Developing apparatus and image forming apparatus equipped therewith

Abstract

To provide a developing device that can prevent the occurrence of development leakage without reducing image density in a two-component development system, and an image forming apparatus including the same.SOLUTION: A developing device comprises: a developer container that stores two-component developer; a developer carrier; a regulation member that is arranged opposite to the developer carrier; and a film member that is in contact with developer carried on the developer carrier. The developer carrier has a developing sleeve that is formed with a magnetic brush on an outer peripheral surface, and a magnet that is arranged, in a circumferential direction, with a plurality of magnetic poles including a regulation pole opposite to the regulation member and a main pole arranged on the downstream side of the regulation pole. The magnet has a minimum point A of the vertical magnetic force gradient near a position where the perpendicular magnetic force from the regulation member to the main pole becomes 0, and a maximum point B of the vertical magnetic force gradient from the downstream side of the minimum point A to a development area. A contact position of the film member is between the maximum point B and a maximum point C of the perpendicular magnetic force located on the downstream side of the maximum point B.SELECTED DRAWING: Figure 4

Description

Technical Field

[0002] , ,

[0005] ,

[0004] , , , , ,

[0003]

[0001] The present invention relates to a developing device mounted on an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine including an image carrier, and particularly to a two-component developing system developing device using a two-component developer including toner and carrier, and an image forming apparatus including the same.

Background Art

[0002] In an image forming apparatus, an electrostatic latent image formed on an image carrier made of a photoreceptor or the like is developed by a developing device and visualized as a toner image. As one such developing device, a two-component developing system using a two-component developer including a magnetic carrier and toner is adopted.

[0003] In the two-component developing system, there is a problem that leak marks appear in the image due to the occurrence of leakage (discharge) in the developing area. The leakage (developing leakage) in the developing area occurs immediately before the magnetic brush contacts the photoreceptor. The reason for this is that immediately before the tip of the magnetic brush contacts the carrier, the distance between the magnetic brush and the photoreceptor becomes very small, making it easy for discharge to occur. Also, when the diameter of the magnetic brush is large and the length is short, the resistance of the magnetic brush becomes low, and a developing current easily flows through that part. As a result, developing leakage is more likely to occur. That is, when the variation in the shape of the magnetic brush is large, there is a high possibility of forming a magnetic brush that is likely to leak as described above.

[0004] Therefore, methods for suppressing the occurrence of developing leakage have been proposed. For example, in Patent Document 1, there is disclosed a developing device including a first flexible seal film member that protrudes from a cover member covering a developer carrier member and contacts an electrostatic latent image holding surface above the developing area, and a second flexible seal film member that is located below the cover member and the first flexible seal film member and contacts a developer layer on the developer carrier member.

[0005] Patent Document 2 discloses a developing apparatus having a flexible plate-like member provided between a photosensitive drum and a developing roller, wherein the plate-like member is provided in a non-contact manner with respect to the developing roller, flexes in the same convex direction as the surface of the developing roller and comes into contact with the photosensitive drum, and the contact portion between the plate-like member and the photosensitive drum and the tip of the plate-like member are substantially within the developing area. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-84905 [Patent Document 2] Japanese Patent Publication No. 2005-10271 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The methods described in Patent Documents 1 and 2 suppress the occurrence of leak marks by providing a film that contacts the photoreceptor within the development area. However, the occurrence of leak marks differs depending on where the film is in contact with the magnetic brush. Specifically, if the film can be made to contact the magnetic brush downstream in the developer transport direction from the position where the magnetic brush is thickest, the magnetic brush will be smoothed out by the film, and development leaks will be less likely to occur. However, if there is a position downstream of the film contact point where the magnetic brush tends to become thicker, even if the magnetic brush is smoothed out by the film, the diameter and length of the magnetic brush will change again afterward, making development leaks more likely to occur.

[0008] Patent documents 1 and 2 do not describe the relationship between the shape of the magnetic brush and the contact position with the film, which meant that there was a risk that development leakage could not be sufficiently suppressed.

[0009] In view of the above problems, the present invention aims to provide a developing apparatus capable of suppressing the occurrence of developing leaks without reducing image density in a two-component developing method, and an image forming apparatus equipped therewith. [Means for solving the problem]

[0010] To achieve the above objective, the first configuration of the present invention is a developing apparatus comprising a developing container, a developer carrier, a regulating member, and a film member. The developing apparatus develops an electrostatic latent image formed on the surface of an image carrier into a toner image in a developing region where the developer carrier is positioned opposite the image carrier. The developing container contains a two-component developer comprising a magnetic carrier and toner. The developer carrier is rotatably supported in the developing container and carries the developer on its outer circumferential surface. The regulating member is positioned opposite the developer carrier at a predetermined distance. The film member contacts the developer carried on the outer circumferential surface of the developer carrier between the regulating member and the developing region. The developer carrier comprises a rotatable developing sleeve on which the developer is carried and magnetic brushes are formed on its surface, and a magnet in which a plurality of magnetic poles are arranged at predetermined intervals in the circumferential direction, including a regulating pole fixed non-rotatably within the developing sleeve and positioned opposite the regulating member, and a main pole positioned downstream of the regulating pole with respect to the rotational direction of the developing sleeve. The magnet has a minimum point A of the perpendicular magnetic field gradient [mT / °] near the position where the perpendicular magnetic field between the regulating member and the main pole is 0 [mT] with respect to the rotation direction of the developing sleeve, and a maximum point B of the perpendicular magnetic field gradient between the downstream side of the minimum point A and the developing region with respect to the rotation direction of the developing sleeve. The contact position of the film member is between the maximum point B and the maximum point C of the perpendicular magnetic field located downstream of the maximum point B with respect to the rotation direction of the developing sleeve. [Effects of the Invention]

