JP5736326B2 - Developing device and image forming apparatus including the same - Google Patents

Description

  The present invention relates to a developing device mounted on an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine thereof, and an image forming apparatus including the developing device, and in particular, a two-component developer including a toner and a magnetic carrier. The present invention relates to a developing device to be used and an image forming apparatus having the same.

  Conventionally, as a developing method in an image forming apparatus using an electrophotographic process, a one-component developing method that does not use a carrier, and a two-component developer containing toner and a magnetic carrier on a developing roller are carried on the surface as a magnetic brush. In addition, a two-component development system is known in which an electrostatic latent image on a photoreceptor is developed with toner in a magnetic brush.

  The one-component development method is suitable for high image quality because the electrostatic latent image on the photoconductor is not disturbed by the magnetic brush, but the toner adheres to a regulating member that regulates the developer layer thickness. The formation may be non-uniform and image defects may occur. On the other hand, the two-component development method can maintain a stable charge amount for a long time and is suitable for extending the life of the toner, but is disadvantageous in terms of image quality due to the influence of the magnetic brush described above.

  As one means for solving these problems, a developing system has been proposed in which a developing roller arranged in a non-contact manner with respect to the photoreceptor and a magnetic roller for forming a magnetic brush are provided. In this developing method, when supplying the developer from the magnetic roller to the developing roller, only the toner is transferred onto the developing roller while leaving the magnetic carrier on the magnetic roller to form a thin toner layer, and the photoconductor by an AC electric field. Toner is attached to the upper electrostatic latent image.

  In the case of the above development method, there is a problem that a part of the immediately developed image appears as an afterimage (ghost) in the next development, that is, so-called history development is likely to occur.

  Regarding the mechanism of history development, when an electrostatic latent image is developed, if a toner consumption area (development area) and a non-consumption area in which a toner thin layer remains are generated on the development roller, a new roller roller is used. When a toner is supplied and a thin toner layer is formed on the developing roller, a difference in toner layer thickness occurs between the developing area and the non-consuming area. When a full-color image or a halftone image is developed in this state, the amount of toner that moves from the immediately preceding developing area to the photosensitive member side is small, and thus the immediately preceding developed image appears as an afterimage.

  Accordingly, various methods have been proposed for eliminating the history development by collecting a thin toner layer that has not been used for development on the developing roller to the magnetic roller side. For example, in the developing device described in Patent Document 1, a developing roller and a magnetic roller face each other, a main magnetic pole is provided in the magnetic roller, and a developing magnetic pole having a polarity different from that of the main magnetic pole is provided in the developing roller. The developing magnetic pole is disposed opposite the main magnetic pole at a position facing the roller. The magnetic field formed between the main magnetic pole and the developing magnetic pole strengthens the binding force of the magnetic brush formed on the magnetic roller, and after development, the toner remaining on the developing roller is scraped off by the magnetic brush. Thus, the history development is eliminated by being collected on the magnetic roller side.

JP 2005-274924 A (paragraphs [0020], [0021], [0025], [0026], FIG. 1)

  However, in the developing device described in Patent Document 1 described above, since the binding force of the magnetic brush is strong, when image formation is performed for a long period of time, toner collection from the developing roller to the magnetic roller by the magnetic brush, and magnetism by bias application are performed. Since toner supply from the roller to the developing roller is repeated, toner deterioration is accelerated. When new toner is replenished to the deteriorated toner, the charge ability of the deteriorated toner is reduced. However, since the new toner has sufficient charging ability, the deteriorated toner is further shifted to the lower charge side and reversely charged. To do. When the reversely charged toner is mixed, the reversely charged toner causes a fogging phenomenon in which many small black spots appear in the background portion of the image. Further, when the binding force of the magnetic brush is strong, the deterioration of the carrier is promoted by repeating the image formation. The carrier resistance changes due to the deterioration of the carrier, and the fog phenomenon occurs in the same manner as described above with the repeated movement of the toner between the magnetic roller and the developing roller. The fog phenomenon due to the change in the carrier resistance is not limited to the developing method using the developing roller and the magnetic roller, but also occurs in the developing method in which, for example, the magnetic brush is formed on the developing roller in the above-described two-component developing method. To do.

  The present invention has been made to solve the above-described problems, and includes a developing device that suppresses the occurrence of fog phenomenon due to a change in carrier resistance due to long-term image formation and obtains a good image, and the developing device. Another object of the present invention is to provide an image forming apparatus.

In order to achieve the above object, a first invention is a developing device for developing an electrostatic latent image formed on the surface of an image carrier into a toner image, comprising a two-component developer containing toner and a magnetic carrier. A magnetic roller carried on the surface as a magnetic brush, a regulating member made of a magnetic material that regulates the magnetic brush carried on the surface of the magnetic roller to a predetermined layer thickness, and facing each of the image carrier and the magnetic roller And a developing roller that carries the toner in the magnetic brush carried on the magnetic roller on the surface and supplies the carried toner to the image carrier, and the regulation on the inner peripheral side of the magnetic roller A regulating magnetic pole disposed opposite to the member, and a main magnetic pole disposed on the inner peripheral side of the magnetic roller opposite to the developing magnetic pole provided on the inner peripheral side of the developing roller, and Sum magnetization is 30~50e mu / g, the magnetic force of the restriction pole is 30～50MT, a magnetic force 45~70mT of the main magnetic pole, the developing pole and at opposite polarity to said main magnetic pole In a state where the magnetic force is small and an electric field of 5 ⁵ V / m is applied to the magnetic carrier, the initial carrier resistance of image formation is R0, and the roller surface running distance by the rotation of the magnetic roller accompanying the image formation is 165 km. When the carrier resistance in a certain case is R, R0 / R ≦ 50.

In order to achieve the above object, a second invention is a developing device for developing an electrostatic latent image formed on the surface of an image carrier into a toner image, and includes two-component development including toner and a magnetic carrier. A developing roller that carries the agent on the surface as a magnetic brush and supplies the toner in the magnetic brush to the image carrier, and a magnetic material that regulates the magnetic brush carried on the surface of the developing roller to a predetermined layer thickness A regulating member, and a regulating magnetic pole disposed opposite to the regulating member on the inner peripheral side of the developing roller, and the saturation magnetization of the magnetic carrier is 30 to 50 e mu / g, force is 30～50MT, wherein the state of applying an electric field of the magnetic carrier to the ⁵ 5 V / m, the initial carrier resistance of the image formed with R0,該Ro by rotation of the developing roller with the image forming When the carrier resistance when Ra surface mileage is 75Km was R, is characterized in that it is R0 / R ≦ 50.

