JP2009122639A - Image forming apparatus and method of charging image carrier of the image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively remove foreign objects, such as, residual toner remaining after a transfer operation and discharge products in charging from an image carrier, and to satisfactorily charge the image carrier. <P>SOLUTION: The foreign objects, such as, the residual toner adhering to a photoreceptor 2 after the transfer operation and the discharge product are charged by a bias showing a polarity same as that of the charged potential of the foreign object by a first charging member 8. The foreign object on the photoreceptor 2, charged by the first charging member 8, is caught and collected by a second charging member 9, to which a bias showing a polarity opposite to the charged potential of toner. The foreign object caught and collected by the second charging member 9 is collected by a collection roller 10, to which a bias is applied. At such a time, by controlling the bias to be applied to the collection member 10, at least a prescribed fixed quantity of external additive is made to adhere to the second charging member 9 after passing by the collection roller 10. The photoreceptor 2 is charged by the second charging member 9 to which the external additive is made to adhere, and the foreign object deposited on the photoreceptor is scraped off. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention includes a charging device that charges a residual toner remaining on an image carrier after transfer with a first charging member, and collects the charged residual toner with a second charging member that charges the image carrier, and the charging device. The present invention also relates to an image forming apparatus including an electrophotographic apparatus such as an electrostatic copying machine, a printer, and a facsimile, and a technical field of an image carrier charging method in the image forming apparatus.

  Conventionally, in an image forming apparatus, an image forming apparatus including a charging device in which two first and second charging members that charge an image carrier on which an electrostatic latent image and a toner image are formed has been proposed ( For example, see Patent Document 1).

In the image forming apparatus described in Patent Document 1, the first charging member is formed of a brush roller, and is based on a positive polarity toner, a reverse polarity toner, or a charging roller that is a second charging member attached to the photoconductor after transfer. By removing discharge products and the like attached to the photosensitive member during charging of the photosensitive member, these foreign substances are prevented from attaching to the surface of the charging roller of the photosensitive member. As a result, the photoreceptor surface potential is stabilized over a long period of time, and an image quality without image distortion can be obtained.
Japanese Patent Application Laid-Open No. 2004-12582.

  However, in the image forming apparatus described in Patent Document 1, the brush roller that is the first charging member temporarily captures the above-described foreign matter from the photosensitive member. For this reason, when the foreign matter captured by the brush roller increases, the foreign matter is transferred again to the photoconductor and removed through the transfer device. For this reason, these foreign substances are deposited on the surface of the photoreceptor in the long term. The foreign matter adhering to the photoconductor after the transfer includes a foreign matter that is not captured by the brush roller, and there is a possibility that the foreign matter is further deposited on the surface of the photoconductor. For this reason, it is difficult to charge the photosensitive member satisfactorily by the charging roller that is the second charging member, and there is a possibility of causing a charging failure.

  The present invention has been made in view of such circumstances, and its purpose is to more effectively remove foreign matters such as residual toner after transfer and discharge products during charging from the image carrier, It is an object of the present invention to provide a charging device, an image forming apparatus, and a method for charging an image carrier in an image forming apparatus that can charge the image bearing member satisfactorily.

  In order to solve the above-described problems, according to the image forming apparatus and the charging method of the image carrier according to the present invention, an electrostatic latent image on the image carrier is formed with toner in which an external additive is added to the toner base particles. Development is performed to form a toner image on the image carrier. The toner image on the image carrier is transferred to a transfer medium. After the transfer of the toner image on the image carrier, foreign matters such as toner remaining after transfer and a ray product upon charging remain on the image carrier. These foreign substances are charged by a first charging member to which a voltage having the same polarity as the charged position of these foreign substances is applied. The foreign matter on the image carrier charged by the first charging member is collected by the second charging member to which a voltage having a polarity opposite to the charged position of the foreign matter is applied. As a result, the toner base particles and some of the external additives out of the transfer residual toner adhering to the second charging member are recovered by the recovery member to which a controlled bias is applied, and after passing through the recovery member A certain amount of external additive adheres to the second charging member.

