Image forming apparatus

Abstract

The present invention provides an image forming apparatus capable of suppressing carrier phenomena in a two-component development method. [Solution] The intermediate transfer belt is a rigid resin belt, and the developer carrier has a rotatable developing sleeve and a magnet. The developing sleeve carries the developer and has magnetic brushes formed on its surface. The magnet is fixed non-rotatably within the developing sleeve, and has multiple magnetic poles, including a main pole positioned in the developing region facing the image carrier with respect to the rotation direction of the developing sleeve, arranged at predetermined intervals in the circumferential direction. When the horizontal magnetic field gradient at the position where the horizontal magnetic field of the main pole is 0 [mT] is A, |A| ≥ 3.74 is satisfied.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multi-functional machine including these, each having an image carrier, and more particularly to an image forming apparatus using a two-component development method using a two-component developer containing toner and carrier.

Background Art

[0002] Conventional image forming apparatuses include an image carrier, a developing device, an intermediate transfer belt, and a secondary transfer roller. The developing device develops an electrostatic latent image formed on the surface of the image carrier into a toner image. The intermediate transfer belt receives the toner image formed on the image carrier by primary transfer. The secondary transfer roller secondarily transfers the toner image primarily transferred to the intermediate transfer belt onto a recording medium. Further, the intermediate transfer belt is a hard resin belt and does not have an elastic layer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a conventional image forming apparatus, when a hard resin belt is used for the intermediate transfer belt, carrier development may easily occur in the blank portion of the photoreceptor.

[0005] In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of suppressing carrier phenomenon in a two-component development method.

Means for Solving the Problems

[0006] To achieve the above objective, the first configuration of the present invention is an image forming apparatus comprising an image carrier, a charging device, an exposure device, a developing device, an intermediate transfer belt, a primary transfer roller, and a secondary transfer roller. The image carrier has a photosensitive layer formed on its surface. The charging device charges the surface of the image carrier. The exposure device exposes the surface of the image carrier, which has been charged by the charging device, to form an electrostatic latent image on the surface of the image carrier. The developing device develops the electrostatic latent image formed on the surface of the image carrier into a toner image. The intermediate transfer belt receives the toner image formed on the image carrier as a primary transfer. The primary transfer roller is pressed against the image carrier via the intermediate transfer belt. The secondary transfer roller secondary transfers the toner image that has been primary transferred to the intermediate transfer belt onto a recording medium. The intermediate transfer belt is made of a hard resin belt. The developing device comprises a developing container and a developer carrier. The developing container contains a two-component developer containing a magnetic carrier and toner. The developer carrier is rotatably supported in the developing container and carries the developer on its outer surface. The developer carrier comprises a rotatable developing sleeve and a magnet. The developing sleeve carries the developer and forms magnetic brushes on its surface. The magnet is fixed non-rotatably within the developing sleeve and has multiple magnetic poles, including a main pole positioned in the developing region facing the image carrier with respect to the rotation direction of the developing sleeve, arranged at predetermined intervals in the circumferential direction. When the horizontal magnetic field gradient at the position where the horizontal magnetic field of the main pole is 0 [mT] is A, |A| ≥ 3.74 is satisfied. [Effects of the Invention]

[0007] According to the first configuration of the present invention, an image forming apparatus capable of suppressing carrier phenomena in a two-component development method can be provided. [Brief explanation of the drawing]

[0008] [Figure 1] Side cross-sectional view showing the internal configuration of an image forming apparatus 100 according to one embodiment of the present invention. [Figure 2] Side cross-sectional view of the developing apparatus 3a of the image forming apparatus 100 according to one embodiment of the present invention. [Figure 3]Graph showing the changes in the vertical magnetic force distribution, horizontal magnetic force distribution, and horizontal magnetic force gradient in the circumferential direction of the developing roller 30 of an image forming apparatus 100 according to one embodiment of the present invention. [Modes for carrying out the invention]

[0009] 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.

[0010] These image forming units Pa to Pd are equipped with photosensitive 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.

[0011] The toner images formed on these photoreceptor drums 1a to 1d are sequentially transferred and superimposed onto an intermediate transfer belt 8 that moves in contact with each photoreceptor drum 1a to 1d. Subsequently, the toner images transferred onto the intermediate transfer belt 8 are secondarily 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 secondarily 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.

