JP2006071730A - Developing apparatus, image forming apparatus and process cartridge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing apparatus wherein screw pitch unevenness is reduced, then, an image is uniform, and also, which is improved in terms of developer deterioration, and to provide a process cartridge and an image forming apparatus equipped with the developing apparatus. <P>SOLUTION: Regarding the developing apparatus 13, magnetic poles C and B are arranged so that the magnetic force in a normal direction on the surface of a developing roller may become the maximum value near a position P<SB>1</SB>facing a stirring screw 18, and the magnetic force may become the minimum value near a position P<SB>2</SB>facing a control blade 16, and also, the magnetic force may gradually become lower as it goes from the maximum value to the minimum value. Magnetic poles C and D are arranged facing the stirring screw 18, and positioned on the upstream side of the position P<SB>1</SB>where the developer 26 is attracted in the rotating direction G of the developing sleeve 32, and also, the most downstream position P3 in the rotating direction G of the developing sleeve 32 may be positioned under the horizontal direction by an angle of ≥20° by taking the rotating center P of the developing sleeve 32 as a center in a separating range R where the magnetic flux density becomes ≤10mt. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a phenomenon apparatus, an image forming apparatus, and a process cartridge used for a copying machine, a facsimile machine, a printer, and the like, and more specifically, a developer carried on a developer carrier, an image carrier and a developer carrier. The present invention relates to a developing device that forms a toner image by developing an electrostatic latent image on the image bearing member by transporting the toner to an opposing developing area with a gap. The present invention also relates to an image forming apparatus and a process cartridge having such a developing device.

  Various image forming apparatuses such as copying machines, facsimile machines, and printers use various developing devices 100 (see, for example, Patent Documents 1 to 4). As shown in FIGS. 9 and 10, this type of developing device 100 conveys developer 101 to a developing area 103 that faces the photosensitive drum 102, and generates an electrostatic latent image formed on the photosensitive drum 102. A developing roller 104 that develops with the developer 101 to form a toner image is provided.

  The developing roller 104 has a cylindrical developing sleeve 105 and a magnet that is accommodated in the developing sleeve 105 and that forms a magnetic field so as to cause the developer 101 to rise on the surface of the developing sleeve 105. A roller 106 is provided. On the developing roller 104, when the developer 101 spikes, the magnetic carrier of the developer 101 spikes on the developing sleeve 105 so as to follow the lines of magnetic force generated by the magnet roller 106. The toner of the developer 101 adheres.

  Further, the developing device 100 includes a storage tank 107 that stores the developer 101 described above, a screw-shaped stirring screw 108 that stirs the developer 101 in the storage tank 107, and a developer pumped up by the developing roller 104. And a regulating blade 109 for making the amount of 101 uniform. The developing device 100 illustrated in FIGS. 9 and 10 includes a pair of a storage tank 107 and a stirring screw 108.

  The developer 101 in the developing device 100 moves in the storage tank 107 as indicated by an arrow K in FIG. The toner replenished from one end of the one storage tank 107a on the side away from the developing roller 104 is conveyed along the axial direction of the stirring screw 108 to the other end of the one storage tank 107a by the stirring screw. Then, the developer 101 is agitated. Then, the developer 101 moves from the other end of the one storage tank 107a into the other storage tank 107b near the developing roller 104.

  The developer 101 transferred to the other storage tank 107b near the developing roller 104 is pumped up to the surface of the developing sleeve 105 by the magnetic force of the developing roller 104 (attaches to the surface of the developing sleeve 105). Thereafter, the amount of the developer 101 is made uniform by the regulating blade 109 and then conveyed to the developing region 103 where the photosensitive drum 102 and the developing roller 104 are opposed to each other with a space therebetween. Developer 101 develops the electrostatic latent image formed on photoconductor drum 102 to form a toner image.

In the developing device 100 shown in FIG. 9, a regulating blade 109 is provided below the developing roller 104, and the developer 101 remaining after development is separated above the developing roller 104. In the developing device 100 shown in FIG. 10, a regulating blade 109 is provided on the upper side or the lateral side of the developing roller 104, and the developer 101 remaining after development is separated below the developing roller 104. As the developing device 100, the one shown in FIGS. 9 and 10 described above is properly used depending on the layout of other units such as the photosensitive drum 102.
JP 2000-194194 A JP 2000-194195 A JP 2002-148941 A Japanese Patent Laid-Open No. 2000-250311

  However, the image forming apparatus provided with the developing device 100 described above has a higher density when printing an image with a relatively large area ratio such as a photograph than when printing an image with a relatively small area ratio such as a text sentence. There was a problem that unevenness (hereinafter referred to as “screw pitch unevenness”) was conspicuous. For example, as shown in FIG. 11, in a monochromatic image 111 having a large area ratio, screw pitch unevenness 112 oblique to the sheet passing direction occurs in a striped shape, and the aesthetic appearance is impaired. In FIG. 11, a portion 113 indicated by a relatively dense parallel oblique line is relatively dark, and a portion 114 indicated by a relatively coarse parallel oblique line is relatively thin.

