JP2012155187A - Developing device - Google Patents

Abstract

A developing device capable of stably preventing leakage of a developer to a bearing portion over a long period of time and avoiding the influence of the leaked developer on the bearing portion over a long period of time.
A magnet member 43 is disposed so as to surround the rotary shaft 40 on the inner side in the axial direction from a bearing portion 41 of the rotary shaft 40 of the stirring screw 26. The screw blades 44 are fixed to the rotary shaft 40 so as to interfere with the magnetic brush of the developer formed on the inner peripheral surface side by the magnet member 43. The screw blade 44 urges the developer of the magnetic brush toward the inside of the developing container 22 as the stirring screw 26 rotates in one direction. In the developing container 22, a space 48 </ b> B is formed between the bearing portion 41 and the magnet member 43 so as to be shielded from the developer in the developing container by a magnetic brush, and the screw blades 44 are magnetized on both sides along the rotating shaft 40. It protrudes outside the member 43.
[Selection] Figure 5

Description

  The present invention relates to a developing device that transports a developer by rotating a developer transport member supported by the bearing portion of the developer container in the developer, and more specifically, the bearing portion of the developer container as the developer transport member rotates. The present invention relates to a seal structure that does not allow developer to enter.

  2. Description of the Related Art Image forming apparatuses in which an electrostatic image formed on an image carrier is developed into a toner image by a developing device using a one-component or two-component developer are widely used. The developing device conveys the developer by rotating the developer conveying member supported by the bearing portion of the developing container in one direction at a position lower than the developer surface in the developing container. For this reason, a seal structure is provided at the end of the developer conveying member in the longitudinal direction so that the developer does not enter the bearing portion of the developer container as the developer conveying member rotates (Patent Document 1).

  In Patent Document 1, the rotating shaft of the developer conveying member is formed of a ferromagnetic material, a cylindrical magnet member is provided so as to surround the rotating shaft, and a gap between the magnet member and the rotating shaft is formed with a developer magnetic brush. By sealing, leakage of the developer to the bearing portion is avoided (see FIG. 4).

JP 2003-215919 A

  In the seal structure of Patent Document 1, since the developer constituting the magnetic seal is difficult to be replaced, the deteriorated developer may leak to the outside through stirring friction in the magnetic brush. The toner nodule fused and grown through stirring friction in the magnetic brush may be returned to the developing container when the developer conveying member is stopped, and an unexpected image defect may occur at the next image formation.

  As will be described later, when the developing device is operated for a long period of time, the toner passes over the seal structure and gradually leaks and accumulates on the bearing portion side, and the developer enters the bearing portion to cause overload and vibration. There was a case.

  An object of the present invention is to provide a developing device that can stably prevent a developer from leaking to a bearing portion over a long period of time and can avoid the influence of the leaked developer on the bearing portion over a long period of time. It is said.

  The developing device of the present invention includes a developing container for storing a developer containing magnetic particles, a conveying member for circulating and conveying the developer in a circulation path formed in the developing container, and the conveying member being rotatable. A bearing portion to be supported, a transport portion for transporting the developer from the outside of the circulation path to the inside of the circulation path, and a gap between the transport section and the developer container, on the circulation path side from the bearing section. And a magnet member that forms a magnetic brush for developer by forming a magnetic field.

  In the developing device of the present invention, since the transport unit receives the pressure from the developer circulation path side to the outside in the developer container, the pressure fluctuation of the developer in the developer container is less likely to directly act on the magnetic brush of the developer. ing. Further, since the conveying unit agitates the magnetic brush of the developer back to the circulation path side with the rotation of the conveying member, a certain degree of replacement is ensured for the developer constituting the magnetic brush. Thereby, the deterioration of the developer and the growth of the toner nodule in the magnetic seal can be suppressed.

  Therefore, the leakage of the developer to the bearing portion can be stably prevented over a long period of time, and the influence of the leaked developer on the bearing portion can be avoided for a long period of time.

1 is an explanatory diagram of a configuration of an image forming apparatus. It is explanatory drawing of a structure of the image development apparatus in a cross section perpendicular | vertical to a longitudinal direction. It is explanatory drawing of the structure of the image development apparatus in the cross section along a longitudinal direction. It is explanatory drawing of the bearing structure of the stirring screw edge part of a comparative example. It is explanatory drawing of the bearing structure of the stirring screw edge part of Example 1. FIG. It is explanatory drawing of the magnetization pattern of a magnet member. FIG. 10 is an explanatory diagram of a configuration of a developing device in Embodiment 2. It is explanatory drawing of the seal structure of Example 2. FIG. It is explanatory drawing of a structure of a magnet member. FIG. 10 is an explanatory diagram of a configuration of a developing device in Embodiment 3. It is explanatory drawing of the seal structure of Example 3. FIG. It is explanatory drawing of another example of arrangement | positioning of a magnet member. It is explanatory drawing of the seal structure of Example 4. FIG. It is explanatory drawing of the seal structure of Example 5. FIG. It is explanatory drawing of a structure of a magnet member. It is explanatory drawing of a structure of another magnet member. It is explanatory drawing of the seal structure of Example 6. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. As long as the screw blades rotate at the center of the magnetic head of the magnet surrounding the rotating shaft and the developer is returned to the circulation path side, the present invention can partially or entirely replace the configuration of the embodiment with the alternative configuration. Other alternative embodiments can also be implemented.

  Accordingly, the present invention can be carried out in a developing apparatus that uses not only a two-component developer but also a one-component developer. In the case of the two-component developer, not only a vertical developing device in which the developing chamber and the agitating chamber are arranged vertically but also a horizontal developing device in which the developing chamber and the agitating chamber are arranged horizontally can be implemented. Such a developing device can be implemented without distinction in a tandem type / 1 drum type, an intermediate transfer type / recording material conveyance type, and a sheet-fed transfer type image forming apparatus.

  In the present embodiment, only main parts related to toner image formation / transfer will be described. However, the present invention includes a printer, various printing machines, a copier, a fax machine, a composite machine, in addition to necessary equipment, equipment, and a housing structure. The image forming apparatus can be used for various purposes such as a printer.

  In addition, about the general matter of the image development apparatus shown by patent document 1, illustration is abbreviate | omitted and the overlapping description is abbreviate | omitted.

<Image forming apparatus>
FIG. 1 is an explanatory diagram of the configuration of the image forming apparatus. As shown in FIG. 1, the image forming apparatus 100 is a tandem intermediate transfer type full color printer in which yellow, magenta, cyan, and black image forming portions Pa, Pb, Pc, and Pd are arranged along an intermediate transfer belt 5. is there.

  The intermediate transfer belt 5 is suspended by rollers 61, 62, 63 and is movable in the direction of arrow R2. In the image forming portion Pa, a yellow toner image is formed on the photosensitive drum 1 a and transferred to the intermediate transfer belt 5. In the image forming portion Pb, a magenta toner image is formed on the photosensitive drum 1 b and transferred to the intermediate transfer belt 5. In the image forming portions Pc and Pd, a cyan toner image and a black toner image are formed on the photosensitive drums 1c and 1d, respectively, and transferred to the intermediate transfer belt 5.

  The four-color toner images transferred to the intermediate transfer belt 5 are conveyed to the secondary transfer portion T2 and secondarily transferred to the recording material P. The recording material P taken out from the recording material cassette 12 by the pickup roller 13 is separated one by one by the separation roller 11 and fed to the registration roller 14. The registration roller 14 sends the recording material P to the secondary transfer portion T2 in time with the toner image on the intermediate transfer belt 5. The recording material P to which the toner image has been transferred is heated and pressurized by the fixing device 16 to fix the toner image on the surface, and then is discharged to the discharge tray 17.

