JP4816352B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image by electrophotography. More specifically, a toner that remains on the image carrier after transfer (hereinafter referred to as “transfer residual toner”) is collected by a developing device, that is, a method in which development and cleaning are performed together in the developing device (hereinafter referred to as “developing residual toner”). The present invention relates to an image forming apparatus of “development simultaneous cleaning method”.

  Conventionally, in an electrophotographic image forming apparatus, a toner image is formed on an image carrier such as a photosensitive drum. More specifically, the image bearing member is uniformly charged and exposed to form an electrostatic latent image, and the electrostatic latent image is developed with toner to form a toner image. The toner image is transferred onto a recording medium such as paper, and the toner image is fixed on the recording medium, thereby forming an image. The transfer residual toner after the transfer is collected and removed by a cleaning device.

  In recent years, from the viewpoint of environmental protection and effective use of resources, there is an image forming apparatus in which the transfer residual toner is returned to the developing device and reused. As one of the methods, an image forming apparatus of a simultaneous development cleaning method in which a dedicated cleaning device is eliminated and a transfer residual toner is collected and reused by a developing device has been proposed.

  The simultaneous development cleaning method is a method in which the transfer residual toner after transfer is directly collected in the developing device by the potential difference with the developing bias in the subsequent development process. According to this method, since the transfer residual toner is collected by the developing device and reused for the development processing in the subsequent steps, it is possible to eliminate the discarded toner and to effectively use the toner. In addition, since a device for processing waste toner is not arranged, it is advantageous for making the device itself compact.

  The simultaneous development cleaning system as described above has the following problems. In other words, the untransferred toner in which the charging polarity is reversed to the polarity opposite to the normal polarity is mixed on the photoconductor after the transfer. In some cases, even if the charging polarity is a normal polarity, the charge amount is reduced due to charge removal. These toners tend to adhere to the charging device when passing through the contact-type charging device, and cause charging failure. Further, it is difficult to collect with the developing device, and accumulation on the photoconductor causes image defects.

As a technique paying attention to this problem, for example, Patent Document 1 discloses an image forming apparatus in which developer charge amount control means is arranged on the downstream side of the transfer means and the upstream side of the charging means in the rotation direction of the photosensitive member. Yes. This developer charge amount control means aligns the charge polarity of the untransferred toner with the normal charge polarity before the charging process. Thereby, the occurrence of charging failure and image failure can be suppressed. Further, for example, in Patent Document 2, a first developer charge amount control unit that performs a charging process with a polarity opposite to the normal polarity on the downstream side of the transfer unit and an upstream side of the charging unit, and a second one that performs a charging process with a normal polarity. An image forming apparatus in which the developer charge amount control means is disposed is disclosed. The two developer charge amount control means can efficiently collect the transfer residual toner in the developing device while preventing adhesion to the charging device.
JP-A-8-137368 JP 2002-99176 A

  However, the conventional image forming apparatus described above has the following problems. That is, in the image forming apparatus of the simultaneous development cleaning method, if there is an amount of transfer residual toner exceeding a predetermined amount, charging failure or exposure failure occurs.

  Specifically, as shown in FIG. 13, when the untransferred toner is concentrated at a specific location, the photoreceptor below the toner concentration location is not sufficiently charged during charging. For this reason, the absolute value of the photosensitive member surface potential V0 'at the toner concentration portion is lower than the absolute value of the photosensitive member surface potential V0 at the normal portion. This potential unevenness (charge failure) appears in the image as a density difference.

  Further, as shown in FIG. 14, the untransferred toner shields the exposed portion during exposure. Therefore, the absolute value of the photoreceptor surface potential Vi 'at the toner concentration portion is higher than the absolute value of the photoreceptor surface potential Vi at the exposure portion. This potential unevenness (exposure failure) also appears in the image as a density difference.

  In Patent Document 1 and Patent Document 2, the charge amount of the transfer residual toner is adjusted by the developer charge amount control means located after the transfer, thereby suppressing the adhesion to the charging device and facilitating the collection to the developing device. . However, no attention is paid to the amount of toner remaining on the photoreceptor. Therefore, when the amount of residual toner exceeds a predetermined amount, the above-described potential unevenness occurs.

  In addition to the transfer residual toner, there are minute external additives added to the toner and discharge products generated during charging on the photoreceptor. These minute substances cause filming and sticking on the photosensitive member over time, and cause image quality deterioration. In the case of a blade type cleaning device, these fine substances are removed at the time of cleaning because the cleaning blade scrapes off the transfer residual toner and polishes the surface of the photoreceptor. However, in the simultaneous development cleaning method, a cleaning member for polishing the surface of the photoreceptor is not installed. Therefore, it is difficult to suppress filming of minute substances.

