JP2011008163A - Developing device, and image forming device equipped therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device capable of enhancing easily and inexpensively sealing performance of a magnetic sealing member, and an image forming device equipped therewith.SOLUTION: This developing device is arranged with the magnetic sealing members 33a, 33b for preventing a developer from being leaked through a gap between a housing 20 and a developing roller 25, in both end parts of the developing roller 25. Each of the magnetic sealing members 33a, 33b is constituted by magnetizing a large number of N-poles and S-poles alternately with a prescribed pitch on an inner circumferential face, and a pitch width p is 1 mm or more to 3 mm or less in the N-poles and S-poles.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and a developing device used therefor, and more particularly, to a method for preventing leakage of developer from a developing device using a magnetic developer.

  In an image forming apparatus using an electrophotographic system such as a copying machine, a printer, and a FAX, a powder developer is mainly used, and an electrostatic latent image formed on an image carrier such as a photosensitive drum is developed with the developer. A general process is to perform a fixing process after visualizing and transferring the toner image onto a recording medium.

  Developers are broadly divided into two-component developers composed of toner and a magnetic carrier (hereinafter also simply referred to as carrier) and one-component developers composed only of magnetic toner, and a regulating blade (developer regulating member). Thus, tribocharging of the developer carried on the developing roller (developer carrying member) is promoted. As the regulating blade, there are known a configuration composed of only a magnetic member, and a configuration in which a magnetic member is disposed in a portion (developer regulating portion) facing a developing roller based on a non-magnetic member.

  In a developing device using such a regulating blade, a part of the developer supplied to the developer regulating unit as the developing roller rotates is passed through the regulating blade and a thin developer layer is formed on the developing roller. However, most of the remaining developer rides on the regulating blade and is returned to the developing device. At this time, the developer tends to go to both ends in the longitudinal direction of the developing roller and the regulating blade. Accordingly, it is necessary to prevent leakage of the developer from the developing device in this portion.

  Conventionally, there has been proposed a method for preventing leakage of a developer by providing magnetic seal members at both ends in the longitudinal direction of a developing device. This prevents leakage of the developer using a magnetic brush formed between the magnetic seal member and the developing roller by a magnetic field between the fixed magnet body and the magnetic seal member arranged in the developer carrying body. It is.

  For example, Patent Document 1 discloses a developing device provided with a magnetic seal member in which NS poles are magnetized in multiple magnetic poles in the circumferential direction of the developing roller. Further, Patent Document 2 discloses a developing device in which a plurality of magnetic seal members magnetized with multiple NS poles are arranged adjacent to both end portions of a developing roller so that different magnetic poles face each other between the magnetic seal members. It is disclosed.

Japanese Patent Laid-Open No. 11-133750 JP 2004-354864 A

  By the way, in order to increase the mixing property between the toner and the carrier in the two-component developer and to smoothly circulate the developer in the developing device and reduce the driving torque of the stirring screw, the circularity or apparent bulk density (AD) High spherical carrier may be used. When such a carrier is used, the magnetic brush on the developer carrying member can be densely and uniformly formed, so that the image quality can be improved. However, when a carrier having a high degree of circularity is used, the adhesion between the carriers is weakened, so that the developer is likely to leak from the developing device.

  Therefore, it is necessary to improve the sealing performance of the magnetic seal member in order to prevent leakage of the developer. As a method of improving the sealing performance, a method of increasing the magnetic force of each magnetic pole magnetized on the magnetic seal member can be considered, but there is a disadvantage that the cost of the magnetic seal member increases. In addition, when a plurality of magnetic seal members are provided as in Patent Document 2, the number of parts and the number of assembling steps are increased, so that the assembling workability is lowered and the cost is disadvantageous.

  In view of the above problems, an object of the present invention is to provide a developing device that can improve the sealing performance of a magnetic seal member easily and at low cost, and an image forming apparatus including the developing device.

  To achieve the above object, the present invention provides a housing for storing a magnetic developer, a developer carrying member for carrying the developer by a magnet member that is rotatably supported by the housing and fixed inside. The developer carrying member is disposed at predetermined intervals along the outer peripheral surface of both longitudinal ends of the developer carrying member, and a plurality of N poles and S poles are provided on the surface of the developer carrying member facing the developer carrying member. In a developing device including a magnetic seal member magnetized alternately in the circumferential direction, the pitch width of the N pole and the S pole of the magnetic seal member is 1 mm or more and 3 mm or less.