  The image forming portions Pa, Pb, Pc, and Pd are substantially the same except that the toner colors used in the developing devices 4a, 4b, 4c, and 4d are different. Hereinafter, the image forming unit Pa will be described, and the image forming units Pb, Pc, and Pd will be described by replacing “a” at the end of the reference numerals attached to the components of the image forming unit Pa with “b”, “c”, and “d”. To do.

  In the image forming portion Pa, a corona charger 2a, an exposure device 3a, a developing device 4a, a primary transfer roller 6a, and a drum cleaning device 19a are arranged around the photosensitive drum 1a.

  The photosensitive drum 1a is formed with a photosensitive layer having a negative polarity on the outer peripheral surface of an aluminum cylinder, and rotates in a direction indicated by an arrow at a predetermined process speed. The corona charger 2a charges the surface of the photosensitive drum 1a to a uniform dark potential VD having a negative polarity. The exposure device 3a scans the laser beam with a rotating mirror and writes an electrostatic image of the image on the surface of the charged photosensitive drum 1a. The developing device 4a develops the electrostatic image using a developer containing toner and a carrier to form a toner image on the surface of the photosensitive drum 1a.

  The primary transfer roller 6 a presses the inner surface of the intermediate transfer belt 5 to form a toner image transfer portion between the photosensitive drum 1 a and the intermediate transfer belt 5. By applying a positive DC voltage to the primary transfer roller 6a, a negative toner image carried on the photosensitive drum 1a is primarily transferred to the intermediate transfer belt 5. The drum cleaning device 19a collects the transfer residual toner remaining on the photosensitive drum 1a by escaping from the transfer to the recording material P.

  Although the photosensitive drum 1a, which is a commonly used drum-shaped organic photosensitive member, is used as the image carrier, an inorganic photosensitive member such as an amorphous silicon photosensitive member may be used, and a belt-shaped photosensitive member is used. It is also possible. The charging method, developing method, transfer method, cleaning method, and fixing method are not limited to the above methods.

<Developing device>
FIG. 2 is an explanatory diagram of the configuration of the developing device in a cross section perpendicular to the longitudinal direction. FIG. 3 is an explanatory diagram of the configuration of the developing device in a cross section along the longitudinal direction. As shown in FIG. 2, the developing device 4a develops an electrostatic image on the photosensitive drum 1a by carrying a developer containing toner and carrier on the developing sleeve 28. The photosensitive drum 1a rotates in the arrow R1 direction at a process speed (peripheral speed) of 273 mm / sec. The developing device 4a uses a two-component developer obtained by mixing a nonmagnetic toner and a magnetic carrier as a developer.

  In the developing container 22, a developing chamber 23 that supplies a developer to the developing sleeve 28 and an agitating chamber 24 that collects the developer from the developing sleeve 28 are arranged vertically. A developing sleeve 28 is rotatably disposed in a region of the developing container 22 facing the photosensitive drum 1a.

  As shown in FIG. 3, the developing chamber 23 and the stirring chamber 24 configured by partitioning the developing container 22 by a partition wall 27 constitute a developer circulation path for transporting the developer while stirring. A stirring chamber 24 is disposed below the developing chamber 23, a developing screw 25 is rotatably provided in the developing chamber 23, and a stirring screw 26 is rotatably provided in the stirring chamber 24. The developing screw 25 and the agitating screw 26 convey the developer in the developing chamber 23 and the agitating chamber 24 in the opposite directions and circulate in the developing container 22. The partition wall 27 is provided with openings 11 and 12 for delivering the developer in the vertical direction at both ends in the longitudinal direction.

  As shown in FIG. 2, the developing sleeve 28 is made of a nonmagnetic material such as aluminum or stainless steel and has a diameter of 20 mm. The diameter of the photosensitive drum 1 is 80 mm, and the closest region between the developing sleeve 28 and the photosensitive drum 1 in the developing unit is about 300 μm. Accordingly, the developer conveyed to the developing unit is set to be in contact with the photosensitive drum 1 in a magnetic brush state so that development can be performed.

  In the developing region, the developing sleeve 28 rotates in the forward direction and the moving direction of the surface of the photosensitive drum 1a, and the circumferential speed ratio with respect to the photosensitive drum is 1.75 times. The higher the peripheral speed ratio with respect to the photosensitive drum, the higher the development efficiency. However, when the ratio is too large, toner scattering, developer deterioration, and the like occur. Therefore, it is preferably set between 0.5 and 2.0 times.

  Inside the developing sleeve 28, there is disposed a magnet roller 29 that is supported non-rotatingly by arranging a plurality of magnetic poles N1, S1, N3, N2, S2, and N3 on the surface. The development pole S2 is disposed to face the photosensitive drum 1 in the development unit. The magnetic pole S <b> 1 is disposed to face the regulation blade 30. The magnetic pole N2 is disposed between the magnetic poles S1 and S2. The magnetic poles N1 and N3 are disposed to face the developing chamber 23 and the stirring chamber 24, respectively. The magnetic flux density of each magnetic pole was 40 mT to 70 mT, but the S2 pole used for development was 100 mT.

  The developing sleeve 28 rotates in the direction of arrow R28, and a layer thickness regulating blade 30 is disposed upstream of the developing region in the rotation direction facing the photosensitive drum 1a. The layer thickness regulating blade 30 regulates the layer thickness of the developer by cutting off the magnetic brush carried on the developing sleeve 28.

  The regulating blade 30 is a non-magnetic metal plate (aluminum) disposed in the longitudinal direction of the developing sleeve 28, and the developer passes between the tip of the regulating blade 30 and the developing sleeve 28 and is sent to the developing area. It is done.

By adjusting the gap between the tip of the regulating blade 30 and the surface of the developing sleeve 28, the amount of developer carried on the developing sleeve 28 and conveyed to the developing region is adjusted. Here, the gap between the regulating blade 30 and the developing sleeve 28 is set to 500 μm, and the developer coating amount per unit area on the developing sleeve 28 is adjusted to 30 mg / cm ² . The gap between the regulating blade 30 and the developing sleeve 28 is set to 200 to 1000 μm, preferably 300 to 700 μm.

  In the two-component magnetic brush development method, the developer is carried on the surface of the developing sleeve 28 while the magnetic carrier is restrained by the magnetic flux formed between the magnetic poles of the magnet 29 during development. On the surface of the developing sleeve 28, the negatively charged toner is electrostatically restrained on the surface of the positively charged carrier to form a magnetic brush.

  The developing sleeve 28 carries a developer and transports it to a developing area facing the photosensitive drum 1a. The development power source D28 superimposes a DC voltage of −500V with an AC voltage of peak-to-peak voltage Vpp = 800V and frequency f = 12 kHz on the DC voltage of −500V in order to improve the development efficiency (rate of toner applied to the electrostatic image). The developed developing voltage is applied to the developing sleeve 28. In general, when an AC voltage is applied, the development efficiency increases and the image becomes high-quality, but conversely, white background toner tends to be generated. For this reason, white background fog toner is prevented by providing a potential difference between the DC voltage applied to the developing sleeve 28 and the charged potential (that is, the white background potential) of the photosensitive drum 1a. However, the combination of DC voltage and AC voltage is not limited to this.

<Developer>
The developer is a two-component developer composed of an insulating nonmagnetic toner and magnetic particles (carrier), and the nonmagnetic toner preferably has a weight average particle diameter of 4 μm or more and 10 μm or less. Here, a toner for a color copying machine having a weight average particle diameter of 8 μm was used.

  Let M be the weight average particle diameter of the toner and r be the particle diameter of the toner. At this time, in order to form a clearer color image, 90% by weight or more of toner particles are included in the range of 1 / 2M <r <2 / 3M, and 99% by weight or more in the range of 0 <r <2M. The toner particles are preferably contained.