[0011] According to the first configuration of the present invention, since the contact position of the film member is downstream of the maximum point B of the vertical magnetic force gradient, the thickened magnetic brush at the maximum point B can be smoothed out, and development leakage can be suppressed. Furthermore, since the contact position of the film member is upstream of the maximum point C of the vertical magnetic force, the amount of developer transported to the development area can be secured, and a decrease in image density can be suppressed. [Brief explanation of the drawing]

[0012] [Figure 1]Side cross-sectional view showing the internal configuration of the image forming apparatus 100 equipped with the developing devices 3a to 3d of the present invention. [Figure 2] Side cross-sectional view of a developing apparatus 3a according to one embodiment of the present invention [Figure 3] Graph showing the change in the perpendicular magnetic field distribution and perpendicular magnetic field gradient in the circumferential direction of the developing roller 30. [Figure 4] Figure 2 is an enlarged view from the regulating blade 27 to the developing area 40, showing the relationship between the contact position P of the film member 43 and the vertical magnetic field gradient. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a cross-sectional view showing the internal structure of an image forming apparatus 100 equipped with developing devices 3a to 3d of the present invention. Inside the main body of the image forming apparatus 100 (here, a color printer), four image forming units Pa, Pb, Pc, and Pd are arranged in order from the upstream side in the transport direction (left side in Figure 1). These image forming units Pa to Pd are provided to correspond to images of four different colors (yellow, cyan, magenta, and black), and sequentially form images of yellow, cyan, magenta, and black through the processes of charging, exposure, development, and transfer, respectively.

[0014] Each of these image forming units Pa to Pd is equipped with photoreceptor drums (image carriers) 1a, 1b, 1c, and 1d, which carry visible images (toner images) of each color. Furthermore, an intermediate transfer belt (intermediate transfer body) 8, which rotates counterclockwise in Figure 1 by a belt-driven motor (not shown), is provided adjacent to each image forming unit Pa to Pd. The toner images formed on these photoreceptor drums 1a to 1d are sequentially transferred and superimposed onto the intermediate transfer belt 8, which moves in contact with each photoreceptor drum 1a to 1d. Subsequently, the toner images transferred onto the intermediate transfer belt 8 are secondaryly transferred onto a transfer paper P, which is an example of a recording medium, by a secondary transfer roller 9. Furthermore, the transfer paper P on which the toner images have been secondary transferred is discharged from the main body of the image forming apparatus 100 after the toner images have been fixed in the fixing unit 13. The image forming process for each photoreceptor drum 1a to 1d is performed while the photoreceptor drums 1a to 1d are rotated clockwise in Figure 1.

[0015] The transfer paper P on which the toner image is secondarily transferred is housed in a paper cassette 16 located at the bottom of the main body of the image forming apparatus 100. The transfer paper P is transported via the paper feed roller 12a and the pair of registration rollers 12b to the nip between the secondary transfer roller 9 and the drive roller 11 of the intermediate transfer belt 8. The intermediate transfer belt 8 is made of a dielectric resin sheet, and a seamless belt is mainly used. In addition, a blade-shaped belt cleaner 19 is positioned downstream of the secondary transfer roller 9 to remove toner and other residues remaining on the surface of the intermediate transfer belt 8.

[0016] Next, the image forming sections Pa to Pd will be described. Around and below the rotatably arranged photoreceptor drums 1a to 1d are charging devices 2a, 2b, 2c, and 2d for charging the photoreceptor drums 1a to 1d, an exposure device 5 for exposing each photoreceptor drum 1a to 1d to image information, developing devices 3a, 3b, 3c, and 3d for forming toner images on the photoreceptor drums 1a to 1d, and cleaning devices 7a, 7b, 7c, and 7d for removing residual developer (toner) etc. on the photoreceptor drums 1a to 1d.

[0017] When image data is input from a host device such as a personal computer, first, the charging devices 2a to 2d uniformly charge the surfaces of the photosensitive drums 1a to 1d. Next, the exposure device 5 irradiates light according to the image data, and an electrostatic latent image corresponding to the image data is formed on each of the photosensitive drums 1a to 1d. The developing devices 3a to 3d are each filled with a predetermined amount of a two-component developer containing yellow, cyan, magenta, and black toner. When the ratio of the toner in the two-component developer filled in each of the developing devices 3a to 3d falls below a specified value due to the formation of the toner image described later, toner is replenished from the toner containers 4a to 4d to each of the developing devices 3a to 3d. The toner in this developer is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and adheres electrostatically. Thereby, a toner image corresponding to the electrostatic latent image formed by the exposure from the exposure device 5 is formed.

