JP2010224402A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and an image forming method, capable of removing toner having a normal charge polarity and toner having a reverse polarity remaining on the surface of a latent image carrier, using a single brush. <P>SOLUTION: While a photoreceptor 2 takes one round after a printing job, charging bias (grid voltage) having the same polarity and the normal charge polarity is applied to an charger 5, so that positively charged toner remaining on the photoreceptor is changed into negatively charged toner. Transfer bias Vt applied to a transfer roller is set to the same potential as surface potential of the photoreceptor 2 charged by the charger. Thus, residual toner adjusted to have the normal charge polarity by the charger passes through a transfer position, as it is, without being restored to the reverse polarity and is conveyed to a cleaning position and removed by brush-cleaning. Hence, the positively charged toner and the negatively charged toner remaining on the surface of the photoreceptor 2 are removed by using a single brush. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method for executing a printing process and a printing process in which a toner image is formed on the surface of a latent image carrier and the toner image is transferred to a recording medium.

  An image forming apparatus that forms a toner image by developing an electrostatic latent image formed on a latent image carrier that circulates in a predetermined rotation direction with toner of a normal charge polarity, and transfers the toner image to a recording medium And methods are known. In this image forming apparatus and image forming method, since the transfer efficiency from the latent image carrier to the recording medium is 100% or less, a small amount of toner of normal charge polarity remains on the surface of the latent image carrier after transfer. There may be. Therefore, in this type of image forming apparatus, a so-called blade method is used in which the cleaning blade is brought into contact with the surface of the latent image carrier at a cleaning position downstream of the transfer position in the rotation direction of the latent image carrier to remove residual toner. The cleaning means was frequently used.

  However, in recent years, a toner having a smaller particle diameter has been adopted for the purpose of increasing the definition of an image, increasing the speed of a process, and decreasing the fixing temperature. The image forming apparatus using such a small particle size toner has a problem that it is difficult to remove residual toner from the latent image carrier by passing through the cleaning blade.

  Therefore, adoption of a brush type cleaning means in place of the blade type is being studied. This cleaning means removes the toner of normal charging polarity that remains on the surface of the latent image carrier by bringing the brush into contact with the surface of the latent image carrier. In general, toner having a polarity opposite to the normal charged polarity (so-called fog toner) attached to a non-image portion to which toner should not be attached is left without being transferred. Only the cleaning means cannot remove residual toner having a polarity opposite to the normal charge polarity from the latent image carrier. As a result, after the printing process is completed, if the toner remains on the latent image carrier, the residual toner adheres to the latent image carrier, which is one of the causes of image defects. It was. In order to solve this problem, it is necessary to remove not only the residual toner having the normal charge polarity but also the residual toner having the opposite polarity from the latent image carrier. For example, the following cleaning technique may be employed. .

  For example, in the apparatus described in Patent Document 1, a cleaning pretreatment charger is provided between the transfer position and the cleaning position. In this pre-cleaning charger, residual toner is neutralized by applying an alternating current, and the polarity of the residual toner is made uniform by weighting the direct current. In addition, since the charged polarity of the residual toner is made uniform in this way, the recovery into the cleaning device is extremely easy.

  As another method, for example, in the apparatus described in Patent Document 2, a first cleaning unit for removing residual toner having a normal charging polarity and a second cleaning unit for removing residual toner having a reverse polarity to the normal charging polarity are used. And cleaning means. That is, a cleaning bias having a polarity opposite to the normal charging polarity of the toner is applied to the brush of the first cleaning unit, and the toner charged to the normal charging polarity remaining on the surface of the latent image carrier is removed. On the other hand, a cleaning bias having the same polarity as the normal charging polarity of the toner is applied to the brush of the second cleaning means to remove residual toner charged to a polarity opposite to the normal charging polarity that remains and adheres to the surface of the latent image carrier.

JP-A-8-305239 (FIG. 2) JP-A-4-330482 (FIG. 1)

  However, in the apparatus described in Patent Document 1, it is necessary to separately provide a cleaning pretreatment charger in addition to the brush. Moreover, in the apparatus described in Patent Document 2, two brushes are required. Therefore, in these cleaning means, there is a problem in that the size of the apparatus is increased by the provision of an additional configuration and the cost of the apparatus is increased as compared with an apparatus that removes residual toner with a single brush or blade.

  The present invention has been made in view of the above problems, and can remove the toner of normal charging polarity and the toner of reverse polarity remaining on the surface of the latent image carrier with one brush without providing an additional configuration. An object is to provide an image forming apparatus and an image forming method.

  The image forming apparatus according to the present invention transfers a toner image formed of toner having a normal charging polarity to a surface of a latent image carrier that circulates in a predetermined rotation direction, and performs image forming to perform a printing process. In order to achieve the above-described object, the apparatus has a charging means for charging the surface of the latent image carrier to a potential having the same polarity as the normal charging polarity at a predetermined charging position, and transfer downstream of the charging position in the rotation direction. A transfer means for bringing the transfer member into contact with the latent image carrier at a position and applying a transfer bias to the transfer member to transfer the toner image to a recording medium passing between the latent image carrier and the transfer member; And a cleaning means for removing toner of normal charging polarity remaining on the surface of the latent image carrier by bringing the brush into contact with the surface of the latent image carrier at a cleaning position downstream from the transfer position, A charging bias having the same polarity as the normal charging polarity is applied to the charging means while the latent image carrier makes one round after the image processing, and a discharge is generated between the surface of the latent image carrier charged by the charging means and the transfer means. A transfer bias having the same polarity as the surface potential of the latent image carrier charged by the charging means or the same polarity as the normal charging polarity and smaller than the surface potential or opposite to the normal charging polarity is applied to the transfer member. It is characterized by.

