JP5346869B2 - Developing device and image forming apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a development device capable of preventing deterioration of a developer while achieving thinning and uniformity of a developer layer, and to provide an image forming apparatus having the development device. <P>SOLUTION: The development device 20 includes: a developer carrier 22 having a carrying surface 26 for carrying the developer and a first magnet 29, and receiving the developer from a developer storage part 11 on the carrying surface 26 while rotating in a predetermined direction, and supplying the developer to a predetermined image carrier 10; a magnetic member 30 forming a predetermined regulatory gap G with the carrying surface 26, and arranged opposite to the first magnet 29; and a second magnet 35 disposed more upstream than the magnetic member 30 when viewed from the rotating direction of the developer carrier 22, and having a magnetic pole of the same polarity as the first magnet 29, wherein magnetic force of the second magnet 35 is set higher than the magnetic force of the first magnet 29. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a developing device that forms a toner image on a predetermined image carrier and an image forming apparatus including the developing device.

  An image forming apparatus such as a copying machine, a printer, a facsimile machine, or a combination machine using an electrophotographic system supplies toner to an image carrier (for example, a photosensitive drum or a transfer belt) and puts the toner on the image carrier. A developing device for forming a toner image;

  The developing device includes, as basic components, a developer storage unit that stores the developer, and receives the developer from the developer storage unit and supplies the developer to the image carrier, thereby the image carrier. A developing roller that forms a toner image thereon, and a regulating blade that faces the developing roller so as to form a regulating gap between the developing roller and regulates the layer thickness of the developer on the developing roller. .

  In such a developing device, in order to form a good toner image on the image carrier, it is necessary to make the developer layer thin and uniform before the developing roller supplies the developer to the image carrier.

  For example, in the developing device of Patent Document 1, a magnet member is disposed on the upstream surface of the regulating blade as viewed from the rotation direction of the developing roller. A magnetic field is generated between the regulation blade made of a magnetic material and the regulation pole formed on the developing roller. The magnetic member increases the magnetic flux density of the magnetic field, and the magnetic field lines of the magnetic field are upstream of the regulation blade. Concentrate on. Thereby, the developer layer (magnetic brush layer) is regulated to be thin and uniform.

JP 2003-255710 A

  However, in the developing device of Patent Document 1, the regulation force that the regulation electrode, the regulation blade, and the magnet member regulate the developer in the regulation gap, that is, the constraint that the regulation electrode, the regulation blade, and the magnet member restrain the developer in the regulation gap. Power is too strong. Therefore, the stress acting on the developer when regulating the magnetic brush layer is increased, and the developer is likely to deteriorate. When the developer deteriorates, it is difficult to form a good toner image on the image carrier, and thus to form a good image on the sheet.

  Therefore, in view of the above circumstances, the present invention provides a developing device capable of suppressing the deterioration of the developer while realizing a thinner and uniform developer layer, and an image forming apparatus including the same. The purpose is to do.

In order to achieve the above object, a developing device according to the present invention includes a developer storage unit that stores a developer containing non-magnetic toner and a magnetic carrier while stirring, and a carrying surface that supports the developer. And a first magnet, receiving the developer from the developer reservoir on the support surface while rotating in a predetermined direction, and supplying the developer to a predetermined image carrier And a magnetic member disposed opposite to the first magnet, and disposed upstream of the magnetic member when viewed from the rotation direction of the developer carrier. And a second magnet having a magnetic pole of the same polarity as the first magnet, the developer reservoir includes a developer circulation path, and the toner is contained in the carrier in the developer circulation path. charged is stirred with the magnetic force of the second magnet The first magnetic force set greater than the of the magnet, the second magnet, said developer carrying member the developer the containing the toner charged received from the reservoir by attaching part of the developer developer Forming a layer and bringing the developer layer into contact with a magnetic brush layer formed of the developer on the developer carrier to scrape off a part of the developer of the magnetic brush layer, thereby It is provided in order to make the thickness of the brush smaller than the size of the restriction gap .

  According to the developing device of the present invention, since the second magnet has a larger magnetic force than the first magnet, the developer is applied from the second magnet to the magnetic member magnetized by the first magnet and the second magnet. Tends to stay, and a developer layer is formed on the second magnet and the magnetic member. The magnetic brush layer formed on the carrying surface when the developer carrying body receives the developer from the developer storing portion, the magnetic member and the second magnetic brush layer pass through the regulation gap as the developer carrying body rotates. Contact with developer layer on two magnets. As a result, the magnetic brush layer on the carrying surface is regulated, and the layer thickness becomes thin and uniform.

  As described above, in the developing device according to the present invention, the magnetic brush layer on the carrying surface is regulated by the magnetic member and the developer layer on the second magnet, so that the magnetic brush layer firmly restrained by the magnetic force is regulated. Unlike the conventional configuration that regulates by the blade, it is possible to reduce the stress acting on the developer when regulating the magnetic brush layer. Thereby, deterioration of the developer due to the stress can be suppressed.