  The particle size distribution and the weight average particle size of the toner were measured as follows. As a measuring device, a Coulter counter TA-II type manufactured by Coulter Co. was used, and an interface made by Nikki and a commercially available personal computer were connected to output the number average distribution and the weight average distribution.

  As an electrolyte for measurement, a 1% NaCl aqueous solution was prepared using first grade sodium chloride. In 100 to 150 ml of the electrolytic aqueous solution, 0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) was added as a dispersant, and 0.5 to 50 mg of a measurement sample was added.

  The electrolyte solution in which the sample was suspended was subjected to dispersion treatment for about 1 to 3 minutes with an ultrasonic disperser, and the particle size distribution of 2 to 40 μm particles was measured using a Coulter counter TA-II type with a 100 μm aperture. And the weight average particle diameter of the sample was calculated from the obtained particle size distribution.

  The toner includes colored resin particles (containing a binder resin, a colorant, and other additives as necessary) itself, and colored resin particles to which external additives such as hydrophobic colloidal silica fine powder are externally added. Yes.

  Examples of the binder resin used in the toner include styrene copolymers or polyester resins such as styrene-acrylic acid ester resins or styrene-methacrylic acid ester resins. In consideration of color mixing at the time of fixing the color toner, the polyester resin is preferable because it has a sharp melting characteristic.

On the other hand, the magnetic carrier has a weight average particle diameter of 30 to 80 μm, preferably 40 to 70 μm, and here, a carrier having a weight average particle diameter of 50 μm was used. The resistance value of the magnetic carrier is preferably 1 × 10 ⁷ Ωcm or more, preferably 1 × 10 ⁸ Ωcm or more, and more preferably 1 × 10 ⁹ to 1 × 10 ¹² Ωcm. As such carrier particles, ferrite particles (Cu—Zn ferrite having a maximum magnetization of about 230 emu / cm ³ ) or those thinly coated with a resin can be used favorably.

In order to measure the weight average particle size of the carrier, the particle size distribution of the carrier was first measured.
1. Weigh out approximately 100 g of sample to the nearest 0.1 g.
2. As the sieve, a standard sieve of 100 to 400 mesh was used. The standard sieving frame has an inner diameter of 200 mm above the sieving surface and a depth from the upper surface to the sieving surface of 45 mm. The standard sieves were stacked in the order of 100, 145, 200, 250, 350, 400 from the top, a saucer was placed on the bottom, and the sample was put on the top sieve and covered.
3. This is shaken by a vibrator at a speed of 285 ± 6 times per minute and 150 ± 10 times per minute for 15 minutes.
4). After sieving, the iron powder in each sieve and tray is weighed to the nearest 0.1 g.
5. Calculate to the second decimal place by weight percentage and round to the first decimal place according to JIS-Z8401. At this time, the sum of the weights of the carrier particles in each portion should not be less than 99% of the mass of the sample taken first.

The average particle diameter is determined according to the following formula from the measured particle size distribution.
Average particle size (μ) = (1/100) × {(100 mesh sieve remaining amount) × 140 + (145 mesh sieve remaining amount) × 122 + (200 mesh sieve remaining amount) × 90 + (250 mesh sieve remaining) Amount) × 68 + (remaining amount of 350 mesh sieve) × 52 + (remaining amount of 400 mesh sieve) × 38 + (total sieve passing amount) × 17}

  The amount of the carrier having a mesh size of 500 mesh or less was calculated from the weight reduction by placing a 50 g sample on a 500 mesh standard sieve and sucking it from below.

The resistance value of the carrier (ferrite particles or resin-coated ferrite particles) was measured using a sandwich type cell having a measurement electrode area of 4 cm ² and a gap between the electrodes of 0.4 cm. The applied voltage E (V / cm) between the two electrodes was applied to one electrode of the cell under a pressure of 10 N (1 kgf), and the resistance value of the magnetic particles was measured from the current flowing through the circuit.

<Resin magnetic carrier>
As the carrier, a resin magnetic carrier made of a binder resin, a magnetic metal oxide, and a nonmagnetic metal oxide may be used which is generated by a polymerization method. The resin magnetic carrier is characterized in that the maximum magnetization is smaller than that of the ferrite particles and is about 190 emu / cm ³ . For this reason, the magnetic interaction between adjacent magnetic brushes is small, and as a result, the ears of the magnetic brushes become dense and short, so that an image having high resolution with no texture unevenness can be provided.

  On the other hand, the magnetization indicates the degree to which the magnetic carrier is magnetized by the magnet. The smaller the magnetization, the harder it is to magnetize, and the smaller the binding force to the magnet. Therefore, the total amount of developer that can be restrained by the magnet is small, and in the conventional configuration, the developer that cannot be restrained easily leaks to the bearing side.

  According to the configuration of the present invention, even when such a resin magnetic carrier is used, the developer that can no longer be constrained is sequentially returned by the stirring screw, so that the effect of preventing the developer from entering the bearing portion for a long time is obtained. can get.

Magnetization of a carrier packed in a cylindrical shape in an external magnetic field of 1 KOe (kiloelsted) with a magnetic field automatic magnetic recording device manufactured by Riken Denshi Co., Ltd. Sought the strength of. Thereafter, the amount of magnetization (emu / cm ³ ) was calculated by multiplying the true specific gravity of the carrier.

<Comparative example>
FIG. 4 is an explanatory view of the bearing structure of the end of the stirring screw of the comparative example. A typical developing device has an agitating member that conveys the developer in the developing container toward the developer carrying member while stirring. As the stirring member, a rotating member such as a screw or a finned shaft is used. Since the rotating member is supported by a bearing portion lower than the developer surface provided on the side wall of the developing container, a seal configuration for preventing leakage of the developer is indispensable in the bearing portion.

  When a bushing is used for a bearing lower than the developer surface, the developer sealing effect can be maintained in the initial stage of use of the developing device, but as the developing operation is repeated, the sliding between the rotating shaft and the bushing is caused by the circulating pressure of the developer. The developer gradually enters the rubbing surface. As a result, the invading developer melts and adheres to increase the driving torque of the rotating shaft, the rubbing surface of the rotating shaft and bushing wears, or the developer melted by frictional heat forms agglomerates and develops. There is a problem that the quality of the output image is deteriorated by mixing with an agent.

  In order to improve the sealing performance of the bushing, it is sufficient to increase the adhesion to the rotating shaft. However, if the adhesion is increased, a large force is applied to the rotating shaft, the load on the drive motor increases, and the toner melts due to frictional heat. Become serious. In recent years, the diameter of toner has been reduced in order to obtain high image quality, and it has become more difficult to increase the sealing performance by relying on the adhesion.

  When a ball bearing was used for the bearing, the developer entered the ball bearing and caused the same problem. Further, the developer may be melted and aggregated by the bearing oil leaking from the seal portion of the bearing, or the developer and the bearing oil entering the bearing may be melted and fixed to lock the bearing.

  The oil seal is more excellent in the developer sealing effect than the bushing or ball bearing. However, the oil seal lacks durability, and the abutting portion is worn and damaged as the rubbing with the rotating shaft is repeated, and the abutting portion is pushed and deformed by the circulating pressure of the developer, resulting in a sealing effect. When thinned, problems similar to bushings and ball bearings occurred.

  As shown in FIG. 3, the four bearing portions 41 of the developing container 22 located at both ends of the developing screw 25 and the agitating screw 26 are each equipped with a bearing with a magnetic seal.

  As shown in FIG. 4, the bearing portion 41 forms a cylindrical space 48 </ b> B inside the ball bearing 42 attached to the developing container 22, and a ring-shaped magnet member 43 is provided at the entrance of the space 48 </ b> B. A magnetic brush MB of developer is formed by the ring-shaped magnet member 43, and the magnetic brush MB is rubbed against the rotating shaft 40 to prevent the developer from entering the ball bearing 42 side.

