Developing device and image forming apparatus including the same

Abstract

To provide a developing device that can accurately detect the concentration of toner in two-component developer and can prevent the occurrence of image fogging caused by oversupply of toner, an image forming apparatus including the same.SOLUTION: A developing device comprises: a developer container; a first stirring and conveying member; a second stirring and conveying member; a developer carrier; a toner concentration sensor; and a scraper. The first stirring and conveying member has a rotation shaft that is rotatably supported in the developer container, a first conveying blade that is formed on an outer peripheral surface of the rotation shaft and conveys developer in a first direction by the rotation of the rotation shaft, and a second conveying blade that is formed on the outer peripheral surface of the rotation shaft to overlap a formation area of the first conveying blade, has an opposite phase to the first conveying blade, and has a lower radial height than the first conveying blade. The scraper is arranged at a position different in an axial direction from the intersection of the first conveying blade and the second conveying blade and substantially in parallel to the rotation shaft. The phase of the scraper is 45°-135° with respect to the intersection located on the immediate upstream side in the first direction.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a developing device used in an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine using an electrophotographic method, and an image forming apparatus including the same, and more particularly, to a developing device using a two-component developer including toner and a carrier, and an image forming apparatus including the same.

Background Art

[0002] In an image forming apparatus, a latent image formed on an image carrier such as a photosensitive drum is developed by a developing device and visualized as a toner image. As one such developing device, a two-component developing method using a two-component developer is adopted. This type of developing device accommodates a two-component developer (hereinafter also simply referred to as a developer) composed of a carrier and toner in a developing container, disposes a developing roller for supplying the developer to the image carrier, and disposes a stirring and conveying member for supplying the developer inside the developing container to the developing roller while stirring and conveying the developer.

[0003] In a two-component developing type developing device, in order to replenish the toner consumed by development, it is necessary to measure the toner concentration in the developer by a toner concentration sensor disposed in the developing container. For example, a developing device has been proposed in which a toner concentration sensor is disposed on the side of the circulation path of the developer that supplies the developer to the developing roller, and a toner supply unit is provided on the side that does not supply the developer to the developing roller. According to this configuration, since the replenished toner reaches the toner concentration sensor after being sufficiently stirred with the developer in the developing container, and the toner concentration of the developer in the portion supplied to the developing roller can be directly detected, the toner supply accuracy can be further improved.

[0004] And, in order to maintain the detection sensitivity of the toner concentration sensor, a method is known in which a scraper for cleaning the sensor surface (detection surface) is attached to a portion of the stirring and conveying member facing the toner concentration sensor.

[0005] For example, Patent Document 1 discloses a stirring and conveying member including a main conveying blade (first spiral blade) that conveys a developer in a first direction on one side in the axial direction as the shaft member rotates, and a sub-conveying blade (second spiral blade) that causes a conveying action of a part of the developer in a second direction on the other side in the axial direction as the shaft member rotates. According to this configuration, convection occurs in a part of the conveyed developer by the sub-conveying blade, and the stirring action is promoted without substantially inhibiting the conveying action of the main spiral blade.

[0006] However, when a scraper is provided on the stirring and conveying member, the developer may be compressed at the scraper portion, the carrier density may increase, and the toner concentration may be detected lower than the actual value. In this case, the amount of toner replenished to the developing device may become excessive, and there is a risk that the toner concentration may become too high and image fogging may occur. In particular, when using a stirring and conveying member including a main conveying blade and a sub-conveying blade as shown in Patent Document 1, the compression of the developer at the scraper portion becomes remarkable.

[0007] Therefore, Patent Document 2 discloses a developing device in which a missing region where the second spiral blade (sub-conveying blade) is missing is formed between one pitch of the first spiral blade (main conveying blade) facing the toner concentration sensor, and a scraper mounting portion is formed so as to extend into the missing region along a straight line parallel to the rotation axis passing through the intersection of the first spiral blade and the second spiral blade.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] In the configuration of Patent Document 2, since a scraper is arranged at the intersection of the first spiral blade and the second spiral blade, the phase of the scraper coincides with the intersection. At the intersection of the first spiral blade and the second spiral blade, convection of the developer is likely to occur and the developer density is likely to increase. Therefore, there has been a problem that the developer is compressed and the carrier density increases, easily leading to misdetection of the toner concentration and image fogging caused by excessive supply of toner resulting therefrom.

[0010] In view of the above problems, an object of the present invention is to provide a developing device that can accurately detect the toner concentration in a two-component developer and suppress the occurrence of image fogging caused by excessive supply of toner, and an image forming apparatus including the same.

Means for Solving the Problems

[0011] In order to achieve the above object, a first configuration of the present invention is a developing device including a developing container, a first stirring and conveying member, a second stirring and conveying member, a developer carrier, a toner density sensor, and a scraper. The developing container includes a plurality of conveying chambers including a first conveying chamber and a second conveying chamber arranged in parallel with each other, a partition wall partitioning the first conveying chamber and the second conveying chamber along the longitudinal direction, and a communication portion communicating the first conveying chamber and the second conveying chamber on both end sides of the partition wall, and accommodates a two-component developer including a carrier and toner. The first stirring and conveying member stirs and conveys the developer in the first conveying chamber in a first direction. The second stirring and conveying member stirs and conveys the developer in the second conveying chamber in a second direction opposite to the first direction. The developer carrier is rotatably supported by the developing container and supports the developer in the second conveying chamber on its surface. The toner density sensor is disposed on the inner wall surface of the first conveying chamber and detects the toner density in the developer. The scraper is attached to the first stirring and conveying member and moves the developer in the vicinity of the toner density sensor by rotating together with the first stirring and conveying member. The first stirring and conveying member includes a rotating shaft rotatably supported in the developing container, a first conveying blade formed on the outer peripheral surface of the rotating shaft and conveying the developer in the first direction by the rotation of the rotating shaft, and a second conveying blade formed on the outer peripheral surface of the rotating shaft so as to overlap the formation region of the first conveying blade, having a phase opposite to that of the first conveying blade and a lower radial height than the first conveying blade. The scraper is disposed substantially parallel to the rotating shaft at a position axially different from the intersection of the first conveying blade and the second conveying blade, and the phase of the scraper is 45° to 135° with respect to the intersection located closest to the upstream side in the first direction.

Advantages of the Invention

[0012] According to the first configuration of the present invention, since there is no intersection of the first conveying blade and the second conveying blade at the portion where the scraper is provided, an increase in the developer density due to the convection of the developer can be suppressed. As a result, an increase in the carrier density due to the compression of the developer is also suppressed, so that the detection result of the toner density sensor can be made closer to the actual toner density. Therefore, false detection of the toner density and occurrence of image fog due to excessive toner supply can be effectively suppressed.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the internal structure of an image forming apparatus 100 according to an embodiment of the present invention. Inside the image forming apparatus 100 (here, a color printer), four image forming units Pa, Pb, Pc, and Pd are arranged in order from the upstream side in the conveyance direction (left side in FIG. 1). These image forming units Pa to Pd are provided corresponding to images of four different colors (yellow, cyan, magenta, and black), and yellow, cyan, magenta, and black images are sequentially formed by respective steps of charging, exposure, development, and transfer.

