JP5423476B2 - Developing device, process cartridge, and image forming apparatus - Google Patents

Description

  The present invention relates to a developing device mounted on an image forming apparatus such as a copying machine, a facsimile machine, a printer, or a multifunction machine having these functions.

  In an electrophotographic image forming apparatus, in a two-component development method in which an electrostatic latent image formed on an image bearing member (photoreceptor) is developed with toner using a two-component developer having a carrier and toner, image quality is improved. In order to improve the development, a developer having a small particle diameter has been used. However, as the particle size of the developer is reduced, the carrier adheres to the image area and the non-image area on the image carrier, and there is a side effect (carrier adhesion) that an offset is generated at the time of image transfer / fixing to deteriorate the image quality. It has deteriorated. Especially in machines for the PP (plain paper) market, such as Ricoh's Aegis (model name), the rotation speed of the developer carrier is larger than that of the medium speed machine, and due to the action of centrifugal force, carrier adhesion occurs. Will further increase.

  Carrier adhesion is more likely to occur as the magnetic restraining force received by one carrier from the developer carrying member is smaller, and there is a difference in the ease of carrier adhesion depending on variations in the characteristics of the carrier in the developer. From this point, at a timing when the image forming apparatus is not performing an image forming operation, a potential difference in a range where toner is not developed is generated between the developer carrying member and the image carrying member, and a carrier (hereinafter referred to as a defective carrier) that easily adheres to the carrier. (Hereinafter referred to as control in the carrier discharge mode) is already known.

  For example, the configuration disclosed in Patent Document 1. Patent Document 1 discloses a technique for forming a latent image in which a fringe electric field is generated on the surface of an image carrier for the purpose of preferentially discharging only defective carriers in the carrier discharge mode.

  However, even if the carrier discharge mode is executed in the conventional developing device including the configuration disclosed in Patent Document 1, the magnetic brush held by the developer carrier is held near the surface of the developer carrier. The defective carrier is difficult to be discharged to the image carrier side because the magnetic restraint force received from the developer carrier is relatively large. Therefore, there is a problem that the operation time required until all the defective carriers in the developing device are discharged is long.

  An object of the present invention is to shorten the operation time required for the carrier ejection mode by increasing the ejection efficiency of the defective carrier in the carrier ejection mode in which the defective carrier is ejected at a timing other than the time of image formation.

The above-described problem is a developing device that develops a latent image on an image carrier with a two-component developer, the developer carrier that carries and transports the developer, and the developer carrier that is built in the developer carrier. A developing device having a magnetic field generating means for forming a magnetic brush, further comprising a disturbing means for disturbing the developer in the magnetic brush in the developing area, from the developer carrying body to the image carrying body side while a force for moving the carrier to rotate the image bearing member and the developer carrying member comprises a carrier discharging mode capable spit career, by actuating the disturbance means in the carrier discharging mode is solved The

  In essence, the present invention involves disturbing the developer in an area in which the developer carrying body and the image carrying body are close to each other (hereinafter referred to as a nip area; substantially corresponding to the development area during the development process). Since the defective carrier passing through the nip area moves toward the image carrier while passing through the nip area, the magnetic restraint force received from the developer carrier does not remain at a high value in the vicinity of the surface of the developer carrier, and the defective carrier The main point is to improve the discharge efficiency of the carrier and shorten the time required for the carrier discharge mode.

The magnetic field generating means is a magnet in which N poles and S poles are alternately magnetized in the circumferential direction, and is rotatable with respect to the developer carrier, and generates a magnetic field with the developer carrier in the carrier discharge mode. It is preferable to disturb the developer in the magnetic brush in the development region by rotating the means. At this time, if the magnetic field generating means rotates even during development, at least one of the developer carrying member and the magnetic field generating means rotates at a higher rotational speed than during image formation in the carrier discharge mode. Is more preferred .

  The carrier discharge mode is set to any one of a waiting time until the developer and the developing device are newly set, or a calibration process of various sensors, a charging start-up process of the developer, and the fixing device rise to a predetermined temperature. It is preferable to carry out together. In the carrier discharge mode, it is preferable that a predetermined latent image pattern that generates a strong electric field region due to an electric field wrap around the surface of the image carrier is formed on the image carrier. In that case, it is assumed that the latent image pattern is one in which dots having the same shape are regularly arranged.