  The rotating shaft 40 is formed of a magnetic material at a portion facing the magnet member 43 and is magnetized by the magnet member 43. A magnetic brush MB of developer is formed by a magnetic field formed between the magnet member 43 and the rotating shaft 40, and the magnetic brush MB prevents the developer from leaking to the ball bell ring 41 side. .

  In the bearing portion 41, the magnetic flux concentrates between the magnet member 43 and the rotating shaft 40, the carrier rises along the magnetic flux to form the magnetic brush MB, and the front side of the ball bearing 42 toward the outside is the curtain of the magnetic brush MB. Sealed with. With the rotation of the rotating shaft 40, a part of the magnetic brush MB is constrained by the magnet member 43, and the remaining portion is rotated with the rotating shaft 40. For this reason, the rubbing of the developer at the bearing portion 41 is soft rubbing between the developers and the temperature is kept low, and the developer is good without forming a fine solidified body due to melting of the toner. Delivers excellent sealing performance.

  In the comparative example, the intrusion of the developer into the ball bearing 42 can be suppressed by providing the ring-shaped magnet member 43 on the inner side of the rotating shaft 40 of the bearing portion 41 to form the magnetic brush MB. However, it is inevitable that the developer gradually leaks to the ball bearing 42 side. Therefore, the developer may cause a problem at the ball bearing 42 during long-time use.

  On the downstream side in the conveying direction of the developing screw 25 and the agitating screw 26, the developer conveyed by the screw blades is intermittently blocked and a large pressure fluctuation occurs. For this reason, in the magnetic seal of the comparative example, a large pressure fluctuation acts on the magnetic brush of the developer formed between the magnet member 43 and the rotary shaft 40, and the outward expansion and contraction are repeated. As a result, the toner particles fall off from the magnetic brush and leak to the ball bearing 42 side.

  In the comparative example, a reverse conveying screw 45 that conveys the developer in a direction away from the magnet member 43 is provided on the upstream side of the magnet member 43 so that the developer does not easily enter the magnet member 43. Although it is possible for the reverse conveying screw 45 to delay the time until the developer arrives at the bearing portion 41, there is a concern about torque increase due to a rubbing load and deterioration of the developer. It is necessary to provide a certain gap between the inner wall surface of the developing container 22. As a result, it is not possible to prevent the developer from reaching the bearing portion 41 through this gap, and considering that the developing device 4a is used for a long time, the developer enters the bearing portion 41. I can't prevent it.

  While the developing device 4a was used for a long time, a part of the developer restrained by the magnet member 43 gradually leaked out to the ball bearing 42 side. Although there is a limit to the amount of developer that the magnet member 43 can constrain, the developer constantly enters the magnet member 43 little by little by the pressure of the developer in the direction along the rotation shaft 40. For this reason, a part of the developer that could not be restrained by the magnet member 43 fell to the ball bearing 42 side.

  Since the developer pressure toward the outside acts directly on the magnetic brush, the developer restrained by the cylindrical magnet member 43 gradually leaks out to the ball bearing 42 side while the developing device 4a is used for a long time. It was. Even if the magnet member 43 is strengthened, it has been difficult to completely prevent the developer from leaking out.

In recent years, in order to achieve high image quality, a magnetic carrier having a relatively small saturation magnetization (for example, 190 emu / cm ³ or less) has been used for a two-component developer. Even in the one-component developer, in order to achieve high image quality, a magnetic toner having a saturation magnetization smaller than that of the conventional toner is employed.

  When the saturation magnetization amount of the developer particles is reduced, the force with which the developer is restrained by the magnet member 43 is reduced, so that the developer is likely to leak to the ball bearing 42 side during long-term use.

  Here, if the magnetic force of the magnet member 43 can be increased, the developer can be held firmly to resist pressure, and leakage to the ball bearing 42 side can be avoided. However, increasing the magnetic force of the magnet member 43 involves an increase in size or cost. In recent years, as a result of the downsizing of developing devices, it has become impossible to provide a large magnet member 43 in the bearing portion 41. The high cost is unacceptable.

  Further, if a sufficient space 48B is secured by increasing the distance between the ball bearing 42 and the magnet member 43, it is possible to delay the arrival of the developer to the ball bearing 42 even if the developer leaks to the ball bearing 42 side. However, the obtained effect is only a life-prolonging effect, which is not an essential solution for the problem to be leaked, and there is a concern that the development apparatus may be increased in size and cost.

  Therefore, in the following embodiment, a screw is provided at the center of the magnet member 43 surrounding the rotating shaft 40 to generate an urging force from the outside to the inside, so that the developer in the developing container 22 has a pressure exerted on the magnetic brush MB. I'm competing. This resists the developer pressure from the inside without increasing the magnetic force of the magnet member 43 and avoids leakage to the ball bearing 42 side.

<Example 1>
FIG. 5 is an explanatory diagram of the bearing structure of the end of the stirring screw according to the first embodiment. FIG. 6 is an explanatory diagram of the magnetization pattern of the magnet member. As shown in FIG. 3, the four bearing portions 41 of the developing container 22 that support both ends of the developing screw 25 and the stirring screw 26 are each equipped with a bearing with a magnetic seal. FIG. 5 shows an enlarged inner wall structure of the developing container 22 including the bearing portion 41 in the region A on the downstream side of the stirring screw 26 shown by the dotted line in FIG. In the following, the region A will be described, but other bearing portions (regions surrounded by dotted lines) 41 corresponding to both ends of the developing screw 25 and the stirring screw 26 are similarly configured as shown in FIG. Yes.

  As shown in FIG. 5, the agitation screw 26, which is an example of a conveying member, circulates and conveys the developer in the circulation path formed in the developing container 22 that stores the developer containing magnetic particles. The bearing part 41 supports the stirring screw 26 rotatably. The magnet member 43, which is an example of a magnet member, is disposed so as to surround the rotating shaft 40 on the circulation path side from the bearing portion 41, and forms a magnetic field in the gap between the screw blade 44, which is an example of a transport unit, and the developing container 22. Thus, a developer magnetic brush is formed. The screw blades 44 convey the developer from the outside of the circulation path to the inside of the circulation path on the circulation path side with respect to the bearing portion 41. The screw blades 44 are fixed to the rotary shaft 40 so as to interfere with the magnetic brush of the developer formed on the inner peripheral surface side thereof by the magnet member 43, and the development of the magnetic brush is performed as the stirring screw 26 rotates. The agent is stirred from the outside of the circulation path toward the inside of the circulation path.

  The screw blade 44 is provided with an interference part where the magnetic brush formed by the magnet member 43 interferes, and a non-interference part where the magnetic brush does not interfere is provided on the circulation path side and the opposite side of the interference part. . The developer is agitated and transported from the non-interference part to the non-interference part through the interference part, thereby assisting the replacement of the developer over the entire magnetic brush.

  In the developing container 22, a space 48 </ b> B that is shielded from the developer in the developing container by a magnetic brush is formed between the bearing portion 41 and the magnet member 43. The screw blades 44 are disposed so as to protrude outside the magnet member 43 on at least one side along the rotation shaft 40.

  At least in the region facing the magnet member 43, when the rotary shaft 40 is formed of a ferromagnetic material and the screw blades 44 are formed of a nonmagnetic material, the rotational load on the stirring screw 26 is reduced. On the other hand, at least in the region facing the magnet member 43, when both the rotating shaft and the screw blade 44 are formed of a ferromagnetic material, the sealing performance by the magnetic brush is enhanced.

