JP2006071734A - 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, also, an image is uniform, and also, developer deterioration is suppressed, and to provide a process cartridge and an image forming apparatus using the developing apparatus. <P>SOLUTION: The developing apparatus 13 is provided with a stirring screw 18 for stirring and carrying the developer containing toner and magnetic carrier, a developing roller 15 for attracting and carrying the developer carried by the stirring screw 18, and a control blade 16 for keeping the thickness of the developer attracted by the developing roller 15 at a prescribed thickness. The summation of the magnetic force of one-degree pitch in a normal direction on the surface of the developing roller 15 at about 20° in a direction facing the stirring screw 18 from the developing roller 15 is equal to or exceeding 3.5×10<SP>-5</SP>[N]. The summation of the magnetic force of one-degree pitch in the normal direction on the surface of the developing roller 15 at about 20° in a direction facing the control blade 16 from the developing roller 15 is smaller than that in a position where the developer roller 15 faces the stirring screw 18. <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 using 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. 6 and 7, this type of developing device 100 conveys the developer 101 to the developing region 103 facing 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 includes a cylindrical developing sleeve 105 and a magnet roller that is accommodated in the developing sleeve 105 and forms a magnetic field so as to cause the developer 101 to rise on the surface of the developing sleeve 105. 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 equalizing the amount of. The developing device 100 shown in FIGS. 6 and 7 includes a pair of a storage tank 107 and a stirring screw 108.

  The developer 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 one storage tank 107 (hereinafter denoted by reference numeral 107a) on the side away from the developing roller 104 is supplied to the other end of the one storage tank 107a by the stirring screw 108. The developer is agitated while being conveyed along the axial direction. Then, the developer 101 moves from the other end of the one storage tank 107a into the other storage tank 107 (hereinafter denoted by reference numeral 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 sleeve 105 by the magnetic force of the developing roller 104 (attaches to the surface of the 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.

A developing device 100 shown in FIG. 6 is provided with a regulating blade 109 on the lower side of the developing roller 104 to separate the developer remaining when the developing is performed on the upper side of the developing roller 104. In the developing device 100 shown in FIG. 7, a regulating blade 109 is provided on the upper side or the lateral side of the developing roller 104 to separate the developer remaining when the developing is performed below the developing roller 104. The developing device 100 shown in FIG. 6 and the developing device 100 shown in FIG. 7 are selectively used according to 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 including the developing device 100 described above prints an image 111 having a relatively large area ratio, such as a photograph, as compared with printing an image 111 having a relatively small area ratio, such as a text sentence. There is a problem that density unevenness (hereinafter referred to as “screw pitch unevenness”) 112 is conspicuous. For example, as shown in FIG. 8, in a monochromatic image 111 with a large area ratio, as shown in FIG. 8, screw pitch unevenness 112 oblique to the sheet passing direction occurs in a striped pattern, and the aesthetic appearance is impaired. It is. In FIG. 8, 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.

  In the color image 111 with a large area ratio, density unevenness of each color appears as a hue shift. For example, generally in the market such as a design occupation, the image 111 having such a large area ratio may be handled, and the commercial value is significantly reduced by the striped screw pitch unevenness 112.

  The pitch of the screw pitch unevenness 112 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. On the surface layer of the agitating screw 108, since there is a large amount of the developer 101 that has been developed and has a low toner concentration that has been detached from the developing roller 104 due to the position where the agent runs out, the toner concentration of the developer 101 at the crest of the stirring screw 108 is particularly Low.

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

  At this time, in the case shown in FIG. 10, the developer 101 having a low toner concentration tends to remain after passing through the regulation 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. 11, not only the surface layer of the developer 101 but also the developer 101 having a predetermined toner concentration that has been sufficiently stirred is transported, so that both are mixed before the regulation blade 109 passes to obtain a uniform concentration. Become. For these reasons, 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 detaching position where the developed developer 101 on the developing roller 104 is detached from the developing roller 104 and the suction position for sucking the new developer 101 are often close. . In such a case, it is difficult to achieve both the above-mentioned reliable release of the developed developer and the reliable suction of the new developer, and the developing roller 104 sucks the developed developer 101 again. There has been a problem that non-uniform images are likely to occur due to the occurrence of the problem.