  According to the present invention, in the carrier discharge mode, the developer in the nip region is disturbed to efficiently discharge the defective carrier, and the operation time required for discharging the defective carrier in the developer is shortened. Can do.

  As a method for selecting and discharging defective carriers, there is a method of providing a step of selecting defective carriers at the time of manufacturing in a factory, in addition to the method using the carrier discharge mode. Specifically, there are a method of selecting and discharging one having a small magnetization per carrier, a method of selecting and discharging a carrier having a small particle diameter, and the like. However, these methods select carriers based on a uniform threshold, and the conditions of various conditions such as the performance of the image forming apparatus main body in which each developer is used and the environment in which the image forming apparatus is used are determined. It does not take into account variations. In the carrier discharge mode, it is possible to efficiently select defective carriers according to the specific conditions of each image forming apparatus and developer, etc., without requiring special maintenance or work by service personnel. The image quality provided to the user can be greatly improved while reducing the man-hours. Further, the defective carrier in the developer may be generated not only in the manufacturing variation but also with the lapse of time while the printing is continued. For example, if the developer circulates in the developing device for a long time, the coat layer on the carrier surface may peel off (film scraping) or the toner component may adhere (spent), and such a carrier may become a defective carrier. Are known. According to the present invention, such defective carriers generated with time can be efficiently discharged in a short time, and the image quality provided to the user can be kept high over a long period of time.

  The magnetic field generating means is a magnet in which N poles and S poles are alternately magnetized in the circumferential direction, and is rotatable with respect to the developer carrier, and generates a magnetic field with the developer carrier in the carrier discharge mode. If the developer in the magnetic brush in the developing area is disturbed by rotating the respective means, it functions as a disturbing means, and the magnetic field alternation surely occurs in the nip area, and the defective carrier can be discharged from the developer. Guaranteed. At that time, if the magnetic field generating means rotates during development, and at least one of the developer carrier and the magnetic field generating means rotates at a higher rotational speed than during image formation in the carrier discharge mode. In addition, the effect of developer disturbance can be enhanced, and the discharge of defective carriers becomes efficient.

  The carrier discharge mode is set to any one of a waiting time until the developer and the developing device are newly set, or a calibration process of various sensors, a charging start-up process of the developer, and the fixing device rise to a predetermined temperature. If they are executed together, special maintenance, support by a service person, instruction from the user, and the like are not required, and a waiting time for executing the carrier discharge mode need not be newly assumed. In addition, in the carrier discharge mode, if a predetermined latent image pattern that generates a strong electric field region due to an electric field wraps around the surface of the image carrier is formed on the image carrier, a carrier is generated in the strong electric field region on the image carrier. It can be discharged including defective carriers that easily adhere.

1 is a schematic configuration diagram of an image forming apparatus according to the present invention. 1 is a schematic configuration diagram of a developing device according to the present invention. It is a figure explaining generation | occurrence | production of carrier adhesion and the mechanism of carrier discharge mode. FIG. 4 is a schematic diagram of a nip region in the carrier discharge mode, where (a) shows the developer behavior in the conventional carrier discharge mode, and (b) shows the development in the carrier discharge mode of the present invention that disturbs the developer in the nip region. The agent behavior is shown. It is a conceptual diagram which shows an example of a developer disturbance means. 6 is a graph showing a change in the number of discharged carriers when the linear velocity of the developing roller and the photosensitive member is constant and the number of magnetic pole alternations in the nip region is changed. It is the graph which compared the change of the defective carrier content rate in normal carrier discharge mode and carry discharge mode which raised rotation speed. It is a conceptual diagram which shows another example of a developer disturbance means. It is a figure which shows an example of the preferable electrostatic latent image pattern used by carrier discharge mode. It is a graph explaining the electric field variation by an edge effect. It is a graph showing the transition of the number of carrier adhesion according to the number of image formation. It is a graph explaining the feature of a defective carrier concretely.