  According to the present invention, in the developing device configured as described above, the magnetic flux density of the N pole and the S pole of the magnetic seal member is 400 G or more and 800 G or less.

  According to the present invention, in the developing device configured as described above, the developer is a two-component developer including a toner and a magnetic carrier, and the circularity of the magnetic carrier is 0.93 or more.

  According to the present invention, in the developing device configured as described above, the magnetic carrier is a coated ferrite carrier in which a carrier core material made of spherical ferrite particles is coated with a resin liquid, and the apparent bulk density of the magnetic carrier is 2.35 or more. It is a feature.

  According to the present invention, in the developing device configured as described above, an interval between the magnetic seal member and the outer peripheral surface of the developer carrier is 0.2 mm or more and 1 mm or less.

  According to the present invention, in the developing device configured as described above, a distance between the magnetic seal member and the magnet member in an axial direction of the developer carrier is 1 mm or less.

  The present invention also provides an image forming apparatus including the developing device having the above-described configuration.

  According to the first configuration of the present invention, a strong magnetic force is not required for the N pole and the S pole magnetized on the magnetic seal member, and a good sealing performance is obtained using a magnet magnetized to a relatively small magnetic flux density. Can be maintained. Even when a carrier having a high degree of circularity is used, leakage of the developer can be effectively prevented.

  Further, according to the second configuration of the present invention, in the developing device of the first configuration, the magnetic flux density of the N pole and the S pole of the magnetic seal member is set to 400 G or more and 800 G or less, which is good at low cost. A seal structure having a sealing property is obtained.

  According to the third configuration of the present invention, in the developing device having the first or second configuration, the developer is a two-component developer including a toner and a magnetic carrier, and the circularity of the magnetic carrier is 0. .93 or more can improve the mixing property of the toner and the carrier in the developing device and cause the developer to smoothly circulate and reduce the agitation drive torque without causing the developer to leak. The magnetic brush on the developer carrying member can be formed densely and uniformly.

  According to the fourth configuration of the present invention, in the developing device of the third configuration, in the case where the magnetic carrier is a coated ferrite carrier in which a carrier core material made of spherical ferrite particles is coated with a resin liquid, the apparent bulk of the magnetic carrier. By setting the density to 2.35 or more, a spherical carrier having a circularity of 0.93 or more can be easily prepared.

  According to the fifth aspect of the present invention, in the developing device having any one of the first to fourth aspects, the distance between the magnetic seal member and the outer peripheral surface of the developer carrier is 0.2 mm or more and 1 mm or less. By doing so, the developer held on the magnetic seal member can sufficiently fill the gap between the magnetic seal member and the developer carrying member, and the sealing performance can be further improved.

  According to the sixth configuration of the present invention, in the developing device having the first or fifth configuration, the distance between the magnetic seal member and the magnet member in the axial direction of the developer carrier is 1 mm or less. By doing, NS forward magnetic field between a magnet member and a magnetic seal member can be strengthened, and sealing performance can be improved more.

  Further, according to the seventh configuration of the present invention, by mounting the developing device having any one of the first to sixth configurations, leakage of the developer from the developing device can be performed over a long period of time with a simple configuration. Thus, the image forming apparatus can be prevented.

Schematic sectional view of an image forming apparatus provided with the developing device of the present invention The top view and front view of the developing device of the present invention Side sectional view of the developing device of the present invention Enlarged view around the developing roller in FIG. The perspective view which shows the state which extended the magnetic seal member in flat form The top view which shows the relationship between the pitch width of the magnetic pole which comprises a magnetic seal member, and the developer hold | maintained at a magnetic seal member The side view which shows the relationship between the gap between a developing roller and a magnetic seal member, and the developer hold | maintained at a magnetic seal member The top view which shows the relationship between the axial distance of the fixed magnet body in a developing roller, and a magnetic seal member, and the developer hold | maintained at a magnetic seal member

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view of an image forming apparatus provided with the developing device of the present invention. In an image forming apparatus (for example, a monochrome printer) 100, when performing a copying operation, an electrostatic latent image is formed based on document image data transmitted from a personal computer (PC) (not shown) in an image forming unit 9 in the apparatus body. Then, the developing device 4 attaches toner to the electrostatic latent image to form a toner image. The toner is supplied to the developing device 4 from the toner container 5. In such an image forming apparatus 100, the image forming process for the photosensitive drum 1 is executed while rotating the photosensitive drum 1 clockwise in FIG.

