Developing apparatus and image forming apparatus

Abstract

Even in situations where highly charged foreign matter may be generated, this suppresses the occurrence of image defects caused by foreign matter such as paper dust getting trapped between the developer carrier and the layer thickness regulating member. [Solution] A developing apparatus 4 supplies developer T from a developer storage section 43 onto a developer carrier 41 using a supply rotating body 42, thins the developer on the developer carrier using a layer thickness regulating member 44, develops the latent image on the latent image carrier 1 in a developing region, and recovers the transfer residue toner on the latent image carrier. The supply rotating body contacts the developer carrier to form a supply nip, and has charge reduction means 47, 48 to reduce the charge amount of foreign matter I1 that is transported together with the transfer residue toner on the latent image carrier along a transport path from a charged region where the surface of the latent image carrier is uniformly charged until it is recovered onto the developer carrier in the developing region and reaches the supply nip.

Description

Technical Field

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

Background Art

[0002] Conventionally, a developing device has been known in which a developer in a developer storage unit is supplied to a developer carrier by a supply rotating body, the developer on the developer carrier is made into a thin layer by a layer thickness regulating member, and then a latent image on a latent image carrier is developed in a developing area, and transfer residual toner on the latent image carrier is recovered.

[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. This developing device is for the purpose of suppressing the occurrence of image defects caused by foreign substances such as paper dust being sandwiched between a developing roller (developer carrier) and a regulating member (layer thickness regulating member), and the supply roller (supply rotating body) and the developing roller have the same surface movement direction at their opposing portions.

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in a conventional developing device, there have been cases where image defects caused by foreign substances such as paper dust being sandwiched between a developer carrier and a layer thickness regulating member cannot be suppressed.

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 container onto a developer carrier using a supply rotating body, thins the developer on the developer carrier using a layer thickness regulating member, develops the latent image on a latent image carrier in a developing region, and recovers the transfer residue toner on the latent image carrier, wherein the supply rotating body contacts the developer carrier to form a supply nip, and has charge reduction means for reducing the amount of charge of foreign matter transported together with the transfer residue toner on the latent image carrier along a transport path from a charged region where the surface of the latent image carrier is uniformly charged until it is recovered onto the developer carrier in the developing region and reaches the supply nip. [Effects of the Invention]

[0006] According to the present invention, even in situations where foreign matter with a large amount of charge may be generated, it is possible to suppress the occurrence of image defects caused by foreign matter such as paper dust getting trapped between the developer carrier and the layer thickness regulating member. [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. [Figure 4] An explanatory diagram illustrating the configuration and operation of reducing the charge amount of foreign matter by the charge amount reduction means in Configuration Example 1. [Figure 5] An explanatory diagram showing an example of a foreign object removal method. [Figure 6] An explanatory diagram showing another example of a foreign object removal method. [Figure 7] An explanatory diagram showing an example with a stirring element. [Figure 8] An explanatory diagram illustrating the configuration and operation of reducing the charge amount of foreign matter by the charge amount reduction means in Configuration Example 2. [Figure 9]An explanatory diagram illustrating the configuration and operation of reducing the charge amount of foreign matter by the charge amount reduction means in Configuration Example 3. [Figure 10] An explanatory diagram illustrating the configuration and operation of reducing the charge amount of foreign matter by the charge amount reduction means in Configuration Example 4. [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 arrow in the figure (counterclockwise), is supplied with toner from the supply roller 42, which is also driven to rotate in the direction of the arrow 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, -250V is applied to the developing roller 41. In addition, the toner sent to the developing area is charged to a negative polarity, which is the 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 charged transferred residual toner T2, most of it becomes the negatively charged transferred residual toner T3 with the normal charging polarity due to the pre-discharge before charging that occurs in the upstream portion of the moving direction of the photoreceptor surface in the charging region. The remaining positively charged transferred residual toner T2 is recovered onto the charging roller 21 by the charging bias in the facing region (charging region) with the charging roller 21 of the charger 2.

[0017] The charger 2 is provided with a cleaning brush 22 as a charging cleaning member for cleaning toner and the like attached to the charging roller 21. When recovering the positively charged transferred residual toner T2, a cleaning bias of, for example, -1300 V is applied to the cleaning brush 22. As a result, the positively charged transferred residual toner T2 attached to the charging roller 21 to which a charging bias of -1100 V is applied moves toward the cleaning brush 22 side and is held by the cleaning brush 22.

[0018] On the other hand, the negatively charged transferred residual toner T3 passes through the charging region while remaining attached to the photoreceptor 1. Since the amount of the transferred residual toner T3 is small, it does not interfere with the charging process by the charger 2 or the exposure process by the optical writing device 3. When the negatively charged transferred residual toner T3 is conveyed to the developing region, it faces the developing roller 41 to which a developing bias of -250 V is applied in the developing region. At this time, due to the potential difference between the potential (-500 V) of the non-exposed portion (base portion) of the photoreceptor 1 and the developing bias (-250 V), the transferred residual toner on the photoreceptor 1 moves toward the developing roller 41 side and is recovered by the developing device 4. As described above, in this embodiment, the transferred residual toner T3 is recovered by the developing device 4 during the image forming operation, realizing a cleanerless system.