The bias applied to the collecting member is controlled based on the image forming unit lifetime information by the collecting member bias control device.
The image forming unit life information includes, for example, image carrier life information and toner cartridge information. The image carrier life information includes, for example, information on the number of printed sheets in the image forming unit. That is, as the number of printed sheets increases, the cleaning property and the charging property become inferior due to the aging deterioration of the second charging member such as a brush bristle sag. For this reason, when the number of printed sheets becomes greater than a preset set number of printed sheets, the bias of the collecting roller is set higher. Conversely, when the number of printed sheets is smaller than the set number of printed sheets, the bias of the collecting roller is set to be low. In this way, by controlling the bias of the collection roller based on the information on the number of printed sheets in the image forming unit, a certain amount of external additive adheres to the second charging member.

  Further, the toner cartridge information includes, for example, information on the remaining amount of toner. That is, when the toner cartridge is full of toner, such as toner full, the amount of external additive released from or easily released from the toner base particles is large, and the bias of the collecting roller is increased. Set to. Conversely, when the toner remaining amount becomes less than or equal to the set toner amount due to toner consumption, the amount of external additive decreases, so the bias of the collecting roller is set low. Thus, by controlling the bias of the collecting roller based on the information on the remaining amount of toner, a certain amount of external additive adheres to the second charging member.

Further, the bias applied to the recovery member is controlled by the recovery member bias control device based on the image forming condition information.
The image forming condition information includes, for example, development bias information and print density information by a patch operation. The development bias information by the patch operation is information on the determined development bias, which is determined by the patch operation in the image forming apparatus. That is, when the developing bias is set higher than a preset developing bias, the external additive easily moves to the image carrier, so the collecting roller bias is set higher. Conversely, when the developing bias is set lower than the set developing bias, the external additive becomes difficult to move to the image carrier, so the bias of the collecting roller is set lower. In this way, by controlling the bias of the collecting roller based on the development bias information by the patch operation, a certain amount of external additive adheres to the second charging member.

  Further, the print density information is, for example, information on print density accumulated by printing so far. That is, when the print density accumulated by the printing so far is larger than the preset print density, the amount of toner increases, so the bias of the collection roller is set to a high bias. Conversely, if the print density is smaller than the set print density, the amount of toner is small, so the bias of the collection roller is set to a low bias. As described above, by controlling the bias of the collecting roller based on the print density information, a certain amount of external additive adheres to the second charging member.

  Then, the image carrier is charged by the second charging member that contacts the image carrier. At this time, since these external additives are attached to the second charging member, these external additives rub against the surface of the image carrier. By rubbing these external additives against the surface of the image carrier, foreign matters such as discharge products and residual toner deposited on the surface of the image carrier are scraped off. Thereby, the image carrier can be more uniformly charged. Therefore, it is possible to realize a good image quality that is stable over a long period of time.

In particular, the use of an external additive having a polishing function as the external additive added to the toner base particles effectively scrapes off foreign matters such as discharge products and residual toner deposited on the surface of the image carrier. Further, by adding an external additive having a charging auxiliary function to the toner base particles, a certain amount of external additive having a charging auxiliary function also adheres to the second charging member that has passed through the recovery member. . As a result, the image carrier can be more uniformly charged, and stable and good image quality can be realized over a long period of time.

The best mode for carrying out the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram schematically and partially showing an example of an embodiment of an image forming apparatus according to the present invention.

  As shown in FIG. 1, the image forming apparatus 1 of this example includes a photoreceptor 2 that is an image carrier on which an electrostatic latent image and a toner image are formed. A charging device 3 for charging the photoconductor 2 is disposed in the vicinity of the outer periphery of the photoconductor 2. Further, in the vicinity of the outer periphery of the photosensitive member 2, an exposure device 4 for writing an electrostatic latent image on the photosensitive member 2 sequentially from the charging device 3 in the rotation direction α (clockwise in FIG. 1) of the photosensitive member 2. A developing device 5 that develops the electrostatic latent image on the body 2 with toner and a transfer device 7 that transfers the toner image on the photoreceptor 2 to a transfer medium 6 such as transfer paper or an intermediate transfer medium are provided. In that case, there is no dedicated photoconductor cleaning device for collecting foreign matter such as residual toner adhering to the photoconductor 2 after transfer. Note that the image forming apparatus 1 of this example is not shown, but when the fixing device, the transfer paper transport device, the transfer paper storage cassette, and the transfer medium 6 are intermediate transfer media as in the conventional general image forming apparatus. At least a transfer device for transferring the toner image of the intermediate transfer medium onto the transfer paper is provided.

  In this example, the photosensitive member 2 is composed of a photosensitive drum, and a photosensitive layer having a predetermined thickness is formed on the outer peripheral surface of a cylindrical metal base tube in the same manner as a conventionally known photosensitive 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. Of course, a photosensitive member other than the photosensitive drum can be used for the photosensitive member 2.