  Further, in a color image having a large area ratio, screw pitch unevenness of each color appears as a hue shift. For example, in the general market such as a design occupation, an image with such a large area ratio may be handled, and the product value is significantly reduced by striped screw pitch unevenness.

  The pitch of the screw pitch unevenness described above is equal to the pitch of the stirring screw 108 in the developing device 100 as shown in FIG. The screw pitch unevenness 112 has a high incidence with the recent reduction in the particle size of magnetic carriers aimed at improving the image quality. It has also been found that the screw pitch unevenness 112 is likely to occur when the developer pumping property of the developing roller 104 is low (when the amount of the developer 101 adhering to the developing roller 104 is small).

  In such an image forming apparatus, the developer 101 moving on the stirring screw 108 is high at the peak of the stirring screw 108 and low at the valley. The surface layer of the agitating screw 108 contains a large amount of the developed developer 101 that has been released from the developing roller 104 due to the out-of-agent position and has a low toner concentration. Is low.

  When the developer 101 pumping property of the developing roller 104 is low, the developer 101 pumped up to the developing roller 104 is conveyed to the regulating blade 109 in the state shown in FIG. On the other hand, when the pumping property of the developer 101 of the developing roller 104 is high (when the amount of the developer 101 adhering to the developing roller is large), the development pumped up to the developing roller 104 in the state shown in FIG. The agent 101 is conveyed to the regulation blade 109.

  In this case, in the case shown in FIG. 13, the developer 101 having a low toner concentration tends to remain after passing through the regulating blade 109, and the image tends to become thin at the same period as the pitch of the stirring screw 108. Further, in the case shown in FIG. 14, not only the surface layer of the developer 101 but also the developer 101 having a predetermined toner concentration which has been sufficiently stirred is transported, so that both are mixed until the regulation blade 109 passes to obtain a uniform concentration. Become. Therefore, as a general design, means such as increasing the magnetic flux density distribution of the magnetic poles of the magnet roller 106 at a position corresponding to the stirring screw 108 or reducing the distance between the stirring screw 108 and the developing roller 104 is used. However, in these cases, as a side effect, the compression load on the developer 101 when passing through the regulating blade 109 becomes large, so that the image quality is deteriorated due to the deterioration of the characteristics of the developer 101 and does not meet the recent high durability needs. was there.

  In addition to the unevenness of the screw pitch 112, the developing roller 104 once again draws the developed developer 101 that has once been separated from the developing roller 104, which causes a problem that a non-uniform image is generated. In particular, with the recent miniaturization of the developing device 100, the separation position where the developed developer 101 on the developing roller separates from the developing roller 104 and the suction position where the new developer 101 is sucked are often close. In such a case, it is difficult to achieve both the above-described reliable release of the developed developer 101 and the reliable suction of the new developer 101, and the developing roller 104 again removes the developed developer 101. There has been a problem that non-uniform images are likely to occur due to suction.

  In order to solve such problems, the developing device disclosed in Patent Document 1 described above attempts to reduce screw pitch unevenness by defining the amount of developer and the magnetic flux density distribution of the magnet roller of the developing roller. ing. However, in this case, since the force acting on the developer from the regulating blade is increased, there is a problem that the developer is rapidly deteriorated and the life of the developer is shortened.

  Further, in the developing devices described in Patent Document 2 and Patent Document 3 described above, the cause of the screw pitch unevenness is again developed without sufficiently stirring the developed developer with toner in the storage tank. Trying to reduce pumping up. However, there is a problem that it is not enough to prevent re-pumping.

  Furthermore, in the developing device shown in Patent Document 4 described above, screw pitch unevenness is reduced by regulating the size of the stirring screw. However, since the unevenness of the developer attached to the developing roller by the stirring screw cannot be erased, there is a problem that screw pitch unevenness cannot be completely erased.

  The present invention has been made in view of the above background, a developing device with little screw pitch unevenness and a uniform image, and with little developer deterioration, a process cartridge having such a developing device, and image formation The object is to provide a device.