  In a preferred embodiment of the present invention, the saturation magnetization of the carrier is set in the range of 40 to 75 emu / g.

  The regulation of the magnetic brush layer on the carrying surface by the developer layer on the magnetic member and the second magnet is affected by the magnetic force of the carrier. However, by setting the saturation magnetization of the carrier in the range of 40 to 75 emu / g, it is possible to satisfactorily regulate the magnetic brush layer on the carrying surface. When the saturation magnetization exceeds 75 emu / g, the amount of developer that adheres to the magnetic member and the second magnet becomes too large, and the regulation gap is likely to be clogged. Therefore, the regulating force by the developer layer on the magnetic member and the second magnet becomes too strong, the stress acting on the developer increases, and the developer tends to deteriorate. On the other hand, when the saturation magnetization is less than 40 emu / g, the developer layer and the magnetic brush layer are not stably formed on the support surface, the magnetic member, and the second magnet.

  In another preferred embodiment of the present invention, the restriction gap is set in the range of 0.5 to 1.2 mm.

  As described above, in the developing device according to the present invention, since the magnetic brush layer is not regulated using the conventional regulating blade, the regulating gap between the magnetic member and the carrying surface of the developer carrying member is set to 0.5 to 1. It can be set in the range of 2 mm. Thereby, it becomes easy to form a magnetic brush layer having a desired thickness.

  In still another preferred embodiment of the present invention, the magnetic member includes an upstream surface facing the upstream side when viewed from the rotation direction of the developer carrying member, and a tip surface that forms the restriction gap facing the carrying surface. The second magnet is a magnet attached to the upstream surface, and has a facing surface facing the carrying surface, and the tip surface of the magnetic member and the facing of the second magnet It is set to be flush with the surface.

  According to this configuration, since no step is formed between the front end surface of the magnetic member and the opposing surface of the second magnet, the developer stays on the front end surface and the opposing surface to form a developer layer. The developer lump is unlikely to form on the front end surface and the opposing surface. As a result, it is possible to prevent image deterioration such as streaks from occurring in the toner image.

  In still another preferred embodiment of the present invention, the magnetic member includes an upstream surface facing the upstream side when viewed from the rotation direction of the developer carrying member, and a tip surface that forms the restriction gap facing the carrying surface. And the second magnet is a magnet attached to the upstream surface, and has a facing surface that faces the carrying surface, and the tip surface of the magnetic member is the surface of the second magnet. It protrudes from the opposing surface toward the carrying surface.

  In still another preferred embodiment of the present invention, the magnetic member includes an upstream surface facing the upstream side when viewed from the rotation direction of the developer carrying member, and a tip surface that forms the restriction gap facing the carrying surface. The second magnet is a magnet attached to the upstream surface, and has a facing surface facing the carrying surface, and the facing surface of the second magnet is the surface of the magnetic member. It protrudes from the front end surface toward the carrying surface.

  It is preferable to set the tip surface of the magnetic member and the facing surface of the second magnet flush with each other. However, the tip surface protrudes from the facing surface and the facing surface protrudes from the tip surface. However, since the second magnet has a larger magnetic force than the first magnet, the deterioration of the developer can be suppressed. Therefore, by setting the magnetic force of the second magnet to be larger than the magnetic force of the first magnet, it is possible to provide a margin for the accuracy of attaching the second magnet to the magnetic member.

  An image forming apparatus according to the present invention includes an image carrier on which a toner image is formed, a developing device that supplies toner to the image carrier and forms the toner image on the image carrier, and the toner image A developing device having the above-described configuration is used as the developing device, including a transfer member to be transferred onto the sheet and a fixing unit for fixing the toner image on the sheet onto the sheet.

  Since the image forming apparatus according to the present invention uses a developing device capable of suppressing the deterioration of the developer while realizing the thinning and uniformization of the developer layer, a good toner image is formed. be able to.

  According to the developing device and the image forming apparatus of the present invention, it is possible to suppress the deterioration of the developer while realizing a thinner and uniform developer layer.

1 is a diagram schematically illustrating an internal structure of an image forming apparatus. It is an enlarged view of the developing device according to the first embodiment. FIG. 5 is an enlarged view of a developing roller of the developing device and its periphery, and shows the operation of a restricting portion. FIG. 7 is an enlarged view of a developing roller of a developing device according to another embodiment and a periphery thereof, and shows an operation of a restricting unit. FIG. 7 is an enlarged view of a developing roller and a peripheral area of a developing device according to still another embodiment, and shows the operation of a restricting portion.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. In the following description, a monochrome type printer is shown as an image forming apparatus as an embodiment of the present invention. However, the present invention is not limited to this, and a copying machine, a facsimile apparatus, and the functions thereof are described. The present invention can also be applied to other image forming apparatuses such as multifunction peripherals that are also included.

