JP2010256593A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that retains excellent image quality by dissolving and removing discharge product adhering to a surface of a secondary transfer roller and improving cleaning performance. <P>SOLUTION: A color printer includes: an image forming part that forms a toner image on an intermediate transfer belt 16; and a secondary transfer part 17 that transfers the toner image on the intermediate transfer belt 16 to a recording medium. The secondary transfer part 17 includes the secondary transfer roller 41 with its surface coated with photocatalyst material, a light source 42 which irradiates the surface of the secondary transfer roller 41 with light that causes the photocatalyst material to produce photocatalyst reaction, a bias power supply 48 which applies bias voltage between the secondary transfer roller 41 and the intermediate transfer belt 16, and a driving part 47 which rotationally drives the secondary transfer roller 41. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus. More specifically, the present invention relates to an image forming apparatus that includes a toner image carrier and a transfer roller, and the toner image is transferred from the toner image carrier to a recording medium by the transfer roller.

  Some electrophotographic image forming apparatuses temporarily transfer a toner image formed based on image data to an intermediate transfer member, and then transfer the toner image to a recording medium such as a printing sheet by a secondary transfer member. Among them, the secondary transfer member does not necessarily have a sheet conveying force, and there is a sheet that is conveyed by a sheet conveying roller or the like provided nearby. On the other hand, in particular, because of low cost and space saving, some secondary transfer rollers have a sheet conveyance property without providing a dedicated sheet conveyance roller.

  Deposits such as untransferred toner and paper dust may adhere to the surface of the secondary transfer roller. If deposits adhere to the surface of the secondary transfer roller, the back surface of the recording medium may be soiled. For this reason, conventionally, many have a cleaning mechanism that cleans the surface of the secondary transfer roller and removes deposits. For example, during non-image formation, a bias having a polarity opposite to that at the time of image formation is applied to the secondary transfer roller so that the adhered matter adhering to the surface of the secondary transfer roller is discharged to the intermediate transfer member or the like. (For example, refer to Patent Document 1).

JP 2006-350161 A

  However, there is a problem that the cleaning performance may not be sufficient even with the above-described conventional image forming apparatus. In particular, due to the recent high functionalization of the toner, there is a problem in that the retention of the toner cannot be completely prevented in an apparatus using a polymer toner having a small diameter and a low melting point.

  When a bias having a polarity opposite to that at the time of image formation is applied for cleaning as described above with such toner attached, a minute discharge is generated on the roller surface, and a discharge product may be generated. is there. Then, the toner and the external additive are further adhered by the discharge product. As a result, the cleaning performance is further deteriorated, and there is a possibility that toner and external additives accumulate on the roller surface. In particular, in an apparatus in which the secondary transfer roller has paper transportability, if such deposits adhere to the surface, the paper transportability of the secondary transfer roller becomes unstable, causing image noise. There was a problem that it might cause.

  The present invention has been made to solve the problems of the conventional image forming apparatus described above. That is, the problem is to provide an image forming apparatus capable of maintaining good image quality by decomposing and removing discharge products adhering to the surface of the secondary transfer roller and improving cleaning properties. It is in.

  In order to solve this problem, an image forming apparatus of the present invention includes an image forming unit that forms a toner image on a toner image carrier, a transfer device that transfers the toner image on the toner image carrier to a recording medium, and A transfer roller having a surface coated with a photocatalytic material, a light source that irradiates the surface of the transfer roller with light that causes a photocatalytic reaction to the photocatalytic material, a transfer roller, and a toner. A bias power source that applies a bias voltage to the image carrier and a drive unit that rotationally drives the transfer roller are included.

  According to the image forming apparatus of the present invention, since the transfer roller is coated with the photocatalytic substance, the photocatalytic reaction can be caused by irradiating light. Therefore, the discharge product generated in the vicinity can be decomposed. As a result, it is possible to prevent the deposits such as toner and external additives from sticking to the transfer roller due to the discharge product. In addition, it is possible to prevent toner and the like from sticking to each other due to the discharge product. And if it is a deposit | attachment which is not stuck, it can remove easily by rubbing with a cleaner etc., for example. As a result, the discharge product adhering to the surface of the secondary transfer roller is decomposed and removed, and the cleaning property is improved, so that the image forming apparatus can maintain a good image quality.

