JP2007078940A - Developing roller, developing device, process cartridge and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing roller capable of surely preventing carrier adhesion, a developing device having such a developing roller, a process cartridge and an image forming apparatus. <P>SOLUTION: A developing sleeve 32 includes a magnet roller 33 and adsorbs developer containing toner and a magnetic carrier on the outer surface by magnetic force of the magnet roller 33. The toner of the developer adsorbed by the developing sleeve 32 of the magnet roller 33 is transferred to a photoreceptor drum 8 at a developing magnetic pole S3. A different magnetic pole N4 adjacent to the developing sleeve 32 on the downstream side in the rotating direction G is provided to the developing magnetic pole S3 so as to have magnetic flux density of at least 90% or more to magnetic flux density of the developing magnetic pole S3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a developing roller, a developing device, a process cartridge, and an image forming apparatus. In particular, the developing includes a magnet roller, a magnet roller, and a toner and a magnetic carrier on the outer surface by the magnetic force of the magnet roller. The present invention relates to a developing roller, a developing device, a process cartridge, and an image forming apparatus having a non-magnetic cylindrical body that adsorbs an agent.

  Various image forming apparatuses such as copying machines, facsimile machines, and printers use various developing devices 100 (see, for example, Patent Documents 1 and 2). As shown in FIG. 7, this type of developing device 100 transports a developer containing a magnetic carrier and toner to a developing region 103 facing the photosensitive drum 102, and forms a static image formed on the photosensitive drum 102. A developing roller 104 is provided that develops the electrostatic latent image with a developer to form a toner image.

  The developing roller 104 has a developing sleeve 105 (cylindrical body) formed in a cylindrical shape and a magnetic field that is accommodated in the developing sleeve 105 and causes the developer sleeve to rise on the surface of the developing sleeve 105. And a magnet roller 106. The magnet roller 106 is formed in a cylindrical shape. The magnet roller 106 includes a plurality of magnetic poles composed of rod-shaped magnets. Of the plurality of magnetic poles, the magnetic pole opposite to the above-described developing region 103 is a developing pole that forms a spike on the surface of the developing sleeve 105 and transfers the developer toner to the photosensitive drum 102. Yes.

  In the developing roller 104, when the developer spikes, the magnetic carrier of the developer spikes (stands up) on the developing sleeve 105 so as to follow the lines of magnetic force generated by the magnet roller 106, and the spiked magnetic carrier The developer toner is adsorbed on the carrier. Further, the developing roller 104 conveys the developer that has risen on the surface of the developing sleeve 105 as at least one of the developing sleeve 105 and the magnet roller 106 rotates.

  In general, the developing roller 104 described above rotates the developing sleeve 105 in order to easily transport the developer. In the developing roller 104 shown in FIG. 7, a flange or the like is attached to the end of the developing sleeve 105, and the flange is supported by a bearing or the like so that the developing sleeve 105 is rotatable. The developing sleeve 105 is close to both the photosensitive drum 102 and a regulating member 107 that regulates the amount of the developer 101 conveyed to the photosensitive drum 102.

  Further, the developing sleeve 105 described above is sandblasted or grooved on the outer surface in order to prevent the developer 101 from slipping on the surface.

  In addition, if the rotation center of the developing sleeve 105 is deviated from the axis, the rotation of the developing sleeve 105 is generated, and the gap (interval) between the regulating member 107 and the photosensitive drum 102 is changed. Unevenness occurs in the amount of developer supplied, resulting in uneven density in the formed image. For this reason, in order to obtain a high-quality image, the developing device 100 described above matches the rotation center of the developing sleeve 105 and the shaft core as much as possible, keeps the shaft core as straight as possible, and has a cross-sectional shape. A perfect circle having a constant size is maintained to prevent the developing sleeve 105 from swinging.

  In the development region 103 described above, it is desired that only the toner constituting the developer and the magnetic carrier adhere to the photosensitive drum 102. However, not only the toner but also the magnetic carrier may adhere to the photosensitive drum 102. is there. A magnetic force from the developing roller 104, an electric force from the photosensitive drum 102, and a centrifugal force due to the rotation of the developing roller 104 are applied to the magnetic carrier. The magnetic force is a force in the direction of attracting the magnetic carrier to the developing roller 104, and the electric force and the centrifugal force are forces in a direction of pulling the magnetic carrier away from the developing roller 104.

  The magnetic carrier should remain on the developing roller 104 due to the magnetic force. However, when the combined force of the electric force and the centrifugal force becomes larger than the magnetic force, the magnetic carrier is separated from the developing roller 104 and adheres to the photosensitive drum 102. This is a phenomenon called carrier adhesion.

  When the magnetic carrier adheres to the photosensitive drum 102, the magnetic carrier moves to the transfer body and paper together with the toner, adversely affects the transfer device and the fixing device, and causes a problem of reducing the reliability of the image forming apparatus. In recent years, with the goal of improving the image quality of image forming apparatuses, the development process has attempted to reduce the size of magnetic carrier particles and the low potential phenomenon, but both are disadvantageous for carrier adhesion.