  The charging device 3 in this example includes a first charging member 8 disposed in contact with the photosensitive member 2 in the rotation direction α of the photosensitive member 2 from the transfer device 7, and the rotation of the photosensitive member 2 by the first charging member 8. A second charging member 9 disposed in contact with the photosensitive member 2 in the direction α, a recovery roller 10 which is a recovery member that contacts the second charging member 9 and recovers a predetermined amount of toner, and the recovery roller And a collecting roller cleaning blade 11 for removing ten collected toners.

The first charging member 8 includes a brush roller that is a charging brush member. The first charging member 8 is applied with a bias (DC voltage) having the same polarity as the charging position of the toner and equal to or higher than the discharge start voltage (Vth). It comes to be charged.
Similarly, the second charging member 9 is composed of a brush roller which is a charging brush member, and charges the photoreceptor 2. Further, the second charging member 9 is applied with a bias (DC voltage) having a polarity opposite to the charging position of the toner, so that the untransferred toner on the photosensitive member 2 charged by the first charging member 8 is transferred to the brush bristles 9a. It is supposed to be collected at.

  Further, the collecting roller 10 is applied with a bias (DC voltage). Then, by controlling the bias applied to the collection roller 10, the collection roller 10 is collected by the brush bristles 9a of the second charging member 9, and the toner base particles and external additives of the transfer residual toner adhering thereto. Collect a part of. Further, as shown in FIG. 2, the external additive adheres to the brush bristles 9 a of the second charging member 9 that has passed through the collection roller 10. The amount of the external additive attached to the second charging member 9 is controlled by controlling the bias of the collection roller 10 so that a certain amount of the external additive is attached to the brush bristles 9a of the second charging member 9. Is done. Thereby, a certain amount of external additive having a polishing function adheres to the second charging member 9 after passing through the collection roller 10.

  The bias applied to the collecting roller 10 is controlled based on the image forming unit lifetime information or the image forming condition information by a collecting roller bias control device which is a collecting member bias control device.

FIG. 3 is a diagram schematically illustrating an example of a device that performs bias control of the collection roller.
As shown in FIG. 3, the image forming apparatus 1 includes a recovery roller bias control device 12 that performs bias control of the recovery roller 10. The collection roller bias control device 12 sets a bias to the collection roller 10 based on the print density determination data accumulated in the previous printing from the print density determination device 13. Then, the collection roller bias control device 12 controls the bias application device 14 that applies a bias to the collection roller 10 so that the set bias is obtained. The bias applying device 14 applies the bias set by the collecting roller bias control device 12 to the collecting roller 10.

FIG. 4 is a flowchart illustrating an example of the bias control of the collection roller.
An example of bias control of the collection roller 10 for attaching a certain amount of external additive to the second charging member 9 will be described.

  In the bias control of the collection roller 10 in this example, two high and low biases set according to the print density (Duty) are used. As shown in FIG. 4, when the image data is transferred to the image forming apparatus 1 in step S1, the accumulated print density (Duty) in the printing so far is determined in step S2.

  Next, it is determined whether or not the accumulated print density (Duty) determined so far in step S3 is larger than a preset print density. If it is determined that the determined print density (Duty) is greater than the set print density, the bias of the collection roller 10 is set to a high bias in step S4. When the accumulated print density (Duty) is larger than the set print density, the amount of toner increases. Therefore, the amount of external additive collected by the collection roller 10 is increased by setting the bias of the collection roller 10 to a high bias. Will increase. Thereby, the amount of the external additive attached to the brush bristles 9a of the second charging member 9 after passing through the collection roller 10 is reduced. Thereafter, printing of the image data transferred in step S5 starts.

  On the other hand, if it is determined that the print density (Duty) accumulated in step S3 is equal to or lower than the set print density, the bias of the collection roller 10 is set to a low bias in step S6. If the accumulated print density (Duty) is less than or equal to the set print density, the amount of toner is decreasing. Therefore, by lowering the bias of the collection roller 10, the external additive collected by the collection roller 10 can be reduced. The amount is reduced. Thereby, the amount of the external additive adhering to the brush bristles 9a of the second charging member 9 after passing through the collection roller 10 increases. Thereafter, the process proceeds to step S5, and printing of the transferred image data starts.

