Developing device and image forming apparatus

Abstract

The invention provides a developing device and an image forming apparatus, which can suppress image defects caused by foreign matters (paper scraps and the like) collected together with transfer residual toner being sandwiched between a developer carrier and a layer thickness restricting member, and maintain image quality with a high image area rate. The developing device (4) supplies a developer in a developer accommodating part (46) to a developer carrier (41) which is rotationally driven by a supply rotating body (42), and after the developer on the developer carrier is thinned by a layer thickness regulating member (44), the latent image on the latent image carrier (1) is developed, and the transfer residual toner (T3) on the latent image carrier is recovered. The developing device is characterized in that the supply rotating body is rotationally driven so as to be in a surface movement direction opposite to a surface movement direction of the developer carrier in a portion facing the developer carrier, and the surface of the supply rotating body is an adhesion suppression surface that suppresses adhesion of foreign matter collected together with the transfer residual toner.

Description

Technical Field

[0001] The present invention relates to a developing device and an image forming device. Background Art

[0002] In the past, there has been known a developing device that supplies the developer in the developer storage portion to a developer carrier that is driven to rotate by a supply rotating body, and after thinning the developer on the developer carrier by a layer thickness limiting component, develops the latent image on the latent image carrier while recovering the transferred residual colorant on the latent image carrier.

[0003] For example, Patent Document 1 discloses a developing device employed in a cleanerless system for recovering transfer residual toner back to a developing device. The device utilizes a supply roller (supply rotator) having a surface layer of a foamed polyurethane layer composed of interconnected bubbles. In this developing device, the supply roller is driven to rotate in a region facing a developing roller (developer carrier) so that its surface movement direction is aligned with that of the developing roller. According to Patent Document 1, this configuration prevents foreign matter (paper scraps) recovered from the latent image carrier along with the transfer residual toner back to the developing roller from being retained in an area upstream of the supply roller's surface movement direction relative to the facing region. This prevents image defects caused by foreign matter (paper scraps) recovered from the latent image carrier along with the transfer residual toner back to the developing roller becoming trapped between the developing roller and the developing blade (layer thickness limiting member).

[0004] However, in the previous developing device used in the cleanerless system, it is difficult to strike a balance between suppressing image defects caused by foreign matter (paper scraps, etc.) recovered together with the transferred residual colorant being sandwiched between the developer carrier and the layer thickness limiting component, and maintaining image quality with a high image area ratio.

[0005] [Patent Document 1] (Japanese) Patent Publication No. 2023-75865

[0006] [Patent Document 2] (Japanese) Patent Publication No. 2014-149328 Summary of the Invention

[0007] In order to solve the above problems, the present invention provides a developing device, which supplies the developer in the developer storage portion to a developer carrier that is rotated and driven by a supply rotating body, and after thinning the developer on the developer carrier by a layer thickness limiting component, while developing the latent image on the latent image carrier, recovers the transfer residual colorant on the latent image carrier. The developing device is characterized in that: the supply rotating body is rotationally driven so that the surface movement direction becomes the opposite direction to the surface movement direction of the developer carrier at the opposite part to the developer carrier, and the surface of the supply rotating body is an adhesion inhibition surface for inhibiting the adhesion of foreign matter recovered together with the transfer residual colorant.

[0008] According to the present invention, it is possible to simultaneously suppress image defects caused by foreign matter (paper dust, etc.) collected together with transfer residual toner being caught between the developer carrier and the layer thickness regulating member, and maintain image quality at a high image area ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 1 is an explanatory diagram showing the configuration of an image forming apparatus according to an embodiment.

[0010] Figure 2 FIG. 1 is an explanatory diagram for explaining an image forming portion of the image forming apparatus.

[0011] Figure 3 FIG. 1 is an explanatory diagram of the structure of the developing device of the image forming apparatus. DETAILED DESCRIPTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0013] The image forming apparatus of this embodiment is an electrophotographic image forming apparatus, specifically a single-drum, direct transfer, monochrome image forming apparatus. However, this embodiment is also applicable to other image forming apparatuses, such as single-drum, intermediate transfer, color image forming apparatuses, or quad-tandem, direct transfer, or intermediate transfer color image forming apparatuses.