  As shown in FIG. 5, the end of the rotating shaft 40 of the stirring screw 26 is rotatably supported on the side wall of the developing container 22 via a bearing 41 having a ball bearing 42. The rotating shaft 40 is made of a ferromagnetic material made of iron, cobalt, nickel, or an alloy thereof. Usually, the rotating shaft 40 is preferably made of iron from the viewpoint of low manufacturing cost. The movement of the rotating shaft 40 in the axial direction is regulated by the stop ring 50 outside the ball bearing 42.

  The bearing portion 41 of the rotary shaft 40 is assembled within the wall thickness of the developing container 22 made of a nonmagnetic material such as synthetic resin. In the bearing portion 41, a cylindrical space 48B is formed inside the ball bearing 42 attached to the developing container 22, and a ring-shaped magnet member (ring-shaped magnet) 43 is fixed to the entrance of the space 48B. The magnet member 43 has a cylindrical shape with a thickness of 3 mm, an inner diameter of 11 mm, and an outer diameter of 15 mm.

  The rotating shaft 40 disposed through the magnet member 43 is provided with a partial spiral screw blade 44. The screw blade 44 was injection-molded integrally with the rotary shaft 40 using ABS resin which is a nonmagnetic resin material. The screw blades 44 are formed of a resin material that integrally covers the outer side of the rotary shaft 40 having a shaft diameter of 3 mm, and have a spiral shape with an outer diameter of 9 mm and a pitch of 2 mm. Therefore, the magnet member 43 is opposed to the outer periphery of the screw blade 44 through a gap having an inner peripheral surface of 1 mm.

  The spiral direction of the screw blade 44 is such that the developer is transported from the ball bearing 42 side to the inner side of the developer container 22 in the direction of the rotation shaft 40 as the screw blade 44 rotates. It is a necessary condition.

  The magnet member 43 is formed of a plastic magnet bound with a rare earth alloy powder and has a maximum magnetic energy product (B · H) max of 7.0 (MOe). The surface magnetic flux density of the magnet member 43 is preferably at least 60 millitesla.

  As shown in FIG. 6A, the magnet member 43 is magnetized so as to form a magnetic flux in the cylindrical thickness direction (the axial direction of the rotating shaft 40). The magnet member 43 is magnetized such that the inner surface facing the inside of the developing container 22 is an N pole and the outer surface facing the ball bearing 42 is an S pole.

  However, the magnetizing pattern is not limited as long as it can form a magnetic brush toward the rotating shaft 40 on the inner cylindrical surface of the magnet member 43. In FIG. 6A, the inner surface is the N pole and the outer surface is S. The poles may be magnetized. As shown in (b) of FIG. 6, S, N or N, S may be magnetized in the radial direction instead of the axial direction.

  As shown in FIG. 5, the magnet member 43 is close to and opposed to the screw blades 44, and the screw blades 44 and the rotating shaft 40 are disposed so as to be positioned in a magnetic field formed by the magnet members 43. By arranging the rotating shaft 40 in the magnetic field of the magnet member 43, the rotating shaft 40 of the ferromagnetic material is magnetized, and a magnetic circuit is formed between the rotating shaft 40 of the ferromagnetic material and the magnet member 43. .

  In the magnetic circuit, most of the magnetic lines of force extending between the magnetic poles N and S of the magnet member 43 extend toward the rotating shaft 40, so that the magnet member 43 stands between the rotating shaft 40 and the magnet member 43. Magnetic field lines increase.

  Since the developer including the magnetic carrier forms a magnetic brush substantially along the magnetic field lines at the location where the magnetic field lines are concentrated, a dense magnetic brush made of the developer is formed in the gap g between the magnet member 43 and the rotating shaft 40. m is concentrated. Then, inside the dense magnetic brush m formed in a strong concentrated magnetic field, the rotating shaft 40 and the screw blades 44 disposed on the rotating shaft 40 rotate integrally. Since the length of the magnetic brush formed on the magnet member 43 is longer than the gap between the screw blades 44 and the magnet member 43, the gap can be filled with the magnetic brush and high sealing performance can be exhibited.

  In this way, high sealing performance is achieved on the inner surface of the cylindrical magnet member 43 at the gap between the magnet member 43 and the rotating shaft 40 and at the gap between the magnet member 43 and the screw blade 44.

As shown in FIG. 4, in the comparative example in which the screw blades are not provided on the rotating shaft 40, it is difficult to completely prevent the leakage of the developer because the pressure of the developer from the inside to the outside cannot be relieved. It was. Since there is no means for pushing back the developer that constantly enters the magnet member 43 little by little, leakage of the developer could not be prevented. In contrast, in Example 1, as shown in FIG. As the screw blade 44 rotates, the developer is pushed inward to relieve the pressure of the developer from the inside to the outside, thereby eliminating the leakage of the developer. The screw blade 44 rotates to generate a force for transporting the developer into the developer container 22, so that even if the developer constantly enters the magnet member 43, the developer is gradually pushed back toward the developer container 22. It is.

  The screw blades 44 can counter the pressure of the developer from the inside to the outside as long as the screw blades 44 face the cylindrical surface inside the magnet member 43 regardless of the axial length. However, as shown in FIG. 5, if the axial length of the screw blade 44 is increased toward the ball bearing 42 and protrudes beyond the magnet member 43, the effect of suppressing developer leakage increases. This is because the developer can be returned to the inside of the developer container 22 by the screw blades 44 before spilling even when the magnetic brush of the developer rises to the ball bearing 42 side.

  Further, as shown in FIG. 5, if the axial length of the screw blade 44 is increased inward of the developing container 22 and protrudes inward of the developing container 22 from the magnet member 43, the developer leaks. Increases the effect of suppressing the sticking out. When the developer constrained by the magnet member 43 is returned to the developing container 22 side by the screw blades 44, if the position where the developer is returned and released is close to the magnet member 43, the developer is pulled back by the magnetic force of the magnet member 43. If the screw blade 44 protrudes to the inside of the developing container 22, the efficiency of returning the developer to the developing container 22 by the screw blade 44 is increased by transporting and releasing to a position where the magnetic force of the magnet member 43 does not reach. is there.

  In particular, when the rotating shaft 40 is made of a ferromagnetic material, the magnetic flux concentrates in a range where the magnet member 43 and the rotating shaft 40 face each other. Therefore, if the magnet member 43 is transported to the outside as much as possible from the axial length, the developer to be transported can be pushed back into the developing container 22 without being pulled back to the magnet member 43. Since the magnetic flux of the magnet member 43 is concentrated and extended in the direction of the rotation axis 40, the magnetic flux density is high in the vicinity of the magnet member 43, and a strong magnetic attractive force acts on the developer. However, if it is slightly outside the magnet member 43, the magnetic flux becomes sparse and the amount of change in the magnetic field is small, so that the magnetic attractive force acting on the developer is almost eliminated. Therefore, if the developer is transported to the outside as much as possible from the magnet member 43, the developer is hardly pulled back to the magnet member 43.

  Further, the rotary shaft 40 on which the screw blades 44 are arranged has a slight backlash in the axial direction by the gap t between the ball bearing 42 and the stop ring 50. Even if the screw blade 44 and the magnet member 43 are displaced in the axial direction due to the presence of such a rattling width, it is necessary to ensure the effect of the above-described axial protrusion. For this purpose, it is necessary to make the protruding amount of the screw blade 44 larger than the backlash width t.

  Based on the above, in Example 1, the thickness of the magnet member 43 is 2 mm, whereas the screw blades 44 having a length of 6 mm are arranged so as to protrude 2 mm each in the direction of the rotation axis 40. The rattle width was 1 mm, and the amount of protrusion was 2 mm before and after the axial direction.

  In addition, the screw blade 44 can be obtained even if it is made of a nonmagnetic resin material. However, if it is made of a ferromagnetic material such as iron, there is an additional advantage. When the screw blade 44 is formed of a ferromagnetic material, a magnetic circuit is formed not only between the magnet member 43 and the rotating shaft 40 but also between the magnet member 43 and the ridge line of the screw blade 44. Since the magnetic lines of force extending from the inner peripheral surface of the cylindrical magnet member 43 extend not only to the rotating shaft 40 but also to the screw blades 44, the lines of magnetic force increase.

