JP2005148366A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can be downsized, obtain a high quality image with no occurrence of unevenness in density, a developing device loaded to the image forming apparatus and a process cartridge. <P>SOLUTION: A developer carrier 30 is installed facing an image carrier 1 on whose surface an electrostatic latent image is formed and a thin layer of developer is carried and transported to a developing range, which is in close proximity to the image carrier, a developer carrying member 32 carrying the developer in circulation while agitating it to supply the developer to developer carrier and a means forming a magnetic field to form the magnetic field are provided in the developing device. A partition plate 35 is installed with its top end positioned below the place set to be the magnetic field, separating the developer from the surface of the developer carrier 30 and the partition plate 35 partitions the space on the side facing the surface of the developer carrier and the dropping space, where the developer is dropped. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus used for a copying machine, a facsimile machine, a printer, and the like, a developing device mounted on the image forming apparatus, and a process cartridge.

2. Description of the Related Art Conventionally, a developing device that forms a toner image by supplying toner to the surface of a photoconductor as an image carrier on which a latent image is formed is transferred to a sheet-like transfer material such as paper. An image forming apparatus configured as described above is known.
An example of a developing device used in such an image forming apparatus is shown in FIG. The developing device contains a two-component developer composed of a carrier and toner. As shown in the figure, there is provided a developing sleeve 10 as a developer carrier disposed so as to be partially exposed from the opening of the casing. In addition, a developer storage unit 17 in which a two-component developer is accommodated, a first transport screw 12 that is a developer supply member provided in the developer storage unit 17, a second transport screw 13, and developer regulation A doctor blade 11 as a member is provided. The developing sleeve 10 includes a sleeve formed in a cylindrical shape and a magnet body (magnet roller) fixedly disposed inside the sleeve.

  As shown in FIG. 2, the first conveying screw 12 is disposed in the vicinity of the developing sleeve 10, and the second conveying screw 13 is disposed in the vicinity of a toner replenishing device (not shown). These two conveying screws are arranged in parallel with each other, and are rotated in opposite directions by driving means (not shown) as indicated by arrows in the drawing. When the developing device 4 enters the developing operation, the two screws rotate in the reverse direction to each other, and circulate and convey the developer in the developer reservoir. At this time, the toner in the developer is frictionally charged to such a polarity as to adhere to the electrostatic latent image by stirring with the magnetic carrier.

  The developer transported to the first transport screw 12 is pumped onto the developing sleeve 10 by the magnetic field on the developing sleeve. Then, a carrier to which charged toner adheres is spiked along the magnetic field lines formed on the surface of the developing sleeve. These developers are transported along the developing sleeve by the magnetic field on the developing sleeve, and the layer thickness is regulated by the doctor blade 11. Then, the developer that has passed through the doctor blade 11 is transported to a development area facing the photoreceptor 1 and is used for development.

  The unconsumed toner and the carrier that have not been used for development in the development area A are separated from the development sleeve in the area where a magnetic field for separating the developer is formed after passing through the development area A, and the first transport Returned to the screw 12. Then, the toner is dispersed in the developer being circulated, and is again drawn up by the developing sleeve and used for development. By repeating such a cycle, a toner image is formed.

However, an image forming apparatus equipped with such a developing device has a problem that density unevenness occurs on a formed image. In particular, it becomes a problem in an image having a high area ratio such as a photograph.
Originally, it is ideal that the developer is separated from the developing sleeve in the region where the magnetic field for releasing the developer is formed, and the developer that is sufficiently mixed and stirred by the conveying screw is pumped onto the developer carrier. It is. However, the developer once detached from the developing sleeve may be pumped up again by the developing sleeve before being dispersed and stirred by the conveying screw. Further, the developer may be transported to the developing area again without detaching from the developing sleeve in the area where the magnetic field for detaching the developer is formed. Due to these poor developer releasability, irregular density unevenness as shown in FIG. 3 occurs.
In addition, density unevenness also occurs when the developer drawability is poor.

  In order to satisfactorily separate the developer from the developing sleeve in a region where a magnetic field for separating the developer is formed, Patent Document 1 proposes a configuration in which a scraping member is brought into contact with the surface of the developing sleeve. ing. As a result, density unevenness can be prevented. However, since the scraping member is brought into contact with the developing sleeve, the developer may be aggregated due to friction between the scraping member and the developing sleeve. If the developer agglomerates, defects may occur on the image. Further, the performance may not be maintained due to the wear of the scraping member over time.