  The image forming unit 9 includes a charging device 2, an exposure unit 3, a developing device 4, a transfer roller 6, a cleaning device 7, and a charge removal device (not shown) along the rotation direction (clockwise) of the photosensitive drum 1. Is arranged. The photosensitive drum 1 is formed, for example, by laminating a photosensitive layer on an aluminum drum, and the charging device 2 uniformly charges the surface. Then, an electrostatic latent image with attenuated charging is formed on the surface that has received a laser beam from the exposure unit 3 described later. The photosensitive layer is not particularly limited, but for example, amorphous silicon (a-Si) having excellent durability is preferable.

  A charging device (charging charger) 2 uniformly charges the surface of the photosensitive drum 1. For example, the charging device 2 is a corona discharge device that discharges by applying a high voltage using a thin wire or the like as an electrode. Instead of the corona discharge device, a contact-type charging device that applies a voltage while a charging member typified by a charging roller is in contact with the surface of the photosensitive member may be used. The exposure unit 3 irradiates the photosensitive drum 1 with a light beam (for example, a laser beam) based on the image data, and forms an electrostatic latent image on the surface of the photosensitive drum 1.

  The developing device 4 forms toner images by attaching toner to the electrostatic latent image on the photosensitive drum 1. In the present embodiment, a two-component developer (hereinafter also simply referred to as a developer) composed of toner and a magnetic carrier is accommodated in the developing device 4. Details of the developing device 4 will be described later. The cleaning device 7 includes a cleaning roller, a blade material, and the like that are in linear contact with the longitudinal direction (paper surface direction) of the photosensitive drum 1, and after the toner image is transferred (transferred) to the paper, the surface of the photosensitive drum 1. The remaining toner (residual toner) is removed.

  A sheet is conveyed from the sheet storage unit 10 to the image forming unit 9 at a predetermined timing via the sheet conveyance path 11 and the registration roller pair 13 toward the photosensitive drum 1 on which the toner image is formed as described above. . The transfer roller 6 shifts (transfers) to the sheet conveyed through the sheet conveyance path 11 without disturbing the toner image formed on the surface of the photosensitive drum 1. Thereafter, in preparation for the subsequent formation of a new electrostatic latent image, residual toner on the surface of the photosensitive drum 1 is removed by the cleaning device 7, and the residual charge is canceled by the static eliminator.

  Then, the sheet on which the toner image is transferred is separated from the photosensitive drum 1, conveyed to the fixing device 8, and heated and pressed to fix the toner image on the sheet. The paper that has passed through the fixing device 8 passes through the discharge roller pair 14 and is discharged to the paper discharge unit 15.

  2A and 2B are a plan view and a front view of the developing device, and FIG. 3 is a side sectional view of the developing device. In FIG. 2A, for the sake of convenience, a state in which the top cover is removed and the inside can be seen is represented. As shown in FIGS. 2 and 3, the inside of the housing 20 is partitioned into a first storage chamber 21 and a second storage chamber 22 by a partition wall 20 a formed integrally with the housing 20. A first stirring screw 23 is disposed in the first storage chamber 21, and a second stirring screw 24 is disposed in the second storage chamber 22.

  Each of the first stirring screw 23 and the second stirring screw 24 has a configuration in which spiral blades are provided around a supporting shaft (rotating shaft), and is rotatably supported by the housing 20 in a state of being parallel to each other. . In addition, as shown to Fig.2 (a), the partition wall 20a does not exist in the both ends of the longitudinal direction of the housing 20 which is the axial direction of the 1st stirring screw 23 and the 2nd stirring screw 24, and the 1st stirring screw 23, the developer can be transferred between the second agitating screws 24. As a result, the first stirring screw 23 transports the developer in the first storage chamber 21 in the direction of arrow P while stirring the developer, and transports it to the second storage chamber 22. The developer conveyed to the chamber 22 is conveyed in the direction of arrow Q while being agitated and supplied to the developing roller 25.