[0015] In these image forming units Pa to Pd, photosensitive drums (image carriers) 1a, 1b, 1c, and 1d that carry visible images (toner images) of respective colors are disposed. Further, an intermediate transfer belt (intermediate transfer member) 8 that rotates in the counterclockwise direction in FIG. 1 by a belt driving motor (not shown) is provided adjacent to each of the image forming units Pa to Pd. The toner images formed on these photosensitive drums 1a to 1d are sequentially primary transferred and superimposed onto the intermediate transfer belt 8 that moves while contacting each of the photosensitive drums 1a to 1d. Thereafter, the toner image primary transferred onto the intermediate transfer belt 8 is secondary transferred onto transfer paper P as an example of a recording medium by a secondary transfer roller 9. Further, after the toner image is fixed in the fixing unit 13, the transfer paper P onto which the toner image has been secondary transferred is discharged from the main body of the image forming apparatus 100. While rotating the photosensitive drums 1a to 1d in the clockwise direction in FIG. 1, an image forming process for each of the photosensitive drums 1a to 1d is executed.

[0016] The transfer paper P onto which the toner image is secondary transferred is housed in a paper cassette 16 disposed at the lower part of the main body of the image forming apparatus 100, and is conveyed to the nip portion between the secondary transfer roller 9 and the driving roller 11 of the intermediate transfer belt 8 via a paper feed roller 12a and a registration roller pair 12b. A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a seamless belt having no seam is mainly used. Further, a blade-shaped belt cleaner 19 for removing toner and the like remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9.

[0017] Next, the image forming units Pa to Pd will be described. Around and below the photosensitive drums 1a to 1d rotatably disposed, charging devices 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d, an exposure device 5 for exposing image information onto each of the photosensitive drums 1a to 1d, developing devices 3a, 3b, 3c, and 3d for forming a toner image on the photosensitive drums 1a to 1d, and cleaning devices 7a, 7b, 7c, and 7d for removing the developer (toner) and the like remaining on the photosensitive drums 1a to 1d are provided.

[0018] When image data is input from a host device such as a personal computer, first, the charging devices 2a to 2d uniformly charge the surfaces of the photosensitive drums 1a to 1d. Next, the exposure device 5 irradiates light according to the image data, and an electrostatic latent image corresponding to the image data is formed on each of the photosensitive drums 1a to 1d. The developing devices 3a to 3d are each filled with a predetermined amount of a two-component developer containing yellow, cyan, magenta, and black toner. When the ratio of the toner in the two-component developer filled in each of the developing devices 3a to 3d falls below a specified value due to the formation of a toner image described later, toner is replenished from the toner containers 4a to 4d to each of the developing devices 3a to 3d. The toner in this developer is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and adheres electrostatically. Thereby, a toner image corresponding to the electrostatic latent image formed by the exposure from the exposure device 5 is formed.

[0019] Then, an electric field is applied at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d by the primary transfer rollers 6a to 6d, and the yellow, magenta, cyan, and black toner images on the photosensitive drums 1a to 1d are primarily transferred onto the intermediate transfer belt 8. These images are formed with a predetermined positional relationship determined in advance. Thereafter, in preparation for the formation of a new electrostatic latent image that will be performed subsequently, toner and the like remaining on the surfaces of the photosensitive drums 1a to 1d after the primary transfer are removed by the cleaning devices 7a to 7d.

[0020] The intermediate transfer belt 8 is stretched between the upstream driven roller 10 and the downstream driving roller 11. When the intermediate transfer belt 8 starts to rotate counterclockwise as the driving roller 11 rotates by a belt driving motor (not shown), the transfer paper P is conveyed to the nip portion (secondary transfer nip portion) between the driving roller 11 and the secondary transfer roller 9 provided adjacent thereto at a predetermined timing from the resist roller pair 12b, and the toner image on the intermediate transfer belt 8 is secondarily transferred onto the transfer paper P. The transfer paper P onto which the toner image has been secondarily transferred is conveyed to the fixing unit 13.

[0021] The transfer paper P conveyed to the fixing unit 13 is heated and pressed by the fixing roller pair 13a, and the toner image is fixed on the surface of the transfer paper P, forming a predetermined full-color image. The transfer paper P on which the full-color image is formed has its conveyance direction distributed by the branching unit 14 branched in a plurality of directions, and is then discharged to the discharge tray 17 by the discharge roller pair 15 as it is (or after being sent to the duplex conveyance path 18 and having images formed on both sides).

[0022] Furthermore, an image density sensor 40 is disposed at a position downstream of the image forming unit 1d and facing the intermediate transfer belt 8. As the image density sensor 40, an optical sensor including a light emitting element generally composed of an LED or the like and a light receiving element composed of a photodiode or the like is used. When measuring the toner adhesion amount on the intermediate transfer belt 8, when the measuring light is irradiated from the light emitting element to each reference image formed on the intermediate transfer belt 8, the measuring light enters the light receiving element as the light reflected by the toner and the light reflected by the belt surface.

[0023] The reflected light from the toner and the belt surface includes specularly reflected light and diffusely reflected light. After being separated by a polarization separation prism, the specularly reflected light and the diffusely reflected light enter different light receiving elements respectively. Each light receiving element photoelectrically converts the received specularly reflected light and diffusely reflected light and outputs an output signal to a control unit (not shown). Then, the toner amount is detected from the characteristic changes of the output signals of the specularly reflected light and the diffusely reflected light, and density correction (calibration) is performed by comparing with a predetermined reference density and adjusting characteristic values such as the developing voltage.

[0024] FIG. 2 is a side cross-sectional view of the developing device 3a mounted on the image forming apparatus 100. In the following description, the developing device 3a disposed in the image forming unit Pa of FIG. 1 is exemplified. However, since the configurations of the developing devices 3b to 3d disposed in the image forming units Pb to Pd are basically the same, the description thereof is omitted.

[0025] As shown in FIG. 2, the developing device 3a includes a developing container 20 that stores a two-component developer (hereinafter simply referred to as a developer) containing a magnetic carrier and toner. The developing container 20 is partitioned into a stirring and conveying chamber 21 and a supply and conveying chamber 22 by a partition wall 20a. In the stirring and conveying chamber 21 and the supply and conveying chamber 22, a stirring and conveying screw 25 and a supply and conveying screw 26 for mixing, stirring, and charging the toner supplied from the toner container 4a (see FIG. 1) with the magnetic carrier are rotatably disposed respectively. In this embodiment, a positively charged toner and a two-component developer composed of a ferrite-resin coated carrier are used. Details of the toner and the carrier will be described later.

[0026] Then, the developer is stirred by the stirring and conveying screw 25 and the supply and conveying screw 26 and conveyed in the axial direction (a direction perpendicular to the plane of FIG. 2), and circulates between the stirring and conveying chamber 21 and the supply and conveying chamber 22 through a developer passage (not shown) formed at both ends of the partition wall 20a. That is, a circulation path for the developer is formed in the developing container 20 by the stirring and conveying chamber 21, the supply and conveying chamber 22, and the developer passage.

