JP2006154636A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image forming apparatus effectively preventing generation of an image quality defect resulting from re-adhesion of shaving power on the surface of an image carrier. <P>SOLUTION: A toner temporary holding brush 34 which collects and holds toner existing on a photo receptor 13 after toner is transferred to an intermediate transfer belt 14 on the contact surface with the photo receptor 13 by rotation while contacting the photo receptor 13, is provided with a contact member 50 which comes in contact with the contact surface at a position different from that of the photo receptor 13. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and in particular, develops an electrostatic latent image formed on an image carrier with toner, and transfers the developed toner image on the image carrier to a transfer medium. The present invention relates to an image forming apparatus to be formed.

  Conventionally, image forming apparatuses such as laser printers, facsimile machines, and copiers are provided with a photosensitive drum as an image carrier, and the surface of the photosensitive drum is uniformly charged, and then a light beam based on image data is irradiated. In some cases, an electrostatic latent image is formed on a photosensitive drum, the electrostatic latent image is developed using toner, and the image developed on the photosensitive drum is transferred to a transfer medium to form an image. It was.

  In this type of image forming apparatus, when the developed image on the photosensitive drum is transferred, all the toner cannot be transferred, and a slight amount of toner remains on the photosensitive drum after the transfer. . The residual toner is hereinafter referred to as transfer residual toner.

  There is also a so-called retransfer toner that is once transferred to a transfer medium but adheres to the photosensitive drum again. In the image forming apparatus corresponding to the formation of the color image, the color image is obtained by superimposing and transferring the images of different colors. Therefore, at the time of transfer, the other color toner already transferred is transferred to the photosensitive drum. May stick to the top.

  The toner adhering to the photosensitive drum after the transfer may adhere to a charger or an exposure device provided around the photosensitive drum or may be mixed into the developing device. This will prevent image formation.

  For this reason, a cleaner having a mechanism for collecting the toner on the photosensitive drum and a mechanism for discarding the collected toner is generally disposed around the photosensitive drum on the downstream side of the transfer position. It was.

  However, in recent years, with the widespread use of such image forming apparatuses, it has been desired to reduce the cost and size of the apparatus, and it has been proposed to simplify the above-described cleaner (see, for example, Patent Document 1). ). Note that the configuration of the image forming apparatus in which the cleaner is simplified may be referred to as a “cleanerless system”.

  That is, the mechanism for discarding toner needs to secure a toner storage space and a space for disposal work. Therefore, by omitting the mechanism, the apparatus can be reduced in size efficiently. In an image forming apparatus that includes a plurality of photosensitive drums and forms a color image by transferring images with toner colors different from each other by the photosensitive drums, the number of the cleaners is the same as the number of the photosensitive drums. Therefore, simplification of the cleaner is particularly effective for downsizing the apparatus.

  By the way, the cleanerless system as described above has an intermediate transfer member and a temporary holding member attached to the intermediate transfer member, and the toner remaining on the intermediate transfer member during image formation is temporarily stored by the temporary holding member. The number of outputs per unit time during continuous image formation is reduced by adopting a configuration in which the toner is collectively collected and collected in the cleaning mode. (For example, refer to Patent Document 2).

By applying this technique as a temporary holding member attached to the photosensitive drum, unnecessary toner adhering to the photosensitive drum after the transfer of the toner image can be efficiently removed.
Japanese Patent Laid-Open No. 9-211978 JP 2001-75448 A

  However, in the technique of attaching the temporary holding member to the photosensitive drum, the surface of the photosensitive drum damaged by charging by the charger is scraped by contact with the temporary holding member, and the scraped powder generated thereby is temporarily held. There is a problem that image quality defects occur as a result of streaking on the surface of the photoconductive drum as a result of streaking on the surface of the photoconductive drum due to accumulation on the member and reattachment to the photoconductive drum.

  The present invention has been made to solve the above problems, and provides an image forming apparatus capable of effectively preventing the occurrence of image quality defects due to reattachment of shaving powder on the surface of an image carrier. For the purpose.

  In order to achieve the above object, an image forming apparatus according to claim 1 includes an image carrier, a charging unit that charges the image carrier, and a charging surface of the image carrier that is charged by the charging unit. An exposure unit that forms an electrostatic latent image by exposure; a developing unit that develops the electrostatic latent image with toner; a transfer medium that is pressed against the image carrier and to which the toner is transferred; and the transfer medium; The toner existing on the image carrier after the toner is transferred to the transfer medium by rotating while being in contact with the image carrier is disposed between the image carrier and the image carrier. Holding means for collecting and holding on the contact surface; and contact means for contacting the contact surface of the holding means at a position different from the image carrier.