  The present invention has been made to solve at least one of the problems of the conventional image forming apparatus of the conventional simultaneous development cleaning system. That is, an object of the present invention is to provide an image forming apparatus capable of forming a high-quality image by suppressing a charging failure at a charging portion and an exposure failure at an exposure portion in an image forming apparatus of a simultaneous development cleaning method. is there.

An image forming apparatus designed to solve this problem includes an image carrier that carries a toner image, a charging unit that uniformly charges the surface of the image carrier, and an electrostatic image on the charged image carrier. An exposure unit for forming a latent image, a development unit having a developing function for applying toner to the image carrier to form a toner image, and a recovery function for collecting the toner on the image carrier, and an image carrier An image forming apparatus having a transfer unit that transfers a formed toner image to a transfer material and performing both development and cleaning, and is upstream of the charging unit in the rotation direction of the image carrier. A first toner amount adjusting unit, which is located downstream of the transfer unit and has a collecting function for collecting toner on the image carrier and an ejection function for discharging the held toner; and the first toner amount adjusting unit collects the toner When processing, the first toner amount adjustment unit A first bias applying unit that applies a DC bias having a polarity opposite to the charging polarity of-and the rotation direction of the image carrier in the upstream of the charging unit and downstream of the transfer unit on the image carrier A second toner amount adjusting unit having a collecting function for collecting the toner and a discharging function for discharging the retained toner, and when the second toner amount adjusting unit performs the toner collecting process, the second toner amount adjusting unit By controlling each bias of the second bias applying unit that applies a DC bias having the same polarity as the charging polarity of the toner, and the first bias applying unit and the second bias applying unit, the first toner amount adjusting unit and the second A control unit that switches between a collection function and a discharge function of the toner amount adjustment unit, and a rotation direction of the image carrier upstream of the charging unit and downstream of the first toner amount adjustment unit and the second toner amount adjustment unit. Located and image carrier A conductive foaming elastic pad member slidably disposed on the surface of the image carrier, which reciprocates in the longitudinal direction of the image carrier to polish the surface of the image carrier and to adjust the toner charge polarity to the normal polarity. And an adjusting portion .

  The image forming apparatus of the present invention is a simultaneous developing cleaning type image forming apparatus having a developing unit that serves both for toner application and toner recovery, and is upstream of the charging unit and downstream of the transfer unit. By applying a predetermined bias, there are two toner amount adjusting sections for collecting the toner on the image carrier and discharging the retained toner. That is, a DC bias having a polarity opposite to the charging polarity of the toner is applied, a first toner amount adjusting unit that collects / discharges the toner charged to the normal polarity, and a DC bias having the same polarity as the charging polarity of the toner is applied. And a second toner amount adjusting unit that collects / discharges the toner charged to the reverse polarity.

  In the image forming apparatus of the present invention, the first toner amount adjusting unit collects the toner charged to the normal polarity, so that the toner amount on the image carrier is kept below a certain value. Thus, potential unevenness during charging and exposure can be suppressed. Further, the second toner amount adjusting unit collects the toner charged to the reverse polarity, whereby the transfer residual toner charged to the reverse polarity before the charging unit can be collected, and contamination of the charging unit can be suppressed. .

  Furthermore, both toner amount adjustment units also have a toner discharge function. Therefore, the toner accumulation in the toner amount adjusting unit can be avoided by discharging the toner at an appropriate timing (for example, between images or after completion of image formation).

  A DC bias is applied to each of the first toner amount adjusting unit and the second toner amount adjusting unit of the image forming apparatus of the present invention. Therefore, there is no concern about the vibration and noise of the image carrier, which is a concern when an AC bias is applied.

  In addition, it is preferable that the first toner amount adjustment unit of the image forming apparatus of the present invention has a higher toner storage capacity than the second toner amount adjustment unit. That is, the charge polarity of the transfer residual toner is overwhelmingly charged to the normal polarity, and there is a difference in the recovered amount between the first toner amount adjustment unit and the second toner amount adjustment unit. Therefore, by increasing the toner storage capacity of the first toner amount adjustment unit that collects the toner charged to the normal polarity, the life balance of both toner amount adjustment units is improved, and as a result, the length of both toner amount adjustment units is increased. Life expectancy is achieved. Further, by reducing the toner accumulation capacity of the second toner amount adjusting unit that collects the toner charged to the reverse polarity, the apparatus can be made compact and the cost can be reduced. That is, the space in the apparatus can be used effectively.

  The first toner amount adjusting unit may be a brush rotating body that counter-rotates with respect to the image carrier. That is, the toner can be easily taken in by rotating the counter.