[0014] Figure 1 It is an explanatory diagram of the configuration of the image forming apparatus according to this embodiment.

[0015] Figure 2 It is an explanatory diagram for explaining the image forming section of the image forming apparatus according to the present embodiment.

[0016] Figure 3 It is an explanatory diagram showing the structure of the developing device 4 according to this embodiment.

[0017] The image forming unit in the image forming apparatus 10 of this embodiment includes a drum-shaped photoreceptor 1 serving as a latent image carrier. The image forming unit is provided with a charger 2 serving as a charging means, an optical writing device 3 serving as a latent image forming means, a developing device 4 serving as a developing means, a transfer device 5 serving as a transfer means, and a static eliminator 6 serving as a static eliminating means around the photoreceptor 1.

[0018] The image forming apparatus 10 of this embodiment is a cleaner-less system image forming apparatus that does not include a dedicated cleaning device for recovering transfer residual toner remaining on the photoreceptor 1 after transfer. Instead, the developer 4 recovers the transfer residual toner on the photoreceptor 1. In a cleaner-less system, the diameter of the photoreceptor 1 can be reduced because the space required to install a cleaning device around the photoreceptor 1 is reduced. Thus, even if the recording material to which the toner image is transferred from the photoreceptor 1 is thin paper, which easily adheres to the photoreceptor surface after transfer, the recording material can be stably separated from the photoreceptor 1 simply by utilizing the curvature of the photoreceptor 1. As a result, there is no need to install a device around the photoreceptor to separate the recording material. Therefore, a cleaner-less system can achieve cost reduction and miniaturization of the image forming apparatus.

[0019] In the image forming apparatus 10 of this embodiment, a charging bias of, for example, -1100V is applied to the charging roller 21 of the charger 2, uniformly charging the surface of the photoreceptor 1 to approximately -500V. Then, the optical writing device 3, comprised of an LED array, is driven to expose the surface of the photoreceptor 1 according to image data, lowering the potential of the exposed portion to form an electrostatic latent image. Next, in the development area, a toner (developer) is supplied by the developing device 4 to the electrostatic latent image on the photoreceptor 1, forming a toner image on the photoreceptor 1. In this embodiment, any residual toner remaining on the photoreceptor 1 from the previous transfer is recovered by the developing device 4.

[0020] In the developing device 4, a developing roller 41, which serves as a developer carrier, and a supply roller 42, which serves as a supply rotator, are arranged inside a developing cartridge 43, which serves as a developer container. A toner container 46 inside the developing cartridge 43 contains toner, and the toner in the toner container 46 is conveyed to the supply roller 42 via an agitator 45. Toner is supplied from the supply roller 42, which is also driven to rotate in the direction indicated by the arrow in the figure (counterclockwise in the figure), to the developing roller 41, which is also driven to rotate in the direction indicated by the arrow in the figure (counterclockwise in the figure). The toner supplied to the developing roller 41 is conveyed as the surface of the developing roller 41 moves, and after being thinned by a limiting scraper 44, which serves as a layer thickness limiting member, it is conveyed to a developing area facing the photoreceptor 1.

[0021] A developing bias of, for example, -300 V is applied to the developing roller 41. Furthermore, the toner transported to the developing area is charged to a negative polarity, which is the normal charging polarity, when passing through the restricting blade 44. In the developing area, the negatively charged toner does not adhere to the bottom portion (approximately -500 V), which is the non-exposed portion, but adheres to the latent image portion (approximately -50 V), which is the exposed portion, thereby developing the electrostatic latent image.

[0022] On the other hand, the paper P, which is a recording material and is fed from the paper feed device 11 at a predetermined timing, is temporarily stopped at the registration roller 12. Then, aligned with the timing at which the toner image T1 on the photoreceptor 1 is transported to the transfer area, the paper P is sent to the transfer area by the registration roller 12. In the transfer area, the transfer roller of the transfer device 5 is arranged to face the surface of the photoreceptor 1, and a positive transfer bias is applied to the transfer roller. As a result, in the transfer area, the toner image T1 on the photoreceptor 1 is transferred to the paper P fed between the photoreceptor 1 and the transfer roller. Then, the paper P to which the toner image T1 is transferred is transported to the fixing device 13, where the toner image T1 is fixed by pressure and heat. The paper P after the fixing process is discharged to the discharge tray 14.