  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. Attempts to reduce pumping (hereinafter referred to as re-pumping). 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.

  SUMMARY OF THE INVENTION 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 less developer deterioration, a process cartridge having such a developing device, and an image. An object is to provide a forming apparatus.

In order to solve the above-described problems and achieve the object, the developing device according to the present invention includes a stirring member that stirs and conveys a developer containing toner and a magnetic carrier, and a magnet having a plurality of fixed magnetic poles. A developer supporting body that sucks and transports the developer transported by the stirring member, and a rotatable nonmagnetic cylindrical body disposed so as to enclose the magnet roller; And a regulating member that keeps the thickness of the developer sucked by the developer carrier at a predetermined thickness, wherein (A) the distance between the developer carrier and the stirring member is 15 mm or less; and (B) The rotation center of the nonmagnetic cylinder is centered across a line segment connecting the position of the outer peripheral surface of the nonmagnetic cylinder facing the stirring member and the rotation center of the nonmagnetic cylinder. Within ± 20 degrees Wherein the sum of the normal direction of the magnetic force of each degree of the outer peripheral surface of the non-magnetic cylindrical body, so as to be 3.5 × 10 ^-5 [N] or more, yet, the outer peripheral surface of the non-magnetic cylinder The nonmagnetic cylinder within a range of ± 20 degrees around the rotation center of the nonmagnetic cylinder with a line segment connecting the position facing the regulating member and the rotation center of the nonmagnetic cylinder interposed therebetween Relative to the stirring member of the fixed magnetic pole so that the sum of the magnetic forces in the normal direction of the outer peripheral surface of the body at a time is smaller than the sum of the magnetic forces at the position facing the stirring member. And a fixed magnetic pole facing the regulating member among the fixed magnetic poles.

  The developing device of the present invention described in claim 2 is characterized in that the magnetic carrier has a particle size of 20 μm or more and 50 μm or less.

  According to a third aspect of the present invention, there is provided a process cartridge having at least a developing device, wherein the developing device includes the developing device according to the first or second aspect.

  According to a fourth aspect of the present invention, there is provided an image forming apparatus according to the first or second aspect, wherein the phenomenon device is an image forming apparatus having at least an image carrier, a charging device, and a developing device. It has a developing device.

  As described above, according to the first aspect of the present invention, since the sum of the magnetic forces at positions facing the stirring member of the developer carrying member is high, the pumping performance of the developer is improved, and the screw generated by the stirring member is increased. Pitch unevenness can be reduced. In addition, since the total magnetic force at the position facing the regulating member is low, deterioration with time of the developer 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 second aspect of the present invention, since the magnetic carrier has a particle size of 20 μm or more and 50 μm or less and satisfies the item of claim 1, the particle size is excellent and the screw pitch unevenness is excellent. It is possible to provide a developing device capable of obtaining an excellent image without any problem.

  According to the third aspect of the present invention, since the developing device according to the first or second aspect is used, it is possible to provide a process cartridge capable of obtaining an excellent image with excellent granularity and no screw pitch unevenness. it can.

  According to the fourth aspect of the present invention, since the developing device according to the first or second aspect is used, an excellent image having excellent granularity and no screw pitch unevenness can be obtained.

  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 the recording paper 7 between the transfer member 4 and a photosensitive drum 8 described later. The transfer member 4 presses a recording sheet 7 as a transfer material against the outer peripheral surface of the photosensitive roller 8 and sends the recording sheet 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 the 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 24 of the second space 21. The developer supply unit 14 supplies the developer 26 to the outer peripheral surface of the developing roller 15 while stirring the toner and the magnetic carrier in the second space 21 and transporting the toner and the magnetic carrier 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 the arrow G so that the 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 A moves the inner toner of the developer 26 adhered to the outer surface of the developing sleeve 32 by the magnetic pole C described later away from the developing sleeve 32 and moves it to the photosensitive drum 8. The magnetic pole A keeps the magnetic carrier of the developer 26 attached to the outer surface of the developing sleeve 32.