The image forming apparatus of the present invention is located upstream of the charging unit and downstream of the first toner amount adjusting unit and the second toner amount adjusting unit in the rotation direction of the image carrier, and the charging polarity of the toner Has a toner charge amount adjusting unit that aligns the toners with normal polarity . Some of the toner discharged from each toner amount adjusting unit may reverse the charging polarity depending on the material, size, etc. of the toner amount adjusting unit. Therefore, by providing the toner charge amount adjusting unit between the toner amount adjusting unit and the charging unit, the charging polarity of the toner on the image carrier is made uniform before passing through the charging unit. As a result, contamination of the charging unit and non-recovery at the developing unit are suppressed.

The toner charge amount adjusting unit of the image forming apparatus according to the present invention is a pad member of a conductive foam elastic body that is slidably disposed on the image carrier and reciprocates in the longitudinal direction of the image carrier . That is, the toner charge amount adjusting unit, which is a pad member of the conductive foamed elastic body , is brought into sliding contact with the image carrier, whereby the surface of the image carrier is polished. As a result, it is possible to remove the minute substance fixed on the surface of the image carrier.

  According to the present invention, in the image forming apparatus of the simultaneous development cleaning system, an image forming apparatus that suppresses charging failure at the charging portion and exposure failure at the exposure portion and forms a high-quality image is realized.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an image forming apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a tandem type color printer.

  The image forming apparatus of this embodiment is a tandem full-color printer, and has four image forming units arranged in parallel as shown in FIG. Specifically, the color printer 100 according to this embodiment includes four color image forming units 1K, 1C, 1M, and 1Y. In addition, an exposure device 8, an intermediate transfer belt 10, a secondary transfer roller 11, a cleaning blade 12, and the like are included. Each image forming unit forms an image of each color on the intermediate transfer belt 10. Each image forming unit corresponds to each color of black (K) for the image forming unit 1K, cyan (C) for the image forming unit 1C, magenta (M) for the image forming unit 1M, and yellow (Y) for the image forming unit 1Y. ing. The arrangement of the image forming units is not limited to the order shown in FIG.

  Further, as shown in FIG. 2, the image forming unit 1K is a rotating drum type electrophotographic photosensitive member, and includes a photosensitive drum 2 which is a negatively chargeable organic photoconductor (OPC). The photosensitive drum 2 rotates at a constant speed in the direction of the arrow in FIG. Further, around the photosensitive drum 2, along the rotation direction, the charging device 3, the developing device 4, the transfer device 5, the first toner output amount control member 6A, the second toner output amount control member 6B, The toner charge amount control members 7 are sequentially arranged. An exposure area where a latent image is formed is provided between the charging device 3 and the developing device 4. The other image forming units have the same configuration.

  The color printer 100 of this embodiment includes a bias applying unit 61A for applying a predetermined DC bias (hereinafter referred to as “first toner amount control bias”) to the first toner extraction amount control member 6A, 2 A bias applying unit 61B for applying a predetermined DC bias (hereinafter referred to as “second toner amount control bias”) to the toner output amount control member 6B and a DC to the toner charge amount control member 7 A bias applying unit 71 for applying a bias (hereinafter referred to as “toner charge amount control bias”), and a control unit 62 for controlling the first toner amount control bias, the second toner amount control bias, and the toner charge amount control bias. And. Although not shown, a power source is connected to each of the charging device 3, the developing device 4, and the transfer device 5, and a predetermined bias is applied.

  The charging device 3 uniformly charges the surface of the photosensitive drum 2. As the charging device 3, in addition to a non-contact type corona charging device that is charged by corona discharge, a contact type charging device that charges a conductive contact charging member by contacting the surface of the photosensitive drum 2 can be applied. . The contact-type charging device can suppress the generation of discharge products, can prevent deterioration of the photosensitive drum 2, and can maintain high image quality. In addition, the equipment can be made compact by ozone-free. There are various types of contact-type charging devices such as a roller type, a blade type, a brush type, and a sheet type.

  In this embodiment, a roller type charging device is used. Specifically, as shown in FIG. 3, the charging device 3 includes a cored bar 31 (SUS, diameter: 6 mm), a foam base layer 32 (film thickness: 2.5 mm) covering the cored bar 31, and a foam base. An intermediate layer 33 (film thickness: 0.45 mm, resistance: 2E + 5Ω, hardness: 75 °, surface roughness Ra: 0.2 μm or less) covering the layer 32, and a surface layer 34 (film thickness: 10 μm) coating the intermediate layer 33 , Resistance: 2E + 5Ω). In addition, the material which comprises the foam base layer 32, the intermediate | middle layer 33, and the surface layer 34 should just be a general resin material.

