Image forming apparatus

Abstract

An image forming apparatus is disclosed. An image forming apparatus includes an image bearing member rotatable around a rotation shaft extending in an axial direction, a charging member, a holding portion holding charged to a predetermined polarity, a developing member, a transfer portion, an electrostatic elimination portion, and a collection member. In the axial direction, when A is an elimination width at which the elimination portion discharges electricity to a surface of the image bearing member, B is an effective charging width at which the charging member charges the surface, and C is a collection contact width at which the collection member contacts the surface, a formula A < B < C is satisfied. A surface potential of the surface in an area outside the effective charging width, inside the collection contact width, and in contact with the collection member in the axial direction is a first potential greater than 0 V in a same polarity direction as the predetermined polarity.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus for forming images on a sheet. Background Technology

[0002] Image forming apparatuses, such as printers with electrophotographic processing, form toner images by developing an electrostatic latent image formed on a photosensitive drum using toner in a developing unit. The toner image is then transferred onto a sheet in a transfer section. After the transfer, deposits such as paper dust or filler generated by the sheet may sometimes accumulate on the photosensitive drum.

[0003] Conventionally, Japanese Patent Application Publication (JP-A) 2007-279431 describes an image forming apparatus that provides a cleaning device to remove residual toner and deposits from a photosensitive drum. The cleaning device includes a cleaning brush mounted to contact the surface of the photosensitive drum. The cleaning brush removes residual toner from the photosensitive drum by applying a bias voltage with a polarity opposite to that of the residual toner. Additionally, the cleaning brush removes deposits from the photosensitive drum by scraping.

[0004] The cleaning brush described in JP-A2007-279431 retains the toner removed from the photosensitive drum for a period of time, so that in some cases, the toner may spread out in the image forming apparatus. Summary of the Invention

[0005] Therefore, the object of the present invention is to provide an image forming apparatus that reduces toner dispersion.

[0006] According to an aspect of the present invention, there is provided an image forming apparatus, comprising: a rotatable image bearing member, wherein the rotatable image bearing member is capable of rotating around a rotating shaft extending in the axial direction of the rotatable image bearing member; a charging member, wherein the charging member is configured to form a charging portion between the charging member and the image bearing member, and charges a surface of the image bearing member; an accommodating portion, wherein the accommodating portion is configured to accommodate toner charged to a predetermined polarity; a developing member, wherein the developing member is configured to form a developing portion between the developing member and the image bearing member, and forms a toner image on the image bearing member by supplying the toner to the developing portion of the image; a transfer portion, wherein the transfer portion is in contact with the surface of the image bearing member and is configured to transfer the toner image; a charge eliminating portion, wherein the charge eliminating portion is configured to eliminate charges on the surface of the image bearing member; and a collecting member, wherein the collecting member is configured to be in contact with the surface of the image bearing member to collect deposits deposited on the surface of the image bearing member, wherein, with respect to the axial direction, when A is defined as a charge eliminating width over which the charge eliminating portion is capable of eliminating charges on the surface, B is defined as an effective charging width over which the charging member is capable of charging the surface, and C is defined as a collecting contact width over which the collecting member is in contact with the surface, the following formula is satisfied: A<B<C, and wherein, with respect to the axial direction, a surface potential of the surface in a region located outside the effective charging width, inside the collecting contact width and in contact with the collecting member is a first potential greater than 0V in a polarity direction same as the predetermined polarity.

[0007] Further, according to one aspect of the present invention, there is provided an image forming apparatus, comprising: a rotatable image bearing member capable of rotating around a rotation shaft extending in an axial direction of the rotatable image bearing member; a charging member configured to form a charging portion between itself and the image bearing member, and charge a surface of the image bearing member; an accommodating portion configured to accommodate toner charged to a predetermined polarity; a developing member configured to form a developing portion between itself and the image bearing member, and form a toner image on the image bearing member by supplying the toner to the developing portion; a transfer portion that contacts the surface of the image bearing member and is configured to transfer the toner image; a collecting member configured to contact the surface of the image bearing member to collect deposits deposited on the surface of the image bearing member, and a cleaning member configured to contact the surface of the image bearing member to remove the deposits, wherein with respect to the axial direction, when B is defined as an effective charging width over which the charging member can charge the surface, C is defined as a collecting contact width over which the collecting member contacts the surface, and D is defined as a cleaning contact width over which the cleaning member contacts the surface, the following formula is satisfied: B<D<C, and wherein with respect to the axial direction, a surface potential of the surface in a region that is located outside the cleaning contact width, inside the collecting contact width and in contact with the collecting member is a first potential greater than 0V in a polarity direction same as the predetermined polarity.

[0008] In addition, according to one aspect of the present invention, there is provided an image forming apparatus, comprising: a rotatable image bearing member capable of rotating around a rotation shaft extending in an axial direction thereof; a charging member configured to form a charging portion between itself and the image bearing member, and charge a surface of the image bearing member; an accommodating portion configured to accommodate toner charged to a predetermined polarity; a developing member configured to form a developing portion between itself and the image bearing member, and form a toner image on the image bearing member by supplying the toner to the developing portion; a charge eliminating portion configured to eliminate charges on the surface of the image bearing member; a transfer portion that contacts the surface of the image bearing member and is configured to transfer the toner image; and a collecting member configured to contact the surface of the image bearing member to collect deposits deposited on the surface of the image bearing member, wherein, with respect to the axial direction, when A is defined as a charge eliminating width over which the charge eliminating portion can eliminate charges on said surface, B is defined as an effective charging width over which the charging member can charge said surface, C is defined as a collecting contact width over which the collecting member contacts said surface, and E is defined as a width over which the surface of the developing member is covered with the toner, the following formula is satisfied: E<A<B<C, and wherein, with respect to the axial direction, a surface potential of said surface in a region outside the effective charging width, inside the collecting contact width, and in contact with the collecting member is a first potential greater than 0V in a same polarity direction as said predetermined polarity.

[0009] Other features of the present invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings. Brief Description of the Drawings

[0010] Figure 1 is a schematic view of the image forming apparatus according to the first embodiment.

[0011] Figure 2 is a view of the brush member.

[0012] Figure 3 is a view illustrating the contact width of a transfer roller, the charge eliminating width of a charge eliminating unit, the effective charging width of a charging roller, and the contact width of a cleaning brush member.

[0013] Figure 4 is a view illustrating the relationship of the surface potential of a photosensitive drum in a region contacted by the brush member.

[0014] Figure 5 is a view illustrating the relationship of the surface potential of a photosensitive drum in a region contacted by the brush member in the second embodiment.

[0015] Figure 6 This is a diagram of the cleaning component in the third embodiment.

[0016] Figure 7 This is a diagram showing the effective charging width of the charging roller, the contact width of the brush component, and the contact width of the cleaning component.

[0017] Figure 8 It is a diagram illustrating the relationship of the surface potential of the photosensitive drum in the area contacted by the brush components.

[0018] Figure 9 It is a diagram showing the contact width of the transfer roller, the charge elimination width of the charge elimination unit, the effective charging width of the charging roller, the contact width of the cleaning brush component, and the toner coating width of the developing roller.

