JP7822766B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus that forms an image on a recording material.

A configuration known as a simultaneous development and cleaning system or cleanerless system is known in electrophotographic image forming devices. In this configuration, residual toner remaining on the surface of an image carrier, such as a photosensitive drum, after a toner image has been transferred from the image carrier to a receiving material (recording material or intermediate transfer material) is not collected by a cleaning device, but is instead collected by a developing member, such as a developing roller, simultaneously with the next development process.

Patent Document 1 describes a cleanerless image forming apparatus in which a brush member is positioned downstream of the transfer roller and upstream of the charging roller in the rotation direction of the photosensitive drum to scatter residual toner adhering to the photosensitive drum. According to this document, by using the brush member to scatter residual toner distributed in the same pattern as the toner image transferred to the recording material, the behavior of residual toner in the charging device and developing device is made uniform, making it less likely that residual images caused by residual toner will appear on the recording material.

JP 2010-14982 A

Generally, the residual toner remaining on the image carrier surface after the transfer process includes toner particles charged to the toner's normal polarity (normal charging polarity), toner particles charged to an irregular polarity opposite to the normal polarity, and toner particles with a charge amount close to zero. If the residual toner reaches the charging member or developing member while still in a wide charge distribution state, the toner with the irregular polarity will mainly adhere to and accumulate on the charging member, which can cause poor charging.

As a result, one approach is to position a brush member downstream of the transfer member and upstream of the charging member in the rotational direction of the image carrier, so that the remaining toner is dispersed while being charged with a charge of the normal polarity. However, depending on the contact conditions of the brush member, it may not be possible to impart a sufficient charge to the remaining toner, or the remaining toner may concentrate in certain areas of the brush member and escape, resulting in a streaky distribution, making it impossible to prevent adhesion to the charging member.

The present invention aims to provide an image forming device that can suppress the occurrence of charging defects in a configuration in which a brush member is arranged in contact with the image carrier.

One aspect of the present invention is a method for manufacturing a toner image forming apparatus, comprising: a rotating image carrier; a charging member that contacts the image carrier to form a charging portion and charges the surface of the image carrier to the same polarity as the normal charging polarity of toner in the charging portion; a developing member that develops an electrostatic latent image formed on the surface of the image carrier using the toner ; a transfer member that transfers the toner image developed by the developing member from the image carrier to a transferee in a transfer portion; and a transfer member that is disposed so as to contact the surface of the image carrier at a contact portion downstream of the transfer portion and upstream of the charging portion in the rotation direction of the image carrier, and that transfers the toner that has not been transferred to the transferee. and a brush member that imparts a charge of normal charging polarity to the developing member, and which recovers toner that has not been transferred to the transfer medium using the developing member, wherein the contact pressure between the brush member and the image carrier at the upstream end of the brush member at the contact portion in the rotation direction is higher than the contact pressure at the downstream end of the brush member at the contact portion in the rotation direction, and the contact area ratio between the brush member and the image carrier at the upstream end of the brush member is greater than the contact area ratio at the downstream end of the brush member.

Another aspect of the present invention is a method for manufacturing a toner image carrier, comprising: a rotating image carrier; a charging member that contacts the image carrier to form a charging portion and charges the surface of the image carrier to the same polarity as the normal charging polarity of toner in the charging portion; a developing member that develops an electrostatic latent image formed on the surface of the image carrier using the toner ; a transfer member that transfers the toner image developed by the developing member from the image carrier to a transferee in a transfer portion; and a transfer member that is disposed so as to contact the surface of the image carrier at a contact portion downstream of the transfer portion and upstream of the charging portion in the rotation direction of the image carrier. and a brush member that imparts a charge of the normal charging polarity to toner that has not been transferred to the transfer medium, and the toner that has not been transferred to the transfer medium is recovered by the developing member. In this image forming apparatus, the amount of penetration of the brush member into the surface of the image carrier at the upstream end of the brush member at the contact portion in the rotation direction is δ1 (mm), and the amount of penetration of the brush member at the downstream end of the brush member at the contact portion in the rotation direction is δ2 (mm), where δ1 > δ2 > 0.

This invention makes it possible to prevent poor charging in a configuration in which a brush member is placed in contact with the image carrier.