  The bias applied to the charging device 3 (charging bias) may be any as long as the surface potential of the photosensitive drum 2 can be set to a predetermined value. For example, it may be a DC voltage or an AC voltage, or may be an oscillating voltage obtained by superimposing the AC voltage on the DC voltage. Further, the voltage may be a pulse voltage, a sine waveform, a rectangular waveform, or other waveform. In this embodiment, a charging bias of a sine wave (Vdc: −520 V, Vpp: 1200 V, frequency: 1 kHz) is applied.

  FIG. 4 shows the result of investigating the toner contamination state of the charging roller when the charging bias parameters (Vdc, Vpp) are changed. FIG. 5 shows the external additive contamination state of the charging roller when the charging bias parameters (Vdc, Vpp) are changed. In both figures, the contamination of the charging roller is judged visually, with ● indicating good, ▲ partially defective, and ■ indicating defective. As shown in both figures, the stain due to the plus toner is noticeable in the upper left area in FIG. 4, and the stain due to the minus toner is noticeable in the lower right area in FIG. Further, in the lower left region in FIG. 5, the external additive was conspicuous. Note that the areas not plotted in both figures are excluded from the investigation because the surface potential of the photosensitive drum is outside the usable range. Thus, as shown in the broken line frame in both figures, the charging bias is used in the charging roller in which Vdc is in the range of −200 V to −650 V and Vpp is in the range of 700 V to 1400 V. It can be seen that it is preferable for suppressing contamination of the substrate.

  The developing device 4 has a function of collecting toner in addition to a function of applying toner onto the latent image. That is, in this embodiment, the transfer residual toner on the photosensitive drum is collected for the white background portion of the electrostatic latent image, and the toner is applied to the other portions. The developing device 4 may be a contact type or a non-contact type. Further, the developing method may be a two-component developing method including toner and a carrier, or a one-component developing method not including a carrier. In this embodiment, negatively charged polarity toner is used. However, if the toner image can be developed, positively charged polarity toner may be used.

  The first toner collection amount control member 6A and the second toner collection amount control member 6B are for adjusting the passing amount of the transfer residual toner on the photosensitive drum 2. When the toner remaining after transfer is collected by each toner output control member, a bias having a polarity opposite to the normal polarity of the toner (positive polarity in this embodiment: +150 V) is applied to the first toner output control member 6A. Then, a bias having the same polarity (negative polarity in this embodiment: −500 V in this embodiment) with respect to the normal polarity of the toner is applied to the second toner collection amount control member 6B.

FIG. 6 shows the relationship between the transfer residual toner adhesion amount and density unevenness. In this graph, the horizontal axis represents the toner adhesion amount on the photosensitive drum, and the vertical axis represents the density change amount of the image sample taken at the adhesion amount. A halftone image (10%, 20%, 30%, 50%) of “present part” and “absent part” of the transfer residual toner is formed in advance and subjected to visual sensory evaluation. * When ab ≦ 2, no concentration difference was recognized. Therefore, filtration be evaluated residual toner within the 0~0.5g / m ^2, as shown in FIG. 6, 2 following the concentration variation Delta] E * ab If 0.2 g / m ² or less I understood that. Therefore, in the first toner output control member 6A and the second toner output control member 6B, the passing amount of the transfer residual toner is adjusted to be 0.2 g / m ² or less.

Further, conductive brush members are applied as the first toner collection amount control member 6A and the second toner collection amount control member 6B. In this embodiment, a nylon brush having a fine diameter of 2.2 dT, a density of 240 kF, a pile length of 3 mm, and a resistance of 1E + 5Ω is used. The configurations of the first toner collection amount control member 6A and the second toner collection amount control member 6B are not limited to those described above. The first toner output control member 6A and the second toner output control member 6B have at least a fine diameter of 1D to 6D (1.1 dT to 6.6 dT), a density of 150 kF to 600 kF, and a pile length of 2 mm to It is applicable if the resistance value of the brush molded product is within the range of 10 ⁴ Ω to 10 ⁶ Ω.

  The first toner collection amount control member 6 </ b> A is a rotating body, and is in sliding contact with the photosensitive drum 2 while rotating in the counter direction with respect to the photosensitive drum 2. On the other hand, the second toner collection amount control member 6B is a fixed body and is in sliding contact with the photosensitive drum 2 without rotating. That is, the first toner output amount control member 6A to which a bias having a polarity opposite to the charging polarity of the toner is applied accumulates more toner than the second toner output amount control member 6B to which a positive polarity bias is applied. The amount is large and the toner can be easily taken in.