Embodiments of the present invention will be described below in detail with reference to the drawings.
The image forming apparatus according to the present invention is basically the same as the entire mechanism thereof, and is an apparatus necessary for forming an image around a photoconductor as an image carrier, such as a charging unit, Exposure means, development means, and the like are provided, and those skilled in the art can easily recognize the overall configuration and operation. The configuration will be briefly described. In FIG. 1, the image forming apparatus includes K (black), Y (yellow), C (cyan), and M (magenta) image forming stations uniformly charged by the charging roller 4. The image read by the scanner 1 is color-separated by the writing device 2 and written for each color on the photosensitive member 3 as the image carrier, thereby forming an electrostatic latent image. As an example, a K (black) station will be described. The latent image formed on the photoconductor 3 is developed by the developing device 5 in accordance with the K toner to form a toner image. The developed K toner image is transferred onto the intermediate transfer belt 7 at a portion where the intermediate transfer belt 7 is in contact with the photoreceptor 3 in a form sandwiched between the photoreceptor 3 and the primary transfer roller 8. Similarly, a toner image is formed on the photosensitive member 3 at each image forming station of Y (yellow), C (cyan), and M (magenta), and the toner image transferred onto the intermediate transfer belt 7 is at the secondary transfer position. The transfer paper is fed from the registration roller in accordance with the arrival timing, and is transferred onto the transfer paper at once by the secondary transfer roller 10. The transferred transfer paper is transported to the fixing device 11 by the transport belt 9, fixed, and discharged as a copy image.

  On the other hand, after the toner 3 is transferred onto the intermediate transfer belt 7, the residual toner is removed by the cleaning device 6, the charge is removed by a charge-removing lamp (not shown), and then uniformly charged by the charging roller 4 again. Repeat the operation. The photosensitive member 3, the charging roller 4, the developing device 5, and the cleaning device 6 constitute a process cartridge for each color, but the process cartridge may be configured without the charging roller 4 and the cleaning device 6.

  The intermediate transfer belt 7 after the transfer onto the transfer paper is subjected to transfer of the toner image from the photoreceptor 3 onto the intermediate transfer belt 7 again after the residual toner is removed by an intermediate transfer belt cleaning device (not shown). However, the image forming process of batch transferring this onto transfer paper is repeated.

  Residual toner removed from the photoreceptor 3 or the intermediate transfer belt 7, that is, waste toner, is disposed in a lower portion of the image forming apparatus 1 through a waste toner conveyance path (not shown) existing in the image forming apparatus 1. It is conveyed to the toner recovery container 12. The waste toner conveyance path extends from each cleaning device to the lower collection container 12. The collection container 12 is installed above the paper discharge tray, but may be arranged in another space.

  In the developing device 5 whose configuration is shown in detail in FIG. 2, the developer circulates in the following flow in the developing device 5 surrounded by the case 20. First, while the carrier and toner are mixed by the agitation / conveyance screws 22 and 23, the carrier and the toner are conveyed in the longitudinal direction of the developing device, and the developer is supplied to the developing roller 25 that is a developer carrying member. The developing roller 25 conveys the developer in the clockwise direction in the drawing, develops the toner in the nip region, and collects the toner to the lower stirring / conveying screw 23. The developer collected by the lower agitating / conveying screw 23 is lifted up to the upper agitating / conveying screw 22 at the end of the developing device 5 while being conveyed in the longitudinal direction, and is used again for development.

  At this time, it is desirable that a predetermined amount of toner moves on the photosensitive member 3 and only the image portion is developed, but in reality, a phenomenon occurs in which the carrier adheres to the image portion or the non-image portion (carrier attachment). . In order to suppress the occurrence of carrier adhesion, a carrier discharge mode is a method in which a defective carrier that is likely to adhere to a carrier is attached to the photosensitive member side at a timing other than the time of image formation and is not used for development. In particular, immediately after setting a new developer or developing device, the carrier discharge mode is executed automatically or manually to sufficiently discharge the defective carrier contained in the initial developer, and at the time of subsequent image formation. Significantly reduce the occurrence of carrier adhesion. In this carrier discharging mode, the developer in the nip region is disturbed to further improve the efficiency of discharging the defective carrier, and the time required for discharging the defective carrier in the developer is shortened. Normally, when a new developing device or developer is set in the main body of the image forming apparatus or when the image forming apparatus is turned on, it is included in the calibration processing of various sensors, the charging start-up of the developer, and the image forming apparatus. Since it takes time to raise the temperature of the fixing device, if the carrier discharge mode is operated in accordance with this time, it is not necessary to secure a dedicated time for carrier discharge, and image quality can be improved without increasing the waiting time of the user. Can do.