  According to a third aspect of the invention, there is provided an image forming apparatus including the developing device having the above-described configuration.

According to the first invention, the saturation magnetization of the magnetic carrier affects the decrease in the carrier resistance when the image formation is repeated, and if it exceeds a predetermined range (30 to 50 e mu / g), the carrier The magnetization characteristic of the toner becomes too large, and fogging phenomenon occurs when new toner is replenished. Further, even when a carrier having a small decrease in carrier resistance due to repeated use is used, if the saturation magnetization exceeds the upper limit, the deterioration of the toner proceeds, resulting in a decrease in density. On the other hand, when the saturation magnetization amount of the magnetic carrier falls below a predetermined range, the magnetization characteristics of the carrier become too small, and the carrier becomes difficult to be held on the magnetic roller and moves onto the image carrier, thereby causing white and black spots due to the carrier. Is developed in the carrier. By using a magnetic carrier having a saturation magnetization in the range of 30 to 50 e mu / g, a good image in which fogging phenomenon, density reduction and carrier development are suppressed can be obtained.

  Further, the magnetic force of the regulating magnetic pole affects the decrease in carrier resistance when image formation is repeated. If the magnetic force exceeds the predetermined range (30 to 50 mT), the magnetic force of the regulating magnetic pole becomes too large and new toner is produced. As a result of fogging, the density decreases. On the other hand, if the magnetic force of the regulating magnetic pole is below a predetermined range, it is difficult to produce a magnet for the regulating magnetic pole having a stable magnetic force. When the magnetic force of the regulating magnetic pole is 30 to 50 mT, a good image in which fogging phenomenon and density reduction are suppressed can be obtained, and the regulating magnetic pole can be easily manufactured.

  In the developing method using the developing roller and the magnetic roller, the density of the carrier increases at the position opposite to the magnetic roller and the developing roller, and therefore the deterioration of the carrier due to repeated image formation is likely to proceed. When the magnetic force of the main magnetic pole exceeds a predetermined range (45 to 70 mT), the change in carrier resistance increases due to repeated use, and fogging phenomenon occurs due to replenishment of new toner. On the other hand, the above developing method is less likely to generate carrier development than the developing method using only the developing roller, so that it is possible to lower the magnetic force of the main magnetic pole, but until the magnetic force of the main magnetic pole falls below a predetermined range. When it is lowered, carrier development occurs remarkably. When the magnetic force of the main magnetic pole is 45 to 70 mT, a good image in which fog phenomenon and carrier development are suppressed can be obtained.

  Further, when the roller surface travel distance of the magnetic roller for repeated image formation is 165 km, if the change in carrier resistance R0 / R relative to the initial image formation exceeds a predetermined range (50 or less), the image formation is repeated. The toner's charging ability is decreased due to the carrier resistance being too small, the carrier's charging ability is reduced, the carrier component is attached to the toner, and the toner is deteriorated due to repeated movement of the toner between the magnetic roller and the developing roller. As a result, the fogging phenomenon occurs when new toner is replenished. When the carrier resistance change R0 / R is 50 or less, a good image in which the fog phenomenon is suppressed can be obtained over a long period of time.

According to the second aspect of the invention, the saturation magnetization of the magnetic carrier affects the decrease in carrier resistance when image formation is repeated, and if it exceeds a predetermined range (30 to 50 e mu / g), the carrier The magnetization characteristic of the toner becomes too large, and fogging phenomenon occurs when new toner is replenished. Even when a carrier with a small decrease in carrier resistance is used even if it is repeatedly used, if the saturation magnetization exceeds the upper limit, the toner deteriorates and the density decreases. On the other hand, when the saturation magnetization amount of the magnetic carrier falls below a predetermined range, the magnetization characteristics of the carrier become too small, and the carrier is not held on the developing roller and moves onto the image carrier, so that white spots and black spots due to the carrier are eliminated. Carrier development that appears in the image occurs. By using a magnetic carrier having a saturation magnetization in the range of 30 to 50 e mu / g, a good image in which fogging phenomenon, density reduction and carrier development are suppressed can be obtained.

  Further, the magnetic force of the regulating magnetic pole affects the decrease in carrier resistance when image formation is repeated. If the magnetic force exceeds the predetermined range (30 to 50 mT), the magnetic force of the regulating magnetic pole becomes too large and new toner is produced. As a result of fogging, the density decreases. On the other hand, if the magnetic force of the regulating magnetic pole is below a predetermined range, it is difficult to produce a magnet for the regulating magnetic pole having a stable magnetic force. When the magnetic force of the regulating magnetic pole is 30 to 50 mT, a good image in which fogging phenomenon and density reduction are suppressed can be obtained, and the regulating magnetic pole can be easily manufactured.

  Further, when the roller surface travel distance of the magnetic roller with repeated image formation is 75 km, if the change in carrier resistance R0 / R with respect to the initial image formation exceeds a predetermined range (50 or less), the image formation is repeated. Since the carrier resistance becomes too small, and the toner deteriorates due to a decrease in the charging ability of the carrier, the adhesion of the carrier component to the toner, etc., the charging ability of the toner is lowered, and a fog phenomenon occurs with the replenishment of new toner. When the carrier resistance change R0 / R is 50 or less, a good image in which the fog phenomenon is suppressed can be obtained over a long period of time.

1 is a diagram schematically illustrating an image forming apparatus including a developing device according to an embodiment of the present invention. Sectional drawing which shows schematically the developing device which concerns on 1st Embodiment Sectional drawing which shows schematically the image development apparatus concerning 2nd Embodiment. Diagram showing measurement of carrier resistance Diagram showing measurement of reversely charged toner amount Diagram showing the relationship between carrier resistance change and reverse charge

  Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. Further, the use of the invention and the terms shown here are not limited thereto.