  The developing roller 25 rotates in accordance with the rotation of the photosensitive drum 1 (see FIG. 1), thereby supplying toner to the photosensitive layer of the photosensitive drum 1. A fixed magnet body 27 made of a permanent magnet having a plurality of magnetic poles is fixed inside the developing roller 25. A magnetic brush is formed by attaching (carrying) developer to the surface of the developing roller 25 by the magnetic force of the fixed magnet body 27. The developing roller 25 is rotatably supported on the housing 20 in a state parallel to the first stirring screw 23 and the second stirring screw 24. The first stirring screw 23, the second stirring screw 24, and the developing roller 25 are rotationally driven by a motor (not shown).

  The regulating blade 29 is formed such that its longitudinal direction (left and right direction in FIG. 2) is larger than the maximum developing width, and is arranged at a predetermined interval from the developing roller 25 so as to be supplied to the photosensitive drum 1. A regulating unit 30 that regulates the toner amount is formed. As the material of the regulating blade 29, magnetic or non-magnetic SUS (stainless steel) or the like is used. Note that magnetism may be imparted by attaching a permanent magnet to the non-magnetic regulating blade 29.

  A toner concentration sensor (not shown) for detecting the toner concentration in the developer stored in the housing 20 is provided on the bottom surface of the second storage chamber 22 facing the second stirring screw 24. In accordance with the detection result of the toner density sensor, the toner stored in the toner container 5 (see FIG. 1) is supplied into the housing 20 through the toner supply port 20b provided in the upper portion of the housing 20.

  DS rollers 31 a and 31 b are rotatably inserted on the rotation shaft of the developing roller 25. The DS rollers 31a and 31b strictly regulate the distance between the developing roller 25 and the photosensitive drum 1 by coming into contact with both end portions of the outer peripheral surface of the photosensitive drum 1. The DS rollers 31a and 31b have built-in bearings, and the drum surface can be prevented from being worn by being rotated by being driven by the photosensitive drum 1. Further, magnetic seal members 33a and 33b for preventing leakage of the developer from the gap between the housing 20 and the developing roller 25 are disposed at both ends of the developing roller 25.

  FIG. 4 is an enlarged view of the periphery of the developing roller in FIG. A method for regulating the amount of toner on the developing roller 25 will be described in detail with reference to FIG. As shown in FIG. 4, the fixed magnet body 27 has five magnetic poles 27a to 27e including N poles 27a and 27c and S poles 27b, 27d, and 27e. Since the N pole (regulation pole) 27 a of the fixed magnet body 27 faces the regulation blade 29, an S pole is induced at the tip of the regulation blade 29, and a magnetic field in a direction attracting the regulation portion 30 is generated.

  By this magnetic field, a magnetic brush in which a carrier and toner are connected is formed between the regulating blade 29 and the developing roller 25, and the layer is regulated to a desired height when the magnetic brush passes through the regulating unit 30. On the other hand, the developer not used for forming the magnetic brush stays along the upstream (right) side surface of the regulating blade 29. Thereafter, when the developing roller 25 rotates counterclockwise and the magnetic brush moves to a position facing the photosensitive drum 1, a magnetic field is applied by the S pole (main pole) 27 b. The electrostatic latent image is developed in contact with the surface of the substrate.

  When the developing roller 25 further rotates counterclockwise, a magnetic field attracted by the N pole 27c is applied this time, and the toner that has not been used to form the toner image together with the magnetic brush is collected in the housing 20. Further, since a magnetic field repelled by the S poles 27 d and 27 e is applied, the magnetic brush is detached from the developing roller 25 in the housing 20. Then, after being stirred and conveyed by the second stirring screw 24, a magnetic brush is again formed on the developing roller 25 by the magnetic field of the south pole 27e.

  Magnetic seal members 33a and 33b are disposed on the housing 20 surrounding both ends of the developing roller 25, respectively. In FIG. 4, only the magnetic seal member 33a is shown. As shown in FIG. 4, the magnetic seal members 33a and 33b are disposed at both ends of the developing roller 25 in a non-contact state with the developing roller 25, that is, at a predetermined distance from the outer peripheral surface of the developing roller 25. Is done. The magnetic seal members 33a and 33b are disposed on the opposite side of the photosensitive drum 1 with the developing roller 25 interposed therebetween.