  Here, the mechanism of carrier adhesion and carrier discharge mode will be described. There are two forces acting on one carrier in the nip area: (1) magnetic restraint force received from the developer carrier and magnetic brush, and (2) force trying to escape from the restraint of the developer carrier and magnetic brush. Can be roughly divided into In the graph in FIG. 3A, the vertical axis represents the magnitude of the force applied to one carrier, the horizontal axis represents the distance from the developer carrier surface as the origin, The approximate tendency of the restraining detachment force with circled number 2 is schematically shown. That is, the carrier moves and adheres to the image carrier side in the shaded area where the magnetic restraining force is less than the restraining and releasing force.

  The magnetic restraint force will be described in detail. The developer carrying member (developing roller) has magnetic field generating means inside, and holds the developer on the surface by the magnetic force. However, the magnetic force received by one carrier from the magnetic field generating means decreases as the distance from the surface of the developer carrying member increases. Furthermore, the carrier in the developer has variations in characteristics, and the magnetic force received from the magnetic field generating means varies from carrier to carrier. Specifically, the particle size variation and the magnetization variation are related to this. Since the magnetic force received by one carrier is proportional to the value of (magnetization) × (particle diameter cubed), a carrier with a small particle diameter and magnetization has a weaker force constrained on the developer carrier side. Such a carrier is a defective carrier and causes carrier adhesion during image formation. In the graph in the figure, circled number 1 is a force acting on a normal carrier, and circled number 1 'is a force acting on a defective carrier. Actually, since the particle diameter and the magnetization have distributions, the normal carrier and the defective carrier cannot be clearly separated, but here, they are simplified and schematically shown in two types.

  The restraining / releasing force will be described. Among the restraining and releasing forces, the forces that exist constantly include centrifugal force due to rotation of the developer carrier, electrostatic force received from the electric field in the nip region, and non-electrostatic adhesion force received from the surface of the image carrier. FIG. 3B illustrates the electrostatic force received from the electric field in the nip region. In a developer in which the carrier is positively charged and the toner is negatively charged, by lowering the potential on the image carrier side, it is possible to apply a force in the attracting direction to the image carrier side only. These potentials and potential differences can be set arbitrarily.

  From the above, it can be seen that a defective carrier having a smaller magnetic restraining force is more likely to adhere to the carrier, and at the same time, the carrier is more likely to adhere to the image carrier. In the carrier discharge mode, except for the time of image formation, a restraint release force is generated within a range where normal carriers are not discharged but defective carriers are discharged, and defective carriers are discharged.

  Next, the developer behavior in the nip region in the carrier discharge mode will be described with reference to FIG. Although the two-component developer actually includes a carrier and a toner, only the carrier is shown here for the sake of simplicity. In the two-component development system, the carrier is positively charged and the toner is negatively charged by frictional charging between the carrier and the toner. Each of these charges may have a reverse polarity. At the time of image formation, an electric field in the direction of attracting toner is applied to the image portion on the image carrier, and usually the carrier does not move to the image carrier. On the other hand, as shown in the figure, an electric field is applied to the non-image portion in a direction that attracts positively charged carriers. However, the specific potential value can be changed according to the characteristics of the developer to be used.

  FIG. 4A is a diagram schematically illustrating the developer behavior in the carrier discharging mode in the conventional developing device. In the conventional developing device, the developer held on the developer carrier is subjected to a magnetic binding force by a magnetic field generating means inside the developer carrier to form a magnetic brush. This magnetic brush includes a defective carrier in a certain ratio together with the normal carrier. Since the magnetic restraint force received from the developer carrier is weaker than that of the normal carrier, the defective carrier easily moves to the image carrier side due to the electrostatic force received from the electric field in the nip region. Using this difference, only the defective carrier is discharged to the image carrier side in the carrier discharge mode. However, since the conventional developing device passes through the nip region while maintaining the magnetic brush, the carrier held near the surface of the developer carrier is subjected to a relatively large magnetic restraint force as described with reference to FIG. Subsequently, even a defective carrier is difficult to be discharged to the image carrier side. In contrast, in the present invention shown in FIG. 4B, the developer in the nip region is disturbed in the manner described below, and the positions of the carriers in the magnetic brush are interchanged. Thereby, the probability that the defective carrier held in the vicinity of the surface of the developer carrier upstream of the nip region is increased toward the image carrier by increasing the distance from the developer carrier.