[0023] After transfer, the surface potential of the photoreceptor 1 is balanced to a negative polarity (e.g., approximately -50 V) by the static eliminator 6. Furthermore, the transfer residual toners T2 and T3 remaining on the photoreceptor 1 after transfer are transported to a charging area facing the charging roller 21 of the charger 2. The transfer residual toners T2 and T3 at this time are a mixture of transfer residual toner T2 that has been reversely charged (charged to a positive polarity) by the positive transfer bias, and transfer residual toner T3 that has maintained its normal charged polarity (negative polarity).

[0024] The positive transfer residual toner T2 is mostly converted into negative transfer residual toner T3, which is the normal charging polarity, due to pre-charge discharge in the portion of the charging area upstream of the photoreceptor surface in the direction of movement. The remaining positive transfer residual toner T2 is collected by the charging bias in the area facing the charging roller 21 of the charger 2 (the charging area).

[0025] The charger 2 is provided with a cleaning brush 22 as a charging cleaning member for cleaning toner and the like adhered to the charging roller 21. When recovering the positive-polarity transfer residual toner T2, a cleaning bias of, for example, -1300 V is applied to the cleaning brush 22. This causes the positive-polarity transfer residual toner T2 adhered to the charging roller 21, to which the -1100 V charging bias is applied, to move toward the cleaning brush 22 and be retained by the cleaning brush 22.

[0026] On the other hand, the transfer residual toner T3 of negative polarity passes through the charging area as it is attached to the photoreceptor 1. Since the amount of the transfer residual toner T3 is small, it does not interfere with the charging process of the charger 2 or the exposure process of the optical writing device 3. Then, when the transfer residual toner T3 of negative polarity is transported to the development area, in the development area, it faces the developing roller 41 to which a developing bias of -300V is applied. At this time, due to the potential difference between the potential (-500V) of the non-exposed part (bottom part) of the photoreceptor 1 and the developing bias (-300V), the transfer residual toner on the photoreceptor 1 moves toward the developing roller 41 side and is recovered in the developing device 4. As described above, in this embodiment, during the image forming action, the transfer residual toner T3 is recovered in the developing device 4, thereby realizing a cleaner-free system.

[0027] Furthermore, the positive transfer residual toner T2 held by the cleaning brush 22 during the image forming operation returns to the surface of the photoreceptor 1 during a non-image forming operation such as during device startup, and is recovered by the developing device 4 .

[0028] Specifically, during the non-image forming period, a charging bias of -1100 V is first applied to the charging roller 21, uniformly charging the surface of the photoreceptor 1 to approximately -500 V. Then, with the transfer bias or static eliminator 6 turned off, when the surface portion uniformly charged to -500 V is transported to the charging area again, a voltage of, for example, -350 V is applied to the charging roller 21, while a voltage of, for example, -150 V is applied to the cleaning brush 22. This causes the positively polarized residual transfer toner T2 held on the cleaning brush 22 to move from the cleaning brush 22 to the charging roller 21, and from there to the surface of the photoreceptor 1.

[0029] The positive transfer residual toner T3 discharged from the charger 2 to the photoreceptor 1 is then transported to the development area. At this time, a voltage of, for example, +250V is applied to the developing roller 41 in the development area. This causes the negative transfer residual toner T2 on the photoreceptor 1 to move toward the developing roller 41 and be recovered, while the positive transfer residual toner T3 passes through the development area.

[0030] The positive transfer residual toner T3 that passes through the development area is then transported again to the charging area. At this point, the static eliminator 6 is turned on, uniformly charging the surface of the photoreceptor 1 to approximately -50V, while simultaneously applying a -1100V charging bias to the charging roller 21. Consequently, the positive transfer residual toner T3 transported to the charging area undergoes pre-charge discharge in the charging area upstream of the photoreceptor surface in the direction of movement, converting it to negative transfer residual toner T3, the properly charged polarity.

[0031] Then, when the negative transfer residual colorant T3 is transported to the development area, in the development area, because it faces the developing roller 41 applied with a development bias of -300V, the negative transfer residual colorant T3 moves to the side of the developing roller 41 and is recovered in the developing device 4.

