Developing device and image forming apparatus

Abstract

To provide a developing device that can prevent bending of a developer conveying member, improve the accuracy of detecting toner concentration, and achieve high-quality image formation.SOLUTION: A developing device 40 comprises: a developer container 41; a first conveying member 42; a second conveying member 43; a developing roller 44; and a toner concentration sensor 46. The toner concentration sensor 46 is arranged on a wall part of a first conveying chamber 412 in which the first conveying member 42 is arranged. The first conveying member 42 and the second conveying member 43 have the same outer diameter and shaft diameter, and the outer diameter is 2.3 times or more and 3.0 time or less of the shaft diameter. When D defines the shaft diameter of the first conveying member 42, L the axial length of the first conveying member 42, and K the distance from a downstream end in a first direction f1 of the first conveying chamber 412 to the position of the center 46c of a detection surface of the toner concentration sensor 46, the following formula (1) is satisfied. (1) 500<(L2×K) / D4<2500.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a developing device and an image forming apparatus including the same.

Background Art

[0002] In electrophotographic image forming apparatuses such as copiers and printers, a device that forms a toner image to be later transferred onto paper by supplying toner to an electrostatic latent image formed on the surface of an image carrier such as a photoreceptor drum is widely used. In order to continuously form a uniform image, the developing device conveys a developer containing toner accommodated in a developing container while stirring the developer in the developing container.

[0003] A conventional developing device disclosed in Patent Document 1 includes a stirring shaft to which spiral stirring blades are fixed, a first stirring member and a second stirring member arranged in parallel with each other, and a developer carrier arranged in parallel close to the second stirring member. Further, the diameter of the stirring shaft of the first stirring member is different from the diameter of the stirring shaft of the second stirring member. Thereby, the difference in the amount of the developer between the upstream side and the downstream side of the second stirring member is alleviated, and a circulation balance of the developer is achieved, and it is possible to avoid the problem that the developer does not adhere to the developer carrier due to an insufficient amount of the developer.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, if the stirring shaft is made thinner as in the prior art, there is a concern that the stirring member becomes easily deflected and unevenness is likely to occur in the amount of the developer conveyed in the axial direction. As a result, the density of the image becomes unstable, and the problem is that the image quality deteriorates.

[0006] Further, when the arrangement of the sensor for detecting the toner concentration in the developing device is inappropriate, there is a risk of affecting the deflection of the stirring member or detecting the toner concentration for the developer that is not sufficiently stirred. As a result, there was a concern that variations in detection accuracy would occur.

[0007] The present invention has been made in view of the above points, and an object thereof is to provide a developing device and an image forming device capable of suppressing the deflection of the conveyance member of the developer, improving the detection accuracy of the toner concentration, and realizing high-quality image formation.

Means for Solving the Problems

[0008] To solve the above problems, the developing device of the present invention includes a developing container, a first conveying member, a second conveying member, a developer supply port, a toner concentration sensor, and a developer carrier. The developing container has a first conveying chamber and a second conveying chamber that are arranged in parallel with each other and communicate with each other at both longitudinal ends, and accommodates a two-component developer containing toner and a carrier. The first conveying member is rotatably arranged in the first conveying chamber and conveys the developer while stirring it in a first direction in the longitudinal direction in the first conveying chamber. The second conveying member is rotatably arranged in the second conveying chamber and conveys the developer while stirring it in a second direction that is opposite to the first direction in the longitudinal direction in the second conveying chamber. The developer supply port is formed in a wall portion on the upstream side in the first direction of the first conveying chamber, and the developer is supplied into the first conveying chamber. The toner concentration sensor is arranged on a wall portion along the first direction of the first conveying chamber and detects the toner concentration in the developer. The developer carrier is rotatably supported by the developing container and carries the developer in the second conveying chamber. The first conveying member and the second conveying member have a rotating shaft extending along the longitudinal direction of the developing container and conveying blades formed on the outer peripheral portion of the rotating shaft, and their outer diameters and shaft diameters are the same, and the outer diameter is 2.3 times or more and 3.0 times or less the shaft diameter. The toner concentration sensor is a headless sensor whose detection surface is buried in the inner wall surface of the first conveying chamber. The center of the detection surface of the toner concentration sensor is on the downstream side in the first direction from the center in the longitudinal direction of the first conveying chamber and is located in a region within a length of 1 / 4 of the total length in the longitudinal direction of the first conveying chamber. When the shaft diameter of the first conveying member is D, the shaft length of the first conveying member is L, and the distance from the downstream end in the first direction of the first conveying chamber to the center position of the detection surface of the toner concentration sensor is K, the following formula (1) is satisfied. 500 < (L 2 × K) / D 4 <2500 ···(1)

Advantages of the Invention

[0009] According to the configuration of the present invention, the structural relationship between the outer diameter, shaft diameter, and shaft length of the developer conveyance member and the arrangement of the toner density sensor can be appropriately defined. As a result, the deflection of the developer conveyance member can be suppressed, and the detection accuracy of the toner density can be improved. Therefore, it becomes possible to realize high-quality image formation.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the following content.