In order to solve this problem, there has been proposed one in which the magnetic characteristics of the developing pole of the developing roller 104 and the adjacent different pole adjacent to the downstream side of the developing pole are improved (Patent Document 3). However, there is no one that clearly discloses the relationship of the magnetic flux density between the developing pole and the adjacent different pole, and generally the magnetic flux density of the adjacent different pole is smaller than the magnetic flux density of the developing pole. When the adjacent different polarity of the developing roller 104 is lower than that of the developing pole, a drop occurs in the combined magnetic flux density distribution obtained by combining the normal direction magnetic flux density distribution with respect to the developing roller 104 and the tangential direction magnetic flux density distribution. There is a problem in that the magnetic force is lowered at the depressed portion and the margin for carrier adhesion is lowered.
Japanese Patent Application No. 2000-194194 JP 2000-194195 A JP 2004-198468 A

  SUMMARY An advantage of some aspects of the invention is that it provides a developing roller capable of reliably preventing carrier adhesion, a developing device having the developing roller, a process cartridge, and an image forming apparatus. .

  The invention according to claim 1, which has been made to solve the above-described problem, adsorbs a developer containing a magnet roller and a magnetic roller that encloses the magnet roller and includes toner and a magnetic carrier on the outer surface by the magnetic force of the magnet roller. A developing roller having a non-magnetic cylindrical body that is downstream of the cylindrical body in the rotation direction with respect to a developing pole that delivers the toner of the developer adsorbed to the cylindrical body of the magnet roller to the photosensitive body In the developing roller, the adjacent adjacent different pole is provided so as to have a magnetic flux density of at least 90% or more with respect to the magnetic flux density of the developing pole.

  According to a second aspect of the present invention, the magnet roller comprises a roller body formed of a magnet made of at least magnetic powder and a polymer material with grooves provided in portions corresponding to the developing pole and the adjacent different pole, 2. The developing roller according to claim 1, further comprising a high magnetic force magnet having a higher magnetic force than that of the magnet and inserted into the groove.

  According to a third aspect of the invention, there is provided the developing roller according to the second aspect, wherein the magnetic powder constituting the magnet is oriented.

  According to a fourth aspect of the invention, there is provided the developing roller according to the second or third aspect, wherein the polymer material is an ethylene ethyl acrylate copolymer.

  A fifth aspect of the present invention resides in the developing roller according to the fourth aspect of the present invention, wherein the molding material constituting the magnet has a magnetic powder content of 92% by weight or more and less than 94% by weight.

  A sixth aspect of the present invention resides in a developing apparatus having a developing roller, wherein the developing roller includes the developing roller according to any one of the first to fifth aspects.

  A seventh aspect of the present invention resides in a process cartridge having a developing device, wherein the developing device includes the developing device according to the sixth aspect.

  The invention according to claim 8 is an image forming apparatus having a process cartridge, wherein the process cartridge includes the process cartridge according to claim 7.

  According to the first aspect of the present invention, the adjacent different pole adjacent to the downstream side in the rotation direction of the cylindrical body with respect to the developing pole is provided so as to have a magnetic flux density of at least 90% or more with respect to the magnetic flux density of the developing pole. The magnetic flux density of the adjacent different pole is set to be at least 90% or more of the magnetic flux density of the developing pole, thereby reducing the drop in the composite density distribution between the developing pole and the adjacent different pole, and the portion having a low magnetic force Therefore, it is possible to obtain a developing roller having a high margin for carrier adhesion.

  According to the invention described in claim 2, the roller body having a complicated shape is formed by a magnet having high moldability made of magnetic powder and a polymer material, and the developing pole and the adjacent different pole are formed by a high magnetic force magnet. As a result, it is possible to obtain a developing roller in which the magnetic force between the developing pole and the adjacent different pole is increased and the margin of carrier adhesion is increased while ensuring the moldability.

  According to the third aspect of the present invention, since the magnetic powder constituting the magnet is oriented, a developing roller having a high magnetic force can be obtained even with multiple magnetic poles.

  According to the invention of claim 4, by using an ethylene ethyl acrylate copolymer as the polymer material, it has sufficient flexibility even near the melting point, and a groove is formed in a portion corresponding to the developing electrode and the adjacent different electrode. Thus, a developing roller capable of molding a complicated shape can be obtained.

  According to the invention described in claim 5, by using ethylene ethyl acrylate copolymer as the polymer material, the magnetic content is set to 92% by weight or more and less than 94% by weight, so that a high magnetic force can be obtained and the developing pole and adjacent It is possible to obtain a developing roller capable of molding a complicated shape in which a groove is formed in a portion corresponding to a different pole.

  According to the sixth to eighth aspects of the present invention, a developing device, a process cartridge, and an image forming apparatus with high image quality and high reliability can be obtained by using a developing roller having a high margin for carrier adhesion.