  In particular, since magnetic lines of force are concentrated toward the tip of the screw blade 44, a dense magnetic brush made of a developer is formed in the gap between the magnet member 43 and the tip of the screw blade 44. For this reason, in the gap between the magnet member 43 and the screw blade 44, a strong sealing performance by the magnetic brush is achieved.

  However, since the cutting of the screw blades 44 with a metal material is expensive, the cost may be reduced by forming the screw blades 44 with a magnetic resin material. As a magnetic resin material capable of injection molding, a resin material in which iron powder or ferrite is mixed is known. In addition, the screw blades 44 may be formed by a method in which a thin plate made of a ferromagnetic material is attached to a blade molded with resin or a ferromagnetic powder is sprayed.

  Further, the shape of the developer is not limited to the so-called screw blade shape, and the conveyance performance of the developer in the axial direction may be secured by a spiral groove. The rotating shaft 40 itself of the ferromagnetic metal material can be cut into a spiral shape, and the scraped mark can be used as a spiral groove. Since the use of the concave portion of the shaving mark, the effect of conveying as much as a screw-blade cannot be obtained, but the performance of conveying a small amount of developer leaking from a small-diameter seal structure can be secured sufficiently.

  According to the seal structure of the first embodiment, the leakage of the developer from the longitudinal end portion of the stirring screw 26 is prevented, and an increase in the driving load of the stirring screw 26 and the occurrence of toner aggregation flaws are prevented over a long period of time. It is possible. Even if the reverse conveying screw 45 is simply provided around the axial direction of the opposing portion of the magnet member 43, the problem that the developer leaks from the gap between the reverse conveying screw 45 and the developing container 22 and is not a complete measure can be solved.

<Experimental result>
A comparative experiment was performed between the comparative example of FIG. 4 and the example 1 of FIG. First, in the comparative example in which the screw blades 44 are not provided, when the developing operation was repeated, the developer leaked through the magnetic seal portion by the magnet member 43 and leaked to the ball bearing 42 side. The developer adhered to the balls of the ball bearing 42 hindered the rotation of the balls when the cumulative number of images formed from the new state of the developing device 4a was about 500,000, and eventually stopped and stopped. The cause of the stop was damage to the drive gear due to overload.

  In Example 1 in which the screw blades 44 are provided, even when the cumulative number of images formed from the new state of the developing device 4a exceeds 1,000,000, leakage of developer to the ball bearing 42 side is hardly observed and normal. The operating condition was confirmed.

  Therefore, it was confirmed that providing the screw blades 44 at the portion of the rotating shaft 40 opposite to the magnet member 43 has the effect of returning the developer that has entered the magnet member 43 toward the inside of the developing container 22. It was confirmed that it is possible to provide the developing device 4a with better durability and less leakage of the developer than the comparative example.

  In the first embodiment, by providing the screw blades 44 at the opposed portions of the rotating shaft 40 and the magnet member (ring-shaped magnet) 43, an effect of returning the developer that has entered the magnet member 43 to the inside of the developing container 22 is produced. Accordingly, it is possible to provide a highly durable developing device that suppresses the leakage of the developer as compared with the magnetic seal of the comparative example.

  In the first embodiment, the magnet member 43 is disposed so as to surround the rotating shaft 40 inside the developing container 22 with respect to the bearing portion 41, and the screw blade 44 is provided at a position facing the magnet member 43, whereby the bearing portion 41. Prevents leakage of developer into

  In the first embodiment, the application example in the developing device using the two-component developer composed of the magnetic carrier and the toner has been described. The present invention can be implemented in the seal structure of the rotating shaft. In the case of a one-component developer, the difference is that a magnetic brush of magnetic toner is formed, but the basic structure of the bearing portion is the same as in the case of a two-component developer. The present invention can be implemented with any developer containing magnetic particles such as a magnetic carrier and magnetic toner.

<Example 2>
FIG. 7 is an explanatory diagram of the configuration of the developing device according to the second embodiment. FIG. 8 is an explanatory diagram of a seal structure according to the second embodiment. FIG. 9 is an explanatory diagram of the configuration of the magnet member. In Example 2, a seal structure using a magnet member is formed by using an existing reverse conveying screw arranged at the end of a stirring screw in the developing container.

  As shown in FIG. 8, the reverse conveying screw 45, which is an example of an end screw blade, is provided at the end portion in the longitudinal direction of the stirring screw 26 and moves away from the bearing portion 41 as the stirring screw 26 rotates in one direction. The developer is conveyed in the direction.

  The magnet member 46 is fixed to the developing container 22 and disposed so as to surround at least the lower half of the outer periphery of the reverse conveying screw 45. The reverse conveying screw 45 is disposed so as to protrude outside the magnet member 46 on at least one side of the stirring screw 26 in the longitudinal direction.

  The developing container 22 is provided between the bearing portion 41 and the magnet member 46 with a space 48 </ b> B. In the space 48B, the developer magnetic brush formed by the magnet member 43 and the reverse conveyance screw 45 that rotates by interfering with the magnetic brush are prevented from flowing in the developer from the developing container.

  When the rotary shaft 40 is formed of a ferromagnetic material in the region facing the magnet member 46 and the reverse conveying screw 45 is formed of a nonmagnetic material, the rotational load on the stirring screw 26 is reduced. On the other hand, when both the rotating shaft and the reverse conveying screw 45 are formed of a ferromagnetic material in a region facing the magnet member 46, the sealing performance by the magnetic brush is enhanced.

  As shown in FIG. 7, the inside of the developing container 22 of the developing device 4a is divided into a developing chamber 23 and a stirring chamber 24 by a partition wall 27. The developing chamber 23 has a developing screw 25, and the stirring chamber 24 has a stirring screw 26. Are arranged respectively. The developer screw 25 and the agitating screw 26 convey the developer in the opposite directions, whereby the developer circulation is formed in the developing chamber 23 and the agitating chamber 24 via the partition wall 27.

  On the downstream side of the agitating screw 26, a reverse conveying screw 45 that conveys the developer in the opposite direction to the agitating screw 26 and relieves the pressure of the developer at the end of the agitating chamber 24 is disposed. Similarly, on the downstream side of the developing screw 25, a reverse conveying screw 45 that conveys the developer in the opposite direction to the developing screw 25 and relieves the pressure of the developer at the end of the developing chamber 23 is disposed. At the most downstream portion in the developer conveying direction, the screw blades of both the developing screw 25 and the agitating screw 26 are wound in the reverse direction to form a developer reverse conveying portion. The reverse conveying screw 45 pushes back the developer toward the bearing portion 41 and suppresses the developer from entering the bearing portion 41.

  However, when the outer periphery of the reverse conveying screw 45 is brought into contact with the inner wall of the developing container 22, there is a concern that the rotational load increases and the deterioration of the developer is accelerated. For this reason, a certain gap is provided between the reverse conveying screw 45 and the developing container 22.

  Therefore, although the reverse conveying screw 45 suppresses the intrusion of the developer into the bearing portion 41, the developer leaks little by little through the gap between the outer periphery of the reverse conveying screw 45 and the developing container 22. As a result, there is a case where leakage of the developer to the bearing portion 41 becomes a problem during long-term use.

  As shown in FIG. 8A, in the second embodiment, a magnet member 46 is disposed at a position facing the reverse conveying screw 45 to prevent the developer from leaking out to the bearing portion 41. The magnet member 46 generates a magnetic field between the reverse conveying screw 45 and the developing container 22 to form a magnetic brush so as to fill the gap between them, thereby achieving a seal between the reverse conveying screw 45 and the developing container 22. To do. If the length of the magnetic brush formed on the inner surface of the developing container 22 by arranging the magnet member 46 is longer than the gap between the reverse conveying screw blade 45 and the inner wall of the developing container 22, a sufficient sealing effect can be obtained. .

