing the thickness of the intermediate transfer belt 8 by changing the tension pressure to 1.2 kgf as a configuration capable of stably transporting the moving speed of the intermediate transfer belt 8. . Table 1 shows the relationship between the thickness of the intermediate transfer belt 8 and the level difference of the wrinkles. In the measurement, as shown in FIG. 4, the intermediate transfer belt 8 is stretched, the drive is rotated for a certain period of time so that the stretched state of the intermediate transfer belt 8 is stabilized, and then the drive is stopped. Measurement is performed at a predetermined point in the circumferential direction of the intermediate transfer belt 8 at the center position between the transfer rollers 10. The measurement method is to scan the laser displacement meter 101 in the axial direction of the first transfer roller 10 and use the measured value (maximum value−minimum value) X as an indicator of the level difference of the wrinkles. Measurement was performed using a sensor LK010). When wrinkles are generated upstream of the secondary transfer unit 34, when the recording material P is conveyed to the secondary transfer unit 34, a contact portion and a non-contact portion between the intermediate transfer belt 8 and the recording material P are formed. There is a concern that the transferability differs due to the occurrence of electric discharge. That is, the discharge area varies in the axial direction, and density unevenness may occur. At this time, the density unevenness of the image becomes conspicuous in a line image or a halftone image formed by dots. This is because when the discharge upstream of the secondary transfer section 34 occurs, the density is greatly changed by transferring the toner to a region where the toner is not placed around. Table 1 shows the relationship between the level difference of the wrinkle and the density difference of the density unevenness formed in the wrinkle shape of the Bk halftone image output this time. For the image evaluation of wrinkles, a high-quality paper (basis weight 85 g / m 2) was used as a recording material, and a Bk halftone image was output. As an evaluation target, the intermediate transfer belt 8 having a different thickness described in relation to the above-described belt thickness and level difference was used. Density measurement was performed using a 504 optical densitometer manufactured by Xrite.

  From this result, as the thickness of the intermediate transfer belt 8 becomes thinner, the level difference of the wrinkles becomes larger, and the density difference of the halftone image output at that time tends to gradually increase when the thickness of the intermediate transfer belt 8 is 60 μm or less. It is in.

  In the evaluation of this example, when the thickness of the intermediate transfer belt is 80 μm or more, the density difference is 0.04 or less, which is not a level that can be recognized as wrinkled density unevenness. When the thickness of the intermediate transfer belt is 60 μm, slight density unevenness can be recognized, and when the thickness is less than that, it is significantly deteriorated.

<Shape of the first transfer roller>
As a method of eliminating this wrinkle, the diameter of the first transfer roller 10 is gradually increased symmetrically from the central portion 200 to the end portion 201 having the largest diameter in the axial direction of the first transfer roller 10. This wrinkle is improved by providing the inclined portion 202 that goes.

The shape of the first transfer roller 10 will be described with reference to FIG.
FIG. 5 shows the first transfer roller 10 as a roller having an inclined portion 202 (shaded portion in FIG. 5) whose diameter increases toward the end portion 201 in the axial direction of the first transfer roller 10. A list of shape examples of one transfer roller 10 will be described. With these shapes, the force directed toward the end 201 by the inclined portion 202 acts on the intermediate transfer belt, and the generation of wrinkles can be reduced. Further, the width of the intermediate transfer belt 8 in the axial direction is larger than the width of the first transfer roller 10 in the axial direction, and both end portions of the intermediate transfer belt are respectively outward in the axial direction from both end portions of the first transfer roller 10. To position. The configuration of each roller shape will be described.

  The roller shape described in FIG. 5A is composed of an inverted crown shape having an inclined portion 202 that gradually increases from the central portion 200 to the end portion 201 and a shape in which the end portion 201 is straight. ing. By the inclined portion 202, the intermediate transfer belt 8 sandwiched between the first transfer roller 10 and the second transfer roller 12 is pulled toward the end portion, and the generation of wrinkles can be reduced. Further, the straight shape of the end portion 201 can reduce the pulling force of the intermediate transfer belt toward the end portion side, and can prevent the intermediate transfer belt 8 from being damaged. Note that the maximum image formable area width is within the area of the central portion 200. Further, the width of the intermediate transfer belt 8 is set to be longer than the length of the central portion 200 + the end portion 201 × 2.

  The roller shape described in FIG. 5B is an inverted crown shape in which an inclined portion 202 that gradually increases from the central portion 200 to the end portion 201 is provided over the entire roller area. By the inclined portion 202, the intermediate transfer belt 8 sandwiched between the first transfer roller 10 and the second transfer roller 12 is pulled toward the end portion, and the generation of wrinkles can be reduced.

  The roller shape described in FIG. 5C is a V-shape provided with an inclined portion 202 that increases from the central portion 200 to the end portion 201 with a constant inclination. By the inclined portion 202, the intermediate transfer belt 8 sandwiched between the first transfer roller 10 and the second transfer roller 12 is pulled toward the end portion, and the generation of wrinkles can be reduced.

  The roller shape described in FIG. 5D is an inverted crown shape provided with an inclined portion 202 that gradually increases from the central portion 200 to the end portion 201, and gradually decreases from the end portion 201 toward the axis. Made of shape. By the inclined portion 202, the intermediate transfer belt 8 sandwiched between the first transfer roller 10 and the second transfer roller 12 is pulled toward the end portion, and the generation of wrinkles can be reduced. Further, the shape that gradually decreases from the end portion 201 toward the shaft reduces the pulling force of the intermediate transfer belt 8 toward the end portion, thereby preventing the intermediate transfer belt 8 from being damaged.