[0012] FIG. 1 is a schematic vertical cross-sectional front view of an image forming apparatus 1 according to an embodiment. FIG. 2 is a schematic vertical cross-sectional front view around an image forming section 20 of the image forming apparatus 1 of FIG. 1. As an example of the image forming apparatus 1 of the present embodiment, it is a tandem type color printer that transfers a toner image to a sheet S using an intermediate transfer belt 31. The image forming apparatus 1 may be a so-called multifunction machine having functions such as printing, scanning (image reading), and facsimile transmission.

[0013] As shown in FIGS. 1 and 2, the image forming apparatus 1 includes a paper feeding section 3, a paper conveyance section 4, an exposure section 5, an image forming section 20, a transfer section 30, a fixing section 6, a paper discharge section 7, and a control section 8 provided in its main body 2.

[0014] The paper feeding unit 3 is disposed at the bottom of the main body 2. The paper feeding unit 3 stores a plurality of sheets of paper S, and separates and feeds out the sheets of paper S one by one during printing. The paper conveyance unit 4 conveys the sheet of paper S fed out from the paper feeding unit 3 to the secondary transfer unit 33 and the fixing unit 6, and further discharges the sheet of paper S after fixing from the paper discharge port 4a to the paper discharging unit 7. When double-sided printing is performed, the paper conveyance unit 4 distributes the sheet of paper S after fixing on the first side to the reverse conveyance unit 4c by the branching unit 4b, and conveys the sheet of paper S to the secondary transfer unit 33 and the fixing unit 6 again. The exposure unit 5 irradiates laser light controlled based on image data toward the image forming unit 20.

[0015] The image forming unit 20 is disposed below the intermediate transfer belt 31. The image forming unit 20 includes an image forming unit 20Y for yellow, an image forming unit 20C for cyan, an image forming unit 20M for magenta, and an image forming unit 20B for black. These four image forming units 20 have the same basic configuration. Accordingly, in the following description, the identification symbols "Y", "C", "M", and "B" representing each color may be omitted unless particularly limited.

[0016] The image forming unit 20 includes a photosensitive drum (image carrier) 21 rotatably supported in a predetermined direction (clockwise in FIGS. 1 and 2). The image forming unit 20 further includes a charging unit 22 disposed along the rotation direction around the photosensitive drum 21, a developing device 40, and a drum cleaning unit 23. Note that a primary transfer unit 32 is disposed between the developing device 40 and the drum cleaning unit 23.

[0017] The photosensitive drum 21 is formed in a cylindrical shape extending in the horizontal direction and has a photosensitive layer on its outer peripheral surface. The charging unit 22 charges the surface of the photosensitive drum 21 to a predetermined potential. The exposure unit 5 exposes the surface of the photosensitive drum 21 charged by the charging unit 22 to form an electrostatic latent image of the original image. The developing device 40 supplies toner to this electrostatic latent image for development to form a toner image. Each of the four image forming units 20 forms a toner image of a different color. The drum cleaning unit 23 removes and cleans toner and the like remaining on the surface of the photosensitive drum 21 after the toner image is primarily transferred to the surface of the intermediate transfer belt 31. In this way, the image forming unit 20 forms an image on the paper S.

[0018] The transfer unit 30 includes an intermediate transfer belt 31, primary transfer units 32Y, 32C, 32M, 32B, a secondary transfer unit 33, and a belt cleaning unit 34. The intermediate transfer belt 31 is disposed above the four image forming units 20. The intermediate transfer belt 31 is rotatably supported in a predetermined direction (counterclockwise in FIG. 1). The intermediate transfer belt 31 is an intermediate transfer member on which the toner images formed on the surface of the photosensitive drum 21 by each of the four image forming units 20 are sequentially superimposed and primarily transferred. The four image forming units 20 are arranged in a so-called tandem manner in a row from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 31.

[0019] The primary transfer units 32Y, 32C, 32M, 32B are disposed above the respective color image forming units 20Y, 20C, 20M, 20B with the intermediate transfer belt 31 interposed therebetween. The secondary transfer unit 33 is disposed on the upstream side in the paper conveyance direction of the fixing unit 6 of the paper conveyance unit 4 and on the downstream side in the rotation direction of the intermediate transfer belt 31 of the transfer unit 30 with respect to the respective color image forming units 20Y, 20C, 20M, 20B. The belt cleaning unit 34 is disposed on the upstream side in the rotation direction of the intermediate transfer belt 31 with respect to the respective color image forming units 20Y, 20C, 20M, 20B.