  A method for disturbing the developer will be described. The developing roller 25 is a cylindrical developing sleeve 26 that rotates, and a magnetic roller 27 provided inside the developing sleeve as a magnetic field generating means for generating a magnetic field so as to generate a spike of developer on the surface of the developing sleeve. As shown in FIG. 5, the mag roller 27 is also configured to be rotatable independently of the developing sleeve 26 in the carrier discharging mode. The developing roller may be of a type in which the mag roller 27 is fixedly supported during image formation, but may be of a type in which the mag roller 27 rotates. The mag roller 27 has N and S poles alternately arranged along the outer periphery thereof, and rotates independently of the developing sleeve 26 in the carrier discharge mode. It may be around. As the mag roller 27 rotates, the magnetic field for holding the developer is alternated, and the magnetic brush held on the surface of the developing roller 25 (developing sleeve 26) moves while rotating. This rotation of the magnetic brush has a disturbing action of the developer. In the type in which the mag roller 27 rotates at the time of image formation, the effect of the developer disturbance can be enhanced by operating the developing sleeve and the mag roller at a higher rotational speed than at the time of image formation in the carrier discharge mode. For example, when the linear velocity of the developing roller and the photosensitive member is fixed to 600 [mm / sec] and the number of times the magnetic poles alternate in the nip region is changed per second, the number of carrier discharges is as shown in FIG. changed. For example, when the number of times of alternating magnetic poles is usually 300 [times / second], the carrier discharge efficiency is doubled by setting 600 [times / second] in the carrier discharge mode, and the time required for defective carrier discharge Was halved. For comparison, FIG. 7 shows the difference in how the defective carrier content decreases in the conventional carrier discharge mode and the carrier discharge mode when the rotation speed of the mag roller is increased.

  In the example shown in FIG. 8, magnetic field generating means 30 that can be switched on and off is provided inside the photoreceptor 3. By generating a magnetic force weaker than that of the mag roller 27 that is a magnetic field generating means provided on the developing roller 25 side, a force for attracting the carrier to the photosensitive member side is applied, and the effect of developer disturbance can be achieved. Furthermore, if the magnetic field generating means 30 is switched on and off at least once while the developer passes through the nip region, the effect of developer disturbance can be provided. For example, when the moving speed of the developer is 600 [mm / sec] and the width of the nip area is 10 [mm], the on / off may be switched at 60 Hz or more. The magnetic field generating means 30 may be an electromagnet, or a permanent magnet attached with a magnetic short-circuit plate that can be opened and closed.

  In the developing area during development (during image formation) and in the carrier discharge mode, there are many cases where an actually non-uniform electric field is actually generated. The factors include the non-uniformity of the characteristics of the surface of the photoreceptor, the electrostatic latent image pattern formed on the photoreceptor, the dielectric constant of the developer itself, and variations thereof. Such non-uniformity may cause an electric field to wrap around, resulting in a local strong electric field region (hereinafter referred to as an edge portion), which may cause carrier adhesion. Such a carrier that easily adheres to the edge portion may not be sufficiently discharged only by setting a uniform potential difference as shown in FIG. In order to cope with this problem, it is preferable to generate a local strong electric field region on the surface of the photoreceptor even in the carrier discharge mode. As an example, there is a method of executing the carrier discharge mode while forming an electrostatic latent image having a pattern as shown in FIG. 9 on the photosensitive member. At that time, if there is a potential difference between the black and white areas in the figure, and considering the potential difference from the surface of the developing roller in either area, the electric field is in the direction of transferring the carrier to the photoconductor. Is set to occur. As a result, as shown in FIG. 10, a strong electric field region is generated at the boundary between the black and white portions in the figure, and carriers that easily adhere to the edges can be discharged. Become.

  As a latent image pattern to be formed on the photoconductor in the carrier discharge mode, it is desirable to use a pattern having a high effect of discharging carrier adhesion. This is because there is a difference in the carrier discharge effect depending on the pattern so that the pattern having a potential difference in the plane has a higher carrier discharge effect than the uniform pattern on the entire surface. For example, the dot-like pattern in which the potential changes in two directions as shown in FIG. 9 has a higher discharging effect than the ladder-like pattern in which the potential changes only in one direction. Even in the same dot-like pattern, the discharge effect varies depending on the size of the dot, and there is an optimum dot size. Since this size and the like varies depending on the configuration of the image forming apparatus to be used, it is preferable to set it according to each condition.