[0018] Then, an electric field is applied at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d by the primary transfer rollers 6a to 6d. Thereby, the yellow, magenta, cyan, and black toner images on the photosensitive drums 1a to 1d are primarily transferred onto the intermediate transfer belt 8. These images are formed with a predetermined positional relationship. Thereafter, in preparation for the formation of a new electrostatic latent image that is subsequently performed, toner and the like remaining on the surfaces of the photosensitive drums 1a to 1d after the primary transfer are removed by the cleaning devices 7a to 7d.

[0019] The intermediate transfer belt 8 is stretched between the upstream driven roller 10 and the downstream driving roller 11. When the intermediate transfer belt 8 starts to rotate counterclockwise as the driving roller 11 rotates by a belt driving motor (not shown), the transfer paper P is conveyed to the nip portion (secondary transfer nip portion) between the driving roller 11 and the secondary transfer roller 9 provided adjacent thereto at a predetermined timing from the resist roller pair 12b, and the toner image on the intermediate transfer belt 8 is secondarily transferred onto the transfer paper P. The transfer paper P onto which the toner image has been secondarily transferred is conveyed to the fixing unit 13.

[0020] The transfer paper P conveyed to the fixing unit 13 is heated and pressed by the fixing roller pair 13a, and the toner image is fixed on the surface of the transfer paper P, forming a predetermined full-color image. The transfer paper P on which the full-color image is formed is diverted in the conveyance direction by the branching unit 14 branched in a plurality of directions, and is discharged to the discharge tray 17 by the discharge roller pair 15 as it is (or after being sent to the duplex conveyance path 18 and images are formed on both sides).

[0021] FIG. 2 is a side cross-sectional view of the developing device 3a mounted on the image forming apparatus 100. In the following description, the developing device 3a disposed in the image forming unit Pa of FIG. 1 is illustrated. However, since the configurations of the developing devices 3b to 3d disposed in the image forming units Pb to Pd are basically the same, the description thereof is omitted.

[0022] As shown in FIG. 2, the developing device 3a includes a developing container 20 in which a two-component developer (hereinafter also simply referred to as a developer) containing a magnetic carrier and toner is stored. The developing container 20 is partitioned into a stirring conveyance chamber 21 and a supply conveyance chamber 22 by a partition wall 20a. In the stirring conveyance chamber 21 and the supply conveyance chamber 22, stirring conveyance screws 25a and supply conveyance screws 25b for mixing, stirring, and charging the toner supplied from the toner container 4a (see FIG. 1) with the magnetic carrier are rotatably disposed respectively.

[0023] In the present embodiment, a resin-coated carrier in which a coat layer such as a silicone resin is formed on the surface of a carrier core which is particles of a magnetic material is used. The silicone-based resin can be coated in a thin film, and the uniformity of the coat layer is high. Also, the smaller the thickness of the coat layer, the higher the capacitance of the coat layer, and the easier it is to exert the effect of the ferroelectric added to the coat layer.

[0024] The carrier shape can range from irregular to spherical. Furthermore, the average particle diameter (number-average particle diameter) of the carrier can be between 20 μm and 65 μm. By setting the average particle diameter of the carrier to 65 μm or less, the specific surface area of ​​the carrier increases, and the amount of toner that the carrier can carry increases. This allows the toner concentration in the magnetic brush to be maintained at a high level, and sufficient toner is supplied to the developing roller 30, thus ensuring a sufficient toner layer thickness. As a result, a sufficient amount of toner is ensured to fly from the toner layer to the electrostatic latent image of the photoreceptor, suppressing a decrease in image density and further reducing density unevenness in the image. In addition, because sufficient toner is supplied to the developing roller 30, toner-depleted areas are less likely to form in the toner layer of the developing roller 30, and the occurrence of hierarchical development is suppressed.

[0025] If the average particle size of the carrier is smaller than 20 μm, carrier development occurs in which the carrier adheres to the photoreceptor drums 1a to 1d. The adhered carrier then moves to the intermediate transfer belt 8, causing transfer errors, or moves to the belt cleaning device 19, leading to poor cleaning. Furthermore, if the average particle size of the carrier is larger than 65 μm, the magnetic brushes of the two-component developer become coarser when moving the toner in the two-component developer from the developing roller 30 to the photoreceptor drums 1a to 1d, resulting in a decrease in image quality.

[0026] Examples of carrier cores include magnetic metals such as iron, nickel, and cobalt, alloys thereof, alloys containing rare earth elements, soft ferrites such as hematite, magnetite, manganese-zinc ferrite, nickel-zinc ferrite, manganese-magnesium ferrite, and lithium ferrite, iron oxides such as copper-zinc ferrite, and mixtures thereof. Carrier cores are manufactured by known methods such as sintering and atomization. Among the above, ferrite carriers are preferred because they have good fluidity and are chemically stable, thus improving image quality and extending lifespan.