[0012] 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, and is transported via the paper feed roller 12a and the pair of registration rollers 12b to the nip section between the secondary transfer roller 9 and the drive roller 11 of the intermediate transfer belt 8. The intermediate transfer belt 8 is a rigid resin belt without an elastic layer, and a seamless belt is mainly used. A blade-shaped belt cleaner 19 is also positioned downstream of the secondary transfer roller 9 to remove toner and other residues remaining on the surface of the intermediate transfer belt 8. In this embodiment, the belt cleaner 19 removes toner and other residues by contacting the blade with the intermediate transfer belt 8, which is made of a rigid resin belt. This simplifies the configuration of the belt cleaner 19 and reduces manufacturing costs compared to roller cleaning performed on an intermediate transfer belt made of an elastic belt.

[0013] Furthermore, the intermediate transfer belt 8 has a surface hardness of 180 N / mm². 2 The above-mentioned resin belt is preferable. For example, the intermediate transfer belt 8 is formed of a resin belt that does not have an elastic layer such as polyurethane. Examples of materials for the intermediate transfer belt 8 include polycarbonate, polyvinylidene fluoride, polyamide, acrylic, nylon, polyimide, and polyamide-imide. However, the present invention does not particularly limit the material of the resin belt constituting the intermediate transfer belt 8. Furthermore, the intermediate transfer belt 8 has a surface hardness of 180 N / mm². 2 By using the above-described resin belt, the intermediate transfer belt 8 can be made thinner, thereby suppressing the occurrence of color misalignment. This improves image quality.

[0014] Next, the image forming sections Pa to Pd will be described. The rotatably arranged photoreceptor drums 1a to 1d have a photosensitive layer (not shown) formed on their surface. In this embodiment, amorphous silicon (a-Si), which has a high dielectric constant, is used for the photosensitive layer. By using amorphous silicon for the photosensitive layer, the film of the photosensitive layer is less likely to peel off compared to organic photoreceptors. This improves the durability of the photoreceptor drums 1a to 1d and extends the lifespan of the unit.

[0015] Around and below the 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 a toner image 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.

[0016] When image data is input from a higher-level device such as a personal computer, the charging devices 2a to 2d first uniformly charge the surfaces of the photoreceptor drums 1a to 1d. Next, the exposure device 5 irradiates the drums with light according to the image data, forming an electrostatic latent image on each photoreceptor drum 1a to 1d corresponding to the image data. The developing devices 3a to 3d are each filled with a predetermined amount of two-component developer containing yellow, cyan, magenta, and black toners. If the proportion of toner in the two-component developer in each developing device 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 developing device 3a to 3d. This toner in the developer is supplied onto the photoreceptor drums 1a to 1d by the developing devices 3a to 3d and adheres electrostatically. This forms a toner image corresponding to the electrostatic latent image formed by the exposure from the exposure device 5.

[0017] Then, the primary transfer rollers 6a to 6d apply an electric field at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photoreceptor drums 1a to 1d, and the yellow, magenta, cyan, and black toner images on the photoreceptor drums 1a to 1d are primary transferred onto the intermediate transfer belt 8. These images are formed in predetermined positional relationships. Subsequently, in preparation for the formation of a new electrostatic latent image, any toner remaining on the surface of the photoreceptor drums 1a to 1d after the primary transfer is removed by the cleaning devices 7a to 7d.

[0018] 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 from the resist roller pair 12b 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, 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.

[0019] The transfer paper P conveyed to the fixing unit 13 is heated and pressurized 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 has been formed is diverted in the conveyance direction by the branching portion 14 branched in a plurality of directions, and is then discharged to the discharge tray 17 by the discharge roller pair 15 (either as it is or after being sent to the duplex conveyance path 18 to form images on both sides).

[0020] 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 exemplified. However, the configurations of the developing devices 3b to 3d disposed in the image forming units Pb to Pd are basically the same, and thus the description thereof is omitted.

