Developing apparatus and image forming apparatus

Abstract

This suppresses image defects such as white streaks caused by foreign matter accumulating and agglomerating on the supply rotating body being released into the developer container. [Solution] A developing apparatus 4 supplies developer from a developer storage section 43 onto a developer carrier by a supply rotating body 42 that contacts the developer carrier 41 to form a supply nip, thins the developer on the developer carrier with a layer thickness regulating member 44, develops the latent image on the latent image carrier 1, and recovers the transfer residue toner on the latent image carrier, wherein the supply rotating body has a surface layer whose hardness, as measured by an Asker rubber hardness tester type F, is less than 65°.

Description

Technical Field

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

Background Art

[0002] Conventionally, a developer in a developer storage section is supplied onto a developer carrier by a supply rotating body that contacts the developer carrier to form a supply nip, and after the developer on the developer carrier is thinned by a layer thickness regulating member, a latent image on a latent image carrier is developed, and a developing device that recovers transfer residual toner on the latent image carrier is known.

[0003] For example, Patent Document 1 discloses a developing device used in an image forming apparatus having a cleanerless configuration that recovers transfer residual toner on a photoreceptor (latent image carrier) with a developing device. The supply roller in this developing device is rotationally driven so that the surface movement direction at the contact portion with the developing roller is opposite to the surface movement direction of the developing roller. The surface of the supply roller is polished so that minute irregularities are formed, and the polishing marks on the surface of the supply roller are formed to be reverse to the surface movement direction of the developing roller at the contact portion with the developing roller. Thereby, foreign matter recovered together with transfer residual toner on the developing roller (developer carrier) is increased in the mechanical frictional force of the supply roller (supply rotating body), and the foreign matter on the developing roller is scraped off with a strong force. has been.

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, it has been found that in a conventional developing device, image defects caused by foreign matter such as paper dust being sandwiched between the developer carrier and the layer thickness regulating member may not be sufficiently suppressed in some cases.

Means for Solving the Problems

[0005] To solve the above-mentioned problems, the present invention provides a developing apparatus that supplies developer from a developer storage section onto a developer carrier by a supply rotating body that contacts the developer carrier to form a supply nip, thins the developer on the developer carrier with a layer thickness regulating member, develops the latent image on a latent image carrier, and recovers the transfer residue toner on the latent image carrier, wherein the supply rotating body has a surface layer whose hardness, as measured by an Asker rubber hardness tester type F, is less than 65°. [Effects of the Invention]

[0006] According to the present invention, it is possible to suppress image defects such as white streaks caused by foreign matter accumulated and aggregated on the supply rotating body being released into the developer container. [Brief explanation of the drawing]

[0007] [Figure 1] An explanatory diagram showing the configuration of an image forming apparatus according to an embodiment. [Figure 2] An explanatory diagram illustrating the image-forming section of the image-forming apparatus. [Figure 3] An explanatory diagram showing the configuration of the developing apparatus of the image forming apparatus. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below with reference to the drawings. The image forming apparatus of this embodiment is an electrophotographic image forming apparatus, specifically a so-called single-drum type direct transfer monochrome machine. However, this embodiment is also applicable to other image forming apparatuses such as single-drum type intermediate transfer full-color machines and four-tandem type direct transfer or intermediate transfer full-color machines.

[0009] Figure 1 is an explanatory diagram showing the configuration of the image forming apparatus according to this embodiment. Figure 2 is an explanatory diagram illustrating the imaging section of the image forming apparatus according to this embodiment. Figure 3 is an explanatory diagram showing the configuration of the developing apparatus 4 in this embodiment. The image forming apparatus 10 of this embodiment includes a drum-shaped photoreceptor 1 as a latent image carrier. The image forming apparatus includes a charger 2 as a charging means, a light writing device 3 as a latent image forming means, a developing device 4 as a developing means, a transfer device 5 as a transfer means, and a static eliminator 6 as a static elimination means, all surrounding the photoreceptor 1.