  In order to achieve the above object, a developing device according to claim 1 includes an agitating member for agitating and conveying a developer containing toner and a magnetic carrier, a magnet roller having a plurality of fixed magnetic poles, and an inner part of the magnet roller. A rotatable non-magnetic cylindrical body arranged so as to absorb the developer carried by the stirring member, and sucked by the developer carrier. And a regulating member for maintaining the thickness of the developer at a predetermined thickness, wherein a magnetic force in a normal direction on the surface of the developer carrying member is opposed to the position of the stirring member Between the position facing the regulating member, the maximum value is present closer to the position facing the stirring member from the center, and the minimum value is present in the vicinity of the position facing the regulating member, And said At least one of the fixed magnetic poles is positioned between the position facing the agitating member and the position facing the regulating member so as to gradually weaken from the large value toward the minimum value. It is characterized by having been arranged in.

  A developing device according to a second aspect is the developing device according to the first aspect, wherein the developing device is located on the upstream side in the rotational direction of the non-magnetic cylindrical body from the position where the developer is sucked, and the magnetic flux density is 10 mT or less. The downstream position in the rotational direction of the separation range in which the developed developer to be detached from the developer carrier is positioned at least 20 ° below the horizontal direction with the rotational center of the nonmagnetic cylindrical body as the center. Among the fixed magnetic poles, (a) a fixed magnetic pole that faces the stirring member, and (b) a fixed magnetic pole that is adjacent to the stationary magnetic pole that faces the stirring member and is located upstream in the rotational direction. It is characterized by the arrangement.

  A magnetic carrier according to a third aspect is characterized in that, in the developing device according to the first or second aspect, a particle diameter of the magnetic carrier is 20 μm or more and 50 μm or less.

  A process cartridge according to a fourth aspect of the invention is a process cartridge having at least a developing device, wherein the developing device includes the developing device according to any one of the first to third aspects.

  The image forming apparatus according to claim 5 is an image forming apparatus having at least an image carrier, a charging device, and a developing device, and the developing device is any one of claims 1 to 3. And a developing device as described above.

  In the developing device according to the first aspect, since the magnetic force at the position facing the stirring member is high, the pumping property of the developer is improved, and the screw pitch unevenness caused by the stirring member can be reduced. Further, since the magnetic force at the position facing the regulating member is low, the stress on the developer is reduced, and the deterioration of the developer with time can be reduced. Therefore, it is possible to provide a developing device that can obtain excellent image quality for a long period of time.

  In the developing device according to claim 2, since the fixed magnetic pole is disposed so that the most downstream position of the developer detachment range is at least 20 ° below the horizontal, re-suction of the developer due to gravity occurs. Thus, an image having a more uniform density can be obtained.

  In the developing device according to claim 3, since the magnetic carrier has a particle size of 20 μm or more and 50 μm or less, a developing device capable of obtaining an excellent image with excellent granularity and no screw pitch unevenness. Can be provided.

  Since the process cartridge according to claim 4 has the developing device according to any one of claims 1 to 3, the image has excellent granularity and no screw pitch unevenness. A process cartridge can be provided.

  In the image forming apparatus according to claim 5, since the developing device according to any one of claims 1 to 3 is used, an excellent image having excellent granularity and no screw pitch unevenness. A forming apparatus can be provided.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing a main part of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the developing device according to the embodiment of the image forming apparatus shown in FIG. FIG. 3 is a cross-sectional view taken along line XYZ in FIG. FIG. 4 is an explanatory diagram showing the operation status of the developing device 13 shown in FIG.

  As shown in FIG. 1, the image forming apparatus 1 includes an apparatus main body 2 (only part of which is shown in FIG. 1), a registration roller 3, a transfer member 4, a fixing device 5, a laser writing device (not shown), a process, and the like. And at least a cartridge 6.

  The apparatus main body 2 is formed in a box shape, for example, and is installed on a floor or the like. The apparatus main body 2 accommodates a registration roller 3, a transfer member 4, a fixing device 5, a laser writing device, and a process cartridge 6. The registration roller 3 feeds a recording sheet 7 as a transfer material between the transfer member 4 and a photosensitive drum 8 described later. The transfer member 4 presses the recording paper 7 against the outer peripheral surface of the photosensitive drum 8 and sends the recording paper 7 toward the fixing device 5. The fixing device 5 fixes the toner image formed on the photosensitive drum 8 or the like to the recording paper 7. The laser writing device irradiates the outer peripheral surface of the photosensitive drum 8 uniformly charged by a later-described charging roller 9 with a laser beam 10 to form an electrostatic latent image.