(First embodiment)
FIG. 1 is a diagram schematically showing a configuration of an image forming apparatus including a developing device according to the first embodiment of the present invention. The image forming apparatus 1 is a tandem type color printer, and the rotatable photoreceptors 11a to 11d use an organic photoreceptor (OPC photoreceptor) as a photosensitive material for forming a photosensitive layer, and are magenta, cyan, and yellow. , And black. Around each of the photoreceptors 11a to 11d, developing devices 2a to 2d, an exposure unit 12, chargers 13a to 13d, and cleaning devices 14a to 14d are disposed.

  The developing devices 2a to 2d are arranged to face the right sides of the photoconductors 11a to 11d, respectively, and supply toner to the photoconductors 11a to 11d. The chargers 13a to 13d are arranged on the upstream side of the developing devices 2a to 2d with respect to the rotation direction of the photoconductors 11a to 11d so as to face the surfaces of the photoconductors 11a to 11d. To charge.

  The exposure unit 12 scans and exposes each of the photoconductors 11a to 11d based on image data such as characters and pictures input to an image input unit (not shown) from a personal computer or the like. The developing device 2a ~ 2d below. The exposure unit 12 is provided with a laser light source and a polygon mirror, and a reflection mirror and a lens are provided corresponding to each of the photoconductors 11a to 11d. Laser light emitted from the laser light source is applied to the surfaces of the photoconductors 11a to 11d from the downstream side of the chargers 13a to 13d in the rotation direction of the photoconductors via the polygon mirror, the reflection mirror, and the lens. Electrostatic latent images are formed on the surfaces of the photoconductors 11a to 11d by the irradiated laser light, and the electrostatic latent images are developed into toner images by the developing devices 2a to 2d.

  The endless intermediate transfer belt 17 is stretched around the tension roller 6, the driving roller 25, and the driven roller 27. The driving roller 25 is rotationally driven by a motor (not shown), and the intermediate transfer belt 17 is circulated and driven by the rotation of the driving roller 25.

  The photoreceptors 11a to 11d are arranged below the intermediate transfer belt 17 so as to be in contact with the intermediate transfer belt 17 along the conveying direction (arrow direction in FIG. 1). The primary transfer rollers 26a to 26d face the photoconductors 11a to 11d with the intermediate transfer belt 17 interposed therebetween, and press contact with the intermediate transfer belt 17 to form a primary transfer portion. In the primary transfer portion, the toner images on the photoconductors 11a to 11d are sequentially transferred to the intermediate transfer belt 17 at a predetermined timing as the intermediate transfer belt 17 rotates. As a result, a toner image is formed on the surface of the intermediate transfer belt 17 by superimposing four color toner images of magenta, cyan, yellow, and black.

  The secondary transfer roller 34 faces the driving roller 25 with the intermediate transfer belt 17 interposed therebetween, and presses against the intermediate transfer belt 17 to form a secondary transfer portion. In this secondary transfer portion, the toner image on the surface of the intermediate transfer belt 17 is transferred to the paper P. After the transfer, the belt cleaning device 31 cleans the toner remaining on the intermediate transfer belt 17.

  A paper feed cassette 32 that stores paper P is disposed below the image forming apparatus 1, and a stack tray 35 that supplies manually fed paper is disposed to the right of the paper feed cassette 32. On the left side of the paper feed cassette 32, a first paper transport path 33 for transporting the paper P sent from the paper feed cassette 32 to the secondary transfer portion of the intermediate transfer belt 17 is disposed. Further, on the left side of the stack tray 35, a second paper transport path 36 for transporting paper fed from the stack tray 35 to the secondary transfer unit is disposed. Further, on the upper left side of the image forming apparatus 1, a fixing unit 18 that performs a fixing process on the paper P on which the toner image is formed, and a third unit that conveys the paper P on which the fixing process has been performed to the paper discharge unit 37. A paper transport path 39 is provided.

  The paper feed cassette 32 enables the replenishment of the paper P by pulling it out of the apparatus (the front side of the paper surface in FIG. 1). The paper P stored therein is one sheet by the pickup roller 33b and the separating roller 33a. Each is sent out to the first paper transport path 33 side.

  The first paper transport path 33 and the second paper transport path 36 merge before the registration roller pair 33c, and the registration roller pair 33c takes the timing of the image forming operation and the paper feeding operation in the intermediate transfer belt 17. Thus, the sheet P is conveyed to the secondary transfer unit. The sheet P conveyed to the secondary transfer unit is secondarily transferred with the toner image on the intermediate transfer belt 17 by the secondary transfer roller 34 to which a transfer bias is applied, and is conveyed to the fixing unit 18.

  The fixing unit 18 includes a fixing belt heated by a heater or the like, a fixing roller inscribed in the fixing belt, and a pressure roller disposed in pressure contact with the fixing roller with the fixing belt interposed therebetween. The fixing process is performed by heating and pressurizing the transferred paper P. After the toner image is fixed by the fixing unit 18 on the paper P, the toner image is reversed by the fourth paper conveyance path 40 as necessary, and the toner image is secondarily transferred to the back surface of the paper by the secondary transfer roller 34 to be fixed. Fixing is performed at the portion 18. The sheet on which the toner image is fixed passes through the third sheet conveyance path 39 and is discharged to the sheet discharge unit 37 by the discharge roller pair 19a.

  FIG. 2 is a cross-sectional view illustrating a configuration of the developing device according to the first embodiment including the developing roller and the magnetic roller, which is used in the image forming apparatus 1 described above. In the following description, the configuration and operation of the developing device 2a corresponding to the photoconductor 11a shown in FIG. 1 will be described. However, the configuration and operation of the developing devices 2b to 2d are the same as those of the developing device 2a. Explanation is omitted, and reference numerals a to d indicating developing devices and photosensitive members of the respective colors are omitted, and reference numerals a to d are given when necessary.

  As shown in FIG. 2, the developing device 2 includes a developing roller 20, a magnetic roller 21, a stirring unit 42, a regulating member 24, a developing container 22, and the like.

  The developing container 22 constitutes the outline of the developing device 2, and is partitioned into a first transport path 22d and a second transport path 22c by a partition member 22b at a lower portion thereof. A two-component developer containing toner and a magnetic carrier is accommodated in the first conveyance path 22d and the second conveyance path 22c. Further, the developing container 22 rotatably holds the first stirring member 44 and the second stirring member 43 of the stirring unit 42, the magnetic roller 21, and the developing roller 20. Further, the developing container 22 has an opening 22a that exposes the developing roller 20 toward the photoconductor 11 as an image carrier.