[0019] The positively charged transferred residual toner T2 held by the cleaning brush 22 during the image forming operation is returned to the surface of the photoreceptor 1 and recovered by the developing device 4 during a non-image forming operation period such as when the device is started up.

[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 polarized transfer residue toner T3 that has passed through the developing area is then transported back to the charged area. At this time, the static eliminator 6 is turned on to uniformly level the surface of the photoreceptor 1 to approximately -50V, and a charging bias of -1100V is applied to the charging roller 21. As a result, the positively polarized transfer residue toner T3 transported to the charged area becomes negatively polarized transfer residue toner T3, which is its normal charging polarity, due to pre-charging discharge that occurs in the upstream portion of the photoreceptor surface movement direction within the charged area.

[0023] Subsequently, when the negatively polarized transfer residue toner T3 is transported to the developing area, it faces the developing roller 41 to which a -300V developing bias is applied. Therefore, the negatively polarized transfer residue toner T3 moves toward the developing roller 41 and is collected by the developing device 4.

[0024] Generally, after transfer, foreign matter such as paper dust adheres not only toner residue but also to the surface of the photoreceptor 1. Therefore, the developing device 4 collects not only toner residue but also foreign matter such as paper dust. While there is no particular problem if such foreign matter simply enters the developing device 4, if the foreign matter gets caught in the contact area between the developing roller 41 and the regulating blade 44, and accumulates, aggregates, and grows there, and then gets stuck between the developing roller 41 and the regulating blade 44 in an aggregated state, a problem occurs in which image defects occur. Specifically, in the area corresponding to the aggregated foreign matter, the toner on the developing roller 41 is blocked, and toner cannot be sent to the developing area in that area, resulting in image defects such as white streaks on the image.

[0025] Normally, foreign matter such as paper dust collected and adhering to the developing roller 41 is mechanically removed from the developing roller 41 at the supply nip between it and the supply roller 42, preventing it from being transported to the regulating blade 44. However, if the amount of charge on the foreign matter collected and adhering to the developing roller 41 is large, the electrostatic adhesion force of the foreign matter to the surface of the developing roller 41 becomes large. In this case, the foreign matter on the developing roller 41 is transported to the regulating blade 44 without being mechanically removed by the supply roller.

[0026] In particular, in this embodiment, pre-charging discharge occurring in the upstream portion of the charged region in the direction of movement of the photoreceptor surface can cause foreign matter on the photoreceptor to acquire a large negative charge. After passing through the charged region, such foreign matter is transported to the developing region, where it comes into contact with the developing roller 41 to which a developing bias of -250V 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 (-250V), the foreign matter with a large negative charge moves toward the developing roller 41 and is collected by the developing device 4. At this time, the foreign matter adheres firmly to the surface of the developing roller 41 due to a large electrostatic adhesion force and a mechanical adhesion force due to pressing in the developing region. As a result, such foreign matter is not mechanically removed by the supply roller and is transported to the location of the regulating blade 44.

[0027] Therefore, in this embodiment, a means for reducing the charge of foreign matter such as paper dust is provided along the transport path in which the transfer residue toner on the photoreceptor is collected on the developing roller 41 in the developing region and transported until it reaches the supply nip. As a result, even foreign matter that has accumulated a large charge when passing through the charging region can have its charge reduced before reaching the supply nip, making it possible for the supply roller 42 to remove the foreign matter. Thus, it is possible to suppress the transport of highly charged foreign matter to the regulating blade 44, thereby suppressing the occurrence of image defects such as white streaks. The transport path of the transfer residue toner from the charging region to the supply nip is also the transport path for foreign matter such as paper dust, and will therefore be referred to as the "foreign matter transport path" as appropriate below.

[0028] [Configuration Example 1] Next, we will describe one example of the configuration of the charge reduction means in this embodiment (hereinafter referred to as "Configuration Example 1"). This configuration example 1 is an example in which a charge reduction means is used to reduce the charge amount of foreign matter in the foreign matter transport path portion from the developing area to the supply nip.

[0029] Figure 4 is an explanatory diagram illustrating the configuration and operation of reducing the charge amount of foreign matter by the charge amount reduction means in this configuration example 1. As shown in Figure 4, the developing apparatus 4 of this embodiment has a toner leak prevention sheet 47 positioned to seal the gap between the developing roller 41 and the inner wall of the developing case 43, serving as a developer leak prevention member. The toner leak prevention sheet 47 is provided such that its fixed end is supported by the developing case 43 and its free end abuts against the surface of the developing roller 41. Since the toner leak prevention sheet 47 is a contact member that comes into contact with foreign matter collected from the photoreceptor 1 onto the developing roller 41, it is possible to reduce the amount of charge on the foreign matter before it reaches the supply nip by utilizing this toner leak prevention sheet 47.