  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 the line ABCD in FIG. FIG. 4 is an explanatory diagram showing an operation state of the developing device 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 paper feed roller 3, a transfer member 4, a fixing device 5, a laser writing device (not shown), And at least a process 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 paper feed roller 3, a transfer member 4, a fixing device 5, a laser writing device, and a process cartridge 6. The paper feed roller 3 feeds a recording paper 7 as a transfer material between the transfer member 4 and a photosensitive drum 8 described later.

  The transfer member 4 is an endless belt, and moves forward in a tangential direction of a photosensitive drum 8 described later. The transfer member 4 presses the recording paper 7 fed from the paper feed roller 3 against the outer peripheral surface of the photosensitive drum 8, and transfers the toner image on the photosensitive drum 8 to the recording paper 7. The transfer member 4 sends the recording paper 7 onto which the toner image has been transferred toward the fixing device 5. The fixing device 5 presses and heats the recording paper 7 sent from the transfer member 4 to fix the toner image transferred from the photosensitive drum 8 onto the recording paper 7 on 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 a photosensitive member (also referred to as an image carrier), a cleaning blade 12 as a cleaning device, a developing device 13, It has. 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 disposed with a gap from a later-described developing roller 15 of the developing device 13. The photosensitive drum 8 is formed in a columnar shape or a cylindrical shape that is rotatable about an axis. An electrostatic latent image is formed on the outer surface of the photosensitive drum 8 by a laser writing device. The photosensitive drum 8 is developed on the electrostatic latent image formed on the outer peripheral surface and the toner adheres to the photosensitive drum 8, 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 case 27, a developing roller 15 as a developer carrying member, 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 toner is spherical fine particles produced by an emulsion polymerization method or a suspension polymerization method. The toner may be obtained by pulverizing a lump composed of a synthetic resin in which various dyes or pigments are mixed and dispersed. The average particle size of the toner is 3 μm or more and 7 μm
m or less. 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. Then, the developer supply unit 14 agitates the toner and the magnetic carrier in the second space 21 and supplies them to the outer surface of the developing roller 15 while transporting them in the axial direction.

  The case 27 is formed in a box shape, is attached to the storage tank 17 of the developer supply unit 14 described above, and covers the development roller 15 and the like together with the storage tank 17. In addition, an opening 27 a is provided in a portion of the case 27 facing the photosensitive drum 8.

  The developing roller 15 is formed in a cylindrical shape, and is provided between the second space 21 and the photosensitive drum 8 and in the vicinity of the opening 27a described above. 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.

  2 to 3, the developing roller 15 includes a core metal 29, a cylindrical magnet roller (also referred to as a magnet body) 33, and a cylindrical developing sleeve 32 as a non-magnetic cylindrical body. ing. The metal core 29 has a longitudinal direction parallel to the longitudinal direction of the photosensitive drum 8 and is fixed to the case 27 without rotating.

  The magnet roller 33 includes a roller main body 33a having a cylindrical shape and a magnetic pole mounting groove 35 described later, and magnet blocks 33b and 33c attached to the roller main body 33a. The roller body 33a is fixed to the outer periphery of the core metal 29 without rotating around the axis. Two magnetic pole mounting grooves 35 are provided in the roller body 33a. The magnetic pole mounting groove 35 is concave from the outer peripheral surface of the roller body 33a and extends linearly along the axial center (longitudinal) direction of the roller body 33a, that is, the magnet roller 33.

  The magnet blocks 33b and 33c are long and rod-like magnets, which are inserted into the magnetic pole mounting groove 35 described above and attached to the roller body 33a. That is, the magnet blocks 33 b and 33 c 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 magnet roller 33 configured as described above is accommodated (enclosed) in the developing sleeve 32.

  The roller body 33a, that is, the magnet roller 33 is magnetized with eight magnetic poles N1, S1, N2, S2, N3, S3, N4, and S4. The magnetic pole N1 is a developer pumping magnetic pole, and is opposed to the agitating screw 18 described above. The magnetic pole N <b> 1 has N polarity and generates a magnetic force on the outer surface of the developing sleeve 32, i.e., the developing roller 15, so that the developer 26 in the second space 21 of the storage tank 17 is transferred to the outer surface of the developing sleeve 32. To suck.

  The magnetic pole S3 is a developing pole and is opposed to the above-described photosensitive drum 8. The magnetic pole S3 has S polarity, and generates a magnetic force on the outer surface of the developing sleeve 32, that is, the developing roller 15, and forms a magnetic field between the developing sleeve 32 and the photosensitive drum 8. The magnetic pole S3 forms a magnetic brush by the magnetic field, so that the toner of the developer 26 attracted to the outer surface of the developing sleeve 32 is delivered to the photosensitive drum 8.