[0019] Figure 10 This is a diagram illustrating the relationship of the surface potential of the photosensitive drum in the area where the brush components are in contact. Detailed Implementation

[0020] Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings. It should be noted that the size, material, shape, and relative position of the constituent elements shown in this embodiment may vary as the configuration of the apparatus and various conditions under which the present invention is applied, and are not limited to the disclosed exemplary embodiments. Furthermore, the image forming apparatus uses recording sheets S, including ordinary or thick paper, plastic film sheets for overhead projectors, sheets of special shapes such as envelopes or index sheets, and various types of sheets of different materials such as cloth.

[0021] [Overall Composition]

[0022] First, a first embodiment of the present invention will be described. According to the first embodiment, the image forming apparatus 100 is a monochrome laser beam printer having an electrophotographic method. In the main body M of the image forming apparatus 100, as Figure 1 As shown, a processing unit 9 with a direct transfer system is provided. The processing unit 9 includes a photosensitive drum 1, a charging roller 2 located around the photosensitive drum 1, a developing unit 20, a charge removal unit 11, and a brush member 12. Additionally, the main body M includes a scanner unit 10 that emits a laser and forms an electrostatic latent image on the photosensitive drum 1, and a transfer roller 13. The transfer roller 13 forms a transfer clamping portion N1 between the photosensitive drums 1 and transfers the toner image onto the recording sheet S within the transfer clamping portion N1. The transfer roller 13 contacts the surface 1a of the photosensitive drum 1 and, through the photosensitive drum 1 and the transfer roller 13 clamping and feeding the recording sheet S in the transfer clamping portion N1, transfers the toner image on the photosensitive drum 1 onto the recording sheet S.

[0023] Note that in this embodiment, the processing unit 9 is configured to be detachable from the main body M; however, it is not limited thereto. For example, the processing unit may be configured not to be detachable from the main body M.

[0024] The photosensitive drum 1, which serves as the image carrier, is a photosensitive component shaped like a cylinder, and can be positioned in the axial direction J1 (see...). Figure 3 The photosensitive drum 1 rotates around a rotating axis CP extending from the image forming apparatus 100. In this embodiment, the photosensitive drum 1 comprises a photosensitive layer formed of an organic photosensitive component having a charge-carrying capacity on a drum-shaped substrate made of aluminum. More specifically, the photosensitive drum 1 is a rigid body constructed by dip-coating the outer peripheral surface of a 24 mm diameter aluminum cylinder in the following order: a resistive layer, a base layer, and a photosensitive layer comprising a charge-generating layer and a charge-transfer layer. The charge-transfer layer is 22 μm thick. The photosensitive drum 1 is driven by a drive motor to rotate at a predetermined rotational speed around the rotating axis CP in the direction of arrow L. Because the rotational speed of the photosensitive drum controls the image forming speed in the image forming apparatus 100, the rotational speed of the photosensitive drum is referred to as the processing speed.

[0025] The charging roller 2, serving as a charging component, contacts the photosensitive drum 1 at a predetermined pressure, forming a charging section N2. Furthermore, by applying a charging voltage (DC voltage) from a charging voltage application circuit (not shown), the surface 1a of the photosensitive drum 1 is uniformly charged to a predetermined potential. In this embodiment, a charging voltage of -1400V is applied to the charging roller 2 to set the surface potential (pre-exposure potential VD) of the photosensitive drum 1 to -800V. That is, the charging roller 2 charges the photosensitive drum 1 with the pre-exposure potential VD, which is the fourth potential and has the same negative polarity as the toner. The charging roller 2, comprising a 6mm diameter core metal, a polyepoxychloropropylene rubber base layer, and a polyurethane surface layer, is configured with an outer diameter of 12mm. Additionally, the resistance of the charging roller 2 is less than 1×10⁻⁶. 6 The hardness of the charging roller 2 is 70 degrees, measured using an MD-1 rubber hardness tester. Note that the charging voltage in this embodiment is not limited to DC voltage, but can be a voltage that combines DC and AC voltages.

[0026] The scanner unit 10 scans and exposes the surface 1a of the photosensitive drum 1 by emitting a laser corresponding to image information input from an external device onto the photosensitive drum 1 using a faceted mirror. This exposure forms an electrostatic latent image corresponding to the image information on the surface 1a of the photosensitive drum 1. The scanner unit 10 is a semiconductor laser that emits an 800nm ​​wavelength laser, and the amount of light can be varied. Note that the scanner unit is not limited to a laser scanning device, but can, for example, employ an LED exposure device including an LED array with multiple LEDs arranged along the longitudinal direction of the photosensitive drum 1.

[0027] The developing unit 20 includes a developing container 8, which serves as the frame body of the developing unit 20, a developing roller 4, and a supply roller 5 for supplying toner to the developing roller 4. Inside the developing container 8, which serves as the holding part, a toner holding chamber 8a for storing toner (developer) and a developing chamber 8b for storing the developing roller 4 are formed. The developing roller 4 and the supply roller 5 are rotatably held by the developing container 8. In addition, the developing roller 4 is located at the opening of the developing container 8, facing the photosensitive drum 1. The supply roller 5 is rotatably in contact with the developing roller 4, and the toner stored in the developing container 8 is applied to the surface 1a of the developing roller 4 through the supply roller 5.

[0028] The developing unit 20 uses a contact developing method, whereby the toner image held by the developing roller 4 comes into contact with the photosensitive drum 1 in the developing section 21 facing the developing roller 4. In other words, the developing roller 4, as a developing member, forms the developing section 21 between itself and the photosensitive drum 1. A developing voltage, which is a DC voltage, is applied to the developing roller 4 from a developing voltage application section (not shown). Under the developing voltage, the toner carried by the developing roller 4 is transferred to the surface 1a of the photosensitive drum 1 according to the potential distribution of the surface 1a, and the electrostatic latent image is developed into a toner image. Note that this embodiment employs a reflective developing method, whereby, in order to form a toner image, the toner is adhered to a surface area of ​​the photosensitive drum 1 whose charging voltage is reduced by exposure in the exposure process after charging in the charging process.

[0029] Furthermore, the toner used in this embodiment is, for example, a polymeric toner with a normal negative polarity and a particle size of 6 μm. Additionally, the toner in this embodiment does not include magnetic components; instead, it is a non-magnetic single-component developer primarily carried by the developing roller 4 using intermolecular forces or electrostatic forces (image forces). Note that single-component developers including magnetic components can also be used. In addition to toner particles, in some cases, single-component developers include additives (e.g., wax or silica particles) to adjust the toner's mobility or charging capability. Furthermore, a two-component developer consisting of a non-magnetic toner and a magnetic carrier can be used as the developer. When using a magnetic developer, a cylindrical developing sleeve, for example, with an internal magnet, is used as the developer carrier. Moreover, the developing apparatus 20 can utilize a non-contact developing method that provides a predetermined gap between itself and the photosensitive drum 1.

[0030] The developing roller 4 has a 6mm core metal coated with silicone rubber as a base layer and polyurethane rubber as an outer layer, resulting in an outer diameter of 15mm. The resistivity of the developing roller 4 is 1×10⁻⁶. 4 Ω and 1×10 12 The resistance is between Ω. Supply roller 5 is a conductive elastic sponge roller made with a foam layer on the outer periphery of a 6mm core metal. The resistance value of supply roller 5 is between 1×10 Ω. 4 Ω and 1×108 The hardness is between Ω and 200gf. Note that the hardness value of the supply roller 5 is measured under a load of 1mm when a 50mm long plate is pressed down from the surface of the supply roller 5.