[0032] Generally, after transfer, the surface of the photoreceptor 1 is not only adhered to the residual toner after transfer, but also to foreign matter such as paper scraps. Therefore, in the developing device 4, not only the residual toner after transfer, but also foreign matter such as paper scraps are recovered. Although such foreign matter does not cause any particular problem when it simply enters the developing device 4, when the foreign matter is caught in the contact area between the developing roller 41 and the limiting scraper 44, and the foreign matter accumulates, aggregates, and grows there, it will cause an undesirable situation in which an image defect occurs. Specifically, in the portion corresponding to the aggregation area of the foreign matter, the toner on the developing roller 41 is blocked, and the toner cannot be fed into the developing area in this portion, resulting in an image defect in the form of white streaks on the image.

[0033] In existing developing devices used in cleanerless systems, there are configurations in which the surfaces of the supply roller and the developing roller move in the same direction at their opposing portions. However, even if this configuration can prevent foreign matter aggregates from being caught in the contact area between the developing roller and the limiting scraper, thereby suppressing image defects, it still presents the problem of difficulty maintaining image quality at high image area ratios. Specifically, in configurations in which the surfaces of the supply roller and the developing roller move in the same direction at their opposing portions, when continuously developing images with high image area ratios, insufficient toner supply to the developing area is likely to occur, resulting in a decrease in image density.

[0034] Therefore, in this embodiment, the supply roller 42 is driven to rotate in a direction opposite to the surface movement direction of the developing roller 41 at the portion facing the developing roller 41. Therefore, even when continuously developing images with a high image area ratio, insufficient toner supply to the developing area is unlikely to occur, and image quality with a high image area ratio can be maintained.

[0035] On the other hand, in configurations where the surfaces of the supply roller and the developing roller move in opposite directions at their opposing locations, a configuration has conventionally been employed to enhance the scraping force of the supply roller's surface (for example, by providing a plurality of protrusions on the supply roller's surface through grinding with a whetstone). This configuration enhances the ability of the supply roller's surface to remove foreign matter, such as paper scraps, that has been recovered from the developing roller. This prevents foreign matter recovered from the developing roller from being directly transported to the contact area between the developing roller and the restricting scraper. Consequently, this prevents foreign matter from being trapped in the contact area between the developing roller and the restricting scraper, preventing the trapped foreign matter from growing and causing image defects.

[0036] However, if the scraping force of the supply roller surface is increased, the scraped foreign matter is captured by the supply roller surface and remains immobilized, causing it to accumulate on the supply roller. The accumulated foreign matter on the supply roller gradually aggregates and grows, and the aggregates gradually peel off and fall off the supply roller surface. This results in a new problem: the aggregates are carried and transported by the developing roller, becoming trapped at the contact point between the developing roller and the restricting blade, causing image defects.

[0037] Therefore, in this embodiment, the surface of the supply roller 42 serves as an adhesion-inhibiting surface that inhibits the adhesion of foreign matter. Specifically, the surface of the supply roller 42 is a non-protruding surface with no protrusions. However, considering the supply roller 42's ability to supply toner to the developing roller 41 and its ability to remove foreign matter from the developing roller 41, it is preferable to provide recessed portions on the non-protruding surface. Specifically, the surface of the supply roller 42 is formed of a foamed layer, such as foamed polyurethane.

[0038] By providing the surface of the supply roller 42 with an adhesion-reducing surface, foreign matter recovered from the photoreceptor 1 onto the developing roller 41 is less likely to accumulate on the surface of the supply roller 42. As a result, foreign matter aggregates are prevented from growing on the supply roller 42, and foreign matter aggregates are prevented from being caught in the contact area between the developing roller 41 and the restricting blade 44, thereby preventing image defects.

[0039] In addition, in this embodiment, if Figure 2 As shown in FIG. 1 , the inlet area of the opposing portion of the supply roller 42 and the developing roller 41 (the area on the upstream side in the surface movement direction of the developing roller 41) is configured to be located vertically downward. With this configuration, foreign matter that is conveyed to the inlet area of the opposing portion as the surface of the developing roller 41 moves and is removed from the developing roller 41 by the surface of the supply roller 42 moves downward due to its own weight and accumulates on the surface of the developing roller 41. Figure 3 On the bottom of the inner wall of the developing box 43 in the area surrounded by the symbol A.