  A plurality of magnetic poles S1, N2, S2, and N3 provided between the magnetic poles N1 and S3 and upstream of the arrow G described later from the magnetic pole S3 are pre-development carrying magnetic poles that carry the developer 26 before development. is there. These magnetic poles S1, N2, S2, and N3 have an S polarity, an N polarity, an S polarity, and an N polarity in order from the magnetic pole N1 side as the developer pumping magnetic pole, and the developing sleeve 32, that is, the outer surface of the developing roller 15 Magnetic force is generated above, and the developer 26 before development is conveyed toward the photosensitive drum 8. Further, one magnetic pole S <b> 2 is arranged at a position facing the regulating blade 16. The single magnetic pole S2 cooperates with the regulating blade 16 to maintain the thickness of the developer 26 on the outer peripheral surface of the developing sleeve 32 at a predetermined thickness.

  The magnetic pole N4 provided between the magnetic poles N1 and S3 and downstream of the magnetic pole S3 in the direction of the arrow G is a transport magnetic pole for transporting the developer 26 that has been developed (hereinafter denoted by reference numeral 26a). The magnetic pole N4 has an N polarity, generates a repulsive magnetic field with the magnetic pole N1 as a developer pumping magnetic pole, and from above the developing sleeve 32 on the outer surface of the developing sleeve 32, that is, the developing roller 15. A developer stripping region R is formed to strip the developed developer 26 toward the storage tank 17. That is, the magnetic pole N4 is adjacent to the magnetic pole N1 as the developer pumping magnetic pole and cooperates with the magnetic pole N1 to form the developer stripping region R (= magnetic pole S4). The developer stripping region R is provided on the outer surface of the developing sleeve 32 from the magnetic pole S3 as the developing pole to the magnetic pole N1 as the developer pumping magnetic pole.

  The developer stripping region R is a region where a weak magnetic force having a magnetic flux density of, for example, about 5 mT (millitesla) is generated, and the developed developer 26a adhering to the outer surface of the developing sleeve 32 is caused by its own weight. This is a region that is detached from the outer surface of 32. As described above, in this specification, a region in which a weak magnetic force is generated and the developed developer 26a is separated from the outer surface of the developing sleeve 32 due to its own weight or the like is referred to as a developer stripping region R. Further, the developer stripping region R is selected in a direction in which the normal magnetic force on the outer surface of at least a part of the developing sleeve 32 pulls the developed developer 26 a away from the outer surface of the developing sleeve 32. Yes. The magnetic pole N4 described above has a different polarity from the developing pole described in the present specification and forms an adjacent magnetic pole provided adjacent to the downstream side. The broken line shown in FIG. 4 represents the magnetic force distribution in the normal direction created by these magnetic poles N1, S1, N2, S2, N3, S3, N4, and S4.

  The developing sleeve 32 is made of a nonmagnetic material, is formed in a cylindrical shape, and is provided so as to be rotatable around an axis. The developing sleeve 32 encloses (accommodates) the magnet roller 33, and rotates in the clockwise direction in FIG. 2 so that the inner peripheral surface thereof is sequentially opposed to the magnetic poles N1, S1, N2, S2, N3, S3, N4, and S4. Rotate along arrow G. 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.

  In addition, a plurality of grooves extending along the axis of the developing sleeve 32, that is, the developing roller 15 are formed on the outer surface of the developing sleeve 32. Further, the outer surface of the developing sleeve 32 may be subjected to a known blasting process to form fine irregularities.

  The regulating blade 16 is provided at the end of the developing device 13 near the photosensitive drum 8. The regulating blade 16 is attached to the case 27 described above with a space from the outer surface of the developing sleeve 32. 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.

  Next, the details of the magnet roller 33 described above will be described. In the present embodiment, the magnetic flux density of the magnetic pole N4 as an adjacent different polarity that is different from the magnetic pole S3 and adjacent to the downstream side of the arrow G is different from the magnetic pole S3 as the development pole of the magnet roller 33 described above. At least 90% or more. More specifically, assuming that the magnetic flux density of the magnetic pole S3 (developing pole) is 100 mT (millitesla), the magnetic pole N4 having a magnetic flux density of at least 90 mT is used.

  FIG. 5 shows the magnetic flux density distribution of the developing roller 15 at this time. In the drawing, a dotted line L1 is a magnetic flux density distribution in the normal direction with respect to the developing roller 15. A one-dot chain line L2 is a magnetic flux density distribution in the tangential direction with respect to the developing roller 15. A two-dot chain line L3 is a combined magnetic flux density distribution obtained by synthesizing a normal direction magnetic flux density distribution and a tangential direction magnetic flux density distribution. As shown in the figure, the peak of the magnetic flux density distribution in the tangential direction between the magnetic pole S3 (developing pole) and the magnetic pole N4 (adjacent different pole) is the peak of the magnetic flux density distribution in the normal direction of the magnetic pole S3 (developing pole). N4 (adjacent heteropolarity) is located approximately in the middle of the peak of the magnetic flux density distribution in the normal direction, that is, approximately in the middle between the magnetic pole S3 and the magnetic pole N4. For this reason, the drop in the combined density distribution obtained by combining the magnetic flux density distribution in the normal direction and the magnetic flux density distribution in the tangential direction between the magnetic pole S3 (developing pole) and the magnetic pole N4 (adjacent pole) is reduced, and the magnetic force is low. The part can be eliminated. For this reason, it is possible to obtain the developing roller 15 having a high margin for carrier adhesion.