[0010] The image forming apparatus 10 according to this embodiment is a cleanerless image forming apparatus that does not have a dedicated cleaning means for recovering the transfer residue toner remaining on the photoreceptor 1 after transfer, and recovers the transfer residue toner on the photoreceptor 1 with a developing apparatus 4. In a cleanerless system, the space required to provide cleaning means around the photoreceptor 1 can be reduced, making it possible to reduce the diameter of the photoreceptor 1. As a result, even if the recording material used to transfer the toner image from the photoreceptor 1 is thin paper or the like, which tends to adhere to the surface of the photoreceptor after transfer, the recording material can be stably separated from the photoreceptor 1 simply by the curvature of the photoreceptor 1. Consequently, there is no need to provide means for separating the recording material around the photoreceptor. Therefore, a cleanerless system makes it possible to reduce the cost and miniaturize the image forming apparatus.

[0011] 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 to uniformly charge the surface of the photoreceptor 1 to approximately -500V. Then, the optical writing device 3, which is composed of an LED array, is driven to expose the surface of the photoreceptor 1 according to the image data, and the potential of the exposed area is lowered to form an electrostatic latent image. Subsequently, in the developing area, toner as a developer is supplied by the developing device 4 to the electrostatic latent image on the photoreceptor 1, and a toner image is formed on the photoreceptor 1. At this time, in this embodiment, the transfer residue toner that remained on the photoreceptor 1 during the previous transfer is collected by the developing device 4.

[0012] The developing device 4 has a developing roller 41 as a developer carrier and a supply roller 42 as a rotating supply body, both located inside a developing case 43, which is a developer container. Toner is stored in a toner storage section 46 inside the developing case 43, and the toner in the toner storage section 46 is sent to the supply roller 42 by an agitator 45. The developing roller 41, which is driven to rotate in the direction of the arrows in the figure (counterclockwise), is supplied with toner from the supply roller 42, which is also driven to rotate in the direction of the arrows in the figure (counterclockwise). The toner supplied to the developing roller 41 is transported as the surface of the developing roller 41 moves, thinned by a regulating blade 44, which is a layer thickness regulating member, and then sent to the developing area facing the photoreceptor 1.

[0013] A development bias of, for example, -300V is applied to the developing roller 41. In addition, the toner sent to the developing area is charged to a negative polarity, which is its normal charging polarity, as it passes through the regulating blade 44. The negatively charged toner does not adhere to the unexposed areas (the background area, approximately -500V) in the developing area, but adheres to the exposed areas (the latent image area, approximately -50V), and electrostatic latent image development is performed.

[0014] Meanwhile, the paper P, which is fed from the paper feeder 11 at a predetermined timing as recording material, is temporarily stopped by the registration roller 12. Then, in accordance with the timing when the toner image T1 on the photoreceptor 1 is transported to the transfer area, the registration roller 12 sends the paper P to the transfer area. In the transfer area, the transfer roller of the transfer device 5 is positioned opposite the surface of the photoreceptor 1, and a positive polarity transfer bias is applied to this transfer roller. As a result, the toner image T1 on the photoreceptor 1 is transferred to the paper P that is fed between the photoreceptor 1 and the transfer roller in the transfer area. The paper P on which the toner image T1 has been transferred is then sent to the fuser 13, where the toner image T1 is fixed by pressurization and heating. After the fixing process, the paper P is discharged to the discharge tray 14.

[0015] The surface potential of the photoreceptor 1 after transfer is neutralized to a negative polarity (for example, around -50V) by the static eliminator 6. In addition, the remaining toner T2 and T3 on the photoreceptor 1 after transfer are transported to the charged region facing the charging roller 21 of the charger 2. At this time, the remaining toner T2 and T3 contain a mixture of toner T2 that has been reverse-charged (charged to a positive polarity) due to the positive polarity transfer bias, and toner T3 that remains in its normal charged polarity (negative polarity).

[0016] Regarding the positively polarized transfer residue toner T2, due to pre-charging discharge occurring in the upstream portion of the photoreceptor surface movement direction in the charged region, most of it becomes negatively polarized transfer residue toner T3, which is the normal charging polarity. The remaining positively polarized transfer residue toner T2 is collected on the charging roller 21 by the charging bias in the region (charged region) opposite the charging roller 21 of the charger 2.

[0017] The charger 2 is equipped with a cleaning brush 22, which serves as a charging cleaning member for cleaning toner and other materials adhering to the charging roller 21. When collecting positively polarized transfer residue toner T2, a cleaning bias of, for example, -1300V is applied to the cleaning brush 22. As a result, the positively polarized transfer residue toner T2 adhering to the charging roller 21, to which a charging bias of -1100V is applied, moves towards the cleaning brush 22 and is held by the cleaning brush 22.

