JP2006337813A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of obtaining a high-quality image by stabilizing a primary transfer nip without deteriorating the durability of an intermediate transfer belt. <P>SOLUTION: In the image forming apparatus, the intermediate transfer belt 10 composed of film material is stretched over between a driving roller 21 and a driven roller endlessly, and toner images formed on a plurality of photoreceptor drums 31 are primarily transferred to the belt 10 by electric field applied from a primary transfer roller 11. A backup roller 25 coming into contact with the inner surface side of the belt 10 is provided between the driving roller 21 and the photoreceptor drum 31 positioned on the upstream side of the driving roller 21, and an angle θ is ≥0° and <10° and a distance L1 is set to ≤40 mm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly, a toner image formed on a plurality of juxtaposed photosensitive drums is primarily transferred to an intermediate transfer belt to be combined, and the toner image is secondarily transferred onto a sheet. The present invention relates to a tandem type image forming apparatus.

  In general, in an electrophotographic tandem image forming apparatus, it is necessary to prevent the toner image transferred on the intermediate transfer belt from being disturbed. For example, Patent Document 1 discloses an intermediate transfer belt. It is disclosed to install in an inclined manner.

  The intermediate transfer belt has a thin film endlessly mounted on a driving roller and a driven roller so as to be rotationally driven, and is deformed by tension from the driving roller (a state in which a wave is struck in a direction perpendicular to the rotational direction) Hereinafter, this is referred to as a wavy phenomenon). Such deformation was significant at the portion that is closest to the drive roller, that is, the portion that contacts the photosensitive drum located upstream of the drive roller in the belt rotation direction. In recent years, along with the demand for higher image quality, the size and weight of each component have been reduced due to the downsizing and cost reduction of the apparatus, and the diameter of the drive roller has also been reduced. Therefore, the deformation of the intermediate transfer belt due to the tension from the driving roller cannot be ignored as the disturbance of the primary transferred toner image.

  Under the circumstances of miniaturization and high image quality, the nip of the primary transfer portion between the intermediate transfer belt and the photosensitive drum is required to contact at a low pressure. This is because if the pressing force of the primary transfer roller against the photosensitive drum is too strong, the intermolecular force between the toners becomes stronger than the electrostatic force, and a void phenomenon occurs in which the central portion of the toner image becomes a transfer defect.

  Here, with reference to FIG. 5, a configuration in the vicinity of the driving roller of the intermediate transfer belt in the conventional image forming apparatus will be described. The intermediate transfer belt 10 is rotationally driven in the direction of arrow A by a driving roller 21. Reference numeral 31 denotes a photosensitive drum, which is located upstream of the driving roller 21 in the rotational direction A of the intermediate transfer belt 10. A primary transfer roller 11 that can move up and down is pressed against the photosensitive drum 31 by its own weight and a pressing force of a spring 13.

  A registration sensor 26 for optically detecting a test pattern is installed between the driving roller 21 and the photosensitive drum 31 in order to correct the position of the image formed on the intermediate transfer belt 10. . In order to set the detection position of the registration sensor 26 to a fixed position, the inner surface side of the intermediate transfer belt 10 is backed up by a resist facing sheet metal 27.

  In the above configuration, the waviness phenomenon occurs in the contact portion of the intermediate transfer belt 10 with respect to the photosensitive drum 31 due to the tension applied to the intermediate transfer belt 10 by the driving roller 21 (particularly, when fluctuations in tension occur). Along with this undulation phenomenon, the primary transfer roller 11 moved upward, a sufficient transfer voltage was not applied, and image disturbance occurred.

In view of the image disturbance, the present inventors studied to move the resist facing sheet metal 27 slightly downward to back up the intermediate transfer belt 10 more strongly from the inner surface side. However, this causes a problem that the durability of the intermediate transfer belt 10 deteriorates.
JP 2002-169350 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of achieving high image quality by stabilizing the primary transfer nip without deteriorating the durability of the intermediate transfer belt.