FIG. 3 is a schematic diagram illustrating the arrangement of a brush member according to the first embodiment. 1 is a schematic diagram of an image forming apparatus according to a first embodiment. FIG. 2 is a schematic view of an image forming unit according to the first embodiment. 1A is a perspective view of a latent image unit according to the first embodiment, FIG. 1B is a cross-sectional view thereof, and FIG. 1C is a view of a brush contact portion as seen from the upstream side in the rotation direction of a photosensitive drum. 3A is a cross-sectional view of the brush member according to the first embodiment in a stand-alone state, and FIG. 3B is a cross-sectional view of the brush member in a contact state with a photosensitive drum. 1A and 1B are diagrams for explaining the calculation method of the Clark-Evans index. 6A and 6B are diagrams for explaining a method for calculating the contact pressure of a brush member. 10A to 10C are diagrams for explaining a method for calculating the contact area ratio of a brush member. 6A is a graph showing the contact pressure of the brush member according to the first embodiment, the contact area ratio of the brush member, and the relationship between the contact pressure and the contact area ratio of the brush member according to the first embodiment. 10A to 10C are diagrams illustrating the case where toner passes through the brush member in a streak-like manner. 5A to 5D are diagrams for explaining the function of the brush member according to the first embodiment. 10A and 10B are schematic diagrams illustrating a brush member according to a second embodiment and a brush member according to a first embodiment, respectively, viewed from the tip side of the bristles. 10A and 10B are schematic diagrams of a brush member according to a third embodiment and a brush member according to a first embodiment, respectively, viewed from the tip side of the bristles. FIG. 10 is a schematic diagram for explaining a method for calculating contact pressure. FIG. 10 is a diagram showing the range of peak pressure and maximum contact area ratio. 13A and 13B are diagrams showing a method for calculating the intrusion amount of the brush member in the fourth embodiment.

Embodiments of the present disclosure will be described below with reference to the drawings.

First Embodiment
An overview of the image forming apparatus 100 according to the first embodiment will be described using Figures 2 and 3. Figure 2 is a schematic diagram of the image forming apparatus 100. Figure 3 is an enlarged view of an image forming unit 101 provided in the image forming apparatus 100. The image forming apparatus 100 is a monochrome printer that forms a monochrome image on a sheet S based on image information received from an external device. As the sheet S, which is the recording material, a variety of sheets of different sizes and materials can be used, including paper such as plain paper and cardboard, surface-treated sheet materials such as plastic film, cloth, and coated paper, and sheet materials of special shapes such as envelopes and index paper.

As shown in Figures 2 and 3, the image forming apparatus 100 includes an electrophotographic image forming unit 101 that forms an image on a sheet S, and a sheet transport mechanism (6, 8, 12) that feeds and transports the sheet S. The image forming unit 101 includes a photosensitive drum 1 as an image carrier, a charging roller 2 as a charging means, an exposure device 3 as an exposure means, a developing device 4 as a developing means, a transfer roller 5 as a transfer means, a brush member 11, and a fixing device 9 as a fixing means. Within the image forming unit 101, the latent image unit 1A having the photosensitive drum 1, charging roller 2, and brush member 11, and the developing device 4 as a developing unit are configured as a cartridge C that is detachable from the image forming apparatus main body 100A.

The photosensitive drum 1 is an electrophotographic photosensitive member molded into a drum shape. The photosensitive drum 1 is, for example, a drum (cylindrical or columnar) with a diameter of 24 mm, and is rotated at a peripheral speed (process speed) of 100 mm/sec during image formation. The charging roller 2 is a contact charging member that contacts the photosensitive drum 1. The contact point between the charging roller 2 and the photosensitive drum 1 is the charging point P2 (charging position) where the surface of the photosensitive drum 1 is charged.

