JP2009020210A - Developing device, process cartridge, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device configured so that a nonuniform density caused by a developing gap difference relative to a developing sleeve is prevented without increasing a cost. <P>SOLUTION: The developing device is configured such that using a developing means 5 with a developer carried thereon, the developer is conveyed to an electrostatic latent image formed on a latent image carrier, and thereby the electrostatic latent image is processed to be visible. The developing means 5 includes: the rotatable developing sleeve 5Y for carrying developer thereon; a magnet roller having a plurality of magnetic poles, including a developing main pole, which are arranged within the developing sleeve along the circumferential direction of the sleeve; and a blade disposed opposite the developing sleeve and used to regulate the thickness of the layer of developer carried on the developing sleeve. The developing sleeve has an inside diameter that is uniform in the axial direction, and an outside diameter that increases from each axial end toward the center in the axial direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a developing device, a process cartridge, and an image forming apparatus, and more particularly to a developing gap maintaining structure in a magnetic brush developing system.

  As is well known, one of image forming methods is an electrophotographic method. In this system, when an electrostatic latent image formed on a photoconductor corresponding to a latent image carrier is subjected to visible image processing upon receiving toner from a developing device, the toner image is recorded on a recording medium such as recording paper. The transferred toner image is fixed by a melting / penetrating action using heat and pressure in a fixing device, and then discharged to form a copy or a printed output.

  As a developing device used for performing visible image processing, a configuration using either a one-component developer using magnetic toner or a two-component developer using magnetic carrier is known.

  The developer carried on the developing sleeve adheres to the electrostatic latent image on the photosensitive member by electrostatic attraction force from the electrostatic latent image. It is important to prevent occurrence of abnormal images such as uneven image density and fading. Therefore, it is practiced to accurately define the distance between the developing sleeve and the photosensitive member.

  Conventionally, as a developing sleeve configuration, a hollow cylindrical sleeve body capable of carrying a developer on its peripheral surface and a plurality of magnetic poles such as a developing main pole and a conveying magnetic pole are provided along the circumferential direction. There is a configuration having a magnet roller, and a configuration in which the developing sleeve is opposed to the photosensitive member with a predetermined interval is known (for example, Patent Document 1).

FIG. 6 is a diagram illustrating the configuration of the developing sleeve described above. In FIG. 6, the developing sleeve 100 rotates when the sleeve body 100A is driven by the rotating shaft 100A1, while the magnet roller 100B rotates the supporting shaft 100B1. The developer is fixed by being integrated with the support portion. As the sleeve body 100A rotates, the developer carried on the peripheral surface rolls while facing the magnetic pole on the magnet roller 100B side, and develops. A magnetic brush can be configured at a position facing the main pole.
That is, in FIG. 6, bearings 100C are respectively attached to end plates fixed to both axial sides of the sleeve body 100A, and the support shaft 100B1 of the magnet roller 100B is inserted into the bearing 100C. A rotating shaft 100A1 of the sleeve main body 100A is integrated with one end plate, and can be rotated via a gear 101 shown in the support structure shown in FIG.

  A D-cut surface 100B2 formed by cutting a part of the peripheral surface is provided near the one end portion in the axial direction of the support shaft 100B1 of the magnet roller 100B so as to be used for magnetic pole alignment. It has become.

FIG. 7 is a view showing an example of a support structure for the developing sleeve 100 and the photosensitive member 200 described above. In FIG. 7, the developing sleeve 100 is formed with respect to the developing portion casing member 150 in the process cartridge. The rotation shaft 100A1 and the support shaft 100B1 of the magnet roller 100B are inserted. The rotation shaft 100A1 is supported by a bearing 150A. Thus, it fits with the D-cut surface 100B2 of the support shaft 100B1. A driving force transmission gear 101 is attached to the rotation shaft 100A1 of the sleeve main body 100A, and the shaft end is rotatably supported using a bearing 301 with respect to a restriction plate 300 described later.
The photosensitive member 200 is rotatably supported on the wall portion 400 of the process cartridge via the bearing 201.