  According to the image forming apparatus of the first aspect, the image carrier is charged by the charging unit, and the charged surface of the charged image carrier is exposed by the exposure unit to form an electrostatic latent image. The electrostatic latent image is developed with toner by the developing means, and the toner is transferred to a transfer medium pressed against the image carrier.

  In the image forming apparatus according to the present invention, the toner is transferred to the transfer medium by being rotated while being in contact with the image carrier by the holding unit disposed between the transfer medium and the charging unit. The toner existing on the image carrier after being collected is collected and held on the contact surface with the image carrier.

  Here, in the present invention, the contact surface of the holding unit is contacted by the contact unit at a position different from the image carrier.

  As described above, according to the image forming apparatus of the first aspect, the toner existing on the image carrier after the toner is transferred to the transfer medium by rotating while being in contact with the image carrier is transferred to the image carrier. The holding means for collecting and holding on the contact surface is provided with contact means for contacting the contact surface at a position different from that of the image carrier. The shaving powder can be attached to the contact means before being reattached to the image carrier, and as a result, it is possible to effectively prevent the occurrence of image quality defects due to the reattachment of the shaving powder on the surface of the image carrier. it can.

  Note that, as in the invention described in claim 2, the present invention may further include a potential equalizing means for making the potential of the contact means the same as that of the holding means.

  According to the present invention, as in the invention described in claim 3, the contact means is formed of the same material as the contact surface with the holding means of the image carrier. It may be a thing.

  Further, according to the present invention, as in the invention described in claim 4, the contact means may be such that the contact surface with the holding means contacts the entire contact surface of the holding means with the image carrier. .

  As described above, according to the present invention, the toner existing on the image carrier after the toner is transferred to the transfer medium by rotating while being in contact with the image carrier is brought into contact with the image carrier. For the holding means that collects and holds the image, the contact means that comes into contact with the contact surface at a position different from that of the image carrier is provided. It can be attached to the contact means before being reattached to the body, and as a result, it is possible to effectively prevent the occurrence of image quality defects due to reattachment of the shaving powder on the surface of the image carrier. An effect is obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, specific numerical values and materials may be mentioned for convenience of explanation, but it goes without saying that the present invention is not limited to these numerical values and materials. In each graph showing the voltage waveform, the amplitude of the waveform of the AC voltage is shown to be relatively smaller than the amplitude of the waveform of the DC voltage.

  FIG. 1 shows a color laser printer 10 (hereinafter referred to as a printer) which is an example of an image forming apparatus according to an embodiment of the present invention. In the printer 10, development units 12C, 12M, 12Y, and 12K for cyan, magenta, yellow, and black and photoconductors 13C, 13M, 13Y, and 13K are arranged in parallel facing the intermediate transfer belt 14, and the intermediate transfer is performed. This is a so-called tandem-type full-color laser printer that superimposes four color toner images while the belt 14 makes one round.

  The printer 10 includes a paper feed tray 16 at the bottom. A paper feed roller 18 is in contact with the leading end of the paper P set in the paper feed tray 16 in the transport direction, and the paper P is fed one sheet at a time by the paper feed roller 18 and a paper handling means (not shown). Paper is fed from the tray 16 to the downstream side in the transport direction. Two sets of transport rollers 20 are arranged on the downstream side in the transport direction of the paper feed roller 18, and the paper P is transported to the upper transfer unit 22 by the transport force from the transport rollers 20.

  The transfer unit 22 is provided with a belt conveyance roller 24A around which the intermediate transfer belt 14 is wound, and a transfer roller 26 pressed against the belt conveyance roller 24A. The intermediate transfer belt 14 is sandwiched between the nip portion between the belt conveying roller 24A and the transfer roller 26, and the toner image is transferred from the intermediate transfer belt 14 when the sheet P passes through the nip portion.

  A fixing unit 28 is disposed above the transfer unit 22 and downstream in the transport direction. The fixing unit 28 is provided with a heat roller 28A that becomes high temperature and a backup roller 28B that is pressed against the heat roller 28A, and the sheet P passes through the nip portion between the heat roller 28A and the backup roller 28B. At this time, the toner is melted and solidified to be fixed on the paper P. Then, the paper P is discharged by a paper discharge roller 29 disposed on the downstream side in the transport direction of the fixing unit 28.