  The process cartridge 6 is detachable from the apparatus main body 2. The process cartridge 6 includes a cartridge case 11, a charging roller 9 as a charging device, a photosensitive drum 8 as an image carrier, a cleaning blade 12 as a cleaning device, and a developing device 13. Therefore, the image forming apparatus 1 includes at least a charging roller 9, a photosensitive drum 8, a cleaning blade 12, and a developing device 13.

  The cartridge case 11 is detachable from the apparatus main body 2 and accommodates a charging roller 9, a photosensitive drum 8, a cleaning blade 12, and a developing device 13. The charging roller 9 uniformly charges the outer peripheral surface of the photosensitive drum 8. The photosensitive drum 8 is formed in a columnar shape or a cylindrical shape that is rotatable about an axis. The photosensitive drum 8 is developed by a toner attached to the electrostatic latent image formed and carried by the laser writing means, and the toner image thus obtained is transferred to the recording paper 7 positioned between the transfer member 4. To do. The cleaning blade 12 removes the transfer residual toner remaining on the outer peripheral surface of the photosensitive drum 8 after the toner image is transferred to the recording paper 7.

  As shown in FIGS. 1 to 3, the developing device 13 includes at least a developer supply unit 14, a developing roller 15 as a developer carrier, and a regulating blade 16 as a regulating member. The developer supply unit 14 includes a storage tank 17 and a pair of stirring screws 18 as stirring members. The storage tank 17 is formed in a box shape whose length is substantially equal to that of the photosensitive drum 8. A partition wall 19 extending along the longitudinal direction of the storage tank 17 is provided in the storage tank 17. The partition wall 19 partitions the storage tank 17 into a first space 20 and a second space 21. The first space 20 and the second space 21 have both end portions 22, 23, 24 and 25 communicating with each other.

  The storage tank 17 stores the developer 26 (shown in FIG. 4) in both the first space 20 and the second space 21. The developer 26 includes toner and a magnetic carrier (also referred to as magnetic powder). The toner is appropriately supplied to one end portion 23 of the first space 20 on the side away from the developing roller 15 in the first space 20 and the second space 21. The magnetic carrier is accommodated in both the first space 20 and the second space 21. The particle size of the magnetic carrier is 20 μm or more and 50 μm or less.

  The stirring screw 18 is accommodated in each of the first space 20 and the second space 21. The longitudinal direction of the stirring screw 18 is parallel to the longitudinal directions of the storage tank 17, the developing roller 15, and the photosensitive drum 8. The agitating screw 18 is provided so as to be rotatable around an axis, and rotates around the axis to agitate the toner and the magnetic carrier and convey the developer 26 along the axis.

  In the illustrated example, the stirring screw 18 in the first space 20 conveys the developer 26 from the one end 23 to the other end 25 described above. The stirring screw 18 in the second space 21 conveys the developer 26 from the other end 24 toward the one end 22.

  According to the above-described configuration, the developer supply unit 14 conveys the toner supplied to the one end portion 23 of the first space 20 to the other end portion 25 while stirring with the magnetic carrier. It is conveyed to the other end 25 of the second space 21. The developer supply unit 14 agitates the toner and the magnetic carrier in the second space 21 and supplies them to the outer peripheral surface of the developing roller 15 while conveying the toner in the axial direction.

  The developing roller 15 is formed in a cylindrical shape, and is provided between the second space 21 and the photosensitive drum 8. The developing roller 15 is parallel to both the photosensitive drum 8 and the storage tank 17. The developing roller 15 is disposed at a distance from the photosensitive drum 8. A space between the developing roller 15 and the photosensitive drum 8 forms a developing region 31 in which the toner of the developer 26 is attached to the photosensitive drum 8 to develop the electrostatic latent image to obtain a toner image. In the developing area 31, the developing roller 15 and the photosensitive drum 8 face each other.

  As shown in FIG. 2, the developing roller 15 includes a cylindrical developing sleeve 32 as a nonmagnetic cylindrical body, and a columnar magnet roller (also referred to as a magnet body) 33. The developing sleeve 32 is made of a non-magnetic material and is provided so as to be rotatable around an axis. The developing sleeve 32 is rotated along an arrow G so that an inner peripheral surface thereof is sequentially opposed to magnetic poles C, B, A, E, and D described later. The developing sleeve 32 is made of aluminum, stainless steel (SUS), or the like. Aluminum is excellent in terms of workability and lightness. When using aluminum, it is preferable to use A6063, A5056, and A3003. When using SUS, it is preferable to use SUS303, SUS304, and SUS316.