[0030] In this configuration example 1, as a means of reducing the amount of charge, a voltage is applied to the toner leak prevention sheet 47 that comes into contact with the foreign object by a power supply 48, which is a voltage application means, to reduce the amount of charge on the foreign object. Specifically, in this configuration example 1, a conductive sheet is attached to the part of the toner leak prevention sheet 47 that comes into contact with the surface of the developing roller 41 to form a conductive part 47a. Then, a voltage with the opposite polarity to the charge polarity (negative polarity) of the foreign object is applied to the conductive part 47a of the toner leak prevention sheet 47.

[0031] Furthermore, if the potential difference between the surface potential of the developing roller 41 and the conductive part 47a of the toner leak prevention sheet 47 becomes a large potential difference, such as +500V, a discharge may occur, which can change the surface potential of the developing roller at the discharge location and potentially cause image noise. Therefore, it is preferable to set the voltage applied to the conductive part 47a of the toner leak prevention sheet 47 to a range in which such a discharge does not occur. Specifically, for example, a voltage that is +300V relative to the surface potential of the developing roller 41, that is, a voltage that is +300V relative to the development bias (e.g., -250V) applied to the developing roller 41 (e.g., +50V), is applied.

[0032] As shown in Figure 4, foreign matter I0 such as paper dust adhering to the photoreceptor 1 in the transfer area may become highly charged foreign matter I1 with a large negative charge due to discharge in the charged area. In the developing area, such highly charged foreign matter I1 moves toward the developing roller 41 due to the potential difference between the background potential (e.g., -500V) of the unexposed area (background area) of the photoreceptor 1 and the surface potential (=developing bias (e.g., -250V)) of the developing roller 41, and is collected by the developing device 4. The highly charged foreign matter I1 collected on the developing roller 41 in this way may adhere firmly to the surface of the developing roller 41 due to a large electrostatic adhesion force and a mechanical adhesion force due to pressing in the developing area. If left in this state, it cannot be mechanically removed by the supply roller 42 at the supply nip and continues to adhere to the developing roller 41, being transported to the regulating blade 44, causing image defects such as white streaks.

[0033] In particular, in this embodiment, as shown in Figure 4, a voltage is applied to the supply nip to apply a supply bias to the supply roller 42, which is charged with a negative polarity, the normal charging polarity, in order to electrostatically move the toner, which is charged with a negative polarity, from the supply roller 42 side to the developer roller 41 side. Therefore, highly charged foreign matter I1, which is strongly charged with the same negative polarity as the toner, receives an electrostatic force towards the developer roller 41 side within the supply nip, and the electrostatic adhesion force of the highly charged foreign matter I1 to the surface of the developer roller 41 becomes very large. As a result, it is difficult to mechanically remove the highly charged foreign matter I1 on the developer roller 41 by the supply roller 42, and it is transported to the regulating blade 44, which is likely to cause image defects.

[0034] In this configuration example 1, the highly charged foreign matter I1 collected on the developing roller 41 comes into contact with the conductive portion 47a of the toner leak prevention sheet 47 before reaching the supply nip. As a result, the voltage (positive voltage) applied to the conductive portion 47a of the toner leak prevention sheet 47 reduces the charge amount (negative charge amount) of the highly charged foreign matter I1, and the highly charged foreign matter I1 becomes a less charged foreign matter I2. Consequently, the electrostatic adhesion force of the foreign matter (less charged foreign matter I2) collected on the developing roller 41 to the developing roller 41 can be reduced. Therefore, even in a configuration where the supply bias described above is applied within the supply nip, the electrostatic adhesion force of the (less charged foreign matter I2) to the surface of the developing roller 41 is reduced, making it easier to mechanically remove it with the supply roller 42.

[0035] Foreign matter such as paper dust (low-charged foreign matter I2) removed by the supply roller 42 adheres to the supply roller 42, but is removed from the supply roller 42 by the toner T in the toner storage section 46 surrounding the supply roller 42 and diffused into the toner storage section 46. As a result, foreign matter does not accumulate or aggregate near the regulating blade 44, and image defects are significantly suppressed.

[0036] Furthermore, a means for removing foreign matter (low-charged foreign matter I2) adhering to the supply roller 42 may be provided. As a simple and inexpensive means for removing foreign matter, for example, a contact member that contacts the surface of the supply roller 42 is used to remove foreign matter on the supply roller 42 to the toner storage section 46 in the developing case 43.

[0037] As a means for removing foreign matter, for example, as shown in Figure 5, a configuration is used in which a removal brush 49 that contacts the supply roller 42 from below removes foreign matter from the supply roller 42. With this configuration, foreign matter such as paper dust that is scraped off from the developing roller 41 by the supply roller 42 and transported adhering to the supply roller 42 is removed by the removal brush 49 at the bottom of the supply roller 42. In this case, it is possible to prevent foreign matter adhering to the supply roller 42 from being transported back to the supply nip while still adhering to the supply roller 42, thereby preventing foreign matter from obstructing the supply of toner to the developing roller 41 at the supply nip.

[0038] In particular, since the foreign matter removed from the supply roller 42 by the removal brush 49 is collected within the removal brush 49, the amount of foreign matter that diffuses and disperses into the toner T in the toner storage section 46 in the developing case 43 can be kept to a minimum. Therefore, the accumulation and aggregation of foreign matter near the regulating blade 44 is further suppressed, and image defects are significantly reduced.