[0018] On the other hand, the negatively polarized transfer residue toner T3 remains attached to the photoreceptor 1 and passes through the charged region. Because the amount of transfer residue toner T3 is small, it does not interfere with the charging process by the charger 2 or the exposure process by the light writing device 3. When the negatively polarized transfer residue toner T3 is transported to the developing region, it comes into contact with the developing roller 41 to which a developing bias of -300V is applied. At this time, due to the potential difference between the potential of the unexposed portion (background) of the photoreceptor 1 (-500V) and the developing bias (-300V), the transfer residue toner on the photoreceptor 1 moves towards the developing roller 41 and is collected by the developing device 4. In this way, in this embodiment, the transfer residue toner T3 is collected by the developing device 4 during the image forming operation, realizing a cleanerless system.

[0019] Furthermore, the positively polarized transfer residue toner T2 held by the cleaning brush 22 during the image forming operation is returned to the surface of the photoreceptor 1 during non-image forming operation periods, such as when the device is started up, and recovered by the developing device 4.

[0020] In detail, during the non-image forming operation period, first, a charging bias of -1100V is applied to the charging roller 21 to uniformly charge the surface of the photoreceptor 1 to approximately -500V. Then, with the transfer bias and static eliminator 6 turned off, when the uniformly charged -500V surface portion is transported back to the charged area, a voltage of, for example, -350V is applied to the charging roller 21, and a voltage of, for example, -150V is applied to the cleaning brush 22. As a result, the positively polarized transfer residue toner T2 held by the cleaning brush 22 moves from the cleaning brush 22 to the charging roller 21, and then from the charging roller 21 to the surface of the photoreceptor 1.

[0021] Subsequently, the positively polarized transfer residue toner T3 discharged from the charger 2 to the photoreceptor 1 is transported to the developing area. At this time, a voltage of, for example, +250V is applied to the developing roller 41 in the developing area. As a result, the negatively polarized transfer residue toner T2 present on the photoreceptor 1 moves towards the developing roller 41 and is collected, while the positively polarized transfer residue toner T3 passes through the developing area.

[0022] The positively charged residual toner T3 that has passed through the development area is then conveyed back to the charging area. At this time, the discharger 6 is turned on to uniformly level the surface of the photoreceptor 1 to about -50 V, and a charging bias of -1100 V is applied to the charging roller 21. As a result, the positively charged residual toner T3 conveyed to the charging area becomes a negatively charged residual toner T3 with the normal charging polarity due to pre-discharge before charging occurring at the upstream portion in the moving direction of the photoreceptor surface in the charging area.

[0023] After that, when the negatively charged residual toner T3 is conveyed to the development area, in the development area, since it faces the developing roller 41 to which a developing bias of -300 V is applied, the negatively charged residual toner T3 moves toward the developing roller 41 side and is collected by the developing device 4.

[0024] Generally, not only residual toner but also foreign substances such as paper dust adhere to the surface of the photoreceptor 1 after transfer. Therefore, in the developing device 4, not only the residual toner but also foreign substances such as paper dust are collected together. Although there is no particular problem just by such foreign substances entering the developing device 4, if the foreign substances are caught between the contact portion of the developing roller 41 and the regulating blade 44 and foreign substances, etc. accumulate, aggregate, and grow there, a defect that image defects occur will occur. Specifically, in the portion corresponding to the aggregation location of the foreign substances, the toner on the developing roller 41 is blocked, and toner cannot be fed into the development area in that portion, resulting in an image defect where white streaks occur on the image.

[0025] Some conventional developing devices used in cleanerless systems have a configuration in which the surface movement direction of the supply roller and the developing roller are the same at their opposing points. However, even if the accumulation of foreign matter at the contact point between the developing roller and the regulating blade is suppressed and the occurrence of image defects is suppressed, the problem of maintaining image quality at high image area ratios remains. In other words, in a configuration in which the surface movement direction of the supply roller and the developing roller are the same at their opposing points, when continuous developing processing is performed on images with high image area ratios, insufficient toner supply to the developing area is likely to occur, and image density tends to decrease.

[0026] 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 part facing the developing roller 41. As a result, even in cases where continuous developing processing is performed on images with a high image area ratio, a shortage of toner supply to the developing area is less likely to occur, and it is possible to maintain image quality with a high image area ratio.