  That is, the magnet roller 33 according to the present embodiment is larger than the magnetic flux density of the adjacent different pole that has been conventionally used, so that the magnetic pole S3 (development pole) and the pole (adjacent different pole) are combined. The drop in density distribution is reduced, and the portion with low magnetic force can be eliminated.

Further, the inventors of the present invention provide a photosensitive drum of a magnetic carrier when the ratio of the magnetic flux density of the magnetic pole N4 (adjacent different pole) to the magnetic flux density of the magnetic pole S3 (developing pole) in the product of the present invention described above is changed. The number of adhered to 8 (pieces / 75 cm ² ) was measured by experiment. The experimental results are shown in FIG. In FIG. 6A, the horizontal axis represents the ratio (%) of the magnetic flux density of the magnetic pole N4 (adjacent different pole) to the magnetic flux density of the magnetic pole S3 (development pole), and the vertical axis represents the magnetic carrier to the photosensitive drum 8. The number of adhered pieces (pieces / 75 cm ² ).

As shown in the figure, when the ratio of the magnetic flux density of the magnetic pole N4 (adjacent different pole) to the magnetic flux density of the magnetic pole S3 (development pole) is 86%, the number of attachments (pieces / 75 cm ² ) is 61, and when it is 88% Is the number of deposits (pieces / 75 cm ² ) 51, 92% is the number of deposits (pieces / 75 cm ² ) 47, 100% is the number of deposits (pieces / 75 cm ² ) 48, 110% is the deposit When the number (pieces / 75 cm ² ) is 47 pieces and 120%, the number of attached pieces (pieces / 75 cm ² ) is 46 pieces. According to this experimental result, the larger the ratio of the magnetic flux density of the magnetic pole N4 (adjacent different pole) to the magnetic flux density of the magnetic pole S3 (developing pole), the smaller the number of magnetic carriers attached on the photosensitive drum 8 decreases. I understand. Further, by setting the magnetic flux density of the magnetic pole N4 (adjacent different pole) to at least 90% or more of the magnetic flux density of the magnetic pole S3 (developing pole), the number of magnetic carriers attached to the photosensitive drum 8 is 50 (pieces / 75 cm ^2). ) It can be seen that the following can be reduced. If the adhesion number (pieces / 75 cm ² ) can be suppressed to 50 or less, even if the magnetic carrier adheres to the photosensitive drum, it moves to the transfer body or paper together with the toner, and does not adversely affect the transfer apparatus or the fixing apparatus. .

  The magnet roller 33 has a roller body 33a in which the magnetic pole mounting groove 35 is formed in the portion corresponding to the magnetic pole S3 (developing pole) and the magnetic pole N4 (adjacent different pole) as described above, and the magnetic roller 33 is developed in the magnetic pole mounting groove 35. It consists of magnet blocks 33b and 33c inserted as poles and adjacent different poles.

  The roller body 33a described above is formed of a magnet (for example, a plastic magnet or a rubber magnet) obtained by using a paste-like molding material in which magnetic powder is mixed with a polymer material as a binder. The magnet blocks 33b and 33c are composed of high magnetic magnets having higher magnetic force than the roller body 33a. As this high magnetic force magnet, for example, it is conceivable that the magnet has a higher magnetic powder content than the magnet constituting the roller main body 33a, and has a higher magnetic force than the roller main body 33a.

  As a magnet used for the magnet roller 33, a sintered magnet has long been known. At present, a magnet made of a molding material in which a magnetic powder is mixed with a polymer material is mainstream because an arbitrary shape can be obtained relatively easily. A magnet made of the above-described polymer material and magnetic powder can obtain higher magnetic properties if the magnetic powder content of the molding material is increased. For example, by increasing the magnetic powder content by 1% (hereinafter wt)%, the 2-3 mT peak magnetic flux density is increased. However, when the magnetic powder content is increased, the viscosity of the molding material is increased and the moldability is deteriorated. Even if the magnetic powder content is increased beyond a certain amount, the magnetic properties are not improved. Because of these restrictions, it is difficult to obtain high magnetic properties with a magnet made of a polymer material and magnetic powder compared to a sintered magnet or the like. As is clear from this, it can be said that generally, the magnet has a higher magnetic force and the moldability is lowered.

  Further, in the present embodiment, in order to obtain higher magnetic characteristics with the magnet composed of magnetic powder and a polymer material, the magnetic powder is molded in a magnetic field using anisotropic magnetic powder, and the easy axis of magnetization of the magnetic powder is Orientation is aligned (orientated). By orienting, the peak magnetic flux density is expected to be improved by about 70% as compared with the case of not orienting. As methods for molding in a magnetic field, injection molding and extrusion molding are conceivable.