The magnetic pole B is disposed at a position P ₁ 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 on the outer peripheral surface of the developing sleeve 32 at a predetermined thickness. That is, the magnetic pole B scrapes off the surface of the developer 26 attached to the outer surface of the developing sleeve 32 by the magnetic pole C described later. Therefore, only the developer 26 having a predetermined toner density remains on the surface of the developing sleeve 32.

The magnetic pole C is disposed at a position P ₂ 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 poles D and E generate a repulsive magnetic field, and peel off the developer 26 containing the development from the development sleeve 32.

  These magnetic poles A, B, C, D, and E constitute fixed magnetic poles described in this specification. In particular, the magnetic pole C is a fixed magnetic pole facing the stirring screw 18. The magnetic pole B is a fixed magnetic pole that faces the regulating blade 16. The magnetic pole A is a fixed magnetic pole adjacent to the magnetic pole B and downstream of the arrow G. The magnetic pole D is a fixed magnetic pole adjacent to the magnetic pole C and upstream of the arrow G. 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.

  The distance between the developing roller 15 and the stirring screw 18 exceeds 0 mm and is 15 mm or less. As a result, the developer 26 on the side of the stirring screw 18 is reliably attached to the developing roller 15. That is, the developer 26 can be efficiently pumped up.

  If the distance between the developing roller 15 and the stirring screw 18 exceeds 15 mm, the developer 26 is difficult to adhere to the developing roller 15 unless the magnetic force of the magnetic pole C is increased. As described above, when the magnetic force of the magnetic pole C is increased, the characteristics of the developer 26 are deteriorated, which is not preferable.

  If the distance between the developing roller 15 and the stirring screw 18 is 0 mm, the developing roller 15 and the stirring screw 18 come into contact with each other. For this reason, the developer 26 cannot be pumped up efficiently. When the distance between the developing roller 15 and the stirring screw 18 is 0 mm or less, it becomes physically impossible. For this reason, it is desirable that the distance between the developing roller 15 and the stirring screw 18 is more than 0 mm and not more than 15 mm.

With a line segment R (shown by a solid line in FIG. 4) connecting the position P ₂ of the outer peripheral surface of the developing sleeve 32 facing the stirring screw 18 and the rotation center P of the developing sleeve 32 as a center, the rotation center P is the center. A magnetic force for each degree of the outer peripheral surface of the developing sleeve 32 within a range of ± 20 degrees is obtained. The magnetic poles C, B, and D are arranged so that the sum of these 40 magnetic forces (hereinafter referred to as the magnetic force sum) is 3.5 × 10 ⁻⁵ [N]. The position P ₂ is located on a line segment connecting the rotation center P and the rotation center of the stirring screw 18.

Centering on the rotation center P across a line segment Q (shown by a solid line in FIG. 4) connecting the position P ₁ of the outer peripheral surface of the development sleeve 32 facing the regulating blade 16 and the rotation center P of the development sleeve 32. A magnetic force for each degree of the outer peripheral surface of the developing sleeve 32 within a range of ± 20 degrees is obtained. The magnetic poles B, C, and A are arranged so that the sum of these 40 magnetic forces is smaller than the sum of the magnetic forces at the position P ₂ facing the stirring screw 18. The position P ₁ is located on a line segment that connects the rotation center P and the position that bisects the thickness of the regulating blade 16.

  In addition, the magnetic force sum mentioned above can be obtained by changing the height of the magnetic flux, the width and the position of the magnetic flux of each of the magnetic poles B and C.

  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 and form a toner image. Then, the developing device 13 scrapes off the developer 26 accommodated by the development 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 roller 8 is positioned between the transfer member 4 and the photosensitive drum 8 with the recording paper 7 conveyed by the registration roller 3 or 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.

According to this embodiment, the magnetic force sum at the position P ₂ facing the stirring screw 18 of the developing roller 15 is 3.5 × 10 ⁻⁵ N or more, the pumping property of the developer 26 is improved, and the stirring screw 18 is improved. The screw pitch unevenness caused by the above can be reduced. In addition, since the magnetic force at the position P ₁ facing the regulating blade 16 is low, deterioration with time of the developer 26 can be reduced. Therefore, it is possible to provide the developing device 13 that can obtain excellent image quality for a long period of time.