  As shown in FIG. 8B, a flexible sheet-like magnet sheet is cut out to a required size, bent into a U-shape to form a magnet member 46, and this is stuck to the outer surface of the developing container 22 with a double-sided tape. . Since the developer in the developing container 22 is accumulated below in the direction of gravity, the magnetic member 46 is formed at least below the developing container 22 in the direction of gravity and higher than the developer surface in the developing container 22. Is desirable. The magnet member 46 is arranged so as to surround the reverse conveying screw 45 half a half below the developing container 22 in the gravity direction of the reverse conveying screw 45.

  If the magnet member 46 is arranged facing the reverse conveying screw 45, a certain degree of sealing effect can be obtained. However, as described in the first embodiment, when the reverse conveying screw 45 is arranged so as to protrude beyond the magnet member 46 toward the bearing portion 41 or toward the inside of the developing container 22, the sealing effect is enhanced.

  Considering the above, the dimensions were determined as follows. The reverse conveying screw 45 forms a spiral blade having an outer diameter of 20 mm on a rotating shaft 40 having an axial diameter of 4 mm, and the inner wall of the developing container 22 is disposed with a gap of 1 mm with respect to the ridge line of the reverse conveying screw 45. On the outer wall of the developing container 22, a magnet member 46 formed by bending a ferrite magnet sheet having a thickness of 2 mm is attached to the region of the reverse conveying screw 45.

  The magnet member 46 was made to protrude 2 mm from the bearing portion 41 side of the reverse conveying screw 45. The dimensions were adjusted so that the reverse conveying screw 45 protrudes from the magnet member 46 also in the inner direction of the developing container 22. The protruding distance was at least the backlash width of the stirring screw 26.

  Also in the configuration of the second embodiment, the developer constantly enters the region of the magnet member 46 little by little by the conveying pressure of the stirring screw 26. Since the amount of developer that can be restrained by the magnet member 46 is limited, a part of the developer that cannot be restrained by the magnet member 46 may gradually leak to the bearing portion 41 side. However, even if the developer constantly enters the region of the magnet member 46 little by little, the reverse conveying screw 45 rotates and constantly pushes the developer back into the developing container 22, so that the developer is moved to the bearing portion 41 side. There is almost no leak.

  As shown in FIG. 7, the reverse conveying screw 45 is not disposed at the upstream end portion of the stirring screw 26. Since the stirring screw 26 conveys the developer away from the bearing portion 41 at the upstream end, the magnet member 56 may be disposed corresponding to a part of the screw blades of the stirring screw 26. By sticking the magnet member 46 to the outer surface of the developing container 22 in the vicinity of the bearing portion 41, the same sealing effect as that of the downstream end portion of the stirring screw 26 is obtained.

  However, a forward-conveying screw dedicated to the seal having a shorter pitch than the stirring screw 26 may be provided at the inner position of the bearing portion 41, and the magnet member 56 may be disposed at a position corresponding to the forward-conveying screw.

  As with both end portions of the agitating screw 26, both end portions of the developing screw 25 disposed in the developing chamber 23 are provided with seal structures. A reverse conveying screw is disposed at the downstream end, and a part of the developing screw 25 is assigned to the seal structure at the upstream end. A magnet member is arranged on the outer periphery of the developing container so as to correspond to each region, and a seal structure is configured in the same manner as the stirring chamber 24.

<Magnet member>
As shown in FIG. 9A, the magnet member 46 is a magnet sheet of a resin magnet in which ferrite is dispersed based on resin, rubber or the like. A magnet sheet having a magnetic pole arrangement in which N pole rows and S pole rows appeared alternately in parallel in the sheet surface was used. When N pole rows and S pole rows are alternately arranged in the sheet surface, magnetic lines of force are formed between the N pole rows and the S pole rows. It is easy to secure the magnetic force necessary to form the film evenly.

  On the other hand, when the N pole surface and the S pole surface are arranged on the front and back surfaces of the magnet sheet, the magnetic lines of force are concentrated only on the end portion of the magnet sheet. For this reason, it is difficult to ensure the magnetic force for uniformly forming the magnetic brush throughout the entire circumference (or half circumference) of the reverse conveying screw 45.

  As shown in FIG. 9B, the magnet member 46 is arranged so that the N pole row and the S pole row of the magnet sheet are substantially perpendicular to the rotating shaft 40. Since the magnetic brush is formed along the magnetic force line, the magnetic brush is uniformly formed so as to surround the axial vertical section of the reverse conveying screw 45 along the N pole row and the S pole row that are the starting point and the ending point of the magnetic force line. . If the N pole row and the S pole row are arranged substantially perpendicular to the rotation shaft 40, the magnetic brush always passes through the dense portion when the developer passes through the gap between the reverse conveying screw 45 and the developer container 22. To do. For this reason, it can endure longer use.

  On the other hand, when the N pole row and the S pole row that are the starting and ending points of the magnetic field lines are arranged in parallel with the rotation axis 40, the portion where the magnetic brush between the N pole row and the S pole row is sparse is reversed. It is formed in a part of the axial vertical section of the conveying screw 45. For this reason, a problem may occur in the sealing performance during long-time use.

<Example 3>
FIG. 10 is an explanatory diagram of the configuration of the developing device according to the third embodiment. FIG. 11 is an explanatory diagram of a seal structure according to the third embodiment. FIG. 12 is an explanatory diagram of another arrangement example of the magnet members. In the third embodiment, the magnet member is arranged on the entire circumference of the reverse conveying screw in accordance with the shape of the developing container.

  As shown in FIG. 10, in the developing device 4 a, the reverse conveying screw 45 is disposed at a portion of the developing container 22 protruding in a cylindrical shape. As shown in FIG. 8B, a sufficient sealing effect can be obtained as long as the magnet member 46 is opposed to the lower portion of the reverse conveying screw 45 in the direction of gravity. However, since the developer surface in the developer container 22 changes according to the temperature and humidity and the operating state (rotational speed), it is desirable that the developer surface be disposed on the entire circumference of the reverse conveying screw (45) as shown in FIG.

  Thus, as shown in FIGS. 11A and 11B, in Example 3, the magnet member 46 was formed in a cylindrical shape and disposed so as to surround the reverse conveying screw 45 in all directions. By forming a magnetic brush in the entire circumferential direction of the reverse conveying screw 45, a higher sealing effect is obtained including scattered toner and the like.

  As shown in (b) of FIG. 9, the magnet member 46 has N poles and S poles arranged alternately along the rotation axis 40. Since the magnetic brush is formed so as to rise inward while communicating between the N pole and the S pole, the magnetic brush is uniformly formed so as to surround the axial vertical section of the reverse conveying screw 45.

  In Example 3, the magnet member 46 was attached to the outside of the developing container 22. The reason for attaching to the outside of the developing container 22 is that the work is easier than attaching to the inside of the developing container 22 and the production productivity is increased.

  However, as shown in FIG. 12, the magnet member 46 may be fixed to the inner surface of the developing container 22. When the magnet member 46 is affixed to the inside of the developer container 22, the developer can be restrained directly on the surface of the magnet member 46, so the restraining force of the developer is increased, and a magnetic brush with a long tip is formed to improve the sealing performance. be able to.

  Accordingly, whether the magnet member 46 is disposed outside or inside the developing container 22 may be appropriately selected according to the sealing performance required for the developing device 4a and the performance of the magnet member 46.