Japanese Patent Application Laid-Open No. 2004-228561 proposes a configuration in which a developer stripping roller is provided in order to satisfactorily separate the developer from the developing sleeve in a region where a magnetic field for separating the developer is formed. In addition, the developer collected by the peeling roller is scraped off by a scraper, and the developer is sequentially conveyed to the developer collection conveyance chamber and the developer supply conveyance chamber, so that the developer concentration is sufficiently mixed and stirred by the conveyance screw. Has been proposed to supply a developer that is stable to the developing sleeve. However, such a developing device is not preferable because the size of the device cannot be increased.
JP 2000-321870 A JP 2002-091157 A

  In recent years, the layout in the developing device has been diversified along with the need for full color and miniaturization of the image forming apparatus. For example, in addition to the layout shown in FIG. 1 described above, a layout shown in FIG. 4 is known. In the developing device 104 of FIG. 1, the doctor blade 11 is provided on the upper side of the developing sleeve 10 in the figure, whereas in the developing device 204 of FIG. 4, the doctor blade 21 is located on the lower side of the developing sleeve 20 in the figure. On the side. Further, in the developing device 104 of FIG. 1, a developer detachment region is provided in the lower region of the developing sleeve 10 in the figure, whereas in the developing device 204 of FIG. A developer detachment region is provided in the region. Further, in the developing device 204 of FIG. 4, the developing sleeve 20 and the first conveying screw 22 are closer to each other than the developing device 104 of FIG. 1, and the lateral width direction of the developing device is narrow.

As a full-color image forming apparatus, there is known an apparatus in which developing devices for four colors (cyan, magenta, yellow, and black) are arranged in parallel as shown in FIG. In such an apparatus, it is desired to reduce the width of the developing device in order to reduce the size of the entire image forming apparatus. For this reason, an increasing number of developing devices have a layout as shown in FIG. 4 in which the developing sleeve 10 and the conveying screw 12 are arranged close to each other in the width direction.
However, in the developing device of FIG. 4 type, as compared with the developing device of FIG. 1 type, as described above, the developing sleeve 20 and the first conveying screw 22 are close to each other in the lateral width direction. Therefore, the degree of freedom of arrangement between the location where the developer is pumped on the surface of the developing sleeve that forms the magnetic field for forming the magnetic field and the location where the magnetic field for separating the developer is formed is limited. Specifically, the developer pumping location and the developer detachment location must be brought close to each other.
As a result, it becomes difficult to satisfy the developer detachability while ensuring the developer pumpability as compared with the layout shown in FIG. 1, and the occurrence of density unevenness becomes more serious. It was. The reason for this will be described later.

  The present invention has been made in view of the above background, and an object of the present invention is to provide the following image forming apparatus, a developing device mounted thereon, and a process cartridge. That is, an image forming apparatus or the like that can reduce the size of the apparatus and can obtain a high-quality image that does not cause density unevenness.

In order to achieve the above object, the invention of claim 1 is arranged to face an image carrier on which an electrostatic latent image is formed on the surface, and carries a thin layer of developer to A developer carrying member that is conveyed to a developing region that is close to the developer, a developer supply member that circulates and conveys the developer and supplies the developer to the developer carrying member, and the developer carrying member on the developer carrying member A magnetic field for pumping the developer from the developer supply member by a magnetic force, a magnetic field for transporting the developer to the development area, and a developer that has not been used for development in the development area from the surface of the developer carrier by a magnetic force. A developing device comprising a magnetic field forming means for forming a magnetic field to be released, wherein an upper end is located below the portion set as the magnetic field for releasing the developer from the surface of the developer carrying member, and the developer carrying A space on the side facing the body surface, and the surface of the developer carrying body It is characterized in that the developer et withdrawal were provided with a partition plate partitioning the falling space to fall.
According to a second aspect of the present invention, in the developing device of the first aspect, the magnetic force on the surface of the developer carrier facing the upper end of the partition plate is such that the developer is detached from the surface of the developer carrier. It is characterized by facing.
According to a third aspect of the present invention, in the developing device of the second aspect, the developer detachment portion on the surface of the developer carrying member where a magnetic field for detaching the developer from the surface of the developer carrying member is formed, A developer holding portion on the surface of the developer carrying member on which the magnetic field for holding the developer on the surface of the developer carrying member is formed adjacent to the developer detaching portion on the upstream side in the movement direction of the developer carrying member; The developer carrying portion on the developer pumping surface on the surface of the developer carrying member where a magnetic field for pumping the developer is formed adjacent to the developer detachment portion on the downstream side in the moving direction of the developer carrying member. The direction of the magnetic force lines on the surface of the body is the same direction, the minimum value of the normal magnetic flux density at the developer removal location is 0 [mT] or more, the maximum value of the normal magnetic flux density at the developer holding location and the developer pumping up Of the maximum value of the normal flux density 0 [%] is characterized in that configured to become less.
According to a fourth aspect of the present invention, in the developing device according to the first, second, or third aspect, the apparatus is normally used among the line segments connecting the developer carrier axis and the developer carrier axis. 45 [°] in the clockwise direction when a line segment that is parallel to the horizontal line when placed in the state and is close to the partition plate is defined as a reference line and the axis of the developer carrier is defined as a reference point. To 90 [°] includes a line segment connecting the developer carrier axis and the developer supply member axis.
According to a fifth aspect of the present invention, in the developing device of the first, second, third, or fourth aspect, the developer is a two-component developer composed of toner and magnetic particles, and the particle size of the magnetic particles is 20 [Μm] or more and 50 [μm] or less.
The invention of claim 6 is the developing device according to claim 5, wherein the magnetic particles are obtained by coating a core material of a magnetic material with a resin coat film, and the resin coat film comprises a thermoplastic resin and a melanin resin. A resin component containing a cross-linked resin component and a charge control agent is used.
According to a seventh aspect of the present invention, there is provided an image carrier that carries an electrostatic latent image, a charging device that charges the image carrier, and a developer that carries the developer on the developer carrier and that faces the image carrier. A developing device that transports the toner image to a region and develops the latent image on the image carrier to form a toner image, and removes residual toner remaining on the image carrier after the developed toner image is transferred to a transfer material In the image forming apparatus having the cleaning device, the developing device according to claim 1, 2, 3, 4, 5, or 6 is used as the developing device.
The invention according to claim 8 is an image carrier that carries an electrostatic latent image, a charging device that charges the image carrier, and a developer that carries the developer on the developer carrier and faces the image carrier. A developing device that transports the toner image to the area and develops the latent image on the image carrier to form a toner image, and removes residual toner remaining on the image carrier after the developed toner image is transferred to a transfer material. In a process cartridge that is used in an image forming apparatus having a cleaning device and is configured to be detachable from a main body of the image forming apparatus and includes at least the image carrier and the developing device, the developing device Further, the present invention is characterized in that one according to claim 1 or 2 is used.