  FIG. 1 schematically shows an internal structure of the image forming apparatus. The image forming apparatus 1 heats the toner image formed on the paper P and an image forming unit 4 that forms a toner image on the paper P (sheet) based on image data from the outside (for example, a personal computer). The fixing unit 5 for fixing on the paper P, the paper feed cassette 7 for storing the paper P, the paper discharge tray 12 for discharging the paper P, and the image forming unit 4 and the fixing unit 5 from the paper feed cassette 7. 1, a manual feed tray 3 provided on the right side in FIG. 1 of the image forming apparatus 1, a plurality of menu setting keys for setting various menus, and the like. And an arranged operation unit (not shown).

  The image forming unit 4 irradiates the photosensitive drum 10 (image carrier), the charger 42 that performs a charging process on the photosensitive drum 10, and the laser beam L to the charged photosensitive drum 10, thereby electrostatically charging the photosensitive drum 10. An exposure device 43 that forms a latent image, a developing device 20 that electrostatically attaches toner to the electrostatic latent image formed on the photosensitive drum 10 to visualize the toner image, and develops the toner filled therein A toner cartridge 45 to be supplied to the apparatus 20, a transfer roller 46 (transfer member) for transferring the developed toner image onto the paper P, and a toner remover for removing and collecting toner remaining on the drum surface of the photosensitive drum 10. 47. Note that the charger 42, the developing device 20, the transfer roller 46, and the toner remover 47 are arranged in this order along the circumferential direction of the photosensitive drum 10 when viewed from the rotation direction of the photosensitive drum 10 (clockwise direction in FIG. 1). Are arranged. The exposure unit 43 is disposed above the charger 42.

  The photoconductor drum 10 is a drum having a photoconductor in which an amorphous silicon layer, which is a positively chargeable photoconductor, is deposited on the surface of an aluminum cylinder, for example. The layer thickness of the amorphous silicon layer and the linear velocity of the photosensitive drum 10 are appropriately set.

  The charger 42 includes a charging roller 50, for example. The charging roller 50 includes a cored bar and an epichlorohydrin rubber layer that covers the cored bar. Further, the charging roller 50 is of a contact charging type in which the peripheral surface thereof is substantially in point contact with the drum surface of the photosensitive drum 10, and a predetermined reference charging voltage (reference charging bias) in which a DC voltage and an AC voltage are superimposed. Is applied to the drum surface to uniformly charge the surface potential of the drum surface.

  The exposure device 43 has a polygon mirror (not shown) that guides laser light L based on image data input from an external PC (personal computer) or the like to the drum surface of the photosensitive drum 10. The polygon mirror scans the laser beam L on the drum surface of the photosensitive drum 10 while rotating by a predetermined driving source, and forms an electrostatic latent image on the drum surface. The developing device 20 supplies toner to the electrostatic latent image to form a toner image on the drum surface.

  The transfer roller 46 is in pressure contact with the drum surface of the photosensitive drum 10 in the conveyance path 6, and a nip portion N is formed between the transfer roller 46 and the drum surface. Since a voltage having a polarity opposite to the surface potential of the drum surface is applied to the transfer roller 46, the toner image on the drum surface is transferred onto the paper P when the paper P passes through the nip portion N. The sheet P that has passed through the nip N is conveyed to the fixing unit 5 through the conveyance path 6.

  After the toner image on the paper P is heated and fixed on the paper P in the fixing unit 5, the paper P is transported to the paper discharge tray 12 through the transport path 6.

  Hereinafter, the developing device 20 will be described in detail with reference to FIG. 2 in addition to FIG. FIG. 2 is an enlarged view of the developing device 20. The developing device 20 uses a two-component developer made of a mixture of a non-magnetic toner and a magnetic carrier. As shown in FIGS. 1 and 2, the developing device 20 has an internal space. The developer container 21 to be defined, the developer storage part 11 for storing the developer, and the developing roller 22 (developer carrier) facing the drum surface of the photosensitive drum 10 are included as basic components.

  The developing container 21 includes a bottom frame 21b and a main body frame 21a that covers the bottom frame 21b from above, and the internal space is defined between the frames 21a and 21b.

  The developer storage section 11 is formed in the developer storage space S that occupies most of the internal space and stores the developer, and the bottom frame 21b in the developer storage space S, and is in the longitudinal direction of the developing device 20 (FIG. 1). And two adjacent developer circulation paths 14 and 15 extending in a direction perpendicular to the sheet surface of FIG.

  The developer circulation paths 14 and 15 are partitioned from each other in the longitudinal direction by a partition plate 17 made of a metal such as aluminum, for example, but communicate with each other at both ends in the longitudinal direction. Further, screw feeders 18 and 19 that convey the developer while being agitated by rotation are rotatably mounted on the developer circulation paths 14 and 15, respectively.

  Since the screw feeders 18 and 19 are set so that the conveying directions are opposite to each other, the developer is conveyed between the developer circulation path 14 and the developer circulation path 15 while being stirred. By this stirring, the non-magnetic toner and the magnetic carrier are mixed, and the toner is charged by the carrier. The charged developer is supplied from the developer circulation path 14 to the developing roller 22. The developer storage unit 11 receives toner from the toner cartridge 45 into the developer storage space S through a supply port (not shown).