[0021] As shown in FIG. 2, the developing device 3a includes a developing container 20, a developing roller (developer carrier) 30, a regulating blade 27, a stirring and conveying screw 25a, and a supply and conveying screw 25b. The developing container 20 stores a two-component developer (hereinafter simply referred to as a developer) including a magnetic carrier and toner. The developing container 20 is partitioned into a stirring and conveying chamber 21 and a supply and conveying chamber 22 by a partition wall 20a. In the stirring and conveying chamber 21 and the supply and conveying chamber 22, a stirring and conveying screw 25a and a supply and conveying screw 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. In this embodiment, a positively charged toner and a two-component developer composed of a ferrite-resin-coated carrier are used. The detailed configuration of the carrier will be described later.

[0022] Then, the developer is stirred by the stirring and conveying screw 25a and the supply and conveying screw 25b and conveyed in the axial direction (a direction perpendicular to the plane of FIG. 2), and circulates between the stirring and conveying chamber 21 and the supply and conveying chamber 22 through a developer passage (not shown) formed at both ends of the partition wall 20a. That is, a circulation path of the developer is formed in the developing container 20 by the stirring and conveying chamber 21, the supply and conveying chamber 22, and the developer passage.

[0023] The developing container 20 extends obliquely upward to the right in FIG. 2, and a developing roller 30 is disposed obliquely upward to the right of the supply and conveying screw 25b in the developing container 20. A part of the outer peripheral surface of the developing roller 30 is exposed from the opening of the developing container 20 and faces the photosensitive drum 1a at a predetermined interval (developing gap) to form a developing region 40. The developing roller 30 rotates in the counterclockwise direction in FIG. 2 (trailing rotation at the facing position with the photosensitive drum 1a).

[0024] The developing roller 30 includes 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 dimples formed on the surface, a developing sleeve with a blast-finished surface, a developing sleeve that has been blast-finished in addition to knurling and dimple formation, a developing sleeve that has been plated or anodized to improve durability, or a developing sleeve that has been treated by 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 aluminum after anodizing.

[0025] In particular, anodized coatings, or coatings treated with a secondary electrolytic coloring method after anodizing, not only improve durability but also have the effect of suppressing the occurrence of development leaks. This is because the anodized surface of the development sleeve 31 makes it difficult for the leakage current generated by the magnetic brush to spread horizontally across the surface of the development roller 30, preventing it from developing into a large leak that involves adjacent magnetic brushes.

[0026] The magnet 32 ​​has multiple magnetic poles, including a main pole N1, which is positioned in the development area facing the photoreceptor drum (image carrier) 1a with respect to the rotational direction of the development sleeve 31, arranged at predetermined intervals in the circumferential direction. In this embodiment, the magnet 32 ​​has a five-pole configuration: a main pole N1, a regulating pole (pushing pole) S1, transport poles S2 and N2, and a peeling pole N3. When a driving force is input to the development device 3a, the development sleeve 31 rotates, but the magnet 32 ​​does not.

[0027] In this embodiment, the magnet 32 ​​consists of a samarium iron nitrogen magnet only for the main pole N1, while the regulating pole (lifting pole) S1, transport poles S2 and N2, and separation pole N3 are made of plastic magnets. By making only the main pole N1 a samarium iron nitrogen magnet, the horizontal magnetic field gradient of the main pole N1 can be increased while suppressing an increase in manufacturing costs. Note that neodymium magnets may be used instead of samarium iron nitrogen magnets.

[0028] 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).

[0029] The regulating blade 27 is mounted in 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 portion 41. In this embodiment, a magnetic blade made of stainless steel (SUS430) is used as the regulating blade 27.

[0030] A magnetic field is generated between the regulating pole S1 of the magnet 32 ​​and the regulating blade 27 in an attractive direction, forming a magnetic brush with developer in a continuous layer 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 is restricted to the desired height. Subsequently, as the developing sleeve 31 rotates counterclockwise and the magnetic brush moves to the developing area 40, a magnetic field is applied by the main pole N1, causing the magnetic brush to contact the surface of the photoreceptor drum 1a and develop the electrostatic latent image.

[0031] As the developing sleeve 31 rotates counterclockwise, the transport electrodes S2 and N2 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 the same polarity as the transport electrode N2, 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 S1 causes the magnetic brush to be formed on the developing sleeve 31 again.