[0027] The developer is then agitated and transported axially (perpendicular to the plane of the paper in Figure 2) by the agitation and transport screw 25a and the supply and transport screw 25b, and circulates between the agitation and transport chamber 21 and the supply and transport chamber 22 through developer passages (not shown) formed at both ends of the partition wall 20a. In other words, a developer circulation path is formed within the developing container 20 by the agitation and transport chamber 21, the supply and transport chamber 22, and the developer passages.

[0028] The developing container 20 extends diagonally upward to the right in Figure 2, and within the developing container 20, the developing roller 30 is positioned diagonally upward to the right of the supply transport screw 25b. A portion of the outer surface of the developing roller 30 is exposed from the opening of the developing container 20 and faces the photoreceptor drum 1a at a predetermined distance (developing gap), forming the developing area 40. The developing roller 30 rotates counterclockwise in Figure 2 (trail rotation at the position facing the photoreceptor drum 1a).

[0029] The developing roller 30 consists of a cylindrical developing sleeve 31 that rotates counterclockwise in Figure 2, and a magnet 32 ​​having multiple magnetic poles fixed non-rotatably inside the developing sleeve 31. In this embodiment, a developing sleeve 31 with a knurled surface is used, but it is also possible to use a developing sleeve with a large number of concave shapes (dimples) formed on the surface, a developing sleeve with a blast-finished surface, a developing sleeve with blast finishing in addition to knurling and concave shapes, a developing sleeve with plating or anodizing to improve durability, or a developing sleeve treated with a so-called secondary electrolytic coloring method in which metal salts such as Ni, Sn, or Mo are treated on the porous parts of the anodized surface after anodizing. In particular, anodized or anodized and then treated with a secondary electrolytic coloring method not only improve durability but also have the effect of suppressing the occurrence of developing leaks. This is because the anodized surface of the developing sleeve 31 makes it difficult for the leakage current generated by the magnetic brush to spread horizontally on the surface of the developing roller 30, preventing it from developing into a large leak that involves adjacent magnetic brushes.

[0030] The magnet 32 ​​has a five-pole configuration consisting of a main pole S1, a regulating pole (pushing pole) N1, transport poles S2 and N2, and a peeling pole N3. When a driving force is input to the developing device 3a, the developing sleeve 31 rotates, but the magnet 32 ​​does not. A developing voltage consisting of a DC voltage Vdc and an AC voltage Vac is applied to the developing roller 30 by a developing voltage power supply (not shown).

[0031] Furthermore, a regulating blade 27 is attached to the developing container 20 along the longitudinal direction of the developing roller 30 (perpendicular to the plane of the paper in Figure 2). A small gap is provided between the tip of the regulating blade 27 and the surface of the developing roller 30, forming a regulating section 41. In this embodiment, a magnetic blade made of stainless steel (SUS430) is used as the regulating blade 27.

[0032] A film member 43 is positioned downstream of the regulating blade 27 in the direction of rotation of the developing roller 30 (counterclockwise direction in Figure 2). The film member 43 is positioned opposite to the developing roller 30 across its entire axial direction (perpendicular to the plane of the paper in Figure 2). The film member 43 is fixed to the opening of the developing container 20 so as to approach the developing sleeve 31 from the upstream side to the downstream side in the direction of rotation of the developing sleeve 31.

[0033] The leading edge of the film member 43 contacts the magnetic brush formed on the outer surface of the developing roller 30, thereby leveling the magnetic brush between the regulating section 41 and the developing area 40, and suppressing the occurrence of leakage. The material of the film member 43 can be a flexible resin film such as polyurethane film. In addition, a toner splash prevention film 44 (see Figure 4) is placed at the opening of the developing container 20. One end (base end) of the toner splash prevention film 44 is attached below the film member 43 (further away from the developing roller 30) and extends over the entire axial area of ​​the developing roller 30. The other end (free end) of the toner splash prevention film 44 is in contact with the photoreceptor drum 1a upstream of the developing area 40 in the rotational direction of the photoreceptor drum 1a. The material of the toner splash prevention film 44 can be a flexible resin film such as polyurethane film, similar to the film member 43.

[0034] A magnetic field is generated between the regulating pole N1 of the magnet 32 ​​and the regulating blade 27 in an attractive direction, forming a magnetic brush with developer between the regulating blade 27 and the developing roller 30. As the magnetic brush passes through the regulating blade 27 (regulating section 41), the layer thickness is restricted to a desired height. Subsequently, as the developing sleeve 31 rotates counterclockwise, the magnetic brush is smoothed by the film member 43 and then moves to the developing area 40. Then, a magnetic field is applied by the main pole S1 in an attractive direction to the photoreceptor drum 1a, and the magnetic brush comes into contact with the surface of the photoreceptor drum 1a to develop the electrostatic latent image.

[0035] As the developing sleeve 31 rotates counterclockwise, the transport electrodes N2 and S2 apply a magnetic field along the outer surface of the developing sleeve 31, and the developer that was not used to form the toner image is collected on the developing sleeve 31 along with the magnetic brush. Furthermore, the magnetic brush detaches from the developing roller 30 at the peeling electrode N3, which has a different polarity from the transport electrode S2, and falls into the supply transport chamber 22. After being agitated and transported by the supply transport screw 25b, the magnetic field of the regulating electrode N1 causes the magnetic brush to be formed on the developing sleeve 31 again.