  This is because only a part of the transfer residual toner whose charge polarity is reversed is the most, and most of the toner remains in the normal polarity (negative polarity in this embodiment). Therefore, the toner accumulation amount of the first toner collection amount control member 6A that collects transfer residual toner of normal polarity is set to be larger than the toner accumulation amount of the second toner collection amount control member 6B that collects transfer residual toner of reverse polarity. Increasing the size improves the balance of the lifespans of both toner yield control members. As a result, the life of the toner discharge amount control member can be extended. In other words, by reducing the toner accumulation amount of the second toner collection amount control member 6B that collects a small amount of toner, the apparatus can be made compact and the cost can be reduced.

  In addition, when the image forming apparatus controls to collect toner during image formation and to discharge the toner during non-image formation, the image formation is performed by increasing the toner accumulation amount of the first toner collection amount control member 6A. It is possible to lengthen the period during which image formation is possible until the operation is interrupted.

  Further, a DC bias is applied to each of the first toner output control member 6A and the second toner output control member 6B. Therefore, the vibration and noise of the photosensitive drum 2 which are a concern when an AC bias is applied are small.

  In this embodiment, the first toner amount control bias Vdc and the second toner amount control bias Vdc are variable, and are controlled by the control unit 62 according to the operation mode. Details of the control will be described later.

The toner charge amount control member 7 is for aligning the charging polarity of the toner on the photosensitive drum 2 with the normal polarity. In this embodiment, since negatively charged polarity toner is used, the charged polarity of the toner is made negative. As the toner charge amount control member 7, a conductive foam pad member in which conductive carbon is dispersed is applied. In this embodiment, the cell diameter distribution is concentrated in the range of 100 μm to 250 μm, the average cell diameter is 200 μm or less, the volume resistivity is in the range of 10 ⁴ Ωcm to 10 ⁶ Ωcm, and the density of the foam (weight per unit volume) uses foam is in the range of ^{0.2g / cm 3 ~0.5g / cm 3} . Further, the pressing force to the photosensitive drum 2 is set to 0.02 MPa.

  A toner charge amount control bias is applied to the toner charge amount control member 7 via a bias applying unit 71 serving as a power source. Specifically, a negative DC bias is applied to the toner charge amount control member 7. In this embodiment, a DC bias within a range of −500V to −300V is applied. The toner charge amount control bias parameter is also variable and is controlled by the control unit 62 in accordance with the control mode.

  FIG. 7 shows the relationship between the toner charge amount control bias and the change amount of the toner charge amount. As shown in FIG. 7, the toner charge amount can be controlled by changing the toner charge amount control bias. FIG. 8 shows the distribution of the toner charge amount before and after passing through the toner charge amount control member 7. As shown in FIG. 8, it can be seen that the variation in the toner charge amount is reduced by passing through the toner charge amount control member 7.

  FIG. 9 shows the relationship between the toner charge amount before charging and the contamination of the charging roller. In FIG. 9, Vdc means Vdc of the charging roller, and Vpp of the charging roller is 1200V. In this graph, the horizontal axis is the toner charge amount (μC / g) immediately after the transfer and just before charging, and the vertical axis is the contamination on the charging roller when the charge amount is (that is, a sticker is applied on the charging roller). The dirt was extracted, and L *) when the dirt was transferred to white paper was measured. In general, if L * is 80 or more, contamination of the charging roller does not affect the image quality. As shown in FIG. 9, when the charge amount of the toner is about −15 μC / g or less, the charging roller is remarkably contaminated. Therefore, in the toner charge amount control member 7 of this embodiment, the charge amount of the transfer residual toner immediately before passing through the charging device on the photosensitive drum is adjusted to be −15 μC / g or less (that is, as an absolute value or more). As shown in FIG. 9, the contamination of the charging roller does not depend on Vdc applied to the charging roller.

  Further, the toner charge amount control member 7 is in sliding contact with the photosensitive drum 2 and is provided so as to be reciprocally movable in the axial direction of the photosensitive drum 2. That is, the surface of the photosensitive drum 2 is polished by the toner charge amount control member 7 which is a foamed material sliding on the surface layer of the photosensitive drum 2. Then, the surface of the photosensitive drum 2 is polished, so that the minute substance fixed on the surface of the photosensitive drum 2 is removed.

  The reciprocating motion of the toner charge amount control member 7 is always performed while the photosensitive drum 2 is rotating. Further, the polishing amount of the photosensitive drum 2 can be controlled by adjusting the moving speed, moving amount, pressing amount and the like of the toner charge amount control member 7.