  In an evaluation using a certain image forming apparatus, when an image is actually output in a pattern as shown in FIG. 9, while each dot size and pitch is changed to 40, 80, 160, and 320 [μm], It was found that the most carrier adhesion occurred at about 160 [μm], and the latent image pattern used in the carrier ejection mode should have the same period.

  Finally, the influence and characteristics of defective carriers will be described. FIG. 11 is a graph showing the transition of the number of adhered carriers according to the number of image formations. Usually, since the initial developer contains a certain percentage of defective carriers, carrier adhesion due to such defective carriers is added to the carrier adhesion of normal carriers. However, by continuing image output, the content of defective carriers is reduced, and the amount of carrier adhesion is stabilized. The specific value varies depending on various conditions such as image forming conditions, developer characteristics, and amount of developer contained in the developing device. What was about 1000 was reduced to about 100 by outputting 500 images of A4 area. That is, when a new developer is used, the carrier adhesion due to the defective carrier can be prevented by discharging the defective carrier in the carrier discharging mode.

  In addition, the defective carrier may be generated over time as the carrier deteriorates while printing is continued. For example, if the developer circulates in the developing device for a long time, the coat layer on the carrier surface may peel off (film scraping) or the toner component may adhere (spent), and these carriers become defective carriers. It has been known. According to the present invention, such defective carriers generated with time can be efficiently discharged in a short time, and the image quality provided to the user can be kept high over a long period of time.

  FIG. 12 is a graph for specifically explaining the characteristics of the defective carrier. Carriers in the developer vary in their characteristics. For example, the particle size distribution of the carrier in the unused developer is different from the particle size distribution of the carrier actually attached on the image carrier in an image forming apparatus using the carrier having such a distribution. It was confirmed that the particle size peak was shifted from about 30 [μm] to about 25 [μm]. That is, it has been found that among the carriers included in the developing device, a carrier having a relatively small particle size preferentially adheres as a defective carrier.

3 Photosensitive member 5 Developing device 20 Case 22, 23 Agitating / conveying screw 25 Developing roller 26 Developing sleeve 27 Mag roller

Japanese Patent No. 3671525

Claims (8)

A developing device that develops a latent image on an image carrier with a two-component developer, the developer carrier that carries and transports the developer, and a magnetic brush that is built in the developer carrier and formed on the developer carrier A developing device having a magnetic field generating means for further disturbing the developer in the magnetic brush in the developing area, and moving the carrier from the developer carrier to the image carrier side. while a force to rotate the image bearing member and the developer carrying member comprises a carrier discharging mode capable spit career, actuates said disturbance means in the carrier discharging mode,
The magnetic field generating means is a magnet in which N poles and S poles are alternately magnetized in the circumferential direction, and is rotatable with respect to the developer carrier, and generates a magnetic field with the developer carrier in the carrier discharge mode. And developing means for disturbing the developer in the magnetic brush in the developing region by rotating the means . The magnetic field generating means is also rotated during development, and at least one of the developer carrier and the magnetic field generating means is rotated at a higher rotational speed than in image formation in the carrier discharge mode. The developing device according to claim 1 . A process cartridge and a developing device and the image bearing member according to claim 1 or 2. An image forming apparatus including a developing device and the image bearing member according to claim 1 or 2. The image forming apparatus according to claim 4 , wherein the carrier discharge mode is executed when a developer and a developing device are newly set. Said carrier discharging mode, the calibration process of the sensors, according to claim 4, charging start-up processing of the developing agent, a fixing device is characterized in that it runs with one of the waiting time until the rise to a predetermined temperature Image forming apparatus. 5. The image forming apparatus according to claim 4 , wherein in the carrier discharge mode, a predetermined latent image pattern that generates a strong electric field region due to an electric field wrapping on the surface of the image carrier is formed on the image carrier. . The image forming apparatus according to claim 7 , wherein the latent image pattern is a pattern in which dots having the same shape are regularly arranged.

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