  The magnet roller 33 is accommodated (enclosed) in the developing sleeve 32, and is fixed without rotating around the axis. A plurality of magnetic poles A, B, C, D, and E are formed on the magnet roller 33. These magnetic poles A, B, C, D, and E extend along the longitudinal direction of the magnet roller 33, that is, the developing roller 15, and are provided over the entire length of the magnet roller 33.

  The magnetic pole A is disposed at a position facing the photosensitive drum 8 of the magnet roller 33. The magnetic pole A forms a magnetic field between the developing sleeve 32 and the photosensitive drum 8, and a magnetic brush is formed by the magnetic field.

  The magnetic pole B is disposed at a position facing the regulating blade 16 of the magnet roller 33. The magnetic pole B cooperates with the regulating blade 16 to keep the thickness of the developer 26 on the outer peripheral surface of the developing sleeve 32 at a predetermined thickness.

  The magnetic pole C is disposed at a position facing the stirring screw 18 in the second space 21 of the magnet roller 33. The magnetic pole C causes the developer 26 in the second space 21 to adhere to the surface of the developing sleeve 32.

  The magnetic pole D and the magnetic pole E generate a repulsive magnetic field, and peel off the developer 26 containing the development from the developing sleeve 32. The magnetic pole D is located adjacent to the magnetic pole C and upstream of the arrow G of the magnetic pole C. These magnetic poles A, B, C, D, and E constitute fixed magnetic poles described in this specification. Also, the broken line shown in FIG. 4 represents the magnetic flux density distribution in the normal direction created by these fixed magnetic poles.

  The regulating blade 16 is provided at the end of the developing device 13 near the photosensitive drum 8. The regulating blade 16 scrapes off the developer 26 on the outer peripheral surface of the developing sleeve 32 exceeding the desired thickness into the storage tank 17, and the developer 26 on the outer peripheral surface of the developing sleeve 32 conveyed to the developing region 31. To the desired thickness.

  In the developing device 13 having the above-described configuration, the toner and the magnetic carrier are sufficiently stirred by the developer supply unit 14, and the stirred developer 26 is attached to the developing sleeve 32 by the magnetic pole C. Then, in the developing device 13, the developing sleeve 32 rotates and conveys the adhered developer 26 toward the developing region 31. The developing device 13 causes the developer 26 having a desired thickness to adhere to the photosensitive drum 8 with the regulating blade 16. In this way, the developing device 13 carries the developer 26 on the developing roller 15 and transports it to the developing area 31 to develop the electrostatic latent image on the photosensitive drum 8 to form a toner image. Then, the developing device 13 scrapes off the absorbed developer 26 from the outer peripheral surface of the developing sleeve 32 with the magnetic poles D and E. The developer 26 that has been scraped off is again sufficiently stirred with the other developer 26 in the second space 21 and used for developing the electrostatic latent image on the photosensitive drum 8.

  The image forming apparatus 1 configured as described above forms an image on the recording paper 7 as described below. First, the image forming apparatus 1 rotates the photosensitive drum 8 and uniformly charges the outer peripheral surface of the photosensitive drum 8 by the charging roller 9. Laser light 10 is applied to the outer surface of the photoconductive drum 8 to form an electrostatic latent image on the outer peripheral surface of the photoconductive drum 8. When the electrostatic latent image is positioned in the development area 31, the developer 26 attached to the outer peripheral surface of the developing sleeve 32 of the developing device 13 adheres to the outer peripheral surface of the photosensitive drum 8 and develops the electrostatic latent image. Then, a toner image is formed on the outer peripheral surface of the photosensitive drum 8. In the image forming apparatus 1, the toner formed on the outer peripheral surface of the photosensitive drum 8 is positioned between the transfer member 4 and the photosensitive drum 8 with the recording paper 7 conveyed by the registration rollers 3 and the like. The image is transferred to the recording paper 7. The image forming apparatus 1 uses the fixing device 5 to fix the toner image on the recording paper 7. Thus, the image forming apparatus 1 forms an image on the recording paper 7.

  Here, the arrangement | positioning condition of the magnetic poles A, B, C, D, and E of the magnet roller 33 of this invention is demonstrated using FIG.5 and FIG.6. FIG. 5 is a graph showing the magnetic force in the normal direction on the surface of the developing roller 15 as a magnetic force (N) on the vertical axis and an angle about the rotation center P of the developing sleeve 32 of the developing roller 15 on the horizontal axis. It is. 6 is a graph showing the magnetic flux density in the normal direction on the surface of the developing roller 15 as a magnetic flux density (mT) on the vertical axis and an angle about the rotation center P of the developing sleeve 32 of the developing roller 15 on the horizontal axis. It is. 5 and 6, the position extending from the rotation center P of the developing sleeve 32 shown in FIG. 4 to the photosensitive drum 8 in the horizontal direction is set to 0 °, and the angle is sequentially increased along the arrow G. .