First, a developer detachment location on the surface of the developer support where a magnetic field for detaching the developer from the surface of the developer support is formed, and adjacent to the developer detachment location on the downstream side in the movement direction of the developer support. FIG. 15 shows why it is difficult to achieve both developer detachability and developer pumpability when the developer pumping site on the developer carrier on which the magnetic field for pumping the developer is formed is brought close. This will be described with reference to FIG.
FIG. 15 is an explanatory diagram showing an example of the developing device when the developer detachment portion and the developer pumping portion are arranged close to each other. Even if the developer is satisfactorily detached from the developer carrying member, as shown in the figure, it may bounce off the unit side plate, and the developer may be pumped up to the developing sleeve again. Further, the developer is generated by the magnetic force of the developer pumping point c on the surface of the developer carrier, where a magnetic field for pumping the developer is formed adjacent to the developer detachment point on the downstream side of the developer carrier surface movement direction. May be pumped up again by the developing sleeve.

  In order to avoid such a problem, as shown in FIG. 16, a method of arranging the developer pumping point c at the lower side in the drawing so as to be separated from the developer detaching point b can be considered. This is to prevent the developer separated from the developing sleeve from being pumped up again by the magnetic force from the developer pumping point c. However, with such a configuration, the width of pumping up the developer is narrowed, and the amount of developer held is reduced. Accordingly, there arises a problem that density unevenness (pitch unevenness) of the conveying screw is likely to occur on the image. Here, it is conceivable to increase the magnetic force at the developer pumping point c, but the developer is held with a strong force, and the stress of the doctor blade increases. As a result, problems such as deterioration of the developer occur, which is not preferable.

In the present invention, by providing the partition plate, it is possible to prevent the developer that is one end away from the developer carrier from bouncing back on the unit side plate and being pumped up to the developer carrier again. In addition, as shown in FIG. 6, the developer pumping point on the surface of the developer carrying member where a magnetic field for pumping the developer is formed adjacent to the developer detachment point on the downstream side in the developer carrier surface moving direction. The magnetic force can prevent the developer from being pumped up again. This is because the developer once separated from the developer carrying member once returns to the developer supplying member as soon as the developer leaves and falls into the space opposite to the space where the partition plate and the developer carrying member face each other. Because it will be. Therefore, the agent releasability of the developer can be improved.
Further, by providing the partition plate, the developer detachment point b, the developer pumping point c, and the developer supply member can be brought close to each other. Similarly to the above, if the developer is separated and dropped into the space opposite to the space where the partition plate and the developer carrying member face each other, even if they are brought close to each other, the developer that has detached once is transported by the transport screw. This is because it is possible to prevent a problem that the developer is again pumped up before being mixed and stirred. Further, since the developer supply member and the developer pumping portion can be brought close to each other, the developer pumpability from the developer supply member to the developer carrying member can be kept good.
From the above, it is possible to achieve both the developer pumping property and the developer detachability. Further, the partition plate has a simple configuration, and the developer detachment site, the developer pumping site, and the developer supply member can be disposed close to each other, so that the apparatus can be downsized.

  According to these inventions, there is an excellent effect that the apparatus can be miniaturized and a high-quality image without density unevenness can be obtained.

Hereinafter, an example of an embodiment in which a color printer as an image forming apparatus (hereinafter simply referred to as “printer”) is applied to the present invention will be described.
FIG. 5 is a schematic configuration diagram of the printer according to the present embodiment. In the figure, a charging device 2, a writing device 3, a developing device 4, a cleaning device 5, a transfer device 6, a static elimination device (not shown), and the like are formed around the photosensitive member 1 on the drum as an image carrier. Visible image forming means is provided.

  This printer includes four sets of process cartridges 7Y, 7M, 7C, and 7K for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (K). Needless to say, Y, M, C, and K appended to the numbers of the respective symbols indicate members for yellow, magenta, cyan, and black (the same applies hereinafter). These process cartridges 7Y, 7M, 7C, and 7K have the same configuration except that each color toner is accommodated. In the present embodiment, the process cartridge includes the photosensitive member 1, the charging device 2, the developing device 4, the cleaning device 5, and the like, and is detachable from the printer main body, and is replaced when the lifetime is reached.