  The stirring unit 42 is provided at the bottom of the developing container 22 and includes two members, a first stirring member 44 and a second stirring member 43. The first stirring member 44 is provided in the first transport path 22d, and the second stirring member 43 is provided in the second transport path 22c adjacent to the right side of the first stirring member 44.

  The first and second stirring members 44 and 43 stir the developer to charge the toner in the developer to a predetermined level. Thus, the toner is held on the magnetic carrier. Further, communication portions (not shown) are provided on both end sides in the longitudinal direction (front and back direction of the paper surface of FIG. 2) of the partition member 22b that partitions the first transport path 22d and the second transport path 22c. 2 When the agitating member 43 rotates, the charged developer is transported into the first transport path 22d from one communicating portion provided in the partition member 22b, and circulates in the first transport path 22d and the second transport path 22c. To do. Then, the developer is supplied from the first stirring member 44 to the magnetic roller 21.

  The magnetic roller 21 is disposed above the first stirring member 44 so as to carry the developer supplied from the first stirring member 44 on the surface as a magnetic brush, and the toner in the magnetic brush carried on the surface. Only to the developing roller 20. A regulating member 24 is disposed to face the surface of the magnetic roller 21.

  The regulating member 24 is formed in a plate shape with a magnetic material such as stainless steel, and is fixedly held in the developing container 22 at an obliquely lower left side of the magnetic roller 21 and below the developing roller 20. The front end of the regulating member 24 faces the surface of the magnetic roller 21 with a predetermined interval, and regulates the layer thickness of the magnetic brush carried on the surface of the magnetic roller 21.

  The magnetic roller 21 includes a rotating sleeve 21e, a magnetic pole member 21f, and a roller shaft 21g.

  The rotating sleeve 21e is formed of a nonmagnetic material in a cylindrical shape and is disposed at a predetermined distance from the magnetic pole member 21f, thereby supporting the developer as a magnetic brush on the surface of the rotating sleeve 21e. The rotating sleeve 21e is rotatably supported by the developing container 22, and conveys the magnetic brush by being rotated in the direction of arrow C by a driving mechanism including a motor and a gear (not shown). Further, the rotating sleeve 21e is applied with a first bias by a first voltage applying unit 55 which is a power source in which an AC voltage 55b is superimposed on a DC voltage 55a.

  The magnetic pole member 21f is fixed to the roller shaft 21g by adhesion or the like and is supported by the developing container 22 through the roller shaft 21g so as not to rotate. The magnetic pole member 21f is composed of a plurality of magnets having different polarities at the outer periphery, and includes a regulation magnetic pole 21f1, a recovery magnetic pole 21f2 in which the same magnetic pole as the regulation magnetic pole 21f1 is adjacent in the circumferential direction, and a main magnetic pole 21f3.

  The restricting magnetic pole 21f1 is disposed to face the restricting member 24, and magnetizes the tip of the restricting member 24 with a polarity opposite to that of the restricting magnetic pole 21f1. A thin layer of a magnetic brush is formed on the surface of the rotating sleeve 21e by a magnetic field formed between the tip of the regulating member 24 and the surface of the rotating sleeve 21e.

  The main magnetic pole 21f3 is disposed toward the position E facing the developing roller 20, and raises the magnetic brush on the rotating sleeve 21e in the vicinity of the facing position E together with the developing magnetic pole 20f of the developing roller 20 described later. Only the toner of the magnetic brush formed on the rotating sleeve 21e at the facing position E is supplied to the surface of the developing roller 20. Further, the toner on the developing roller 20 that has not been subjected to the development after the image formation is peeled off from the surface of the developing roller 20 by the binding force of the magnetic brush formed on the rotating sleeve 21e in the vicinity of the facing position E, and rotated. It is collected on the surface of the sleeve 21e.

  The recovery magnetic pole 21f2 has a weaker magnetic force than the other magnetic poles of the magnetic pole member 21f, does not carry the developer on the surface of the rotating sleeve 21e, and recovers the developer that has not been developed to the stirring unit 42 side. To do.

  The developing roller 20 is opposed to the magnetic roller 21 at a facing position E with a predetermined interval left obliquely above the magnetic roller 21, and includes a developing sleeve 20e, a developing magnetic pole 20f, a fixed shaft 20g, and the like. ing.

  The developing magnetic pole 20f is supported by the developing container 22 through the fixed shaft 20g in a non-rotatable manner at a position E facing the magnetic roller 21 with a predetermined distance from the developing sleeve 20e. The developing magnetic pole 20f is composed of a magnet having a different polarity and a small magnetic force with respect to the main magnetic pole 21f3 of the magnetic roller 21, and the magnetic brush on the magnetic roller 21 together with the main magnetic pole 21f3 is raised and restrained in the vicinity of the facing position E. Giving power.

  The developing sleeve 20e is formed of a nonmagnetic material in a cylindrical shape and is rotatably supported by the developing container 22. Further, the developing sleeve 20e faces the photoconductor 11 and is arranged on the right side of the photoconductor 11 with a predetermined interval. The developing sleeve 20e supplies toner to the photoconductor 11 at a position close to the photoconductor 11. Region D is formed. Further, the developing sleeve 20e is rotated in the arrow B direction, which is the same direction as the rotating sleeve 21e, by a drive mechanism including a motor and gears (not shown). Furthermore, a second bias is applied to the developing sleeve 20e by a second voltage application unit 56 that is a power source in which an AC voltage 56b is superimposed on a DC voltage 56a.