  The developing roller 22 is made of a nonmagnetic material such as aluminum, for example, and has a cylindrical developing sleeve 24 extending in the longitudinal direction of the developing device 20 (that is, the axial direction of the photosensitive drum 10), and the developing sleeve 24 in FIG. A roller member including a rotation shaft (not shown) that rotates in a counterclockwise direction.

  The developing sleeve 24 is disposed to face the photosensitive drum 10 with a gap of 0.2 mm to 0.4 mm formed between the outer peripheral surface 26 (carrying surface) and the drum surface of the photosensitive drum 10. . The developing sleeve 24 incorporates a so-called magnet roll 25 extending in the longitudinal direction of the developing sleeve 24 in a state of being fixedly supported by a support shaft 28.

  The magnet roll 25 is formed with a pumping pole 27 for magnetically pumping the developer from the developer reservoir 11 onto the outer peripheral surface 26 of the developing sleeve 24. The pumping pole 27 is disposed opposite to the developer circulation path 14 via the outer circumferential surface 26 of the developing sleeve 24, and the developer in the developer circulation path 14 is magnetically applied to the outer circumferential surface 26 of the rotating developing sleeve 24. To adhere (support). The developer pumped up on the outer peripheral surface 26 by the pumping pole 27 is conveyed toward the regulating portion R as the developing sleeve 24 rotates as a magnetic brush layer D1 (FIG. 3) made of a so-called magnetic brush DB.

  The restricting portion R is provided to make the thickness of the magnetic brush layer D1 on the outer peripheral surface 26 thinner and uniform. In the present embodiment, the restricting portion R includes a restricting pole 29 (first magnet), a magnetic member 30, and a magnet member 35 (second magnet). Hereinafter, the restricting portion R will be described with reference to FIG.

  The magnetic member 30 is a thin plate-like member that is disposed above the developing sleeve 24 so as to face the developing sleeve 24 and extends in the longitudinal direction of the developing sleeve 24. The magnetic member 30 has a front end portion 31 extending toward the outer peripheral surface 26 of the developing sleeve 24, and a predetermined size restriction is provided between the front end surface 32 of the front end portion 31 and the outer peripheral surface 26 of the developing sleeve 24. A gap G is formed. The size of the regulation gap G is set to any value in the range of 0.5 mm to 1.2 mm.

  The restriction pole 29 is a magnetic pole, for example, an N pole, formed on the magnet roll 25 (FIG. 2) so as to face the tip surface 32 of the magnetic member 30. In the present embodiment, the regulation pole 29 is set to be positioned about 5 ° upstream from the magnetic member 30 when viewed from the rotation direction of the developing sleeve 24. With this position setting, the peak of the magnetic force of the regulation pole 29 is located upstream of the tip 31 of the magnetic member 30.

  The magnet member 35 is a plate-like magnet that is joined to the upstream surface 33 of the magnetic member 30 as viewed from the rotation direction of the developing sleeve 24 and extends in the longitudinal direction of the developing sleeve 24. The magnet member 35 has a distal end portion 34 extending toward the outer peripheral surface 26 of the developing sleeve 24, and a magnetic pole having the same polarity as the regulation pole 29, for example, an N pole is formed at the distal end portion 34. The magnetic force of the magnet member 35 is set larger than the magnetic force of the regulation pole 29. Further, the tip portion 34 of the magnet member 35 has a facing surface 36 that faces the outer peripheral surface 26 of the developing sleeve 24. The size of the step formed between the facing surface 36 and the tip surface 32 of the magnetic member 30 is suppressed to 3 mm or less. The step is preferably about 1 mm to 2 mm.

  In the developing device 20 having the restriction portion R configured as described above, the magnetic brush layer D1 on the outer peripheral surface 26 is restricted as follows. A magnetic pole opposite to the regulation pole 29 and the magnet member 35, for example, the S pole is induced at the tip 31 of the magnetic member 30 by the magnetic field of the regulation pole 29 and the magnetic field of the magnet member 35. Since the magnetic force of the magnet member 35 is set to be larger than the magnetic force of the regulating pole 29, the developer of the magnetic brush layer D1 on the outer peripheral surface 26 formed by the scooping pole 27 is accompanied by the rotation of the developing sleeve 24. Then, as it goes to the restricting portion R, a part thereof adheres from the facing surface 36 of the magnet member 35 to the distal end surface 32 of the magnetic member 30 and stays there. Thereby, the developer layer D <b> 2 is formed on the facing surface 36 and the tip surface 32. The amount of the developer that stays can be adjusted by appropriately setting either or both of the magnetic force of the regulation pole 29 and the magnetic force of the magnet member 35.

  When the magnetic brush layer D1 on the outer peripheral surface 26 passes through the regulation gap G as the developing sleeve 24 rotates, the developer layer D2 on the opposing surface 36 of the magnet member 35 and the front end surface 32 of the magnetic member 30. A part is scraped off. Thereby, the magnetic brush layer D1 on the outer peripheral surface 26 is regulated (the magnetic brush DB is cut off). As a result, the layer thickness of the regulated magnetic brush layer D3 becomes a predetermined thickness T smaller than the size of the regulation gap G, and is made thin and uniform.