As shown in FIG. 5, in this embodiment, the position P ₁ (shown in FIG. 4) that opposes the apex of the stirring screw 18 and sucks the developer 26, and the position P ₂ that faces the regulating blade 16 (FIG. 4). Between the magnetic poles C and C so that the maximum value f (max) of the normal direction magnetic force on the surface of the developing roller 15 is located closer to the position P ₁ relative to the stirring screw 18 from the center. B is disposed (in the illustrated example, the position P ₁ is 235 ° and the position P ₂ is 285 °). The higher the peak (maximum value) of the magnetic force is, the higher the pumping property of the developer 26 is, and the more difficult the screw pitch unevenness is. The screw pitch unevenness is the downstream of the arrow G (downstream from the top of the stirring screw 18). Is unlikely to occur.

Further, as shown in FIG. 5, in the present invention, the minimum value f (min) of the magnetic force in the normal direction on the surface of the developing roller 15 is positioned in the vicinity of the position P ₂ facing the regulating blade 16. , Magnetic poles C and B are arranged. Since the magnetic force is weak in the vicinity of the regulating blade 16, the stress on the developer 26 is reduced, and deterioration with time of the developer 26 can be reduced. Further, the magnetic poles C and B are arranged so that the magnetic force in the normal direction on the surface of the developing roller 15 gradually becomes weaker from the maximum value f (max) toward the minimum value f (min). ing.

As described above, the developing device 13 according to the present invention has a maximum value f (max) from the center to the stirring screw 18 between the position P ₁ facing the stirring screw 18 and the position P ₂ facing the regulating blade 16. as present in relative position P ₁ closer, the minimum value f (min), so as to present in the vicinity of the position corresponding P ₂ to the regulating blade 16, and the minimum from the maximum value f (max) value f ( min) between at least one of the magnetic poles B and C between a position P ₁ facing the agitating screw 18 and a position P ₂ facing the regulating blade 16 so as to gradually weaken. It is arranged. Therefore, it is possible to provide the developing device 13 that improves the pumping property of the developer 26, has less screw pitch unevenness caused by the stirring screw 18, has a uniform image, and is excellent in developer deterioration.

Furthermore, as shown in FIG. 6, in the present invention, the magnetic poles C and D are arranged so that a separation range R in which the magnetic flux density is 10 mT or less is formed on the upstream side of the arrow G from the position P ₁ facing the stirring screw 18. It is arranged. The separation range R is a range in which the developer 26 that has been developed and adhered to the developing sleeve 32 of the developing roller 15 is separated from the developing sleeve 32.

  The separation range R varies slightly depending on the developer magnetic characteristics, the outer diameter of the developing roller 15, the rotational speed of the developing roller 15, and the like, but when the magnetic poles C and D having the same polarity are disposed adjacent to each other, The normal direction magnetic flux density is 8 mT or less.

In the developing device 13 according to the present embodiment, the most downstream position P ₃ (shown in FIG. 4) in the rotation direction G of the separation range R is located 20 ° or more below the horizontal direction with the rotation center P of the developing sleeve 32 as the center. The magnetic poles C and D are arranged so as to be (in the example shown, the position of P ₃ is 205 °). Therefore, the developed developer 26 that has once detached from the developing roller 15 due to gravity is surely separated from the developing roller 15, so that the developer 26 is not re-sucked, and only the developer 26 having the necessary toner concentration is obtained. Since it is conveyed, an image having a more uniform density can be obtained.

Note that P ₁ , P ₂ , and P ₃ respectively correspond to the position corresponding to the stirring member, the position facing the regulating member, and the most downstream position in the rotational direction of the nonmagnetic cylindrical body in the separation range.

  In addition, the magnetic pole arrangement | positioning which can obtain the magnetic force and magnetic flux density which were mentioned above is realizable by changing the height of magnetic flux, the width | variety of magnetic flux, and a position of each magnetic pole B, C, D.

  Next, the inventors change the position of the stirring screw 18 of the developing device 13, the separation range R of the developer 26, and the particle size of the magnetic carrier to form a test image on the recording paper 7. The effect of the present invention was confirmed. The results are shown in Table 1 below.