[0020] The toner images are primarily transferred onto the surface of the intermediate transfer belt 31 by the primary transfer units 32Y, 32C, 32M, and 32B for each color. Then, as the intermediate transfer belt 31 rotates, the toner images from the four image forming units 20 are successively and overlappedly transferred onto the intermediate transfer belt 31 at a predetermined timing. As a result, a color toner image in which the toner images of yellow, cyan, magenta, and black are overlapped is formed on the surface of the intermediate transfer belt 31.

[0021] The color toner image on the surface of the intermediate transfer belt 31 is transferred onto the sheet S that has been fed in synchronization by the sheet conveyance unit 4 at the secondary transfer nip formed in the secondary transfer unit 33. The belt cleaning unit 34 removes and cleans the toner and the like remaining on the surface of the intermediate transfer belt 31 after secondary transfer.

[0022] The fixing unit 6 is disposed above the secondary transfer unit 33. The fixing unit 6 heats and presses the sheet S onto which the toner image has been transferred to fix the toner image onto the sheet S.

[0023] The sheet discharge unit 7 is disposed above the transfer unit 30. The sheet S on which the toner image has been fixed and the printing has been completed is conveyed to the sheet discharge unit 7.

[0024] The control unit 8 includes a CPU, an image processing unit, a storage unit, and other electronic circuits and electronic components (all not shown). The CPU controls the operations of the respective components provided in the image forming apparatus 1 based on the control programs and data stored in the storage unit, and performs processes related to the functions of the image forming apparatus 1. Each of the paper feeding unit 3, the sheet conveyance unit 4, the exposure unit 5, the image forming unit 20, the transfer unit 30, and the fixing unit 6 receives individual commands from the control unit 8 and cooperates to perform printing on the sheet S. The storage unit is composed of a combination of a non-volatile storage device such as a program ROM (Read Only Memory) and a data ROM, and a volatile storage device such as a RAM (Random Access Memory).

[0025] Next, the configuration of the developing device 40 will be described with reference to FIG. 3 in addition to FIG. 2. FIG. 3 is a horizontal cross-sectional plan view of the developing device 40 of the image forming unit 20 in FIG. 2. Since the basic configurations of the developing devices 40 for each color are the same, the description and the identification symbols representing each color for the components are omitted. Also, in this description, the "axial direction" represents the axial direction of rotation of each of the photosensitive drum 21, the first conveying member 42, the second conveying member 43, and the developing roller 44 that extend parallel to each other (the depth direction of the paper surface in FIG. 2, the left-right horizontal direction in FIG. 3), and coincides with the width direction orthogonal to the conveying direction of the paper S.

[0026] The developing device 40 supplies toner to the surface of the photosensitive drum 21. The developing device 40 includes a developing container 41, a first conveying member 42, a second conveying member 43, a developing roller (developer carrier) 44, a regulating member 45, and a toner concentration sensor 46.

[0027] The developing container 41 has an elongated shape extending along the axial direction of the photosensitive drum 21 and is arranged with its longitudinal direction horizontal. That is, the longitudinal direction of the developing container 41 is parallel to the axial direction of the photosensitive drum 21. The developing container 41 accommodates, as a developer containing toner to be supplied to the photosensitive drum 21, for example, a two-component developer containing toner and a magnetic carrier.

[0028] The developing container 41 has a partition portion 411, a first conveying chamber 412, a second conveying chamber 413, a first communication portion 414, a second communication portion 415, and a developer supply portion 416.

[0029] The partition portion 411 is provided at the lower part inside the developing container 41. The partition portion 411 is disposed at a substantially central portion in the direction intersecting the longitudinal direction of the developing container 41 (the left-right horizontal direction in FIG. 2, the up-down direction in FIG. 3). The partition portion 411 is formed in a substantially plate shape extending in the longitudinal direction and the up-down direction of the developing container 41. The partition portion 411 divides the inside of the developing container 41 in the direction intersecting the longitudinal direction.

[0030] The first transfer chamber 412 and the second transfer chamber 413 are provided inside the developing container 41. The first transfer chamber 412 and the second transfer chamber 413 are formed by partitioning the inside of the developing container 41 by the partition portion 411. The first transfer chamber 412 and the second transfer chamber 413 are arranged in parallel at substantially the same height.

[0031] The second transfer chamber 413 is arranged adjacent to the arrangement region of the developing roller 44 inside the developing container 41. The first transfer chamber 412 is arranged in a region inside the developing container 41 that is farther from the developing roller 44 than the second transfer chamber 413. A developer supply unit 416 having a developer supply port 416a is connected to the upstream side in the first direction f1 of the first transfer chamber 412 described later. The developer supply port 416a is formed in the wall portion of the developer supply unit 416 on the upstream side in the first direction f1 of the first transfer chamber 412, and the developer is supplied into the first transfer chamber 412.