  In order to achieve the above object, the present invention provides an intermediate transfer belt made of a film material stretched endlessly on a driving roller and a driven roller, and rotationally driven in one direction, so that a plurality of image carriers are carried on the surface of the intermediate transfer belt. In the image forming apparatus, the image bearing member positioned on the upstream side in the rotational direction of the intermediate transfer belt with respect to the drive roller, wherein the primary transfer roller is pressed against the respective image bearing members from the inner surface side of the intermediate transfer belt. A backup roller that is in contact with the inner surface side of the intermediate transfer belt is provided between the driving roller, a nip position between the image carrier and the intermediate transfer belt that is located upstream of the driving roller in the intermediate transfer belt rotation direction, and a primary transfer roller. And the nip position of the intermediate transfer belt, the nip position of the primary transfer roller and the intermediate transfer belt, and the nip of the backup roller and the intermediate transfer belt. Is 0 ° or more and less than 10 °, and the distance L1 from the nip position between the primary transfer roller and the intermediate transfer belt to the nip position between the backup roller and the intermediate transfer belt is 40 mm or less. It is characterized by.

  In the image forming apparatus according to the present invention, the angle θ is set as small as less than 10 °, and the distance L1 is set at 40 mm or less, so that the image carrier is located upstream of the drive roller in the intermediate transfer belt rotation direction. The wavy phenomenon of the intermediate transfer belt at the portion in contact with the toner is reduced. This stabilizes the nip between the image carrier and the primary transfer roller, eliminates the primary transfer failure, and prevents image quality deterioration. Further, the backup roller does not apply such a load to the intermediate transfer belt, and does not deteriorate the durability of the intermediate transfer belt.

  In the image forming apparatus according to the present invention, it is preferable that the intermediate transfer belt has a thickness of 70 to 120 μm and a tension of 20 to 40 [N / m] is applied. As the material, a polyamideimide resin can be suitably used.

  The backup roller may be installed corresponding to a detection position of a toner test pattern formed on the intermediate transfer belt. Since the backup roller also serves as a conventional resist-facing sheet metal, the number of parts can be reduced.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings.

(Schematic configuration of image forming apparatus, see FIG. 1)
The image forming apparatus shown in FIG. 1 is an electrophotographic color printer, which includes a printer main body 1 configured to synthesize four-color images in a so-called tandem method, an image reading device 2, and a control unit 3. It is configured.

  The image reading device 2 is a well-known device that reads an image of an original placed on an original platen glass (not shown) by an image sensor such as a CCD element. The original image is RGB (red, green, blue) by the image sensor. They are separated into the three primary colors and converted into electrical signals. The image data is subjected to various types of data processing in the control unit 3 and further converted into YMCK (yellow, magenta, cyan, black) reproduction colors. The YMCK image data is stored in the memory 4 of the control unit 3 and subjected to necessary correction such as misalignment correction.

  In the printer main body 1, a print head 30 (30Y, 30M, 30C, 30K) that forms a YMCK image including a photosensitive drum 31, a laser scanning optical device 32, a developing device 33, and the like is juxtaposed directly below the intermediate transfer belt 10. ing. In each print head 30, the laser scanning optical device 32 receives the transfer of the YMCK image data, forms a latent image on the photosensitive drum 31, and forms a toner image by the developing device 33. Such an electrophotographic process is well known and will not be described.

  The intermediate transfer belt 10 is stretched endlessly between a driving roller 21 and a driven roller 22 for applying tension, and is rotationally driven in the direction of arrow A by a rotational driving force transmitted from the driving roller 21. A primary transfer roller 11 is disposed on the inner side surface of the intermediate transfer belt 10 at a position facing each photosensitive drum 31.

  A secondary transfer roller 19 is disposed on the intermediate transfer belt 10 at a portion facing the driving roller 21. Further, a cleaning blade 15 for wiping residual toner comes into contact with the intermediate transfer belt 10 at a portion facing the driven roller 22, and the toner wiped by the blade 15 is stored in a waste bottle 16.

  An automatic paper feeding unit 40 that feeds the stacked sheets one by one is installed in the lower part of the printer main body 1. Further, a fixing unit 50 for heating and fixing the toner is disposed immediately above the secondary transfer portion.

  The toner images formed on the respective photosensitive drums 31 are sequentially primary-transferred onto the intermediate transfer belt 10 that is rotationally driven in the direction of arrow A, and four color images are combined. On the other hand, the sheets are fed one by one from the automatic sheet feeder 40, and the composite toner image is secondarily transferred from the intermediate transfer belt 10 in the secondary transfer section. Thereafter, the sheet is conveyed to the fixing unit 50 where the toner image is heated and fixed, and is discharged from the discharge roller 51 onto the tray 52.