  Next, an operation when an image is formed by the color printer 100 of this embodiment will be described. FIG. 10 shows the transition of the surface potential of the photosensitive drum 2. First, the charging device 3 uniformly charges the surface of the photosensitive drum 2 to a predetermined potential V0 (FIG. 10A).

  Next, the exposure device 8 irradiates the exposure area on the photosensitive drum 2 with light, whereby an electrostatic latent image of the first page is formed. In this step, the portion exposed by the laser beam becomes the potential Vi, and an electrostatic latent image is formed by the contrast between the potential V0 and the potential Vi (FIG. 10B).

  Next, in the developing device 4, a developing bias is applied to the developing roller carrying the negatively charged toner, and the electrostatic latent image passes over the developing roller having the potential Vd (V0 <Vd <Vi). Development is performed during the process. At this time, the toner on the developing roller moves to the photosensitive drum 2 at the exposed portion (black background portion) at the potential Vi, and does not move at the non-exposed portion (white background portion) at the potential V0 (FIG. 10). (C)). As a result, a toner image is formed on the photosensitive drum 2.

  Next, the toner image is transferred onto the intermediate transfer belt 10 by the transfer device 5. That is, the toner on the photosensitive drum 2 moves onto the intermediate transfer belt 10 by the positive transfer bias Vt of the transfer device 5 (FIG. 10D). At this time, a part of the toner remains on the photosensitive drum 2 without being transferred, and becomes a transfer residual toner. The transfer residual toner may be positively charged or negatively charged.

Next, the transfer residual toner charged to the normal polarity (negative polarity in this embodiment) is collected by the first toner collection amount control member 61 by the first toner collection amount control member 61 (FIG. 10E). . At this time, it is not always necessary to collect 100% of the toner, and it is sufficient that the toner amount is a predetermined amount or less (in this embodiment, 0.2 g / m ² or less).

  Next, the transfer residual toner charged to the reverse polarity (positive in this embodiment) is collected by the second toner collection amount control member 62 by the second toner collection amount control member 62 (FIG. 10 (f)). . Also at this time, it is not always necessary to collect 100% of the toner, and it is sufficient that the toner amount is a predetermined amount or less.

  Next, the toner charge amount control member 7 aligns the charge polarity of the toner that has passed through both toner collection amount control members or the toner discharged from both toner collection amount control members with the normal polarity (in this embodiment, negative polarity). (FIG. 10 (g)). That is, the charge amount of the toner changes due to friction between the toners, transfer bias, toner amount control bias, and the like. In addition, the toner discharged from each toner collection amount control member, which is a brush member, varies in charge amount depending on the material type, density, fine diameter, length, etc. of the brush, and the charge polarity of some toners is reversed. . The toner whose charge amount has changed, that is, the toner with poor charge (overcharge, overcharge) is set to a specified charge amount.

  Thereafter, the surface of the photosensitive drum 2 is charged again from above the untransferred toner by the charging device 3 (FIG. 10 (h)). At this time, since the adhesion amount of the transfer residual toner is suppressed to a predetermined amount or less by the first toner output control member 6A and the second toner output control member 6B, the transfer residual toner is not obstructed. The surface of the photosensitive drum 2 is uniformly charged. In addition, since the charge amount of the transfer residual toner is set to the specified value by the toner charge amount control member 7, adhesion of the transfer residual toner to the charging device 3 is suppressed.

  Thereafter, an electrostatic latent image of the second page is formed at the exposure portion (FIG. 10 (i)). Similarly, at this time, the toner collection amount control member 6 suppresses the transfer residual toner adhesion amount to a predetermined amount or less, so that the exposure process is performed without being blocked by the transfer residual toner.

  Next, development and residual toner collection are performed simultaneously in the developing device 4. That is, among the transfer residual toner, the toner existing in the non-exposed portion (white background portion) is collected by the developing device 4, and the toner existing in the exposed portion (black background portion) becomes a toner image (FIG. 10 (j)). At this time, since the charge amount of the transfer residual toner is set to the specified value by the toner charge amount control member 7, the transfer residual toner is smoothly collected.

  Such an operation is repeated for each image forming unit, and the toner images of the respective colors are superimposed on the intermediate transfer belt 10. A color image is formed on the intermediate transfer belt 10 by superimposing the four color toner images. This color image is transferred onto the recording paper by the secondary transfer roller 11. Then, the recording paper is output to the discharge tray via the fixing device.

  Next, the toner amount adjustment procedure will be described based on the flowchart of FIG. 11 and the time chart of FIG. Note that several operation modes are set in advance in the image forming apparatus of this embodiment.

Specifically, an end sequence discharge mode (hereinafter referred to as “mode 1”) performed after the end of image formation is set. The setting of each bias in the mode 1, the image forming mode, and the inter-image mode is as shown in Table 1 below.