  In this way, the ba ice applied to the collection roller 10 is controlled according to the print density (Duty) of the image data. As a result, an external additive having a polishing function always adheres to the second charging member 9 after passing through the collection roller 10 at a constant amount or a substantially constant amount. The bias control method for the collection roller 10 is not limited to the example shown in FIG. 4, and various methods can be employed.

That is, the image forming unit life information includes, for example, photoconductor life information and toner cartridge information. The photoconductor life information includes, for example, information on the number of printed sheets in a photoconductor unit that is an image forming unit. The photoreceptor unit is detachably provided in the apparatus main body, but is not limited to this. When the number of printed sheets increases, the cleaning property and the charging property become inferior due to the aging of the second charging member 9 such as a brush bristle sag. For this reason, when the number of printed sheets becomes greater than a preset set number of printed sheets, the bias of the collecting roller 10 is set higher than a preset set collecting roller bias. Conversely, when the number of printed sheets is smaller than the set number of printed sheets, the bias of the collecting roller 10 is set lower than the set collecting roller bias. In this way, by controlling the bias of the collecting roller 10 based on the information on the number of printed sheets in the photosensitive unit, a certain amount of external additive having a polishing function adheres to the second charging member 9.

  Further, the toner cartridge information includes, for example, information on the remaining amount of toner. That is, when the toner cartridge is full of toner, such as toner full, the amount of external additive released from or easily released from the toner base particles is large when the toner remaining amount is larger than the preset toner amount, the bias of the collecting roller 10 is Set higher than the preset collection roller bias. On the contrary, when the toner remaining amount becomes equal to or less than the set toner amount due to toner consumption, the amount of the external additive decreases, so the bias of the collection roller 10 is set lower than the set collection roller bias. Thus, by controlling the bias of the collecting roller 10 based on the information on the remaining amount of toner, a certain amount of external additive having a polishing function adheres to the second charging member 9.

On the other hand, the image forming condition information includes, for example, information on development bias by a patch operation and print density information. The development bias information by the patch operation is information of the determined development bias, which is determined by the patch operation in the image forming apparatus 1. That is, when the developing bias is set higher than a preset developing bias, the external additive easily moves to the photosensitive member 2, and therefore the bias of the collecting roller 10 is equal to or higher than a preset setting collecting roller bias. Set higher. On the contrary, if the developing bias is set lower than the set developing bias, the external additive becomes difficult to move to the photosensitive member 2, and therefore the bias of the collecting roller 10 is set lower than the set collecting roller bias. In this way, by controlling the bias of the collecting roller 10 based on the development bias information by the patch operation, a certain amount of external additive having a polishing function adheres to the second charging member 9.
Further, the recovery roller cleaning blade 11 removes the transfer residual toner on the recovery roller 10 that has been recovered from the recovery roller 10 to clean the recovery roller 10.

The exposure device 4 writes an electrostatic latent image on the photosensitive member 2 by irradiating the photosensitive member 2 with light such as laser light.
The developing device 5 uses a toner in which an external additive having at least a charge assist function and a polishing function is added to toner base particles. In that case, conventionally known toner materials such as polyester and styrene acrylic can be used for the toner base particles. In addition, a conventionally known charge control agent such as silica or titania can also be used as an external additive having a charge assist function. Furthermore, conventionally known external additives such as cerium oxide, strontium titanate, or alumina can be used as the external additive having a polishing function. In that case, the particles of the external additive having a polishing function may be, for example, an angular cubic shape as shown in FIG. 5A, a needle shape as shown in FIG. 5B, or FIG. ), The circularity is low (the circularity is desirably 90 or less). Of course, the external additive particles having a polishing function may have other shapes as long as they can be polished.
Then, the toner regulated to a predetermined layer thickness is conveyed on the developing roller toward the photosensitive member 2 by the developing roller, and the electrostatic latent image on the photosensitive member 2 is developed with the conveyed toner to thereby develop the photosensitive member. 2 forms a toner image.

The transfer device 7 transfers the toner image on the photoconductor 2 to a transfer medium 6 such as transfer paper or an intermediate transfer medium with a transfer roller, for example. When the toner image is transferred onto the transfer paper that is the transfer medium 6, the image forming apparatus 1 fixes the toner image on the transfer paper with a fixing device (not shown) and forms an image on the transfer paper. When the toner image is transferred to an intermediate transfer medium, which is the transfer medium 6, the toner image on the intermediate transfer medium is further transferred to transfer paper by a transfer device, and then the toner image on the transfer paper is not shown. To fix and form an image on the transfer paper.