[0040] Specifically, foreign matter transported to the inlet area of the opposing portion as the surface of the developing roller 41 moves is prevented from entering the opposing portion by the surface movement of the supply roller 42, and is removed from the developing roller 41 and retained in the inlet area of the opposing portion. The foreign matter retained in the inlet area of the opposing portion then moves downward due to its own weight and accumulates on the curved portion ( Figure 3 As a result, it is possible to prevent the recovered foreign matter from entering the toner storage portion 46 in the developing cartridge 43 and being carried by the developing roller 41. It is also possible to prevent the foreign matter from being caught in the contact portion between the developing roller 41 and the restricting scraper 44 and growing, thereby causing image defects.

[0041] In particular, if Figure 3 As shown, the inner bottom of the developer cartridge 43 in this embodiment has a curved surface that matches the outer circumference of the developing roller 41 and the outer circumference of the supply roller 42. Furthermore, a protrusion 43a is formed on the inner bottom of the developer cartridge 43, in the inlet region facing the opposing portion of the supply roller 42 and the developing roller 41. The location A where foreign matter accumulates is located farther from the toner container 46 within the developer cartridge 43 than the protrusion 43a on the inner bottom of the developer cartridge 43. Therefore, the protrusion 43a on the inner bottom of the developer cartridge 43 functions to prevent foreign matter accumulated at location A from moving toward the toner container 46 within the developer cartridge 43. This prevents foreign matter accumulated on the inner bottom of the developer cartridge 43 due to its own weight from entering the toner container 46 within the developer cartridge 43 and being carried by the developing roller 41. Furthermore, it prevents foreign matter from being caught and growing between the contact area between the developing roller 41 and the restricting blade 44, thereby preventing image defects.

[0042] Furthermore, in this embodiment, the surface movement speed (linear speed) of the supply roller 42 is preferably set to be slower than the surface movement speed (linear speed) of the developing roller 41, that is, the linear speed ratio (supply roller linear speed / developing roller linear speed) is set to be less than 1. This makes it easier for foreign matter on the developing roller 41 to be scraped off by the surface of the supply roller, thereby improving the white streak suppression effect.

[0043] In this embodiment, the developing roller 41 preferably bites into the supply roller 42 by at least 1 mm at the facing portion between the developing roller 41 and the supply roller 42. This allows foreign matter on the developing roller 41 to be easily scraped off by the surface of the supply roller, improving the white streak suppression effect.

[0044] The present inventors evaluated the types and diameters of cells suitable as an adhesion-inhibiting surface when the surface of the supply roller 42 is formed of a foamed layer in the developing device 4 of this embodiment. The evaluation results are shown in Table 1 below.

[0045] Table 1

[0046]

[0047] As shown in Table 1, it was confirmed that when the surface of the supply roller 42 is composed of a foam layer containing connected cells of 300 μm or larger (the equivalent circular diameter of the cells opening on the surface of the supply roller 42, i.e., the diameter of a circle having an area equal to the area of the opening), foreign matter such as paper scraps is captured within the cells (recesses formed by the bubbles) on the surface of the supply roller 42. Furthermore, it was confirmed that aggregates of foreign matter become trapped in the contact area between the developing roller 41 and the restricting blade 44, causing image defects (white streaks). In contrast, when the surface of the supply roller 42 is composed of a foam layer containing single cells of less than 300 μm, foreign matter such as paper scraps is not captured within the cells on the surface of the supply roller 42, and image defects (white streaks) do not occur.

[0048] The above description is just an example, and each of the following methods has its own unique effects.

[0049] [First method]

[0050] The first method is a developing device 4, which supplies the developer (e.g., colorant) in the developer containing section (e.g., colorant containing section 46) to the developer carrier (e.g., developing roller 41) that is driven by rotation through a supply rotating body (e.g., supply roller 42), and after thinning the developer on the developer carrier (e.g., photosensitive body 1) through a layer thickness limiting component (e.g., limiting scraper 44), while developing the latent image on the latent image carrier, recovers the transfer residual colorant T3 on the latent image carrier. The developing device is characterized in that: the supply rotating body is driven by rotation so that the surface movement direction becomes the opposite direction to the surface movement direction of the developer carrier in the opposite part to the developer carrier, and the surface of the supply rotating body is composed of a foaming layer containing single bubbles less than 300 μm.