A shaft support portion between the developing sleeve 100 and the photosensitive member 200 is provided with a defining plate 300 for defining a developing gap that is a distance between the two.
The defining plate 300 is inserted through the shaft end of the rotation shaft of the sleeve main body 100A and the support shaft end portion of the magnet roller 100B, and the rotation shaft shaft end of the photoconductor 200 is inserted therethrough. This is a member for setting the distance between the axis 200 and the distance at which a predetermined development gap is obtained.
The shaft end of the support shaft 100B1 on the developing sleeve 100 side with respect to the regulating plate 300 is inserted as it is, and the rotating shaft 100A and the rotating shaft 200A on the photosensitive member 200 side are rotatably supported via bearings 301 and 201. Yes. A transmission mechanism 202 capable of transmitting a driving force is provided at one axial end of the rotation shaft on the photoconductor 200 side. Note that the regulation plate 300 and the side wall 400 of the process cartridge may be configured integrally.

Japanese Patent Laid-Open No. 8-179631

  The above-described distance between the developing sleeve 100 and the photosensitive member 200, that is, a so-called developing gap is a state where the developer is not carried on the developing sleeve 100, that is, the developer is not present on the peripheral surface facing the photosensitive member 200. At present, it is specified and managed for the state or the driving state, but it is an invention that the development gap differs between the case where no developer is present and the case where the developer is transported on the development sleeve 100. Confirmed. In particular, the nip pressure, which is the contact pressure with respect to the photosensitive member depending on the amount of developer carried on the developing sleeve, is substantially uniform in the axial direction of the developing sleeve, although it is substantially uniform in the axial direction of the developing sleeve. However, it was confirmed that the development gap was larger than both ends.

  It can be said that this phenomenon is caused by the support method of the developing sleeve. That is, since the developing sleeve is a member having a beam structure that is supported at both ends in the axial direction, there is a tendency that the deflection at the center portion is larger than the end portion on the support side. For this reason, the central portion of the developing gap is also larger than both axial end portions of the developing sleeve.

  Due to the difference in the development gap, the image density is lower at the axial center of the development sleeve than at both ends. In other words, if the development gap is widened and the nip width corresponding to the contact area of the developer with the photosensitive member is narrowed, the influence of the developing electric field of the toner acting on the latent image is also weakened. In many cases, the image density at the central portion becomes thin.

Such inconvenience due to the difference in the development gap cannot be solved by the positioning accuracy when setting the facing relationship between the development sleeve and the photosensitive member. Therefore, simple means as a method of suppressing the bending of the sleeve may be to make the material used for the developing sleeve high-strength or to increase the thickness of the sleeve in the axial direction. The present inventor conducted an intensity distribution experiment. From the results, if the development gap is about 0.2 to 0.5 mm, the case of comparing aluminum and stainless steel, the case of stainless steel compared to aluminum It was confirmed that the gap difference was about half.
From this result, it is effective to use stainless steel in order to suppress the deviation of the development gap, but in the material cost, stainless steel is disadvantageous compared to aluminum. In addition, when the surface of the developing sleeve is subjected to a surface treatment for improving the developer transportability, the processing method may be limited. In other words, the developer transportability may be limited to the surface of the developing sleeve. In other words, in order to facilitate the movement of the developer carried on the surface of the developing sleeve by following the rotation of the developing sleeve, sand blasting by spraying processing using fine particle abrasive grains or grooving using a cutting tool is performed. However, when stainless steel is used, processing becomes difficult due to its surface characteristics.

  On the other hand, when the thickness of the developing sleeve is increased, the influence of the magnetic force from the magnetic pole roller arranged in the developing sleeve may be weakened, and a magnetic pole having a strong magnetic force is used to solve this. It is possible. However, the magnet used for such a magnetic pole is very expensive, which not only causes an increase in cost but also makes it difficult to reduce the size of the developing sleeve, and increases the inertia due to the increase in size. As a result, the torque required for rotational driving also increases. As a result, there arises a new problem that it is difficult to realize energy saving due to downsizing, light weight and low power consumption of the image forming apparatus.

  SUMMARY OF THE INVENTION In view of the above problems in the conventional developing device, an object of the present invention is to provide a developing device having a configuration capable of eliminating density unevenness due to different developing gaps in the developing sleeve without causing an increase in cost, and a process cartridge using the developing device. And providing an image forming apparatus.