  FIG. 5 is a perspective view showing a state where the magnetic seal member is extended in a flat plate shape. In the following, the configuration of the magnetic seal member 33a will be described, but the same applies to the magnetic seal member 33b, and the description thereof will be omitted. As shown in FIG. 5, the magnetic seal member 33a is obtained by alternately magnetizing a number of N poles and S poles on the inner peripheral surface with a predetermined pitch width p, and along the magnetic lines generated by the magnetic pole pattern. This improves the sealability of the developer. As a material of the magnetic seal member 33a, for example, an anisotropic rubber magnet magnetized to a predetermined magnetic flux density or a neodymium magnet is used.

  The length L of the magnetic seal member 33a is determined according to the diameter of the developing roller 25 so that the magnetic seal member 33a can be arranged in an arc shape from the regulating blade 29 to below the developing roller 25 as shown in FIG. . Further, the width W and the thickness t of the magnetic seal member 33a may be determined according to the specifications of the developing device 4, respectively.

  Next, the two-component developer used in the developing device of the present invention will be described. The two-component developer contains a toner and a carrier. The weight ratio (T / C) between the toner and the carrier in the two-component developer is preferably 5 to 20 parts by weight, more preferably 8 to 15 parts by weight with respect to 100 parts by weight of the carrier.

  The toner is obtained by adding an external additive to toner base particles. The toner base particles contain a binder resin and a colorant. The toner base particles may contain a release agent, a charge control agent, magnetic powder and the like as necessary. The weight average particle diameter of the toner base particles is preferably 5 to 12 μm, and more preferably 6 to 10 μm. The weight average particle diameter of the toner base particles is measured by a particle size distribution measuring device (for example, Multisizer II type manufactured by Coulter, Inc.). The toner base particles are produced by a known method such as a pulverization classification method, a melt granulation method, a spray granulation method, or a polymerization method.

  Examples of the external additive include inorganic oxides such as silica, titanium oxide, and alumina, and metal soaps such as calcium stearate. The amount of the external additive is usually 0.1 to 5 parts by weight with respect to 100 parts by weight of the toner base particles.

  Examples of the carrier include magnetic particles or resin particles in which a magnetic material is dispersed in a binder resin. Examples of magnetic materials include magnetic metals such as iron, nickel, cobalt, alloys thereof, alloys containing rare earths, hematite, magnetite, manganese-zinc ferrite, nickel-zinc ferrite, manganese-magnesium Examples thereof include soft ferrites such as ferrite and lithium ferrite, iron-based oxides such as copper-zinc ferrite, and mixtures thereof.

  Examples of the binder resin include vinyl resins, polyester resins, epoxy resins, phenol resins, urea resins, polyurethane resins, polyimide resins, cellulose resins, polyether resins, and mixtures thereof. Magnetic particles are produced by a known method such as a sintering method or an atomizing method. The carrier may have a coating layer made of a coating resin on its surface.

  Here, in order to improve the mixing property of the toner and the carrier in the two-component developer and to smoothly circulate the developer in the developing device and to reduce the driving torque of the agitating screws 23 and 24, the circularity is 0. 93 or more spherical carriers may be used. When such a carrier is used, the magnetic brush on the developing roller 25 can be densely and uniformly formed, so that the image quality can be improved.

  Further, the spherical carrier may be defined by the apparent bulk density instead of the circularity. For example, in the case of a coated ferrite carrier in which a carrier core material composed of spherical ferrite particles is coated with a resin solution and then heat-treated, the apparent bulk density (AD) is 2.35 or more when the circularity is 0.93 or more. It becomes.

  However, when a carrier having a high degree of circularity or apparent bulk density is used, the adhesion between the carriers is weakened, so that leakage of the developer from the housing 20 is likely to occur. Therefore, it is necessary to improve the sealing performance of the magnetic seal member 33a.

  FIG. 6 is a plan view showing the relationship between the pitch width p of the magnetic poles constituting the magnetic seal member and the developer held on the magnetic seal member. In the magnetic seal member 33a in which a large number of north and south poles are alternately magnetized, a developer magnetic brush is formed along the NS forward magnetic field generated at the boundary between the north and south poles. Therefore, when the magnetic pole pitch width p is wide as shown in FIG. 6A, a gap is formed in the developer D held on the magnetic seal member 33a, and the developer leaks through the gap.