  The regulated magnetic brush layer D3 is conveyed toward the drum surface of the photosensitive drum 10 as the developing sleeve 24 rotates. The toner in the magnetic brush layer D3 adheres to the electrostatic latent image on the surface of the photosensitive drum 10 due to the potential difference between the developing bias applied to the developing sleeve 24 and the drum bias applied to the photosensitive drum 10. Thereby, a toner image is formed on the drum surface.

  As described above, in the developing device 20 according to this embodiment, the magnetic brush layer D1 on the outer peripheral surface 26 of the developing sleeve 24 is formed by the developer layer D2 on the opposing surface 36 of the magnet member 35 and the tip surface 32 of the magnetic member 30. It is regulated. Therefore, unlike the conventional configuration in which the magnetic brush layer firmly restrained by the magnetic force is regulated by the regulating blade, the developing device 20 can reduce the stress acting on the developer when regulating the magnetic brush layer D1. it can. Thereby, deterioration of the developer due to the stress can be suppressed.

  Further, in the developing device 20 according to the present embodiment, as described above, the magnetic brush layer is not regulated using the conventional regulating blade, so that the regulating gap G is larger than the conventional one, specifically 0.5. It can be set to any value in the range of ˜1.2 mm. Accordingly, the magnetic brush layer D3 having a thickness T can be easily formed by the developer layer on the facing surface 36 of the magnet member 35 and the tip surface 32 of the magnetic member 30.

  The developing device 20 described above has a configuration in which the front end surface 32 of the magnetic member 30 protrudes downward toward the outer peripheral surface 26 rather than the facing surface 36 of the magnet member 35. As shown in FIG. 4, a configuration in which the front end surface 32 of the magnetic member 30 and the facing surface 36 of the magnet member 35 are set to be flush with each other can be employed. Even in the case of the configuration shown in FIG. 4, the magnetic force of the magnet member 35 is set to be larger than the magnetic force of the regulation pole 29, so that the developer layer D <b> 2 is formed from the facing surface 36 to the tip surface 32. The fact that the layer thickness of the magnetic brush layer D1 on the outer peripheral surface 26 is regulated by the developer layer D2 is as described with reference to FIG. 3, and the deterioration of the developer can be suppressed. In the case of the configuration shown in FIG. 4, there is no step between the tip surface 32 of the magnetic member 30 and the facing surface 36 of the magnet member 35, and a developer lump is formed on the tip surface 32 and the facing surface 36. hard. As a result, it is possible to prevent image deterioration such as streaks from occurring in the toner image.

  Further, in the developing device 20, instead of the configuration shown in FIGS. 3 and 4, as shown in FIG. 5, the facing surface 36 of the magnet member 35 is lower than the front end surface 32 of the magnetic member 30 toward the outer peripheral surface 26. It is possible to adopt a configuration that protrudes into the area. The step between the facing surface 36 and the tip surface 32 is preferably suppressed to about 1 mm. Even in the case of the configuration shown in FIG. 5, the magnetic force of the magnet member 35 is set to be larger than the magnetic force of the regulating pole 29, so that the developer layer D <b> 2 is formed from the facing surface 36 to the tip surface 32. The fact that the layer thickness of the magnetic brush layer D1 on the outer peripheral surface 26 is regulated by the developer layer D2 is as described with reference to FIG. 3, and the deterioration of the developer can be suppressed.

  The tip surface 32 of the magnetic member 30 and the facing surface 36 of the magnet member 35 are preferably set to be flush with each other as shown in FIG. 4, but even with the configuration shown in FIGS. Deterioration can be suppressed. Therefore, by setting the magnetic force of the magnet member 35 to be larger than the magnetic force of the restriction pole 29, it is possible to provide a margin for the accuracy of attaching the magnet member 35 to the magnetic member 30.

(Experiment 1)
Next, Experiment 1 performed using the developing device 20 will be described. In Experiment 1, the stability of thinning of the magnetic brush layer, the decrease in image density when printed, and the occurrence of streak noise (hereinafter referred to as roughness) were investigated. Examples 1 to 10 and Comparative Examples 1 to 3 were used as experimental objects. In Examples 1 to 10, as shown in Table 1 below, the magnetic force of the magnet member 35 is set to be larger than the magnetic force of the restriction pole 29 and the size of the restriction gap G is 0.5 mm to 1.2 mm. Set to any value in the range. In Comparative Example 1, the magnet member 35 was not used, only the conventional regulating blade was used, and the size of the regulating gap G was set to 0.3 mm. In Comparative Examples 2 and 3, the magnetic force of the magnet member 35 was set smaller than the magnetic force of the restriction pole 29, and the size of the restriction gap G was set to 0.3 mm and 0.4 mm, respectively. The regulation gap G was set so that the amount of the magnetic brush layer after regulation was 8 to 12 mg / cm ² in all of Examples 1 to 10 and Comparative Examples 1 to 3.