In order to achieve this object, the present invention has the following configuration.
(1) Visual development of the electrostatic latent image is possible by transporting the developer toward the electrostatic latent image formed on the latent image carrier using a developing unit carrying the developer. A developing device,
The developing means includes a rotatable developing sleeve for carrying the developer, a magnet roller having a plurality of magnetic poles including a developing main pole disposed along the circumferential direction in the developing sleeve, and the developing sleeve. A blade disposed oppositely and defining a layer thickness of the developer carried on the developing sleeve,
The developing device is characterized in that the developing sleeve is set to have the same inner diameter in the axial direction and has an outer diameter that is thicker in the axial center than the outer diameter at the end in the axial direction.

  (2) The developing device according to (1), wherein the outer diameter of the central portion in the axial direction of the developing sleeve is set to an increase rate of 1 to 10% with respect to the outer diameter of both end portions in the axial direction. .

  (3) The blade is characterized in that a regulating surface is positioned at a position where the facing distances at both axial end portions and the central portion are substantially uniform with reference to the bending deformation of the axial central portion of the developing sleeve. The developing device according to (1).

  (4) The developing sleeve includes a plurality of grooves extending in one direction inclined at an acute angle with respect to the rotational thrust direction, and a plurality of grooves extending at an acute angle in a direction opposite to the one direction with respect to the rotational thrust direction. Having iris-shaped grooves configured to intersect with the grooves, and the iris-shaped grooves are set in a range of 1.3 mm or more and 4.8 mm or less as a distance between groove intersections in the rotational thrust direction. The developing device according to any one of (1) to (3), wherein:

  (5) A process cartridge comprising a latent image carrier, a charging unit, and a cleaning unit in addition to the developing device according to any one of claims 1 to 4.

  (6) The developing device is characterized in that a distance between the developing sleeve of the developing device and the latent image carrier is 0.2 to 0.5 mm, and a developing bias with respect to the developing sleeve is a direct current component (5). ) Process cartridge.

  (7) An image forming apparatus comprising the process cartridge according to (5) or (6).

  (8) The image forming apparatus according to (7), wherein the process cartridge is provided in each of image forming units for a plurality of color images.

  (9) According to (7) or (8), the shape factor SF-1 is set to 100 to 180 and the shape factor SF-2 is set to 100 to 180, respectively, as the toner used in the developing device. The image forming apparatus described.

  According to the present invention, the developing sleeve has the same inner diameter in the axial direction and is set to an outer diameter that is thicker in the axial center than the outer diameter at the axial end. When the bending deformation occurs, a substantially uniform development gap can be set at both ends in the axial direction. In other words, it is possible to prevent an increase in the developing gap due to the bending deformation by adding a dimension corresponding to the enlarged portion of the developing gap due to the bending deformation to the outer diameter of the central portion in the axial direction. As a result, an image free from density unevenness can be obtained without causing an increase in cost by a simple configuration of only the configuration of the developing sleeve.

Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating an example of an image forming apparatus. The image forming apparatus illustrated in FIG. 1 is a color printer that uses a tandem method in which a plurality of image forming units that can independently form images of different colors are arranged side by side. is there.
In FIG. 1, the color printer 1 can form an image using yellow (Y), cyan (C), magenta (M), and black (Bk), which are toners of complementary colors with respect to color separation colors. Photosensitive drums 2Y, 2C, 2M, and 2Bk are juxtaposed on the same line in the horizontal direction.
Each photoconductor drum is provided in an image forming unit described later, and a belt having an extending surface parallel to the juxtaposing direction of the photoconductor drums 2Y, 2C, 2M, and 2Bk is used in the upper portion of the image forming unit. A transfer device 3 is arranged.

  The image forming unit constitutes a photosensitive drum and a process cartridge for performing an image forming process related to the photosensitive drum, and an image forming process for the photosensitive drum will be described later with reference to FIG. Among them, devices 4, 5, and 6 for collectively performing a charging process, a developing process for performing a visible image process using a developing sleeve as a developer supply member, and a cleaning process are collectively accommodated.