  Here, the printing unit 30 in which the photoreceptors 13C, M, Y, and K superimpose the toner image on the intermediate transfer belt 14 will be described. In addition, when distinguishing each color of cyan, magenta, yellow, and black, explanation is made by adding C, M, Y, K after the code. However, when it is not necessary to distinguish each color, C, M, Y, and K are omitted.

  As shown in FIG. 2, the intermediate transfer belt 14 includes the above-described belt conveyance roller 24A, a belt conveyance roller 24B disposed below the belt conveyance roller 24A, and an obliquely upper side of the belt conveyance roller 24B and in the sheet conveyance path. It is wound around a belt conveying roller 24C disposed on the opposite side.

  A surface of the intermediate transfer belt 14 between the belt conveyance roller 24B and the belt conveyance roller 24C facing obliquely downward is a transfer surface 14A on which the toner image is transferred from the photoreceptors 13C, M, Y, and K. The developing units 12C, M, Y, and K and the photoconductors 13C, M, Y, and K are arranged in parallel so as to face the transfer surface 14A, and the photoconductors 13C, M, Y, and K are transferred to the transfer surface. 14A. Further, the transfer rollers 32C, M, Y, and K are pressed against the photoreceptors 13C, M, Y, and K via the transfer surface 14A.

  As shown in FIG. 3A, the intermediate transfer belt 14, the temporary toner holding brush 34, the charging roller 36, and the developing roller 38 are in contact with the photosensitive surface 13A of the photosensitive member 13 in order in the rotation direction. The developing roller 38 rotates in the same direction as the rotation direction of the photosensitive member 13. That is, the developing roller 38 rotates in the reverse direction with respect to the photoreceptor 13 at the nip portion. As a result, the development efficiency from the developing roller 38 to the photosensitive member 13 is increased. Further, between the charging roller 36 and the developing roller 38, an LED array head 40 that performs line exposure of the photosensitive surface 13A is disposed.

The temporary toner holding brush 34 is rotatable around a rotation axis parallel to the photosensitive member 13, and a large number of brushes are implanted around the toner holding brush 34. An AC power supply 62, a positive power supply 64, and a negative power supply 66 are connected to the temporary toner holding brush 34 via a connection line 48, and one of these three power supplies is selected and a predetermined voltage is applied to the surrounding brushes. It has become so. In this embodiment, as an example, the AC power supply 62 has a peak-to-peak voltage V _PP = 600 V, a frequency f = 3 kHz, a positive power supply 64 has a voltage V ₊ = 400 V (DC), and a negative power supply 66 has a voltage V ₋ = -400V (direct current). FIG. 3B shows the voltage applied to the temporary toner holding brush 34.

  On the other hand, a contact member 50 is disposed on the opposite side of the toner temporary holding brush 34 from the photoreceptor 13.

As shown in FIG. 4, the contact member 50 is configured to include a base 52 having conductivity and rigidity and having an arc shape in cross section, and the inner surface of the arc shape has a temporary toner holding brush 34. Is arranged so as to be in contact with the outer circumference of the toner temporary holding brush 34 with a predetermined pressing force over the entire region in the rotation axis direction of the toner temporary holding brush 34. In the printer 10 according to the present embodiment, as the temporary toner holding brush 34, the brush material is nylon, the pile height (hair length) of the brush is 2.5 mm, the thickness per brush is 2d (denier), the brush The hair density is 120 kf / inch ² and the amount of biting into the photoconductor 13 is 0.5 mm. As the predetermined pressing force suitable for this condition, an experiment by the inventor of the present invention is used. 40 to 45 gf / 300 mm derived from the above is applied.

  In the contact member 50 according to this embodiment, the contact surface 54 with the temporary toner holding brush 34 is coated with the same material as the contact surface with the temporary toner holding brush 34 of the photoreceptor 13. In the printer 10 according to the present embodiment, a material composed of a polymer resin using polycarbonate as a binder and a triphenylamine-based charge transport agent is employed as the substance.

  As shown in FIG. 3, a branch connection line 49 branched from the connection line 48 is connected to the base 52 of the contact member 50, and the potential of the contact member 50 is always the same as that of the temporary toner holding brush 34. It is configured as follows.