[0039] Furthermore, as a means for removing foreign matter, for example, as shown in Figure 6, a configuration is used in which foreign matter on the supply roller 42 is removed by a removal Mylar 50 that contacts the supply roller 42 from above. With this configuration, foreign matter such as paper dust that adheres to and is transported on the supply roller 42 is blocked by the removal Mylar 50 at the top of the supply roller 42 and taken into the toner T of the toner storage unit 46. However, most of the foreign matter blocked by the removal Mylar 50 remains on the upstream side of the removal Mylar 50 in the direction of movement of the supply roller surface. Therefore, the foreign matter taken into the toner T of the toner storage unit 46 does not move beyond the supply roller 42 to the regulating blade 44 side, so foreign matter is less likely to accumulate and aggregate near the regulating blade 44, and image defects are significantly suppressed.

[0040] Furthermore, as shown in Figure 7, by providing an agitator 54 above the supply roller 42 in the toner storage section 46 inside the developing case 43, the agitator 54 prevents foreign matter that has detached from the supply roller 42 and been taken into the toner T in the toner storage section 46 from moving beyond the supply roller 42 towards the regulating blade 44. As a result, foreign matter is less likely to accumulate and aggregate near the regulating blade 44, and image defects are significantly suppressed. In particular, as shown in Figure 7, if the agitator 54 rotates in a direction opposite to the direction of surface movement of the supply roller 42, it can prevent foreign matter from moving towards the regulating blade 44 due to the surface movement of the supply roller 42, thus preventing foreign matter from accumulating and agglomerating near the regulating blade 44, and image defects are significantly suppressed.

[0041] [Configuration Example 2] Next, we will describe another configuration example of the charge reduction means in this embodiment (hereinafter referred to as "Configuration Example 2"). This configuration example 2, like configuration example 1 described above, is an example in which a charge reduction means is used to reduce the charge amount of foreign matter in the foreign matter transport path portion from the developing area to the supply nip. However, the specific configuration of the charge reduction means differs from that of configuration example 1 described above. In other words, the charge reduction means of this configuration example 2 is configured to reduce the charge amount of foreign matter based on the relationship of the triboelectric series with respect to the foreign matter at the contact member that comes into contact with the foreign matter.

[0042] Figure 8 is an explanatory diagram illustrating the configuration and operation of reducing the charge amount of foreign matter by the charge amount reduction means in this configuration example 2. In this configuration example 2, the toner leak prevention sheet 47 is used to reduce the charge of foreign matter before it reaches the supply nip. Specifically, a contact charging part 47b made of a material that is more easily negatively charged than foreign matter such as paper dust is provided at the part of the toner leak prevention sheet 47 that comes into contact with the surface of the developing roller 41.

[0043] According to this, the highly charged foreign matter I1 collected on the developing roller 41 comes into contact with the contact charging portion 47b of the toner leak prevention sheet 47 before reaching the supply nip. This contact generates a positive charge on the highly charged foreign matter I1, and this positive charge cancels out the negative charge of the highly charged foreign matter I1, which is heavily negatively charged. As a result, the amount of charge (amount of negative charge) of the highly charged foreign matter I1 decreases, and the highly charged foreign matter I1 becomes a less charged foreign matter I2. Consequently, the electrostatic adhesion force of the foreign matter (less charged foreign matter I2) collected on the developing roller 41 to the developing roller 41 can be reduced, making it easier to remove it mechanically by the supply roller 42.

[0044] PTFE (polytetrafluoroethylene) is preferred as the material used for the contact-charging portion 47b of the toner leak prevention sheet 47. In particular, using a conductive PTFE sheet as the contact-charging portion 47b is more preferable because it allows the charge accumulated on the contact-charging portion 47b to be released.

[0045] [Configuration Example 3] Next, we will describe yet another configuration example of the charge reduction means in this embodiment (hereinafter referred to as "Configuration Example 3"). This configuration example 3, like the configuration example 1 described above, is an example in which a charge reduction means is used to reduce the charge amount of foreign matter in the foreign matter transport path portion from the developing area to the supply nip. However, the specific configuration of the charge reduction means differs from that of the configuration example 1 described above. In other words, the charge reduction means of this configuration example 3 uses a contact member other than the toner leakage prevention sheet 47.

[0046] Figure 9 is an explanatory diagram illustrating the configuration and operation of the charge reduction means in this configuration example 3, which reduces the charge amount of foreign matter. The charge reduction means in this configuration example 3 involves applying a voltage with the opposite polarity to the charge polarity (negative polarity) of the foreign matter to a contact member 51 separate from the toner leak prevention sheet 47, thereby reducing the charge of the foreign matter. In the above-described configuration example 1, a conductive part 47a is provided on the toner leak prevention sheet 47, so the existing toner leak prevention sheet 47 cannot be used. However, in this configuration example 3, since a separate contact member 51 to which voltage is applied is provided, the existing toner leak prevention sheet 47 can be used.