  According to the image forming apparatus 1 of this example configured as described above, after the toner image on the photoconductor 2 is transferred to the transfer medium 6 by the transfer device 7, untransferred toner remains on the photoconductor 2. Further, a discharge product during charging is also adhered on the photoreceptor 2 after the transfer. Foreign matters such as the transfer residual toner and the discharge product are charged by the rotation of the brush roller of the first charging member 8 to which a voltage having the same polarity as the charged position of the foreign matter (that is, toner) is applied. The foreign matter on the photoreceptor 2 charged by the first charging member 8 is collected by the rotation of the brush roller of the second charging member 9 to which a voltage having a polarity opposite to the charged position of the toner is applied. As a result, among the foreign matters adhering to the brush bristles 9a of the second charging member 9, foreign particles such as toner mother particles, a part of the external additive, and discharge products are collected by the collection roller 10 to which a controlled bias is applied. A certain amount of external additive is recovered by rotation and adheres to the brush bristles 9 a of the second charging member 9. Thus, a constant amount of the external additive having an auxiliary charging function and the external additive having a polishing function always adheres to the brush bristles 9a of the second charging member 9 respectively.

  Accordingly, the photoreceptor 2 is charged by the second charging member 9 in which a constant amount of external additive is always attached to the brush bristles 9a. At this time, out of a certain amount of the external additive always adhered to the brush bristles 9a, the external additive having a charging auxiliary function serves as a charging auxiliary agent, so that the photoreceptor 2 can be uniformly charged. Of the above-mentioned fixed amount of external additives, the external additive having a polishing function serves as an abrasive that scrapes off foreign matters such as discharge products adhering to the photoreceptor 2 due to discharge during charging. Accumulation of foreign matter on the photoreceptor 2 can be effectively prevented. As a result, in the image forming apparatus 1 of this example, it is possible to realize a stable and good image quality over a long period of time.

  Further, the toner base particles and the external additive collected on the collecting roller 10 are removed by the collecting roller cleaning blade 11. Thereby, the collection roller 10 can effectively collect a part of the toner base particles and the external additive adhering to the second charging member 9 over a long period of time.

  The external additive used in the image forming apparatus 1 of the present invention does not necessarily need to use an external additive having a charging assist function, and it is only necessary to use an external additive having a polishing function. When good chargeability of the toner is required, an external additive having an auxiliary charging function can be used as necessary.

FIG. 6 is a diagram schematically showing another example of the embodiment of the image forming apparatus according to the present invention.
In the example shown in FIG. 1 described above, a rotating brush roller is used as the first charging member 8 of the charging device 3. However, as shown in FIG. 6, in the image forming apparatus of this example, the first charging member 3 of the charging device 3 is used. A fixed brush is used for one charging member 8.
Other configurations of the image forming apparatus 1 in this example are the same as those in the above-described example. Further, the effect of the image forming apparatus 1 of this example is substantially the same as the above-described example.

  Next, examples of the image forming apparatus according to the present invention and experiments of a comparative example will be described. The experiment was conducted on 4 examples and 9 comparative examples. The image forming apparatus used in the experiment was a laser printer LP-9000C manufactured by Seiko Epson. The charging unit of the LP-9000C photoconductor unit was modified so that a charging brush as the first charging member 8, a charging brush as the second charging member, and a recovery roller including a metal roller were attached. The photoreceptor cleaning blade of the LP-9000C photoreceptor unit was removed. The first charging member 8 uses the brush (1) shown in Table 1, and the second charging member 9 uses two types of brushes (1) and (2) shown in Table 1 (the second charging member (each 1) and (2)) were used. Both of these brushes (1) and (2) are Toei Sangyo Co., Ltd. brushes.

As shown in Table 1, the material of the brush (1) is 6 nylon, the fineness is 220T / 96F, the density is 120 kf / inch ² , the yarn resistance is 7.1 LogΩ, and the pile length is The shape is 300 mm long, 5 mm wide, and 5 mm high. The brush (2) is made of 6 nylon, the fineness is 330T / 48F, the density is 80 kf / inch ² , the yarn resistance is 9.3 LogΩ, the pile length is 5 mm, Has a length of 300 mm, a width of 5 mm, and a height of 5 mm.