Below the image forming unit, a scanning device 7 used for the writing process is arranged.
In FIG. 2, the reference numerals relating to the devices in the image forming unit are given only for yellow, but the devices for other colors have the same configuration.

  The transfer device 3 has a configuration in which a belt wound around a plurality of rollers is used as a transfer body, and a primary transfer process in which images of different colors are sequentially transferred onto a developing surface facing each photoconductor drum. And a secondary transfer process in which the images superimposed in the primary transfer process are collectively transferred to a sheet fed from a paper feeding device (not shown).

  In the transfer device 3, primary transfer devices 9Y, 9C, 9M, and 9Bk constituted by rollers are arranged at positions facing the respective photosensitive drums, and a sheet is brought into contact with the transfer device 3 at the secondary transfer position. A conveying belt 10 and a secondary transfer device 112 are arranged while conveying.

In the color printer 1, an electrostatic latent image corresponding to writing scanning is formed after charging each photosensitive drum, and when the electrostatic latent image is subjected to visible image processing by the developing device 5, each photosensitive member is transferred to the transfer device 3. The color image from the drum is sequentially transferred through the primary transfer device 9 to form a superimposed image, and the superimposed image is collectively transferred to the sheet by the secondary transfer device 11.
The sheet on which the superimposed images are collectively transferred from the transfer device 3 is subjected to a fixing process by the fixing device 12 provided in the conveyance path to the paper discharge tray 1A and is discharged. In FIG. 1, reference numeral 13 indicates a belt cleaning device of the transfer device 3.

  FIG. 2 shows an image forming unit for a process cartridge capable of forming a yellow image. In FIG. 2, the image forming unit includes a charging device 4 and an optical path of writing light around the photosensitive drum 2Y. A slit ST, a developing device 5 and a cleaning device 6 are provided.

  The charging device 4 uses a charging roller that faces the photosensitive drum 2Y in a contact or non-contact state, and uniformly charges the photosensitive drum 2Y.

  The developing device 5 includes a developing sleeve 5Y facing the photosensitive drum 2Y shown in FIG. 1 and a frictionally charged developer that is stirred and mixed while circulating in the reciprocating direction by a plurality of stirring and mixing screws 5Y1 and 5Y2. A doctor blade 5P for defining the layer thickness and a new toner introduction portion 5Y4 from a toner tank constituting a developer replenishment portion indicated by reference numerals T1 to T4 in FIG. 1 are provided. In FIG. 2, reference numeral 5Z denotes a developer scattering prevention seal provided at a position where the developer conveyed by the developing sleeve 5Y starts to face the photosensitive drum 2Y, and reference numeral S1 denotes a developer (toner) concentration. The sensor is shown.

  If the developer concentration sensor S1 detects the developer (toner) concentration in the developing device, if it is determined that the concentration is low, the toner tank T1 to T4 of the corresponding color is supplied to the developing device via the replenishing device. An appropriate amount of developer (toner) is replenished, and the remaining amount of developer in the toner tank to which the developer has been replenished is a toner remaining amount detection sensor (not shown) disposed on the toner tank side. If the developer (toner) replenishment request is issued and it is detected that no developer (toner) remains even after a lapse of a predetermined time, the developer (toner) in the toner tank is detected. ) Is judged and managed.

  The developing sleeve 5Y shown in FIG. 2 includes a magnet roller (a member indicated by reference numeral 5Y1 in FIG. 6) in the same manner as in the case shown in FIG. A plurality of grooves extending in one direction inclined at an acute angle and a plurality of grooves extending inclined at an acute angle in a direction opposite to the one direction with respect to the rotational thrust direction are as distances between groove intersections in the rotational thrust direction. It is set as a range of 1.3 mm or more and 4.8 mm or less and is provided as an iris-shaped groove. Thereby, unlike the case where the surface is smooth, the collecting action of the developer is enhanced. In particular, such a configuration is effective in reducing an excessive load (stress) on the developer that occurs when the developer passes through the position facing the doctor blade 5P or the development nip. . In other words, when the developer passes through each of the above positions, the load is distributed by utilizing the inclination angle of the groove of the iris stripe, so that the torque for extending the life of the developer and driving the developing sleeve is reduced. Thus, density unevenness that occurs when the development gap is excessively widened by reducing the stress at the development nip portion and the spread becomes excessive can be prevented. Such advantages are clarified in Japanese Patent Application No. 2005-321628 filed by the present applicant.