[0027] On the other hand, in configurations where the surface movement directions of the supply roller and the developing roller are opposite at opposing points, conventional methods have been employed to increase the scraping force of the supply roller's surface (for example, a configuration in which numerous protrusions are created on the surface of the supply roller by polishing with an abrasive). This configuration increases the ability of the supply roller's surface to remove foreign matter such as paper dust collected on the developing roller, thereby suppressing the foreign matter collected on the developing roller from being sent directly to the contact point between the developing roller and the regulating blade. As a result, the accumulation of foreign matter at the contact point between the developing roller and the regulating blade is suppressed, and the growth of trapped foreign matter that causes image defects is suppressed.

[0028] However, when a configuration is adopted that increases the scraping force of the feed roller's surface, the scraped-off foreign matter remains trapped on the feed roller's surface, accumulating on the feed roller. The foreign matter accumulated on the feed roller gradually aggregates and grows, and eventually the aggregated foreign matter peels off from the feed roller's surface. As a result, it was found that a new problem arises: the detached aggregated foreign matter gets stuck in the contact area between the developing roller and the regulating blade, causing image defects.

[0029] Therefore, in this embodiment, the supply roller 42 is made of a material having a surface layer with a hardness of less than 65° as measured by an Asker rubber hardness tester type F. Such a supply roller 42 has a relatively soft (low hardness) surface layer. As a result, the contact pressure at the contact point (supply nip) between the developing roller 41 and the supply roller 42 is relatively small. By reducing the contact pressure at the supply nip, the force with which foreign matter such as paper dust adhering to the developing roller 41 is pressed against the surface of the supply roller 42 within the supply nip is weakened. As a result, the mechanical adhesion force of foreign matter removed from the developing roller 41 to the supply roller 42 side to the supply roller surface can be reduced. Consequently, foreign matter adhering to the supply roller 42 is detached and released from the supply roller 42 before it can agglomerate and grow, suppressing the accumulation and agglomeration of foreign matter on the supply roller 42. Thus, it is possible to suppress the accumulation and agglomeration of foreign matter on the supply rotating body from getting stuck in the contact point between the developing roller and the regulating blade, which would cause image defects.

[0030] Furthermore, in this embodiment, as shown in Figure 2, the inlet region of the contact area (supply nip) between the supply roller 42 and the developing roller 41 (the region upstream in the direction of surface movement of the developing roller 41) is configured to be located vertically downward. With this configuration, foreign matter that is transported to the inlet region of the supply nip 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, or foreign matter that initially adhered to the surface of the supply roller 42 but then peeled off, moves downward due to its own weight and accumulates on the bottom of the inner wall of the developing case 43 at the area enclosed by the symbol A in Figure 3.

[0031] More specifically, foreign matter that moves downward due to its own weight accumulates on the curved portion of the inner wall bottom of the developing case 43 that faces the developing roller 41 (the area enclosed by the symbol A in Figure 3). Therefore, the collected foreign matter is prevented from circling around the toner storage section 46 inside the developing case 43 and being carried on the developing roller 41, and the situation in which foreign matter gets caught in the contact area between the developing roller 41 and the regulating blade 44 and grows, causing image defects, is also prevented.

[0032] In particular, as shown in Figure 3, the bottom of the inner wall of the developing case 43 in this embodiment is curved, following the circumferential surfaces of the developing roller 41 and the supply roller 42. A protrusion 43a is formed on the bottom of the inner wall of the developing case 43, facing the inlet area of ​​the supply nip between the supply roller 42 and the developing roller 41. The location A where foreign matter accumulates is on the side of the protrusion 43a on the bottom of the inner wall of the developing case 43 that is farther from the toner storage section 46 inside the developing case 43. Therefore, the protrusion 43a on the bottom of the inner wall of the developing case 43 functions to prevent foreign matter accumulated at location A from moving to the toner storage section 46 inside the developing case 43. As a result, foreign matter accumulated on the bottom of the inner wall of the developing case 43 due to its own weight is prevented from rotating around the toner storage section 46 inside the developing case 43 and being carried on the developing roller 41, and the situation in which foreign matter gets caught in the contact area between the developing roller 41 and the regulating blade 44 and grows, causing image defects, is also prevented.