A voltage of −1200 V was applied to the first charging member 8, and a voltage of +200 V was applied to the second charging member 9.
Two types of mother particles (1) and (2) shown in Table 2 were used as the toner mother particles of the toner used.

  As shown in Table 2, the mother particles (1) were made of polyester and produced by a polymerization method. The production of toner mother particles by this polymerization method uses a conventionally known method and is not a characteristic part of the present invention, and therefore detailed description thereof is omitted. The mother particles (2) were made of styrene acrylic and were produced by a pulverization method. The production of toner mother particles by this pulverization method is also performed using a conventionally known method and is not a characteristic part of the present invention, and thus detailed description thereof is omitted.

  Three types of external additives (1) to (3) shown in Table 3 were used as external additives for the toner used.

As shown in Table 3, the external additive (1) uses two materials of silica (RX200) and cerium oxide, 1% by weight of silica (RX200) is added to the toner base particles, and the toner base particles 1% by weight of cerium oxide was added. At this time, the charge amount of cerium oxide is relatively high and is 40 μC / g. As the external additive (2), two materials of silica (RY50) and strontium titanate are used, 1% by weight of silica (RY50) is added to the toner base particles, and titanium is added to the toner base particles. 1% by weight of strontium acid was added. At this time, the charge amount of strontium titanate is relatively high and is 60 μC / g. Further, as the external additive (3), three materials of silica (RX200), titania (T805), and alumina are used, and silica (RX200) is added by 0.5% by weight based on the toner base particles. (T805) was added in an amount of 0.5% by weight based on the toner base particles, and alumina was further added in an amount of 1% by weight based on the toner base particles. At this time, the charge amount of alumina is relatively low and 15 μC / g.

  The other configuration of the image forming apparatus 1 used in the experiment is the same as that of the laser printer LP-9000C, and the experiment is performed based on the image formation control in the laser printer LP-9000C while controlling the bias of the collection roller 10. It was. In the experiment, 100 sheets of 5% density printing patterns on the entire surface and 100 sheets of white solids following this were alternately printed, and printing was continuously performed up to 1000 sheets. Thereafter, a halftone image was printed and the halftone image was visually confirmed to determine the state of the photoreceptor 2. In the evaluation, a halftone image determined to have good image quality was evaluated as good (◯), and a halftone image determined not to have good image quality was evaluated as poor (×). .

  Table 4 shows the combination of the brush of the second charging member 9, the toner base particles and the external additive, and the applied voltage (bias) of the recovery roller used in each example and each comparative example. Table 4 also shows the determination results (evaluations) in each of the bad examples and the comparative examples.

  As shown in Table 4, in Example 1, the second charging member 9 is the brush (1), the toner mother particles are the mother particles (1), and the external additive is the external additive (1). The applied voltage of the collecting roller at the time of printing the 5% density printing pattern on the entire surface is + 500V, and the applied voltage of the collecting roller at the time of white solid printing is + 400V. In the evaluation, it was determined that the halftone image had a good image quality, and the evaluation was good (◯). In Example 2, the second charging member 9 is the brush (1), the toner base particles are the base particles (1), the external additive is the external additive (2), and the entire surface has a 5% density print pattern. The applied voltage of the collecting roller at the time of printing is + 400V, and the applied voltage of the collecting roller at the time of white solid printing is + 300V. In the evaluation, it was determined that the halftone image had a good image quality, and the evaluation was good (◯).

In Example 3, the second charging member 9 is the brush (2), the toner base particles are the base particles (1), the external additive is the external additive (1), and the entire surface has a 5% density print pattern. The applied voltage of the collecting roller at the time of printing is + 550V, and the applied voltage of the collecting roller at the time of white solid printing is + 500V. In the evaluation, it was determined that the halftone image had a good image quality, and the evaluation was good (◯). In Example 4, the second charging member 9 is the brush (2), the toner base particles are the base particles (2), the external additive is the external additive (2), and the entire surface has a 5% density print pattern. The applied voltage of the collecting roller at the time of printing is + 500V, and the applied voltage of the collecting roller at the time of white solid printing is + 450V. In the evaluation, it was determined that the halftone image had a good image quality, and the evaluation was good (◯).