[0047] In this configuration example 3, the charge reduction means is described as reducing the charge of the foreign object by applying a voltage to the contact member 51 that comes into contact with the foreign object. However, as in the configuration example 2 described above, a configuration in which no voltage is applied is also possible, that is, a configuration in which the contact member 51 is made of a material that reduces the charge of the foreign object based on its relationship to the triboelectric series.

[0048] [Configuration Example 4] Next, we will describe yet another configuration example of the charge reduction means in this embodiment (hereinafter referred to as "Configuration Example 4"). Unlike configuration examples 1 to 3 described above, this configuration example 4 uses a charge reduction means to reduce the amount of charge on foreign matter in the foreign matter transport path portion from the charging region to the developing region.

[0049] Figure 10 is an explanatory diagram illustrating the configuration and operation of reducing the charge amount of foreign matter by the charge amount reduction means in this configuration example 4. In this configuration example 4, as a means of reducing the amount of charge, a power supply 53, which is a voltage application means, applies a voltage with the opposite polarity to the charge polarity (negative polarity) of the foreign matter to the contact roller 52 that comes into contact with the surface of the photoreceptor 1, thereby reducing the amount of charge of the foreign matter adhering to the photoreceptor 1.

[0050] Furthermore, if the potential difference between the surface potential of the photoreceptor 1 and the contact roller 52 becomes large, such as +500V, a discharge may occur, which can change the surface potential of the photoreceptor at the discharge site and potentially cause image noise. Therefore, it is preferable to set the voltage applied to the contact roller 52 to a range in which such a discharge does not occur.

[0051] As shown in Figure 10, foreign matter I0 such as paper dust adhering to the photoreceptor 1 in the transfer region may become highly charged foreign matter I1 with a large negative charge due to discharge in the charged region. Even such highly charged foreign matter I1, when passing through the contact point with the contact roller 52, decreases in charge (negative charge) due to the voltage (positive voltage) applied to the contact roller 52, and the highly charged foreign matter I1 becomes less charged foreign matter I2. Subsequently, the less charged foreign matter I2 on the photoreceptor 1 moves towards the developing roller 41 in the developing region due to the potential difference between the photoreceptor 1 and the developing roller 41, and is collected by the developing device 4. Because the electrostatic adhesion force of the less charged foreign matter I2 collected on the developing roller 41 is small, it can be easily removed mechanically by the supply roller 42 even in a configuration where a supply bias is applied in the supply nip.

[0052] In this configuration example 4, the charge reduction means is described as reducing the charge of foreign matter by applying a voltage to the contact roller 52. However, as in the configuration example 2 described above, a configuration in which no voltage is applied is also possible, that is, a configuration in which the contact roller 52 is made of a material that reduces the charge of foreign matter due to its relationship with the triboelectric series.

[0053] [Configuration Example 5] Next, we will describe yet another configuration example of the charge reduction means in this embodiment (hereinafter referred to as "Configuration Example 4"). In configurations such as those described in Configuration Examples 1, 3, and 4 above, where a voltage is applied to reduce the charge of foreign matter, the voltage value may be a predetermined fixed value. However, in Configuration Example 5, this voltage value is made changeable by the control unit 100, which acts as a voltage control means.

[0054] Table 1 below shows an example of how to change the voltage value depending on the conditions of the device's operating environment. Note that this example in Table 1 is a configuration in which voltage is applied to the contact roller 52 that contacts the photoreceptor 1, as in Configuration Example 4 described above.

[0055] [Table 1]

[0056] The example shown in Table 1 sets the applied voltage value at normal temperature and humidity to a value that can reduce the charge of foreign matter such as paper dust to the maximum extent possible without causing discharge. When the operating environment of the device (temperature, humidity) changes, the discharge initiation potential changes. Therefore, if the voltage value is not corrected according to the change in the operating environment from normal temperature and humidity, discharge may occur or the charge of foreign matter may not be sufficiently reduced. For example, discharge is more likely to occur at high temperatures or high humidity, so as shown in Table 1, the voltage value should be corrected to be lower at higher temperatures or humidity.

[0057] In addition, in the above-described configuration examples 1 and 3, the voltage value may be changed by the control unit 100 according to the conditions of the device usage environment, as in this configuration example 4.

[0058] Table 2 below shows an example of how to change the voltage value according to the cumulative number of images formed (number of prints). Note that the example in Table 2 is a configuration in which voltage is applied to the contact roller 52 that contacts the photoreceptor 1, as in Configuration Example 4 described above.

[0059] [Table 2]

[0060] The example shown in Table 2 sets the voltage applied initially to a value that can reduce the charge of foreign matter such as paper dust to the maximum extent possible without causing a discharge. As the number of prints in this image forming apparatus increases, the characteristics of the photoreceptor 1, such as its electrical resistance, change due to surface wear over time. As a result, the discharge initiation voltage between the photoreceptor 1 and the contact roller 52 changes, and if the voltage value is not corrected according to the number of prints, a discharge may occur or the charge of foreign matter may not be sufficiently reduced. For example, as shown in Table 2, the voltage value is corrected so that it increases as the number of prints increases.