[0033] Furthermore, in this embodiment, it is preferable to set the surface movement speed (linear velocity) of the supply roller 42 to be slower than the surface movement speed (linear velocity) of the developing roller 41, that is, to set the ratio of these linear velocities (supply roller linear velocity / developing roller linear velocity) to be less than 1. This makes it easier to scrape off foreign matter on the developing roller 41 with the surface of the supply roller, thereby enhancing the white streak suppression effect.

[0034] The following describes an effectiveness verification test conducted in the developing apparatus 4 of this embodiment, which confirmed that no image quality defects occur when a supply roller 42 having a surface layer with a hardness of less than 65° as measured by an Asker rubber hardness tester type F is used. The results of this effectiveness verification test are shown in Table 1 below.

[0035] [Table 1]

[0036] The surface layer of the supply roller 42 used in this effectiveness verification test was made of urethane foam material, and its hardness was measured using an Asker rubber hardness tester type F as follows.

[0037] The Asker Rubber Hardness Tester Type F is a hardness tester designed for foams such as urethane foam and sponge. It measures the hardness by placing a disc-shaped pressure surface on the sample and using the weight of the hardness tester as the measurement pressure. In measurements using the Asker Rubber Hardness Tester Type F, roller-shaped samples (the surface layer of the supply roller 42) are difficult to measure due to insufficient thickness. Therefore, a sheet-like sample (thus thicker than the surface layer of the supply roller 42) made of the material used as the surface layer of the supply roller 42, with a thickness that can be measured by the Asker Rubber Hardness Tester Type F, was used to measure the hardness. Multiple measurements were taken by changing the measurement point on the sample, and the average value was derived as the hardness of the surface layer of the supply roller 42.

[0038] Furthermore, in this effectiveness verification test, images with an image area ratio of 0.5% were continuously formed on the paper. This was done under conditions that made it difficult for foreign matter such as paper dust to be transferred to the paper, thus reducing the amount of foreign matter in the developing device 4 (conditions that resulted in a large amount of foreign matter being present in the developing device 4). Super White Plus paper, available from Askul Corporation, was used as the paper. In this effectiveness verification test, a total of 40,000 images were formed repeatedly, and the occurrence of white streaks was visually evaluated.

[0039] As shown in Table 1, the results of this effectiveness verification test revealed that when a supply roller 42 with a surface layer hardness of 65° or higher, obtained by the aforementioned measurement method, image defects with white streaks occurred before reaching the specified number of printed sheets (40,000 sheets). In contrast, when a supply roller 42 with a surface layer hardness of less than 65°, obtained by the aforementioned measurement method, image defects with white streaks did not occur even after reaching the specified number of printed sheets.

[0040] Next, we will describe an effectiveness verification test in the developing apparatus 4 of this embodiment, in which a supply roller 42 with a cell diameter of less than 300 μm used as the surface layer of the urethane foam material used for the supply roller 42 is used. The results of this effectiveness verification test are shown in Table 2 below.

[0041] [Table 2]

[0042] As shown in Table 2 above, when a supply roller 42 with a surface layer hardness of less than 65° was used, no white streak image defects occurred even after reaching a specified number of prints, regardless of the cell diameter of the urethane foam material used as the surface layer of the supply roller 42. The cell diameter referred to here is calculated by measuring the opening area of ​​the cells opening on the surface of the supply roller 42 using a microscope, and then determining the equivalent circular diameter of the cell (the diameter of a circle with an area equal to the opening area) based on the measured cell opening area.

[0043] On the other hand, even when using a supply roller 42 with a surface layer hardness of 65° or higher, if the cell diameter of the urethane foam material used as the surface layer of the supply roller 42 is less than 300 μm, while white streaks may temporarily appear before reaching the specified number of printed sheets, continuous white streaks do not occur.

[0044] Considering these results, it is thought that although aggregates of foreign matter temporarily get stuck at the contact point of the regulating blade 44, the cohesive force of the foreign matter is weak, so the external force at the contact point of the regulating blade 44 breaks up the aggregate, and the white streak image quality defect is quickly resolved. In other words, by making the cell diameter of the surface layer of the supply roller 42 less than 300 μm, it becomes difficult for foreign matter such as paper dust to enter the recesses of the cells that open on the surface of the surface layer of the supply roller 42, or it becomes difficult for foreign matter to enter deep into the recesses of the cells. As a result, the aggregation of foreign matter with a high cohesive force when pushed into the recesses of the cells is suppressed, and even if some aggregates of foreign matter are generated on the supply roller 42 because the hardness of the surface layer of the supply roller 42 is 65° or higher, the cohesive force of the foreign matter is weak, and even if it gets stuck at the contact point of the regulating blade 44, the aggregate is quickly broken up, and the white streak image quality defect is quickly resolved.