  On the other hand, when the pitch width p of the magnetic poles is narrow as shown in FIG. 6B, the interval of the NS forward magnetic field is also narrowed, and the developer D held on the magnetic seal member 33a overlaps, so that the gap is filled. In order to eliminate the gap due to the overlap of the developer D, the pitch width p needs to be 3 mm or less. Further, when the pitch width p is less than 1 mm, the gap of the developer D is filled, but since the N pole and the S pole are reduced, the generated NS forward magnetic field is also reduced. As a result, the height of the developer D held on the magnetic seal member 33a (the paper surface direction in FIG. 6) becomes low, and a gap is generated between the developing roller 25 and the developer D, causing developer leakage. appear.

  Therefore, in the present invention, the pitch width p between the N pole and the S pole is set to 1 mm or more and 3 mm or less. With this configuration, a strong magnetic force is not required for the N pole and S pole magnetized on the magnetic seal member 33a, and good sealing performance is obtained using a rubber magnet or the like magnetized to a relatively small magnetic flux density of 400 to 800G. Can be maintained. Even when a carrier having a high degree of circularity is used, leakage of the developer can be effectively prevented.

  FIG. 7 is a side view showing the relationship between the gap between the developing roller and the magnetic seal member and the developer held on the magnetic seal member. When the gap d between the developing roller 25 and the magnetic seal member 33a is wide as shown in FIG. 7A, the developer easily leaks from the gap between the developer D held on the magnetic seal member 33a and the developing roller 25. . On the other hand, when the gap d between the developing roller 25 and the magnetic seal member 33a is narrow as shown in FIG. 7B, the developer D held on the magnetic seal member 33a fills the gap d, so that the developer is difficult to leak. .

  Therefore, the leakage of the developer can be more effectively prevented by narrowing the gap d. Specifically, although depending on the pitch width p of the N pole and the S pole and the strength of the magnetic flux density, in order for the developer D held on the magnetic seal member 33a to fill the gap d without any gap, the gap d is formed. It is preferable to be 1 mm or less. In addition, the gap d is preferably set to 0.2 mm or more in consideration of the dimensional tolerance of the developing roller 25, the mounting error, and the like.

  FIG. 8 is a plan view showing the relationship between the axial distance between the fixed magnet body in the developing roller and the magnetic seal member and the developer held by the magnetic seal member. The developer D held on the magnetic seal member 33a includes not only the NS forward magnetic field generated at the boundary between the north and south poles constituting the magnetic seal member 33a, but also the fixed magnet body 27 and the magnetic seal member 33a. Affected by NS forward magnetic field generated during

  That is, when the axial distance r between the fixed magnet body 27 and the magnetic seal member 33a is large as shown in FIG. 8A, the magnetic field between the fixed magnet body 27 and the magnetic seal member 33a becomes weak, so that the developer. The holding width of D becomes small, and the developer is likely to leak from the gap of the developer D. On the other hand, when the axial distance r is small as shown in FIG. 8B, the amount of developer D held is increased and the width of developer D is increased, so that the developer is less likely to leak.

  Therefore, the leakage of the developer can be more effectively prevented by reducing the axial distance r. Specifically, although depending on the pitch width p of the NS pole and the strength of the magnetic flux density, the distance r is preferably 1 mm or less. Further, the magnetic seal member 33a and the fixed magnet body 27 may overlap in the axial direction. However, if the magnetic seal member 33a is applied to the developing region of the developing roller 25, the formation of the toner thin layer on the developing roller 25 is affected. Therefore, it is necessary to dispose the magnetic seal member 33a in a range that does not cover the development area.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, the present invention is not limited to the developing device as shown in FIG. 2, but includes a magnetic roller (developer carrier) and a developing roller, and a toner is left on the developing roller while leaving a carrier on the magnetic roller. It can be applied in exactly the same manner to a sealing structure at both ends of a magnetic roller in a developing device in which only a toner is transferred to form a thin toner layer and toner is attached to an electrostatic latent image on a photoreceptor by an alternating electric field. Of course, the present invention can be applied not only to a developing device using a two-component developer containing toner and a carrier but also to a seal structure of a developing device using a magnetic one-component developer.