  In the present invention, the image forming apparatus further includes a control unit that controls the transfer device. The control unit rotates the transfer roller by the driving unit without supplying the recording medium to the transfer roller during non-image formation, and performs normal charging by a bias power source. Apply a voltage in the direction to move the toner from the transfer roller to the toner image carrier, execute a cleaning mode to turn on the light source, and rotate the transfer roller by the drive unit during image formation to transfer the toner image carrier and transfer It is desirable to execute an image forming mode in which the recording medium is transported between the rollers, a voltage in a direction to move the normally charged toner from the toner image carrier to the transfer roller is applied by a bias power source, and the light source is turned off.

  If this is the case, the cleaning mode is executed during non-image formation. In this mode, light is irradiated to the entire circumference of the surface of the transfer roller by irradiating light while rotating the transfer roller. Further, since a bias voltage having a polarity opposite to that at the time of image formation is applied, the deposits peeled off from the surface of the transfer roller, particularly regular charged toner, can be returned to the toner image carrier. Therefore, good cleaning is possible. At the time of image formation, the image formation mode is executed, so that normal image formation is performed.

Further, in the present invention, the control unit rotates the transfer roller by the driving unit instead of the image forming mode, conveys the recording medium between the toner image carrier and the transfer roller, and supplies the normally charged toner by the bias power source. It is desirable to be able to execute a backing paper mode in which a voltage in the direction of movement from the toner image carrier to the transfer roller is applied and the light source is turned on.
By doing so, the removed deposit adheres to the back surface of the recording medium. For example, when the back paper mode is executed using the back paper, the back side of the back paper is soiled, so that the front and back can be easily distinguished. Further, the same effect as in the cleaning mode can be obtained without taking time for cleaning during non-image formation.

Further, in the present invention, at least a portion to be coated of the transfer roller that is coated with the photocatalytic material is formed of a foam member, and the photocatalytic material is a material containing titanium oxide having a particle diameter in the range of 7 to 20 nm. It is desirable that
If it is such, it can decompose | disassemble a discharge product more effectively.

  According to the image forming apparatus of the present invention, it is possible to maintain good image quality by decomposing and removing the discharge products adhering to the surface of the secondary transfer roller and improving the cleaning property.

1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. It is explanatory drawing which shows schematic structure of a secondary transfer part. It is explanatory drawing which shows the layer structure of a secondary transfer roller. It is explanatory drawing which shows the state of the surface of a secondary transfer roller. It is explanatory drawing which shows the conveyance force by a secondary transfer roller.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a so-called four-cycle type image forming apparatus.

  As shown in FIG. 1, the color printer 10 of this embodiment includes a photosensitive member 12, a charging unit 13, an exposure unit 14, a developing unit 15, an intermediate transfer belt 16, a secondary transfer unit 17, a fixing unit 18, and a paper feed cassette 19. It is what has. The operation of the color printer 10 during image formation will be briefly described. The photoconductor 12 is rotated clockwise in the figure. Then, after the surface of the photoconductor 12 is charged by the charging unit 13, the exposure unit 14 is exposed based on the image data to form an electrostatic latent image.

  As shown in FIG. 1, the developing unit 15 includes a substantially cross-shaped rotating rack 21 and developing units 22Y, 22M, 22C, and 22K of the respective colors fitted therebetween. As the rotating rack 21 rotates, one of the developing devices for each color is arranged at a position facing the photoconductor 12. Then, the electrostatic latent image formed on the photoconductor 12 is developed by the opposing developing device, whereby a toner image of that color is formed on the photoconductor 12.

  As shown in FIG. 1, the intermediate transfer belt 16 is wound around a driving roller 31, a tension roller 32, a driven roller 33, a winding roller 34, and a primary transfer roller 35. When the image is formed, it is rotated counterclockwise in the figure. Furthermore, in this embodiment, a cleaner 37 that contacts the surface of the intermediate transfer belt 16 is provided at the upper left portion in the drawing. The cleaner 37 has a cleaning blade 38 for removing dirt by rubbing the surface of the intermediate transfer belt 16.

  The toner image formed on the photoreceptor 12 is transferred to the intermediate transfer belt 16 by the primary transfer roller 35. As the rotating rack 21 rotates, toner images of the respective colors are sequentially formed and superimposed on the intermediate transfer belt 16. Then, the images are transferred to the sheet conveyed from the sheet feeding cassette 19 by the secondary transfer unit 17 at a time. Further, the sheet is discharged outside the apparatus after the transferred toner image is fixed by the fixing unit 18.

  As shown in FIG. 2, the secondary transfer unit 17 of this embodiment includes a secondary transfer roller 41, a light source 42, a charge removal member 43, and a housing 44. The secondary transfer roller 41 is disposed so as to face the driving roller 31 with the intermediate transfer belt 16 interposed therebetween. The secondary transfer roller 41 is a driving roller that receives a rotational driving force. The secondary transfer unit 17 further includes a guide 46 for guiding the sheet to be conveyed. During the secondary transfer, the sheet is conveyed from the bottom to the top in the drawing along the guide 46.

