JP2006337683A - Image forming apparatus and electric charge control member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, wherein the amount of charge of toner is satisfactorily controlled by avoiding accumulation of the toner in a charge control member. <P>SOLUTION: The image forming apparatus has a charge control member 6 that is a conductive foam, which has a micro cell structure. More specifically, cells constituting the charge control member have an average cell diameter of ≤200μm, and ((the average cell diameter)±2σ) lies within a range of 100μm to 300μm. The charge control member 6 switches the application bias by the variations in the environment, such as humidity or temperature and a processing mode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image by electrophotography. More specifically, the present invention relates to an image forming apparatus that uses a developing device that combines development and cleaning (hereinafter referred to as a “development simultaneous cleaning method”) for the purpose of reducing waste toner and reducing the size of the apparatus. It is.

  2. Description of the Related Art Conventionally, an image forming apparatus using a simultaneous development cleaning method has been put into practical use (for example, Patent Document 1 and Patent Document 2). In this simultaneous development cleaning type image forming apparatus, the developer remaining on the transferred image carrier (hereinafter referred to as “residual toner”) is collected by the developing device.

  In this simultaneous development cleaning type image forming apparatus, it is important to adjust the charge amount of the residual toner. That is, the residual toner includes many toners having a transfer history and reverse polarity toner such as fog toner. Then, if the residual toner having the opposite polarity or the residual toner having a low charge amount is sent to the charging unit as it is, the charging device collects the residual toner. As a result, the charging device is contaminated. In particular, in the case of a contact charging device such as a roller type, the charging device is easily contaminated.

In view of this, in the image forming apparatus of the simultaneous development cleaning system, a charge control member is provided in order to adjust the adhesion amount and the charge amount of the residual toner. This charge control member is located between the transfer unit and the charging unit during the image forming process, and applies a predetermined bias to uniformize the charge (polarity) of the residual toner that has not been transferred at the transfer unit. Yes. That is, the reverse polarity toner contained in the residual toner is shifted to the normal polarity to avoid collection by the charging device. The charge control member also functions as a precharge function for the image carrier as well as a charge amount control function for the residual toner.
Japanese Patent No. 3113803 JP-A-2-259784

  However, the conventional image forming apparatus described above has the following problems. That is, the charge amount control in the charge control member includes charge and charge removal. When the charge amount is controlled, if a bias having a polarity opposite to that of the developing toner is applied to the charge control member, the charge control member takes in the residual toner. In particular, when a foam having a large cell diameter or a brush type is used as the charge control member, a large amount of toner is taken into the cell. As a result, toner accumulates on the charge control member and residual toner cannot be conveyed to the developing member.

  When the toner accumulates on the charge control member, the charge control function is degraded. In addition, the function of adjusting the residual toner adhesion amount by the charge control member is degraded. Then, with the collection failure at the charge control member, the passing amount of residual toner increases, making it difficult to collect at the developing device. That is, the recoverability in the developing device is deteriorated. Further, in order to reduce the amount of accumulated toner, it is necessary to provide a plurality of charge control members, or to clean the charge control members.

  The present invention has been made to solve the problems of the conventional image forming apparatus described above. That is, it is an object of the present invention to provide an image forming apparatus that avoids toner accumulation on the charge control member and that has good adjustment of the toner charge amount.

  An image forming apparatus designed to solve this problem includes an image carrier that carries a toner image, a charging member that charges the surface of the image carrier to a predetermined level, and a function and an image that apply toner to the image carrier. Image forming comprising: a developing member having a function of collecting toner on the carrier; and a charge control member to which a bias is applied to adjust a charge amount of the toner that contacts the image carrier and adheres to the image carrier. The charge control member is a conductive foam having an average cell diameter of 200 μm or less and an average cell diameter ± 2σ (σ: standard deviation of cell diameter) in the range of 100 μm to 300 μm. It is characterized by that.