  In addition, in order to achieve the above object, the image forming method according to the present invention rotates the latent image carrier in a predetermined rotation direction, and the surface of the latent image carrier by a charging unit disposed at a predetermined charging position. Is charged to a potential of normal charging polarity, a toner image is formed on the surface of the latent image carrier with toner of normal charging polarity, and the toner image is recorded by a transfer means at a transfer position downstream of the charging position in the rotation direction. A printing process for transferring to the medium, and a cleaning process for removing the residual toner on the latent image carrier while moving the latent image carrier once around the printing process. The cleaning process has the same polarity as the normal charging polarity. Is applied to the charging means, and no discharge is generated between the surface of the latent image carrier charged by the charging means and the transfer means, and the surface potential of the latent image carrier charged by the charging means is The transfer bias is applied to the transfer means with the same polarity or the same polarity as the normal charge polarity and less than the surface potential or opposite to the normal charge polarity, and the brush is placed on the surface of the latent image carrier at the cleaning position downstream of the transfer position in the rotation direction. And a step of removing the toner of the normal charge polarity remaining on the surface of the latent image carrier by contacting the toner.

In the invention thus configured (image forming apparatus and image forming method), a charging bias having the same polarity as the normal charging polarity is applied to the charging means while the latent image carrier makes one turn after the printing process or printing process, Toner having a polarity opposite to the normal charging polarity remaining on the latent image carrier, such as fog toner, is changed to the normal charging polarity when passing through the charging position, and the toner remaining on the surface of the latent image carrier is charged to the charging position. All of them have normal charging polarity at the time of passing. In this way, the toner having the regular charging polarity passes through the transfer position before being conveyed to the cleaning position. In the present invention, the transfer bias applied to the transfer means is set so as to satisfy two conditions. That is, the first condition (1) is that no discharge is caused between the surface of the latent image carrier charged by the charging means and the transfer means.By satisfying this condition (1), the transfer position Thus, it is possible to prevent the polarity of the toner on the latent image carrier from being greatly changed. The second condition (2) is that the transfer bias is one of the following:
(2-1) The same potential as the surface potential of the latent image carrier charged by the charging means,
(2-2) It is the same polarity as the normal charging polarity and less than the surface potential.
(2-3) normal charging polarity and reverse polarity,
Is set to By satisfying these two conditions, the residual toner having the normal charging polarity aligned by the charging means as described above does not change to the reverse polarity, and the transfer position is maintained while being held on the surface of the latent image carrier. Passes and is transported to the cleaning position. Then, the residual toner having the regular charge polarity is removed by the brush.

  During the printing process (printing process) and during the cleaning process (cleaning process), a part of the normally charged polarity toner adhering to the surface of the latent image carrier is transferred to the transfer unit. there is a possibility. In this case, as described above, the toner of the normally charged polarity that has moved to the transfer means is adjusted by adjusting the transfer bias while the latent image carrier moves one or more times after the latent image carrier has made one round. It can be returned to the carrier and removed with a brush. That is, the surface of the latent image carrier charged by the charging unit without causing discharge between the surface of the latent image carrier charged by the charging unit and the transfer unit and having the transfer bias of the same polarity as the normal charging polarity. A value larger than the potential may be set.

  Here, when the transfer bias is set to the same potential as the surface potential of the latent image carrier charged by the charging means, the normally charged polarity toner remaining on the latent image carrier moves from the latent image carrier to the transfer means. Can be reliably prevented. Of course, when the same potential is set, no discharge occurs between the surface of the latent image carrier and the transfer means, and the toner with the regular charge polarity set by the charging means passes directly through the transfer position to the cleaning position. And is removed from the surface of the latent image carrier by a brush.

Also, it is desirable that the cleaning bias applied to the brush satisfies two conditions. First, the first condition is to set the potential so as not to cause a discharge between the surface of the latent image carrier charged by the charging means and the brush. By satisfying this condition, the brush cleaning ability of the residual toner is set. Can be lowered. In addition, as a second condition, the cleaning bias is one of the following:
-It is smaller than the surface potential of the latent image carrier charged by the charging means with the same polarity as the normal charging polarity,
・ The electric potential is of the opposite polarity to the normal charging polarity.
Therefore, when the second condition is satisfied, the residual toner having the normally charged polarity conveyed to the cleaning position is reliably removed by the brush. By satisfying the above two conditions as described above, the residual toner can be efficiently removed from the surface of the latent image bearing member efficiently and reliably at the cleaning position.