Example 1
In this embodiment, the outer diameter of the developing roller 15 is 18 mm, the roller angular speed (rotation speed) is 294 RPM, the outer diameter of the stirring screw 18 is 12 mm, the pitch of the stirring screw 18 is 20 mm, and the rotation speed of the stirring screw 18 is 376 RPM. The position of the rotation center of the stirring screw 18 is 253 ° (position on the coordinates shown in FIG. 4), the most downstream position P ₃ of the separation range R is 202 ° (position on the coordinates shown in FIG. 4), and the regulating blade 16 was 285 ° (position on the coordinates shown in FIG. 4), and the particle size of the magnetic carrier was 50 μm. Further, the point where the normal direction magnetic flux density on the downstream side in the rotation direction of the arrow G in the separation range R is 8 mT or less is defined as downstream from 200 °.

  As a result of developing under the above conditions, forming an image, and outputting a test image, as shown in Table 1, a result that can withstand practical use was obtained in granularity. Furthermore, excellent results were obtained in terms of screw pitch unevenness, image uniformity, and developer durability.

  The evaluation criteria in Table 1 are ◯ for those that can withstand practical use, ◎ for excellent ones, and Δ, x for those that are less than practical.

(Comparative Example 1)
Next, in Example 1, when the test image was output under the same conditions as in Example 1 with the most downstream position of the separation range R being 195 °, screw pitch unevenness occurred and the result was not practical. It was. In terms of image uniformity and developer durability, satisfactory results that could withstand practical use were not obtained.

(Example 2)
In Example 1, a magnetic carrier having a particle diameter of 50 μm was used. In Example 2, a magnetic carrier having a particle diameter of 35 μm was used, and the other conditions were the same as in Example 1, and a test image was output. However, excellent results were obtained in all of screw pitch unevenness, image uniformity, and developer durability. Further, in terms of granularity, results that could withstand practical use were obtained in Comparative Example 1 and Example 1, but more excellent results were obtained in Example 2.

  Here, FIG. 7 shows the magnetic force in the normal direction on the surface of the developing roller 15, and FIG. 8 shows the magnetic flux density in the normal direction on the surface of the developing roller 15. Since the magnetic force is higher at the developer pumping position (position of 253 °) in Example 1 (Example 2 is almost the same numerical value as in Example 1 compared with Comparative Example 1), the screw pitch unevenness is high. And the durability of the developer 26 is improved because the magnetic force at the regulating blade is low.

  As described above, in the developing devices 13 of the present invention arranged so that the magnetic force becomes the maximum value at the pumping position of the first and second embodiments, that is, the developer 26, and the magnetic force becomes the minimum value in the vicinity of the regulating blade. From the above, it has become clear that not only a good image without oblique screw pitch unevenness can be obtained, but also the durability of the developer 26 can be improved.

  Further, in Examples 1 and 2, that is, in the developing device 13 of the present invention in which the normal direction magnetic flux density on the most downstream side of the separation range R is 8 mT or less, the developing device 13 of the present invention once detached from the developing roller 15. It has become clear that a uniform image without screw pitch unevenness can be obtained because only the developer 26 having the necessary toner concentration is transported without absorbing the developer 26 again.

  In Example 2, a magnetic carrier having a particle diameter of 20 μm or more and 50 μm or less is used. If the particle size of the magnetic carrier exceeds 50 μm, the image quality deteriorates, and if the particle size of the magnetic carrier is less than 20 μm, the magnetic carrier adheres to the photosensitive drum 8 and the magnetic carrier scatters into the developing device 13 easily occurs. It is to become.

  In the above-described embodiment, the process cartridge 6 includes the cartridge case 11, the charging roller 9, the photosensitive drum 8, the cleaning blade 12, and the developing device 13. However, in the present invention, the process cartridge 6 only needs to include at least the developing device 13, and does not necessarily include the cartridge case 11, the charging roller 9, the photosensitive drum 8, and the cleaning blade 12. In the above-described embodiment, the image forming apparatus 1 includes the process cartridge 6 that is detachable from the apparatus main body 2. However, in the present invention, the image forming apparatus 1 only needs to include the developing device 13, and does not necessarily include the process cartridge 6.

  In the above-described embodiment, the magnetic poles C and B are arranged at a position facing the stirring screw 18 and a position facing the regulating blade 16, respectively. However, in the present invention, the maximum value of the magnetic force is applied to the stirring screw 18. The magnetic poles may be arranged so that they are located closer to each other, the minimum value is in the vicinity of the position facing the regulating blade 16, and gradually weaken from the maximum value toward the minimum value. The magnetic poles do not have to be arranged at the position facing the control blade 18 and the position facing the regulating blade 16. That is, in the present invention, at least one magnetic pole may be disposed between a position facing the stirring screw 18 and a position facing the regulating blade 16.