  In other words, the image forming apparatus of the present invention is an image forming apparatus of a simultaneous development cleaning system provided with a developing member that serves both for toner application and toner recovery, and is in contact with an image carrier and applied with a predetermined bias. Thus, a charge control member for adjusting the charge amount of the toner on the image carrier is provided. In other words, the charge control member can be applied with a bias for charging the toner on the image carrier and a bias for removing the charge with respect to the toner on the image carrier, and an appropriate bias can be applied as necessary. Is done. In general, a DC bias or an AC bias (including a bias in which an AC bias is superimposed on a DC bias) is applied so that the DC component Vdc is within a range of −2000 V to +1000 V.

  This charge control member is a conductive foam (for example, polyurethane resin). Further, the average cell diameter is 200 μm or less, and the range of the average cell diameter ± 2σ is included in the range of 100 μm to 300 μm. That is, the cell diameter distribution is concentrated in the range of 100 μm to 300 μm, and the average cell diameter is 200 μm or less.

  Since the charge control member has a microcell structure that satisfies the above conditions, toner uptake is reduced. Further, since the cell diameter is small, toner accumulation is small. Therefore, the deterioration of the charge control function can be suppressed. Further, since the cell diameter is small, the contact area with the image carrier is large, and the charging and discharging performance is good.

  Further, the charge control member of the image forming apparatus of the present invention is preferably a roller-like rotating body. As a result, the toner charge amount can be adjusted without applying mechanical stress due to sliding to the residual toner or the image carrier. Furthermore, since it is a rotating body, the toner is not mechanically scraped off even if the pressing force is set high.

  Further, the charge control member of the image forming apparatus of the present invention may be a pad-like non-rotating body. As a result, the size can be reduced compared to the rotating body. Even in the case of a fixed type, the toner passage can be improved by adjusting the pressure and setting the bias. In addition, the fixed type increases the nip width and allows more charge control.

  The bias applied to the charge control member of the image forming apparatus of the present invention is preferably variable depending on at least one of the environment and the mode. That is, the control of the charge amount by the charge control member is easily affected by environmental changes. Therefore, the bias value to be applied is switched to the optimum value for the environment according to the environmental change (for example, at high temperature and high humidity and at low temperature and low humidity). In addition, the bias value to be applied is switched depending on the mode such as the charge mode, the charge removal mode, and the cleaning mode. Thereby, finer charge control can be performed.

  According to the present invention, by providing a charge control member of a conductive foam having a microcell structure, toner uptake by the charge control member is reduced. Therefore, an image forming apparatus is realized in which toner accumulation in the charge control member is avoided and the toner charge amount is well adjusted.

  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 intermediate transfer belt 8, a secondary transfer roller 9, a cleaning blade 10 and the like are provided. Each image forming unit forms an image of each color on the intermediate transfer belt 8. 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 above order.

  Further, the image forming unit 1K has a photosensitive drum 2 that carries a toner image as shown in FIG. The photosensitive drum 2 rotates at a constant speed in the direction of the arrow in FIG. Further, around the photosensitive drum 2, a charging device 3, a developing device 4, a transfer device 5, and a charge control member 6 are sequentially arranged along the rotation direction. An exposure unit for forming a latent image is provided between the charging device 3 and the developing device 4. The other image forming units have the same configuration.

  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 in contact with the surface of the photosensitive drum 2 can be applied. . There are various types of contact-type charging devices such as a roller type, a blade type, a brush type, and a sheet type.

  Further, in the charging device 3 of this embodiment, different biases are applied during image formation and during non-image formation. The form of 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. Also, a pulse voltage or other waveform voltage may be used. Further, the surface potential of the photosensitive drum 2 is not limited to the minus side, and may be the plus side.

  The developing device 4 has a function of collecting toner in addition to a function of applying toner onto the latent image. That is, the residual toner on the photosensitive drum is collected for the white background portion of the electrostatic latent image, and the toner in the toner tank 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, a negatively charged toner is used. However, a positively charged toner may be used as long as the toner image can be developed.