[0045] Therefore, setting the cell diameter of the surface layer of the supply roller 42 to less than 300 μm has the effect of improving image quality defects such as white streaks. Thus, when using a supply roller 42 with a surface layer hardness of 65° or higher, setting its cell diameter to less than 300 μm can enhance the effect of suppressing white streaks in image quality.

[0046] Next, we will describe an effectiveness verification test in the developing apparatus 4 of this embodiment, in which the urethane foam material used as the surface layer of the supply roller 42 is made of single-cell foam. The results of this effectiveness verification test are shown in Table 3 below.

[0047] [Table 3]

[0048] As shown in Table 3 above, when a supply roller 42 with a surface layer hardness of less than 65° was used, no white streak image defects occurred even after reaching the specified number of printed sheets, regardless of whether the urethane foam material used as the surface layer of the supply roller 42 was monocellular or continuous. Here, monocellular refers to a case where each cell in the foam is not connected to adjacent cells, and continuous refers to a case where cells are connected.

[0049] On the other hand, even when using a supply roller 42 with a surface layer hardness of 65° or higher, if the urethane foam material used as the surface layer of the supply roller 42 is in the form of a single cell, while white streaks may temporarily appear before reaching the specified number of printed sheets, continuous white streaks do not occur.

[0050] Considering these results, it is thought that although aggregates of foreign matter temporarily get stuck at the contact point of the regulating blade 44, the cohesive force of the foreign matter is weak, so the external force at the contact point of the regulating blade 44 breaks up the aggregate, and the white streak image quality defect is quickly resolved. In other words, because the cell morphology of the surface layer of the supply roller 42 is single-cell, foreign matter such as paper dust is less likely to enter the recesses of the cells that open to the surface of the surface layer of the supply roller 42, or rather, it is less likely for foreign matter to enter deep into the recesses of the cells, compared to when it is a continuous-cell type. As a result, the aggregation of foreign matter with high cohesive force by being pushed into the recesses of the cells is suppressed, and even if some aggregates of foreign matter occur on the supply roller 42 because the hardness of the surface layer of the supply roller 42 is 65° or higher, the cohesive force of the foreign matter is weak, and even if it gets stuck at the contact point of the regulating blade 44, the aggregate is quickly broken up, and the white streak image quality defect is quickly resolved.

[0051] Therefore, making the cell morphology of the surface layer of the supply roller 42 a single-cell structure has the effect of improving image quality defects such as white streaks. Thus, when using a supply roller 42 with a surface layer hardness of 65° or higher, making its cell morphology a single-cell structure can enhance the effect of suppressing white streaks in image quality.