[0036] Figure 3 is a graph showing the change in the vertical magnetic force distribution and vertical magnetic force gradient in the circumferential direction of the developing roller 30. Figure 4 is an enlarged view from the regulating blade 27 to the developing area 40 in Figure 2, and shows the relationship between the contact position P of the film member 43 and the vertical magnetic force gradient. Using Figures 3 and 4, the relationship between the magnetic force distribution of the magnet 32 ​​in the circumferential direction of the developing roller 30, which is a characteristic feature of the present invention, and the contact position of the film member 43, and more specifically, the relationship between the circumferential magnetic force gradient of the vertical magnetic force, which is the radial magnetic force of the developing roller 30 (hereinafter referred to as the vertical magnetic force gradient), and the contact position of the film member 43 will be explained in detail. In Figure 3, the vertical magnetic force is shown by a solid line, and the vertical magnetic force gradient is shown by a dotted line.

[0037] The magnetic attraction force, which draws the developer to the developing roller 30, increases with increasing absolute value of the perpendicular magnetic force [mT]. It also increases with increasing absolute value of the perpendicular magnetic gradient (derivative of the perpendicular magnetic force) [mT / °]. Typically, areas with a large magnetic attraction force have a strong force pulling the magnetic brush to the developing roller 30, causing the magnetic brush to collapse with strong force, which makes toner scattering more likely. The diameter of the magnetic brush also tends to become larger in such areas.

[0038] In particular, the magnetic brush tends to become thicker at the point where the vertical magnetic field gradient reaches its maximum value. This is because the magnetic attraction force is low before and after the point where the vertical magnetic field gradient reaches its maximum value (upstream and downstream), so the magnetic attraction force at the maximum value point becomes higher, making it easier for the magnetic brush to remain in that area.

[0039] For example, as shown in Figure 3, if there is a point A (hereinafter referred to as minimum point A) where the perpendicular magnetic field gradient is at a minimum value near where the perpendicular magnetic field is 0 [mT], even in a region where the magnetic brush is prone to tilting and toner scattering is likely to occur, the magnetic attraction force weakens, making it possible to reduce toner scattering further. However, thereafter, the perpendicular magnetic field gradient increases rapidly and reaches a maximum value at point B, so the diameter of the magnetic brush tends to increase in this area. When the magnetic brush, in this enlarged state, moves to the developing area 40, leakage becomes significant due to the low resistance of the magnetic brush.

[0040] Therefore, as shown in Figure 4, if the contact position P between the film member 43 and the developer layer G is designed to be downstream of point B (hereinafter referred to as maximum point B), where the vertical magnetic force gradient reaches its maximum value, the thickened magnetic brush can be smoothed out, and developer leakage can be suppressed. The contact position of the film member 43 is the part where the film member 43 first contacts the magnetic brush (the upstream end of the contact portion with the developer layer G).

[0041] Furthermore, if the film member 43 comes into contact with the developer layer G downstream of point C where the perpendicular magnetic force is maximum (hereinafter referred to as maximum point C), the amount of developer delivered to the developing region 40 cannot be secured, resulting in a decrease in image density. Therefore, it is necessary to design the film member 43 to come into contact with the developer layer G upstream of point C.

[0042] In this specification, a "minimum" refers to the point where the absolute value of the perpendicular magnetic force (or perpendicular magnetic gradient) is closest to zero within a certain range, while a "maximum" refers to the point where the absolute value of the perpendicular magnetic force (or perpendicular magnetic gradient) is furthest from zero within a certain range. Therefore, these definitions differ from the mathematical definitions of minimum and maximum points.

[0043] In summary, the perpendicular magnetic force distribution and perpendicular magnetic force gradient in the circumferential direction of the developing roller 30 are configured such that the perpendicular magnetic force gradient is at its minimum value when the perpendicular magnetic force is near 0 [mT] between the regulating section 41 and the developing area 40, and the perpendicular magnetic force gradient has a minimum and maximum value when moving from the upstream side to the downstream side in the developer transport direction. In this configuration, the contact position of the film member 43 is set between the maximum point B of the perpendicular magnetic force gradient and the maximum point C of the perpendicular magnetic force located downstream of the maximum point B. This effectively suppresses the occurrence of developing leaks without reducing image density.

[0044] Furthermore, development leaks are more likely to occur in the white areas of the image, and are more likely to occur when the photoreceptor drums 1a to 1d are amorphous silicon (a-Si) photoreceptors than OPC photoreceptors (organic photoreceptors). This is because, with OPC photoreceptors, almost no development current flows through the white areas, but with amorphous silicon photoreceptors, development current flows easily through the white areas. Therefore, the arrangement of the film members 43 described above is more effective with amorphous silicon photoreceptors than with OPC photoreceptors.