[0032] The first communication portion 414 and the second communication portion 415 are respectively arranged outside both ends in the longitudinal direction of the partition portion 411. The first communication portion 414 and the second communication portion 415 communicate the first transfer chamber 412 and the second transfer chamber 413 in a direction intersecting the longitudinal direction of the partition portion 411 (the left - right horizontal direction in FIG. 2, the up - down direction in FIG. 3), that is, in the thickness direction of the partition portion 411 having a substantially plate shape. In other words, through the first communication portion 414 and the second communication portion 415, the first transfer chamber 412 and the second transfer chamber 413 communicate with each other on both ends in the longitudinal direction.

[0033] The first transfer member 42 is arranged inside the first transfer chamber 412. The second transfer member 43 is arranged inside the second transfer chamber 413. The second transfer member 43 extends in parallel close to the developing roller 44. The first transfer member 42 and the second transfer member 43 are rotatably supported by the developing container 41 around an axis extending horizontally in parallel with the developing roller 44. The basic configurations of the first transfer member 42 and the second transfer member 43 are the same.

[0034] The first conveying member 42 has a rotating shaft 42a extending along the longitudinal direction of the developing container 41, and spiral conveying blades 42b formed on the outer peripheral portion of the rotating shaft 42a. The second conveying member 43 has a rotating shaft 43a extending along the longitudinal direction of the developing container 41, and spiral conveying blades 43b formed on the outer peripheral portion of the rotating shaft 43a.

[0035] In the first conveying chamber 412, the first conveying member 42 conveys the developer while stirring it in a first direction f1 from the first communication portion 414 side toward the second communication portion 415 side along the axial direction of rotation. In the second conveying chamber 413, the second conveying member 43 conveys the developer while stirring it in a second direction f2 from the second communication portion 415 side toward the first communication portion 414 side along the axial direction of rotation. The second direction f2 is opposite to the first direction f1.

[0036] The first communication portion 414 communicates the downstream end in the second direction f2 of the second conveying chamber 413 with the upstream end in the first direction f1 of the first conveying chamber 412. The developer is conveyed from the second conveying chamber 413 side toward the first conveying chamber 412 side through the first communication portion 414. The second communication portion 415 communicates the downstream end in the first direction f1 of the first conveying chamber 412 with the upstream end in the second direction f2 of the second conveying chamber 413. The developer is conveyed from the first conveying chamber 412 side toward the second conveying chamber 413 side through the second communication portion 415. Note that the white arrows including the first direction f1 and the second direction f2 shown in FIG. 3 represent the conveying direction of the developer.

[0037] The developing roller 44 is disposed above the second conveying chamber 413 in the developing container 41. A part of the surface of the developing roller 44 is exposed from the developing container 41 and faces the photosensitive drum 21. The developing roller 44 is rotatably supported by the developing container 41 around an axis extending parallel to the axis of the photosensitive drum 21. The developing roller 44 carries the developer in the second conveying chamber 413. The developing roller 44 supplies the toner in the developing container 41 to the surface of the photosensitive drum 21 in the facing area with the photosensitive drum 21, and develops the electrostatic latent image to form a toner image.

[0038] The regulating member 45 is disposed on the upstream side in the rotational direction of the developing roller 44 in the facing region between the developing roller 44 and the photosensitive drum 21. The regulating member 45 faces the developing roller 44 in proximity thereto, and is disposed with a predetermined gap provided between its tip and the surface of the developing roller 44. The regulating member 45 extends over the entire axial direction of the developing roller 44. The regulating member 45 regulates the layer thickness of the developer (toner) carried on the surface of the developing roller 44 that passes through the gap between the tip of the regulating member 45 and the surface of the developing roller 44.

[0039] The toner density sensor 46 is disposed on the wall portion along the first direction in the first conveyance chamber 412. In the present embodiment, a headless sensor is used as the toner density sensor 46. The toner density sensor 46, which is a headless sensor, has its detection surface buried in the inner wall surface of the first conveyance chamber 412. The toner density sensor 46 detects the toner density in the developer.

[0040] Specifically, the toner density sensor 46 is a magnetic permeability detection type sensor that obtains the toner density (mixing ratio of toner to magnetic carrier in the developer) by detecting a change in the magnetic permeability of the two-component developer. If the ratio of toner to magnetic carrier in the developer in the first conveyance chamber 412 changes, the magnetic permeability also changes, and accordingly, the output signal of the toner density sensor 46 also changes. The control unit 8 controls the start and stop of the supply of the developer to the developing device 40 based on the output signal of the sensor received from the toner density sensor 46.