  The roller shape described in (e) of FIG. 5 includes a shape in which the central portion 200 is straight, and a shape in which an inclined portion 202 that increases with a certain inclination from the central portion 200 to the end portion 201 is provided. The end 201 has a straight shape. By the inclined portion 202, the intermediate transfer belt 8 sandwiched between the first transfer roller 10 and the second transfer roller 12 is pulled toward the end portion, and the generation of wrinkles can be reduced. Further, the straight shape of the central portion 200 and the end portion 201 can reduce the pulling force of the intermediate transfer belt 8 toward the end portion, thereby preventing the intermediate transfer belt 8 from being damaged.

  The roller shape described in FIG. 5 (f) includes a shape in which the central portion 200 is straight and a shape in which an inclined portion 202 that increases from the end portion 201 to the shaft with a constant inclination is provided. . By the inclined portion 202, the intermediate transfer belt 8 sandwiched between the first transfer roller 10 and the second transfer roller 12 is pulled toward the end portion, and the generation of wrinkles can be reduced. Further, the straight shape of the central portion 200 can reduce the pulling force of the intermediate transfer belt 8 toward the end portion, thereby preventing the intermediate transfer belt 8 from being damaged.

  The roller shape shown in FIG. 5G is composed of a shape in which the central portion 200 is straight and a reverse crown shape in which an inclined portion 202 that gradually increases from the central portion 200 to the end portion 201 is provided. ing. By the inclined portion 202, the intermediate transfer belt 8 sandwiched between the first transfer roller 10 and the second transfer roller 12 is pulled toward the end portion, and the generation of wrinkles can be reduced. Further, the straight shape of the central portion 200 can reduce the pulling force of the intermediate transfer belt 8 toward the end portion, thereby preventing the intermediate transfer belt 8 from being damaged.

  The roller shape described in (h) of FIG. 5 includes an inverted crown shape provided with an inclined portion 202 that increases with a certain inclination from the central portion 200 to the end portion 201, and gradually from the end portion 201 toward the axis. It consists of a smaller shape. By the inclined portion 202, the intermediate transfer belt 8 sandwiched between the first transfer roller 10 and the second transfer roller 12 is pulled toward the end portion, and the generation of wrinkles can be reduced. Further, the shape that gradually decreases from the end portion 201 toward the shaft reduces the pulling force of the intermediate transfer belt 8 toward the end portion, thereby preventing the intermediate transfer belt 8 from being damaged.

  Next, a difference in diameter between the central portion 200 and the end portion 201 of the first transfer roller 10 (maximum difference in diameter of the inclined portion) will be described based on experimental results.

  When the thickness of the intermediate transfer belt 8 is 40 μm, if the difference in diameter between the central portion 200 and the end portion 201 of the first transfer roller 10 is 2.5 μm or more, image defects due to wrinkles are improved.

  When the thickness of the intermediate transfer belt 8 is 50 μm, if the difference in diameter between the central portion 200 and the end portion 201 of the first transfer roller 10 is 5.0 μm or more, image defects due to wrinkles are improved.

  When the thickness of the intermediate transfer belt 8 is 60 μm, if the difference in diameter between the central portion 200 and the end portion 201 of the first transfer roller 10 is 7.5 μm or more, image defects due to wrinkles are improved.

  From these results, it can be seen that when the thickness of the intermediate transfer belt 8 changes, the diameter difference for improving wrinkles changes. This can be said that wrinkles cannot be eliminated even if the first transfer roller 10 having the same diameter difference is used for the intermediate transfer belt 8 having different thicknesses. Therefore, from this result, in order to eliminate wrinkles generated in the intermediate transfer belt 8, if the difference in diameter of the first transfer roller 10 with respect to the thickness of the intermediate transfer belt 8 is 7% or more, image defects due to wrinkles are improved. You can ask.

  As described above, according to the present invention, in the moving direction of the intermediate transfer belt, the driving roller is provided on the upstream side of the transfer portion, and even if the amount of sag of the intermediate transfer belt at the transfer portion is large, It is possible to reduce the tendency of the intermediate transfer belt to move easily.

2a to 2d Photosensitive drum 8 Intermediate transfer belt 10 First transfer roller 11 Stretching roller 12 Second transfer roller 59 Driving roller 200 Central portion 201 End portion 202 Inclined portion 203 Axis P Recording material

Claims (4)

An image carrier, a rotatable intermediate transfer belt carrying a toner image transferred from the image carrier, a first transfer roller contacting an inner surface of the intermediate transfer belt, and an outer surface of the intermediate transfer belt; A second transfer roller that presses the first transfer roller via the intermediate transfer belt, and a transfer unit that forms a transfer portion that transfers a toner image formed on the intermediate transfer belt to a recording material; A tension roller that is in contact with an inner surface of the transfer belt and stretches the intermediate transfer belt; and a driving roller that transmits a driving force for rotating the intermediate transfer belt to the intermediate transfer belt, The transfer roller is disposed downstream of the drive roller and upstream of the stretching roller in the moving direction of the intermediate transfer belt, and the first transfer roller is located adjacent to the drive roller. In the image forming apparatus,
The first transfer roller has an inclined portion formed by increasing the diameter from the center of the first transfer roller toward the end of the first transfer roller in the axial direction of the first transfer roller. An image forming apparatus.   Image forming means for forming a toner image on the intermediate transfer belt between the stretching roller and the driving roller, and the first transfer roller and the driving roller are spaced by a distance between the stretching roller and the driving roller. The image forming apparatus according to claim 1, wherein the interval is narrow.   The image forming apparatus according to claim 1, wherein a shape of the second transfer roller is a straight shape in an axial direction of the second transfer roller.   The image forming apparatus according to claim 1, wherein a maximum diameter of the first transfer roller is smaller than a diameter of the driving roller.

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