[0051] In a developing device using a cleanerless system, foreign matter such as paper scraps, recovered from the latent image carrier along with residual toner after transfer, can become trapped between the developer carrier and the layer thickness regulating member. This accumulation, aggregation, and growth of foreign matter can easily lead to image defects. Specifically, when foreign matter becomes trapped between the developer carrier and the layer thickness regulating member and forms aggregates, the developer can become dammed on the developer carrier at the location corresponding to the aggregates, resulting in image defects such as white streaks.

[0052] In order to suppress such image defects, a developing device has been proposed in which a supply rotator is driven to rotate in a direction of surface movement that is the same as the surface movement direction of the developer carrier at a portion facing the developer carrier (Patent Document 1). However, this developing device has difficulty in sufficiently suppressing the occurrence of such image defects.

[0053] Specifically, in a conventional developing device in which the surface movement directions of the supply rotator and the developer carrier are in the same direction in the opposing portion, developer present in an inlet area upstream of the developer carrier's surface movement direction in the opposing portion is fed into the opposing portion as both the supply rotator and the developer carrier move on the surface. Meanwhile, in this inlet area, foreign matter recovered from the latent image carrier along with the transfer residual toner is transported as the developer carrier moves on the surface. Therefore, foreign matter transported to this inlet area is easily transported into the opposing portion by the flow of developer that is fed into the opposing portion as both the supply rotator and the developer carrier move on the surface. The foreign matter transported into the opposing portion is then carried on the developer carrier and transported to the position of the layer thickness limiting member. As a result, the foreign matter becomes trapped between the developer carrier and the layer thickness limiting member, causing image defects such as white streaks.

[0054] Furthermore, even if conventional developing devices can be configured so that foreign matter transported from the latent image carrier as the developer carrier's surface moves is not fed into the facing portion but instead remains in the inlet area, maintaining image quality at high image area ratios remains difficult. Specifically, in a configuration where the directions of movement of the supply rotator and the developer carrier's surface are aligned in the facing portion, insufficient developer supply to the developing area is often prone to occur during continuous development of images with high image area ratios, resulting in a decrease in image density.

[0055] On the other hand, among the existing developing devices used in the cleanerless system, there is also known a developing device in which the surface movement directions of the supply rotating body and the developer carrier are opposite in the opposing direction (for example, Patent Document 2). This structure is generally such that even when continuously developing an image with a high image area ratio, it is difficult for the developer supply to the developing area to be insufficient, and the image quality of the high image area ratio can be maintained. However, in order to effectively scrape and recover foreign matter such as paper scraps on the developer carrier, the structure of this existing developing device is to grind the surface of the supply rotating body with a grindstone, and make the grinding groove in the opposing part opposite to the front movement direction of the developer carrier. According to this structure, since foreign matter transported along with the surface movement of the developer carrier is scraped off the developer carrier by the grinding groove (protrusion) on the surface of the supply rotating body, it is possible to prevent the foreign matter from being directly transported between the developer carrier and the layer thickness limiting component. This is believed to suppress the occurrence of image defects caused by foreign matter being caught between the developer regulating member and the layer thickness regulating member, accumulating there, agglomerating, and growing.

[0056] However, in this conventional developing device, scraped foreign matter is captured by the abrasive grooves on the surface of the supply rotor and held in place, causing it to accumulate on the supply rotor. The accumulated foreign matter then gradually aggregates and grows, eventually flakes off the supply rotor. This results in a new problem: the aggregated foreign matter is carried and transported by the developer carrier, becoming trapped between the developer carrier and the layer thickness regulating member, leading to image defects.