[0031] A stirring member 7 is provided in the developing container 8. The stirring member 7 is rotated by a drive motor to stir the toner in the developing container 8 and deliver the toner to the developing roller 4 and the supply roller 5. In addition, the stirring member 7 is assigned the task of circulating and equalizing the toner that is not used in development and is scraped off from the developing roller in the developing container.

[0032] A developing blade 6 is provided in the opening of the developing container 8, where the developing roller 4 is located, to limit the amount of toner carried by the developing roller 4. The toner supplied to the surface of the developing roller 4 is uniformly and thinly layered as it passes the portion of the developing blade 6 facing the developing roller 4 through the rotation of the developing roller 4, and becomes negatively charged due to frictional charging.

[0033] The developing blade 6 is a 0.1 mm thick SUS metal plate. The developing blade 6 is positioned relative to and in contact with the developing roller 4 on the downstream side of the developing roller 4 in the direction of rotation, with its free end located theredown. In this embodiment, the developing blade 6 is made of an SUS metal plate whose edges are machined and cut from the contact side with the developing roller 4. The edges of the developing blade 6 are bent along the cutting direction by the machining cut.

[0034] The transfer roller 13, serving as the transfer section, includes an ion-conductive sponge substrate layer covering a 6mm diameter core metal, resulting in an outer diameter of 15mm. At 22°C, the resistance of the transfer roller 13 is 4 × 10⁻⁶. 7 Ω, and its hardness is 30 degrees as measured by an Asker C hardness tester manufactured by Asker Kobunshi Keiki Co., Ltd.

[0035] When the image forming apparatus receives a command to form an image, it begins image forming processing based on image information input from an external device such as a computer connected to the image forming apparatus 100. At the start of the image forming processing, the photosensitive drum 1 is driven by a power supply (not shown) to move at a predetermined speed... Figure 1 The direction of arrow L in the diagram is rotated. According to this embodiment, the processing speed of the photosensitive drum 1 is 140 rpm.

[0036] In the processing unit 9, a charge removal unit 11 is provided downstream of the transfer clamping section N1 in the rotational direction (arrow L direction) relative to the photosensitive drum 1 and upstream of the charging section N2 to remove static charge from the photosensitive drum 1. More specifically, the charge removal unit 11, as the removal section, is located between the brush member 12 and the charging roller 2 in the rotational direction relative to the photosensitive drum 1. The charge removal unit 11 discharges the surface potential of the photosensitive drum 1 before it reaches the charging section N2, thereby generating a stable discharge at the charging section N2.

[0037] Then, the charging roller 2 charges the rotating photosensitive drum 1, making its surface potential (potential VD before pre-exposure) uniformly -800V. The scanner unit 10 emits a laser onto the photosensitive drum 1 based on the input image information. Therefore, an electrostatic latent image is formed on the uniformly charged surface 1a of the photosensitive drum 1. In this embodiment, since the potential VL of the photosensitive drum 1 after exposure is -100V, the scanner unit 10 charges at 0.45μJ / cm². 2 The amount of light emitted by the laser.

[0038] At this time, a toner layer with a designed polarity is formed on the surface of the developing roller 4. Then, by applying a developing voltage to the developing roller 4 from the developing voltage application section (not shown in the figure), the electrostatic latent image on the photosensitive drum 1 is developed at the developing section 21, and a toner image is formed on the photosensitive drum 1. In this embodiment, the developing voltage applied to the developing roller 4 is -400V.

[0039] Simultaneously with the image forming process described above, the recording sheet S stored in the bottom portion of the image forming apparatus is fed. At the precise timing of the toner image formed on the photosensitive drum 1 reaching the transfer clamping section N1, the recording sheet S is fed into the transfer clamping section N1. Furthermore, at the precise timing of the toner image formed on the photosensitive drum 1 reaching the transfer clamping section N1, a transfer voltage, which is a direct current, is applied to the transfer roller 13 from a transfer voltage application circuit (not shown in the figure). Therefore, the toner image carried by the photosensitive drum 1 is transferred onto the recording sheet S passing through the transfer clamping section N1. In this embodiment, the transfer voltage applied to the transfer roller 13 is +1500V.

[0040] Recording material S, with a toner image transferred onto it, is fed to fixing unit 14. Fixing unit 14 is a thermal fixing method that performs image fixing processing by heating and melting the toner on the recording sheet S. Fixing unit 14 includes a fixing film 14a, a fixing heater such as a ceramic heater for heating the fixing film 14a, and a pressure roller 14b pressing on the fixing film 14a. As the recording sheet S passes through the clamping portion between the fixing film 14a and the pressure roller 14b, the toner image is heated and pressurized. As a result, the toner particles are melted and adhered, and then the toner image is fixed onto the recording sheet S. After passing through fixing unit 14, the recording sheet S is discharged outside the image forming apparatus 100 via a pair of discharge rollers (not shown).

[0041] [Collect leftover toner from the transfer process]

[0042] The following process removes residual toner from the photosensitive drum 1 that was not transferred to the recording film S. After the transfer process, the surface potential of the photosensitive drum 1 decreases due to the transfer voltage applied as the photosensitive drum 1 passes through the transfer clamping section N1. In this embodiment, the surface potential of the photosensitive drum 1 after the transfer process is -150V. After the transfer process, the residual potential of the photosensitive drum 1 decreases to 0V by using the charge elimination unit 11 and rotating the photosensitive drum 1 toward the charging section N2. The residual toner includes a mixture of positively charged toner without sufficient charge and negatively charged toner. The charge elimination unit 11 reduces the charge on the photosensitive drum 1 after the transfer process and uniformly discharges the residual toner through the charging roller 2, causing it to become negatively charged. As the photosensitive drum 1 rotates, the residual toner, which is again negatively charged in the charging section N2, reaches the developing section 21. After passing through the charging unit N2, the image is exposed by the scanner unit 10 while the remaining toner from the transfer is still adhered to the surface area of ​​the photosensitive drum 1, forming an electrostatic latent image.

[0043] Here, the movement of the remaining transfer toner reaching the developing section 21 is described separately for the exposed and unexposed sections of the photosensitive drum 1. The remaining transfer toner adhering to the unexposed section of the photosensitive drum 1 is transferred to the developing roller 4 in the developing section 21 by the potential difference between the pre-exposure potential VD of the unexposed section and the developing voltage, and is then collected in the developing container 8. Because the normal charged polarity of the toner is negative, the developing voltage applied to the developing roller 4 is relatively positive relative to the pre-exposure potential VD of the unexposed section. Note that the toner collected in the developing container 8 is mixed and dispersed with other toners in the developing container 8 by the mixing member 7, and then repeatedly used for the developing process by being carried by the developing roller 4.

[0044] On the other hand, the residual toner adhering to the exposure section of the photosensitive drum 1 is not transferred to the developing roller 4 and remains on the surface of the drum. This is because when the normal charged polarity of the toner is negative, the developing voltage applied to the developing roller 4 is more negative relative to the pre-exposure potential VD of the exposure section. The residual toner remaining on the surface 1a of the photosensitive drum, along with other toner that has moved from the developing roller 4 to the exposure section, is carried by the photosensitive drum 1 to the transfer clamping section N1, where it is transferred onto the recording sheet S.