[0027] The developing container 20 extends obliquely upward to the right in FIG. 2, and a developing roller 30 is disposed obliquely upward to the right of the supply and conveying screw 26 in the developing container 20. A part of the outer peripheral surface of the developing roller 30 is exposed from the opening 20b of the developing container 20 and faces the photosensitive drum 1a at a predetermined interval (developing gap). The developing roller 30 rotates in the counterclockwise direction in FIG. 2 (trailing rotation at the position facing the photosensitive drum 1a).

[0028] The developing roller 30 is composed of a cylindrical developing sleeve that rotates in the counterclockwise direction in Fig. 2, and a magnet (not shown) having a plurality of magnetic poles fixed inside the developing sleeve. Here, a developing sleeve with a knurled surface is used, but those with a large number of concave shapes (dimples) formed on the surface, those with a blasted surface, those with both knurling and concave shape formation and blasting, or those with plating can also be used. A developing voltage composed of a DC voltage Vdc and an AC voltage Vac is applied to the developing roller 30 by a developing voltage power source (not shown).

[0029] Also, a regulating blade 27 is attached to the developing container 20 along the longitudinal direction of the developing roller 30 (the direction perpendicular to the plane of Fig. 2). A slight gap is formed between the tip of the regulating blade 27 and the surface of the developing roller 30. In this embodiment, a magnetic blade made of stainless steel (SUS430) is used as the regulating blade 27.

[0030] A toner density sensor 29 is arranged on the side surface of the stirring and conveying chamber 21 opposite to the stirring and conveying screw 25. The toner density sensor 29 detects the toner density in the developer in the developing container 20 (the mixing ratio of toner to carrier in the developer; T / C). As the toner density sensor 29, for example, a permeability sensor that detects the permeability of a two-component developer composed of toner and magnetic carrier in the developing container 20 is used. The toner in the toner container 4a (see Fig. 1) is replenished into the developing container 20 together with the carrier via the developer replenishing port 22g (see Fig. 3) according to the toner density detected by the toner density sensor 29.

[0031] Next, the configuration of the stirring section of the developing device 3a will be described in detail. Fig. 3 is a plan sectional view showing the stirring section of the developing device 3a (a sectional view taken along the arrow AA' in Fig. 2).

[0032] As described above, the developing container 20 is formed with a stirring and conveying chamber 21, a supply and conveying chamber 22, a partition wall 20a, an upstream communication portion 20e, and a downstream communication portion 20f. In addition, a developer supply port 20g, a developer discharge portion 20h, an upstream side wall portion 20i, and a downstream side wall portion 20j are formed. In the stirring and conveying chamber 21, the left side in FIG. 3 is the upstream side, and the right side in FIG. 3 is the downstream side. In the supply and conveying chamber 22, the right side in FIG. 3 is the upstream side, and the left side in FIG. 3 is the downstream side. Therefore, the communication portion and the side wall portion are referred to as upstream and downstream with reference to the supply and conveying chamber 22.

[0033] The partition wall 20a extends in the longitudinal direction of the developing container 20 and partitions the stirring and conveying chamber 21 and the supply and conveying chamber 22 in parallel. The right end portion in the longitudinal direction of the partition wall 20a forms the upstream communication portion 20e together with the inner wall portion of the upstream side wall portion 20i. On the other hand, the left end portion in the longitudinal direction of the partition wall 20a forms the downstream communication portion 20f together with the inner wall portion of the downstream side wall portion 20j. The developer sequentially passes through the stirring and conveying chamber 21, the upstream communication portion 20e, the supply and conveying chamber 22, and the downstream communication portion 20f and circulates inside the developing container 20.

[0034] The developer supply port 20g is an opening for supplying new toner and carrier into the developing container 20 from a toner container 4a (see FIG. 1) provided at the upper part of the developing container 20, and is arranged on the upstream side (the left side in FIG. 3) of the stirring and conveying chamber 21.

[0035] The developer discharge portion 20h is a portion for discharging the surplus developer in the stirring and conveying chamber 21 and the supply and conveying chamber 22 due to the supply of the developer, and is continuously provided in the longitudinal direction of the supply and conveying chamber 22 on the downstream side of the supply and conveying chamber 22.

[0036] The stirring and conveying screw 25 has a rotating shaft 25a, a first conveying blade 25b formed in a spiral shape with a constant pitch in the axial direction of the rotating shaft 25a, and a second conveying blade 25c that is wound in the opposite direction (opposite phase) to the first conveying blade 25b with the same pitch as the first conveying blade 25b in the axial direction of the rotating shaft 25a. Further, the first conveying blade 25b and the second conveying blade 25c extend to both end portions on the longitudinal direction side of the stirring and conveying chamber 21, and are also provided to face the upstream and downstream communication portions 20e and 20f. The rotating shaft 25a is rotatably supported by the upstream side wall portion 20i and the downstream side wall portion 20j of the developing container 20. Note that the first conveying blade 25b and the second conveying blade 25c are integrally molded with the rotating shaft 25a by a synthetic resin.

[0037] The supply and conveying screw 26 has a rotating shaft 26a, a first conveying blade 26b formed in a spiral shape with a constant pitch in the axial direction of the rotating shaft 26a, and a second conveying blade 26c that is wound in the opposite direction (opposite phase) to the first conveying blade 26b with the same pitch as the first conveying blade 26b in the axial direction of the rotating shaft 26a. The first conveying blade 26b has the same pitch as the first conveying blade 25b of the stirring and conveying screw 25 and is wound in the opposite direction (opposite phase) to the first conveying blade 25b. Further, the first conveying blade 26b and the second conveying blade 26c have a length equal to or greater than the axial length of the developing roller 30, and furthermore, they extend to a position facing the upstream communication portion 20e. The rotating shaft 26a is arranged in parallel with the rotating shaft 25a and is rotatably supported by the upstream side wall portion 20i and the downstream side wall portion 20j of the developing container 20. And the first conveying blade 26b and the second conveying blade 26c are formed so as to intersect at two intersection points 31 spaced 180° apart during one rotation of the rotating shaft 26a.

[0038] Further, on the rotating shaft 26a of the supply and conveying screw 26, a regulating portion 52, a discharge blade 53, and a disk 55 are integrally formed together with the first conveying blade 26b and the second conveying blade 26c. Furthermore, a scraper 41 is attached to a portion of the stirring and conveying screw 25 that faces the toner density sensor 29. The scraper 41 is fixed to a scraper attachment portion (not shown) integrally formed with the rotating shaft 25a. The detailed configuration of the scraper 41 will be described later.

[0039] The regulating unit 52 blocks the developer conveyed downstream in the supply and conveyance chamber 22 and conveys the developer that has reached a predetermined amount or more to the developer discharge unit 20h. The regulating unit 52 is composed of a spiral blade that rotates in the reverse direction (reverse phase) to the first conveyance blade 26b provided on the rotary shaft 26a, has an outer diameter substantially the same as that of the first conveyance blade 26b, and a pitch smaller than that of the first conveyance blade 26b. Also, a predetermined gap is formed between the inner wall portion of the developing container 20 such as the downstream side wall portion 20j and the outer peripheral portion of the regulating unit 52. Excess developer is discharged to the developer discharge unit 20h through this gap.