The developing device 4 includes a developing roller 41, a supply roller 42, an agitating member 43, a developing blade 44, and a toner storage unit 45. The developing roller 41 is a developing member or developer carrier that carries toner T and rotates to supply toner T to a developing unit P4 (developing position) where the developing roller 41 faces the photosensitive drum 1. In this embodiment, a so-called contact development method is used, in which a toner layer carried by the developing roller 41 contacts the surface of the photosensitive drum 1 at the developing unit P4. The developing roller 41 is disposed in the opening of the toner storage unit 45, which is located opposite the photosensitive drum 1. The supply roller 42 supplies (applies) toner T from a supply chamber 45a of the toner storage unit 45 to the developing roller 41. The agitating member 43 is disposed in the toner storage unit 45 and rotates to agitate the toner T in the toner storage unit 45 and supply it to the supply chamber 45a. The toner storage unit 45 is a container that stores toner T as a developer. The developing blade 44 is brought into contact with the surface of the developing roller 41, which rotates from inside the toner storage section 45 toward the developing section P4, with a predetermined pressure. The developing blade 44 is mainly composed of a material (for example, iron or copper) that is on the positive polarity (non-regular polarity) side of the toner T's main component (binder resin) in the electrification series. As a result, the developing blade 44 rubs against the toner T, causing the toner T to be triboelectrically charged to a negative polarity (regular polarity).

The developing roller 41 is, for example, a roller with a diameter of 12 mm and a conductive rubber layer (elastic layer). The supply roller 42 is, for example, a roller with a diameter of 10 mm and a sponge-like outer layer.

The transfer roller 5 is positioned in contact with the surface of the photosensitive drum 1. The nip where the transfer roller 5 and the photosensitive drum 1 face each other is the transfer section P5 where the toner image is transferred from the photosensitive drum 1 to the sheet S.

The brush member 11 is positioned downstream of the transfer portion P5 and upstream of the charging portion P2 in the rotation direction R1 of the photosensitive drum 1. The brush member 11 is positioned so that it comes into contact with the surface of the photosensitive drum 1 under predetermined contact conditions. Details of the brush member 11 will be described later.

The fixing device 9 has a fixing roller 9a or flexible fixing film as a first rotating body, a pressure roller 9b as a second rotating body that contacts the first rotating body with a predetermined pressure, and a heating means that heats the image on the sheet S via the first rotating body. The heating means can be a halogen lamp that generates radiant heat or a heater substrate with a heating resistor pattern formed on a ceramic substrate.

The sheet transport mechanism includes a cassette 6, a feed roller 7, a pair of transport rollers 8, and a pair of discharge rollers 12. The cassette 6 is a stacking unit on which sheets S are stacked. The feed roller 7 is a feed member that feeds sheets S one by one from the cassette 6. The pair of transport rollers 8 is a transport member that transports sheets S fed from the cassette 6 to the transfer unit P5. The pair of discharge rollers 12 is a discharge member that discharges sheets S on which an image has been formed by the image forming unit 101.

The image forming operation performed by the image forming apparatus 100 is outlined below. When an instruction to perform an image forming operation is input to the image forming apparatus 100, the photosensitive drum 1 is rotated in a predetermined rotation direction R1, and the charging roller 2 uniformly charges the surface of the photosensitive drum 1. The charging roller 2 rotates in a rotation direction R2 along with the photosensitive drum 1 at the charging section P2. Based on image information received from an external device, the exposure device 3 irradiates the photosensitive drum 1 with laser light L through a window 3a between the latent image unit 1A and the developing device 4, exposing the surface of the photosensitive drum 1. This writes an electrostatic latent image onto the surface of the photosensitive drum 1.

This embodiment uses a reversal development method. Therefore, the charging roller 2 is applied with a negative voltage (charging voltage) that is the same as the normal polarity of the toner T, thereby charging the surface of the photosensitive drum 1 to a negative dark potential Vd. After charging, the light potential Vl of the area (image area) exposed by the exposure device 3 becomes lower than the dark potential Vd. In the exemplary configuration of this embodiment, charging is performed to Vd = -500 (V), for example, using a DC charging voltage of -1100 V.

In the developing device 4, the toner T contained in the toner storage section 45 is homogenized by the agitator 43 and supplied to the developing roller 41 by the supply roller 42. The toner T carried by the developing roller 41 is frictionally charged to the normal polarity by friction with the developing blade 44 and is restricted to a predetermined layer thickness as the developing blade 44 passes. As the developing roller 41 rotates, the toner T charged to the normal polarity is supplied to the developing section P4. A voltage (developing voltage) of the same negative polarity as the normal polarity of the toner T is applied to the developing roller 41, causing the toner T to transfer to the photosensitive drum 1 in accordance with the potential distribution on the surface of the photosensitive drum 1. This develops the electrostatic latent image on the surface of the photosensitive drum 1 and makes it visible as a toner image. The developing voltage is, for example, -350 V. In addition, the developing roller 41 rotates in a rotational direction R4 along with the photosensitive drum 1 at the developing section P4 at a peripheral speed (for example, 140 mm/sec) faster than the peripheral speed of the photosensitive drum 1. The toner image formed on the surface of the photosensitive drum 1 is transported to the transfer section P5 while still being carried by the photosensitive drum 1.