Further, on the surface of the latent image carrier, an image portion where a toner image is formed and a non-image portion where a toner image is not formed are mixed. These image portions and non-image portions have different surface potentials. In view of this, a neutralizing means for neutralizing the latent image carrier at the neutralization position downstream of the transfer position and upstream of the cleaning position in the rotation direction is provided to uniformly level the surface potential of the latent image carrier before cleaning. Thus, the entire surface of the latent image carrier can be uniformly cleaned. In addition, when the surface of the latent image carrier is neutralized before cleaning as described above, it is preferable that the cleaning bias applied to the brush satisfies the following two conditions. That is, one of these conditions is to set a potential that does not cause discharge between the surface of the latent image carrier that has been neutralized by the neutralizing means and the brush, and satisfying this condition can improve the brush cleaning ability. Good brush cleaning is possible without reduction. In addition, as a second condition, the cleaning bias is one of the following:
-Less than the surface potential of the latent image carrier that has the same polarity as the normal charging polarity and has been neutralized by the neutralizing means,
・ The electric potential is of the opposite polarity to the normal charging polarity.
By satisfying the second condition, the residual toner having the normally charged polarity conveyed to the cleaning position is surely removed by the brush. By satisfying the above two conditions as described above, the residual toner can be efficiently removed from the surface of the latent image bearing member efficiently and reliably at the cleaning position.

  Various charging means can be used, and it is particularly preferable to use a scorotron charger as the charging means. For example, when the latent image carrier is charged by the contact DC roller charging method, the latent image charged by the contact DC roller is charged in accordance with the change in the film thickness of the photoreceptor formed on the surface of the latent image carrier due to durability. The surface potential of the image carrier changes. Therefore, in this case, it is necessary to change the transfer bias according to the change in the surface potential. On the other hand, in the scorotron charger, the surface potential of the latent image carrier almost coincides with the potential applied to the grid electrode of the scorotron charger regardless of the film thickness of the latent image carrier and is not affected by durability. .

  Further, in the present invention, the toner remaining on the surface of the latent image carrier after the printing process is removed from the latent image carrier by the brush after the charging means has made the regular charging polarity uniform. Even if the toner has a small particle diameter and a circularity of 0.95 or more, the toner remaining on the latent image carrier can be reliably removed by cleaning.

1 is a diagram schematically illustrating a main configuration of an embodiment of an image forming apparatus according to the present invention. The block diagram which shows the electric constitution of the apparatus of FIG. 2 is a timing chart showing the operation of the image forming apparatus in FIG. 1. FIG. 2 is a schematic diagram illustrating an operation (during printing) of the image forming apparatus in FIG. 1. FIG. 2 is a schematic diagram illustrating an operation (paper interval) of the image forming apparatus in FIG. 1. FIG. 2 is a schematic diagram illustrating an operation (first cleaning round) of the image forming apparatus in FIG. 1. FIG. 3 is a schematic diagram illustrating an operation (second cleaning cycle) of the image forming apparatus in FIG. 1.

  FIG. 1 is a diagram schematically showing the main configuration of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the apparatus of FIG. In the image forming apparatus 1, image formation is performed using a nonmagnetic one-component negatively charged toner. That is, in this embodiment, the negative polarity is “regular charging polarity”. Of course, it is also possible to form an image using a positively charged toner having positive polarity as a normal charging polarity. In the following description, the image forming apparatus 1 is described as using negatively charged toner. However, when positively charged toner is used, the charging potential of each member described below may be reversed. In addition, the toner has toner base particles and external additives that are externally added to the toner base particles. In the following description, when simply referred to as “toner”, external additives are added to the toner base particles. Indicates the entire particle to which is added externally.

  As shown in FIG. 1, the image forming apparatus 1 includes a photoreceptor 2 on which an electrostatic latent image and a toner image are formed. The photoreceptor 2 is composed of a photoreceptor drum, and a photosensitive layer having a predetermined film thickness (for example, 25 μm) is formed on the outer peripheral surface of a cylindrical metal base tube in the same manner as a conventionally known photoreceptor drum. A conductive tube such as aluminum is used for the metal base tube in the photoreceptor 2 and a conventionally known organic photoreceptor is used for the photosensitive layer.

  Around the photoreceptor 2, a charger 5 that is a corona charger that charges the surface of the photoreceptor 2 to a predetermined potential, and exposure that forms an electrostatic latent image by exposing the surface of the photoreceptor 2 in accordance with an image signal. A unit 6; a developing unit 7 that visualizes the electrostatic latent image as a toner image; a transfer unit 8 to which the toner image is transferred; a static eliminator 3 that eliminates static electricity by irradiating the surface of the photosensitive member 2 with static elimination light; The units 4 are arranged in the order of rotation along the rotation direction D2 (clockwise in FIG. 1) of the photoreceptor 2.

  The charger 5 is not in contact with the surface of the photoreceptor 2, and a conventionally well-known and commonly used corona charger can be used as the charger 5. When a scorotron charger is used as the corona charger, a negative wire current Iw flows through the charge wire 5b of the scorotron charger, and a negative direct current (DC) grid charging bias Vg is applied to the grid 5a. Is done. The charger 5 is charged with corona discharge having the same polarity (negative polarity) as that of the toner by the charger 5, so that the surface potential of the photoreceptor 2 is set to a substantially uniform negative potential, more specifically, at the time of image formation. Is set to the potential Vo.