[0045] As described above, in this embodiment, the processing unit 9 is configured as a cleaner-free device that collects residual transfer toner in the developing unit 20 for reuse. The cleaner-free structure of the processing unit 9 allows the image forming apparatus 100 to be more compact because it eliminates the need for space in a collection container for collecting residual transfer toner, and it also reduces printing costs by reusing the residual transfer toner.

[0046] [Brush Component]

[0047] like Figure 1 and Figure 2 As shown, a brush member 12 is provided in the processing unit 9, located downstream of the transfer clamping part N1 and upstream of the charge elimination unit 11, relative to the rotational direction (direction of arrow L) of the photosensitive drum 1. The brush member 12, serving as a collecting member, is positioned to contact the photosensitive drum 1 and removes adhering material (hereinafter simply referred to as paper dust) from the photosensitive drum 1 by wiping the surface 1a of the photosensitive drum 1 as it rotates. The adhering material described above is a material such as paper dust or filler generated by the recording sheet S.

[0048] The brush component 12 includes a conductive base fabric 12b and a bundle of wires 12a made of conductive nylon. The bundle of wires 12a is woven into the base fabric 12b. When the density of the bundle of wires 12a is high and / or the amount of ink penetrating the brush component 12 onto the photosensitive drum 1 is large, the permeability of the toner (including residual toner from transfer) decreases, and toner accumulates on the brush component 12. Therefore, the configuration of the brush component 12 should be selected considering both toner permeability and the ability to collect paper dust.

[0049] In this embodiment, each wire in a bundle of wires 12a has a fineness of 2 denier and a wire density of 170 kF / inch. 2Without any external force bending the thread 12a, the distance L1 from the base fabric 12b to the cut edge of the thread 12a is 6.5 mm. Furthermore, in the processing unit 9, the brush member 12 is positioned such that the edge of the thread 12a is pressed downwards onto the photosensitive drum 1 by fixing the base fabric 12b to the holding member (not shown). In this case, the distance L2 from the base fabric 12b to the photosensitive drum 1 is 5.5 mm. The difference L3 between distance 1 and distance 2 is defined as the intrusion amount, and in this embodiment, the intrusion amount L3 is 1.0 mm.

[0050] The configuration described above enables the brush member 12 to collect paper dust while inhibiting toner buildup on the brush member 12. However, during long-term use, a small amount of toner accumulated on the brush can escape from the brush member 12 in the axial direction J1 (see reference). Figure 3 The toner spreads from the ends of the brush member 12 in the axial direction J1, and in some cases contaminates the equipment. Therefore, in this embodiment, the positional and potential relationships of the components of the brush member 12 in the axial direction J1 are configured to satisfy the conditions described below in order to suppress the toner spreading from the ends of the brush member 12 in the axial direction J1.

[0051] [Positional relationship of each component in the axial direction]

[0052] Next, we will utilize Figure 3 Each component of the processing unit 9 is described; in detail, the positional relationship of the photosensitive drum 1, charging roller 2, charge elimination unit 11, brush component 12, and transfer roller 13 in the axial direction J1 is described. The charging roller 2, transfer roller 13, charge elimination unit 11, and brush component 12 are arranged symmetrically with respect to the center of the photosensitive drum 1 in the axial direction J1. Figure 3 This diagram illustrates the charge elimination width A of the charge elimination unit 11, the effective charging width B of the charging roller 2, the contact width C of the brush component 12, and the contact width F of the transfer roller 13. Figure 3 As shown, the charge elimination width A is the width at which the charge elimination unit 11 in the axial direction J1 can reduce the charge on the surface 1a of the photosensitive drum 1. The contact width F, which is the transfer contact width, is the width at which the transfer roller 13 in the axial direction J1 can contact the surface 1a of the photosensitive drum 1 and transfer the toner image formed on the photosensitive drum 1. The effective charging width B is the width at which the charging roller 2 in the axial direction J1 can charge the surface 1a of the photosensitive drum 1 at the charging section N2. The contact width C, which is the collection contact width, is the width at which the brush member 12 can contact the surface 1a of the photosensitive drum 1 and remove paper dust from the photosensitive drum 1.

[0053] Due to discharge from the transfer roller 13 and / or injection charging when passing through the transfer nip N1, the potential of the surface of the photosensitive drum 1 corresponding to the contact width F with the transfer roller 13 is affected in the opposite polarity direction. This is because the transfer roller 13 is applied with a transfer voltage having a polarity opposite to that of the toner. When this effect is repeated, the surface potential of the photosensitive drum 1 corresponding to the contact width F gets closer to the transfer voltage and is charged with the opposite polarity to the toner. When the contact width F of the photosensitive drum 1 contacts the end of the effective charging width B through the charging roller 2, discharge becomes active in the contact area, so drum leakage may occur. As a result, toner is developed on the area where leakage occurs, and an image defect unexpectedly occurs. In order to prevent drum leakage, it is necessary to configure the contact width F to be shorter than the effective charging width B of the charging roller 2 (F<B).

[0054] In addition, the following situation is considered: the charging roller 2 and the charge eliminating unit 11 are positioned such that the end of the charge eliminating width A of the charge eliminating unit 11 and the end of the effective charging width B overlap in the axial direction J1. In this case, at the end of the effective charging width B, discharge of the photosensitive drum becomes active, the photosensitive drum 1 is consumed at an accelerated rate, and drum leakage may occur. Furthermore, the area where residual transfer toner remains needs to be decharged. Therefore, in this embodiment, the charge eliminating width A of the charge eliminating unit 11 is configured to be wider than the contact width F of the transfer roller 13 and shorter than the effective charging width B of the charging roller 2 (F<A<B) in the axial direction J1. In other words, in the axial direction J1, both ends of the charge eliminating unit 11 are located outside the two ends of the transfer roller 13 and inside the two ends of the charging roller 2.

[0055] The contact width F of the transfer roller 13 is an area where more paper dust and filler are generated on the recording sheet S. In addition, when paper dust adheres to the surface 1a of the photosensitive drum 1 on the effective charging width B of the charging roller 2, since the area with adhering paper dust is not sufficiently charged by the charging roller 2, a speckled defective image may occur. Therefore, when properly removing paper dust from the surface 1a of the photosensitive drum 1 in the area of the effective charging width B, the contact width C needs to be configured to be wider than the effective charging width B (B<C).

[0056] As described above, the relationship among the charge eliminating width A, the effective charging width B and the contact width C is A<B<C. It should be noted that, in this embodiment, the charge eliminating width A is 220 mm, the effective charging width B is 230 mm, and the contact width C is 240 mm, but they are not limited as long as the above relationship is satisfied.