In the copying machine having such a configuration, the photosensitive member 1 is rotationally driven at a constant speed by driving means such as a motor (not shown). Then, after the surface is uniformly charged by the charging device 2 in the dark, the writing device 3 performs optical scanning based on the image information. By this optical scanning, an electrostatic latent image is formed on the surface of the photoreceptor 1. When the electrostatic latent image passes through a developing nip where a developing sleeve 30 which is a developer carrying member provided in a developing device 4 (described later) and the photosensitive member 1 are in contact with each other, toner (not shown) is adhered to the toner. Developed into an image.
The toner image formed on the photoreceptor 1 by development is transferred onto a transfer medium by the transfer device 6. Then, this transfer medium is sent to a fixing device, and the toner is fused by means such as heat and pressure and discharged outside the apparatus. On the other hand, the untransferred toner remaining on the photoreceptor 1 after the transfer is scraped off by the cleaning device 5. Then, after the cleaning, the photoreceptor 1 is subjected to residual charge removal by a static elimination device (not shown), and is prepared for the next charging by the charging device 2.

  FIG. 6 is a schematic configuration diagram showing the configuration of the developing device 4 of the present embodiment. The developing device contains a two-component developer composed of a carrier and toner. As shown in the figure, a developing sleeve 30 is provided so as to be partially exposed from the opening of the casing. In addition, a developer storage section 37 in which a two-component developer is stored, a first transport screw 32 that is a developer supply member provided in the developer storage section 37, a second transport screw 33, and developer regulation. A doctor blade 31 as a member is provided.

  The developing sleeve 30 is made of a non-magnetic material such as aluminum formed in a hollow cylindrical shape, and a plurality of magnets for forming a magnetic field at predetermined positions on the surface of the developing sleeve are fixedly disposed therein. With these magnets, a developer pumping magnetic field for supporting the developer on the developing sleeve, a developer conveying magnetic field for conveying the developer to the developing area, and a developer detaching magnetic field for releasing the developer from the developing sleeve. Is formed. Here, a part where the developer is released on the surface of the developing sleeve where a magnetic field for releasing the developer from the surface of the developing sleeve is formed is defined as a developer leaving part b. Further, a developer holding portion on the surface of the developing sleeve where a magnetic field for holding the developer on the surface of the developer carrying member is formed adjacent to the developer detachment portion on the upstream side of the developing sleeve surface moving direction is held by the developer. The location where the developer is pumped up on the surface of the developing sleeve where the magnetic field for pumping up the developer is formed adjacent to the developer detachment location on the downstream side of the developing sleeve surface moving direction is defined as the developer pumping location c. . The developer holding part a and the developer pumping part c will be described later.

  The first transport screw 32 and the second transport screw 33 are arranged in parallel to each other and are driven to rotate in directions opposite to each other, as described with reference to FIG. When the developing device 4 enters the developing operation, the two screws rotate in the reverse direction to each other and circulate and convey the developer. At this time, the toner in the developer is frictionally charged to such a polarity as to adhere to the electrostatic latent image by stirring with the magnetic carrier.

  The developer conveyed to the first conveying screw 32 is pumped onto the developing sleeve 30 by a magnetic field on the surface of the developing sleeve 30. Then, a carrier to which charged toner is attached is spiked along the lines of magnetic force formed on the surface of the developing sleeve. These developers are conveyed along the developing sleeve by the magnetic field on the developing sleeve, and the layer thickness is regulated by the doctor blade 31. Then, the developer that has passed through the doctor blade 31 is transported to a development area facing the photoreceptor 1 and is used for development.

  The carrier that has passed through the development area A and the toner that has not been developed are separated from the development sleeve by the magnetic force of the developer detachment magnetic pole provided in the development sleeve 30 and returned to the developer reservoir. It is. Then, the toner is dispersed in the developer being circulated, and is again drawn up by the developing sleeve and used for development. By repeating such a cycle, a toner image is formed.

  Next, the characteristic part of this embodiment is demonstrated. As shown in FIG. 6, the upper end is located in the casing below the position set for the magnetic field to be detached from the surface of the developing sleeve, and the space on the side facing the surface of the developing sleeve and the developer falls after being detached. A partition plate 35 is provided to partition the space for this purpose. The partition plate 35 is made of a nonmagnetic material so as not to affect the magnetic field from the inside of the developing sleeve. The partition plate 35 may be configured integrally with the casing, or may be configured as a separate body.