[0040] The rotary shaft 26a extends into the developer discharge unit 20h. A discharge blade 53 is provided on the rotary shaft 26a within the developer discharge unit 20h. The discharge blade 53 is composed of a spiral blade that rotates in the same direction (in-phase) as the first conveyance blade 26b, but has a smaller pitch and outer diameter than the first conveyance blade 26b. Therefore, when the rotary shaft 26a rotates, the discharge blade 53 also rotates, and the excess developer conveyed into the developer discharge unit 20h over the regulating unit 52 is sent to the left side in FIG. 3 and discharged to the outside of the developing container 20 from a developer discharge port (not shown).

[0041] Gears 61 to 64 are disposed on the outer wall of the developing container 20. The gears 61 and 62 are fixed to the rotary shaft 25a, the gear 64 is fixed to the rotary shaft 26a, and the gear 63 is rotatably held by the developing container 20 and meshes with the gears 62 and 64.

[0042] When the gear 61 rotates by the development drive motor (not shown), the agitation conveyance screw 25 rotates. The developer in the agitation conveyance chamber 21 is conveyed in the main conveyance direction (the first direction, the direction of arrow P) by the first conveyance blade 25b, and then is conveyed into the supply conveyance chamber 22 through the upstream communication part 20e. Further, when the supply conveyance screw 26 rotates via the gears 62 to 64, the developer in the supply conveyance chamber 22 is conveyed in the main conveyance direction (the second direction, the direction of arrow Q) by the second conveyance blade 26b. During development without newly supplying the developer, the developer is conveyed from the agitation conveyance chamber 21 into the supply conveyance chamber 22 through the upstream communication part 20e while greatly varying its bulk, and is conveyed into the agitation conveyance chamber 21 through the downstream communication part 20f without overcoming the restricting part 52.

[0043] In this way, the developer circulates from the agitation conveyance chamber 21 through the upstream communication part 20e, the supply conveyance chamber 22, and the downstream communication part 20f while being agitated, and the agitated developer is supplied to the development roller 30.

[0044] Next, the case where the developer is supplied from the developer supply port 20g will be described. When the toner is consumed by development, the developer containing the toner and the carrier is supplied from the container 4a into the agitation conveyance chamber 21 through the developer supply port 20g.

[0045] The supplied developer is conveyed in the main conveyance direction (the direction of arrow P) in the agitation conveyance chamber 21 by the agitation conveyance screw 25 in the same manner as during development, and then is conveyed into the supply conveyance chamber 22 through the upstream communication part 20e. Further, by the supply conveyance screw 26, the developer is conveyed in the main conveyance direction (the direction of arrow Q) the developer in the supply conveyance chamber 22. When the restricting part 52 rotates with the rotation of the rotary shaft 26a, a conveyance force in the direction opposite to the main conveyance direction (the reverse conveyance direction) is applied to the developer by the restricting part 52. The developer is blocked by the restricting part 52 and becomes bulky, and the surplus developer (the same amount as the developer supplied from the developer supply port 20g) overcomes the restricting part 52 and is discharged to the outside of the developing container 20 through the developer discharge part 20h.

[0046] The conveying force of the developer conveyed in the main conveying direction (the direction of arrow Q) by the second conveying blade 26b is blocked by the disk 55 and weakened once. Then, a reverse conveying force is applied to the developer by the restricting portion 52 to push the developer back in the direction opposite to the main conveying direction. That is, the disk 55 serves to reduce the conveying force (pressure) of the developer from the supply conveying chamber 22 toward the restricting portion 52. As a result, the undulation (fluctuation) of the developer surface moving to the restricting portion 52 and the downstream communication portion 20f is suppressed, and a substantially constant amount of the developer can be retained near the restricting portion 52 regardless of the conveying speed of the developer.

[0047] Then, when the developer is replenished from the developer replenishing port 20g and the bulk of the developer in the developing container 20 increases, the developer staying upstream of the restricting portion 52 gets over the disk 55 and the restricting portion 52 and moves to the discharge blade 53 (developer discharge portion 20h), and the surplus developer is discharged from the developer discharge portion 20h. When the discharge of the developer from the developer discharge portion 20h stops, the bulk of the developer in the developing container 20 becomes stable. The volume of the developer when the bulk becomes stable is defined as the stable volume.

[0048] According to the stirring and conveying screw 25 configured as described above, the first conveying blade 25b is provided on the outer peripheral surface of the rotating shaft 25a, and the first conveying blade 25b conveys the developer while stirring it in the first direction (the direction of arrow P in FIG. 3) by the rotation of the rotating shaft 25a. Further, on the outer peripheral surface of the rotating shaft 25a, a second conveying blade 25c having a reverse phase to the first conveying blade 25b and a smaller diameter than the first conveying blade 25b is provided between the pitches of the first conveying blades 25b (between the blades). The second conveying blade 25c causes the developer to have a conveying action in the second direction (the direction of arrow Q) opposite to the first direction by the rotation of the rotating shaft 25a.

[0049] Also, according to the supply and conveyance screw 26 configured as described above, a first conveyance blade 26b is provided on the outer peripheral surface of the rotation shaft 26a. The first conveyance blade 26b conveys the developer in the second direction (the direction of arrow Q in FIG. 3) while stirring it by the rotation of the rotation shaft 26a. Further, on the outer peripheral surface of the rotation shaft 26a, a second conveyance blade 26c is provided between the pitches of the first conveyance blades 26b (between the blades), which has a reverse phase to the first conveyance blade 26b and a smaller diameter than the first conveyance blade 26b. The second conveyance blade 26c causes a conveyance action in the first direction (the direction of arrow P), which is the direction opposite to the second direction, on the developer by the rotation of the rotation shaft 26a.

[0050] Since the second conveyance blades 25c and 26c are located inward of the outer peripheral edges of the first conveyance blades 25b and 26b in the radial direction, the conveyance action in the second direction caused by the rotation of the second conveyance blades 25c and 26c occurs on a part of the developer existing near the rotation shafts 25a and 26a. Therefore, it does not inhibit the conveyance actions in the first and second directions by the first conveyance blades 25b and 26b.

[0051] In this way, by using the second conveyance blades 25c and 26c to cause a conveyance action in the direction opposite to the conveyance direction (main conveyance direction) of the developer by the first conveyance blades 25b and 26b, convection of the developer occurs between the pitches of the first conveyance blades 25b and 26b, and stirring of the developer between the first conveyance blades 25b and 26b is promoted without inhibiting the powder (developer) conveyance action of the first conveyance blades 25b and 26b. Therefore, the newly supplied toner and carrier from the developer supply port 20g can be quickly and sufficiently stirred with the two-component developer in the agitation conveyance chamber 21 and the supply conveyance chamber 22, and a decrease in the developer conveyance speed in the agitation conveyance chamber 21 and the supply conveyance chamber 22 can be effectively prevented.