  In the first to sixth embodiments, the facing surface 36 of the magnet member 35 is set to be positioned about 1 mm above the front end surface 32 of the magnetic member 30 (that is, the configuration of FIG. 3). The tip surface 32 and the facing surface 36 are set to be flush with each other (that is, the configuration of FIG. 4), and in Examples 9 and 10, the facing surface 36 is set to be positioned about 1 mm below the tip surface 32. (That is, the configuration of FIG. 5).

Table 1 shows the results after driving the developing devices 20 of Examples 1 to 10 and Comparative Examples 1 to 2 for 2 hours under the above conditions. The evaluation criteria for the stability of thinning of the magnetic brush layer, the decrease in image density, and the roughness are as follows. Regarding the stability of thinning, when the amount of the magnetic brush layer is in the range of 8 to 12 mg / cm ² even after the developing device 20 is driven for 2 hours, the thinning stability of the magnetic brush layer is stable. When it was evaluated as high (circle) and it was out of the said range, it evaluated as x which has low stability of thinning of a magnetic brush layer. Moreover, the thickness of the magnetic brush layer was also investigated in Examples 1-10 and Comparative Examples 1-3. The thickness of the magnetic brush layer was measured by observing under a microscope at a magnetic pole downstream of the regulating pole 29 as viewed from the rotation direction of the developing sleeve 24, that is, a so-called conveying pole.

  The image density was evaluated based on the measurement result of the reflection densitometer. When the reflection density at the start of driving of the developing device 20 is set to 1.4 and the developing device 20 is driven for 2 hours and the reflection density is 1.2 or more, the image density is evaluated as good. When the image density was less than 2, the image density was evaluated as poor. As for the roughness, it was evaluated as “◯” when it was visually confirmed that no streaks were generated on the printed paper, and “△” when streaks were within the allowable range.

  As shown in Table 1, in Examples 1 to 10, since the magnetic brush layer was regulated by the developer layer on the facing surface 36 of the magnet member 35 and the tip surface 32 of the magnetic member 30, the magnetic brush layer As a result, the stability of the thin layer and the evaluation of the image density were high. On the other hand, since the comparative example 1 employs a conventional configuration in which the developer is restrained by the magnetic force of the regulation pole 29 and the magnetic brush layer is regulated by the regulation blade, for example, the regulation gap G is clogged with the developer, The inconvenience that the size of the gap G fluctuated easily occurred. Due to such inconvenience, the magnetic brush layer was not thinned and uniformed, resulting in a low evaluation of thin layer stability and image density. In Comparative Examples 2 and 3, the evaluation of the thin layer stability was high, but the evaluation of the image density was low. This is considered because the magnetic force of the restriction pole 29 is set to be larger than the magnetic force of the magnet member 35, so that the binding force of the developer by the restriction pole 29 becomes too strong and the toner does not move to the photosensitive drum 10. .

  Regarding the roughness, no streaks were confirmed in Example 1, Example 2, Example 4, Example 5, Example 7 to 10, Comparative Example 2 and Comparative Example 3. On the other hand, in Example 3 and Example 6, the streak of what was an allowable range was confirmed. This is because in Example 3, the regulation gap G is set to 1.2 mm, and in Example 6, the regulation gap G is set to 1.1 mm. As a result, the thickness of the magnetic brush layer is compared with other examples. This is thought to be a little larger. However, when the size of the regulation gap G is in the range of 0.5 mm to 1.2 mm, it has been confirmed that an image that normally has no problem can be obtained even if a few streaks are generated.

  In the present embodiment described above, in addition to setting the magnetic force of the magnet member 35 to be larger than the magnetic force of the regulating pole 29, the saturation magnetization of the carrier of the developer is set, so that the opposing surface 36 of the magnet member 35 and the magnetic force are set. It becomes possible to better regulate the magnetic brush layer D1 by the developer layer D2 on the front end surface 32 of the member 30.

  Specifically, since the regulation of the magnetic brush layer D1 by the developer layer D2 on the opposing surface 36 and the tip surface 32 is influenced by the magnetic force of the carrier, in this embodiment, the saturation magnetization of the carrier is 40 emu / It is set to any value in the range of g to 70 emu / g.

  When the saturation magnetization of the carrier exceeds 75 emu / g, the amount of the developer staying on the tip surface 32 of the magnetic member 30 and the facing surface 36 of the magnet member 35 becomes too large, and the regulation gap G is easily clogged. Therefore, the regulating force by the developer layer D2 on the front end surface 32 of the magnetic member 30 and the opposing surface 36 of the second magnet becomes too strong, the stress acting on the developer increases, and the developer tends to deteriorate.

  On the other hand, if the saturation magnetization is less than 40 emu / g, the magnetic restraint force that restrains the developer by the magnetic pole 35 and the magnet member 35 becomes weak. Therefore, it is difficult to stably form the magnetic brush layer D1 on the outer peripheral surface 26 of the developing sleeve 24, and the developer layer D2 is stably formed on the front end surface 32 of the magnetic member 30 and the opposing surface 36 of the magnet member 35. And difficult to form. As a result, the magnetic brush layer D1 cannot be thinned and made uniform.