[0041] The developer in the developing container 41 circulates between the first conveyance chamber 412 and the second conveyance chamber 413 in a predetermined circulation direction through the first communication portion 414 and the second communication portion 415 by the rotation of the first conveyance member 42 and the second conveyance member 43. At this time, the toner in the developing container 41 is agitated, charged, and carried on the surface of the developing roller 44. The toner carried on the surface of the developing roller 44 has its layer thickness regulated by the regulating member 45 and is then conveyed to the opposing region between the developing roller 44 and the photosensitive drum 21 by the rotation of the developing roller 44. When a predetermined developing voltage is applied to the developing roller 44, the toner carried on the surface of the developing roller 44 moves to the surface of the photosensitive drum 21 in the opposing region due to the potential difference with the potential of the surface of the photosensitive drum 21. In this way, the electrostatic latent image on the surface of the photosensitive drum 21 is developed with toner.

[0042] Subsequently, a more detailed configuration of the developing device 40 will be described with reference to FIG. 3. Note that FIG. 3 shows the total length W1 in the longitudinal direction (paper width direction) of the first conveyance chamber 412, the length W2 that is half of the total length W1, and the length W3 that is one-fourth of the total length W1.

[0043] As described above, the first conveyance member 42 has a rotary shaft 42a and spiral conveyance vanes 42b. The second conveyance member 43 has a rotary shaft 43a and spiral conveyance vanes 43b. The first conveyance member 42 and the second conveyance member 43 have the same outer diameter (outer diameter of the conveyance vanes) and shaft diameter. Also, the first conveyance member 42 and the second conveyance member 43 are formed such that the outer diameter is 2.3 times or more and 3.0 times or less the shaft diameter.

[0044] Also, as described above, the toner density sensor 46 is a headless sensor, and the detection surface is buried in the inner wall surface of the first conveyance chamber 412. The center 46c of the detection surface of the toner density sensor 46 is on the downstream side in the first direction f1 from the center 412c in the longitudinal direction of the first conveyance chamber 412 and is located in a region within the length W3 that is one-fourth of the total length W1 in the longitudinal direction of the first conveyance chamber 412.

[0045] When the shaft diameter of the first conveying member 42 is D, the shaft length of the first conveying member 42 is L, and the distance from the downstream end of the first conveying chamber 412 in the first direction f1 to the center 46c of the detection surface of the toner density sensor 46 is K, the developing device 40 satisfies the following formula (1).

[0046] 500 < (L 2 × K) / D 4 <2500 ···(1)

[0047] Note that the shaft length L of the first conveying member 42 is the length of the first conveying member 42 between two bearings 47 that support both ends in the axial direction of the rotation shaft 42a of the first conveying member 42.

[0048] Next, the influence of the respective relationships between the outer diameter of the first conveying member 42, the shaft diameter D of the first conveying member 42, the shaft length L of the first conveying member 42, and the distance K from the downstream end of the first conveying chamber 412 in the first direction f1 to the center 46c of the detection surface of the toner density sensor 46 of the developing device 40 on the density of the image formed on the paper S was evaluated. The results are shown in Table 1. For the density of the image formed on the paper S, samples of 14 types of developing devices 40 (Examples 1 to 7, Comparative Examples 8 to 14) with different outer diameters, shaft diameters D, shaft lengths L, and distances K were prepared, and the printing rate was changed every 5 sheets in the range of 2% to 50%, and the evaluation was performed after 10,000 sheets of printing were performed.

[0049]

Table 1

[0050] Regarding the configuration and operating conditions of the image forming apparatus 1, the paper size is A4 vertical (the long side is parallel to the paper width direction), the printing speed is 45 sheets / min, the distance between the photosensitive drum 21 and the developing roller 44 is 0.340 ± 0.025 mm, and the ratio of the peripheral speed of the developing roller 44 to the peripheral speed of the photosensitive drum 21 is 1.8 (the opposing regions move in the same direction). For the developing device 40, the surface of the developing roller 44 is subjected to knurling with 80 rows of recesses in the circumferential direction, the outer diameter of the developing roller 44 is 20 mm, and the developer conveyance amount is 320 to 370 g / m 2It is as follows. The AC bias of the developing voltage is a rectangular wave, Duty = 50%, Vpp = 1360 V, and the frequency is 4 kHz. The toner has a positive chargeability, an outer diameter of 6.8 μm, and an initial concentration of 6%. The distances from the downstream end in the first direction of the first conveying member 42 to the end of the nearest partition portion 411 and from the downstream end in the second direction of the second conveying member 43 to the end of the nearest partition portion 411 are both 30 mm.