[0052] The above is just one example; each of the following embodiments produces its own unique effects. [First aspect] The first embodiment is a developing apparatus 4 that supplies developer (e.g., toner) from a developer storage section (e.g., developing case 43) onto a developer carrier (e.g., developing roller 41) by a supply rotating body (e.g., supply roller 42) that contacts the developer carrier to form a supply nip, thins the developer on the developer carrier with a layer thickness regulating member (e.g., regulating blade 44), develops the latent image on a latent image carrier (e.g., photoreceptor 1), and recovers the transfer residue toner on the latent image carrier, wherein the supply rotating body has a surface layer whose hardness, as measured by an Asker rubber hardness tester type F, is less than 65°. In a cleanerless image forming apparatus, residual toner on the latent image carrier is recovered by the developing unit. After transfer, not only residual toner but also foreign matter such as paper dust adheres to the surface of the latent image carrier, so the developing unit recovers not only the residual toner but also foreign matter such as paper dust. While there is no particular problem if such foreign matter simply enters the developing unit, if such foreign matter accumulates and aggregates and gets stuck between the developer carrier and the layer thickness regulating member, it can cause image defects. Specifically, in the areas where foreign matter has aggregated, the developer on the developer carrier is blocked, preventing the developer from being delivered to the developing area in those areas, resulting in image defects such as white streaks on the image. Foreign matter collected and adhering to the developer carrier is mechanically removed from the developer carrier by mechanical friction of the supply rotating body. This prevents the foreign matter on the developer carrier from being transported directly to the layer thickness regulating member, thereby suppressing image defects such as white streaks. However, if the mechanical friction force of the supply rotating body is increased, the foreign matter removed from the developer carrier by the mechanical friction of the supply rotating body will be collected on the supply rotating body, resulting in accumulation and aggregation on the supply rotating body. When the accumulated and aggregated foreign matter on the supply rotating body is released into the developer container, the aggregated foreign matter moves to the layer thickness regulating member, causing image defects such as white streaks. In this embodiment, the feed rotating body used has a surface layer with a hardness of less than 65° as measured by an Asker rubber hardness tester type F. Such a feed rotating body has a relatively soft (low hardness) surface layer. Therefore, the contact pressure at the contact point (feed nip) between the developer carrier and the feed rotating body is relatively small. By reducing the contact pressure at the feed nip, the force pressing foreign matter on the developer carrier against the surface of the feed rotating body within the feed nip is weakened. Therefore, the mechanical adhesion force of foreign matter removed from the developer carrier to the feed rotating body side to the surface of the feed rotating body can be reduced. As a result, foreign matter adhering to the feed rotating body is released from the feed rotating body at an early stage, preventing the accumulation and aggregation of foreign matter on the feed rotating body. Thus, image defects such as white streaks caused by foreign matter accumulated and aggregated on the feed rotating body being released into the developer container can be suppressed.

[0053] In this embodiment, the contact pressure at the supply nip is small, which weakens the force with which the supply rotating body mechanically removes the developed developer, transfer residue toner, and foreign matter adhering to the developer carrier. If the supply nip's ability to remove the developed developer from the developer carrier is insufficient, a large amount of the developed developer and transfer residue toner will be transported directly to the development area, potentially leading to a decrease in development capacity and degradation of image quality. Furthermore, if the supply nip's ability to remove foreign matter from the developer carrier is insufficient, as described above, the foreign matter on the developer carrier will be transported directly to the layer thickness regulating member, resulting in image defects such as white streaks. However, in this embodiment, since the supply rotating body has a relatively soft surface layer with a hardness of less than 65° as measured by the Asker rubber hardness tester type F, the width of the supply nip (length in the direction of surface movement of the supply rotating body) becomes wider. By widening the width of the supply nip, the area on the developer carrier that can be mechanically removed by the supply rotating body is expanded, and thus the ability to remove foreign matter from the developer carrier by the supply nip increases. As a result, the decrease in the ability to remove foreign matter from the developer carrier by the supply nip due to the reduced contact pressure within the supply nip can be compensated for by the increase in this ability due to the wider width of the supply nip.

[0054] [Second aspect] The second aspect is characterized in that, in the first aspect, the surface layer of the supply rotating body is made of a foamed material having a cell diameter of less than 300 μm. According to this embodiment, a relatively soft surface layer can be easily obtained in which the hardness measured by the Asker rubber hardness tester type F is less than 65°. On the other hand, when using a feed rotating body in which the surface layer is composed of foamed material, recesses formed by cells open up in the surface layer. As a result, foreign matter such as paper dust removed from the developer carrier can enter the recesses that open up in the surface layer of the feed rotating body. Therefore, foreign matter is more easily collected on the feed rotating body than in the case of a surface layer with a flat surface, and is more likely to accumulate and aggregate on the feed rotating body. However, in this embodiment, since the surface layer is relatively soft with a hardness of less than 65° as measured by the Asker rubber hardness tester type F, as described above, the contact pressure at the supply nip can be reduced, thereby weakening the force that pushes foreign matter on the developer carrier into the recesses of each cell that open to the surface layer of the supply rotating body. As a result, foreign matter is less likely to be pushed deep into the recesses of each cell, so even if foreign matter enters the recesses of each cell on the supply rotating body, it is released from the supply rotating body at an early stage, and the accumulation and aggregation of foreign matter on the supply rotating body is suppressed.