  When performing the above-described injection molding, the molten material is fed into the mold, the magnetic powder is oriented by applying a magnetic field, and after holding in the mold until the viscosity is such that the orientation of the magnetic powder is maintained. Because of cooling, the magnetic component is easily oriented, and the magnetic properties of the material can be fully utilized. However, in the case of a long length such as that used in the magnet roller 33, a difference in the orientation of the magnetic powder tends to occur depending on the distance from the gate, and the deviation in the magnetic characteristics in the longitudinal direction tends to increase.

  On the other hand, when extrusion molding is performed, the molding material is oriented so that the direction in which the molding material is extruded is perpendicular to the direction in which the magnetic powder is oriented unless the viscosity is somewhat low in the region where the magnetic field is applied. The magnetic powder is easily disturbed. For this reason, it is generally difficult to obtain higher magnetic characteristics than injection molding. However, even when the magnet roller 33 is long, the deviation of the magnetic characteristics in the longitudinal direction is small. Moreover, since continuous integral molding is possible, the process can be simplified and the processing time can be shortened. Since the mold structure has advantages such as simple and small size and easy cost compared with injection molding, extrusion molding is adopted in this embodiment.

  Generally, each magnetic pole of the developing roller 15 of the developer 26 containing toner and magnetic powder is required to have a peak magnetic flux density of 40 mT to 90 mT. Further, in order to maintain a good dispersion state of the toner of the developer 26 and the magnetic carrier, it is necessary to increase the number of magnetic poles of the magnet roller 33 to at least 8 or more, for example. Thus, in order to achieve a magnetic characteristic of 40 mT to 90 mT for each pole by setting the number of magnetic poles of the magnet roller 33 to 8 poles or more, it is difficult to achieve unless the orientation is previously 8 poles or more at the time of extrusion molding. For orientation, a magnetic field is applied in the mold at the time of molding, but for orientation to 8 poles or more, a magnetic field of 8 poles or more must be applied. There are two methods for generating magnetic poles: an electromagnet method and a permanent magnet method, but in any case, it is difficult to increase the degree of orientation in order to generate a magnetic field of 8 poles or more, and a high peak magnetic flux density cannot be obtained. Occurs.

  Among the magnetic poles, a high peak magnetic flux density is required for the developing pole and the adjacent different pole. When the peak magnetic flux density of the developing pole is low, high developing ability cannot be obtained. Further, when the peak magnetic flux density of the pole adjacent to the downstream side of the developing pole is low, the margin for carrier adhesion is lowered. In this embodiment, in order to prevent this, magnet blocks 33b and 33c made of a high magnetic force magnet having a higher magnetic force than that of the magnet constituting the roller 33a are inserted in portions corresponding to the developing pole and the adjacent different pole. Thereby, the peak magnetic flux density of the development pole and the adjacent different pole could be increased.

  That is, the roller body 33 has a cylindrical shape and a complicated shape in which the magnetic pole mounting groove 35 is provided, but high magnetic characteristics are not required as compared with the developing pole and the adjacent different pole. In this embodiment, the roller body 33a is formed of a magnet having a high moldability made of magnetic powder and a polymer material but having a low magnetic property. On the other hand, the magnet blocks 33b and 33c inserted into the magnetic pole mounting groove 35 are rod-like and simple in shape, but are required to have high magnetic characteristics because they function as a developing pole and an adjacent different pole. In the present embodiment, the magnet blocks 33b and 33c are formed of a high magnetic force magnet having a high magnetic force although the moldability is lower than that of the magnet forming the roller body 33a. For this reason, it is possible to obtain the developing roller 15 having a high carrier adhesion margin by easily increasing the magnetic force of the developing pole and the adjacent different pole while ensuring the moldability. Further, since the magnetic powder constituting the magnet is oriented as the roller body 33a, a high magnetic force can be imparted even if the magnetic pole is composed of eight or more poles.

  Further, in order to arrange the magnet blocks 33b and 33c, it is necessary to form the magnetic pole mounting groove 35 in the roller body 33a. Since the poles for arranging the magnetic pole mounting grooves 35 are adjacent to each other, it is difficult to form a wall between the magnetic pole mounting grooves 35. If the wall between the magnetic pole mounting grooves 35 is eliminated, the magnetic force drops between the magnetic poles, and the margin for carrier adhesion decreases. As the polymer material constituting the molding material of the roller body 33a, it is necessary to have sufficient flexibility near the melting point even if the magnetic powder content is increased, and an olefin-based thermoplastic elastomer is suitable. Examples of olefin-based thermoplastic elastomers include ethylene vinyl acetate copolymer and ethylene ethyl acrylate copolymer. Among them, by using a more flexible ethylene ethyl acrylate copolymer, the magnetic powder content is set to 92% by weight or more. However, sufficient moldability can be ensured, and the wall portion between the magnetic pole mounting grooves 35 can be oriented to eliminate the drop in the combined magnetic flux density in the normal and tangential directions.