The charge control member 6 is for adjusting the charge amount of the residual toner and the adhesion amount. The charge control member 6 has a cell diameter distribution concentrated in the range of 100 μm to 300 μm (average cell diameter ± 2σ is in the range of 100 μm to 300 μm, see FIG. 3), and the average cell diameter is 200 μm or less, 1 mm It is a member made of a conductive foam in which the number of cells per ² is in the range of 50 to 100. The charge control member 6 is a roller type and is rotatably provided. As the conductive foam, for example, a polyurethane resin foam in which a conductive material is dispersed is applicable.

  The charge control member 6 is a single-bubble type foam. Strictly speaking, there are some cells that become open bubbles in the process of foaming, but it is assumed that they are single bubbles in manufacturing. In other words, single-bubble cells and open-cell cells are mixed, and the ratio of single-bubble cells is high.

  Moreover, although the charge control member 6 is a roller-type member, it is not always necessary to rotate, and may be stopped as necessary. Also, the rotation speed and direction can be set freely. The charge control member 6 is not limited to a roller type rotating body. For example, as shown in FIG. 4, a pad-type non-rotating body may be used. In the case of a roller type rotating body, it is advantageous in terms of the degree of freedom in design of the passing ability of residual toner and the pressing force of members. On the other hand, the pad type which is a non-rotating body is advantageous in terms of chargeability of residual toner and compactness of the apparatus. Further, the charge control member 6 may be provided with a slide mechanism or a separation mechanism.

  A bias for controlling the charge amount of the residual toner is applied to the charge control member 6. Generally, a DC or AC bias is applied so that Vdc is within a range of −2000V to + 1000V.

  The bias applied to the charge control member 6 is variable depending on the system, environment, mode, and the like. That is, the control of the charge amount by the charge control member is easily affected by environmental changes, and it is very difficult to strictly adjust the charge amount of the residual toner. For example, in a low temperature and low humidity environment where it is relatively easy to apply a charge to the residual toner, the residual toner is charged more than necessary by the charge control member. As a result, the mirror image force between the residual toner and the image carrier is increased, resulting in poor recovery in the developing device. Therefore, due to poor collection of residual toner, toner sticking to the image carrier and image noise occur. On the other hand, if a bias tailored to a low temperature / low humidity environment is applied to the charge control member, the charge will be insufficient in a normal environment or a high temperature / high humidity environment. For this reason, the discharge property of the toner from the charge control member is poor, and the toner accumulates on the charge control member. Even if the bias applied to the charge control member is changed according to the humidity or temperature, the charge characteristics do not necessarily change depending on the humidity or temperature. Further, it varies depending on the control mode of the charge control member 6.

  Therefore, in this embodiment, the environmental parameters are classified into three categories: high temperature and high humidity environment (temperature: 30 ° C or higher, humidity: 85% or higher), normal environment, and low temperature and low humidity environment (temperature: 10 ° C or lower, humidity: 15% or lower). Prepare an optimum bias according to each environment. An optimum bias is selected for each mode. For example, it is -300V in a low temperature and low humidity environment, -500V in a normal environment, -700V in a high temperature and high humidity environment, and -1000V when charging a toner of reverse polarity. Is set to + 500V and -100V in the cleaning mode. The bias applied to the charge control member 6 is a rectangular wave (Vpp: 500 V, frequency: 2 kHz, duty ratio: 50%) in which a DC voltage and an AC voltage are superimposed. These setting values are merely examples, and are not limited to these.

  Further, the bias applied to the charge control member 6 may be a DC voltage. Also, a pulse voltage or other waveform voltage may be used. Further, since the charge control member 6 imparts charges not only to the residual toner but also to the surface of the photosensitive drum 2, the charge control member 6 also has a function as preliminary charging before main charging by the charging device 3.

  Next, an operation when an image is formed by the color printer 100 of this embodiment will be described. First, the surface of the photosensitive drum 2 is charged to a predetermined potential by the negative bias of the charging device 3. Next, a latent image of the first page is formed at the exposure unit. Any exposure means may be used as long as it can form an electrostatic latent image. For example, laser exposure is applicable.