[0057] When A<B<C, that is, specifically when F<A<B<C, there are a region R11, a region R12 and a region R13 on the photosensitive drum 1. The region R11 is in contact with the brush member 12, but is not charged by the charging roller 2 or the transfer roller 13. In other words, the region R11 is located outside the effective charging width B in the axial direction J1, inside the contact width C, and is also at a position in contact with the brush member 12. The region R12 is in contact with the brush member 12 and charged by the charging roller 2, but is not in contact with the transfer roller 13. In other words, the region R12 is located outside the contact width F in the axial direction J1, inside the effective charging width B, and is also at a position in contact with the brush member 12. The region R13 is in contact with the brush member 12, and charged by the charging roller 2 and the transfer roller 13. In other words, the region R13 is located inside the contact width F in the axial direction J1, and is also in contact with the brush member 12.

[0058] [Surface Potential in Region in Contact with Brush Member]

[0059] Next, the Figure 4 will be used to describe the surface potential of the photosensitive drum in the region in contact with the brush member 12. Figure 4 is a diagram illustrating the relationship of the surface potential of the photosensitive drum in the region in contact with the brush member 12. Unless otherwise stated, the surface potential of the photosensitive drum 1 described below refers to the surface potential of the photosensitive drum 1 in the region in contact with the brush member 12.

[0060] As Figure 4 shows, since the region R12 is inside the effective charging width B and outside the contact width F, the surface potential in the region R12 is close to the pre-exposure potential VD, especially in a non-exposed portion. In addition, in the region R11, since the region R11 is not charged by the charging roller 2, the surface potential is 0V. Therefore, the toner accumulated on the brush member 12 receives electric field force caused by the potential difference between the region R11 and the region R12, and moves outward in the axial direction J1—that is, in the direction from the region 12 toward the region R11. As a result, the toner accumulated on the brush member 12 scatters in the image forming apparatus 100 from the end portion of the brush member 12 in the axial direction J1.

[0061] Therefore, in this embodiment, the surface potential of the region R11 is configured to be greater than 0V with respect to a predetermined polarity direction, so as to reduce the potential difference between the region R11 and the region R12. It should be noted that the normal polarity of the region R11 and the normal polarity of the pre-exposure potential VD and the toner in the developing container 8 are negative.

[0062] In this embodiment, injection charging is performed from the brush member 12 to the photosensitive drum 1, so that the surface potential of region R11 becomes a first potential value T1 between 0V and the pre-exposure potential VD. That is, the absolute value of value T1 is less than the pre-exposure potential VD. The brush member 12 is charged from the brush voltage application circuit 60 (refer to...) which is a voltage application section. Figure 1 A brush voltage, which is a direct current, is applied. In this embodiment, the brush voltage is -400V, with the same polarity as the normal polarity of the toner. Therefore, the potential of the brush member 12 increases in the negative polarity direction, which is the same as the normal polarity of the toner. As a result, in the region R11 where the brush member 12 contacts the photosensitive drum 1, injection charging is performed by the potential difference between the photosensitive drum 1 and the brush member 12, causing the surface potential of region R11 to become a value T1 (-400V) that is larger relative to the negative polarity direction. In addition, as described above, the surface potential of region R12 is close to the pre-exposure potential VD. Therefore, the value T1 of the surface potential of region R11 is less than the pre-exposure potential VD, which is the second potential of the surface potential of region R12.

[0063] Note that the surface potential of the area R13 of the photosensitive drum 1 that is in contact with the transfer roller 13 is close to 0V in the exposed section, and is also affected by the transfer voltage to -150V in the non-exposed section. Figure 4 The example shown illustrates a region R13 with a surface potential of approximately 0V as an exposure zone. That is, the absolute value of the surface potential of region R13, which is the third potential, is less than the value T1 of the surface potentials of regions R11 and R12, or the pre-exposure potential VD.

[0064] [Experiment 1]

[0065] Here, an experiment using comparative examples will be described to demonstrate the effectiveness of this embodiment. In this experiment, 1000 full-page white images were continuously printed in an environment with 50% humidity and 23°C to analyze whether toner dispersion from the brush component 12 occurred.

[0066] By observing the state of the ends of the brush member 12 in the axial direction J1 after continuous printing, toner scattering is evaluated in three grades: no scattering (O), slight scattering (Δ), and heavy scattering (x). As examples for comparing the effect of the present embodiment, experiments were conducted with the configurations of Comparative Example 1-1 and Comparative Example 1-2 shown in Table 1, and toner scattering was also evaluated in three grades. Comparative Example 1-1 is configured by setting the applied voltages of a plurality of brush members 12 when the relationship between contact width F and contact width C satisfies F>C. In addition, Comparative Example 1-2 is configured by setting the applied voltages of a plurality of brush members 12 having a polarity (+ polarity) opposite to the normal polarity of toner when the relationship between contact width F and contact width C satisfies F<C. Table 1 shows each configuration and each result of the present Example 1, Comparative Example 1-1 and Comparative Example 1-2.

[0067] [Table 1]

[0068]

[0069]

[0070] In the configuration of Comparative Example 1-1 where the relationship between contact width F and contact width C is F>C, when the contact width contacts the end of the effective charging width B of the charging roller 2, discharge becomes active in the contact area, so drum leakage may occur. Therefore, toner is developed on the area where drum leakage occurs, causing image defects. In addition, a certain amount of toner scatters from the ends of the brush member 12 in the axial direction J1.

[0071] In addition, in the configuration of Comparative Example 1-2, although the relationship between contact width F and contact width C is F<C, since a voltage of the polarity opposite to that of toner is applied to the brush member 12, the region R11 becomes the polarity opposite to that of toner. Therefore, the potential difference between the region R11 and the region R12 becomes large. As a result, toner scatters from the ends of the brush member 12 in the axial direction J1.

[0072] On the other hand, in the configuration of the present embodiment, satisfying F<A<B<C and performing injection charging on the region R11 reduces the potential difference between the region R11 and the region R12, and can suppress toner scattering from the ends of the brush member 12 in the axial direction J1.

[0073] Next, a second embodiment of the present invention will be described. In the second embodiment, the positional relationship of the photosensitive drum 1, charging roller 2, charge elimination unit 11, brush member 12, and transfer roller 13 in the axial direction J1 is the same as in the first embodiment. On the other hand, the second embodiment is configured such that the surface potential (value T2) of region R11 is greater than the pre-exposure potential VD in the negative polarity direction. Hereinafter, if the second embodiment includes the same configuration as the first embodiment, the configuration of the second embodiment will not be shown in the figures or will be given the same reference numerals.

[0074] like Figure 5 As shown, the brush component 12 is supplied with voltage from the brush voltage application circuit 60 (see reference). Figure 1 A brush voltage, which is a direct current, is applied. In this embodiment, the brush voltage has the same polarity as the normal polarity of the toner—that is, it is greater than the pre-exposure potential VD in the negative polarity direction. In this embodiment, by injecting charge from the brush member 12 to the photosensitive drum 1, the potential surface value T2 of region R11 of the photosensitive drum 1 becomes greater than the pre-exposure potential VD. In other words, the value T2, which is the first potential, is greater than the pre-exposure potential VD, which is the second potential of the surface potential of region R12.

[0075] Therefore, the potential of region R11 becomes greater than that of region R12 in the same polarity direction of the toner, resulting in an electric field moving from region R12 to region R11. Since the toner in this embodiment is negatively charged, the toner adhering to the photosensitive drum 1 receives electricity from the aforementioned electric field in the direction from region R11 towards region R12. Therefore, the toner dispersion from the end of the photosensitive drum 1 in the axial direction J1 of the brush member 12 can be effectively suppressed.