  The exposure unit 6 exposes the surface of the photoreceptor 2 with a light beam L in accordance with an image signal given from an external device, and forms an electrostatic latent image corresponding to the image signal. More specifically, as shown in FIG. 2, when an image signal is given via an interface 112 from an external device such as a host computer that generates an image signal, the image signal is subjected to predetermined processing by the image processing unit 111. Applied. This image signal is transferred to the exposure unit 6 via the CPU 101 that controls the operation of the entire apparatus. The exposure unit 6 exposes the surface of the photoconductor 2 by irradiating the light beam L in accordance with the image signal, and the exposed surface area (exposed portion) of the photoconductor 2 is neutralized and the surface is not exposed. It changes to a surface potential different from the region (non-exposed portion). Thus, an electrostatic latent image corresponding to the image signal is formed on the photoreceptor 2.

  Toner is applied from the developing unit 7 to the electrostatic latent image thus formed, and the electrostatic latent image is developed with the toner. The developing unit 7 of the image forming apparatus 1 is a non-contact developing type developing device in which the developing roller 7 a does not contact the photoreceptor 2. The developing roller 7a is disposed opposite to the photosensitive member 2 with a predetermined gap, and is driven to rotate in the arrow direction D7 in FIG. A predetermined developing bias Vb is applied from the developing bias power supply 71 to the developing roller 7a.

  Further, the transfer unit 8 has a transfer roller 8a as a “transfer member” of the present invention. The transfer roller 8a is pressed against the photosensitive member 2 to form a transfer nip portion, and a recording medium M such as a recording sheet or paper is carried into the transfer nip portion. Further, a transfer bias Vt having a polarity opposite to the charging polarity of the toner is applied from the transfer bias power source 81 to the transfer roller 8a, and the toner image developed on the photosensitive member 2 is transferred to the recording medium M by the action. The The recording medium M onto which the toner image has been transferred in this manner is conveyed to the fixing unit 9 by a conveyance mechanism (not shown), and is permanently fixed on the recording medium M by the fixing unit 9 and output.

The cleaning unit 4 includes a brush roller 4a that is rotatably provided. The brush roller 4a is formed of a metal core, and a plurality of conductive brush bristles 4b such as acrylic-carbon, nylon-carbon, polyester-carbon, and polypropylene-carbon are wound around the brush roller 4a. A brush roller 4a is disposed so that these bristles 4b come into contact with the surface of the photoreceptor 2. The brush roller 4a rotates and forwardly rotates the photosensitive member 2 (the direction of the tangential speed of rotation of the photosensitive member 2 at the contact portion between the photosensitive member 2 and the brush hair 4b and the tangential speed of rotation of the brush hair 4b). The direction is the same as the direction of), that is, so-called with rotation. In the present embodiment, conductive brush bristles 4b having a brush raw yarn resistance of 1.0 × 10 ^{4 to} 1.0 × 10 ⁸ Ω are used.

  The brush roller 4a is applied with a cleaning bias Vbr having a polarity opposite to the normal charging polarity of the toner, that is, a positive direct current (DC) cleaning bias Vbr. As a result, among the transfer residual toner (residual toner) on the photosensitive member 2 that has passed through the transfer position, that is, the transfer nip portion, the toner charged to the normal charging polarity is attracted to the brush roller 4a and adheres to the brush bristles 4b. By using the brush type cleaning unit 4 in this way, a small particle size toner (for example, the volume average particle size is 5 μm or less and the circularity of the toner is 0.95 which has been difficult to be collected by the blade type cleaning unit. The above toner) can be reliably recovered and removed from the surface of the photoreceptor 2.

  In the following description, the position at which the photosensitive member 2 and the charger 5 are opposed to each other is the charging position CP, the surface where the light beam L from the exposure unit 6 is irradiated to the surface of the photosensitive member 2 is the exposure position EP, and the photosensitive member 2. And the developing roller 7a are positioned at the developing position DP, the contact position between the photosensitive member 2 and the transfer roller 8a is the transferring position TP, the position where the discharging light is irradiated is the pre-cleaning discharging position PP, and the photosensitive member 2 is the cleaning unit. The position where 4 abuts is called a cleaning position BP. In this embodiment, these positions are provided in the above order from the upstream side to the downstream side in the rotation direction D2 of the photosensitive member 2.

  Next, the operation of the embodiment configured as described above will be described with reference to FIGS. FIG. 3 is a timing chart showing the operation of the image forming apparatus of FIG. 4 to 7 are schematic diagrams showing the operation of the image forming apparatus of FIG. 1. In each figure, white circles indicate negatively charged toner, while hatched circles indicate positively charged toner. ing.

  In the image forming apparatus 1 configured as described above, when a print command signal including an image signal is given from an external device such as a host computer to the CPU 101 (see FIG. 2), each part of the device is predetermined according to the command from the CPU 101. The image forming operation is executed to form an image corresponding to the image signal on the recording paper as the recording medium M. In the timing chart of FIG. 3, after a print job for forming an image on six recording sheets M is executed as “printing process” or “printing process” of the present invention, the cleaning sequence is “cleaning process” of the present invention. The operation to be executed as is shown as an example. The features of the embodiment will be described below along with this operation example.