In parallel with the above process, sheets S are fed one by one from cassette 6 by feed roller 7 and transported to transfer section P5 by transport roller pair 8. A voltage (transfer voltage) of positive polarity, opposite to the normal polarity of toner T, is applied to transfer roller 5, causing the toner image to be transferred from photosensitive drum 1 to sheet S at transfer section P5. The transfer voltage is, for example, +1000V.

After passing through transfer section P5, sheet S is transported to fixing device 9. In fixing device 9, sheet S is sandwiched between the nip portion of the first and second rotating bodies and transported, while the image on sheet S is heated and fixed by the first rotating body heated by the heating means. After passing through fixing device 9, sheet S is discharged by a pair of discharge rollers 12 onto a discharge tray 13 provided at the top of image forming apparatus 100.

(Cleanerless brush system)
Next, a cleanerless brush system using the brush member 11 will be described. This embodiment employs a simultaneous development and cleaning system in which residual toner that has not been transferred to the transfer target (sheet S) at the transfer unit P5 is collected by the developing roller 41 when the residual toner next reaches the developing unit P4. In the simultaneous development and cleaning system, the residual toner collected by the developing roller 41 is agitated with other toner T in the toner storage unit 45 and is reused for development.

In the simultaneous development and cleaning method, the developing roller 41 collects the residual toner that was not transferred to the transfer medium at the transfer section P5, so the brush member 11 basically allows the residual toner to pass through. Therefore, the "brush member" in this embodiment differs from the brush member that serves as a cleaning device (drum cleaner) intended to remove residual toner from the photosensitive drum 1. Note that the simultaneous development and cleaning method is sometimes called a cleanerless method because it does not employ a cleaning device to collect residual toner.

In the cleanerless brush system, a brush member 11 is placed downstream of the transfer station P5 and upstream of the charging station P2 in the rotation direction R1 of the photosensitive drum 1 to scatter residual toner adhering to the surface of the photosensitive drum 1 that has passed through the transfer station P5. By placing the brush member 11, it is possible to alleviate the condition in which residual toner is locally concentrated on the photosensitive drum 1. If residual toner is locally concentrated on the photosensitive drum 1, this can lead to poor charging due to contamination of the charging roller 2 or poor collection at the developing station P4, resulting in poor image quality. In contrast, the cleanerless brush system scatters residual toner using the brush member 11, which uniforms the behavior of residual toner at the charging station P2 and the developing station P4, thereby minimizing the above-mentioned problems.

It is also preferable to provide a brush power supply E11 (Figure 3) that applies a bias voltage (brush voltage) to the brush member 11 that is co-polarized with the normal polarity of the toner T. By applying the brush voltage, toner T charged with an irregular polarity can be held on the brush member 11 while allowing toner T with normal polarity to pass through. Furthermore, when the toner T with an irregular polarity held on the brush member 11 is converted to a normal polarity due to friction with the bristles of the brush member 11, it is carried on the surface of the photosensitive drum 1 and moves toward the charging section P2.

In this embodiment, the brush voltage applied to the brush member 11 is large enough to prevent discharge from occurring between the brush member 11 and the photosensitive drum 1. However, by applying a brush voltage to the brush member 11, it is also possible to inject charges of normal polarity from the brush member 11 into the remaining toner, thereby normalizing the polarity of the remaining toner.

It is also possible to configure the brush member 11 so that no brush voltage is applied. Even in this case, the toner T can be frictionally charged at the brush contact point, thereby normalizing the toner T to a normal polarity. Furthermore, in a configuration in which no brush voltage is applied, the brush member 11 can be a component electrically connected to ground potential.

(Operation specific to the cleanerless brush method)
In the cleanerless brush system, residual toner that passes through the contact point between the brush member 11 and the photosensitive drum 1 reaches the charging section P2. Because a charging voltage of the same polarity as the normal polarity is applied to the charging roller 2, toner particles among the residual toner that are charged to the normal polarity are pressed against the photosensitive drum 1 and pass through the charging section P2. On the other hand, toner particles among the residual toner that are charged to the non-normal polarity or toner particles with a charge amount close to zero partially adhere to the charging roller 2 at the charging section P2. When residual toner accumulates on the charging roller 2, uniform charging of the photosensitive drum 1 is hindered, and image defects caused by poor charging become apparent.