  With the above configuration, the charged developer is carried on the surface of the rotating sleeve 21e of the magnetic roller 21 by forming a magnetic brush by the magnetic force of the magnetic pole member 21f, and the rotating sleeve 21e rotates in the direction of arrow C. Be transported. This magnetic brush is adjusted to a predetermined layer thickness by the regulating member 24 and the regulating magnetic pole 21f1. Then, the magnetic brush having a predetermined layer thickness is conveyed to the facing position E by the rotation of the rotating sleeve 21e. At the facing position E, the magnetic brush is raised by the main magnetic pole 21f3 and the developing magnetic pole 20f and comes into contact with the developing sleeve 20e. Here, a potential difference is provided between the first bias of the first voltage application unit 55 and the second bias of the second voltage application unit 56, and the first voltage application unit 55 and the second voltage application unit 56 are applied. As a result, only the toner of the magnetic brush is supplied from the rotating sleeve 21e to the developing sleeve 20e. The magnetic brush that has not been supplied to the developing sleeve 20e is not carried on the rotating sleeve 21e by the recovery magnetic pole 21f2 as the rotating sleeve 21e rotates in the direction of arrow C, and is returned to the first stirring member 44 side.

  Then, the toner carried on the developing sleeve 20e is transported to the developing region D by the developing sleeve 20e rotating in the direction of arrow B. Here, when the second bias of the second voltage application unit 56 is applied, the toner carried on the developing sleeve 20e is exposed to light by the potential difference between the potential of the second bias and the potential of the exposed portion of the photoconductor 11. Fly to the body 11. As the photoconductor 11 rotates in the direction of arrow A, the flying toner sequentially adheres to the exposed portion on the photoconductor 11 and the electrostatic latent image on the photoconductor 11 is developed. The toner that has not been used for development on the developing roller 20 is peeled off from the surface of the developing sleeve 20e by the binding force of the magnetic brush formed in the vicinity of the position E and collected on the surface of the rotating sleeve 21e of the magnetic roller 21. .

The magnetic carrier used in the developing device 2 having the above-described configuration is configured such that its saturation magnetization is in the range of 30 to 50 e mu / g.

The saturation magnetization of the magnetic carrier affects the decrease in carrier resistance when image formation is repeated. Above this range, the magnetization characteristics of the carrier become too large, and the fog phenomenon caused by replenishment of new toner. Will occur. Further, even when a carrier having a small decrease in carrier resistance due to repeated use is used, if the saturation magnetization exceeds the upper limit, the deterioration of the toner proceeds, resulting in a decrease in density. On the other hand, below the above range, the magnetization characteristic of the carrier becomes too small, and the carrier becomes difficult to be held on the magnetic roller 21 and moves onto the photosensitive member 11, whereby carrier development in which white spots and black spots due to the carrier appear in the image. Will occur. By using a magnetic carrier having a saturation magnetization in the range of 30 to 50 e mu / g, a good image in which fogging phenomenon, density reduction and carrier development are suppressed can be obtained.

  Further, the magnetic force of the regulation magnetic pole 21f1 is configured to be in the range of 30 to 50 mT.

  The magnetic force of the regulating magnetic pole 21f1 affects the decrease in carrier resistance when image formation is repeated. If the magnetic field exceeds the above range, the magnetic force of the regulating magnetic pole 21f1 becomes too large, and fogging due to replenishment of new toner occurs. As the phenomenon occurs, the density decreases. On the other hand, below the above range, it is difficult to manufacture a magnet for the regulation magnetic pole 21f1 having a stable magnetic force. When the magnetic force of the regulating magnetic pole 21f1 is 30 to 50 mT, a good image in which fogging phenomenon and density reduction are suppressed is obtained, and the regulating magnetic pole 21f1 is easy to manufacture.

  The magnetic force of the main magnetic pole 21f3 is in the range of 45 to 70 mT, and the developing magnetic pole 20f is different in polarity from the main magnetic pole 21f3 and has a small magnetic force.

  In the developing method using the developing roller and the magnetic roller, the density of the carrier increases at the position E where the magnetic roller 21 and the developing roller 20 face each other. Therefore, the deterioration of the carrier due to repeated image formation is likely to proceed. When the magnetic force of the main magnetic pole 21f3 exceeds the above range, the change in the carrier resistance increases due to repeated use, and a fogging phenomenon occurs due to the replenishment of new toner. On the other hand, in the above developing method, carrier development is less likely to occur than in a developing method using only a developing roller, so that the magnetic force of the main magnetic pole 21f3 can be lowered, but the magnetic force of the main magnetic pole 21f3 is below a predetermined range. When the value is lowered, carrier development occurs remarkably. When the magnetic force of the main magnetic pole 21f3 is in the range of 45 to 70 mT and the developing magnetic pole 20f is different in polarity from the main magnetic pole 21f3 and has a small magnetic force, the magnetic brush at the facing position E has an appropriate restraining force. Thus, a good image in which the fog phenomenon and the carrier development are suppressed can be obtained.

Further, in the present embodiment, in a state of applying an electric field of 5 ^{5 V} / m in the carrier, the initial carrier resistance of the image formed with R0, the rollers due to the rotation of the rotating sleeve 21e (magnetic roller 21) associated with the image forming Carry resistance change R0 / R ≦ 50, where R is the carrier resistance when the surface travel distance is 165 km.

  When the roller surface travel distance of the magnetic roller 21 due to repeated image formation is 165 km, if the carrier resistance change R0 / R with respect to the initial stage of image formation exceeds the above range, the carrier resistance due to repeated image formation becomes too small. The toner is deteriorated due to the deterioration of the charging ability of the carrier, the adhesion of the carrier component to the toner, the deterioration due to the repeated movement of the toner between the magnetic roller 21 and the developing roller 20, and the like. A fogging phenomenon occurs when new toner is replenished. When the carrier resistance change R0 / R is 50 or less, a good image in which the fog phenomenon is suppressed can be obtained over a long period of time.

(Second Embodiment)
FIG. 3 is a cross-sectional view schematically showing the two-component developing type developing apparatus 2 according to the second embodiment of the present invention. The developing device 2 includes a developing roller 20, a stirring unit 42, a regulating member 24, a developing container 22, and the like.

  The developing container 22 constitutes the outline of the developing device 2 and partitions the first transport path 22d and the second transport path 22c by a partition portion 22b protruding from the lower part thereof. A two-component developer containing toner and a magnetic carrier is accommodated in the first conveyance path 22d and the second conveyance path 22c. Further, the developing container 22 rotatably holds the first stirring member 44, the second stirring member 43, and the developing roller 20. In addition, a regulating member 24 facing the surface of the developing roller 20 is attached to the developing container 22.