  However, even if an ethylene ethyl acrylate copolymer is used as the polymer material, moldability cannot be ensured when the magnetic powder content is in the region of 94 wt% or more. For this reason, in this embodiment, the magnetic powder content of the magnet forming the roller body 33a is set to 92 wt% to less than 94 wt%, and the molding of the roller body 33 a is secured while obtaining a high magnetic force.

  Next, specific examples of the present invention will be described. The magnetic powder constituting the molding material of the roller body 33a is not particularly limited, but strontium ferrite, which is an anisotropic ferrite, is used in this embodiment. Ferrite is most commonly used among magnetic powders, and is inexpensive and readily available. However, the present invention is not limited to this, and rare-earth magnetic powders such as Nd—Fe—B, Sm—Co, and Sm—Fe—N that have high magnetic properties can also be used.

  If the content of the magnetic powder in the molding material is larger, a molded product having higher magnetic properties can be obtained, but the flexibility is impaired and the moldability cannot be ensured. With general plastic magnets and rubber magnets, moldability cannot be obtained at 91 wt% to 92 wt%. As the polymer material as in the present invention, among the ethylene ethyl acrylate copolymer, a material having a higher ethyl acrylate content which is an amorphous component can provide a more flexible material. In this example, an ethylene ethyl acrylate copolymer having an ethyl acrylate content of 35 wt% was used. Thereby, even if the magnetic powder content was 92 wt% or more, sufficient flexibility could be secured. In this example, the magnetic powder content was 92.6 wt%.

  Further, as a magnetic field generating means for orienting the magnets constituting the roller body 33a, permanent magnets were used and arranged at portions corresponding to the respective poles in the mold. In order to orient the roller body 33a, a generated magnetic field of at least 3T is required, and the mold is heated to 150 ° C. to 200 ° C. Therefore, there is no need to demagnetize due to heat of about 200 ° C. . In order to satisfy these requirements, Sm-Co magnets are suitable. In this embodiment, a magnet having a maximum energy product BHmax 24 MGOe and a residual magnetic flux density Br 1.02T was used.

  Extrusion molding is carried out using a mold in which permanent magnets are arranged to obtain a roller body 33a in which magnetic pole mounting grooves 35 are formed. The molding temperature was 160 ° C. The shape of the roller body 33a was a reference outer diameter of 23 mm, an inner hole reference diameter of 10 mm, and a length of 314 mm. The oriented roller body 33a is demagnetized, and a shaft (SU303) having an outer diameter of 10 mm is inserted into the inner hole of the roller body 33a. The magnetized magnet blocks 33b and 33c were inserted into the magnetic pole mounting groove 35 and adhered and fixed. The magnet blocks 33b and 33c are not particularly limited as long as they have a higher magnetic force than the roller body 33a.

  For adhesion, a cyanoacrylate adhesive was used. A magnet roller 33 having magnet blocks 33b and 33c bonded and fixed to the roller body 33a is magnetized with a yoke. Finally, the outer periphery of the magnet roller 33 was covered with a developing sleeve 32 (aluminum A6063, outer diameter 25 mm) as a nonmagnetic cylindrical body. The shape of the magnet block 33b inserted into the magnetic pole S3 (developing pole) is 3 mm high and 3 mm wide, and the shape of the magnet block 33c inserted into the magnetic pole N4 (adjacent different pole) is 2.3 mm high and 5 mm wide. In any case, the material is Nd-Fe-B + PA6 (6 nylon), and the maximum energy product BHmax is 10 MGOe.

  The inventors manufactured a plurality of magnet rollers 33 having different configurations and measured the magnetic characteristics of these magnet rollers 33. The results are shown in Table 1 below.

Example 1
In Example 1, the roller main body 33a was molded by orienting the magnetic powder in the molding material as described above. As described above, the magnet blocks 33b and 33c are made of the material: Nd-Fe-B + PA6 (6 nylon), the maximum energy product BHmax: 10 MGe, the magnetic pole S3 (developing pole), and the shape: height 3 mm, width 3 mm, magnetic pole N4 ( Adjacent Heteropolarity) Shape: 2.3 mm height and 5 mm width.

(Comparative Example 2)
In Comparative Example 2, the magnetic powder in the roller body 33a was molded without being oriented. The same magnet blocks 33b and 33c as in Example 1 were used.

(Comparative Example 3)
In the comparative example 3, magnet blocks 33b and 33c are not used. The roller body 33a was formed by orienting the magnetic powder without forming the magnetic pole mounting groove 35.

  According to Table 1, in Example 1 and Comparative Example 1, the magnetic flux density of the magnetic pole S3 (developing pole) and the magnetic pole N4 (adjacent different pole) can be increased. In contrast, in Comparative Example 2, the magnetic flux density of the magnetic pole S3 (developing pole) and the magnetic pole N4 (adjacent different pole) cannot be increased.