  The secondary transfer roller 41 is attached with a drive unit 47 that rotates its rotating shaft. A bias power supply 48 for applying a bias voltage to the secondary transfer roller 41 is also connected. The bias power supply 48 applies a bias voltage in a direction that attracts the normally charged toner from the intermediate transfer belt 16 to the secondary transfer roller 41 during image formation. Further, in this embodiment, a control unit 49 for controlling the light source 42, the drive unit 47, and the bias power supply 48 is also provided.

  As shown in FIG. 3, the secondary transfer roller 41 of this embodiment includes a core metal 51, a rubber layer 52, and a coating layer 53. The core metal 51 is, for example, an iron shaft. The rubber layer 52 is preferably an ion conductive foam rubber. The coating layer 53 is a layer coated with a photocatalytic substance. For example, a coating agent containing titanium oxide having a particle diameter of 7 to 20 nm may be applied. As the coating means, an appropriate one is selected from known means such as a wet process such as dip coating or spray coating, or a dry process such as CVD or sputtering.

  The light source 42 of the secondary transfer unit 17 performs light irradiation in order to cause a photocatalytic reaction to the photocatalytic substance of the secondary transfer roller 41. For example, an ultraviolet LED that emits ultraviolet light having a wavelength of 380 nm may be used. The light source 42 has an irradiation range in the depth direction in the drawing that is approximately the same as the axial length of the secondary transfer roller 41. The neutralization member 43 performs neutralization to peel off the sheet that has undergone the secondary transfer from the surface of the secondary transfer roller 41. A sawtooth type is suitable.

  In this embodiment, at the time of secondary transfer, as shown in FIG. 2, the secondary transfer roller 41 is brought close to the drive roller 31 and rotated clockwise in the drawing. Thus, the sheet is sandwiched between the intermediate transfer belt 16 and the secondary transfer roller 41 and conveyed from the bottom to the top in the figure. That is, the sheet is conveyed by the rotation of the secondary transfer roller 41 within the range in the vicinity of the secondary transfer unit 17. Further, a bias voltage is applied to the secondary transfer roller 41 when the sheet is between the intermediate transfer belt 16 and the secondary transfer roller 41. Then, the toner image formed on the intermediate transfer belt 16 is electrically drawn and transferred to one side of the paper (the left side in FIG. 2). This is the image forming mode.

  Further, in this embodiment, the light source 42 is turned on and the secondary transfer roller 41 is rotated by one turn or more during non-image formation such as between jobs or between papers. The intermediate transfer belt 16 is also rotated. In this way, a photocatalytic reaction occurs in the coating layer 53 of the secondary transfer roller 41 by the ultraviolet rays emitted from the light source 42. As a result, the discharge product can be decomposed and the adhering matter such as the toner adhering to the surface of the secondary transfer roller 41 as a lump due to the discharge product or the like can be separated. Further, a bias having a polarity opposite to that at the time of image formation is applied to the secondary transfer roller 41 to transfer the decomposed deposits to the intermediate transfer belt 16. The deposits transferred to the intermediate transfer belt 16 are removed by the cleaner 37. This is the cleaning mode.

  FIG. 4 shows the adhesion state of the deposit on the surface of the secondary transfer roller 41. Since the rubber layer 52 is an ion conductive foam rubber, its surface has an uneven shape. A relatively large toner 61 and a very small external additive 62 are adhered to the surface by a discharge product 63. Further, a part of the toner is agglomerated by the discharge product. When the secondary transfer roller 41 in this state is irradiated with light, the discharge product 63 is decomposed by the photocatalytic reaction of the coating layer 53 and loses its sticking power. Therefore, the adhered toner 61 and the external additive 62 are easily peeled off. Therefore, it can be easily removed by the cleaner 37.

  By doing so, most of the deposits on the surface of the secondary transfer roller 41 are removed. Then, the sheet conveying force that has been reduced due to the adhering matter is recovered and becomes constant. FIG. 5 shows the difference in sheet conveying force between the secondary transfer roller 41 of this embodiment and the comparative example in which the photocatalytic substance is not coated. In the drawing, a solid line L1 indicates a sheet conveying force by the secondary transfer roller 41 of the present embodiment. In addition, a broken line L2 in the figure shows the comparative example. Here, the cleaning mode was experimentally performed even on one sheet of paper. For this reason, in the comparative example, although a high conveying force is shown immediately after cleaning, the sheet descends immediately and the paper conveying force is greatly undulated. On the other hand, in this embodiment, a stable paper conveying force can be maintained.