[0076] [Experiment 2]

[0077] In this embodiment, the same experiments as those performed in the first embodiment were also conducted. Furthermore, as an example to compare the effects of this embodiment, experiments were conducted on the configurations of Example 1 and Comparative Examples 1-2 to evaluate the toner dispersion. Table 2 shows the configurations and experimental results of Example 2, Example 1, and Comparative Examples 1-2.

[0078] [Table 2]

[0079]

[0080] Same as the result of Experiment 1, with the configuration of Comparative Examples 1-2, since a voltage of opposite polarity to that of the toner is applied to the brush member 12, the toner scatters from the end portion in the axial direction J1 of the brush member 12. In addition, in Example 1, since the brush member 12 is applied with a brush voltage greater than 0 V in the negative polarity direction opposite to the normal polarity of the toner, scattering of the toner can be suppressed. On the other hand, in Example 2, since the brush voltage in the negative polarity direction is greater than the pre-exposure potential VD such that the absolute value satisfies the relationship VD < T2, scattering of the toner can be suppressed more effectively compared with Example 1.

[0081] Next, a third embodiment will be described. The third embodiment is configured such that a cleaning member 15 replaces the charge eliminating unit 11 of the first embodiment. In other words, the processing unit 9 in the third embodiment is not a cleanerless method. Hereinafter, if the third embodiment includes the same configuration as the first embodiment, the configuration of the third embodiment will not be shown in the drawings or will be assigned the same reference numerals.

[0082] [Cleaning Member]

[0083] As Figure 1 and Figure 7 shown, the cleaning member 15 located downstream of the transfer nip N1 and upstream of the brush member 12 in the rotation direction of the photosensitive drum 1 (direction of arrow L) removes adhering materials (including residual toner after transfer and paper dust) on the surface 1a of the photosensitive drum 1. In this embodiment, the cleaning member 15 and the brush member 12 are combined to remove adhering materials that cannot be completely removed by the cleaning member 15 (hereinafter simply referred to as paper dust).

[0084] As Figure 6 shown, the cleaning member 15 includes a metal sheet 15b made of a metal material and an elastic member 15a fixed to the metal sheet 15b. The elastic member 15a removes residual toner after transfer and paper dust by scraping against the surface 1a of the rotating photosensitive drum 1. In this embodiment, the elastic member 15a is made of 2 mm thick polyurethane rubber having an MD-1 hardness of 60 to 80 degrees in an environment of 23°C.

[0085] In Figure 6In the figure, a virtual photosensitive drum 1' having the same shape as the photosensitive drum 1 is indicated by a dashed line, and the center of the virtual photosensitive drum 1' is referred to as center O. The point of the elastic member 15a closest to the center O is referred to as point P, and the intersection point between a line extending vertically through the point P and the virtual photosensitive drum 1' is referred to as point Q. The distance between the point P and the point Q is the indentation amount δ. Further, when the tangent line of the virtual photosensitive drum 1' at the point Q is referred to as tangent line LN1, the angle formed by the tangent line LN1 and the bottom side of the elastic member 15a is referred to as the set angle θ. Note that in the present embodiment, the indentation amount is 1.0 mm and the set angle is 22°.

[0086] [Position relationship of each component in the axial direction]

[0087] Next, the following will use Figure 7 to describe each component of the processing unit 9: specifically, the positional relationship in the axial direction J1 of the photosensitive drum 1, the charging roller 2, the brush member 12 and the cleaning member 15. The charging roller 2, the brush member 12 and the cleaning member 15 are symmetrically positioned relative to the center of the photosensitive drum 1 in the axial direction J1. Figure 7 is a diagram showing the effective charging width B of the charging roller 2, the contact width C of the brush member 12, and the contact width D which is the cleaning contact width of the cleaning member 15. As Figure 7 shown, the contact width D is the width that can remove transfer residual toner and paper dust on the photosensitive drum 1 by contacting the surface 1a of the photosensitive drum 1.

[0088] The contact width D needs to be configured to be larger than the effective charging width B, so as to sufficiently remove transfer residual toner and paper dust in the region of the effective charging width B on the surface 1a of the photosensitive drum 1 (B<D).

[0089] Here, when the relationship between the contact width C of the brush member 12 and the contact width D of the cleaning member 15 satisfies D<C, toner scattering from the end portions of the brush member 12 occurs as in the first embodiment. Therefore, when the relationship among the effective charging width B, the contact width C and D includes B<D<C, the potential relationship described below needs to be included.

[0090] When B < D < C is satisfied, there are regions R21, R22 and R23 on the photosensitive drum 1. Region R21 is a region that is in contact with the brush member 12, is not charged by the charging roller 2, and is not in contact with the cleaning member 15. In other words, region R21 is located outside the contact width D and inside the contact width C in the axial direction J1, and is in contact with the brush member 12. Region R22 is a region that is in contact with both the brush member 12 and the cleaning member 15, and is not charged by the charging roller 2. In other words, region R22 is located outside the effective charging width B and inside the contact width D in the axial direction J1, and is also in contact with the brush member 12. Region R23 is a region that is in contact with both the brush member 12 and the cleaning member 15, and is charged by the charging roller 2.

[0091] [Surface Potential of Photosensitive Drum in Area Contacted by Brush Member]

[0092] Next, Figure 8 will be used to describe the surface potential of the photosensitive drum 1 in the region contacted by the brush member 12. Figure 8 is a diagram illustrating the relationship of the surface potential of the photosensitive drum 1 in the region contacted by the brush member 12. Unless otherwise specified, the surface potential of the photosensitive drum 1 described below refers to the surface potential of the photosensitive drum 1 in the region contacted by the brush member 12.

[0093] As shown in Figure 8 , since regions R21 and R22 are located outside the effective charging width B, their surface potential is 0V as they are not charged by the charging roller 2. On the other hand, the surface potential of region R23 is close to 0V in the exposure portion and -150V in the non-exposure portion under the influence of the transfer voltage. In Figure 8 , the surface potential of region R23 is shown as about 0V as an example in the exposure portion.

[0094] Here, since region R22 is a position contacted by the cleaning member 15, the amount of residual transfer toner or paper dust accumulated on the brush member 12 is small in the region corresponding to R22. On the other hand, since region R21 is a position not contacted by the cleaning member 15, the amount of residual transfer toner or paper dust accumulated on the brush member 12 is large in the region corresponding to R21. In particular, the toner accumulated on the brush member 12 in region R21 receives the electric force from the electric field caused by the potential difference between region R21 and region R23, so it moves outward in the axial direction J1 — that is, in the direction from region R23 toward region R21. As a result, the toner accumulated on the brush member 12 scatters from the end in the axial direction J1 to the inside of the image forming apparatus 100.

[0095] Therefore, in this embodiment, the surface potential of region R21 is configured to be at least greater than 0V relative to a predetermined polarity direction, so as to minimize the potential difference between regions R21 and R23. Note that the normal polarity of region R21, as well as the normal polarity of the pre-exposure potential VD and the toner in the developing container 8, are negative.

[0096] Furthermore, in this embodiment, the surface potential of region R22 is configured to be at least greater than 0V relative to a predetermined polarity direction, so as to minimize the potential difference between region R22 and region R23. Note that the normal polarity of region R22, as well as the normal polarity of the pre-exposure potential VD and the toner in the developing container 8, are negative.