  When the print job is started, a negative wire current Iw is supplied to the charge wire 5b of the charger 5, and a negative direct current (DC) grid charging bias Vg is applied to the grid 5a. In this embodiment, a grid charging bias Vg of −600 V is applied. Thus, the surface potential of the photoconductor 2 is set to a substantially uniform negative potential (−600 V) by charging the photoconductor 2 with corona discharge having the same polarity (negative polarity) as that of the toner. Note that bias application to the charger 5 is continued from the start of the print job to the completion of the cleaning sequence.

  In this way, the surface of the negatively charged photoreceptor 2 is exposed to the light beam L corresponding to the image signal, and an electrostatic latent image corresponding to the image signal is formed. The surface area of the photoreceptor 2 exposed in this way is an “exposed area” and changes to a surface potential different from that of the unexposed surface area, ie, the “non-exposed area”. This electrostatic latent image is developed with toner by the developing unit 7. In this embodiment, a polymerized toner having a volume average particle size of 5 μm or less and a circularity of 0.95 or more is used. Therefore, a high-definition toner image can be formed on the surface of the photoreceptor 2.

  When the toner image is conveyed to the transfer position TP, it is transferred to the recording paper M by the transfer unit 8. At this time, +1500 V is applied as a transfer bias Vt from the transfer bias power supply 81 to the transfer roller 8a of the transfer unit 8, and the toner image developed on the photosensitive member 2 by the action is transferred onto one recording sheet M. Is done. Further, the transfer bias Vt applied to the transfer roller 8a every time the transfer to the recording paper M is completed is lowered to + 200V. Thus, the potential difference between the surface potential V0 of the photoconductor 2 and the transfer bias Vt is set to 800 V while preventing the surface potential of the photoconductor 2 from being charged to the positive potential side. In the photosensitive member 2 having a photosensitive layer thickness of 25 μm, which is a general apparatus configuration, the discharge start voltage is about 600 V. Therefore, by setting the potential difference to 800 V as described above, discharging is performed between the photosensitive member 2 and the transfer roller 8 a. As a result, the negatively charged toner on the photosensitive member 2 moving to the transfer position TP is made positive to make it difficult to move to the transfer roller 8a. However, it is difficult to make all of the negatively charged toner that has moved to the transfer position TP between the sheets positive, and as shown in FIG. 5, some of the negatively charged toner remains on the transfer roller 8a while having a negative polarity. It will move. Further, when the transfer process is performed on the next recording sheet M, the transfer bias Vt is again increased to 1500V. That is, the transfer bias during the execution of the print job is set to + 1500V during printing as shown in FIG. 4, while it is set to + 200V between sheets as shown in FIG. The recording paper M on which the toner image has been transferred as described above is conveyed to the fixing unit 9 and subjected to a predetermined fixing process, and then output onto a tray (not shown).

  The surface area of the photoconductor 2 that has passed through the transfer position TP is neutralized by receiving the neutralizing light from the static eliminator 3, so that the surface potential difference between the exposed portion and the non-exposed portion disappears, and the surface potential of the photoconductor 2 becomes a predetermined potential. In this embodiment, after being equalized to −50 V, the cleaning unit 4 performs brush cleaning at the cleaning position BP. In this embodiment, as shown in FIG. 3, +500 V is applied to the brush roller 4a as the cleaning bias Vbr from the start of the print job to the completion of the cleaning sequence. That is, in this embodiment, the potential difference between the surface potential of the photoconductor 2 subjected to static elimination and the cleaning bias Vbr is about 550 V, and is suppressed to a potential difference lower than the discharge start voltage. Therefore, the residual toner can be reliably removed from the photosensitive member 2 without generating a discharge between the photosensitive member 2 and the brush and without reducing the brush cleaning ability due to the occurrence of the discharge. That is, among the transfer residual toner (residual toner) on the photoconductor 2 that has passed through the transfer position TP and the charge removal position, the negatively charged toner charged to the normal charge polarity is attracted to the brush roller 4a and the photoconductor by the brush bristles 4b. 2 removed from the surface.

  On the other hand, the positively charged toner is not collected by the cleaning unit 4 and moves to the charging position CP as it is, and most of the positively charged toner is negatively charged. Then, it is returned to the developing roller 7a during printing. However, since positively charged toner is supplied as fog toner from the developing roller 7a to the photosensitive member 2 at that time, a constant amount of positively charged toner is always applied on the photosensitive member 2 during a print job as shown in FIGS. Toner is present.

  If the toner remains on the photoconductor 2 for a long time as described above, the toner is fixed to the photoconductor 2 and may cause image defects. Further, since the negatively charged toner remains on the transfer roller 8a, there also arises a problem that the toner adheres to the back side (back side) of the recording paper M and becomes dirty. Therefore, in the present embodiment, after the print job is completed, the cleaning sequence shown in FIGS. 3, 6, and 7 is executed.