  In Examples 2 and 3, the rotating shaft 40 of the reverse conveying screw 45 is formed of a ferromagnetic material. As described in the first embodiment, if the rotating shaft 40 is made of a ferromagnetic material, the magnetic lines of force concentrate between the magnet member 46 and the rotating shaft 40, so that the magnetic brush is formed densely and the sealing performance is improved. Because.

  In Examples 2 and 3, the screw blades of the reverse conveying screw 45 were formed of a non-magnetic resin material. This is because if the screw blades of the reverse conveying screw 45 are made of a ferromagnetic material, the magnetic brush directly communicates between the reverse conveying screw 45 and the magnet member 46, and thus the rotational load of the stirring screw 26 increases.

  However, in Examples 2 and 3, as described in Example 1, if the reverse conveying screw 45 is made of a ferromagnetic metal, magnetic lines of force concentrate between the reverse conveying screw 45 and the magnet member 46. The sealing performance with a magnetic brush can be further improved.

  As another method of making the screw blades of the reverse conveying screw 45 ferromagnetic, there is a method of forming the reverse conveying screw 45 with a resin material containing ferromagnetic powder metal powder. In addition, there is a method of attaching a ferromagnetic material to the screw blades of the reverse conveying screw 45 formed of resin or spray-coating.

<Example 4>
FIG. 13 is an explanatory diagram of a seal structure according to the fourth embodiment. In the fourth embodiment, in the developing device 4a shown in FIG. 10, the sealing structure of the third embodiment and the sealing structure of the first embodiment are combined to further enhance the sealing performance.

  As shown in FIG. 13, around the reverse conveying screw 45 at the downstream end of the stirring screw 26, as described with reference to FIG. Is placed. As described with reference to FIG. 5, the bearing portion 41 of the stirring screw 26 is provided with a seal structure that causes the screw blades 44 to interfere with the magnetic brush of the developer by the magnet member 43.

  That is, if the seal structure of the third embodiment and the seal structure of the first embodiment are arranged in series, the seal function to the bearing portion 41 can be achieved more effectively, and the structure can withstand long-time use. .

<Example 5>
FIG. 14 is an explanatory diagram of a seal structure according to the fifth embodiment. FIG. 15 is an explanatory diagram of the configuration of the magnet member. FIG. 16 is an explanatory diagram of a configuration of another magnet member. In the fifth embodiment, in the developing device 4a shown in FIG. 7, a magnetic member is formed on the screw blade of the reverse conveying screw at the downstream end of the stirring screw to form a magnetic brush for sealing. As shown in FIG. 15, the reverse conveying screw 45 has a ferromagnetic material disposed on the ridge line portion of the screw blade.

  As shown in FIG. 14A, when the magnet member 47 is arranged on the outer peripheral surface of the reverse conveying screw 45, a magnetic brush m of developer is formed at that portion. The magnetic brush m seals the gap between the developing container 22 and the reverse conveying screw 45 and prevents leakage of the developer to the bearing portion 41 side through the gap.

  Since the developer in the developing container 22 is accumulated in the lower direction of gravity, it is desirable that the gap between the reverse conveying screw 45 and the developing container 22 in the lower direction of gravity is sealed by the magnetic brush m. Therefore, as shown in FIG. 14B, the magnet member 47 disposed on the outer periphery of the reverse conveying screw 45 and the inner wall surface of the developing container 22 are opposed to each other on the lower half in the gravity direction of the reverse conveying screw 45. It was.

  As shown in FIG. 15, the reverse conveying screw 45 of Example 5 is made of a resin molded member, and has a concave cross section on the ridge line (tip portion) of the reverse conveying screw 45 in order to secure a surface to which the magnet member 47 is attached. A concave groove 45m having a shape is formed.

  A concave groove 45m is provided on the ridge line of the reverse conveying screw 45, and a belt-like and elastic magnet member 47 is half-embedded in the concave groove 45m and fixed by an adhesive. By providing the concave groove 45m, the positioning of the magnet member 47 is facilitated, and the magnetic member 47 can be easily attached even on a narrow ridgeline, and the adhesive can be prevented from flowing out to the conveying inclined surface 45a of the reverse conveying screw 45.

  On the other hand, when the adhesive member leaks when the tip of the reverse conveying screw 45 is flattened and the magnet member 47 is attached, the conveying accuracy of the stirring screw 26 may be affected. In addition, the appearance quality of the stirring screw 26 as a part may be affected due to its poor appearance.

  For the magnet member 47 in Example 5, a magnetic sheet having a magnetic pole arrangement in which the front surface is an N pole surface and the back surface (inside the concave groove 45m) is an S pole surface is cut into a linear shape. The N pole surface and S pole surface of the magnet sheet may be reversed. By adopting such a configuration, the magnetic brush is formed so as to swell on the outer peripheral surface of the magnet member 47, so that a developer magnetic brush without break is formed along the ridge line of the reverse conveying screw 45. Thereby, it is possible to improve the sealing performance of the developer by the magnetic brush.

  In addition, as shown in FIG. 16, you may cut and use the magnetic sheet in which the south pole and the north pole are arrange | positioned alternately. Also in this case, it is possible to form a magnetic brush that can sufficiently fill the space between the outer peripheral surface of the stirring screw 26 and the inner wall surface of the developing container 22. Moreover, since the magnet sheet in which the S pole and the N pole are alternately arranged can be manufactured at low cost, it is convenient in terms of cost.

<Example 6>
FIG. 17 is an explanatory diagram of a seal structure according to the sixth embodiment. In the sixth embodiment, in the developing device 4a shown in FIG. 10, a magnetic member is arranged on the screw blade of the reverse conveying screw at the downstream end of the stirring screw to form a magnetic brush for sealing.

  As shown in FIGS. 17A and 17B, the reverse conveying screw 45, which is an example of an end screw blade, has a magnet member 47 that faces the inner peripheral surface of the developing container 22 along the ridge line portion of the screw blade. Has been fixed. The magnetic brush of the developer formed on the ridge line portion of the reverse conveying screw 45 by the magnet member 47 rubs against the inner peripheral surface of the developing container 22 as the developing sleeve 28 rotates. In parallel with this, the reverse conveying screw conveys the developer and suppresses the flow of the developer from the inside of the developing container toward the bearing portion 41.

  When the part of the developing container 22 corresponding to the reverse conveying screw 45 attached with the magnet member 47 on the ridgeline is formed in a cylindrical shape, the magnetic brush formed on the magnet member 47 continuously extends the cylindrical inner peripheral surface. To seal. As a result, the magnetic brush m closes the gap in the entire circumferential direction so as to surround the reverse conveying screw 45 in all directions, so that higher sealing performance including scattered toner and the like is exhibited.

1a, 1b, 1c, 1d Photosensitive drums 3a, 3b, 3c, 3d Exposure devices 4a, 4b, 4c, 4d Developing device 22 Developing container, 23 Developing chamber, 24 Stirring chamber 25 Developing screw, 26 Stirring screw 28 Developing sleeve, 29 Magnet roller 40 Rotating shaft, 41 Bearing portion, 42 Ball bearing 43, 46, 47 Magnet member, 44 Screw blade 45 Reverse feed screw, 48A, 48B Space

Claims (2)

A developer container containing a developer containing magnetic particles;
A transport member for circulating and transporting the developer in the circulation path formed in the developer container;
A bearing that rotatably supports the transport member;
A transport unit for transporting the developer from the outside of the circulation path toward the inside of the circulation path on the circulation path side from the bearing;
A developing device comprising: a magnetic member that forms a magnetic brush of developer by forming a magnetic field in a gap between the transport unit and the developing container.   The conveyance unit is provided with an interference unit that interferes with a magnetic brush formed by the magnet member, and a non-interference unit that does not interfere with the magnetic brush closer to the circulation path than the interference unit. The developing device according to claim 1.

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