  Since the distance between the developing roller 15 and the stirring screw 18 is more than 0 mm and not more than 15 mm, the developer 26 can be pumped up efficiently without deteriorating the characteristics. For this reason, screw pitch unevenness can be reduced.

  Since the particle size of the magnetic carrier is 20 μm or more and 50 μm or less, it is possible to provide a developing device that can obtain an excellent image with excellent granularity and no screw pitch unevenness.

Next, the inventors of the present invention formed the magnetic poles A, B, C, D, and E so that the above-described magnetic force sum was changed from 1.7 × 10 ⁻⁵ to 4.0 × 10 ⁻⁵ . The effect of the present invention when an image was formed on the recording paper 7 using the developing roller 15 was confirmed. The screw pitch unevenness rank when an image was formed on the recording paper 7 by each developing roller 15 was obtained. Moreover, the regression curve L was calculated | required from this result. The results are shown in FIG. Note that the screw pitch unevenness rank on the vertical axis in FIG. 5 is obtained by setting step samples from good to bad images formed on recording paper and ranking them with reference to the sample images. .

As shown in FIG. 5, when the magnetic force sum is smaller than 3.5 × 10 ⁻⁵ [N], the screw pitch unevenness rank is less than 4, and the screw pitch unevenness is sufficiently suppressed. It became clear that it was not possible. When the magnetic force sum is 3.5 × 10 ⁻⁵ [N] or more, the screw pitch unevenness rank is 4 or more, and it has become clear that the screw pitch unevenness can be sufficiently suppressed. For this reason, it became clear that the magnetic force in the vicinity of the position P ₂ of the developing roller 15 facing the stirring screw 18 had an influence on the pumping property of the developer 26. Therefore, by increasing the magnetic force sum in the necessary range (the aforementioned ± 20 ° range) and lowering the magnetic force sum at the position P ₁ facing the regulating blade 16, the screw pitch unevenness is reduced and the developer 26 is reduced. It has been clarified that the developing device 13 is less deteriorated.

Next, the inventors of the present invention have various effects of the present invention when an image is formed on the recording paper 7 by variously changing the magnetic force at the position P ₂ facing the stirring screw 18 and the particle diameter of the magnetic carrier. It was confirmed. The results are shown in Table 1 below.

(Comparative Example 1)
The magnetic force at the position P ₂ facing the stirring screw 18 was 2.5 × 10 ⁻⁵ N, and the particle size of the magnetic carrier was 50 μm. The outer diameter of the developing roller 15 was 18 mm, and the angular velocity (number of rotations) was 294 RPM. The position of the stirring screw 18 from the developing roller 15 was set to a position of 253 °. As shown in FIG. 4, when the straight line connecting the rotation center P of the developing sleeve 32 and the rotation center of the photosensitive drum 8 is set to 0 degrees, and the rotation is performed in the arrow G direction around the rotation center P, the angle gradually increases. The position of the agitation screw 18 described above is indicated by increasing coordinates. The outer diameter of the stirring screw 18 was 12 mm, the pitch was 20 mm, and the rotation speed was 376 RPM. As a result, the granularity was excellent. The screw pitch unevenness was outside the allowable limit. Image uniformity was outside acceptable limits. The durability of the developer was outside the allowable limit.

Example 1
The magnetic force at the position P ₂ facing the stirring screw 18 was 3.7 × 10 ⁻⁵ N, and the particle size of the magnetic carrier was 50 μm. The outer diameter of the developing roller 15 was 18 mm, and the angular velocity (number of rotations) was 294 RPM. The position of the stirring screw 18 from the developing roller 15 was set to a position of 253 °. The outer diameter of the stirring screw 18 was 12 mm, the pitch was 20 mm, and the rotation speed was 376 RPM. As a result, the granularity was excellent. The screw pitch unevenness was very excellent. The image uniformity was very good. The durability of the developer was very excellent.