By providing the partition plate 35 in this manner, it is possible to prevent the developer that is separated from the developing sleeve 30 from bounce-off on the unit side plate and pumped up to the developing sleeve 30 again. Further, it is possible to prevent the toner from being pumped up again to the developing sleeve 30 before being mixed and stirred by the conveying screw. This is because once the developer one end away from the developing sleeve 30 separates and falls into the space on the left side in FIG. 6 of the partition plate 35, it is returned to the conveying screw as it is, and the developing separated from the developing sleeve 30 is removed. This is because it is possible to prevent the agent from being pumped up again by the developing sleeve 30 before being mixed and stirred by the conveying screw. Therefore, the agent releasability of the developer can be improved.
In addition, the developer pumping point c, the developer detaching point b, and the first conveying screw 32 can be brought close to each other. This is because if the developer one end away from the developing sleeve falls into the space on the left side of the partition plate 35 in the drawing, it is possible to prevent the problem that the developer is pumped again before being mixed and stirred by the conveying screw. Since the first conveying screw 32 and the developer pumping point c can be brought close to each other, the developer pumping property from the first conveying screw 32 to the developing sleeve can be kept good.
From the above, it is possible to achieve both the developer pumping property and the developer detachability. Further, the partition plate 35 has a simple configuration, and the developer detachment point b, the developer pumping point c, and the first transport screw 32 can be disposed close to each other, so that the apparatus can be downsized.
In this embodiment, the developer is pumped up on the surface of the developer carrying member c where a magnetic field is formed adjacent to the developer pumping point c and the developer pumping point c on the downstream side of the developing sleeve surface movement direction. It plays its role depending on the location.

  In the present embodiment, the magnetic force on the developing sleeve 30 facing the upper end of the partition plate 35 is within a range where the magnetic force in the direction in which the developer is separated from the developing sleeve 30 (hereinafter referred to as “repulsive force”). It is set. By setting in this way, the developer receives a combined force of a magnetic force and a centrifugal force as a repulsive force as indicated by an arrow A in FIG. As a result, the developer is directed to the developing casing side plate. Since the developer passes through the left side of the partition plate 35 in the drawing without fail, the developer separated from the developing sleeve 30 is not pumped up again to the developing sleeve 30 before being dispersed and stirred by the conveying screw, and an excellent developer. Separation can be obtained.

  The lower end of the partition plate 35 passes through the maximum peak value of the normal magnetic flux density on the developing sleeve 30 due to the developer pumping point c, and is set below the horizontal line when the printer is left in a normal use state. It is preferable to do. By installing in this way, the developer separated from the developing sleeve 30 can be more effectively prevented from being pumped onto the developing sleeve 30 before being stirred by the first conveying screw 32. It should be noted that the lower end of the partition plate 35 needs to ensure a gap that does not give a frictional force to the developer with the first conveying screw 32. The normal magnetic flux density means the magnetic flux density on the developing sleeve surface in the normal direction of the developing sleeve surface.

Further, the direction of the magnetic lines of force at the developer holding point a, the developer pumping point c, and the developer detaching point b are the same direction, and the minimum value of the normal magnetic flux density at the developer detaching point b is 0 [mT] or more. The maximum value of the normal magnetic flux density at the developer holding point a and the maximum value of the normal magnetic flux density at the developer pumping point c are set to 20% or less of the larger value.
By setting in this way, the magnetic force on the developing sleeve facing the upper end portion of the partition plate can be easily set as a repulsive force.
At this time, an angle formed by the maximum value of the normal magnetic flux density on the developing sleeve by the developer holding portion a, the developing sleeve axial center T, and the maximum value of the normal magnetic flux density on the developing sleeve by the developer pumping location c. When the angle is less than 40 [°], the area where the magnet can be arranged is narrow, and the setting is substantially difficult. Further, if the same angle is larger than 120 [°], it is difficult to set the direction of the magnetic force lines at the developer detachment point b on the developing sleeve at the developer holding point a and the developer pumping point c. . Accordingly, it is preferable that the same angle be 40 [°] or more and 120 [°] or less.

  In the present embodiment, the line segment connecting the axis of the developing sleeve 30 and the axis of the first conveying screw 32 is parallel to the horizontal line when the apparatus is placed in a normal use state, and the partition. When the line segment on the side close to the plate 35 is a reference line and the axial center of the developing sleeve 30 is a reference point, the axial center of the developing sleeve 30 is in the range of 45 [°] to 90 [°] in FIG. And a line segment connecting the axial center of the first conveying screw 32 is included. With this configuration, the lateral width of the developing device 4 can be reduced, and the overall width of the printer can be reduced.

Next, the developer used in this embodiment will be described.
As the carrier for the two-component developer, it is desirable to use a coat film having elasticity and strong adhesive force and coated with a coat film containing particles having a diameter larger than the film thickness on the surface. FIG. 8 is an explanatory diagram of the carrier 500. Ferrite 501 is used as the core material of the carrier 500. The surface of the ferrite 501 is coated with a coating film 502 containing a charge adjusting agent in a resin component obtained by crosslinking a thermoplastic resin such as acrylic and a melamine resin. The coat film 502 has elasticity and strong adhesive force. Further, particles having a diameter larger than the film thickness of the coat film 502, for example, alumina particles 503 are dispersed on the surface. The alumina particles 503 are held with a strong adhesive force of the coating film 502. Whereas the conventional carrier is configured on the basis of the idea of obtaining a long life while gradually scraping off the hard coat film, the carrier 500 shown in the figure absorbs the impact by the elasticity of the coat film 502 and absorbs the impact. Suppress cutting. Further, by dispersing alumina particles 503 having a diameter larger than the film thickness on the surface of the carrier 501, it is possible to prevent the impact on the coat film 502 and to clean the spent material. As described above, since the coating film can be prevented from being scraped and spent, it is possible to achieve a longer life than conventional carriers. Accordingly, it is possible to expect stabilization of the toner pumping amount, that is, stabilization of quality over a long period of time.