  As is apparent from the above, in addition to setting the magnetic flux density of the magnetic pole N4, which is the adjacent different pole, to at least 90% or more with respect to the magnetic flux density of the magnetic pole S3, which is the developing pole, the magnet roller 33 is provided with the magnetic pole mounting groove 35. A roller main body 33a formed of a magnet made of at least magnetic powder and a polymer material, and a high magnetic force magnet having a higher magnetic force than the magnet forming the roller main body 33a and inserted into the magnetic pole mounting groove 35. By configuring, it is possible to increase the margin of carrier adhesion by increasing the magnetic force of the developing pole and the adjacent different pole while ensuring moldability.

  Further, Example 1 and Comparative Example 2 achieve the 8-pole magnetization specification, but Comparative Example 1 does not satisfy the 8-pole magnetization specification. As is clear from this, by orienting the magnetic powder of the roller main body 33a, the roller main body 33a can be formed in, for example, a multi-pole of 8 poles or more, and the toner 26 and the magnetic carrier in the developer 26 are well dispersed. Can keep.

  In the above-described embodiment, the magnetic forces of the magnetic pole S3 (development pole) and the magnetic pole N4 (adjacent different pole) are increased by using the magnet blocks 33b and 33c. However, the present invention is not limited to this, for example, the magnet block 33b. The magnetic flux density of the magnetic pole N4 (adjacent different pole) may be at least 90% or more with respect to the magnetic pole S3 (development pole) of the magnet roller 33 that does not use 33c.

  In the above-described embodiment, the magnetic powder of the magnet forming the roller body 33a is oriented. However, the present invention is not limited to this, and the magnet is not oriented unless the roller body 33a needs to have multiple magnetic poles. The roller body 33a may be formed.

  In the above-described embodiment, the ethylene ethyl acrylate copolymer is used as the polymer material that is a molding material of the magnet constituting the roller body 33a. However, the present invention is not limited to this, and the magnet material may be a magnet. Any binder can be used.

  In the above-described embodiment, the magnetic powder content is 92 wt% or more and 94% or more when an ethylene ethyl acrylate copolymer is used as the polymer material that is a molding material of the magnet constituting the roller body 33a. The present invention is not limited to this, and the magnetic powder content may be less than 92 wt.

  In the above-described embodiment, the developing device 13 includes the developer supply unit 14, the case 27, the developing roller 15, and the regulating blade 16. However, in the present invention, the developing device 13 only needs to include at least the developing roller 15, and does not necessarily include the developer supply unit 14, the case 27, and the regulating blade 16.

  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 the developing device according to the embodiment of the present invention of the image forming apparatus shown in FIG. It is sectional drawing which follows the ABCD line | wire in FIG. FIG. 3 is an explanatory diagram illustrating an operation state of the developing device illustrated in FIG. 2. It is magnetic flux density distribution of the developing roller 15 of FIG. (A) and (b) respectively show the number of magnetic carriers attached to the photosensitive drum 8 when the ratio of the magnetic flux density of the magnetic pole N4 (adjacent different pole) to the magnetic flux density of the magnetic pole S3 (development pole) is changed ( It is a graph and a table | surface which show a piece / 75cm < ² >). It is principal part sectional drawing of the developing device which has the conventional developing roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 6 Process cartridge 8 Photosensitive drum (photosensitive body)
13 Developing device 26 Developer 32 Developing sleeve (non-magnetic cylindrical body)
33 Magnet roller S3 Magnetic pole (development pole)
N4 magnetic pole (adjacent different pole)

Claims (8)

In a developing roller comprising a magnet roller and a non-magnetic cylindrical body that encloses the magnet roller and adsorbs developer containing toner and magnetic carrier on the outer surface by the magnetic force of the magnet roller.
With respect to the developing pole that delivers the toner of the developer adsorbed on the cylindrical body of the magnet roller to the photosensitive body, the adjacent different polarity adjacent to the downstream side in the rotation direction of the cylindrical body is the magnetic flux density of the developing pole. A developing roller provided so as to have a magnetic flux density of at least 90% or more.   The magnet roller has a roller body formed of a magnet made of at least magnetic powder and a polymer material with grooves provided in portions corresponding to the developing pole and the adjacent different pole, and has a higher magnetic force than the magnet. The developing roller according to claim 1, comprising a high magnetic force magnet inserted into the groove.   The developing roller according to claim 2, wherein the magnetic powder constituting the magnet is oriented.   4. The developing roller according to claim 2, wherein the polymer material is an ethylene ethyl acrylate copolymer.   The developing roller according to claim 4, wherein the molding material constituting the magnet has a magnetic powder content of 92 wt% or more and less than 94 wt%.   A developing device having a developing roller, wherein the developing roller includes the developing roller according to claim 1.   A process cartridge having a developing device, comprising the developing device according to claim 6 as the developing device.   An image forming apparatus having a process cartridge, wherein the process cartridge is the process cartridge according to claim 7.

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