The connecting structure between the toner tank and the new toner introduction part on the developing device 5 side (for the sake of convenience, the part indicated by reference numeral 5Y4 in FIG. 2) has an inner diameter of 4 to 10 and has flexibility and toner deterioration resistance. The material member CH is used, and a rubber material (ex polyurethane, nitrile, EPDM, silicon, etc.), a plastic material (polyethylene, polyamide), or the like is selected as the material.
In FIG. 1, symbol EXP indicates a conveyance path for conveying the toner collected from the cleaning device provided in the image forming unit toward the waste toner tank EXPB.

On the other hand, the toner used in the developing device in this embodiment has the following specifications. The toner used in the developing device according to the present embodiment is preferably a spherical toner that can be defined by the values of the shape factors SF-1 and SF-2 below.
3 and 4 are diagrams schematically showing the shape of the toner in order to explain the shape factor SF-1 and the shape factor SF-2.
The shape factor SF-1 indicates the ratio of the roundness of the toner shape, and the square of the maximum length MXLNG of the shape formed by projecting the toner onto the two-dimensional plane represented by the following formula (1) is represented by the graphic area. Divide by AREA and multiply by 100π / 4.
SF-1 = {(MXLNG) ² / AREA} × (100π / 4) (1) When the value of SF-1 is 100, the shape of the toner becomes a true sphere, and the value of SF-1 increases. It becomes indefinite.

The shape factor SF-2 indicates the ratio of the unevenness of the toner shape, and is expressed by the square of the perimeter PERI of the figure formed by projecting the toner on the two-dimensional plane represented by the following formula (2). It is a value obtained by dividing the figure area AREA and multiplying by 100 / 4π.
SF-2 = {(PERI) ² / AREA} × (100 / 4π) (2) When the value of SF-2 is 100, the toner surface has no irregularities and the value of SF-2 is large. As the result, the unevenness of the toner surface becomes remarkable.
Specifically, the shape factor is measured by taking a photograph of the toner with a scanning electron microscope (S-800: manufactured by Hitachi, Ltd.), introducing it into an image analyzer (LUSEX 3: manufactured by Nireco) and analyzing it. Calculated.

  When the shape of the toner is close to a sphere, the contact between the toner and the toner or the toner and the photoconductor is close to a point contact, so that the adsorbing force between the toners becomes weak and the fluidity becomes high. The adhesion force to the surface of the drum 11 is also reduced, and the transfer rate is increased. If any of the shape factors SF-1 and SF-2 exceeds 180, the transfer rate is lowered, which is not preferable.

  In this embodiment, the interval between the developing sleeve 5Y and the photosensitive member 2Y is set to 0.2 to 0.5 mm, and a DC bias is used as the developing bias. This prevents the occurrence of abnormal images due to carrier adhesion and charge leakage when using the toner conditions described above. This reason is clearly demonstrated by experiments in Japanese Patent Application Laid-Open No. 2003-323050, which is a prior application of the present applicant.

Next, features of the present embodiment will be described.
In the developing device 5 in this embodiment, as shown in FIG. 5, when the outer diameter size in the axial direction of the developing sleeve 5Y is uniform in the axial direction and the both ends in the axial direction are standard, the axial direction The outer diameter at the center is thicker than that at both ends.

  Thereby, the thickness in the axial center is thicker than both ends, and the increase rate of the outer diameter is set to an increase rate of 1 to 10% with respect to the external light at both ends. This increase rate is such that the dimension of the predetermined development gap is not greatly changed, and the gap is slightly narrowed within the development gap range in which the necessary developer carrying amount can be obtained.