[0045] Next, the relationship between changes in magnetic attraction force, toner scattering, and carrier development will be explained. When the magnetic attraction force increases rapidly, toner scattering at the maximum point B of the vertical magnetic field gradient increases. The scattered toner is prevented from leaking out of the developing container 20 by the film member 43, which contacts the developer layer G from the upstream side of the maximum point B with respect to the rotation direction of the developing sleeve 31. However, toner accumulated on the inside of the film member 43 may fall onto the magnetic brush and cause image staining. On the other hand, if the change in magnetic attraction force between the minimum point A and the maximum point B of the vertical magnetic field gradient is too gradual, the vertical magnetic force necessary to suppress carrier development cannot be secured.

[0046] Therefore, in this embodiment, the change in magnetic attractive force from the minimum point A to the maximum point B of the vertical magnetic field gradient is defined within a predetermined range. Specifically, when the vertical magnetic field gradients at the minimum point A and the maximum point B of the vertical magnetic field gradient are X[mT / °] and Y[mT / °], respectively, and the angle between the minimum point A and the maximum point B (the central angle with respect to the center O of the magnet 32) is Z[°], it is preferable that the following equation (1) is satisfied. 0.13≦(YX) / Z≦0.23 (1)

[0047] If (YX) / Z > 0.23, the increase in magnetic attraction force becomes too rapid, increasing toner scattering and causing toner accumulated on the inside of the film member 43 to fall onto the magnetic brush, resulting in image smudges, which is undesirable. On the other hand, if (YX) / Z < 0.13, the increase in magnetic attraction force becomes too gradual, failing to secure enough magnetic force to suppress carrier development, thus causing carrier development, which is also undesirable.

[0048] Next, a method for measuring the vertical magnetic field gradient of the magnet 32 ​​of the developing roller 30 will be described. In this embodiment, the developing roller 30 was mounted on an angle adjustment jig and measured using a magnetic field measuring device (GAUSS METER Model GX-100, manufactured by Nippon Denji Sokki Co., Ltd.) while rotating it by a fixed angle. If the measurement accuracy is very high, the vertical magnetic field gradient can be obtained by dividing the difference in vertical magnetic fields measured at different angles by the difference in measurement angles. However, if the measurement accuracy is low, it is not possible to obtain the vertical magnetic field gradient accurately. Therefore, in this invention, the vertical magnetic field was measured by changing the measurement angle by 0.02° increments, and the gradient 1 at the midpoint within that 0.08° range was taken as (difference in vertical magnetic field at a 0.08° difference / 0.08°). Then, the average gradient per 2° of gradient 1 was taken as the vertical magnetic field gradient. An example of vertical magnetic field gradient measurement is shown in Table 1.

[0049] [Table 1]

[0050] In Table 1, for example, the gradient 1 at an angle of 10.00° (6.25 [mT / °]) is calculated by dividing the difference between the perpendicular magnetic force G1 at 9.96° and the perpendicular magnetic force G2 at 10.04° (G1-G2) by 0.08°. Furthermore, the average gradient at 10.00° (6.25 [mT / °]) is the average value of the gradient 1 values ​​per 2° (2° / 0.02° = 100 values) from 9.00° to 11.00°.

[0051] Furthermore, the present invention is not limited to the above embodiments, and various modifications are possible without departing from the spirit of the invention. For example, in the above embodiment, a configuration was used in which the main pole S1 was arranged as the downstream magnetic pole of the regulating pole N1 as the magnet 32 ​​of the developing roller 30, but a magnet in which a magnetic pole (transport pole) is arranged between the regulating pole and the main pole can also be used.

[0052] Furthermore, although the above embodiment described an image forming apparatus 100 using a color printer as an example as shown in Figure 1, the present invention is not limited to color printers and can be applied to various image forming apparatuses equipped with a two-component developing apparatus, such as monochrome and color copiers, monochrome printers, and digital multifunction devices. The effects of the present invention will be described in more detail below with reference to examples. [Examples]

[0053] [Evaluation of development leak, image density, and pitch unevenness when the contact position of the film component is changed] The development leak and image density were evaluated when the contact position of the film member 43 with respect to the developing roller 30 was changed. The test method involved using developing devices 3a to 3d as shown in Figure 2, with a magnetic force distribution configuration as shown in Figure 3, having a minimum point A, a maximum point B, and a maximum point C of the vertical magnetic force in the section from the regulating blade 27 (regulating section 41) to the developing area 40. The contact position of the film member 43 was changed to the minimum point C of the vertical magnetic force gradient, 3 mm downstream of the maximum point B of the vertical magnetic force gradient, and 1 mm downstream of the maximum point C of the vertical magnetic force, and a configuration without the film member 43 was also prepared and mounted on a test machine as shown in Figure 1. In all cases, the toner scattering prevention film 44 (see Figure 4) was attached below the film member 43, and the free end of the toner scattering prevention film 44 was in contact with the photoreceptor drums 1a to 1d upstream of the developing area 40 with respect to the rotation direction of the photoreceptor drums 1a to 1d.

[0054] Using this test machine, the number of magnetic brushes [brushes / mm] in the development area 40, the AC voltage [V] at which development leakage occurs, and the image density and pitch uniformity of the solid (flat) image were evaluated.