  Furthermore, the carrier particle size can be reduced to form an image with more excellent dot reproducibility. Specifically, the carrier particle size is desirably 20 [μm] or more and 50 [μm] or less. By setting the carrier particle size smaller than that of the conventional one and further setting the particle size in such a range, it is possible to uniformly reduce the thickness of the developer spike (carrier chain) at the time of image formation. Therefore, it is possible to deliver a more precise toner. In addition, since the density of developer spikes per unit area on the developing sleeve is increased, toner can be delivered to the latent image on the photoreceptor without any gap. Thereby, an image with more excellent dot reproducibility can be formed. If the carrier particle size is too larger than 50 [μm], when compared with the same carrier amount, the total surface area of the carrier becomes small and the amount of toner held decreases. For this reason, the toner density is lowered. Although it is possible to increase the pumping amount to maintain the developing ability, toner sticking is likely to occur. On the other hand, if the carrier particle diameter is too smaller than 20 [μm], the magnetic force holding force by the mag roller is reduced, causing carrier scattering and increasing the carrier adhesion to the photoreceptor, so 20 μm or more is desirable. .

［実施例２］
表２に示す条件以外は、上記実施例１と同様の条件下（図１０参照）、現像剤離れ性不良に起因する画像ムラと現像剤汲み上げ性不良に起因する画像ムラについて評価を実施した。

［実施例３］
表３に示す条件以外は、上記実施例１と同様の条件下（図１１参照）、現像剤離れ性不良に起因する画像ムラと現像剤汲み上げ性不良に起因する画像ムラについて評価を実施した。

〔比較例１〕
表４に示す条件以外は、上記実施例１と同様の条件下（図１２参照）、現像剤離れ性不良に起因する画像ムラと現像剤汲み上げ性不良に起因する画像ムラについて評価を実施した。

〔比較例２〕
表５に示す条件以外は、上記実施例１と同様の条件下（図１３参照）、現像剤離れ性不良に起因する画像ムラと現像剤汲み上げ性不良に起因する画像ムラについて評価を実施した。

〔比較例３〕
表６に示す条件以外は、上記実施例１と同様の条件下（図１４参照）、現像剤離れ性不良に起因する画像ムラと現像剤汲み上げ性不良に起因する画像ムラについて評価を実施した。

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. The evaluation results for each example and comparative example are summarized in Table 7 below.
[Example 1]
Under the following configuration (see Table 1), evaluation was performed for image unevenness due to poor developer separation and image unevenness due to poor developer pumpability. FIG. 9 shows the configuration of the developing device at this time. The angle shown in the figure is a line segment connecting the center of the developing sleeve and the surface of the developing sleeve, which is a line segment parallel to the horizontal line when the printer is left in a normal use state, and the partition plate 9 represents the angle when the rotation direction in the clockwise direction in FIG. 9 is positive from this position, with the line segment having a larger distance from the reference line as the reference line and the developing sleeve axis as the reference point. In Example 1, the developer holding portion a, the developer detaching portion b, and the developer pumping portion c on the developing sleeve are all set to the N pole.
Further, the magnetic force of the developing sleeve at the front end position of the partition plate was obtained in the same manner as the method described in JP-A-5-249821.

[Example 2]
Except for the conditions shown in Table 2, the same conditions as in Example 1 above (see FIG. 10) were used to evaluate image unevenness due to poor developer separation and image unevenness due to poor developer pumpability.

[Example 3]
Except for the conditions shown in Table 3, under the same conditions as in Example 1 (see FIG. 11), evaluation was performed for image unevenness due to poor developer separation and image unevenness due to poor developer pumping property.

[Comparative Example 1]
Except for the conditions shown in Table 4, under the same conditions as in Example 1 above (see FIG. 12), evaluation was performed for image unevenness due to poor developer separation and image unevenness due to poor developer pumpability.

[Comparative Example 2]
Except for the conditions shown in Table 5, under the same conditions as in Example 1 (see FIG. 13), evaluation was performed for image unevenness due to poor developer separation and image unevenness due to poor developer pumpability.

[Comparative Example 3]
Except for the conditions shown in Table 6, under the same conditions as in Example 1 above (see FIG. 14), evaluation was performed for image unevenness due to poor developer separation and image unevenness due to poor developer pumping property.

The evaluation results for the above examples and comparative examples are summarized in Table 7 below. The allowable levels for each evaluation item are as follows.
[Image unevenness due to poor developer separation]
The image output was evaluated by sensory evaluation.
Rank ◎: Excellent rank ○: No problem rank △: Inferior rank ×: Remarkably inferior [image unevenness due to poor developer pumping property]
The image output was evaluated by sensory evaluation.
Rank ○: No problem Rank △: Inferior

From Table 7, it can be seen that the provision of the partition plate improves both image unevenness due to poor developer separation and image unevenness due to poor developer pumping property. It was also found that the best results were obtained when a partition plate was provided and the magnetic force on the developing sleeve at the tip of the partition plate was a repulsive force.
On the other hand, when the partition plate is not provided, it can be seen that image unevenness appears. Even if the developer detachability from the developing sleeve is good, the developer is pumped up again to the developing sleeve due to the bounce of the unit side plate as shown in FIG. It is probable that the drug withdrawal property has deteriorated.