  Such setting of the outer diameter takes into account the amount of deflection at the center in the axial direction, and as shown in FIG. 5B, the development gap when the central portion in the axial direction is deflected by the development nip pressure or the like. Is uniform between both axial ends and the center. In other words, originally, it is desirable to make the developing gap uniform in the entire axial direction so as not to bend in the axial center, but because of the beam structure that supports both ends in the axial direction, the axial center Therefore, in addition to suppressing the bending, the development gap when the bending occurs is prevented from being different in the axial direction. In addition to the outer diameter described above, the bending rigidity is a condition for making the developing gap uniform between both ends in the axial direction when the axial center is bent by a load such as a developing nip pressure. There is a thickness to provide a shadow. Therefore, since the amount of deflection can be predicted based on the development nip pressure from the amount of developer carried on the developing sleeve, it is necessary to define the inner diameter dimension at which the deflection amount can be set on the basis of the material strength of the developing sleeve. Is desirable. Further, instead of making the inner diameter uniform, it is also possible to make the wall thickness uniform so that the center in the axial direction bulges outward as compared to both ends.

  The increase rate related to the difference in outer diameter is influenced by the axial (longitudinal) dimension of the developing sleeve and the bending strength of the material, and particularly by the thickness. And the bending becomes large, so that the length of an axial direction (longitudinal direction) is long. In this embodiment, since the length of the developing sleeve in the axial direction (longitudinal direction) is determined based on the paper size targeted by the image forming apparatus, the outer diameter is increased by calculating the amount of deflection from the length and the material strength. The rate is set.

  In particular, the material used for the developing sleeve must be a non-magnetic material, and aluminum or stainless steel is selected from the viewpoint of mass productivity. However, stainless steel has poor processability for surface treatment. Aluminum is often used because of its high cost. For this reason, the increase rate of the above-mentioned outer diameter is set based on the fact that the deflection amount when using aluminum is 4 to 10% of the wall thickness and the deflection amount when using stainless steel is 1 to 6%. Has been.

On the other hand, with respect to the development bias, the DC bias is less susceptible to the development gap deviation than when a development bias having a wide development gap and including an AC component is used. For this reason, in this embodiment, as described above, the developing bias uses a DC component. The reason is as follows.
When applying a developing bias using a direct current component, the inventor has confirmed that the sensitivity of the image density to the widening of the developing gap at the center in the axial direction of the developing sleeve is low. This is considered to be caused by the amount of developer carried with respect to the development gap. In other words, if the development gap is wide, it is necessary to increase the amount of developer carried, that is, the amount of developer pumped up so that the latent image is easily contacted. The amount of toner to be applied increases, and the amount of toner affected by the electric field increases when a uniform developing electric field is applied across the axial direction of the developing sleeve. There is a need to do more. For this reason, if there is a deviation in the developing gap in the axial direction, particularly a portion having a large developing gap, an electric field strength targeting the amount of toner present in that portion is required, which may adversely affect power consumption.

  However, if the development gap is reduced, in other words, if there is no deviation in the development gap and the development gap can be reduced in the entire axial direction, the amount of toner in the development nip can be reduced and the development electric field can be reduced. The influence is small, and the development bias can be converted to a direct current to prevent excessive toner movement.

  The doctor blade 5P that defines the amount of developer carried on the surface of the developing sleeve is a cross-hatched shape in which the opposing distances at both ends and the center in the axial direction are substantially uniform with reference to the bending deformation at the center in the axial direction of the developing sleeve 5Y It is said that. That is, in FIG. 2, apart from the case where the center in the thickness direction of the doctor blade 5P is located on the normal extending from the developing sleeve 5Y, the position of the regulating surface for scraping off the developer, particularly the developing sleeve. The ridge line position (blade corner) of the regulating surface on the side where the developer carried on 5Y moves toward the doctor sleeve 5P does not coincide with the above normal line in the thickness direction center described above. It may be arranged on the side where the developer enters. In this case, the shape of the ridgeline is such that the facing distances at both axial end portions and the central portion are substantially uniform with reference to the bending deformation of the central portion in the axial direction of the developing sleeve 5Y. Thereby, when the axial center of the developing sleeve 5Y bends and the developing gap becomes substantially uniform in the axial direction, the layer thickness of the developer carried on the developing sleeve 5Y can be uniformly regulated in the axial direction. become. In the doctor blade 5P, in consideration of the fact that the developing gap at the center in the axial direction of the developing sleeve 5Y is different, it may be possible to use a shape that increases the amount of developer carried in that portion. There is no need for such a special configuration.