[0052] FIG. 4 is a side view of the vicinity of the scraper 41 of the stirring and conveying screw 25 used in the developing device 3a of the present embodiment, and FIG. 5 is a cross-sectional view (a cross-sectional view taken along the arrow BB' in FIG. 4) of the vicinity of the scraper 41 of the stirring and conveying screw 25 used in the developing device 3a of the present embodiment, which is cut in the radial direction. As shown in FIGS. 4 and 5, the scraper 41 is formed at a position that does not overlap the intersection 31 of the first conveying blade 25b and the second conveying blade 25c in the axial direction. More specifically, the scraper 41 is attached substantially parallel to the rotation axis 25a at a position where the phase is shifted by approximately 90° from the intersection 31 (the position of 0° in FIG. 5) of the first conveying blade 25b and the second conveying blade 25c.

[0053] As the scraper 41 rotates with the rotation of the rotation axis 25a, the developer near the detection surface (the surface facing the stirring and conveying screw 25) of the toner density sensor 29 is moved by the tip 40a of the scraper 41, and a new developer is fed in. As the scraper 41, for example, a fiber sheet such as felt or non-woven fabric is laminated on the downstream side surface in the rotation direction of a base material made of a flexible film such as a PET film.

[0054] As described above, the stirring and conveying screw 25 having the first conveying blade 25b and the second conveying blade 25c has a function of dispersing the developer by the second conveying blade 25c, and the stirring of the developer is promoted. However, convection of the developer is likely to occur in the vicinity of the intersection 31 of the first conveying blade 25b and the second conveying blade 25c, and the developer is compressed and the developer density is likely to increase. Therefore, if the scraper 41 is arranged so as to overlap the intersection 31, the carrier density in the vicinity of the scraper 41 increases due to the compression of the developer, and the toner density is detected lower than the actual value by the toner density sensor 29.

[0055] Therefore, in this embodiment, the scraper 41 is disposed at a different axial position (different phase) from the intersection 31 between the first transport blade 25b and the second transport blade 25c. With this configuration, the intersection 31 does not exist where the scraper 41 is disposed, thereby suppressing an increase in developer density due to developer convection. As a result, an increase in carrier density due to developer compression is also suppressed, allowing the detection result of the toner concentration sensor 29 to approach the actual toner concentration. Therefore, the occurrence of image fogging due to excessive toner supply can be effectively suppressed. As shown in Example 1 described later, by positioning the scraper 41 at a phase of 45° to 135° with respect to the intersection 31, located immediately upstream in the developer transport direction (first direction) within the agitation / transport chamber 21, fluctuations in toner concentration can be suppressed.

[0056] Furthermore, if the scraper 41 is positioned too far from the intersection 31, a large amount of developer will flow into the vicinity of the scraper 41 through the gaps between the scraper 41 and the first and second transport blades 25b and 25c, which may reduce the accuracy of detecting the toner concentration and cause image fogging. In other words, there is an optimum range for the positional relationship (phase) between the intersection 31 and the scraper 41. As shown in the first embodiment, by positioning the scraper 41 at a phase angle of 45° to 90° relative to the intersection 31, which is located immediately upstream in the developer transport direction (arrow P direction), fluctuations in toner concentration and the occurrence of image fogging can be effectively suppressed.

[0057] Next, the location of the toner concentration sensor 29 will be described. The toner charge amount can be stabilized by uniformly dispersing the toner newly replenished from the developer supply port 20g throughout the developer in the developing container 20. By arranging the toner concentration sensor 29 and the scraper 41 at a position downstream of ¾ of the axial length of the stirring and conveying screw 25 when viewed from the upstream side of the developer conveying direction in the stirring and conveying chamber 21 (the left side in FIG. 3), the toner concentration can be detected when the replenished toner is uniformly dispersed throughout the developer in the stirring and conveying chamber 21.

[0058] On one hand, in the upstream communication part 20e, the transfer of the developer from the agitation and conveyance chamber 21 to the supply and conveyance chamber 22 causes the retention of the developer. At the location where the developer is retained, the conveying force (conveying pressure) of the developer by the agitation and conveyance screw 25 decreases, so the developer density is likely to decrease and the toner detection accuracy decreases. By arranging the toner concentration sensor 29 at least one pitch upstream of the first conveying blade 25b from the upstream communication part 20e, the toner concentration can be detected without being affected by the decrease in the conveying pressure of the developer.

[0059] That is, when viewed from the upstream side in the developer conveying direction in the agitation and conveyance chamber 21, by arranging the toner concentration sensor 29 downstream of 3 / 4 of the axial length of the agitation and conveyance screw 25 and at least 1 / 2 pitch upstream of the first conveying blade 25b from the upstream communication part 20e, the detection accuracy of the toner concentration can be improved and the toner concentration can be stabilized.

[0060] Furthermore, in this embodiment, a headless sensor is used as the toner concentration sensor 29. The headless sensor has a detection surface buried in the inner wall surface 21a of the agitation and conveyance chamber 21, and detects the toner concentration in the developer in the agitation and conveyance chamber 21 through the inner wall surface 21a.

[0061] By using a headless sensor for the toner concentration sensor 29, no step is generated between the detection surface and the inner wall surface 21a like in the conventional sensor, so the density variation of the developer at the step part is eliminated, and the detection accuracy of the toner concentration can be further improved.

[0062] Next, the two-component developer used in the developing devices 3a to 3d of the present invention will be described. The two-component developer contains toner and carrier. The toner concentration (weight ratio of toner to carrier, T / C) in the two-component developer is preferably 5 to 20 parts by mass of toner with respect to 100 parts by mass of carrier.

[0063] [Toner] As the toner, for example, a positively chargeable toner can be used. The positively chargeable toner is positively (plus) charged by friction with a carrier. The toner particles include toner mother particles and, if necessary, external additives attached to the surface of the toner mother particles. The composition of the toner mother particles is not particularly limited. Note that if not necessary, the external additives may not be added. When the external additives are not added, the toner mother particles correspond to the toner particles.

[0064] The toner mother particles contain a binder resin and a colorant. The toner mother particles may contain a release agent, a charge control agent, magnetic powder, etc. as necessary. The weight average particle diameter of the toner mother particles is preferably 5 to 12 μm, more preferably 6 to 10 μm. The weight average particle diameter of the toner mother particles is measured by a particle size distribution measuring device (for example, Multi-Sizer II type manufactured by Coulter). The toner mother particles are manufactured by known methods such as a pulverization classification method, a melt granulation method, a spray granulation method, and a polymerization method.

[0065] When adding external additives, in order to obtain a toner with excellent fluidity, it is preferable to use inorganic particles with a number average primary particle diameter of 5 nm or more and 30 nm or less. In order to obtain a toner with excellent heat-resistant storage stability by making the external additives function as spacers between the toner particles, it is preferable to use resin particles with a number average primary particle diameter of 50 nm or more and 200 nm or less as the external additive particles. Examples of the external additives include inorganic oxides such as silica, titanium oxide, and alumina, and metal soaps such as calcium stearate. In order to fully exhibit the function of the external additives while suppressing the desorption of the external additives from the toner mother particles, the addition amount of the external additives is preferably 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the toner mother particles.