[0032] Next, 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, will be described. Figure 3 is a graph showing the changes in the vertical magnetic force distribution, horizontal magnetic force distribution, and horizontal magnetic force gradient in the circumferential direction of the developing roller 30, with an enlarged view from the regulating blade 27 to the main pole N1. In Figure 3, the vertical magnetic force is shown by a solid line, the horizontal magnetic force by a dashed line, and the horizontal magnetic force gradient by a dashed line.

[0033] In the developing apparatus 3a to 3d of this embodiment, carrier development can be suppressed by adjusting the magnetic force distribution of the magnet 32 ​​in the circumferential direction of the developing roller 30, or more specifically, by adjusting the circumferential magnetic force gradient of the horizontal magnetic force, which is the circumferential magnetic force of the developing roller 30 (hereinafter referred to as the horizontal magnetic force gradient). This improves the scraping effect of the developer by the magnetic brush.

[0034] As shown in Figure 3, the horizontal magnetic force becomes 0 [mT] near the peak of the vertical magnetic force of the main pole N1 (point S in Figure 3), and the horizontal magnetic force gradient in that vicinity is related to the scraping of the developer from the surface of the photoreceptor drums 1a to 1d by the magnetic brush.

[0035] In this embodiment, when the horizontal magnetic field gradient at the position of the main pole N1 with a horizontal magnetic field of 0 [mT] (point S in Figure 3) is A [mT / °], it is preferable that |A| ≥ 3.74 is satisfied. This makes it possible to increase the horizontal magnetic field gradient of the main pole N1 and suppress carrier development, even when a hard resin belt is used for the intermediate transfer belt 8.

[0036] Furthermore, the scraping effect of the magnetic brush on the surface of the photoreceptor drums 1a to 1d is affected by the amount of developer (developer transport amount) delivered to the developing area 40. Therefore, if the developer transport amount is prone to fluctuations, the scraping effect will also vary, making it impossible to obtain stable scraping performance.

[0037] This fluctuation in the amount of developer transported is affected by the horizontal magnetic field gradient at the position where the developing roller 30 faces the regulating blade 27 (regulating section 41). Specifically, if the horizontal magnetic field gradient at the regulating section 41 is small, the change in vertical magnetic field will also be small, and the influence of the magnetic field on the change in developer fluidity due to changes in toner concentration and charge in the developer can be reduced.

[0038] In other words, by increasing the horizontal magnetic field gradient at the position of the main pole N1 (development area 40) to increase the scraping force, and by decreasing the horizontal magnetic field gradient at the position of the regulating pole S1 (regulating section 41) to improve robustness (stability against noise), it becomes possible to stably suppress carrier development.

[0039] In this embodiment, by setting the horizontal magnetic field gradient A at the main pole N1 to a high value, the horizontal magnetic field gradient B at the regulating pole S1 can be set to a low value. More specifically, by setting the horizontal magnetic field distribution at the main pole N1 such that |A|≧3.74 satisfies, the horizontal magnetic field gradient B[mT / °] at the upstream side of the regulating blade 27 (T1 in Figure 3) can be suppressed to |B|≦1.37. As a result, the magnet 32 ​​can be configured with a magnet with low magnetic force at the regulating pole S1. Therefore, the increase in manufacturing costs of the magnet 32 ​​can be further suppressed while suppressing the carrier phenomenon.

[0040] Next, the arrangement of the regulating blade 27 will be explained. Between the position where the horizontal magnetic force of the regulating pole S1 is 0 [mT] (point P in Figure 3) and the position where the horizontal magnetic force is at its maximum value (point R in Figure 3), the horizontal magnetic force acts in the direction from R to P. Therefore, if the regulating blade 27 is located downstream of point P, a force acts on the developer in the regulating section 41 that pulls it back in the direction of P, thereby mitigating the developer transport force generated by (vertical magnetic force × friction coefficient between the developer and the developer sleeve 31). As a result, highly robust regulation against fluctuations in the fluidity of the developer can be achieved.