  First, when image formation is started, the operation mode is switched to the image formation mode (S1). Specifically, a bias for collecting toner is applied to the first toner collection amount control member 6A and the second toner collection amount control member 6B. At the time of image formation, the transfer residual toner is collected by the first toner output control member 6A and the second toner output control member 6B, so that there is almost no transfer residual toner on the photosensitive drum 2. . Therefore, the toner charge amount control bias Vdc is set to −300 V, and the influence on the charging device 3 is suppressed.

  Thereafter, it is determined whether or not the image formation is completed (S2), and the operation mode is switched to the inter-image mode between the images. Specifically, a bias for discharging the toner is applied to the first toner collection amount control member 6A (S3). As a result, the toner accumulated in the first toner collection amount control member 6A is discharged onto the photosensitive drum 2. Even if the charging polarity of the toner is reversed during the discharge, the toner is collected by the second toner collection amount control member 6B. Therefore, the charging device 3 is not contaminated. Thereafter, the bias in the imaging mode and the bias in the inter-image mode are repeated until all the imaging is completed.

  When all the images are formed, the operation mode is switched to mode 1 (S4). Specifically, the toner is positively discharged by intermittently applying a bias for discharging the toner to the first toner collection amount control member 6A, the second toner collection amount control member 6B, and the charging device 3. . Further, by applying a toner charge amount control bias with Vdc of −500 V to the toner charge amount control member 7, the charge amount of the toner on the photosensitive drum 2 is adjusted even when the reverse polarity toner is ejected. The discharged toner is collected by the developing device 4. When the operation in mode 1 ends, the printing operation ends.

  In the present embodiment, the discharge processing of the second toner collection amount control member 6B is not performed between images. This is because the amount of toner collected by the second toner collection amount control member 6B is very small, and it is not necessary to frequently perform discharge processing unlike the first toner collection amount control member 6A. However, the present invention is not limited to this process, and the ejection process may be performed between images.

  In this embodiment, each toner amount control bias or toner charge amount control bias is controlled for each operation mode. However, the present invention is not limited to this. For example, the printing rate may be detected from the dot counter of the exposure device 8, the amount of the transfer residual toner may be predicted from the printing rate, and each toner amount control bias may be switched based on the predicted value.

  As described in detail above, the color printer 100 according to the present embodiment is a simultaneous development cleaning system, and firstly collects / discharges transfer residual toner charged to a normal polarity between the transfer device 5 and the charging device 3. The toner collection amount control member 6 </ b> A and the second toner collection amount control member 6 </ b> B that collects / discharges the transfer residual toner charged to the reverse polarity are provided. A DC bias is applied to each toner collection amount control member, and toner collection / discharge is switched by controlling the bias. That is, the transfer residual toner can be collected before charging by the first toner collection amount control member 6A, and the toner amount on the photosensitive drum 2 can be maintained below a certain value. Therefore, uneven charging or uneven exposure due to toner concentration is suppressed. Further, the transfer residual toner charged in reverse polarity before the charging device 3 can be collected by the second toner collection amount control member 6B, and contamination of the charging roller can be suppressed. Further, since the control of each toner output amount control member is performed by a DC bias, there is no problem of vibration or noise.

  Further, a toner charge amount control member 7 for adjusting the charge amount of the toner is provided on the upstream side of the charging device 3 in the rotation direction of the photosensitive drum 2. The toner charge amount control member 7 is applied with a bias having a normal charging polarity of the toner so that the charging polarity of the toner is aligned with the normal charging polarity. That is, even if the second toner collection amount control member 6B cannot collect the toner charged to the reverse polarity or the charging failure occurs at the time of transfer or the like, Can be aligned. Therefore, contamination of the charging device 3 can be suppressed, and collection by the developing device 4 can be performed smoothly.

  Further, the toner charge amount control member 7 reciprocates with respect to the axial direction of the photosensitive drum 2. As a result, the surface of the photosensitive drum 2 is polished, and minute substances fixed to the surface of the photosensitive drum 2 are removed. Therefore, in the image forming apparatus of the simultaneous development cleaning system, an image forming apparatus that suppresses charging failure at the charging portion and exposure failure at the exposure portion and forms a high-quality image is realized.

  Further, the first toner collection amount control member 6A and the second toner collection amount control member 6B appropriately discharge the toner, and the collected toner is only temporarily held. That is, the transfer residual toner is not retained as waste for a long time. For this reason, the amount of accumulated toner is smaller and the size thereof can be smaller than that of a cleaning device intended to discard toner. Therefore, this does not hinder downsizing of the entire image forming apparatus.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, as an image forming apparatus, a printer, a copier, a scanner, a FAX, or the like that can form an image by an electrophotographic method is applicable. Further, it may be one that forms a color image or one that is dedicated to a monochrome image. Further, a tandem method or a four-cycle method may be used.