[0097] In this embodiment, as in the first embodiment, injection charging is performed from the brush member 12 to the photosensitive drum 1 so that the surface potentials of regions R21 and R22 are values ​​T1, which are the first and second potentials, between 0V and the pre-exposure potential VD. Note that the surface potential of region R22 does not need to be the same as the surface potential of region R21.

[0098] Brush component 12 is subjected to a brush voltage application circuit 60 (in Figure 1 (As shown in the diagram) A brush voltage, which is a direct current, is applied. In this embodiment, the brush voltage is -400V, which is the same polarity as the normal polarity of the toner. Therefore, the potential of the brush member 12 increases in the negative polarity direction, which is the same as the normal polarity of the toner. As a result, in regions R21 and R22 of the photosensitive drum 1 that the brush member 12 contacts, the surface potential of regions R21 and R22 is injected and charged by the potential difference between the photosensitive drum 1 and the brush member 12, causing the surface potential of regions R21 and R22 to become a larger value T1 (-400V) in the negative polarity direction.

[0099] [Experiment 3]

[0100] In this embodiment, the same experiments as those conducted in Example 1 were performed. Furthermore, as an example to compare the effects of this embodiment, experiments were conducted on the configuration of Comparative Example 2 shown in Table 3 to evaluate toner dispersion. Comparative Example 2 was configured with several brush members 12 having opposite polarities and applied voltages. Table 3 shows the configurations and experimental results of Example 3 and Comparative Example 2.

[0101] [Table 3]

[0102]

[0103] In the configuration of Comparative Example 2, since a voltage of opposite polarity to that of toner is applied to the brush member 12, regions R21 and R22 become potentials of the same polarity as the toner. Therefore, the potential difference between the region R21 and the region R23 becomes large. As a result, toner scatters from the end portions of the brush member in the axial direction J1.

[0104] On the other hand, in the configuration of the present embodiment, when B<D<C is satisfied and injection charging is performed on the region R21, the potential difference between the region R21 and the region R23 becomes small. Therefore, toner scattering from the end portions of the brush member 12 in the axial direction J1 can be suppressed.

[0105] Next, a fourth embodiment of the present invention will be described. The fourth embodiment changes the width of the developing roller 4 of the first embodiment. In other words, the processing unit 9 of the fourth embodiment adopts the same cleaner-less method as that of the first embodiment. Hereinafter, if the fourth embodiment includes the same configuration as that of the first embodiment, the configuration of the fourth embodiment will not be illustrated in the drawings or will be assigned the same reference numerals.

[0106] [Positional Relationship in Axial Direction of Each Component]

[0107] Next, the Figure 9 will be used to describe the positional relationship in the axial direction J1 of each component of the processing unit 9: specifically, the photosensitive drum 1, the charging roller 2, the developing roller 4, the charge eliminating unit 11, the brush member 12, and the transfer roller 13. The charging roller 2, the developing roller 4, the transfer roller 13, the charge eliminating unit 11, and the brush member 12 are positioned symmetrically with respect to the center of the photosensitive drum 1 in the axial direction J1. Figure 9 is a diagram showing the charge eliminating width A of the charge eliminating unit 11, the effective charging width B of the charging roller 2, the contact width C of the brush member 12, the toner application width E of the developing roller 4, and the contact width F of the transfer roller 13. As shown in Figure 9 , the toner application width E is the width of a region on the surface of the developing roller 4 covered with toner supplied by the supply roller 5. In order to reliably transfer the toner image on the photosensitive drum 1, the contact width F where toner is transferred by the transfer roller 13 needs to be larger than the toner application width E (E<F).

[0108] Here, when the relationship between the contact width C of the brush member 12 and the toner application width E of the developing roller 4 satisfies E<C, toner scattering from the end portions of the brush member 12 occurs as in the first embodiment. Therefore, when the charge eliminating width A, the effective charging width B, the contact widths C and F, and the toner application width E satisfy the relationship E<F<A<B<C, the potential relationship described below needs to be satisfied.

[0109] When E<F<A<B<C, there are regions R31, R32 and R33 on the photosensitive drum 1. The region R31 is a region that is in contact with the brush member 12 but is not charged by the charging roller 2 or the transfer roller 13 and is not in contact with the toner application region (corresponding to the toner application width E) of the developing roller 4. In other words, the region R31 is outside the effective charging width B in the axial direction J1, inside the contact width C, and is in contact with the brush member 12. The region R32 is a region that is in contact with the brush member 12 and charged by the charging roller 2 but is not in contact with the transfer roller 13 and is not in contact with the toner application region of the developing roller 4. The region R33 is a region that is in contact with the brush member 12, charged by the charging roller 2, and in contact with the transfer roller 13 and the toner application region of the developing roller 4.

[0110] [Surface Potential of Photosensitive Drum in Region Contacted by Brush Member]

[0111] Next, use Figure 10 to describe the surface potential of the photosensitive drum 1 in the region contacted by the brush member 12. Figure 10 is a diagram illustrating the relationship of the surface potential of the photosensitive drum 1 in the region contacted by the brush member 12. Unless otherwise stated, the surface potential of the photosensitive drum 1 described below refers to the surface potential of the photosensitive drum 1 in the region contacted by the brush member 12.

[0112] As shown in Figure 10 , since the region R31 is located outside the effective charging width B, the surface potential is not charged by the charging roller 2 and is 0V. On the other hand, since the region R32 is located inside the effective charging width B and outside the contact width F, especially in a non-exposed region, the surface potential is close to the pre-exposure potential VD.

[0113] Therefore, the toner accumulated on the brush member 12 is subjected to the electric force from the electric field generated by the potential difference between the region R31 and the region R32, and moves outward in the axial direction J1—that is, in the direction from the region R32 toward the region R31. As a result, the toner accumulated on the brush member 12 scatters from the end portion in the axial direction J1 into the inside of the image forming apparatus 100.

[0114] For this reason, in the present embodiment, the surface potential of the region R31 is configured to be greater than 0V with respect to the predetermined polarity direction, so as to minimize the potential difference between the region R31 and the region R32. It should be noted that the normal polarity of the region R31, the pre-exposure potential VD, and the normal polarity of the toner in the developing container 8 are negative.

[0115] In this embodiment, as in the first embodiment, injection charging is performed from the brush member 12 to the photosensitive drum 1, such that the surface potential of the region R31 becomes a first potential value T1 between 0V and the pre-exposure potential VD. The brush member 12 is supplied with a brush voltage as a direct current from the brush voltage applying circuit 60 (shown in Figure 1 ). In this embodiment, the brush voltage is -400V, which has the same polarity as the normal polarity of the toner. Therefore, the potential of the brush member 12 increases in the negative direction that is the same as the normal polarity of the toner. As a result, in the region R31 of the photosensitive drum 1 in contact with the brush member 12, the surface potential of the region R31 becomes a larger value T1 (-400V) in the negative polarity direction through injection charging based on the potential difference between the photosensitive drum 1 and the brush member 12.

[0116] It should be noted that the surface potential of the region R33 of the photosensitive drum 1 contacted by the transfer roller 13 is close to 0V in the exposed portion, and is -150V in the unexposed portion under the influence of the transfer voltage. In Figure 4 , an example where the surface potential of the region R33 is 0V for an exposed portion is shown.