[0051] For the image density, the density value (I.D.) was measured using a fluorescence spectroscopic densitometer FD-5 manufactured by Konica Minolta, Inc., and the density followability and density variation were evaluated. For the density followability, it was determined as unacceptable if the density difference between the front end and the rear end in the paper conveyance direction of the solid image on the entire surface of the A4 paper exceeded 0.1. For the density variation, it was determined as unacceptable if the maximum and minimum density differences at six locations (the center and both end sides) in the paper width direction at the front end and the rear end in the paper conveyance direction of the solid image on the entire surface of the A4 paper exceeded 0.1. In the "Evaluation" column of Table 1, "○" was marked for those where both the density followability and the density variation were acceptable, and "×" was marked for those where either one was unacceptable.

[0052] In the developing devices 40 of Examples 1 to 7 in Table 1, the outer diameters of both the first conveying member 42 and the second conveying member 43 are 2.3 times or more and 3.0 times or less the shaft diameter, and satisfy the above formula (1). On the other hand, in the developing devices of Comparative Examples 8 to 14, none of them satisfy at least one of the conditions that the outer diameters of the first conveying member 42 and the second conveying member 43 are 2.3 times or more and 3.0 times or less the shaft diameter and the above formula (1).

[0053] According to Table 1, it can be seen that in the developing devices 40 of Examples 1 to 7, both the density followability and the density variation are less than 0.1, and a suitable image density is obtained. On the other hand, in the developing devices of Comparative Examples 8 to 14, it can be seen that one of the density followability and the density variation exceeds 0.1, and a suitable image density is not obtained.

[0054] As described above, by appropriately defining the relationships among the outer diameters, shaft diameters, and shaft lengths of the first transport member 42 and the second transport member 43, the deflection of the first transport member 42 and the second transport member 43 can be suppressed. Thereby, the transport performance of the developer can be stabilized, and unevenness in the amount of the developer can be suppressed. Further, the toner density sensor 46 can be made a headless sensor so as not to directly contact the developer in the developing container 41. Thereby, the toner density sensor 46 does not affect the flow of the developer and does not cause a factor that causes deflection in the first transport member 42 and the second transport member 43. Furthermore, by defining the distance K with respect to the first direction f1 of the first transport chamber 412, the toner density can be detected for the developer in a sufficiently agitated state. That is, by appropriately defining the arrangement of the toner density sensor 46, the detection accuracy of the toner density can be improved. Therefore, according to the configuration of the present embodiment, a suitable image density can be obtained, and high-quality image formation can be realized.

[0055] Next, the carrier of the developer is formed by forming a coating layer such as a silicone resin on the surface of a carrier core that is magnetic particles. The silicone-based resin can be coated in a thin film, and the uniformity of the coating layer is high. Further, when the thickness of the coating layer is thinner, the capacitance of the coating layer also becomes higher, and the effect of the ferroelectric added to the coating layer is more easily exhibited.

[0056] The shape of the carrier can be used from amorphous to spherical. Further, the average particle size of the carrier can be 20 μm or more and 65 μm or less. By setting the number average particle size of the carrier to 65 μm or less, the specific surface area of the carrier increases, and the amount of toner that the carrier can carry increases. As a result, the toner concentration in the magnetic brush can be maintained at a high level, and the toner supply to the developing roller 44 is sufficiently performed, so that the thickness of the toner layer can be sufficiently ensured. As a result, a sufficient amount of toner can be ensured to fly from the toner layer to the electrostatic latent image on the photoreceptor, the decrease in image density can be suppressed, and further, the density unevenness of the image can be suppressed. Further, since the toner supply to the developing roller 44 is sufficiently performed, it becomes difficult to form a toner missing portion in the toner layer of the developing roller 44, and the occurrence of history development can be suppressed.

[0057] When the average particle size of the carrier is less than 20 μm, carrier development in which the carrier adheres to the photoreceptor drum 21 occurs. The carrier adhering to the photoreceptor drum 21 migrates to the intermediate transfer belt 31, causing transfer omission or moving to the belt cleaning unit 34 and causing poor cleaning. Further, when the average particle size of the carrier is larger than 65 μm, when moving the toner in the two-component developer from the developing roller 44 to the photoreceptor drum 21, the magnetic brush of the two-component developer becomes rough and the image quality deteriorates.

[0058] Examples of the carrier core include magnetic metal such as iron, nickel, and cobalt, alloys thereof, or alloys containing rare earths, soft ferrites such as hematite, magnetite, manganese-zinc ferrite, nickel-zinc ferrite, manganese-magnesium ferrite, and lithium ferrite, iron-based oxides such as copper-zinc ferrite, and mixtures thereof. The carrier core is manufactured by a known method such as a sintering method or an atomizing method. Among the above, ferrite carriers are preferably used from the viewpoints of high image quality and long life because they have good fluidity and are chemically stable.