  Next, development with a negative toner is performed by the developing device 4, and a first-page toner image is formed on the photosensitive drum 2. Next, the toner image of the first page is transferred onto the intermediate transfer belt 8 by the transfer device 5. That is, the toner on the photosensitive drum 2 is transferred to the intermediate transfer belt 8 by the positive polarity bias of the transfer device 5. At this time, a part of the toner remains on the photosensitive drum 2 without being transferred and becomes residual toner. Further, a part of the residual toner is shifted to positive polarity.

  Next, charge control of the residual toner is performed by the charge control member 6. Further, the surface of the photosensitive drum 2 is also charged to a negative polarity. Thereby, the charge amount of the residual toner is increased, and the adhesion of the residual toner to the charging device 3 is suppressed. Thereafter, the surface of the photosensitive drum 2 is charged again by the charging device 3.

  Next, an electrostatic latent image of the second page is formed at the exposure unit. Next, development and recovery of residual toner are performed simultaneously in the developing device 4. That is, of the residual toner, the toner existing on the white background is collected by the developing device 4, and the toner existing on the other part is transferred as a toner image again.

  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 8. A color image is formed on the intermediate transfer belt 8 by superimposing the four color toner images. This color image is transferred onto the recording paper by the secondary transfer roller 9. Then, the recording paper is output to the discharge tray via the fixing device.

  Next, the relationship between the cell diameter of the charge control member and the charge characteristics will be described in detail. The applicant conducted two experiments in order to investigate the relationship between the cell diameter and the charge characteristics. In these experiments, each foam roller type charge control member (cell diameter: 600 μm, 500 μm, 400 μm, 300 μm, 150 μm) and a brush type charge control member were prepared, and the same experiment was repeated.

  In the first experiment, the bias applied to the charge control member was changed, and the change in the toner adhesion amount before and after passing through the charge control member, that is, the toner passage rate was examined. FIG. 5 shows the relationship between the applied bias and the toner passage rate. As shown in FIG. 5, it can be seen that the brush-type charge control member has a low toner passage rate and is easy to take in the toner. In particular, it can be seen that the passing rate on the opposite polarity side (plus side in this experiment) is extremely low, and most of the toner is taken in.

  On the other hand, it can be seen that the foam roller type charge control member has a higher pass rate than the brush type. However, focusing on the cell diameter, it can be seen that a foam member having an average cell diameter of 300 μm or more has a passing rate of 60% or less on the reverse polarity side when an applied bias of 500 V or more is applied, and takes in a large amount of toner. . On the other hand, in the foam member having an average cell diameter of 150 μm, the passing rate is 80% or more even with an applied bias of 500 V or more, and it can be seen that the incorporation of toner is small. From this experiment, it can be seen that even when a bias on the reverse polarity side is applied, the incorporation of toner can be suppressed if the foam member has an average cell diameter of 150 μm.

  In the second experiment, the bias applied to the charge control member was changed, and the change in the toner charge amount before and after passing through the charge control member, that is, the chargeability of the toner was examined. FIG. 6 shows the relationship between the applied bias and the charge amount of the toner. As shown in FIG. 6, it can be seen that the charge control member of the brush type is not much different in chargeability from the charge control member of the foam roller type having an average cell diameter of 300 μm or more.

  On the other hand, in the foam roller member having an average cell diameter of 150 μm, it can be seen that the change when a reverse polarity bias is applied is extremely large. That is, it can be seen that the static elimination effect is large and the static elimination effect is obtained even when the applied bias value is small. From this experiment, it can be seen that a foam roller type having an average cell diameter of 150 μm has better charging performance than a brush member or a foam roller member having a cell diameter of 300 μm or more.