[0055] The image formation conditions were as follows: the printing speed (process speed) was set to 70 frames / minute, and the developing roller 30 used a developing sleeve 31 with an outer diameter of 20 mm and a 10-point average roughness (JIS) of 5-10 μm, whose outer surface was blast-processed. The regulating blade 27 was a 1.5 mm thick stainless steel (SUS430) magnetic blade, and the distance (regulating gap) between the regulating blade 27 and the developing roller 30 was set to 0.5 ± 0.03 mm. The developing roller 30 was subjected to a developing voltage obtained by superimposing an AC voltage with a peak-to-peak value (Vpp) of 900-1300 V (determined by Vac calibration) on a DC voltage of 90-280 V (determined by Vdc calibration).

[0056] The photoreceptor drums 1a to 1d used amorphous silicon (a-Si) photoreceptors with a dielectric constant of 11. The peripheral speed ratio of the developing roller 30 to the photoreceptor drums 1a to 1d was set to 1.8 (trail rotation at opposing positions), and the distance between the photoreceptor drums 1a to 1d and the developing roller 30 (DS distance) was set to 0.375 ± 0.025 mm. The surface potential (light potential) of the photoreceptor drums 1a to 1d was set to 160 to 350 V (determined by Vdc calibration, Vo-Vdc=70 V), and the image potential (dark potential) was set to 20 V. An elastic resin belt was used for the intermediate transfer belt 8. The film member 43 was a polyurethane film with a thickness of 100 μm.

[0057] A positively charged toner with an average particle size of 6.8 μm was used, and a resin-coated carrier was used as the carrier. The initial toner concentration in the developer (weight ratio of toner to carrier) was set to 6%.

[0058] For the evaluation method, the number of magnetic brushes in the development area 40 was counted with the photoreceptor drums 1a to 1d not facing each other. For image density, the density (ID) of the solid image was measured with an image densitometer, and a score of ○ was given when ID > 1.2, and a score of × was given when ID ≤ 1.2. For pitch unevenness, the solid image was observed visually, and a score of ○ was given when no pitch unevenness occurred, and a score of × was given when pitch unevenness occurred. The evaluation results, along with the contact position of the film member 43, are shown in Table 2.

[0059] [Table 2]

[0060] As is clear from Table 2, when the film member 43 is not provided, the magnetic brushes are transported to the development area 40 in an unleveled state. As a result, the number of magnetic brushes in the development area 40 is low at 12.7 [brushes / mm], and the diameter of the magnetic brushes is found to be thicker. Consequently, the AC voltage at which development leakage occurs is also low at 1125 [V], making development leakage more likely. In addition, pitch unevenness in the solid image also occurred.

[0061] Furthermore, when the contact position of the film member 43 was set to the minimum point A of the vertical magnetic force distribution, the number of magnetic brushes in the development area 40 was low at 13.5 [brushes / mm], and the AC voltage at which development leakage occurs was also low at 1175 [V], making development leakage more likely. In addition, pitch unevenness occurred in the solid image. This is thought to be because the magnetic brushes are initially leveled at the minimum point A by the film member 43, but then concentrate again at the maximum point B, causing the diameter of the magnetic brushes to increase.

[0062] In contrast, when the contact position of the film member 43 was set to 3 mm downstream of the maximum point B of the vertical magnetic force distribution (between the maximum point B and the maximum point C of the vertical magnetic force), the magnetic brushes were transported to the development area 40 in a state where they were leveled at the maximum point B by the film member 43. As a result, the number of magnetic brushes in the development area 40 increased to 17.7 [brushes / mm], and it was confirmed that the diameter of the magnetic brushes became thinner. Consequently, the AC voltage at which development leakage occurs was also high at 1325 [V], making development leakage less likely. Furthermore, no decrease in image density or pitch unevenness occurred in the solid image.

[0063] On the other hand, when the contact position of the film member 43 was set to 1 mm downstream of the maximum point C of the perpendicular magnetic force, the number of magnetic brushes in the development area 40 increased to 17.9 [brushes / mm], and the AC voltage at which development leakage occurs also increased to 1350 [V], making development leakage less likely. However, the image density (ID) fell to 1.2 or less, resulting in a decrease in image density. This is thought to be because the amount of developer transported was insufficient, as the magnetic brushes were leveled just before being transported to the development area 40.

[0064] From the above results, it was confirmed that by setting the contact position of the film member 43 between the maximum point B of the vertical magnetic field gradient and the maximum point C of the vertical magnetic field, development leakage can be effectively suppressed, and a decrease in image density and pitch unevenness can also be suppressed. [Examples]

[0065] [Evaluation of carrier development and image contamination when the perpendicular magnetic field gradient is changed] Carrier development and image contamination were evaluated when the vertical magnetic field gradient of the developing roller 30 was varied. The test method involved varying the derivative value X [mT / °] of the vertical magnetic field at the minimum point A, the derivative value Y [mT / °] of the vertical magnetic field at the maximum point B, and the angle Z [°] between the minimum point A and the maximum point B, as shown in Figure 2. These developing devices 3a to 3d were mounted on a test machine as shown in Figure 1. Using this test machine, carrier development and image contamination were visually evaluated when a half-print image with a print density of 5% was printed. The image formation conditions were the same as in Example 2.