  In Comparative Example 1, the second charging member 9 is the brush (1), the toner base particles are the base particles (1), the external additive is the external additive (1), and the entire surface has a 5% density print pattern. The applied voltage of the collecting roller at the time of printing is + 500V, and the applied voltage of the collecting roller at the time of white solid printing is also + 500V. In the evaluation, it was determined that the halftone image had uneven density and the image quality was not good, and was poor (×). In Comparative Example 2, the second charging member 9 is the brush (1), the toner base particles are the base particles (1), the external additive is the external additive (1), and the entire surface has a 5% density print pattern. The applied voltage of the collecting roller at the time of printing is + 400V, and the applied voltage of the collecting roller at the time of white solid printing is + 400V. In the evaluation, it was determined that the halftone image had uneven density and the image quality was not good, and was poor (×).

  In Comparative Example 3, the second charging member 9 is the brush (1), the toner base particles are the base particles (1), the external additive is the external additive (1), and the entire surface has a 5% density print pattern. The applied voltage of the collecting roller at the time of printing is + 300V, and the applied voltage of the collecting roller at the time of white solid printing is also + 300V. In the evaluation, the halftone image was fogged, it was determined that the image quality was not good, and the result was poor (x). In Comparative Example 4, the second charging member 9 is the brush (1), the toner base particles are the base particles (1), the external additive is the external additive (3), and the entire surface has a 5% density print pattern. The applied voltage of the collecting roller at the time of printing is + 600V, and the applied voltage of the collecting roller at the time of white solid printing is + 500V. In the evaluation, streaks were generated in the halftone image, it was determined that the image quality was not good, and the result was poor (x).

  In Comparative Example 5, the second charging member 9 is the brush (1), the toner mother particles are the mother particles (1), no external additive is added, and the entire surface is collected when printing a 5% density printing pattern. The applied voltage of the roller is + 500V, and the applied voltage of the recovery roller at the time of white solid printing is also + 400V. In the evaluation, streaks were generated in the halftone image, it was determined that the image quality was not good, and the result was poor (x). In Comparative Example 6, the second charging member 9 is the brush (1), the toner base particles are the base particles (2), the external additive is the external additive (2), and the entire surface has a 5% density print pattern. The applied voltage of the collecting roller at the time of printing is + 500V, and the applied voltage of the collecting roller at the time of white solid printing is + 500V. In the evaluation, the halftone image had uneven density, and it was determined that the image quality was not good, and was poor (x).

  In Comparative Example 7, the second charging member 9 is the brush (2), the toner base particles are the base particles (1), the external additive is the external additive (2), and the entire surface has a 5% density print pattern. The applied voltage of the collecting roller at the time of printing is + 550V, and the applied voltage of the collecting roller at the time of white solid printing is also + 550V. In the evaluation, the halftone image had uneven density, and it was determined that the image quality was not good, and was poor (×).

  In Comparative Example 8, the second charging member 9 is the brush (1), the toner base particles are the base particles (1), the external additive is the external additive (1), and the entire surface has a 5% density print pattern. The applied voltage of the collecting roller at the time of printing is + 500V, and the applied voltage of the collecting roller at the time of white solid printing is also + 600V. In the evaluation, the halftone image had uneven density, and it was determined that the image quality was not good, and was poor (×). In Comparative Example 9, the second charging member 9 is the brush (1), the toner base particles are the base particles (1), the external additive is the external additive (2), and the entire surface has a 5% density print pattern. The applied voltage of the collecting roller at the time of printing is + 400V, and the applied voltage of the collecting roller at the time of white solid printing is also + 450V. In the evaluation, the halftone image had uneven density, and it was determined that the image quality was not good, and was poor (×).

From the above experimental results, the bias of the collecting roller 10 is increased because the printing density is high when printing the 5% density printing pattern on the entire surface, and the bias of the collecting roller 10 is low when printing the white solid. By reducing the value, good image quality can be obtained.

  In addition, it was found that even when the bias of the collection roller 10 at the time of white solid printing is set lower than at the time of printing the entire surface 5% density printing pattern as in Comparative Example 4, good image quality may not be obtained. This is presumably because, in Comparative Example 4, the charge amount of alumina added as an external additive having a polishing function is relatively low at 15 μC / g, so that charging is not effectively performed. As described above, the external additive having a polishing function can effectively control the bias of the collection roller 10 when the charge amount is relatively high like cerium oxide or strontium titanate, and is charged like alumina. It was confirmed that the bias control of the collecting roller 10 cannot be effectively performed when the amount is relatively low.