[0061] Furthermore, in the above-described configuration examples 1 and 3, as the number of prints in this image forming apparatus increases, the characteristics of the developing roller 41, such as its electrical resistance, change due to surface wear of the developing roller 41 over time. As a result, the discharge initiation voltage between the developing roller 41 and the conductive part 47a or contact member 51 of the toner leakage prevention sheet 47 changes. Therefore, if the voltage value is not corrected according to the number of prints, discharge may occur or the amount of charge of foreign matter may not be sufficiently reduced. Accordingly, in the above-described configuration examples 1 and 3, the voltage value may be changed according to the cumulative number of image formed (number of prints).

[0062] Table 3 below shows an example of how the voltage value is changed depending on the type of paper P on which the image is formed. Note that the example in Table 3 is a configuration in which voltage is applied to the conductive part 47a or contact member 51 of the toner leakage prevention sheet 47 that contacts the developing roller 41, as in the configuration examples 1 and 3 described above.

[0063] [Table 3]

[0064] The example shown in Table 3 sets the voltage value for when a paper type that generates a large amount of paper dust is used to a voltage value that can reduce the amount of charge of foreign matter such as paper dust to the maximum extent possible without causing a discharge. The less paper dust is generated, the lower the voltage value required to reduce the amount of charge of the paper dust to the maximum extent can be. Lowering the voltage value suppresses the filming level caused by additives such as calcium carbonate contained in the paper, thereby suppressing the deterioration of the developing roller 41 over time and extending the life of the developing roller 41. Therefore, for example, as shown in Table 3, the voltage value should be adjusted to be lower when a paper type that generates less paper dust is used.

[0065] Furthermore, in the above-described configuration example 4, lowering the voltage value suppresses the filming level caused by additives such as calcium carbonate contained in the paper, thereby suppressing the deterioration of the photoreceptor 1 over time and extending the lifespan of the photoreceptor 1. Therefore, in the above-described configuration example 3, the voltage value may be adjusted to be smaller when using paper types that generate less paper dust.

[0066] Table 4 below explains the difference in effects depending on the ratio (peripheral speed ratio) of the surface movement speed (peripheral speed) of the supply roller 42 to the surface movement speed (peripheral speed) of the developing roller 41.

[0067] [Table 4]

[0068] In Example 1, as in Configuration Example 1 described above, a conductive sheet is attached to the toner leakage prevention sheet 47 as a conductive part 47a, and a voltage of +300V relative to the surface potential (development bias) of the developing roller 41 is applied to the conductive sheet. The number of printed pages until white streaks appeared was then evaluated.

[0069] Example 2 is a configuration in which a PTFE sheet is attached to the toner leakage prevention sheet 47 as a contact charging part 47b, as in Configuration Example 2 described above. In Example 2, the peripheral speed ratio of the supply roller 42 to the developing roller 41 was changed at three levels, and the number of printed pages until white streaks appeared was evaluated.

[0070] Example 3 is a configuration that adds a removal brush 49 as a foreign matter removal means, as shown in Figure 5, to the configuration of Example 2, and the number of printed sheets until white streaks appear was evaluated.

[0071] For these Examples 1-3, as a comparative example, the number of printed sheets until white streaks appeared was evaluated for a configuration without a means for reducing the amount of charge.

[0072] In all three of Examples 1 to 3, it was confirmed that the number of printed sheets before white streaks appeared could be significantly increased compared to the comparative example without a means for reducing the amount of charge, and that the occurrence of white streaks was suppressed. In particular, by providing a removal brush 49 as a means for removing foreign matter from the supply roller 42, as in Example 3, the number of printed sheets before white streaks appeared could be extended to four times that of the comparative example.

[0073] Furthermore, in Example 2, the smaller the peripheral speed ratio of the supply roller 42 to the developing roller 41, the fewer prints were required before white streaks appeared. This is thought to be because, as the peripheral speed ratio decreases, the supply roller 42's ability to mechanically remove foreign matter from the developing roller 41 decreases, making it easier for foreign matter to be carried to the regulating blade 44 while still attached to the developing roller 41. Based on the results of Example 2, it is preferable to set the peripheral speed ratio to 1 or higher.