  Magnetic pole pitch width p, gap d between the developing roller and magnetic seal member, fixed magnet body and magnetic seal in the axial direction of the developing roller when a magnetic seal member having N and S poles alternately magnetized is used The relationship between the distance r to the member, the magnetic flux density ρ of the magnetic pole, and the developer leakage was investigated.

  As a test method, magnetic seal members 33a and 33b as shown in FIG. 5 are mounted on the developing device 4 shown in FIG. 3 while changing any one of the parameters p, d, r, and ρ. The developer leakage from both ends of the developing roller 25 when the developing device 4 was driven was visually observed. The dimensions of the magnetic seal member are 50 mm in length, 6 mm in width, and 1 mm in thickness. The developer is a positively charged toner having an average particle diameter of 6.8 μm and a specific gravity of 1.2, a number average particle diameter of 35 μm, and a circularity of 0.95. A two-component developer composed of a coated ferrite carrier having an apparent bulk density of 2.35 was used, and the toner mixing ratio (T / C) with respect to the carrier was 9% by weight. The results are shown in Tables 1 to 4. In the table, a case where no leakage of the developer was observed was indicated as ◯, and a case where leakage was observed was indicated as ×.

  As can be seen from Table 1, by setting the magnetic pole pitch width p to 1 mm to 3 mm, even when a spherical carrier having a circularity of 0.95 and an apparent bulk density of 2.35 is used, the magnetic flux density ρ is 700 G. It was confirmed that the leakage of the developer can be prevented by using the magnetic seal member. As shown in Tables 2 and 3, when the magnetic pole pitch width p is 3 mm, the gap d between the developing roller and the magnetic seal member, or the distance between the fixed magnet body and the magnetic seal member in the axial direction of the developing roller. When r exceeded 1 mm, developer leakage occurred. Further, as shown in Table 4, when the magnetic flux density ρ was less than 400 G, developer leakage occurred.

  INDUSTRIAL APPLICABILITY The present invention can be used for a seal mechanism of a developing device using a magnetic developer, and has a N-pole and S-pole of a magnetic seal member in which a plurality of N-poles and S-poles are alternately magnetized on the inner peripheral surface. The pitch width is 1 mm or more and 3 mm or less. Accordingly, it is possible to provide a developing device that can effectively prevent leakage of a developer by using a magnetic seal member magnetized with a relatively small magnetic flux density even when a carrier having a high circularity is used. it can.

  Further, by installing the developing device of the present invention, it is possible to provide a maintenance-free image forming apparatus that can prevent leakage of the developer over a long period of time with a simple configuration.

4 Developing device 9 Image forming unit 20 Housing (housing)
23 1st stirring screw 24 2nd stirring screw 25 Developing roller (developer carrier)
27 Fixed magnet body (magnet member)
29 Regulation blade 33a, 33b Magnetic seal member 100 Image forming apparatus

Claims (7)

A housing for storing a magnetic developer;
A developer carrying member that carries the developer by a magnet member that is rotatably supported by the housing and fixed inside;
A plurality of N poles and S poles are arranged at predetermined intervals along the outer peripheral surface of both ends in the longitudinal direction of the developer carrying member, and a plurality of N poles and S poles are disposed on the surface of the developer carrying member. Magnetic seal members magnetized alternately in the direction;
In a developing device comprising:
The developing device according to claim 1, wherein a pitch width of the N pole and the S pole of the magnetic seal member is 1 mm or more and 3 mm or less.   2. The developing device according to claim 1, wherein a magnetic flux density of the N pole and the S pole of the magnetic seal member is 400 G or more and 800 G or less.   The developing device according to claim 1, wherein the developer is a two-component developer including a toner and a magnetic carrier, and the circularity of the magnetic carrier is 0.93 or more.   4. The developing device according to claim 3, wherein the magnetic carrier is a coated ferrite carrier in which a carrier core material made of spherical ferrite particles is coated with a resin liquid, and the apparent bulk density of the magnetic carrier is 2.35 or more.   5. The developing device according to claim 1, wherein a distance between the magnetic seal member and an outer peripheral surface of the developer carrying member is 0.2 mm or more and 1 mm or less.   6. The developing device according to claim 1, wherein a distance between the magnetic seal member and the magnet member in the axial direction of the developer carrier is 1 mm or less.   An image forming apparatus comprising the developing device according to claim 1.

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