  Hereinafter, a flow until the toner image is transferred to the intermediate transfer belt 14 will be described.

  When the photosensitive member 13 rotates counterclockwise in the figure, first, the photosensitive surface 13A is uniformly charged to a predetermined polarity potential by the charging roller. In the present embodiment, −1100V is applied, and the photosensitive surface 13A is charged to, for example, −200V.

  When the photosensitive member 13 is further rotated, the charged surface of the photosensitive surface 13A is exposed by the LED array head 40, the potential of the exposed portion of the charged surface is lowered (for example, −200 V), and an electrostatic latent image is formed. It is formed. Thereafter, the electrostatic latent image is developed (visualized) by electrically attaching the developing toner charged to the same polarity as the charged polarity of the photosensitive member 13 to the potential lowering portion of the charging surface by the developing roller 38. . The toner is electrically attracted to the transfer roller 32 to which a transfer voltage having a polarity opposite to that of the toner is applied. As a result, the toner image is transferred from the photoreceptor 13 to the intermediate transfer belt 14.

  Here, when the toner image is transferred from the photoconductor 13 to the intermediate transfer belt 14, untransferred toner remaining on the photoconductor 13 without being transferred to the intermediate transfer belt 14 is generated. Further, retransfer toner (hereinafter referred to as retra toner) is generated in which the toner transferred on the upstream side to the intermediate transfer belt 14 is offset to the downstream photoconductor 13. For this reason, it is necessary to remove the transfer residual toner and the retraction toner from the photoreceptor 13.

  Therefore, as shown in FIG. 3B, an AC voltage is applied from the AC power supply 62 to the temporary toner holding brush 34 during image formation. The transfer residual toner remaining on the photosensitive member 13 after the transfer of the toner image from the photosensitive member 13 to the intermediate transfer belt 14 includes a positively charged toner and a negatively charged toner. By applying an AC voltage, Both of these transfer residual toners can be temporarily held by the toner temporary holding brush 34 to clean the photosensitive surface 13A of the photosensitive member 13.

  Next, in the present embodiment, in order to remove the transfer residual toner held by the temporary toner holding brush 34, the following toner discharge mode is performed.

  First, during non-image formation, a negative voltage (−400 V in this embodiment) is applied from the negative power source 66 to the temporary toner holding brush 34 for a predetermined time. As a result, negatively charged toner held by the temporary toner holding brush 34 is discharged onto the photoreceptor 13. Next, a positive voltage (+400 V in this embodiment) is applied from the positive power source 64. As a result, the positively charged toner held by the temporary toner holding brush 34 is discharged onto the photoreceptor 13.

  The toner discharged from the temporary toner holding brush 34 passes through an exposure area by the LED array head 40, and is further electrically collected by the developing roller 38 to which a predetermined voltage (for example, −400V) is applied, and is supplied to the developing unit 12. The blade 39 that is in sliding contact with the developing roller 38 is scraped off from the developing roller 38 to the toner storage portion 41. The toner remaining on the photoreceptor 13 without being collected is transferred to the intermediate transfer belt 14 and collected by the cleaner 42 (see FIGS. 1 and 2) on the intermediate transfer belt 14.

  By the way, in the toner image transfer process as described above, the surface of the photosensitive member 13 is damaged by the charging by the charging roller 36, so that the surface is scraped by the contact with the temporary toner holding brush 34, and this occurs. The scraped powder accumulates on the toner temporary holding brush 34.

  However, the shaving powder collected on the temporary toner holding brush 34 is attached to the contact surface of the contact member 50 with the temporary toner holding brush 34 before being reattached to the photosensitive member 13, and as a result, the photosensitive member 13. It is possible to effectively prevent the occurrence of image quality defects due to re-adhesion of the shaving powder on the surface.

  As described above in detail, according to the present embodiment, toner is transferred to the transfer medium (here, the intermediate transfer belt 14) by being rotated while being in contact with the image carrier (here, the photoreceptor 13). The holding means (here, the temporary toner holding brush 34) for collecting and holding the toner present on the transferred image carrier at the contact surface with the image carrier is different from the image carrier. Since the contact means (here, the contact member 50) that contacts the contact surface at a position is provided, the contact means before the scraped powder on the surface of the image carrier accumulated in the holding means is reattached to the image carrier. As a result, it is possible to effectively prevent the occurrence of image quality defects due to the reattachment of the shaving powder on the surface of the image carrier.