  Further, in the embodiment described above, the magnetic poles A, B, C, D, and E are arranged by embedding magnets in the magnet roller 33. However, in the present invention, it is not always necessary to embed magnets in the magnet roller 33 and arrange the magnetic poles A, B, C, D, and E. That is, the magnetic poles A, B, C, D, and E may be arranged by magnetizing necessary portions of the magnet roller 33, or a well-known magnet piece may be bonded and fixed to the magnet roller main body. C, D, and E may be arranged. In short, the magnet roller in the present invention may be any magnetic roller as long as it forms the magnetic poles A, B, C, D, and E described in the embodiment, and various magnet rollers may be used as long as they satisfy the gist of the present invention. good.

  In addition, this invention is not limited to the said Example. That is, various modifications can be made without departing from the scope of the present invention.

1 is a cross-sectional view showing a main part of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of a developing device of the image forming apparatus shown in FIG. 1. It is sectional drawing which follows the XYZ line | wire in FIG. FIG. 3 is an explanatory diagram illustrating an operation state of the developing device illustrated in FIG. 2. It is a graph which shows the magnetic force of the normal line direction on the surface of a developing roller. It is a graph which shows the magnetic flux density of the normal line direction on the developing roller surface. It is a graph for comparing the magnetic force of the normal direction on the developing roller surface of a present Example and a comparative example. It is a graph for comparing the magnetic flux density of the normal direction on the developing roller surface of a present Example and a comparative example. It is explanatory drawing which shows the operation condition of the conventional image development apparatus. It is sectional drawing which shows the stirring screw of the conventional image development apparatus. It is a figure which shows the screw pitch nonuniformity which generate | occur | produced at the time of image formation of the conventional developing device. It is a figure explaining the screw pitch nonuniformity by the stirring screw shown by FIG. It is explanatory drawing explaining the problem of the developer pick-up property in the conventional developing device. It is explanatory drawing explaining the problem of the developer pick-up property in the conventional developing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Apparatus main body 6 Process cartridge 7 Recording paper (transfer material)
8 Photosensitive drum (image carrier)
9 Charging roller (charging device)
12 Cleaning blade (cleaning device)
13 Developing Device 15 Developing Roller (Developer Carrier)
16 Regulating blade (regulating agent)
18 Stirring screw (stirring member)
26 Developer 31 Development area 32 Development sleeve (non-magnetic cylindrical body)
33 Magnet roller A, B, C, D, E Magnetic pole P Rotation center of the non-magnetic cylinder P ₁ Position relative to the stirring member P ₂ Position opposite to the regulating member P ₃ Most downstream position G Non-magnetic cylinder Rotation direction R Release range

Claims (5)

A stirring member that stirs and conveys a developer including toner and a magnetic carrier, a magnet roller having a plurality of fixed magnetic poles, and a rotatable nonmagnetic cylindrical body disposed so as to contain the magnet roller. And a developer carrying member that sucks and conveys the developer carried by the stirring member, and a regulating member that maintains the thickness of the developer sucked by the developer carrying member at a predetermined thickness. A developing device,
The magnetic force in the normal direction on the surface of the developer carrier is between a position facing the stirring member and a position facing the regulating member.
The maximum value is present closer to the position facing the stirring member than the center,
A minimum value is present in the vicinity of the position facing the regulating member; and
To gradually weaken from the maximum value toward the minimum value,
A developing device, wherein at least one of the fixed magnetic poles is disposed between a position facing the agitating member and a position facing the regulating member. The detachment range in which the developed developer, which is located upstream of the non-magnetic cylindrical body in the rotation direction of the non-magnetic cylindrical body and has a magnetic flux density of 10 mT or less, is separated from the developer carrier. The most downstream position in the rotation direction is
So as to be positioned 20 ° or more lower than the horizontal direction around the rotation center of the non-magnetic cylinder,
Of the fixed magnetic poles, (a) a fixed magnetic pole that faces the stirring member, and (b) a fixed magnetic pole that is adjacent to the fixed magnetic pole that faces the stirring member and is located upstream in the rotational direction,
The developing device according to claim 1, wherein the developing device is disposed.   The developing device according to claim 1, wherein the magnetic carrier has a particle size of 20 μm or more and 50 μm or less.   A process cartridge having at least a developing device, wherein the developing device includes the developing device according to any one of claims 1 to 3.   An image forming apparatus having at least an image carrier, a charging device, and a developing device, wherein the developing device includes the developing device according to any one of claims 1 to 3. Image forming apparatus.

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