[0041] On the other hand, if the downstream side of the regulating blade 27 (T2 in Figure 3) is positioned downstream of the position where the horizontal magnetic force and the vertical magnetic force are equal (point Q in Figure 2), the vertical magnetic force at the regulating section 41 will weaken, making it impossible to secure sufficient magnetic regulating force. As a result, stable transport of the developer will not be possible. Therefore, with respect to the rotation direction of the developing sleeve 31, the upstream side of the regulating blade 27 (T1 in Figure 5) must be positioned downstream of the position where the horizontal magnetic force of the regulating pole S1 is 0 [mT] (point P in Figure 3), and the downstream side of the regulating blade 27 (T2 in Figure 3) must be positioned upstream of the position where the vertical magnetic force and the horizontal magnetic force are equal (point Q in Figure 5).

[0042] As described above, by defining the horizontal magnetic field gradient and the arrangement of the regulating blades 27, carrier development can be effectively suppressed while ensuring magnetic regulating force in the regulating section, thereby stably transporting the developer.

[0043] Next, a method for measuring the horizontal 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 horizontal magnetic field gradient can be obtained by dividing the difference in horizontal 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 horizontal magnetic field gradient accurately. Therefore, in this invention, the horizontal 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 (horizontal magnetic field difference at a 0.08° difference / 0.08°).

[0044] Next, the carriers used in the developing apparatus 3a to 3d of this embodiment will be described. As carriers, a coating layer of silicone resin or the like is formed on the surface of a carrier core, which is a magnetic particle. Silicone resins can be used for thin-film coating, and the uniformity of the coating layer is high. In addition, the thinner the coating layer, the higher the capacitance of the coating layer, and the more easily the effect of the ferroelectric material added to the coating layer is exerted.

[0045] The carrier shape can range from irregular to spherical. Furthermore, the average particle size of the carrier can be between 20 μm and 65 μm. By setting the number-average particle size 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 thickness of the toner layer. 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.

[0046] 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.

[0047] 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.

[0048] Barium titanate particles are added to the coating layer as a ferroelectric material. Methods for producing barium titanate include hydrothermal polymerization and oxalate polymerization, but the physical properties of barium titanate vary depending on the manufacturing method. In particular, barium titanate produced by hydrothermal polymerization has internal voids, resulting in a lower true specific gravity and a sharper particle size distribution. As a result, it exhibits better dispersibility in the coating resin compared to barium produced by other methods, enabling uniform dispersion. Therefore, the carrier charge performance is also uniform, making it suitable for use in this invention.

[0049] The volume-average particle size of barium titanate is preferably between 100 nm and 500 nm. If the particle size of barium titanate is smaller than 100 nm, the dielectric constant of barium titanate decreases sharply, resulting in a reduced effect related to the dielectric constant. On the other hand, if the particle size of barium titanate is 500 nm or larger, uniform dispersion in the coating layer becomes difficult.

[0050] When 5 parts by mass or more of barium titanate are added relative to the weight of the coating, a stabilizing effect on the amount of charge begins to appear, and when 25 parts by mass or more are added, the stabilizing effect on the amount of charge becomes more pronounced. However, if too much barium titanate is added, it cannot be contained in the coating layer and will be released from the coating layer. If the released barium titanate moves to the photoreceptor drums 1a to 1d and gets caught in the edges of the cleaning blades 32 of the cleaning devices 7a to 7d, it can cause cleaning failures. In particular, in the method of mixing a carrier with the toner in the toner containers 4a to 4d and supplying it to the developing devices 3a to 3, the barium titanate released during use is supplied to the developing devices 3a to 3d, which increases the load on the cleaning blades 32. For this reason, it is preferable to add 5 parts by mass or more and 45 parts by mass or less of barium titanate.

[0051] Carbon black is added to the coating layer as a conductor. If too much carbon black is added, the carbon black released from the coating layer adheres to the toner, causing discoloration of toners other than black. On the other hand, if too little carbon black is added, the transfer of charge from the carrier to the toner is difficult, and the increase in toner charge cannot be achieved smoothly. In the carrier of the present invention, the carrier resistance is reduced by adding barium titanate (ferroelectric) to the coating layer, making it possible to reduce the amount of carbon black added by the amount of the reduction in carrier resistance.

[0052] By adding a ferroelectric material (barium titanate) to the coating layer, the charge retention capacity of carriers is increased, making it possible to impart sufficient charge to the toner. Furthermore, by adding a conductor (carbon black) to the coating layer, the transfer of charge from carriers to toner can be facilitated. Due to the synergistic effect of these two factors, even when the toner concentration increases and the number of toner particles that need to be charged increases, it becomes possible to impart charge to the toner particles up to the saturation charge level.