  Further, according to the present embodiment, since the potential equalizing means (here, the branch connection line 49) for making the potential of the contact means the same as the holding means is provided, the contact means and the holding Since it is possible to prevent the occurrence of discharge with the means, the contact surface of the contact means with the holding means is not damaged by the discharge, and the contact surface comes into contact with the holding means. As a result of preventing scraping, it is possible to more effectively prevent the occurrence of image quality defects due to redeposition of shaving powder on the surface of the image carrier.

  According to the present embodiment, the contact means is formed of the same material as the contact surface with the holding means of the image carrier, since the contact surface with the holding means is the holding means. The shaving powder accumulated in the means can be more effectively adhered to the contact means.

  Further, according to the present embodiment, the contact means is configured such that the contact surface with the holding means is in contact with the entire contact surface of the holding means with the image carrier. The shaving powder can be more effectively adhered to the contact means.

  In this embodiment, the case where the toner temporary holding brush 34 is applied as the holding means of the present invention has been described. However, the present invention is not limited to this, and as an example, as shown in FIG. As a means, the toner temporary holding roller 35 may be applied. Since the toner temporary holding roller 35 holds the toner on the surface, the toner can be easily discharged to the photoreceptor 13. Also in this case, the same effects as in the present embodiment can be obtained.

  In addition, the configuration of the printer 10 described in the present embodiment is an example, and it is needless to say that the configuration can be appropriately changed without departing from the gist of the present invention.

  For example, in the present embodiment, the case where the contact member 50 having a circular cross-sectional shape is applied as the contact means of the present invention, but the shape of the contact means of the present invention is not particularly limited, For example, any shape that can contact the temporary toner holding brush 34 as the holding means of the present invention, such as an L-shaped cross section or an I-shaped cross section, is applicable. Can do.

  In this embodiment, the case where the present invention is applied to a tandem type image forming apparatus has been described. However, the present invention is not limited to this, for example, an image having only a single image forming unit. The present invention may be applied to a forming apparatus. Also in this case, the same effects as in the present embodiment can be obtained.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. 1 is a schematic configuration diagram of a printing unit of an image forming apparatus according to an embodiment. (A) is an enlarged view showing a configuration of a printing unit of the image forming apparatus according to the embodiment, and (B) is a graph showing a voltage applied to a toner temporary holding brush of the image forming apparatus. FIG. 3 is a perspective view illustrating configurations of a temporary toner holding brush and a contact member of the image forming apparatus according to the embodiment. (A) is an enlarged view showing a configuration of a printing unit of an image forming apparatus according to a modification of the embodiment, and (B) is a graph showing a voltage applied to a toner temporary holding roller of the image forming apparatus. It is.

Explanation of symbols

10 Color laser printer (image forming device)
12 Development unit 13 Photoconductor (image carrier)
13A Photosensitive surface 14 Intermediate transfer belt (transfer medium)
14A Transfer surface 22 Transfer section 26 Transfer roller 30 Print section 32 Transfer roller 34 Temporary toner holding brush (holding means)
35 Temporary toner holding roller (holding means)
36 Charging roller (charging means)
38 Developing roller (developing means)
40 LED array head (exposure means)
49 Branch connection line (potential equalization means)
50 Contact member (contact means)
62 AC power supply 64 Positive power supply 66 Negative power supply P Paper

Claims (4)

An image carrier;
Charging means for charging the image carrier;
Exposure means for exposing a charged surface of the image carrier charged by the charging means to form an electrostatic latent image;
Developing means for developing the electrostatic latent image with toner;
A transfer medium on which the toner is transferred in pressure contact with the image carrier;
The toner that is disposed between the transfer medium and the charging unit and rotates while contacting the image carrier to transfer the toner to the transfer medium is transferred to the image carrier. Holding means for collecting and holding at the contact surface with the carrier;
Contact means for contacting the contact surface of the holding means at a position different from the image carrier;
An image forming apparatus. The image forming apparatus according to claim 1, further comprising a potential equalizing unit configured to make the potential of the contact unit the same as that of the holding unit. The image forming apparatus according to claim 1, wherein the contact unit is formed of the same material as a contact surface with the holding unit of the image carrier. 4. The image forming apparatus according to claim 1, wherein a contact surface of the contact unit with the holding unit is in contact with an entire contact surface of the holding unit with the image carrier. 5.

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