Since the present embodiment is configured as described above, the developing gap with respect to both ends in the axial direction can be made uniform when the axial center of the developing sleeve assuming the support structure at both ends in the axial direction is bent. Deviation in the development gap can be eliminated. Thereby, the deviation of the developing gap can be eliminated by the structure of the developing sleeve itself, and the occurrence of uneven image density can be prevented.
In particular, a support structure that increases the positioning accuracy of the developing sleeve relative to the photosensitive member, for example, a member that defines the distance between the central axes of the developing sleeve and the photosensitive member, or a flange that contacts the photosensitive member is provided on the developing sleeve. However, since the deviation of the developing gap at the center in the axial direction cannot be eliminated, the developing gap in the axial direction is made uniform by a simple configuration using the deviation of the developing gap as in this embodiment. It becomes possible.

  In the above embodiment, four process cartridges are provided. However, the present invention is not limited to this, and a single color image or a two color image is formed by providing a single or two process cartridges. It is also possible to target the configuration.

1 is a schematic diagram for explaining a configuration of an image forming apparatus using a developing device according to the present invention. FIG. 2 is a schematic diagram for explaining a configuration of a process cartridge used in the image forming apparatus shown in FIG. 1. FIG. 6 is a diagram for explaining an example of a shape factor of toner used in the developing device according to the embodiment of the present invention. It is a figure for demonstrating the other example of the shape factor of the toner used for the image development apparatus by the Example of this invention. It is sectional drawing of the developing sleeve for demonstrating the characterizing part of the developing device by the Example of this invention. It is a figure for demonstrating the conventional structure of a developing sleeve. It is a figure for demonstrating the conventional structure regarding the support structure of a developing sleeve and a photoreceptor.

Explanation of symbols

1 color printer 5 developing device 5Y developing sleeve 5Y1 magnet roller 5Y2, 5Y3 magnetic pole 5P doctor blade

Claims (9)

A developing device capable of performing visible image processing of the electrostatic latent image by conveying the developer toward the electrostatic latent image formed on the latent image carrier using a developing unit carrying the developer. There,
The developing means includes a rotatable developing sleeve for carrying the developer, a magnet roller having a plurality of magnetic poles including a developing main pole disposed along the circumferential direction in the developing sleeve, and the developing sleeve. A blade disposed oppositely and defining a layer thickness of the developer carried on the developing sleeve,
The developing device is characterized in that the developing sleeve is set to have the same inner diameter in the axial direction and has an outer diameter that is thicker in the axial center than the outer diameter at the end in the axial direction.   2. The developing device according to claim 1, wherein an outer diameter of an axially central portion of the developing sleeve is set to an increase rate of 1 to 10% with respect to an outer diameter of both axial end portions.   The regulating surface of the blade is positioned at a position where the opposing distances at both ends and the center in the axial direction are substantially uniform with reference to the bending deformation of the central portion in the axial direction of the developing sleeve. 2. The developing device according to 1.   The developing sleeve has a plurality of grooves extending in one direction inclined at an acute angle with respect to the rotational thrust direction, and a plurality of grooves extending at an acute angle in a direction opposite to the one direction with respect to the rotational thrust direction. It has an iris-shaped groove configured to intersect, and the iris-shaped grooves are set in a range of 1.3 mm or more and 4.8 mm or less as a distance between groove intersections in the rotational thrust direction. The developing device according to claim 1, wherein:   5. A process cartridge comprising a latent image carrier, a charging unit, and a cleaning unit in addition to the developing device according to claim 1.   6. The developing apparatus according to claim 5, wherein a distance between the developing sleeve and the latent image carrier in the developing device is 0.2 to 0.5 mm, and a developing bias with respect to the developing sleeve is a direct current component. Process cartridge.   An image forming apparatus comprising the process cartridge according to claim 5.   The image forming apparatus according to claim 7, wherein the process cartridge is provided in each of image forming units for a plurality of color images.   9. The image forming apparatus according to claim 7, wherein the toner used in the developing device has a shape factor SF-1 set to 100 to 180 and a shape factor SF-2 set to 100 to 180, respectively. .

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