  Further, in the present embodiment, the second toner extraction amount control to which the bias of the same polarity is applied upstream from the first toner extraction amount control member 6A to which a bias having a polarity opposite to the normal polarity of the toner is applied. The member 6B is arranged downstream, but the arrangement may be reversed.

  In this embodiment, the first toner collection amount control member 6A is a rotating body, and the second toner collection amount control member 6B is a non-rotating body, so that a difference in toner accumulation capability is provided. However, the method of making a difference in the toner storage capacity is not limited to this. For example, it can be realized by increasing the fiber density or increasing the surface area of the brush.

1 is a schematic diagram illustrating a configuration of a color printer according to an embodiment. 1 is a schematic diagram illustrating a configuration of an image forming unit according to an embodiment. It is sectional drawing which shows the structure of the charging roller which concerns on embodiment. 6 is a graph showing toner contamination on a charging roller. 6 is a graph showing the external additive contamination of the charging roller. 6 is a graph showing the relationship between the amount of toner remaining after transfer and density unevenness. 6 is a graph showing a relationship between a toner charge amount control bias and a toner charge amount change amount. 6 is a graph showing a toner charge amount distribution before and after passing through a toner charge amount control pad. It is a graph which shows the relationship between the charging amount before charging, and charging roller dirt. It is a figure which shows transition of the surface potential of a photoconductor drum. 4 is a flowchart illustrating a procedure for adjusting the amount of toner on a photosensitive drum. FIG. 5 is a diagram illustrating biases for each mode of a toner collection amount control member, a toner charge amount control member, and a charging device. It is a figure which shows the image of a charging failure. It is a figure which shows the image of exposure failure.

Explanation of symbols

1K Image forming unit 2 Photosensitive drum (image carrier)
3 Charging device (charging unit)
4 Development device (development unit)
5 Transfer device (transfer section)
6A First toner collection amount control member (first toner amount adjustment unit)
6B Second toner collection amount control member (second toner amount adjustment unit)
61A First bias application unit 61B Second bias application unit 62 Control unit 7 Toner charge amount control member (toner charge amount adjustment unit)
8 Exposure equipment (exposure section)
10 Intermediate transfer belt 100 Color printer (image forming apparatus)

Claims (3)

An image carrier that carries a toner image, a charging unit that uniformly charges the surface of the image carrier, an exposure unit that forms an electrostatic latent image on the charged image carrier, and the image carrier A developing unit having a developing function for applying toner on the body to form a toner image and a collecting function for collecting the toner on the image carrier, and transferring the toner image formed on the image carrier to a transfer material An image forming apparatus having a transfer portion that performs both development and cleaning.
A recovery function for recovering the toner on the image carrier, which is located upstream of the charging unit and downstream of the transfer unit in the rotation direction of the image carrier, and an ejection function for discharging the toner to be held; A first toner amount adjustment unit comprising:
A first bias applying unit configured to apply a DC bias having a polarity opposite to the charging polarity of the toner to the first toner amount adjusting unit when the first toner amount adjusting unit performs a toner collecting process;
A recovery function for recovering the toner on the image carrier, which is located upstream of the charging unit and downstream of the transfer unit in the rotation direction of the image carrier, and an ejection function for discharging the toner to be held; A second toner amount adjustment unit comprising:
A second bias applying unit configured to apply a DC bias having the same polarity as the charging polarity of the toner to the second toner amount adjusting unit when the second toner amount adjusting unit performs a toner collecting process;
A control unit that switches between a recovery function and an ejection function of the first toner amount adjustment unit and the second toner amount adjustment unit by controlling each bias of the first bias application unit and the second bias application unit ;
Positioned upstream of the charging unit and downstream of the first toner amount adjustment unit and the second toner amount adjustment unit in the rotational direction of the image carrier, and is in sliding contact with the image carrier. A conductive chargeable elastic pad member that reciprocates in the longitudinal direction of the image carrier to polish the surface of the image carrier and to adjust the toner charge polarity to a normal polarity; ,
An image forming apparatus comprising: The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein the first toner amount adjusting unit is a brush rotating body, and has a higher toner storage capacity than the second toner amount adjusting unit which is a brush fixed body . The image forming apparatus according to claim 1, wherein:
The image forming apparatus according to claim 1, wherein the first toner amount adjusting unit is a brush rotating body that rotates counter to the image carrier.

Images