  The first stirring member 44 is provided in the first transport path 22d. The second stirring member 43 is provided in the second transport path 22 c adjacent to the right side of the first stirring member 23.

  The first and second stirring members 44 and 43 stir the developer to charge the toner in the developer to a predetermined level. Thus, the toner is held on the magnetic carrier. In addition, communication portions (not shown) are provided on both ends in the longitudinal direction (front and back direction of the paper surface of FIG. 3) of the partition 22b that partitions the first transport path 22d and the second transport path 22c. 2 When the agitating member 43 rotates, the charged developer is transported into the first transport path 22d from one communicating portion provided in the partition member 22b, and circulates in the first transport path 22d and the second transport path 22c. To do. Then, the developer is supplied from the first stirring member 44 to the developing roller 20.

  The developing roller 20 is disposed facing the upper left of the first stirring member 44, and supports the developer supplied from the first stirring member 44 as a magnetic brush on the surface, and the magnetic roller in the magnetic brush supported on the surface. Only toner is supplied to the photoreceptor 11. A regulating member 24 is disposed to face the peripheral surface of the developing roller 20.

  The regulating member 24 is formed in a plate shape with a magnetic material such as stainless steel, and is fixedly held in the developing container 22 above the developing roller 20. The tip of the regulating member 24 faces the surface of the developing roller 20 with a predetermined interval, and regulates the layer thickness of the magnetic brush carried on the surface of the developing roller 20.

  The developing roller 20 includes a developing sleeve 20h and a fixed magnet 20m.

  The fixed magnet 20m is non-rotatably supported by the developing container 22 via a roller shaft, is composed of a plurality of magnets having different polarities on the outer peripheral portion, and has a regulation magnetic pole 20n. The restricting magnetic pole 20n is disposed to face the restricting member 24, and magnetizes the tip of the restricting member 24 with a polarity opposite to that of the restricting magnetic pole 20n. A thin layer of a magnetic brush is formed on the surface of the developing roller 20 by a magnetic field formed between the tip of the regulating member 24 and the surface of the developing roller 20.

  The developing sleeve 20h is disposed at a predetermined interval from the fixed magnet 20m, thereby carrying the developer as a magnetic brush on the surface of the developing sleeve 20h. The developing sleeve 20h is rotatably supported by the developing container 22, and conveys the magnetic brush by being rotated in the direction of an arrow by a driving mechanism including a motor and a gear (not shown). Further, the developing sleeve 20 h faces the photoconductor 11, is arranged on the right side of the photoconductor 11 with a certain interval, and develops to supply toner to the photoconductor 11 at a facing position close to the photoconductor 11. Region D is formed. Further, a developing bias is applied to the developing sleeve 20h by a second voltage applying unit 56 that is a power source in which an AC voltage 56b is superimposed on a DC voltage 56a.

  With the above configuration, the charged developer is carried on the surface of the developing sleeve 20h by forming a magnetic brush by the magnetic force of the fixed magnet 20m, and the developing brush 20h rotates in the direction of the arrow, whereby the magnetic brush is conveyed. This magnetic brush is adjusted to a predetermined layer thickness by the regulating member 24 and the regulating magnetic pole 20n. Then, the magnetic brush having a predetermined layer thickness is conveyed to the developing region D by the rotation of the developing sleeve 20h. Here, when the developing bias of the second voltage application unit 56 is applied, the toner of the magnetic brush carried on the developing sleeve 20 h is caused by the potential difference between the potential of the developing bias and the potential of the exposed portion of the photoconductor 11. Supplied to the photoreceptor 11. As the photoconductor 11 rotates, the supplied toner sequentially adheres to the exposed portion on the photoconductor 11 and the electrostatic latent image on the photoconductor 11 is developed. The developer containing toner that has not been used for development on the developing roller 20 is returned to the first stirring member 44 side as the developing sleeve 20 h rotates in the direction of the arrow.

The magnetic carrier used in the developing device 2 having the above-described configuration is configured such that its saturation magnetization is in the range of 30 to 50 e mu / g.

The saturation magnetization of the magnetic carrier affects the decrease in carrier resistance when image formation is repeated. Above this range, the magnetization characteristics of the carrier become too large, and the fog phenomenon caused by replenishment of new toner. Will occur. Further, even when a carrier having a small decrease in carrier resistance due to repeated use is used, if the saturation magnetization exceeds the upper limit, the deterioration of the toner proceeds, resulting in a decrease in density. On the other hand, below the above range, the magnetization characteristics of the carrier become too small, and it becomes difficult for the carrier to be held on the developing roller 20 and shifts onto the photoconductor 11, whereby carrier development in which white spots and black spots due to the carrier appear in the image. Will occur. By using a magnetic carrier having a saturation magnetization in the range of 30 to 50 e mu / g, a good image in which fogging phenomenon, density reduction and carrier development are suppressed can be obtained.

  Further, the magnetic force of the regulation magnetic pole 20n is configured to be in the range of 30 to 50 mT.

  When the image formation is repeated, the magnetic force of the regulating magnetic pole 20n affects the decrease in carrier resistance. If the magnetic field exceeds the above range, the magnetic force of the regulating magnetic pole 20n becomes too large, and fogging due to replenishment of new toner occurs. As the phenomenon occurs, the density decreases. On the other hand, below the above range, it is difficult to produce a magnet for the regulation magnetic pole 20n having a stable magnetic force. When the magnetic force of the regulating magnetic pole 20n is 30 to 50 mT, a good image in which fogging phenomenon and density reduction are suppressed is obtained, and the regulating magnetic pole 20n is easy to manufacture.

Further, in the state of applying an electric field of 5 ^{5 V} / m in the carrier, the initial carrier resistance of the image formed with R0, the roller surface distance traveled by the rotation of the developing sleeve 20h (developing roller 20) associated with the image formation is 75Km When the carrier resistance in the case of R is R, carry resistance change R0 / R ≦ 50.

    When the roller surface travel distance of the developing roller 20 due to repeated image formation is 75 km, if the carrier resistance change R0 / R with respect to the initial stage of image formation exceeds the above range, the carrier resistance due to repeated image formation becomes too small. The toner deteriorates due to a decrease in the charging ability of the carrier, the adhesion of the carrier component to the toner, and the like, so that the charging ability of the toner is reduced, and a fog phenomenon occurs due to replenishment of new toner. When the carrier resistance change R0 / R is 50 or less, a good image in which the fog phenomenon is suppressed can be obtained over a long period of time.