(Example 2)
The magnetic force at the position P ₂ facing the stirring screw 18 was 3.7 × 10 ⁻⁵ N, and the particle size of the magnetic carrier was 37 μm. The outer diameter of the developing roller 15 was 18 mm, and the angular velocity (number of rotations) was 294 RPM. The position of the stirring screw 18 from the developing roller 15 was set to a position of 253 °. The outer diameter of the stirring screw 18 was 12 mm, the pitch was 20 mm, and the rotation speed was 376 RPM. As a result, the granularity was very excellent. The screw pitch unevenness was very excellent. The image uniformity was very good. The durability of the developer was very excellent.

  Since the durability of the developer varies depending on the characteristics of the developer itself, the characteristics of the developing roller sleeve, the development process conditions, and the like, the relative evaluation is performed under the above conditions. In addition, in the evaluation criteria in Table 1, “A” indicates that it is very excellent (no problem in practical use). ○ indicates excellent (no problem in practical use). Δ and × indicate that it is outside the allowable limit (it cannot withstand practical use).

  From this, in Example 1, compared with Comparative Example 1, the magnetic force at the position where the developer 26 is pumped up to the developing roller 15 is high, so that the screw pitch unevenness is reduced. Therefore, it has been clarified that the developing device 13 described above can obtain an excellent image without screw pitch unevenness. At this time, the magnetic carrier of the developer 26 preferably has an average particle diameter of 20 μm or more and 50 μm or less. This is because the image quality deteriorates when the magnetic carrier exceeds 50 μm. Further, when the magnetic carrier is less than 20 μm, there arises a problem that the magnetic carrier adheres to the photosensitive drum and the magnetic carrier scatters easily into the developer supply unit.

  In the above-described embodiment, the process cartridge 6 includes the photosensitive drum 8, the developing device 13, the charging roller 9, and the cleaning blade 12. 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 photosensitive drum 8, the charging roller 9, 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 may not necessarily include the process cartridge 6 as long as it includes the developing device 13.

  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, magnetic poles A, B, C, D, and E may be disposed by attaching / detaching necessary portions of the magnet roller 33, or a well-known magnet piece may be bonded and fixed to the magnet roller main body. , D, 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, embodiment mentioned above only showed the typical form of this invention, and this invention is not limited to embodiment. 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 the developing device according to the embodiment of the present invention 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 explanatory drawing which shows the magnetic force summation of the vicinity of the opposing position of a developing roller and a stirring screw. It is sectional drawing which shows the operation condition of the conventional developing device. 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 another 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 6 Process cartridge 8 Photosensitive drum (image carrier)
9 Charging roller (charging device)
12 Cleaning blade (cleaning device)
13 Developing Device 15 Developing Roller (Developer Carrier)
16 Regulation blade (regulation member)
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 (fixed magnetic pole)
P rotation center P ₁ , P ₂ position R, Q line segment

Claims (4)

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. In the developing device,
(A) The distance between the developer carrying member and the stirring member is 15 mm or less, and
(B) Centering on the rotation center of the nonmagnetic cylinder with a line segment connecting the position of the outer peripheral surface of the nonmagnetic cylinder facing the stirring member and the rotation center of the nonmagnetic cylinder sandwiched therebetween The sum of the magnetic forces in the normal direction for each degree of the outer peripheral surface of the non-magnetic cylinder within the range of ± 20 degrees is 3.5 × 10 ⁻⁵ [N] or more, and ± 20 degrees around the rotation center of the nonmagnetic cylinder with a line segment connecting the position of the outer peripheral surface of the nonmagnetic cylinder facing the regulating member and the rotation center of the nonmagnetic cylinder The fixed magnetic pole so that the sum of the magnetic forces in the normal direction for each degree of the outer peripheral surface of the non-magnetic cylindrical body within the range is smaller than the sum of the magnetic forces at the position facing the stirring member. A fixed magnetic pole opposed to the stirring member, and a fixed magnetic pole opposed to the regulating member of the fixed magnetic poles. A developing device characterized by comprising:   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 claim 1 or 2.   An image forming apparatus having at least an image carrier, a charging device, and a developing device, wherein the developing device according to claim 1 or 2 is used as the phenomenon device.

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