Here, in order to avoid image density unevenness without a partition plate, a method of arranging the position of the developer pumping point c below the unit as shown in FIG. 16 can be considered. This is for preventing the developer separated from the developing sleeve from being pumped up again by the magnetic field at the developer pumping point c. However, with such a configuration, the width of pumping up the developer is narrowed, and the amount of developer held is reduced. Accordingly, there arises a problem that density unevenness (pitch unevenness) of the conveying screw is likely to occur on the image. Here, it is conceivable to increase the magnetic force at the developer pumping point c, but the developer is held with a strong force, and the stress of the doctor blade increases. As a result, problems such as deterioration of the developer occur, which is not preferable.

In the present embodiment, the upper end is located below the portion set as the magnetic field to be separated from the surface of the developing sleeve 30, and the partition plate 35 partitions the space facing the surface of the developing sleeve and the falling space from which the developer has separated. Is arranged. By adopting such a configuration, it becomes possible to achieve both developer drawing-up performance and developer release performance. As a result, a high-quality image without density unevenness can be provided. Further, the apparatus can be downsized.
In the present embodiment, the magnetic force on the developing sleeve facing the upper end of the partition plate 35 has a range in which the magnetic force in the direction in which the developer is separated from the developing sleeve (hereinafter referred to as “repulsive force”). It is set to be. By setting in this way, the developer can be reliably detached from the developing sleeve 30 and collected in the developer storage section. Therefore, both the developer separating property and the developer pumping property can be achieved, and an excellent image quality can be obtained.
In the present embodiment, the direction of the magnetic force lines at the developer holding portion a, the developer pumping portion c, and the developer detaching portion b are the same direction, and the minimum value of the normal magnetic flux density at the developer detaching portion b is set. Is set to 0 [mT] or more and 20 [%] or less of the larger value of the maximum value of the normal magnetic flux density of the developer holding portion a and the maximum value of the normal magnetic flux density of the developer pumping location c. It is set. With such an arrangement, it is possible to easily provide a developing device in which the magnetic force on the developing sleeve facing the upper end of the partition plate 35 is a repulsive force.
In the present embodiment, the line segment connecting the axis of the developing sleeve 30 and the axis of the first conveying screw 32 is parallel to the horizontal line when the apparatus is placed in a normal use state, Further, when the line segment on the side close to the partition plate 35 is a reference line and the axial center of the developing sleeve 30 is a reference point, the developing sleeve 30 is within a range of 45 [°] to 90 [°] in FIG. A line segment connecting the axis and the axis of the first conveying screw 32 is included. With this configuration, the lateral width of the developing device can be reduced, and the overall width of the printer can be reduced.
Further, according to the present embodiment, the developer is a two-component developer including a toner and a carrier as magnetic particles, and the carrier particle size is set to 20 [μm] or more and 50 [μm] or less. By setting the carrier particle size to 50 [μm] or less, the thickness of the developer spike (carrier chain) at the time of image formation can be uniformly thinned, and more precise toner can be delivered. . In addition, since the density of developer spikes per unit area on the developing sleeve is increased, toner can be delivered to the latent image on the photoreceptor without any gap. Thereby, an image with more excellent dot reproducibility can be formed. Note that if the carrier particle size is too smaller than 20 [μm], carrier adhesion to the photoconductor increases, so 20 μm or more is desirable.
Further, according to the present embodiment, the carrier has a resin coating film on the magnetic core material, and the resin coating film is a resin component obtained by crosslinking a thermoplastic resin and a melanin resin, What contained the modifier was used. The conventional carrier is configured to obtain a long life while gradually scraping a hard coat film, whereas this carrier absorbs an impact and suppresses the film scraping because the coat film has elasticity. Therefore, the lifetime can be further extended as compared with the conventional carrier. Accordingly, it is possible to expect stabilization of the toner pumping amount, that is, stabilization of quality over a long period of time.
Further, according to the present embodiment, the photosensitive member, the charging device, and the developer are carried on the developing sleeve and conveyed to the developing region facing the photosensitive member, and the latent image on the photosensitive member is developed to form a toner image. The above-described developing device is used in a printer as an image forming apparatus having a developing device and a cleaning device that removes transfer residual toner remaining on the photosensitive member after transferring the developed toner image to a transfer material. By using this developing device, it is possible to obtain a good image without density unevenness.
Further, according to the present embodiment, the photosensitive member, the charging device, and the developer are carried on the developing sleeve and conveyed to the developing region facing the photosensitive member, and the latent image on the photosensitive member is developed to form a toner image. In an image forming apparatus having a developing device and a cleaning device that removes transfer residual toner remaining on the photoconductor after the developed toner image is transferred to a transfer material, the photoconductor, the developing device, the charging device, and the cleaning The developing device described above is used in a process cartridge that integrally supports at least a device including a developing device selected from the devices and is detachable from the main body of the image forming apparatus. By using this developing device, it is possible to obtain a good image without density unevenness. Furthermore, maintenance and replacement of the image forming means including the photosensitive member and the developing device are facilitated.