(Experiment 2)
Next, Experiment 2 performed using the developing device 20 will be described. In Experiment 2, the stability of magnetic brush layer thinning, the decrease in image density when printed, and the occurrence of roughness were investigated using experimental subjects with different carrier saturation magnetization. As shown in Table 2, Examples 11 and 12 using a carrier A having a saturation magnetization of 62 emu / g, and Example 13 using a carrier B having a saturation magnetization of 75 emu / g, as shown in Table 2, are saturated. Example 14 using carrier C having a magnetization of 40 emu / g, Comparative example 4 using carrier D having a saturation magnetization of 80 emu / g, and Comparative Example 5 using carrier E having a saturation magnetization of 35 emu / g Used. In all of Examples 11 to 14 and Comparative Examples 4 and 5, the magnetic force of the magnet member 35 was set larger than the magnetic force of the regulation pole 29.

  Carriers A to E were prepared as follows.

  Carrier A: First, ferrite particles (weight average particle diameter 35 μm) were held for 1 hour in a rotary atmospheric furnace held at 500 ° C., and the ferrite particles were subjected to an oxide film treatment to form a carrier core material. . Next, 1000 parts by mass of the carrier core material was coated by a dipping method with a resin solution obtained by diluting 20 parts by mass of KR-251 (manufactured by Shin-Etsu Silicone Co., Ltd., methyl silicone resin) with 500 parts by mass of a solvent (toluene). After the coating treatment, the carrier core material was baked at 250 ° C. for 3 hours, and crushed and coarse powder was removed to prepare Carrier A having a circularity of 0.913, a saturation magnetization of 62 emu / g, and a particle size of 35 μm.

  Carrier B: First, spherical ferrite particles (weight average particle diameter of 35 μm) are held in a rotary atmospheric furnace maintained at 500 ° C. for 1 hour, and the ferrite particle surface is subjected to an oxide film treatment as a carrier core material. did. Next, 1000 parts by mass of this carrier core material was coated by a dipping method with a resin solution in which 20 parts by mass of KR-251 (manufactured by Shin-Etsu Silicone Co., Ltd., methyl silicone resin) was diluted with 500 parts by mass of a solvent (toluene). After the coating treatment, baking was performed at 250 ° C. for 3 hours, pulverization and coarse powder removal were performed, and carrier B having a circularity of 0.967, a saturation magnetization of 75 emu / g, and a particle size of 35 μm was produced.

  Carrier C: First, a ferrite core (weight average particle diameter: 35 μm) of ferrite particles subjected to an oxide film treatment was used as a carrier core material. Next, 1000 parts by mass of the carrier core material was coated by a dipping method with a resin solution obtained by diluting 20 parts by mass of KR-251 (manufactured by Shin-Etsu Silicone Co., Ltd., methyl silicone resin) with 500 parts by mass of a solvent (toluene). After the coating treatment, baking was performed at 250 ° C. for 3 hours, pulverization and coarse powder removal were performed, and carrier C having a circularity of 0.912, a saturation magnetization of 40 emu / g, and a particle size of 35 μm was produced.

  Carrier D: In a resin solution in which spherical ferrite particles (weight average particle diameter 35 μm) are used as a carrier core, 20 parts by mass of KR-251 (manufactured by Shin-Etsu Silicone Co., Ltd., methyl silicone resin) are diluted with 500 parts by mass of a solvent (toluene). Then, 1000 parts by mass of the carrier core material was coated by an immersion method. After the coating treatment, baking was performed at 250 ° C. for 3 hours, pulverization and coarse powder removal were performed, and carrier D having a circularity of 0.968, a saturation magnetization of 80 emu / g, and a particle diameter of 35 μm was produced.

  Carrier E: First, a ferrite core (weight average particle diameter of 35 μm) obtained by subjecting the ferrite particle surface to an oxide film treatment was used as a carrier core material. Next, 1000 parts by mass of the carrier core material was coated by a dipping method with a resin solution obtained by diluting 20 parts by mass of KR-251 (manufactured by Shin-Etsu Silicone Co., Ltd., methyl silicone resin) with 500 parts by mass of a solvent (toluene). After the coating treatment, baking was performed at 250 ° C. for 3 hours, pulverization and coarse powder removal were performed, and carrier E having a circularity of 0.913, a saturation magnetization of 35 emu / g, and a particle diameter of 35 μm was produced.

  The weight average particle diameter of the carriers A to E was unified to 35 μm as described above. If the weight average particle size is too large, the uniformity of the bethamra and the halftone becomes low, and it becomes difficult to obtain a high-quality image. On the other hand, if the weight average particle size is too small, carrier adhesion tends to occur.

  Each of the carriers A to E was mixed with a black toner having a volume average particle diameter of 6.8 μm to produce a developer. The ratio of carrier to toner in the developer was set at 11: 100 by weight.