[0074] 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) using a supply rotating body (e.g., supply roller 42), thins the developer on the developer carrier using a layer thickness regulating member (e.g., regulating blade 44), develops the latent image on a latent image carrier (e.g., photoreceptor 1) in a developing region, and recovers the transfer residue toner on the latent image carrier, wherein the supply rotating body contacts the developer carrier to form a supply nip, and has charge reduction means for reducing the charge amount of foreign matter transported together with the transfer residue toner on a transport path (e.g., foreign matter transport path) through which the transfer residue toner on the latent image carrier is transported from a charged region where the surface of the latent image carrier is uniformly charged until it is recovered onto the developer carrier in the developing region and reaches the supply nip. 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 normally mechanically removed from the developer carrier at the supply nip between it and the supply rotating body, preventing it from being transported to the layer thickness regulating member. However, if the amount of charge of the foreign matter collected and adhering to the developer carrier is large, the electrostatic adhesion of the foreign matter to the surface of the developer carrier may be large, making it impossible to mechanically remove it by the supply rotating body. For example, foreign matter adhering to the surface of the latent image carrier after transfer may acquire a large charge due to discharge during the charging process when passing through the charged region. In such cases, the amount of charge of the foreign matter becomes particularly large, resulting in a high electrostatic adhesion force to the surface of the developer carrier. In particular, if the supply nip is configured to apply a supply bias to electrostatically move the developer from the supply rotating body side to the developer carrier side, foreign matter that is heavily charged with the same polarity as the developer will have an increased electrostatic adhesion force to the surface of the developer carrier within the supply nip. Furthermore, if the electrostatic adhesion of foreign matter to the surface of the developer carrier is high, the foreign matter on the developer carrier cannot be mechanically removed by the supply rotating body and is transported to the layer thickness regulating member, which can lead to image defects. In this embodiment, the charge reduction means can reduce the charge of foreign matter along the transport path in which the transfer residue toner on the latent image carrier is transported from the charging region to the developing region where it is recovered onto the developer carrier and then transported to the supply nip. As a result, even foreign matter with a large charge, such as foreign matter that has acquired a large charge when passing through the charging region, will have its charge reduced before reaching the supply nip, making it possible to remove the foreign matter by the supply rotating body. This makes it possible to suppress the transport of highly charged foreign matter to the layer thickness regulating member, even in situations where highly charged foreign matter may be generated, thereby suppressing the occurrence of image defects such as white streaks.

[0075] [Second aspect] The second embodiment is characterized in that, in the first embodiment, the charge reduction means applies a voltage to a contact member (for example, a toner leak prevention sheet 47, a contact member 51, or a contact roller 52) that comes into contact with the foreign object to reduce the charge of the foreign object. According to this, the amount of charge on a foreign object can be reduced by applying a voltage to a contact member that comes into contact with the foreign object.

[0076] [Third aspect] The third aspect is characterized in that, in the first aspect, the charge reduction means reduces the charge of the foreign object based on the relationship of the triboelectric series with respect to the foreign object at the contact member (for example, toner leak prevention sheet 47, contact member 51, contact roller 52) that comes into contact with the foreign object. According to this method, the amount of charge on foreign objects can be reduced without applying voltage.

[0077] [Fourth aspect] The fourth embodiment is characterized in that, in any of the first to third embodiments, the charge reduction means reduces the charge amount of the foreign matter in the portion of the transfer path from the charging region to the developing region. According to this, there is no need to place a means for reducing the amount of charge inside the developing device, so it is possible to use the existing configuration of the developing device as is.

[0078] [Fifth aspect] The fifth embodiment is characterized in that, in any of the first to third embodiments, the charge reduction means reduces the charge amount of the foreign matter in the portion of the transfer path from the developing area to the supply nip. According to this, there is no need to place charge reduction means on the latent image carrier, so there is no concern that the charge reduction means will disturb the latent image on the latent image carrier.

[0079] [Sixth aspect] The sixth embodiment is characterized in that, in the fifth embodiment, the charge reduction means brings a developer leak prevention member (for example, a toner leak prevention sheet 47) that is arranged to block the space between the developer carrier and the inner wall of the developer storage section in the transfer path portion into contact with the foreign matter, thereby reducing the charge amount of the foreign matter. According to this, the amount of charge of foreign matter can be reduced by utilizing existing developer leak prevention components.

[0080] [Seventh aspect] The seventh embodiment is characterized in that, in the fifth embodiment, the charge reduction means reduces the charge amount of foreign matter in the transport path portion from the contact position where a developer leak prevention member (e.g., toner leak prevention sheet 47), which is arranged to close the space between the developer carrier and the inner wall of the developer storage portion, contacts the surface of the developer carrier to the supply nip. According to this, the amount of charge from foreign matter can be reduced without changing the configuration of existing developer leak prevention components.

[0081] [8th aspect] The eighth aspect is characterized in that, in any of the first to seventh aspects, the invention has foreign matter removal means (for example, a removal brush 49, a removal Mylar 50) for removing the foreign matter from the supply rotating body. According to this, it is possible to prevent foreign matter adhering to the supply rotating body from being transported back to the supply nip while still adhering to the supply rotating body, thereby preventing foreign matter from obstructing the supply of developer to the developer carrier at the supply nip.

[0082] [Ninth aspect] The ninth aspect is characterized in that, in the eighth aspect, the foreign matter removal means removes foreign matter on the supply rotating body into the developer storage section by contacting a contact member (for example, a removal brush 49, a removal Mylar 50) that contacts the surface of the supply rotating body. According to this, foreign matter can be removed from the supply rotating body with a simple configuration.

[0083] [Tenth aspect] The tenth embodiment is characterized in that, in any of the first to ninth embodiments, the supply rotating body is driven to rotate such that, at the portion facing the developer carrier, its surface movement direction is opposite to that of the developer carrier, and the ratio of the surface movement speed of the supply rotating body to the surface movement speed of the developer carrier (e.g., peripheral speed ratio) is 1 or more. 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.

[0084] [Aspect 11] The 11th embodiment is characterized in that, in any of the first to tenth embodiments, it has a stirring member 54 for stirring the developer in the developer container. This prevents foreign matter that has detached from the supply rotating body and been incorporated into the developer in the developer container from moving to the layer thickness regulating member, thereby reducing the accumulation and aggregation of foreign matter near the layer thickness regulating member and suppressing image defects.