  In this cleaning sequence, the photosensitive member 2 is rotated two to three times after the print job is completed, and a grid charging bias Vg of −600 V is applied to the charger 5 during that time. For this reason, the surface potential V0 of the photoreceptor 2 becomes −600 V, and the positively charged toner remaining on the surface of the photoreceptor 2 is charged to a negative potential at the charging position CP to become a negatively charged toner. Further, the developing bias is turned off, and the negatively charged toner is not collected from the photosensitive member 2 to the developing roller 7a, but the fog toner is not supplied from the developing roller 7a to the photosensitive member 2. Further, while the photoreceptor 2 is rotated once after the print job is completed, the transfer bias Vt is set to the same potential as the surface potential V0 of the photoreceptor 2 charged by the charger 5, that is, -600V. Thus, by setting the surface potential V0 and the transfer bias to the same potential, it is difficult for the toner to move from the photoreceptor 2 to the transfer roller 8a regardless of the toner polarity. Of course, since the surface potential V0 and the transfer bias are set to the same potential, no discharge occurs between the photosensitive member 2 and the transfer roller 8a. Therefore, as shown in FIG. 6, the positively charged toner is made negative while the photoreceptor 2 is rotated once after the print job, and the toner remaining on the surface of the photoreceptor 2 is made negative. In this embodiment, also in the cleaning sequence, the surface of the photosensitive member 2 is irradiated with static elimination light before cleaning to equalize the surface potential of the photosensitive member 2 to −50V, and the cleaning bias Vbr is set to + 500V for cleaning. The unit 4 makes it possible to collect negatively charged toner reliably and efficiently.

  Residual toner is cleaned and collected by the cleaning unit 4 by the operation of “first cleaning after job” shown in FIG. 6 described above. Further, in order to collect negatively charged toner adhering to the transfer roller 8a, In this embodiment, as shown in FIGS. 3 and 7, the photosensitive member 2 is further rotated once or twice, and the transfer bias Vt is increased to −1000 V to transfer the negatively charged toner from the transfer roller 8a to the photosensitive member 2. ing. In this embodiment, since the potential difference between the surface potential of the photosensitive member 2 and the transfer bias Vt is set to be smaller than the discharge start voltage (600 V), the discharge between the photosensitive member 2 and the transfer roller 8a is performed in the cleaning sequence. Is prevented from occurring. Therefore, the toner adhering to the surfaces of the transfer roller 8a and the photosensitive member 2 is transported to the cleaning position BP while maintaining the negative polarity without being positively positive and is reliably collected by the cleaning unit 4.

  In this manner, the polarity of the toner remaining on the surface of the photoconductor 2 is made equal to the normal charging polarity by the “first cleaning after job” shown in FIG. 6 and collected by brush cleaning, and the “job” shown in FIG. The remaining toner, including the toner adhering to the transfer roller 8a, is collected by the cleaning unit 4 by the “second cleaning round 2 to 3”. When the cleaning sequence is completed in this manner, the application of the neutralizing light is stopped and the bias application of each part is stopped. Then, it waits for the next print command signal to be sent.

  As described above, according to the present embodiment, the normal charging polarity (in the present embodiment, “in the present embodiment,“ corresponding to “printing process” or “printing process” of the present invention) is performed while the photoconductor 2 makes one round. A charging bias Vg having the same polarity as the negative polarity ”) is applied to the charger 5 to change the positively charged toner remaining on the photosensitive member 2 into a negatively charged toner. In addition, the transfer bias applied to the transfer roller 8 a is set to the same potential as the surface potential of the photosensitive member 2 charged by the charger 5. For this reason, the residual toner that has been aligned with the normal charging polarity by the charger 5 as described above passes through the transfer position TP as it is without being returned to the reverse polarity, and is conveyed to the cleaning position BP for brush cleaning. Therefore, the positively charged toner and the negatively charged toner remaining on the surface of the photoreceptor 2 can be removed with one brush (brush roller 4a + brush bristles 4b).

  Further, in the above embodiment, as shown in FIG. 5, a part of the regular charged polarity toner adhering to the surface of the photoreceptor 2 during the print job is transferred to the transfer roller 8a, but as shown in FIG. The surface of the photoreceptor 2 charged by the charger 5 with the same polarity as the normal charging polarity without causing a discharge between the surface of the photoreceptor 2 charged with the transfer bias Vt by the charger 5 and the transfer roller 8a. A value larger than the potential V0 is set. For this reason, as shown in FIG. 7, the toner adhering to the transfer roller 8 a is returned to the photoreceptor 2, and then conveyed to the cleaning position BP and collected by the cleaning unit 4. Therefore, it is possible to effectively prevent the back surface of the recording paper M from being stained with toner.

  Further, in the above embodiment, brush cleaning is performed for residual toner adhering to the exposed portion by uniformly leveling the surface potential of the photosensitive member 2 with static elimination light before brush cleaning, and for residual toner adhering to the non-exposed portion. It is adjusted to a state suitable for. Accordingly, the entire surface of the photoreceptor 2 can be cleaned uniformly.