[0053] Furthermore, by adding barium titanate, a highly hard ferroelectric material, to the carrier's coating layer, wear on the coating layer is reduced, extending the carrier's lifespan. Additionally, the addition of barium titanate lowers carrier resistance compared to adding only carbon black, allowing for a reduction in the amount of carbon black needed. As a result, color dullness caused by carbon black adhering to the toner can be suppressed. Moreover, the carrier's electrification performance is improved, resulting in smaller changes in toner charge even at high toner concentrations in the developer. Consequently, the toner charge becomes more stable, leading to greater stability of the magnetic restricting force at the restricting blade 27 compared to carriers without barium titanate. Therefore, the developer transport volume becomes more stable, enabling stable carrier development.

[0054] 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 in which a regulating pole S1 and a main pole N1 are arranged was used as the magnet 32 ​​of the developing roller 30, but the polarities of the regulating pole and the main pole may be reversed.

[0055] 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]

[0056] [Manufacturing of ferroelectric particle-containing carriers] 200 parts by mass of silicone resin (Shin-Etsu Chemical Co., Ltd., KR-255, non-volatile content = 50%), 20 parts by mass of barium titanate (Sakai Chemical Co., Ltd., volume average particle size 304 nm), 7 parts by mass of carbon black (Lion Corporation, Ketjenblack EC), and 800 parts by mass of toluene were dispersed in a homomixer to obtain a coating solution. The obtained coating solution was sprayed onto 5 kg of carrier cores (Mn ferrite carrier, volume average particle size 34.7 μm, saturation magnetization 80 emu / g, coercivity 8 Oe, DOWA IP Creation Co., Ltd.) under heating at 70-80°C using a fluidized bed coating apparatus to coat the carrier cores with the coating solution. Subsequently, the cores were fired in an electric furnace at 200-250°C for 1 hour, and after cooling, they were crushed and classified using a sieve to obtain carriers containing ferroelectric particles in the coating layer. [Examples]

[0057] [Evaluation of carrier development when the horizontal magnetic field gradient is changed] The carrier development process was evaluated when the horizontal magnetic field gradient of the developing roller 30 was varied. The test method involved mounting developing apparatuses 3a to 3d (invention 1, 2, and comparative example) as shown in Figure 2, with varying vertical magnetic fields and horizontal magnetic field gradients of the main pole N1 and regulating pole S1, onto a test machine as shown in Figure 1. Using this test machine, the carrier development process was evaluated when the developing apparatus was driven in a high-temperature, high-humidity environment (32.5°C, 80%) and a low-temperature, low-humidity environment (10°C, 15%).

[0058] The image formation conditions were as follows: the printing speed (process speed) was set to 55 frames / minute, and the developing roller 30 used a developing sleeve 31 with an outer diameter of 20 mm and 80 rows of recesses (knurling) formed on its outer surface. 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 regulating blade 27 was positioned between points P and Q. The developing roller 30 was subjected to a developing voltage obtained by superimposing an AC voltage with a peak-to-peak value (Vpp) of 1125 V, a frequency of 10 kHz, and a duty cycle of 50% on a DC voltage of 250 V.

[0059] The photoreceptor drums 1a to 1d had a photosensitive layer (not shown) formed on their surface, and the photosensitive layer was made of amorphous silicon (a-Si) 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. In addition, a hard resin belt without an elastic layer was used for the intermediate transfer belt 8.

[0060] Positively charged toner with an average particle size of 6.8 μm was used, and the resin-coated carrier manufactured in Example 1 was used as the carrier. The initial toner concentration in the developer (weight ratio of toner to carrier) was set to 5% and 7%. In addition, two types of developer were used: unused and durable (equivalent to 100,000 pages printed).

[0061] For carrier development, the number of carriers that moved onto the photoreceptor drums 1a to 1d was observed using a magnifying glass. The result was "OK" if no white spots were observed, and "NG" if white spots were observed. The evaluation results, along with the perpendicular magnetic force of the main pole N1 and regulating pole S1, and the horizontal magnetic force gradient of the main pole N1 and regulating pole S1, are shown in Table 1.