  Table 1 shows the results after driving the developing devices 20 of Examples 11 to 14 and Comparative Examples 4 and 5 for 2 hours under the above conditions. Note that the stability of the magnetic brush layer is reduced, the image density is lowered, and the evaluation criteria for the roughness are the same as those in Experiment 1 described above, and thus the description thereof is omitted.

  As shown in Table 1, since the saturation magnetization of the carriers A to C was set in the range of 40 to 75 emu / g, Examples 11 to 14 were highly evaluated for thin layer stability and image density. In Comparative Example 4, although the evaluation of the thin layer stability was high, the evaluation of the image density was low. This is because the saturation magnetization of the carrier D exceeds the upper limit of 75 emu / g. In Comparative Example 5, although the evaluation of the image density was high, the evaluation of the thin layer stability was low. This is because the saturation magnetization of the carrier E is less than the lower limit of 40 emu / g.

  Regarding the roughness, no streak was observed in Example 11, Example 13, Example 14, Comparative Example 4 and Comparative Example 5. On the other hand, in Example 12, a streak of an allowable range was confirmed. In the twelfth embodiment, both the magnetic force of the carrier A and the magnetic force of the magnet member 35 are set to be relatively larger than those of the other embodiments, so that the tip surface 32 of the magnetic member 30 and the magnet member 35 face each other. This is probably because the amount of the developer staying on the surface 36 is increased, and the regulating force by the developer layer on the front end surface 32 and the opposed surface 36 is increased.

  In addition to setting the saturation magnetization of the carrier in the range of 40 to 75 emu / g, the image deterioration can also be suppressed by setting the resistance value of the carrier in the range of 1E + 6 to 9Ω. Further, image deterioration can be suppressed by using a toner externally added with alumina.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Developer storage part 20 Developing apparatus 21 Developer container 22 Developing roller (developer carrier)
24 Development sleeve 29 Restriction pole 30 Magnetic member 35 Magnet member D1, D3 Magnetic brush layer D2 Developer layer DB Magnetic brush G Restriction gap R Restriction part

Claims (7)

A developer storage section for storing a developer containing a non-magnetic toner and a magnetic carrier while stirring;
A developer surface that carries a developer and a first magnet, receives the developer from the developer reservoir on the carrier surface while rotating in a predetermined direction, and receives the developer on a predetermined image carrier. A developer carrier to be supplied to
A magnetic member that forms a predetermined regulating gap with the carrying surface and is disposed opposite to the first magnet;
A second magnet disposed upstream of the magnetic member as viewed from the rotation direction of the developer carrier, and having a magnetic pole having the same polarity as the first magnet;
With
The developer reservoir includes a developer circulation path,
The toner is agitated and charged with the carrier in the developer circulation path,
The magnetic force of the second magnet is set larger than the magnetic force of the first magnet ,
The second magnet forms a developer layer by adhering a part of the developer containing the charged toner received by the developer carrier from the developer reservoir, and the developer layer is developed with the developer. A part of the developer of the magnetic brush layer is scraped off by contacting with the magnetic brush layer formed of the developer on the agent carrier, and the thickness of the magnetic brush is made smaller than the size of the regulation gap. A developing device provided for the purpose .
  The developing device according to claim 1, wherein the saturation magnetization of the carrier is set in a range of 40 to 75 emu / g.   3. The developing device according to claim 1, wherein the restriction gap is set in a range of 0.5 to 1.2 mm. 4. The developing device according to claim 1, wherein the magnetic member includes an upstream surface facing an upstream side when viewed from a rotation direction of the developer carrier, and the regulation facing the carrier surface. A tip surface forming a gap,
The second magnet is a magnet attached to the upstream surface, and has a facing surface facing the carrying surface,
The developing device, wherein the tip surface of the magnetic member and the facing surface of the second magnet are set to be flush with each other. 4. The developing device according to claim 1, wherein the magnetic member includes an upstream surface facing an upstream side when viewed from a rotation direction of the developer carrier, and the regulation facing the carrier surface. A tip surface forming a gap,
The second magnet is a magnet attached to the upstream surface, and has a facing surface facing the carrying surface,
The developing device, wherein the tip surface of the magnetic member protrudes toward the carrying surface from the facing surface of the second magnet. 4. The developing device according to claim 1, wherein the magnetic member includes an upstream surface facing an upstream side when viewed from a rotation direction of the developer carrier, and the regulation facing the carrier surface. A tip surface forming a gap,
The second magnet is a magnet attached to the upstream surface, and has a facing surface facing the carrying surface,
The developing device, wherein the facing surface of the second magnet protrudes toward the carrying surface from the tip surface of the magnetic member. An image carrier on which a toner image is formed;
A developing device for supplying toner to the image carrier and forming the toner image on the image carrier;
A transfer member for transferring the toner image onto a sheet;
A fixing unit for fixing the toner image on the sheet onto the sheet;
With
An image forming apparatus in which the developing device according to claim 1 is used as the developing device.

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