  Further, various types of chargers 5 can be used. In the present embodiment, since the scorotron charger is used as the charger 5 in particular, the following effects can be obtained. That is, for example, when the photosensitive member 2 is charged by the contact charging method, the surface potential of the photosensitive member 2 that has been charged according to the change in the film thickness of the photosensitive member 2 formed on the surface of the photosensitive member 2 due to durability. V0 changes. Therefore, in order to appropriately perform the cleaning sequence, it is necessary to change and set the transfer bias Vt according to the change in the surface potential V0 based on the durability. On the other hand, in the present embodiment, the surface potential of the photoconductor 2 is substantially the same as the potential Vg applied to the grid electrode of the charger 5 regardless of the film thickness of the photoconductor 2. Control can be simplified.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, as shown in FIG. 6, the transfer bias Vt applied to the transfer roller 8 a in “first cleaning after job” is −600 V, which is the same as the surface potential V0 of the photoreceptor 2 charged by the charger 5. However, a potential on the positive polarity side, that is, a potential having the same polarity as the normal charging polarity and smaller than the surface potential V0, or a voltage having a polarity opposite to the normal charging polarity may be applied. However, if the potential difference between the set potential and the surface potential V0 exceeds the discharge start voltage and discharge occurs between the surface of the photosensitive member 2 and the transfer roller 8a, one of the toners on the surface of the photosensitive member arranged to have a negative polarity. The part changes to positive polarity. Accordingly, the transfer bias Vt applied to the transfer roller 8a in “the first cleaning after the job” satisfies the conditions (1) and (2) described in the section “Means for Solving the Problems”. Thus, similarly to the above-described embodiment, the residual toner that has been aligned with the normal charging polarity by the charger 5 passes through the transfer position TP without returning to the reverse polarity, and the photoconductor at the cleaning position BP. The residual toner on 2 can be brush cleaned. Further, as long as the above conditions (1) and (2) are satisfied, the charging bias in the cleaning sequence may be different from that of the print job.

  In the above-described embodiment, the photosensitive member 2 is rotated once after the print job and the operation of “the first cleaning cycle after job” in FIG. 6 is performed. The same operation as “first cleaning after job” may be executed.

  Moreover, in the said embodiment, although the static elimination before cleaning by the static eliminator 3 is performed, this is not an essential component and it is also possible to omit static elimination before cleaning.

  In the above embodiment, the cleaning bias Vbr is set to +500 V. However, the value is not limited to this value, and the discharge is performed between the surface of the photoreceptor 2 that has been neutralized before cleaning by the static eliminator 3 and the brush. And a potential on the positive polarity side relative to the surface potential of the photosensitive member 2 (that is, a potential lower than the surface potential of the photosensitive member 2 having the same polarity as the normal charging polarity and neutralized by the static eliminator 3) The potential can be set to a polarity opposite to the polarity). In the apparatus that does not perform static elimination before cleaning by the static eliminator 3 as described above, the surface of the photosensitive element 2 has a potential that does not cause discharge between the surface of the photosensitive element 2 charged by the charger 5 and the brush. What is necessary is just to set the potential on the positive polarity side relative to the potential (that is, the potential having the same polarity as the normal charging polarity and smaller than the surface potential of the photoreceptor 2 charged by the charger 5 or the potential having the opposite polarity to the normal charging polarity). Similarly to the above, the cleaning unit 4 can reliably and efficiently collect the toner with the regular charge polarity.

  Furthermore, in the above-described embodiment, the present invention is applied to an image forming apparatus that forms a toner image using a small particle size toner. However, the application target of the present invention is not limited to this, and photosensitive The present invention can be applied to all image forming techniques in which a toner image is formed with charged toner on the surface of a latent image carrier such as a body, and the toner image is transferred to a recording medium such as recording paper or paper.

  Next, examples of the present invention will be shown. However, the present invention is not limited by the following examples as a matter of course, and it is needless to say that the present invention can be implemented with appropriate modifications within a range that can meet the gist of the preceding and following descriptions. These are all included in the technical scope of the present invention.

In order to verify the effectiveness of the cleaning sequence, the present inventor performed printing processing on 1000 sheets of A4 recording paper in Example 1, Comparative Example 1 and Comparative Example 2 in an environment of a temperature of 35 ° C. and a humidity of 65%. When the printing process is performed for 12 hours after printing, and the printing process is performed immediately after the printing is left, printing surface contamination on the front surface (printing surface) of the recording paper and back surface contamination on the back surface (the surface in contact with the transfer roller 8a) occur. It was visually confirmed whether or not.
Example 1:
The cleaning sequence shown in FIGS. 3, 6 and 7 was executed once every 100 printing processes, and after the 1000 printing process, the cleaning sequence was left as it was.
Comparative Example 1:
Although the cleaning sequence is executed once every 100 printing processes, the cleaning sequence is not performed after 1000 printing processes.
Comparative Example 2:
Without performing any cleaning sequence, the printing process was performed and left unattended.
Immediately after being left for 12 hours, a printing process was performed, and the stains on the front surface (printing surface) and the back surface (surface contacting the transfer roller 8a) of each recording paper were visually observed.