[0117] <Experiment 4>

[0118] In this embodiment, the same experiment as that performed in the first embodiment and the second embodiment is also carried out. In addition, as an example for comparing the effect of the present embodiment, an experiment was conducted on the configuration of Comparative Example 3 shown in Table 4 to evaluate toner scattering. Comparative Example 3-1 is configured by setting applied voltages of a plurality of brush members 12 in an arrangement where the relationship between the contact width F and the toner coating width E satisfies E>F. In addition, Comparative Example 3-2 is configured by setting applied voltages of a plurality of brush members 12 having opposite polarities in an arrangement where the relationship between the contact width F and the toner coating width E satisfies E<F. The configurations and experimental results of Example 4, Comparative Example 3-1 and Comparative Example 3-2 are shown in Table 4.

[0119] [Table 4]

[0120]

[0121]

[0122] In the configuration of Comparative Example 3-1, since the relationship between the contact width F and the toner coating width E satisfies E>F, the toner image formed on the toner coating width E cannot be transferred outside the contact width F, and remains on the photosensitive drum 1 as residual toner after transfer. The residual toner after transfer adheres to the photosensitive drum 1, rotates together with the photosensitive drum 1, enters the brush member 12, and accumulates on the brush member 12. As a result, the toner scatters from the end portions of the brush member 12 in the axial direction J1.

[0123] In addition, in the configuration of Comparative Example 3-2, since a reverse polarity voltage is applied to the brush member 12, the region R31 has the reverse polarity of the toner. Therefore, the potential difference between the region R31 and the region R32 becomes large. As a result, the toner scatters from the end portion of the brush member 12 in the axial direction J1.

[0124] On the other hand, in the configuration of the present embodiment, when E<F<A<B<C is satisfied and injection charging is performed, the potential difference between the region R31 and the region R32 becomes small, and scattering of the toner can be suppressed.

[0125] It should be noted that, in any of the above embodiments, the brush member 12 including the base fabric 12b and the bristles 12a collects the adhering material on the photosensitive drum 1, but the present invention is not limited thereto. For example, a roller in which the outer peripheral surface of a core metal is formed of a conductive foam elastic material, or a resin brush in which the outer peripheral surface of a core metal is flocked with carbon-dispersed conductive nylon fibers may collect the adhering material.

[0126] In addition, in any of the above embodiments, injection charging from the brush member 12 to the photosensitive drum 1 is performed to increase the surface potential of predetermined regions (regions R11, R21, R22, and R31) of the photosensitive drum 1, but the present invention is not limited thereto. For example, a corona charger may be provided that charges the surface 1a of the photosensitive drum 1 when the corona charger is located downstream of the transfer nip N1 in the direction of arrow L and upstream of the brush member 12. In these configurations, since injection charging is not used, the material of the brush member 12 does not need to be conductive.

[0127] Furthermore, in any of the above embodiments, the surface 1a is charged by the charging roller 2 in the charging portion N2, but the present invention is not limited thereto. For example, a corona charger may be used instead of the charging roller 2.

[0128] Furthermore, in any of the above embodiments, the image forming apparatus is described as a monochrome image forming apparatus including only one image bearing member. However, the present invention is not limited thereto, and the same control is applicable to a multicolor image forming apparatus that forms an image using a plurality of developers of different toner colors and includes a plurality of image bearing members. The multicolor image forming apparatus may employ an intermediate transfer method in which monochrome images formed on the plurality of image bearing members are primarily transferred onto an intermediate transfer member (e.g., an intermediate transfer belt) and then secondarily transferred onto a recording sheet at one time. In addition, a sequential transfer method in which monochrome toner images are transferred onto a recording sheet one by one may be employed. In other words, a transfer method in which monochrome toner images formed on a plurality of image bearing members are directly transferred onto a recording sheet fed by a recording sheet feeding belt may also be employed.

[0129] While the invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the appended claims should be given the broadest interpretation to include all such modifications and equivalent structures and functions.

Claims

1. An image forming apparatus, comprising: a rotatable image bearing member rotatable about a rotation shaft extending in an axial direction thereof; a charging member configured to form a charging portion between itself and the image bearing member and charge a surface of the image bearing member; a containing portion configured to contain toner charged to a predetermined polarity; a developing member configured to form a developing portion between itself and the image bearing member and form a toner image on the image bearing member by supplying toner to the developing portion; a transfer portion that is in contact with a surface of the image bearing member and configured to transfer the toner image; a charge eliminating portion configured to eliminate charges on the surface of the image bearing member; and a collecting member configured to be in contact with the surface of the image bearing member to collect deposits deposited on the surface of the image bearing member, wherein, with respect to the axial direction, when A is defined as a charge eliminating width over which the charge eliminating portion can eliminate charges on the surface, B is defined as an effective charging width over which the charging member can charge the surface, and C is defined as a collecting contact width over which the collecting member contacts the surface, the following formula is satisfied: A < B < C, and wherein, with respect to the axial direction, a surface potential of the surface in a region that is located outside the effective charging width, inside the collecting contact width and in contact with the collecting member is a first potential greater than 0 V in a polarity direction same as the predetermined polarity, wherein a transfer contact width F is defined as a width over which the transfer portion contacts the surface with respect to the axial direction, wherein, with respect to the axial direction, a surface potential of the surface in a region that is located outside the transfer contact width F, inside the effective charging width B and in contact with the collecting member is a second potential greater than 0 V in a polarity direction same as the predetermined polarity, wherein the first potential is smaller than the second potential in the polarity direction same as the predetermined polarity, and wherein the developing member is configured to collect transfer residual toner remaining on the surface of the image bearing member after transfer performed by the transfer portion in the developing portion.

2. The image forming apparatus according to claim 1, wherein, with respect to the axial direction, a surface potential of the surface in a region that is located inside the transfer contact width and in contact with the collecting member is a third potential, and wherein the third potential is smaller than the second potential in absolute value.

3. The image forming apparatus according to claim 1, wherein, with respect to the axial direction, a surface potential of the surface in a region that is located inside the transfer contact width F and in contact with the collecting member is a third potential, and wherein the third potential is smaller than the first potential in absolute value.

4. The image forming apparatus according to claim 1, wherein, in the charging portion, the charging member charges the surface of the image bearing member to a fourth potential in a polarity direction same as the predetermined polarity, and wherein the first potential is smaller than the fourth potential in absolute value.

5. The image forming apparatus according to claim 1, further comprising a voltage applying unit configured to apply a voltage in the same polarity direction as the predetermined polarity to the collecting member.

6. The image forming apparatus of claim 1, further comprising a corona charger configured to charge the surface of an image carrier member to the first potential.

7. The image forming apparatus according to claim 1, wherein, The collecting components include conductive brush components.

8. The image forming apparatus according to claim 1, wherein, The transfer unit transfers the toner image from the image carrier component onto the recording material.

9. The image forming apparatus according to claim 1, further comprising a belt, wherein the toner image is transferred from the image carrying member to the belt via a transfer section, and the belt is configured to carry toner.

10. The image forming apparatus according to claim 1, wherein, The predetermined polarity is negative.

Images