[0059] Barium titanate particles are added to the coat layer as a ferroelectric material. Examples of the production method of barium titanate include the hydrothermal polymerization method and the oxalate method. However, barium titanate has different physical properties depending on the production method. Among them, barium titanate produced by the hydrothermal polymerization method has a small true specific gravity due to having voids inside, and the particle size distribution also becomes sharp. As a result, compared with those produced by other methods, the dispersibility in the coating resin is good, and uniform dispersion is possible. Therefore, it is suitable for use in this embodiment because the charging performance of the carrier is also made uniform.

[0060] The volume average particle size of barium titanate is preferably 100 nm or more and 500 nm or less. When the particle size of barium titanate becomes smaller than 100 nm, the relative permittivity of barium titanate decreases rapidly, so the effect on the relative permittivity becomes small. On the other hand, when the particle size of barium titanate becomes 500 nm or more, it becomes difficult to achieve uniform dispersion in the coat layer.

[0061] When 5 parts by mass or more of barium titanate is added based on the coat weight, the effect of stabilizing the charge amount starts to appear, and when 25 parts by mass or more is added, the effect of stabilizing the charge amount becomes more prominent. However, if the addition amount of barium titanate is too large, it cannot be completely contained in the coat layer and will separate from the coat layer. If the separated barium titanate moves to the photoreceptor drum 21 and gets caught in the edge part of the cleaning blade of the drum cleaning part 23, it will cause poor cleaning. In particular, in the method of mixing the carrier with the toner in the toner container (not shown) and supplying it to the developing device 40, the barium titanate separated through use is supplied to the developing device 40, increasing the load on the cleaning blade. Therefore, the addition amount of barium titanate is preferably 5 parts by mass or more and 45 parts by mass or less.

[0062] Carbon black is added to the coating layer as a conductor. If the amount of carbon black added is too large, the carbon black released from the coating layer adheres to the toner, causing color turbidity of the toner other than black. On the other hand, if the amount of carbon black added is too small, it is difficult for the charge to move from the carrier to the toner, and the increase in the toner charge amount cannot be smoothly achieved. In the carrier of this embodiment, since the carrier resistance is reduced by adding barium titanate (a ferroelectric) to the coating layer, it is possible to reduce the amount of carbon black added by the amount corresponding to the reduction in the carrier resistance.

[0063] By adding a ferroelectric (barium titanate) to the coating layer, the charge holding ability of the carrier is enhanced, making it possible to impart sufficient charge to the toner. Also, by adding a conductor (carbon black) to the coating layer, the charge transfer from the carrier to the toner can be smoothly performed. Due to these two synergistic effects, even when the toner concentration increases and the number of toner particles to be charged increases, it is possible to impart charge up to the saturation charge amount level of the toner particles.

[0064] The carrier of this embodiment is designed to satisfy the following formula (2) by adjusting the addition amounts of the ferroelectric and the conductive agent to the coating layer, and by adjusting the particle diameter and the coating film thickness.

[0065] 0.73 ≦ FR × AD / Shape factor ≦ 2.10 ···(2)

[0066] Thereby, the toner chargeability is stabilized, and a state with less image fogging can be maintained over a long period.

[0067] The "shape factor" in formula (2) is a coefficient representing the particle shape and is defined by the following formula (3).

[0068] Shape factor = Measured carrier volume average particle diameter / Carrier particle diameter calculated from the BET specific surface area ···(3) However, Carrier particle diameter calculated from BET specific surface area = 6 / (BET specific surface area × true specific gravity) is as follows.

[0069] If the shape factor becomes too large, the shape factor is likely to change due to scraping of the coating layer during durable printing, etc., resulting in poor durability stability. On the other hand, if the shape factor is too small, the toner chargeability will decrease. Therefore, there is an appropriate range for the shape factor.

[0070] The BET specific surface area is the specific surface area measured by the BET method (nitrogen adsorption specific surface area method). Specifically, it is obtained from the adsorption amount of liquid nitrogen adsorbed on the surface of the carrier. More specifically, for example, using an automatic specific surface area measuring device Macsorb (registered trademark) model 1208 manufactured by Mountech Co., Ltd., etc., nitrogen is adsorbed on the sample surface, and the BET specific surface area of the sample [m 2 / g] can be measured.

[0071] "FR × AD" in formula (2) is an index representing the fluidity of the carrier. If the fluidity of the carrier is too high, the miscibility with the toner will decrease and the toner chargeability will decrease. On the other hand, if the fluidity of the carrier is too low, the conveyance speed of the developer in the developing container 41 will decrease, and when high-printing-rate images are continuous, the image density will decrease. Therefore, there is an appropriate range for the fluidity of the carrier.