[0066] For carrier development, ○ indicates that almost no carrier development occurred; △ indicates that toner transfer around the carrier was not possible due to carrier development, resulting in slight but inconspicuous white spots; and × indicates that toner transfer around the carrier was not possible due to carrier development, resulting in noticeable white spots. For image staining, ○ indicates that no image staining occurred; △ indicates that slight but inconspicuous image staining occurred; and × indicates that image staining occurred and was noticeable. The evaluation results, along with the differential values ​​X, Y[mT / °], angle Z[°], and (YX) / Z, are shown in Table 3.

[0067] [Table 3]

[0068] As is clear from Table 3, in test examples 1 to 7 where (YX) / Z was between 0.13 and 0.23, no image smudges occurred due to carrier development or toner, or if they did occur, they were not noticeable.

[0069] In contrast, in test examples 8-10, where (YX) / Z is less than 0.13, the change in magnetic attraction force from the minimum point A to the maximum point B of the perpendicular magnetic field distribution is gradual, so sufficient magnetic force to suppress carrier development cannot be secured, and carrier development occurs. Also, in test examples 11-13, where (YX) / Z is greater than 0.23, the magnetic attraction force increases rapidly from the minimum point A to the maximum point B of the perpendicular magnetic field distribution, so toner scattering at the maximum point B increases, and toner accumulated on the inside of the film member 43 falls onto the magnetic brush, causing image staining.

[0070] From the above results, it was confirmed that carrier development and image contamination can be effectively suppressed when the derivative of the perpendicular magnetic force at the minimum point A of the perpendicular magnetic field gradient, X[mT / °], the derivative of the perpendicular magnetic force at the maximum point B, Y[mT / °], and the angle Z[°] between the minimum point A and the maximum point B satisfy 0.13≦(YX) / Z≦0.23. [Industrial applicability]

[0071] The present invention is applicable to a two-component developing apparatus that uses a two-component developer containing toner and a carrier. By utilizing the present invention, it is possible to provide a developing apparatus and an image forming apparatus equipped therewith that can suppress the occurrence of developing leaks without reducing image density in a two-component developing apparatus. [Explanation of Symbols]

[0072] Pa~Pd Image Forming Unit 1a~1d Photoreceptor drum (image carrier) 2a~2d Charging device 3a~3d developing device 5. Exposure apparatus 20 developing containers 27. Regulating blade (regulating member) 30. Developing roller (developer carrier) 31 Developing Sleeves 32 Magnets 40 Development area 41 Regulatory Department 43 Film component 44 Toner Shatterproof Film 100 Image forming apparatus N1 Regulatory Pole S1 main pole N2, S2 transport poles S3 Exfoliation electrode

Claims

1. A developing container containing a two-component developer including a magnetic carrier and toner, A developer carrier that is rotatably supported in the developing container and carries the developer on its outer surface, A regulating member is positioned opposite the developer carrier at a predetermined distance, A developing apparatus comprising the developing region in which the developer carrier is positioned opposite the image carrier, for developing an electrostatic latent image formed on the surface of the image carrier into a toner image, The regulating member and the developing region are provided with a film member that contacts the developer supported on the outer circumferential surface of the developer carrier, The developer carrier is A rotatable developing sleeve on which the developer is carried and on which magnetic brushes are formed on the surface, A magnet comprising a plurality of magnetic poles arranged at predetermined intervals in the circumferential direction, including a restricting pole fixed immovably within the developing sleeve and positioned opposite the restricting member, and a main pole positioned downstream of the restricting pole with respect to the rotational direction of the developing sleeve, It has, The magnet has a minimum point A of the vertical magnetic field gradient [mT / °] near the position where the vertical magnetic field between the regulating member and the main pole is 0 [mT] with respect to the rotation direction of the developing sleeve, and has one maximum point B of the vertical magnetic field gradient between the downstream side of the minimum point A and the developing region with respect to the rotation direction of the developing sleeve, and has one maximum point C of the vertical magnetic field downstream of the maximum point B with respect to the rotation direction of the developing sleeve. The developing apparatus is characterized in that the contact position of the film member is between the maximum point B and the maximum point C.

2. The developing apparatus according to claim 1, characterized in that when the perpendicular magnetic field gradient at the minimum point A is X [mT / °], the perpendicular magnetic field gradient at the maximum point B is Y [mT / °], and the central angle between the minimum point A and the maximum point B with respect to the center of the magnet is Z [°], the following equation (1) is satisfied. 0.13≦(Y-X) / Z≦0.23...(1)

3. The developing apparatus according to claim 1 or 2, characterized in that the film member is arranged such that its leading edge approaches the developing sleeve from the upstream side to the downstream side in the rotational direction of the developing sleeve.

4. The image carrier having a photosensitive layer formed on its surface, A developing apparatus according to any one of claims 1 to 3, wherein the toner is attached to the electrostatic latent image formed on the image carrier to form a toner image, An image forming apparatus equipped with [a specific feature].

5. The image forming apparatus according to claim 4, characterized in that the image carrier has an amorphous silicon layer as the photosensitive layer.

Images