[0055] [Third aspect] The third aspect is characterized in that, in the first or second aspect, the surface layer of the supply rotating body is composed of a foamed material consisting of single-cell foam. Compared to continuous-cell architecture, single-cell architecture allows for shallower recesses in each cell that open into the surface layer of the feed rotating body. Therefore, even if foreign matter such as paper dust removed from the developer carrier gets into the recesses of each cell, it is more easily released from the feed rotating body at an early stage, preventing the accumulation and aggregation of foreign matter on the feed rotating body.

[0056] [Fourth aspect] The fourth embodiment is characterized in that, in any of the first to third embodiments, the supply rotating body is driven to rotate such that, at the portion in contact with the developer carrier, its surface movement direction is opposite to that of the surface movement direction of the developer carrier. One method to prevent foreign matter on the developer carrier from being collected on the supply rotating body by the supply nip is to ensure that the surface movement directions of the supply rotating body and the developer carrier are the same at their contact points. However, with this method, when developing images with a high image area ratio in succession, or when the amount of developer (toner) consumed per unit time is large, the supply capacity of the supply nip to supply developer to the developer carrier tends to be insufficient, which may lead to image quality degradation such as a decrease in image density. In this embodiment, the surface movement directions of the supply rotating body and the developer carrier are opposite at the contact point between them. In this case, even if the amount of developer (toner) consumed per unit time is large, the supply capacity to supply developer to the developer carrier at the supply nip is less likely to be insufficient, and image quality degradation such as a decrease in image density can be suppressed.

[0057] [Fifth aspect] The fifth aspect is characterized in that, in the fourth aspect, the ratio of the surface movement speed of the supply rotating body to the surface movement speed of the developer carrier is less than 1. According to this, the supply rotating body can be used to mechanically remove foreign matter from the developer carrier, thereby reliably suppressing the occurrence of image defects such as white streaks caused by foreign matter.

[0058] [Sixth aspect] The sixth embodiment is a cleanerless image forming apparatus in which residual toner on a latent image carrier (e.g., photoreceptor 1) is recovered by a developing apparatus 4, characterized in that any of the first to fifth developing apparatuses is used as the developing apparatus. This provides an image forming apparatus that can suppress image defects such as white streaks caused by foreign matter accumulating and agglomerating on the supply rotating body and being released into the developer container. [Explanation of Symbols]

[0059] 1: Photoreceptor 2: Charger 3: Optical writing device 4: Developing equipment 5: Transfer device 6: Static eliminator 10: Image forming apparatus 11: Paper feeder 12: Registroller 13: Fixing device 14: Output tray 21: Electrostatic roller 22: Cleaning brush 41: Developing roller 42: Supply roller 43: Developing Case 43a: Convex part 44: Regulatory Blade 45: Agitator 46: Toner storage compartment P:Paper T1: Toner image T2: Positive polarity transfer residue toner T3: Negative polarity transfer residue toner [Prior art documents] [Patent Documents]

[0060] [Patent Document 1] Japanese Patent Publication No. 2014-149328

Claims

1. A developing apparatus that supplies developer from a developer container onto a developer carrier by a supply rotating body that contacts the developer carrier to form a supply nip, thins the developer on the developer carrier using a layer thickness regulating member, develops the latent image on the latent image carrier, and recovers the transfer residue toner on the latent image carrier, The developing apparatus is characterized in that the supply rotating body has a surface layer whose hardness, as measured by an Asker rubber hardness tester type F, is less than 65°.

2. In the developing apparatus according to claim 1, The developing apparatus is characterized in that the surface layer of the supply rotating body is made of a foamed material having a cell diameter of less than 300 μm.

3. In the developing apparatus according to claim 1 or 2, The developing apparatus is characterized in that the surface layer of the supply rotating body is composed of a foaming material consisting of single-cell foam.

4. In the developing apparatus according to claim 1 or 2, The developing apparatus is characterized in that the supply rotating body is driven to rotate such that, at the portion in contact with the developer carrier, its surface movement direction is opposite to that of the surface movement direction of the developer carrier.

5. In the developing apparatus according to claim 4, A developing apparatus characterized in that the ratio of the surface movement speed of the supply rotating body to the surface movement speed of the developer carrier is less than 1.

6. A cleanerless image forming apparatus in which residual toner on a latent image carrier is recovered by a developing device, An image forming apparatus characterized in that the developing apparatus described in claim 1 or 2 is used as the developing apparatus.

Images