Further, even when an external additive having a polishing function and an external additive having a charging assist function are not added as in Comparative Example 5, the recovery roller 10 at the time of white solid printing rather than at the time of printing a 5% density printing pattern on the entire surface. It was found that good image quality may not be obtained even with a low bias.
Further, as in Comparative Examples 8 and 9, when the bias of the collection roller 10 at the time of white solid printing is set to be equal to or higher than the bias of the collection roller 10 at the time of printing the entire 5% density printing pattern, a good image quality can be obtained. Not confirmed.
Accordingly, it was confirmed that the charging device 3, the image forming apparatus 1, and the charging method of the image carrier according to the present invention can obtain the desired effects.

  The present invention is not limited to the examples of the above-described embodiments, and various modifications can be made within the scope of matters described in the claims.

1 is a diagram schematically and partially showing an example of an embodiment of an image forming apparatus according to the present invention. It is a figure which expands and shows the state in which the external additive has adhered to the brush hair of the 2nd charging member with a microscope. It is a figure which shows typically an example of the apparatus which performs bias control of a collection | recovery roller. It is a figure which shows the flow of an example of bias control of a collection | recovery roller. (A) thru | or (c) is a figure which expands and shows various shapes of the particle | grains of the external additive which has a grinding function with a microscope. It is a figure showing other examples of an embodiment of an image forming device concerning the present invention typically and partially.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Photoconductor, 3 ... Charging apparatus, 4 ... Exposure apparatus, 5 ... Developing apparatus, 6 ... Transfer medium, 7 ... Transfer apparatus, 8 ... 1st charging member, 9 ... 2nd charging member, DESCRIPTION OF SYMBOLS 10 ... Collection roller, 11 ... Collection roller cleaning blade, 12 ... Collection roller bias control device, 13 ... Print density determination device, 14 ... Bias application device to collection roller

Claims (11)

  A first charging member that is in contact with an image carrier on which a toner image of a toner in which an external additive is added to toner base particles is formed and a bias having the same polarity as the charged position of the toner is applied; and the first charging member A second charging member that is disposed in the moving direction of the image carrier and is in contact with the image carrier and to which a polarity opposite to the charged position of the toner is applied; a bias is applied and the second charging member is contacted; A recovery member that recovers toner adhering to the second charging member, and a recovery member bias control device that controls a bias applied to the recovery member based on image forming condition information. Charging device.   The charging device according to claim 1, wherein the image forming condition information is information on a developing bias.   The charging device according to claim 1, wherein the image forming condition information is information on a print density of image data to be printed.   A first charging member that is in contact with an image carrier on which a toner image of a toner in which an external additive is added to toner base particles is formed and a bias having the same polarity as the charged position of the toner is applied; and the first charging member A second charging member that is disposed in the moving direction of the image carrier and is in contact with the image carrier and to which a polarity opposite to the charged position of the toner is applied; a bias is applied and the second charging member is contacted; And a recovery member bias controller for controlling a bias applied to the recovery member based on image forming unit life information. The charging device.   The charging device according to claim 1, wherein a charging brush member is used for each of the first and second charging members.   6. The charging device according to claim 5, wherein at least the charging brush member of the second charging member is a brush roller.   The charging device according to claim 1, wherein the collecting member is a collecting roller.   8. The charging device according to claim 1, wherein the toner is a toner obtained by adding at least an external additive having a polishing function to toner base particles.   8. The charging device according to claim 1, wherein the toner is a toner obtained by adding at least an external additive having a polishing function and an external additive having a charging assist function to toner base particles. . An image carrier on which an electrostatic latent image and a toner image are formed, a charging device for charging the image carrier, an exposure device for writing an electrostatic latent image on the image carrier by exposure, and an image on the image carrier The electrostatic latent image is developed with toner in which an external additive is added to toner base particles to form a toner image on the image carrier, and the toner image on the image carrier is transferred to a transfer medium. And at least a transfer device,
The image forming apparatus according to claim 1, wherein the charging device is a charging device according to claim 1. A toner image in which an external additive is added to toner base particles is used to form a toner image on the image carrier, and residual toner adhering to the image carrier after transfer of the toner image formed on the image carrier is charged with the toner. A bias having a polarity opposite to the charged position of the toner is applied to the transfer residual toner on the image carrier charged by the first charging member. The toner collected by the second charging member is collected by the collecting member to which a bias is applied, and attached to the second charging member after passing through the collecting member by controlling the bias applied to the collecting member. Charging the image carrier in an image forming apparatus, wherein the amount of the external additive is controlled, and the image carrier is charged by a second charging member to which the controlled amount of the external additive is attached. Method.