  Hereinafter, Examples 1 to 5 and Comparative Examples 1 to 7 that further embody the embodiment of the present invention will be described. In addition, this invention is not limited only to a following example.

  The developing device 1 used in Examples 1 to 3 and Comparative Examples 1 to 5 includes the configuration of the first embodiment having the developing roller 20 and the magnetic roller 21, and Examples 4, 5 and Comparative Example 6, The developing device 1 used for 7 has the configuration of the second embodiment having only the developing roller 20.

  In the developing device 1 used in Examples 1 to 3 and Comparative Examples 1 to 5, the developing sleeve 20e of the developing roller 20 has a diameter of 20 mm and a rotation speed of 700 rpm. The diameter of the rotating sleeve 21e of the magnetic roller 21 is 20 mm, and its rotation speed is 878 rpm. The gap between the photoconductor 11 and the developing roller 20 is 110 μm, the gap between the developing roller 20 and the magnetic roller 21 is 300 μm, and the gap between the regulating member 24 and the magnetic roller 21 is 0.3 mm. A developer having a toner particle diameter of 6.8 μm and a carrier particle diameter of 35 μm is used, and the toner / carrier weight ratio is 11%. The developing roller voltage (bias of the second voltage application unit 56) has a frequency of 4 KHz, Vpp 1.6 Kv, Vdc 100 v, and a duty of 40%, and the magnetic roller voltage (bias of the first voltage application unit 55) has a frequency of 4 KHz, Vpp 0.9 Kv, Vdc300v, duty 60%.

  In the developing devices 1 used in Examples 4 and 5 and Comparative Examples 6 and 7, the diameter of the developing sleeve 20h of the developing roller 20 is 20 mm, and the rotation speed is 353 rpm. The gap between the photoconductor 11 and the developing roller 20 is 300 μm, and the gap between the regulating member 24 and the developing roller 20 is 0.3 mm. A developer having a toner particle diameter of 6.8 μm and a carrier particle diameter of 35 μm is used, and the toner / carrier weight ratio is 11%. The development bias (the bias of the second voltage application unit 56) has a frequency of 10 KHz, Vpp 1.2 Kv, Vdc 300 v, and a duty of 50%.

  The carriers of Examples 1, 3, 4 and Comparative Examples 2, 3, 4, 6 were prepared by adding 10 parts by mass of polyamideimide resin to 1000 parts by mass of carrier core material (ferrite particles, weight average particle diameter 35 μm, saturation magnetization 40 emu / g). Covered. In the carriers of Examples 2 and 5, 1000 parts by mass of carrier core material (ferrite particles, weight average particle diameter 35 μm, saturation magnetization 40 emu / g) was coated with 10 parts by mass of melamine resin. In the carriers of Comparative Examples 1 and 7, 1000 parts by mass of carrier core material (ferrite particles, weight average particle diameter 35 μm, saturation magnetization 55 emu / g) was coated with 10 parts by mass of polyamideimide resin. The carrier of Comparative Example 5 was obtained by coating 1000 parts by mass of carrier core material (ferrite particles, weight average particle diameter 35 μm, saturation magnetization 55 emu / g) with 10 parts by mass of melamine resin.

  The carrier should have a resin coating on the surface of the core, and it must be coated so that the carrier core is not exposed on the surface. As the coating resin, in addition to polyamideimide resin and melamine resin, fluorine resin such as PTFE and PFA, silicon resin, acrylic resin, and combinations of these resins can be used. In order to reduce the carrier resistance change, it is preferable to use a resin having a high pencil hardness (3H or more). When the resistance change of the carrier becomes large, the ability to charge the toner decreases due to the exposure of the carrier core, and the charging ability of the toner decreases due to the carrier component moving to the toner side. When new toner is replenished in such a state, the deteriorated toner is charged to a reverse polarity, and replenishment fogging (fogging phenomenon associated with replenishment of new toner) occurs.

Table 1 shows the configuration of the carrier and the configuration of each magnetic pole such as the magnetic pole member 21f and the regulating magnetic pole 20n in the examples and comparative examples.

  The saturation magnetic pole of the carrier shown in Table 1 has a variation of about 10 emu / g in the production of the core due to the firing of the core, for example, in the range of 40 ± 5 emu / g in Example 1 and the like.

Moreover, the carrier resistance of Table 1 is the result measured by the bridge method shown in FIG. FIG. 4 is a diagram showing measurement of carrier resistance using a bridge type electrical resistance measuring instrument 100 and a super insulation meter (SM-5E type, manufactured by Toa Denpa Kogyo Co., Ltd.) 109. This measurement method measures the static resistance in a state where carrier particles are chained in a magnetic field, and approximates a magnetic brush, and measures the electric resistance of the carrier as a value that is not affected by development conditions. it can. On the upper surface of the acrylic resin substrate 108, copper electrode plates 101 and 102 are fixed in parallel with a gap of 2 mm. 1000 gauss magnets 103 and 104 are disposed on the back side of the electrode plates 101 and 102, respectively, to form a magnetic field between the electrode plates 101 and 102. When 0.2 g of the carrier sample 107 is set between the electrode plates 101 and 102, it is filled in a state having a chain structure as shown in FIG. The carrier electrical resistance value 10 seconds after the application of a 1000 V DC voltage (electric field 5 ⁵ V / m) between the terminals is read by the superinsulator 109. From the read value, the volume resistivity (unit: Ωcm) was obtained from the area (3 cm ² ) of the magnets 103 and 104 and the distance (2 mm) between the electrodes, and used as carrier resistance. The carrier resistance in Table 1 is R0 as the initial carrier resistance of image formation.