[0085] [Twelfth aspect] The twelfth embodiment is a cleanerless image forming apparatus in which residual toner on a latent image carrier (e.g., a photoreceptor 1) is recovered by a developing apparatus 4, characterized in that the developing apparatus is one of the developing apparatuses of the first to eleventh embodiments. According to this, it is possible to provide an image forming apparatus that can suppress the occurrence of image defects caused by foreign matter such as paper dust getting trapped between the developer carrier and the layer thickness regulating member, even in situations where foreign matter with a large amount of charge may be generated.

[0086] [The 13th aspect] The 13th aspect is characterized in that, in the 12th aspect, the charge reduction means in the developing apparatus reduces the charge of the foreign object by applying a voltage to a contact member that comes into contact with the foreign object, and has a voltage control means (for example, a control unit 100) that changes the voltage value applied to the contact member according to at least one of the following conditions: the operating environment of the apparatus, the cumulative number of images formed, and the type of recording material on which the image is formed. According to this, the amount of charge of foreign matter can be appropriately reduced even if the device operating environment, the cumulative number of images formed, or the type of recording material on which the image is formed changes. [Explanation of symbols]

[0087] 1: Photoreceptor 2: Charger 3: Optical writing device 4: Developing equipment 5: Transfer device 6: Static eliminator 10: Image forming apparatus 41: Developing roller 42: Supply roller 43: Developing Case 44: Regulatory Blade 45: Agitator 46: Toner storage compartment 47: Toner leak prevention sheet 47a: Conductive part 47b: Contact charging part 48,53:Power supply 49: Removal brush 50: Remove Mylar 51: Contact member 52: Contact roller 54: Stirring member 100: Control Unit [Prior art documents] [Patent Documents]

[0088] [Patent Document 1] Japanese Patent Publication No. 2023-075865

Claims

1. A developing apparatus that supplies developer from a developer container onto a developer carrier using a rotating supply body, thins the developer on the developer carrier using a layer thickness regulating member, develops the latent image on the latent image carrier in a developing area, and recovers the transfer residue toner on the latent image carrier, The supply rotating body contacts the developer carrier to form a supply nip. A developing apparatus characterized in that it has a charge reduction means for reducing the charge amount of foreign matter transported together with the transfer residue toner on the latent image carrier along a transport path from a charged region where the surface of the latent image carrier is uniformly charged, to the developing region where it is recovered onto the developer carrier and reaches the supply nip.

2. In the developing apparatus according to claim 1, The charging amount reduction means is characterized by applying a voltage to a contact member that comes into contact with the foreign object to reduce the amount of charge on the foreign object.

3. In the developing apparatus according to claim 1, The charging amount reduction means is characterized by reducing the amount of charge on the foreign object based on the relationship of the triboelectric series with respect to the foreign object at a contact member that comes into contact with the foreign object.

4. In the developing apparatus according to any one of claims 1 to 3, The charging amount reduction means is characterized by reducing the charging amount of the foreign matter in the portion of the transfer path from the charging area to the developing area.

5. In the developing apparatus according to any one of claims 1 to 3, The charging amount reduction means is characterized by reducing the charging amount of the foreign matter in the portion of the transfer path from the developing area to the supply nip.

6. In the developing apparatus according to claim 5, The charging amount reduction means is characterized by bringing a developer leak prevention member, which is positioned to seal the space between the developer carrier and the inner wall of the developer storage section in the transfer path portion, into contact with the foreign matter to reduce the amount of charge on the foreign matter.

7. In the developing apparatus according to claim 5, The charging amount reduction means is characterized in that it reduces the amount of charge of foreign matter in the transfer path portion from the contact position where a developer leak prevention member, which is positioned to close the space between the developer carrier and the inner wall of the developer storage portion, contacts the surface of the developer carrier to the supply nip.

8. In the developing apparatus according to any one of claims 1 to 3, A developing apparatus characterized by having a foreign matter removal means for removing the foreign matter from the supply rotating body.

9. In the developing apparatus according to claim 8, The developing apparatus is characterized in that the foreign matter removal means removes foreign matter on the supply rotating body into the developer storage section by a contact member that contacts the surface of the supply rotating body.

10. In the developing apparatus according to any one of claims 1 to 3, The supply rotating body is driven to rotate in a direction opposite to the surface movement direction of the developer carrier at the portion facing the developer carrier, 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 1 or more.

11. In the developing apparatus according to any one of claims 1 to 3, A developing apparatus characterized by having a stirring member for stirring the developer in the developer container.

12. 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 any one of claims 1 to 3 is used as the developing apparatus.

13. In the image forming apparatus according to claim 12, The charge reduction means in the developing apparatus applies a voltage to a contact member that comes into contact with the foreign object to reduce the charge of the foreign object. An image forming apparatus characterized by having a voltage control means for changing the voltage value applied to the contact member according to at least one of the following conditions: the operating environment of the apparatus, the cumulative number of images formed, and the type of recording material on which the image is formed.

Images