  As a result, the print surface was not stained in Example 1, whereas the print surface was stained in Comparative Example 1 and Comparative Example 2. Further, in Example 1 and Comparative Example 1, no paper back stain was observed, whereas in Comparative Example 2, paper back stain was generated. In Comparative Example 2 in which no cleaning sequence is performed in this way, an image defect occurs when left for a long time, as in the conventional technique. Further, in Comparative Example 1, the cleaning sequence is performed, but the cleaning sequence is not performed before being left, so that the print surface is stained. This can be considered as follows. That is, in Comparative Example 1, toner adhesion to the transfer roller 8a is suppressed by the cleaning sequence for every 100 sheets, so that the paper back is not soiled. However, since the cleaning sequence is not performed before leaving, the surface of the photoreceptor 2 is not cleaned. It can be considered that the toner remains on the surface of the photosensitive member 2 with the toner remaining, particularly the toner adhesion on the surface area where the transfer roller 8a contacts and the transfer nip portion is formed. It is presumed that the image is defective because the exposure is blocked by the presence of the toner fixing. From these verification results, it can be seen that it is very important to prevent the image defect by executing the cleaning sequence after completion of the printing process and the printing process and preparing for leaving for a long time.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Photoconductor (latent image carrier), 3 ... Static elimination device (static elimination means), 4 ... Cleaning unit, 4a ... Brush roller, 4b ... Conductive brush hair, 5 ... Charger, 5a ... Grid, 5b ... Charge wire, 8 ... Transfer unit, 8a ... Transfer roller (transfer member), 81 ... Transfer bias power supply, BP ... Cleaning position, CP ... Charging position, D2 ... Rotation direction, M ... Recording paper (recording medium) TP: Transfer position, Vbr: Cleaning bias, Vg: Charging bias, Vt: Transfer bias

Claims (8)

In an image forming apparatus for executing a printing process, in which a toner image formed of toner having a normal charging polarity is transferred to a surface of a latent image carrier that circulates in a predetermined rotation direction onto a recording medium.
Charging means for charging the surface of the latent image carrier to a potential having the same polarity as the normal charging polarity at a predetermined charging position;
A transfer member is brought into contact with the latent image carrier at a transfer position downstream of the charging position in the rotation direction, and a transfer bias is applied to the transfer member to cause a gap between the latent image carrier and the transfer member. Transfer means for transferring the toner image to the recording medium passing therethrough;
Cleaning means for removing toner of normal charging polarity remaining on the surface of the latent image carrier by bringing a brush into contact with the surface of the latent image carrier at a cleaning position downstream of the transfer position in the rotational direction; Prepared,
While the latent image carrier makes one round after the printing process,
A charging bias having the same polarity as the normal charging polarity is applied to the charging means,
No discharge occurs between the surface of the latent image carrier charged by the charging means and the transfer means, and the same or normal charging polarity as the surface potential of the latent image carrier charged by the charging means An image forming apparatus, wherein a transfer bias having the same polarity as that of the surface potential but less than the surface potential or a polarity opposite to the normal charging polarity is applied to the transfer unit.   2. The image according to claim 1, wherein a transfer bias substantially the same as the surface potential of the latent image carrier charged by the charging unit is applied to the transfer unit while the latent image carrier makes one round after the printing process. Forming equipment.   During the round of the latent image carrier after the printing process, no discharge is generated between the surface of the latent image carrier charged by the charging unit and the brush, and the same polarity as the normal charging polarity. The image forming apparatus according to claim 1, wherein a cleaning bias smaller than the surface potential of the latent image carrier charged by the charging unit or having a polarity opposite to a normal charging polarity is applied to the brush.   3. The image forming apparatus according to claim 1, further comprising: a neutralizing unit that neutralizes the latent image carrier at a neutralization position downstream of the transfer position and upstream of the cleaning position in the rotation direction.   After the printing process, the latent image that has been discharged by the charge eliminating unit with the same polarity as the normal charging polarity without causing a discharge between the brush and the surface of the latent image carrier that has been discharged by the charge eliminating unit. 5. The image forming apparatus according to claim 4, wherein a cleaning bias smaller than the surface potential of the carrier or having a polarity opposite to the normal charging polarity is applied to the brush.   The image forming apparatus according to claim 1, wherein the charging unit is a scorotron charger.   The image forming apparatus according to claim 1, wherein the toner has a volume average particle diameter of 5 μm or less, and the toner has a circularity of 0.95 or more. The surface of the latent image carrier is charged to a potential of a normal charging polarity by a charging means disposed at a predetermined charging position while the latent image carrier rotates in a predetermined rotation direction. A printing step in which a toner image is formed with toner having a regular charge polarity and the toner image is transferred to a recording medium by a transfer unit at a transfer position downstream of the charging position in the rotation direction;
A cleaning step of removing residual toner on the latent image carrier while moving the latent image carrier one round after the printing step;
The cleaning step includes
Apply a charging bias of the same polarity as the normal charging polarity to the charging means,
No discharge occurs between the surface of the latent image carrier charged by the charging means and the transfer means, and the same or normal charging polarity as the surface potential of the latent image carrier charged by the charging means A transfer bias having the same polarity as that of the surface potential or less than the surface potential or having a polarity opposite to the normal charging polarity is applied to the transfer means,
A step in which a brush is brought into contact with the surface of the latent image carrier at a cleaning position downstream of the transfer position in the rotation direction to remove toner of normal charging polarity remaining on the surface of the latent image carrier. An image forming method.

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