[0062] [Table 1]

[0063] As is clear from Table 1, when the horizontal magnetic field gradient A at the main pole N1 satisfies |A| ≥ 3.74, no carrier development was observed. This confirmed that the occurrence of carrier development was suppressed. Furthermore, when the horizontal magnetic field gradient B at the regulating pole S1 satisfies |B| = 1.37, no carrier development was observed. In contrast, when the horizontal magnetic field gradient A at the main pole N1 satisfies |A| < 3.74, carrier development was observed.

[0064] From the above results, it was confirmed that by setting the horizontal magnetic field distribution such that the horizontal magnetic field gradient A at the main pole N1 satisfies |A|≧3.74, carrier development can be effectively suppressed even if the horizontal magnetic field gradient B at the regulating pole S1 is |B|≦1.37. Furthermore, it was confirmed that by setting the horizontal magnetic field distribution such that the horizontal magnetic field gradient A at the main pole N1 satisfies |A|≧3.74, carrier development can be effectively suppressed even when amorphous silicon (a-Si), which results in a large amount of carrier development, is used as the photoreceptor drum (image carrier).

[0065] In this example, we show the results obtained using a resin-coated carrier with barium titanate added as ferroelectric particles, as manufactured in Example 1. However, it has been confirmed that similar effects can be obtained when using other carriers. [Industrial applicability]

[0066] 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 carrier development while maintaining the stability of the magnetic restricting force of the restricting member in a two-component developing apparatus. [Explanation of Symbols]

[0067] 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 100 Image forming apparatus S1 Regulatory Pole N1 Main pole S2, N2 transport poles N3 peeling electrode

Claims

1. An image carrier having a photosensitive layer formed on its surface, A charging device for charging the surface of the image carrier, An exposure apparatus that exposes the surface of the image carrier, which has been charged by the charging device, to form an electrostatic latent image on the surface of the image carrier, A developing apparatus for developing the electrostatic latent image formed on the surface of the image carrier into a toner image, An intermediate transfer belt on which the toner image formed on the image carrier is first transferred, A primary transfer roller that is pressed against the image carrier via the intermediate transfer belt, A secondary transfer roller that transfers the toner image, which has been primary transferred to the intermediate transfer belt, onto a recording medium, Equipped with, The aforementioned intermediate transfer belt is a rigid resin belt. The developing apparatus is A developing container containing a two-component developer including a magnetic carrier and toner, The developing container has a developing agent carrier that is rotatably supported and has the developing agent on its outer surface, The developer carrier is A rotatable developing sleeve on which the developer is carried and on which magnetic brushes are formed on the surface, The magnet comprises a magnet that is fixed in a non-rotatable manner within the developing sleeve and has multiple magnetic poles arranged at predetermined intervals in the circumferential direction, including a main pole that is positioned in the developing region facing the image carrier with respect to the rotational direction of the developing sleeve, An image forming apparatus that satisfies |A| ≥ 3.74, where A is the horizontal magnetic field gradient at the position where the horizontal magnetic field of the main pole is 0 [mT].

2. The aforementioned intermediate transfer belt has a surface hardness of 180 N / mm². 2 The image forming apparatus according to claim 1, wherein the resin belt is as described above.

3. The image forming apparatus according to claim 1 or claim 2, wherein the magnet is composed solely of a samarium iron nitrogen magnet for the main pole.

4. The image forming apparatus according to claim 1 or claim 2, wherein the photosensitive layer is made of amorphous silicon.

5. The developing apparatus is The device further comprises a regulating member positioned opposite the developer carrier at a predetermined distance, The aforementioned magnet is The regulating electrode is further arranged in a regulating portion facing the regulating member, The regulating member is positioned downstream of the position where the perpendicular magnetic force of the regulating pole is 0 [mT] with respect to the rotational direction of the developing sleeve, and upstream of the position where the perpendicular magnetic force and the horizontal magnetic force of the regulating pole are equal. The image forming apparatus according to claim 1 or claim 2, wherein when the horizontal magnetic force gradient on the upstream side of the regulating member with respect to the rotation direction of the developing sleeve is B, |B| ≤ 1.37 is satisfied.

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