[0072] "FR" is the carrier fluidity, which is a value [s / 50g] representing the time for discharging 50 g of the carrier. Since the discharge amount of the carrier is more consistent with the actual behavior when considered by volume rather than by weight, in this embodiment, "FR × AD" corrected by the bulk specific gravity AD [g / cm 3 of the carrier is used as the index of the fluidity of the carrier.

[0073] "FR" can be measured in accordance with "JIS (Japanese Industrial Standard) Z2502". Specifically, prepare a metal funnel (conical angle: 60 degrees, orifice diameter: 2.5 mm, orifice length: 3.2 mm). With the orifice of the funnel blocked, put 50 g of the sample (carrier) into the funnel. Subsequently, start measuring the time using a stopwatch simultaneously when the orifice of the funnel is opened, and end the measurement at the moment when the last carrier leaves the orifice. The measured time (passing time) corresponds to "FR". "AD" can be measured in accordance with "Test Method for Apparent Density of Metal Powders, JIS-Z2504".

[0074] Since the charge amount fluctuation is suppressed by the carrier satisfying the above formula (2), it is possible to suppress the fluctuation of the image density and stabilize the density control. Therefore, a suitable image density can be obtained, and high-quality image formation can be realized.

[0075] As described above, the embodiments of the present invention have been explained, but the scope of the present invention is not limited thereto, and various modifications can be made and implemented without departing from the gist of the invention.

[0076] For example, in the above embodiment, the image forming apparatus 1 is a so-called tandem type image forming apparatus for color printing that sequentially forms images of a plurality of colors. However, it is not necessarily limited to such a model. The image forming apparatus may be an image forming apparatus for color printing that is not of the tandem type or an image forming apparatus for monochrome printing.

Industrial Applicability

[0077] The present invention can be used in a developing device and an image forming device.

Explanation of Reference Numerals

[0078] 1 Image forming apparatus 8 Control unit 20 Image forming unit 21 Photoconductor drum (image carrier) 30 Transfer unit 40 Developing device 41 Developing container 42 First conveying member 42a Rotation axis 42b Conveying blade 43 Second conveying member 43a Rotation axis 43b Conveying blade 44 Developing roller (developer carrier) 46 Toner density sensor 46c Center 411 Partition section 412 First conveying chamber 412c Center 413 Second conveying chamber 416a Developer supply port D Shaft diameter K Distance L Shaft length S Paper f1 First direction f2 Second direction

Claims

1. A developing container having a first transport chamber and a second transport chamber that are arranged in parallel with each other and communicate with each other on both longitudinal ends, and accommodating a two-component developer containing toner and carrier as a developer; A first transport member rotatably disposed in the first transport chamber and transporting the developer while stirring the developer in a first direction in the longitudinal direction in the first transport chamber; A second transport member rotatably disposed in the second transport chamber and transporting the developer while stirring the developer in a second direction that is opposite to the first direction in the longitudinal direction in the second transport chamber; A developer supply port formed in a wall portion on the upstream side in the first direction of the first transport chamber, through which the developer is supplied into the first transport chamber; A toner concentration sensor disposed on a wall portion along the first direction of the first transport chamber for detecting the toner concentration in the developer; A developer carrier rotatably supported by the developing container and carrying the developer in the second transport chamber; Comprising: The first transport member and the second transport member have a rotation axis extending along the longitudinal direction of the developing container and transport vanes formed on the outer peripheral portion of the rotation axis, and have the same outer diameter and shaft diameter, and the outer diameter is 2.3 times or more and 3.0 times or less the shaft diameter; The toner concentration sensor is a headless sensor in which a detection surface is buried in the inner wall surface of the first transport chamber; The center of the detection surface of the toner concentration sensor is on the downstream side in the first direction from the center in the longitudinal direction of the first transport chamber and is located in a region within a length of 1 / 4 of the total length in the longitudinal direction of the first transport chamber; When the shaft diameter of the first transport member is D, the shaft length of the first transport member is L, and the distance from the downstream end in the first direction of the first transport chamber to the center position of the detection surface of the toner concentration sensor is K, the following formula (1) is satisfied; 500 < (L 2 × K) / D 4 < 2500...(1) The carrier is formed by forming a resin coat layer on the surface of a carrier core that is a magnetic particle, and is characterized by satisfying the following formula (2). A developing device. 0.73 ≦ FR × AD / shape factor ≦ 2.10... (2) However, FR: The time [s / 50g] when 50 g of carrier is discharged; AD: Apparent specific gravity of the carrier [g / cm3]; Shape factor: Carrier particle diameter calculated from the actually measured carrier volume average particle diameter / BET specific surface area.

2. An image carrier; The image forming apparatus according to claim 1, further comprising a developing device that develops an electrostatic latent image formed on the surface of the image carrier with the toner to form a toner image. Characterized by comprising.

Images