  In this embodiment, for example, the light source 42 may be turned on during image formation when printing on a sheet that does not care about the quality of the back, such as a back paper, or during test printing. In this way, the discharge product generated during the secondary transfer is decomposed, and deposits such as toner that have been captured and stuck by the discharge product are released. Then, it is peeled off from the front surface of the secondary transfer roller 41 and transferred to the back surface of the paper. This is the backing paper mode. According to this back paper mode, the back side of the back paper becomes dirty to some extent, so that the front and back can be easily distinguished. In addition, the effect of the present invention can be obtained without taking time for cleaning during non-image formation such as between sheets.

  The color printer 10 of the present embodiment compared the paper transportability when image formation was repeated on various papers by experiments. In this experiment, 30 sheets were printed on each of the back sheets of various papers with monochrome coverage of 5% coverage on one side, and the number of slips generated during that time was measured. In the embodiment of the present embodiment, a secondary transfer roller coated with a photocatalytic substance is used, and the light source 42 is continuously turned on during printing for each sheet. In the comparative example, a secondary transfer roller not coated with a photocatalytic substance is used, and the light source 42 is not turned on. The occurrence of slip was grasped by detecting the distortion of the image by visual inspection and detecting the number of occurrence points of image noise (for example, voids).

  The results of this experiment are shown in Table 1 below. In this table, slips did not occur in the examples and comparative examples with a small paper basis weight (thin paper; upper in the table). However, some slips occurred on paper with a large paper basis weight (thick paper; lower in the table). In particular, a large number occurred in the comparative example, but a small number occurred in the examples.

  As described in detail above, according to the color printer 10 of the present embodiment, the surface of the secondary transfer roller 41 is coated with the photocatalytic substance, and the photocatalytic substance can be caused to react with the photocatalytic substance by the light source 42. Accordingly, the adhesive force of the deposit on the surface of the secondary transfer roller 41 is reduced by the light irradiation, and is easily peeled off. Therefore, when the light source 42 is turned on and a reverse polarity bias is applied during non-image formation, the deposit can be transferred to the intermediate transfer belt 16 and removed by the cleaner 37. Therefore, it is possible to maintain good image quality by decomposing and removing the discharge products adhering to the surface of the secondary transfer roller and improving the cleaning property.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, the present invention can be applied not only to the 4-cycle type but also to the tandem type. Further, the present invention is not limited to a device that performs transfer twice, but can also be applied to a single transfer type such as a monochrome device.

DESCRIPTION OF SYMBOLS 10 Color printer 16 Intermediate transfer belt 17 Secondary transfer part 41 Secondary transfer roller 42 Light source 47 Drive part 48 Bias power supply

Claims (4)

In an image forming apparatus having an image forming unit that forms a toner image on a toner image carrier, and a transfer device that transfers the toner image on the toner image carrier to a recording medium,
The transfer device is
A transfer roller having a photocatalytic material coated on the surface;
A light source for irradiating the surface of the transfer roller with light causing a photocatalytic reaction to the photocatalytic substance;
A bias power source for applying a bias voltage between the transfer roller and the toner image carrier;
An image forming apparatus comprising: a drive unit that rotationally drives the transfer roller. The image forming apparatus according to claim 1,
The image forming apparatus further includes a control unit that controls the transfer device,
During non-image formation,
Rotating the transfer roller by the drive unit without supplying a recording medium to the transfer roller;
Applying a voltage for moving the normally charged toner from the transfer roller to the toner image carrier by the bias power source;
Executing a cleaning mode for turning on the light source;
During image formation,
The transfer roller is rotated by the drive unit to convey a recording medium between the toner image carrier and the transfer roller,
Applying a voltage in a direction to move the normally charged toner from the toner image carrier to the transfer roller by the bias power source;
An image forming apparatus that executes an image forming mode in which the light source is turned off. The image forming apparatus according to claim 2,
In place of the image forming mode, the control unit
The transfer roller is rotated by the drive unit to convey a recording medium between the toner image carrier and the transfer roller,
Applying a voltage in a direction to move the normally charged toner from the toner image carrier to the transfer roller by the bias power source;
An image forming apparatus capable of executing a backing paper mode for turning on the light source. In the image forming apparatus according to any one of claims 1 to 3,
Of the transfer roller, at least the portion to be coated with the photocatalytic substance is formed of a foam member,
The image forming apparatus according to claim 1, wherein the photocatalytic substance is a substance containing titanium oxide having a particle diameter in a range of 7 to 20 nm.

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