1 is a schematic configuration diagram illustrating an example of a conventional developing device. The top view which shows arrangement | positioning with a developing sleeve and a conveyance screw. Explanatory drawing of irregular density unevenness. 1 is a schematic configuration diagram illustrating an example of a conventional developing device. FIG. 2 is a schematic explanatory diagram illustrating a configuration of a printer. FIG. 2 is a schematic configuration diagram of a developing device according to the present embodiment. Explanatory drawing which shows a motion of a developing agent. Schematic diagram of the carrier. 1 is a schematic configuration diagram of a developing device according to Embodiment 1. FIG. FIG. 6 is a schematic configuration diagram of a developing device according to Embodiment 2. FIG. 9 is a schematic configuration diagram of a developing device according to Embodiment 3. FIG. 2 is a schematic configuration diagram of a developing device according to Comparative Example 1. FIG. 6 is a schematic configuration diagram of a developing device according to Comparative Example 2. FIG. 9 is a schematic configuration diagram of a developing device according to Comparative Example 3. Explanatory drawing which shows a motion of the developer when there is no partition plate. Explanatory drawing at the time of bringing up the developer drawing-up location c below the developing sleeve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging device 4, 104, 204 Developing device 5 Cleaning device 10, 20, 30 Developing sleeve 11, 21, 31 Doctor blade 12, 22, 32 First conveying screw 13, 23, 33 Second conveying screw 35 Partition Plate 500 Carrier 502 Coat film

Claims (8)

A developer carrier that is disposed so as to face an image carrier on which an electrostatic latent image is formed, carries a thin layer of developer, and conveys it to a development region that is close to the image carrier; ,
A developer supplying member for circulating and supplying the developer to the developer carrying member while stirring the developer;
A magnetic field for pumping the developer from the developer supply member onto the developer carrier by a magnetic force, a magnetic field for transporting the developer to the development area, and a developer that was not used for development in the development area by the magnetic force In a developing device comprising a means for forming a magnetic field for forming a magnetic field to be detached from the surface of the developer carrying member,
The upper end is located below the portion set to the magnetic field for releasing the developer from the developer carrying surface, the space facing the developer carrying surface, and the developer separated from the developer carrying surface. A developing device characterized in that a partition plate is provided for partitioning a falling space where the water drops. The developing device according to claim 1.
The developing device according to claim 1, wherein the magnetic force on the surface of the developer carrying member facing the upper end portion of the partition plate is directed in a direction in which the developer is detached from the surface of the developer carrying member. The developing device according to claim 2.
A developer detachment point on the surface of the developer carrier where a magnetic field for detaching the developer from the surface of the developer carrier is formed, and adjacent to the developer detachment point upstream in the direction of movement of the developer carrier. A developer holding portion on the surface of the developer carrying member where a magnetic field for holding the developer on the surface of the developer carrying member is formed, and the developer detaching portion on the downstream side in the movement direction of the developer carrying member. The direction of the lines of magnetic force on the surface of the developer carrying body on the surface of the developer carrying body where the magnetic field for pumping the developer is formed adjacent to the developer carrying surface is the same direction, The minimum value of the normal magnetic flux density is 0 [mT] or more, and the larger one of the maximum value of the normal magnetic flux density of the developer holding portion and the maximum value of the normal magnetic flux density of the developer pumping portion is 20 [%] Current Apparatus. The developing device according to claim 1, 2, or 3,
Of the line connecting the developer carrier axis and the developer carrier axis, the side parallel to the horizontal line when the apparatus is placed in a normal use state and close to the partition plate When the line segment is a reference line and the axis of the developer carrier is a reference point, the developer carrier axis and the developer supply member axis are in the range of 45 [°] to 90 [°] in the clockwise direction. A developing device configured to include a line segment connecting the heart. The developing device according to claim 1, 2, 3, or 4.
A developing device, wherein the developer is a two-component developer composed of toner and magnetic particles, and the particle size of the magnetic particles is 20 [μm] or more and 50 [μm] or less. The developing device according to claim 5.
As the magnetic particles, a magnetic core material is coated with a resin coating film, and the resin coating film contains a resin component obtained by crosslinking a thermoplastic resin and a melanin resin, and a charge control agent. A developing device characterized by using An image carrier that carries an electrostatic latent image, a charging device that charges the image carrier, a developer carried on the developer carrier, and transported to a development area facing the image carrier, and the image carrier An image forming apparatus comprising: a developing device that develops a latent image on the image to form a toner image; and a cleaning device that removes transfer residual toner remaining on the image carrier after the developed toner image is transferred to a transfer material. In
An image forming apparatus using the developing device according to claim 1, 2, 3, 4, 5 or 6 as the developing device. An image carrier that carries an electrostatic latent image, a charging device that charges the image carrier, a developer carried on the developer carrier, and transported to a development area facing the image carrier, and the image carrier An image forming apparatus comprising: a developing device that develops a latent image on the image to form a toner image; and a cleaning device that removes transfer residual toner remaining on the image carrier after the developed toner image is transferred to a transfer material. And a process cartridge that is configured to be detachable from the image forming apparatus main body and includes at least the image carrier and the developing device.
3. A process cartridge according to claim 1, wherein the developing device is the one of claim 1 or 2.

Images