The endurance test that repeats image formation is in the case of the developing method using the developing roller 20 and the magnetic roller 21 at a printing rate of 5% and a magnetic brush amount of 20 to 40 mg / cm ² at 23 ° C. and 50% temperature and humidity. The carrier resistance is bridged every 10k (8.5Km), 50k (42.4Km), 100k (84.8Km), 200k (169.7Km), and 500k (424.1Km) sheets. And the amount of reversely charged toner was measured. The numerical value in parentheses is a value obtained by converting each number of printed sheets into the roller surface travel distance (unit: Km) by the rotation of the rotary sleeve 21e. In the case of the developing method using only the developing roller 20, the carrier resistance is measured by the bridge method every 10k (7.9Km), 50k (39.6Km), and 100k (79.2Km) printed sheets, and the reverse charging is performed. The amount of toner was measured. The numerical value in parentheses is a value obtained by converting the number of printed sheets to the roller surface travel distance (unit: Km) by the rotation of the developing sleeve 20e.

  The reversely charged toner amount was measured by a charge amount measuring device 110 shown in FIG. The charge amount measuring device 110 adds rotational vibration energy to the developer by rotation of a magnet roller 113 built in the sleeve 112, and generates a flying electric field by a DC power source applied between the sleeve 112 and the electrode 111, thereby generating a sleeve. The carrier is scattered from the developer on 112 to the electrode 111 side, and the scattered toner is measured as a reversely charged toner amount. While holding 1 g of developer on the sleeve 112 and setting the gap between the sleeve 112 and the electrode to 5 mm, the magnet roller 113 having a magnetic force of 100 mT is rotated at 300 rpm, and the bias power supply 115 is applied to −3 Kv for 30 seconds, The amount of toner scattered on the electrode 111 was measured.

  Based on the above measurement results, the change R0 / R of the carrier resistance R after each endurance with respect to the initial carrier resistance R0 and the reversely charged toner amount (unit: g) are shown in the table below. Tables 2 and 3 show the carrier resistance change and the reversely charged toner amount of the developing method using the developing roller 20 and the magnetic roller 21, and Tables 4 and 5 show the carrier resistance change and the reverse of the developing method using only the developing roller 20. Indicates the amount of charged toner.

表２の比較例４は、ローラー表面走行距離が８．５Ｋｍを超えるとキャリア現像が発生し耐久試験を中止した。また、比較例５は、ローラー表面走行距離が８．５Ｋｍを超えると濃度低下が発生し耐久試験を中止した。

In Comparative Example 4 in Table 2, when the roller surface travel distance exceeded 8.5 km, carrier development occurred and the durability test was stopped. Further, in Comparative Example 5, when the roller surface travel distance exceeded 8.5 km, the concentration decreased and the durability test was stopped.

  FIG. 6 is a graph plotting the relationship between the carrier resistance change R0 / R and the reverse charge amount at the roller surface travel distances in Tables 2 to 5 above. The horizontal axis of the graph in FIG. 6 represents the carrier resistance change R0 / R, and the vertical axis represents the charged toner amount (unit: g). As shown in FIG. 6, when the carrier resistance change R0 / R increases, the charge of the deteriorated toner decreases due to reasons such as a decrease in carrier charging ability, adhesion of carrier components to the toner, and promotion of deterioration due to reciprocating movement of the toner. Reversely charged toner is likely to be generated. When the carrier resistance change R0 / R exceeds the value 50 (the position of the broken line in FIG. 6), the amount of reversely charged toner exceeds a certain amount, so that replenishment fogging occurs on the blank paper portion of the image. Further, as shown in Comparative Examples 1 and 7, when the saturation magnetization exceeds 50 emu / g, replenishment fog is likely to occur. Further, as shown in Comparative Examples 2 and 6, replenishment fog is likely to occur when the regulation magnetic pole exceeds 50 mT. In the developing method using the developing roller 20 and the magnetic roller 21, when the roller surface running distance is 165 km as shown in Examples 1 to 3, a good image is obtained, and only the developing roller 20 is obtained. In the developing method using No. 4, in the predetermined numerical range as shown in Examples 4 and 5, a good image was obtained even when the roller surface travel distance was 75 km.

  INDUSTRIAL APPLICABILITY The present invention can be used for a developing device mounted on an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine thereof, and an image forming apparatus including the same, and particularly includes a toner and a magnetic carrier. The present invention can be used for a developing device using a two-component developer and an image forming apparatus having the developing device.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2a-2d, 2 Developing apparatus 11a-11d, 11 Photoconductor (image carrier)
20a to 20d, 20 developing roller 20e, 20h developing sleeve 20f developing magnetic pole 20m fixed magnet 20n, 21f1 regulating magnetic pole 21a to 21d, 21 magnetic roller 21e rotating sleeve 21f magnetic pole member 21f2 recovery magnetic pole 21f3 main magnetic pole 22 developing container 42 stirring section 55 first 1 voltage application unit 55a DC voltage 55b AC voltage 56 second voltage application unit 56a DC voltage 56b AC voltage 100 bridge type electric resistance measuring device 101, 102 electrode plate 103, 104 magnet 107 carrier sample 108 substrate 109 super insulation meter 110 charge amount Measuring device 111 Electrode 112 Sleeve 113 Magnet roller 115 Bias power supply

Claims (2)

A developing device that develops an electrostatic latent image formed on the surface of an image carrier into a toner image,
A magnetic roller carrying a two-component developer containing toner and a magnetic carrier on the surface as a magnetic brush;
A regulating member made of a magnetic material that regulates the magnetic brush carried on the surface of the magnetic roller to a predetermined layer thickness;
A developing roller disposed opposite to each of the image carrier and the magnetic roller, carrying a toner in a magnetic brush carried on the magnetic roller on a surface, and supplying the carried toner to the image carrier; ,
A regulating magnetic pole disposed opposite to the regulating member on the inner circumferential side of the magnetic roller;
A main magnetic pole disposed on the inner peripheral side of the magnetic roller opposite to the developing magnetic pole provided on the inner peripheral side of the developing roller,
The saturation magnetization of the magnetic carrier is 30-50 e mu / g,
The magnetic force of the regulation magnetic pole is 30-50 mT,
The magnetic force of the main magnetic pole is 45 to 70 mT,
The developing magnetic pole is different in polarity from the main magnetic pole and has a small magnetic force,
The carrier when the initial carrier resistance of image formation is R0 and the roller surface travel distance by rotation of the magnetic roller during image formation is 165 Km in a state where an electric field of 5 ⁵ V / m is applied to the magnetic carrier. When the resistance is R,
R0 / R ≦ 50
A developing device characterized by the above. An image forming apparatus comprising the developing device according to claim 1 .

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