[0066] The toner particles may be non-encapsulated toner particles without a shell layer, or encapsulated toner particles with a shell layer. The encapsulated toner particles include toner mother particles including a toner core and a shell layer covering the surface of the toner core. The configuration of the toner core is not particularly limited. The shell layer may consist essentially of only a thermosetting resin, may consist essentially of only a thermoplastic resin, or may contain both a thermoplastic resin and a thermosetting resin. In order to obtain a toner suitable for image formation, the volume average particle diameter (D50) of the toner mother particles is preferably 4 μm or more and 9 μm or less.

[0067] Furthermore, hydrophobic silica particles and styrene-acrylic resin fine particles are attached to the toner mother particles. The hydrophobic silica particles are a charge control agent for adjusting the charge amount of the toner. The styrene-acrylic resin fine particles are spacers for preventing the silica particles from being buried in the toner mother particles. The styrene-acrylic resin fine particles usually adhere to the carrier surface during durability and cause a decrease in the charge performance of the carrier. However, they have a weak adhesion to the silicone resin coating layer containing the ferroelectric particles described later, and the accumulation on the carrier does not continue to increase. Although the detailed principle is unknown, it is presumed that this is because the adhesion to the ferroelectric body exposed on the surface of the coating layer is small and it is easy to peel off.

[0068] [Carrier] The carrier used in the present invention is obtained by forming a coating layer such as a silicone resin on the surface of a carrier core which is a magnetic particle. The silicone-based resin can be coated in a thin film, and the uniformity of the coating layer is high. Also, the thinner the coating layer, the higher the capacitance of the coating layer, and the easier it is to exhibit the effect of the ferroelectric body added to the coating layer.

[0069] The carrier can be of any shape, from irregular to spherical. Furthermore, the average particle diameter of the carrier can be 20 μm or more and 65 μm or less. By setting the number-average particle diameter of the carrier to 65 μm or less, the specific surface area of the carrier increases, increasing the amount of toner that the carrier can carry. This allows the toner concentration in the magnetic brush to be maintained at a high level, and sufficient toner is supplied to the developing roller 31, ensuring a sufficient thickness of the toner layer. As a result, a sufficient amount of toner can be dispersed from the toner layer to the electrostatic latent image on the photoreceptor, preventing a decrease in image density and further reducing density unevenness in the image. Furthermore, sufficient toner is supplied to the developing roller 31, preventing toner voids from forming in the toner layer on the developing roller 31 and reducing the occurrence of hysteresis.

[0070] If the average particle diameter of the carrier is smaller than 20 μm, carrier development occurs in which the carrier adheres to the photosensitive drums 1a to 1d, and the adhered carrier transfers to the intermediate transfer belt 8, causing transfer defects, or moves to the belt cleaning device 19, causing cleaning defects. Also, if the average particle diameter of the carrier is larger than 65 μm, the magnetic brush of the two-component developer becomes coarse when transferring the toner in the two-component developer from the development roller 31 to the photosensitive drums 1a to 1d, resulting in reduced image quality.

[0071] Examples of carrier cores include magnetic metals such as iron, nickel, and cobalt, alloys of these metals, alloys containing rare earth elements, soft ferrites such as hematite, magnetite, manganese-zinc ferrite, nickel-zinc ferrite, manganese-magnesium ferrite, and lithium ferrite, iron oxides such as copper-zinc ferrite, and mixtures thereof. Carrier cores are produced by known methods such as sintering and atomization. Among the above, ferrite carriers are preferred from the viewpoints of high image quality and long life because of their good fluidity and chemical stability.

[0072] Barium titanate particles are added to the coating layer as a ferroelectric. 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, its dispersibility in the coating resin is better than that of those produced by other methods, and uniform dispersion is possible. Therefore, it is suitable for use in the present invention because the charging performance of the carrier is also made uniform.

[0073] 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 coating layer.

[0074] When 5 parts by mass or more of barium titanate is added based on the coating 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 coating layer and will separate from the coating layer. When the separated barium titanate moves to the photoreceptor drums 1a to 1d and gets caught in the edge part of the cleaning blade 32 of the cleaning devices 7a to 7d, it will cause cleaning failure. In particular, in the method of mixing the carrier with the toner in the toner containers 4a to 4d and supplying it to the developing devices Ia to 3d, the load on the cleaning blade 32 increases because the barium titanate separated during use is supplied to the developing devices 3a to 3d. Therefore, the addition amount of barium titanate is preferably 5 parts by mass or more and 45 parts by mass or less.

[0075] Carbon black is added to the coating layer as a conductor. If the addition amount of carbon black 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 addition amount of carbon black is too small, the transfer of charges from the carrier to the toner hardly occurs, and the increase in the toner charge amount cannot be smoothly performed. In the carrier of the present invention, since the carrier resistance is reduced by adding barium titanate (ferroelectric) to the coating layer, it is possible to reduce the addition amount of carbon black by the amount corresponding to the reduction in the carrier resistance.

[0076] By adding a ferroelectric (barium titanate) to the coating layer, the charge holding ability of the carrier is increased, and it becomes possible to impart sufficient charges to the toner. In addition, by adding a conductor (carbon black) to the coating layer, the transfer of charges 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 charges up to the saturation charge amount level of the toner particles.

[0077] In the present embodiment, by adjusting the addition amounts of the ferroelectric and the conductive agent to the coating layer of the carrier, and by adjusting the particle diameter and the coating film thickness, it is designed to satisfy the following formula (1). 0.73 ≦ FR × AD / Shape factor ≦ 2.10 ···(1) Thereby, the toner chargeability is stabilized, and a state with less image fogging can be maintained over a long period of time.

[0078] The shape factor in formula (1) is a factor representing the particle shape and is defined by the following formula (2). Shape factor = Measured carrier volume average particle diameter / Carrier particle diameter calculated from the BET specific surface area ···(2) However, Carrier particle diameter calculated from the BET specific surface area = 6 / (BET specific surface area × true specific gravity) That is.

[0079] If the shape coefficient becomes too large, the shape coefficient is likely to change due to scraping of the coating layer in durable printing, etc., resulting in poor durability stability. On the other hand, if the shape coefficient is too small, the toner chargeability will decrease. Therefore, there is an appropriate range for the shape coefficient.

[0080] 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 model 1208, manufactured by Mountech Co., Ltd.), etc., nitrogen is adsorbed on the sample surface, and the BET specific surface area [m 2 / g] of the sample can be measured by the flow method (BET single point method).

[0081] FR×AD in formula (1) is an index representing the fluidity of the carrier. If the fluidity of the carrier is too high, the mixability with the toner decreases and the toner chargeability decreases. On the other hand, if the fluidity of the carrier is too low, the conveyance speed of the developer in the developing container 20 decreases, and when high print rate images are continuous, image density decrease occurs. Therefore, there is an appropriate range for the fluidity of the carrier.

[0082] FR is the carrier fluidity and 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 weight, in this embodiment, FR corrected by the bulk specific gravity AD [g / cm 3 of the carrier, i.e., FR×AD, is used as the index of the fluidity of the carrier.