(See the first embodiment, FIG. 2)
Here, the first embodiment will be described in detail with reference to FIG. FIG. 2 shows the vicinity of the driving roller 21 and the photosensitive drum 31 positioned on the upstream side of the driving roller 21 in the rotation direction A of the intermediate transfer belt 10.

  The primary transfer roller 11 is rotatably attached to a shaft 12 that can move up and down, and a pressing force is applied to the photosensitive drum 31 by a spring 13 that presses the shaft 12. A backup roller 25 that is in contact with the inner surface of the intermediate transfer belt 10 with a predetermined pressure is rotatably provided between the photosensitive drum 31 and the driving roller 21.

  In addition, in order to correct the position of the image formed on the intermediate transfer belt 10, a registration sensor 26 for detecting a test pattern is provided. In order to set the detection position of the registration sensor 26 to a fixed position, the inner surface side of the intermediate transfer belt 10 is backed up by a resist facing sheet metal 27.

  The intermediate transfer belt 10 is made of a polyamide-imide resin film material, and has a width of 357 mm, a thickness of 85 μm, and a surface resistance of 10-11Ω / □. The primary transfer roller 11 is made of a conductive NBR foam sponge, and has an outer diameter of 16 mm and a hardness of 26 degrees (JIS K 6253E E type). The distance L between the nip position a between the photosensitive drum 31 and the intermediate transfer belt 10 and the nip position b between the primary transfer roller 11 and the intermediate transfer belt 10 is 2 mm. The primary transfer roller 11 has a length of 322 mm, and is in low-pressure contact with the photosensitive drum 31 via the intermediate transfer belt 10 with a load of 4 N by its own weight and the pressing force of the spring 13.

  The backup roller 25 is made of a metal material, has an outer diameter of 8 mm, contacts the inner surface side of the intermediate transfer belt 10, and is driven to rotate as the intermediate transfer belt 10 rotates. Further, it is electrically set in a floating state. The nip position a between the photosensitive drum 31 and the intermediate transfer belt 10, the straight line g1 connecting the primary transfer roller 11 and the nip position b of the intermediate transfer belt 10, and the nip position b, the backup roller 25, and the nip of the intermediate transfer belt 10. The angle θ with the straight line g2 connecting the position c is set to 2 °. The distance L1 from the nip position b to the nip position c is set to 15 mm.

  The resist-facing sheet metal 27 is covered with a conductive and highly slidable tape, and the intermediate transfer belt 10 is pushed downward by 0.3 mm with respect to tangent lines passing through the surfaces of the backup roller 25 and the drive roller 21. Set to position. Further, it is electrically set in a floating state.

  The drive roller 21 has a rubber material wound around the surface of a metal pipe, and the outer diameter including the rubber material is 22 mm. The driven roller 22 is made of metal and has a length of 344 mm, an outer diameter of 24 mm, and a tension of 28 N is applied to the intermediate transfer belt 10. The metal parts of the rollers 21 and 22 are dropped to the ground.

  The secondary transfer roller 19 is made of a conductive NBR foam sponge, has a length of 318 mm, an outer diameter of 26 mm, a hardness of 32 degrees (JIS K 6253E E type), and a driving roller 21 with a load of 20 N. Is in pressure contact.

  In the first embodiment, a backup roller 25 is installed, the angle θ is set sufficiently small, and the distance L1 is set to an appropriate value, so that the photosensitive drum 31 closest to the drive roller 21 is provided. On the other hand, the undulation phenomenon at the portion where the intermediate transfer belt 10 contacts is reduced. As a result, the nip position b between the photosensitive drum 31 and the primary transfer roller 11 is stabilized, the primary transfer failure is eliminated, and the deterioration of the image is prevented.

  Next, FIG. 4 shows the result of measuring the amount of waviness of the intermediate transfer belt 10 by variously changing the distance L1 between 20 and 80 mm in the first embodiment having the above-described configuration.

  Here, the undulation amount is a difference value of the vertical movement of the surface of the belt 10 measured by rotating the intermediate transfer belt 10 by disposing a non-contact type displacement sensor in place of the photosensitive drum 31. According to the experiments by the present inventors, it has been found that when the amount of belt waviness exceeds 0.5 mm, primary transfer failure occurs and image quality deteriorates.