  As described above in detail, the color printer 100 of the present embodiment is a conductive foam and has the charge control member 6 that adjusts the charge amount of the residual toner. The charge control member 6 has a microcell structure, an average cell diameter of 200 μm or less, and an average cell diameter of ± 2σ is included in a range of 100 μm to 300 μm. By providing such a delicate cell structure, it is possible to suppress the intake of residual toner. For this reason, even when a reverse polarity bias is applied, the amount of toner taken in is small, and toner accumulation in the charge control member 6 is suppressed. Further, the charging performance can be improved by reducing the cell diameter.

  In addition, the charge control member 6 switches the applied bias according to environmental changes such as humidity and temperature and the processing mode. Thereby, finer charge control can be performed. Therefore, an image forming apparatus is realized in which toner accumulation in the charge control member is avoided and the toner charge amount is well adjusted.

  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.

  In this embodiment, one charge control member is provided in each image forming unit, but the present invention is not limited to this. For example, as shown in FIG. 7, two charge control members may be provided. Of course, three or more charge control members may be provided. When a plurality of charge control members are provided, charge control members having different cell diameters may be arranged. Alternatively, one member may be of a brush type as shown in FIG.

  By disposing a plurality of charge control members, for example, one member can be used for toner charge amount control and the other member can be used for toner transport amount control. Further, by arranging a plurality of charge control members, it is possible to apply different biases. For this reason, it is possible to perform charge control more suited to the environment and mode.

1 is a schematic diagram illustrating a configuration of a color printer according to an embodiment. 1 is a schematic diagram (roller type) illustrating a configuration of an image forming unit according to an embodiment. It is a graph which shows distribution of the cell diameter of a charge control member. 1 is a schematic diagram (pad type) illustrating a configuration of an image forming unit according to an embodiment. FIG. 3 is a graph showing a relationship between an applied bias and a toner passing rate. 6 is a graph showing a relationship between an applied bias and a charge amount of toner. It is the schematic (the 1) which shows the structure of the image forming unit which concerns on an application example. FIG. 6 is a schematic diagram (part 2) illustrating a configuration of an image forming unit according to an application example.

Explanation of symbols

1K Image forming unit 2 Photosensitive drum (image carrier)
3 Charging device (charging member)
4 Development device (developing member)
5 Transfer Device 6 Charge Control Member (Charge Control Member)
8 Intermediate transfer belt 100 Color printer (image forming device)

Claims (7)

An image carrier that carries a toner image, a charging member that charges the surface of the image carrier to a predetermined level, a function that applies toner to the image carrier, and a function that collects toner on the image carrier An image forming apparatus comprising: a developing member provided; and a charge control member to which a bias for adjusting a charge amount of toner that contacts the image carrier and adheres to the image carrier is applied.
The charge control member is a conductive foam having an average cell diameter of 200 μm or less and an average cell diameter of ± 2σ (σ: standard deviation of cell diameter) in a range of 100 μm to 300 μm. Image forming apparatus. The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein the charge control member is capable of switching between a bias for charging the toner on the image carrier and a bias for discharging the toner on the image carrier. The image forming apparatus according to claim 1, wherein:
An image forming apparatus, wherein a DC component Vdc of a bias applied to the charge control member is in a range of −2000V to + 1000V. The image forming apparatus according to any one of claims 1 to 3,
The image forming apparatus, wherein the charge control member is a roller-like rotating body. The image forming apparatus according to any one of claims 1 to 3,
The image forming apparatus, wherein the charge control member is a pad-like non-rotating body. The image forming apparatus according to any one of claims 1 to 5,
The image forming apparatus according to claim 1, wherein the bias applied to the charge control member is variable depending on at least one of an environment and a mode. In a charge control member that adjusts the charge amount of the toner that comes into contact with the image carrier carrying the toner image and adheres to the image carrier,
A charge control member, wherein the charge control member is an electrically conductive foam having an average cell diameter of 200 μm or less and an average cell diameter of ± 2σ (σ: standard deviation of cell diameter) in a range of 100 μm to 300 μm.

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