[0083] FR can be measured in accordance with JIS (Japanese Industrial Standards) Z2502. Specifically, a metal funnel (cone angle: 60°, orifice diameter: 2.5 mm, orifice length: 3.2 mm) is prepared, and 50 g of sample (carrier) is placed in the funnel with the orifice blocked. The orifice of the funnel is then opened, and timing is started using a stopwatch. The timing ends when the last carrier leaves the orifice. The measured time (passage time) corresponds to FR. AD can be measured in accordance with JIS-Z2504, a test method for apparent density of metal powders.

[0084] The carrier used in this embodiment has high fluidity and is easily dependent on the rotation of the stirring / conveying screw 25 and the supply / conveying screw 26. Therefore, it is easily compressed at the intersection 31 between the first conveying blade 25b and the second conveying blade 25c of the stirring / conveying screw 25. Therefore, by combining the stirring / conveying screw 25 with the above-described intersection 31 between the first conveying blade 25b and the second conveying blade 25c not overlapping with the scraper 41, it is possible to suppress compression of the developer near the toner concentration sensor 29 and the scraper 41, improve the detection accuracy of the toner concentration, and stabilize the toner concentration in the developing container 20.

[0085] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention. For example, the present invention is not limited to a developing device equipped with the developing roller 30 as shown in FIG. 2, but is applicable to various developing devices that use a two-component developer containing toner and carrier. For example, the present invention is equally applicable to a developing device equipped with a magnetic roller (toner supply roller) that carries developer on its outer circumferential surface, and that supplies only the toner in the developer carried by the magnetic roller to the developing roller 30, thereby forming a toner layer on the outer circumferential surface of the developing roller 30 and developing an electrostatic latent image on a photosensitive drum.

[0086] Furthermore, the present invention is not limited to the tandem color printer shown in FIG. 1, and can be applied to various image forming apparatuses using a two-component development system, such as digital or analog monochrome copiers, monochrome printers, color copiers, facsimiles, etc. Hereinafter, the effects of the present invention will be described more specifically with reference to examples.

Example

[0087] [Manufacture of ferroelectric particle-containing carrier] [Production Example 1] 500 g of silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd., KR-255), 150 g of barium titanate (manufactured by Sakai Chemical Co., Ltd., hydrothermal synthesis method), 10 g of carbon black (manufactured by Lion Corporation, Ketjenblack EC), and 1450 g of toluene were dispersed using a homomixer to obtain a coating solution. The obtained coating solution was sprayed onto 5 kg of carrier cores (Mn ferrite carriers, volume average particle diameter 34.7 μm, saturation magnetization 70 emu / g, coercive force 8 Oe, manufactured by DOWA IP Creation Co., Ltd.) under heating at 200 °C using a fluidized bed coating apparatus to coat the carrier cores with the coating solution. Thereafter, firing was performed at 250 °C for 1 hour using an electric furnace, and after cooling, crushing and classification were performed using a sieve to obtain a carrier having a volume average particle diameter (D50) of 52.3 μm containing 30 parts by mass of ferroelectric particles (barium titanate) in the coating layer.

[0088] The volume average particle diameter (D50) of barium titanate and the carrier core was measured using a laser diffraction / scattering particle size distribution measuring apparatus (LA-950, manufactured by Horiba, Ltd.).

Example

[0089] [Effect of stabilizing toner concentration by scraper arrangement] We investigated the effect of stabilizing the toner concentration measured by the toner concentration sensor 29 when changing the positional relationship between the intersection 31 of the first transport blade 25b and the second transport blade 25c and the scraper 41. The test was conducted by filling the two-component developer containing the carrier manufactured in Manufacturing Example 1 into developing devices 3a to 3d as shown in FIG. 2 and mounting them on a testing machine. The test was conducted in the cyan image forming unit Pa, which includes the photosensitive drum 1a and the developing device 3a.

[0090] For the test method, a developing device 3a was prepared in which a headless sensor (without a head) and a headed sensor (with a head) were arranged as the toner concentration sensor 29 downstream of 3 / 4 of the axial length of the stirring and conveying screw 25 in the developer conveying direction (direction of arrow P) within the stirring and conveying chamber 21 and one pitch upstream of the upstream connecting portion 20e of the first conveying blade 25b (hereinafter referred to as the downstream side), and a developing device 3a in which a headless sensor and a headed sensor were arranged as the toner concentration sensor 29 upstream of 3 / 4 of the axial length of the stirring and conveying screw 25 (hereinafter referred to as the downstream side).

[0091] The above four types of developing devices 3a were fitted with stirring and conveying screws 25 in which the phase of the scraper 41 relative to the intersection point 31 located immediately upstream in the developer conveying direction was changed to 0°, 45°, 90°, or 135°, and the developing container 20 was filled with 300 g of developer, respectively.

[0092] Then, 100,000 test images with a print rate of 2% were continuously printed in a normal temperature and humidity environment (R / R environment, 23°C, 50%), and the toner concentration fluctuation detected by the toner concentration sensor 29 and the occurrence of image fogging were evaluated. Image fogging was evaluated visually, with very noticeable fogging being rated as ×, occurring but not bothersome being △, and barely occurring being rated as ○.

[0093] The first conveying blade 25b of the stirring and conveying screw 25 has an outer diameter of 18 mm and a pitch of 30 mm, and the second conveying blade 25c has an outer diameter of 12 mm and a pitch of 30 mm, and the ratio of the outer diameters of the first conveying blade 25b and the second conveying blade 25c is 1.6.

[0094] The development conditions were as follows: a developing roller 31 with an outer diameter of 20 mm, on the outer peripheral surface of which 80 rows of recesses were formed (knurling), was used, and a magnetic blade made of stainless steel (SUS430) with a thickness of 1.5 mm was used as the regulating blade 27. The amount of developer conveyed by the developing roller 31 was 320 to 370 g / m 2 and the peripheral speed ratio of the developing roller 31 to the photosensitive drums 1a to 1d was set to 1.8 (trailing rotation at the opposing position). A developing voltage obtained by superimposing an AC voltage with a peak-to-peak value (Vpp) of 1125 V, a frequency of 10 kHz, and a duty = 50% on a DC voltage of 50 to 250 V was applied to the developing roller 31.

[0095] The photosensitive drums 1a to 1d used an amorphous silicon (a-Si) photosensitive body with a relative permittivity of 11, and the distance between the photosensitive drums 1a to 1d and the developing roller 31 (DS distance) was 0.375 ± 0.025 mm, and the amount of developer conveyed by the developing roller 31 was 350 g / m 2 A positively charged toner with an average particle diameter of 6.8 μm was used as the toner, and the initial toner concentration (weight ratio of toner to carrier) in the developer was set to 6%. The results are shown in Table 1.

[0096]

Table 1

[0097] As is clear from Table 1, in all of the developing devices 3a, when the phase of the scraper 41 with respect to the intersection 31 is between 45° and 135°, the toner concentration fluctuation is smaller than when the phase is 0°. This is because the intersection 31 of the first transport blade 25b and the second transport blade 25c is not located near the scraper 41, which suppresses an increase in carrier density due to developer compression and improves the accuracy of toner concentration detection. In particular, when the phase of the scraper 41 is between 45° and 90°, the occurrence of image fogging is further suppressed.