[0057] In this method, the supply rotatable body is driven to rotate in a surface movement direction opposite to the surface movement direction of the developer carrier in the portion opposite to the developer carrier, and the surface of the supply rotatable body is composed of a foam layer containing single bubbles smaller than 300 μm. As a result, the surface movement directions of the supply rotatable body and the developer carrier are opposite in the opposing portion, so even when continuously developing images with a high image area ratio, it is difficult for the developer supply to the developing area to be insufficient, and the image quality of the high image area ratio can be maintained. Moreover, since the surface of the supply rotatable body is a foam layer containing single bubbles smaller than 300 μm, it is possible to achieve a surface of the supply rotatable body that is difficult for foreign matter to be captured while maintaining its function as a supply rotatable body. That is, the supply rotatable body of this method ensures the developer supply function of the supply rotatable body to the developer carrier and the foreign matter removal function of the developer carrier by the single bubbles (recesses) on its surface. On the other hand, since the size of the single cells (equivalent circle diameter) is less than 300 μm, foreign matter is less likely to be trapped in the recessed portions (cells) on the surface of the supply rotator. Consequently, foreign matter aggregates do not grow on the supply rotator, thus preventing image defects caused by foreign matter aggregates being trapped between the developer carrier and the layer thickness regulating member.

[0058] Therefore, it is possible to achieve both suppression of image defects caused by foreign matter (paper dust, etc.) collected together with the transfer residual toner being caught between the developer carrier and the layer thickness regulating member and maintenance of image quality at a high image area ratio.

[0059] [Second Method]

[0060] A second aspect is characterized in that, in the first aspect, an upstream side of the surface movement direction of the developer carrying member is located vertically downward relative to the facing portion.

[0061] As a result, foreign matter that is transported to the opposing portion as the surface of the developer carrier moves and removed from the developer carrier by the surface of the supply rotator moves downward due to its own weight and accumulates on the bottom of the inner wall of the developer storage portion. This prevents the recovered foreign matter from being carried around one side of the developer storage portion by the developer carrier, thereby preventing the foreign matter from being trapped and growing between the developer carrier and the layer thickness limiting member, causing image defects.

[0062] [Third Method]

[0063] A third aspect is characterized in that, in the first or second aspect, a surface movement speed of the supply rotating body is slower than a surface movement speed of the developer carrying body.

[0064] As a result, foreign matter on the developer carrier is easily scraped off by the surface of the supply rotary body, and the effect of suppressing image defects caused by foreign matter is improved.

[0065] [Fourth Method]

[0066] A fourth aspect is characterized in that, in any one of the first to third aspects, in the facing portion, the developer carrier bites into the supply rotator by 1 mm or more.

[0067] As a result, foreign matter on the developer carrier is easily scraped off by the surface of the supply rotary body, and the effect of suppressing image defects caused by foreign matter is improved.

[0068] [Fifth Method]

[0069] The fifth embodiment is an image forming apparatus 10 having a cleaner-less structure in which a developing device collects transfer residual toner on a latent image bearing member, wherein any one of the developing devices of the first to fourth embodiments is used as the developing device.

[0070] According to this aspect, it is possible to achieve both suppression of image defects caused by foreign matter (paper dust, etc.) collected together with transfer residual toner being caught between the developer carrier and the layer thickness regulating member and maintenance of image quality at a high image area ratio.

Claims

1. A developing device that supplies developer from a developer storage portion to a rotationally driven developer carrier via a supply rotator, thins the developer layer on the developer carrier via a layer thickness limiting member, and simultaneously develops a latent image on the latent image carrier while recovering transfer residual toner on the latent image carrier, the developing device being characterized by: The supply rotating body is driven to rotate so that the surface movement direction thereof becomes the opposite direction to the surface movement direction of the developer carrying body at the portion facing the developer carrying body. The surface of the supply rotating body is composed of a foamed layer containing single bubble cells smaller than 300 μm.

2. The developing device according to claim 1, wherein: The upstream side of the surface movement direction of the developer carrier is located vertically downward relative to the facing portion.

3. The developing device according to claim 1 or 2, wherein: The surface movement speed of the supply rotating body is slower than the surface movement speed of the developer carrying body.

4. The developing device according to claim 1 or 2, wherein: In the facing portion, the developer carrier bites into the supply rotator by 1 mm or more.

5. An image forming apparatus having a developing device for recovering transfer residual toner on a latent image bearing member without a cleaner, characterized in that: As the developing device, the developing device according to claim 1 or 2 is used.

Images