  As is apparent from the graph of FIG. 4, when the distance L1 is 40 mm or less, the back-up roller 25 has a wavy amount of the belt 10 of 0.5 mm or less and can ensure the stability of the primary transfer.

  With respect to the angle θ, a smaller numerical value can stabilize the nip portion of the primary transfer, and the backup roller 25 is driven to rotate so that the intermediate transfer belt 10 can be rotated during a long period of operation. It is possible to suppress the generation of abnormal noise and the occurrence of scratches on the belt 10.

  Here, the distance from the nip position b to the driving roller 21 and the upstream nip position d of the intermediate transfer belt 10 is L2, and this distance L2, the distance L1, the radius R1 of the backup roller 25, and the primary transfer roller 11 The relationship with the radius R2 will be described. That is, it is preferable to satisfy the relationship of L1-R1-R2> 0 mm and L1 <L2 / 2.

  When L1-R1-R2 becomes 0 mm, the primary transfer roller 11 and the backup roller 25 come into contact with each other, the smooth driven rotation of the backup roller 25 is hindered, and the primary transfer nip becomes unstable. If L1 is greater than L2 / 2, the amount of winding of the intermediate transfer belt 10 around the driving roller 21 is insufficient, and the driving of the belt 10 becomes unstable, and color misregistration tends to occur in the primary transferred image. .

(Refer to the second embodiment, FIG. 3)
In the second embodiment, as shown in FIG. 3, the backup roller 25 is slightly moved toward the drive roller 21 so that the backup roller 25 also has the function of the resist-facing sheet metal 27 shown in FIG. The other configuration is the same as that of the first embodiment, and the operation and effect such that the backup roller 25 suppresses the wavy phenomenon of the intermediate transfer belt 10 are the same as those of the first embodiment. In FIG. 3, the same reference numerals are given to the same members and parts as those in FIG. 2, and duplicate descriptions are omitted.

(Other examples)
Note that the image forming apparatus according to the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the gist thereof.

  For example, the dimensions and materials of the various rollers 11 and 25 shown in each embodiment and the numerical values such as the tension applied to the intermediate transfer belt 10 are only examples.

  In particular, the backup roller 25 does not necessarily need to be driven and rotated with respect to the intermediate transfer belt 10, and the material thereof is not limited to a metal material, and may be a resin material or the like. The surface hardness should just be a grade which does not damage the intermediate transfer belt 10. It may be electrically floating or dropped to ground.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present invention. It is an elevational view showing the main part of the first embodiment. It is an elevation which shows the principal part of 2nd Example. 6 is a graph showing the amount of undulation of the intermediate transfer belt according to the first embodiment. FIG. 10 is an elevation view showing a main part of a conventional image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Printer main body 10 ... Intermediate transfer belt 11 ... Primary transfer roller 21 ... Drive roller 22 ... Driven roller 25 ... Backup roller 31 ... Photoconductor drum

Claims (3)

An intermediate transfer belt made of a film material is stretched endlessly on a driving roller and a driven roller, and is rotated in one direction, and a plurality of image carriers are brought into contact with the surface of the intermediate transfer belt, and each image carrier is in the middle. In the image forming apparatus in which the primary transfer roller is pressed from the inner surface side of the transfer belt,
A backup roller that is in contact with the inner surface side of the intermediate transfer belt is provided between the image bearing member located upstream of the drive roller in the intermediate transfer belt rotation direction and the drive roller;
A straight line connecting the nip position of the image bearing member, the intermediate transfer belt, the nip position of the primary transfer roller, and the intermediate transfer belt, the primary transfer roller and the intermediate transfer belt, located upstream of the drive roller in the intermediate transfer belt rotation direction; An angle θ between the nip position of the backup roller and a straight line connecting the nip position of the backup roller and the intermediate transfer belt is 0 ° or more and less than 10 °, and
The distance L1 from the nip position between the primary transfer roller and the intermediate transfer belt to the nip position between the backup roller and the intermediate transfer belt is 40 mm or less;
An image forming apparatus.   The image forming apparatus according to claim 1, wherein the intermediate transfer belt has a thickness of 70 to 120 μm and a tension of 20 to 40 [N / m] is applied thereto. The image forming apparatus according to claim 1, wherein the backup roller is installed in correspondence with a detection position of a test pattern of toner formed on the intermediate transfer belt.

Images