[0098] Furthermore, when toner concentration sensor 29 is located downstream, fluctuations in toner concentration are smaller than when it is located upstream. This is because the toner supplied from developer supply port 20g is uniformly dispersed in the developer in stirring / transport chamber 21, and the toner concentration reaches toner concentration sensor 29 and scraper 41 in a stable state.

[0099] Furthermore, when a headless sensor is used as toner concentration sensor 29, fluctuations in toner concentration are smaller than when a sensor with a head is used. This is because, with a headless sensor, there is no step between the detection surface and inner wall surface 21a, so fluctuations in developer density at the step are eliminated, improving the accuracy of toner concentration detection.

[0100] From the above results, it was confirmed that the developing device 3a using the stirring / conveying screw 25 in which the phase of the scraper 41 relative to the intersection 31 of the first conveying blade 25b and the second conveying blade 25c is 45° to 135° can stably detect the toner concentration and can suppress image fogging. Furthermore, it was confirmed that by locating the toner concentration sensor 29 downstream of ¾ of the axial length of the stirring / conveying screw 25 and one pitch upstream of the upstream communicating portion 20e of the first conveying blade 25b, and further using a headless sensor as the toner concentration sensor 29, it can be more effectively suppressed the toner concentration fluctuation and image fogging. [Example]

[0101] [Effect of eliminating image fog by the addition amount of barium titanate in the carrier coating layer] The effect of eliminating image fog when the addition amount of barium titanate in the carrier coating layer was changed was investigated. As a test method, the addition amount of barium titanate to the coating resin forming the coating layer was changed to 0 parts by mass (not added), 10 parts by mass, 30 parts by mass, and 50 parts by mass, and carriers were produced in the same manner as in Example 1. Using the produced carriers, under the same image forming conditions as in Example 2, the image fog of the developing device 3a left in a high temperature and high humidity environment (HH environment, 32.5 °C, 80%) for 48 hours was confirmed. For the evaluation of image fog, white paper was continuously printed, and the number of printed sheets until the image fog was improved to a certain level was confirmed. The level of image fog was evaluated visually. The results are shown in Table 2.

[0102]

Table 2

[0103] As is clear from Table 2, it can be seen that the more barium titanate is added to the carrier coating layer, the faster the image fog is eliminated. More specifically, when the addition amount of barium titanate is 5 to 50 parts by mass, there is an effect of improving image fog. However, when the addition amount of barium titanate is 30 parts by mass or more, the decrease in the number of printed sheets for eliminating image fog tends to slow down and saturate. Therefore, it is considered that around 30 parts by mass is the most preferable as the addition amount of barium titanate. Although not described here, it has been confirmed that the addition of barium titanate improves toner scattering as well as image fog.

Industrial Applicability

[0104] The present invention can be used in a developing device having a toner concentration sensor that detects the toner concentration of a two-component developer in a developing container, and a scraper that rotates together with a stirring and conveying member to clean the detection surface of the toner concentration sensor.By using the present invention, it is possible to provide a developing device that can accurately detect the toner concentration in the developing container and suppress the occurrence of image fogging due to excessive toner supply, and an image forming apparatus equipped with the same. [Explanation of symbols]

[0105] 1a to 1d Photosensitive drum 3a~3d developing device 20 Developer container 20a Partition wall 22e Upstream communication section 22f Downstream communication section 20g developer supply port 20h Developer discharge section 21 Transport Room 1 22 Second Transport Room 25 Agitation conveying screw (first agitation conveying member) 25a Rotating shaft 25b First conveying blade 25c Second conveying blade 26 supply conveying screw (second stirring conveying member) 26a Rotation axis 26b First conveying blade 26c Second conveying blade 27 Regulatory Blade 29 Toner density sensor 30 Developing roller (developer carrier) 31 intersection 41 Scraper 100 Image forming device

Claims

1. A plurality of transport chambers including a first transport chamber and a second transport chamber arranged in parallel with each other, a partition wall that partitions the first transport chamber and the second transport chamber along the longitudinal direction, a communication portion that communicates the first transport chamber and the second transport chamber on both end sides of the partition wall, a developing container that houses a two-component developer including a carrier and toner, a first stirring and transporting member that stirs and transports the developer in the first transport chamber in a first direction, a second stirring and transporting member that stirs and transports the two-component developer in the second transport chamber in a second direction opposite to the first direction, a developer carrier that is rotatably supported by the developing container and supports the two-component developer on the surface, a toner concentration sensor disposed on the inner wall surface of the first transport chamber for detecting the toner concentration in the two-component developer, a scraper attached to the first stirring and transporting member and moving the two-component developer in the vicinity of the toner concentration sensor by rotating together with the first stirring and transporting member, in a developing device comprising: the first stirring and transporting member a rotating shaft rotatably supported in the developing container, a first transport blade formed on the outer peripheral surface of the rotating shaft for transporting the two-component developer in the first direction by the rotation of the rotating shaft, a second transport blade formed on the outer peripheral surface of the rotating shaft so as to overlap the formation region of the first transport blade, having a reverse phase to the first transport blade, and having a lower radial height than the first transport blade, having the second spiral blade is continuously formed between one pitch of the first spiral blade facing the toner concentration sensor, the scraper is disposed substantially parallel to the rotating shaft at a position axially different from the intersection of the first transport blade and the second transport blade, the developing device, wherein the phase of the scraper is 45° to 135° with respect to the intersection located closest to the upstream side in the first direction.

2. The developing device according to claim 1, wherein the phase of the scraper is 45° to 90° with respect to the intersection located closest to the upstream side in the first direction.

3. The toner concentration sensor is disposed downstream of 3 / 4 of the axial length of the first stirring and transporting member and upstream of at least 1 / 2 pitch of the first transport blade from the communication portion when viewed from the upstream side in the developer transport direction in the first transport chamber. The developing device according to claim 1 or claim 2, characterized in that.

4. The developing device according to any one of claims 1 to 3, wherein the toner density sensor is a headless sensor having a detection surface buried in the inner wall surface of the first transfer chamber.

5. The carrier is formed by forming a resin coat layer on the surface of a carrier core that is a magnetic particle, and satisfies the following formula (1). The developing device according to any one of claims 1 to 4. 0.73 ≦ FR × AD / shape factor ≦ 2.10... (1) However, FR: Time [s / 50 g] for discharging 50 g of the carrier AD; Bulk density of the carrier [g / cm ３ ​ Shape factor: Carrier particle diameter calculated from the measured carrier volume average particle diameter / BET specific surface area is.

6. The coat layer contains barium titanate as a ferroelectric, The developing device according to claim 5, wherein the addition amount of the barium titanate is 5 to 45 parts by mass with respect to 100 parts by mass of the coat resin forming the coat layer.

7. An image carrier, The developing device according to any one of claims 1 to 6, which attaches the toner to an electrostatic latent image formed on the image carrier to form a toner image, An image forming apparatus comprising:

Images