In this embodiment, a peripheral speed difference is set between the charging roller 2 and the photosensitive drum 1 to reduce adhesion of residual toner to the charging roller 2. Specifically, the peripheral speed of the charging roller 2 is set to a value at least 5%, and more preferably at least 10%, faster than the peripheral speed of the photosensitive drum 1. Furthermore, the materials of the surface layers of the charging roller 2 and the photosensitive drum 1 are selected so that the residual toner is charged to the normal polarity through friction with the charging roller 2 or the photosensitive drum 1. In other words, in the charging series, the materials of the surface layers of the charging roller 2 and the photosensitive drum 1 are positioned higher (on the positive polarity side, on the non-normal polarity side) than the main component of the toner (binder resin). By configuring the peripheral speed difference and materials as described above, the residual toner is charged to the normal polarity through friction with the charging roller 2 or the photosensitive drum 1 at the charging section P2, thereby reducing adhesion of residual toner to the charging roller 2.

The remaining toner that has passed through the charging section P2 reaches the developing section P4 as the photosensitive drum 1 rotates. The toner particles charged to the normal polarity among the remaining toner carried in the non-image area (non-exposed area) on the photosensitive drum 1 are transferred to the developing roller 41 due to the potential difference between the dark area potential Vd and the developing voltage, and are then collected in the toner storage section 45. Meanwhile, the toner particles charged to the normal polarity among the remaining toner carried in the image area (exposed area) on the photosensitive drum 1 are retained on the photosensitive drum 1 without transferring to the developing roller 41 due to the potential difference between the light area potential Vl and the developing voltage. In this case, the toner particles are sent to the transfer section P5 as part of the developed toner image. The voltage value of the developing voltage is the same polarity as the normal polarity of the toner, and is higher than the light area potential Vl and lower than the dark area potential Vd.

Ideally, residual toner particles charged to an irregular polarity and toner particles with a charge close to zero are converted to a regular polarity at charging unit P2, do not adhere to charging roller 2, and are collected by developing roller 41 at developing unit P4. However, when a large amount of residual toner charged to an irregular polarity enters charging unit P2, the residual toner that was not converted to a regular polarity at charging unit P2 is more likely to adhere to charging roller 2. Furthermore, when residual toner that was not converted to a regular polarity at charging unit P2 reaches developing unit P4, it passes through developing unit P4 without being collected by developing roller 41. This can result in contamination of transfer roller 5 or image defects (white background fog) in which a faint toner image is formed on the white background (non-image area) on the sheet.

The components of the image forming device 100 are described in detail below.

(Brush member)
First, the brush member 11 in this embodiment will be described. As shown in Figures 2 and 3, the brush member 11 contacts the surface of the photosensitive drum 1 downstream of the transfer portion P5 and upstream of the charging portion P2 in the rotation direction R1 of the photosensitive drum 1. In other words, the image forming apparatus 100 includes the brush member 11, which is disposed downstream of the transfer member and upstream of the developing member in the rotation direction of the image carrier, and which contacts the surface of the image carrier. Hereinafter, the area where the brush member 11 contacts the photosensitive drum 1 will be referred to as the "brush contact portion."

Figure 4(a) is a perspective view of latent image unit 1A, and Figure 4(b) is a cross-sectional view of latent image unit 1A in a plane perpendicular to the rotation axis of photosensitive drum 1. Figure 4(c) is a diagram showing the brush contact portion as viewed in the direction of arrow 4C in Figure 4(b) from the upstream side of the rotation direction R1 of photosensitive drum 1. The brush member 11 is fixed to a seat surface 14a provided on a frame 14 of latent image unit 1A, which rotatably supports the photosensitive drum 1 and charging roller 2, and is supported by the frame 14.

Figure 5(a) is a cross-sectional view of the brush member 11 in a standalone state, cut along a plane perpendicular to the longitudinal direction. The standalone state refers to a state in which the brush member 11 is not attached to the frame 14 of the latent image unit 1A as a support member, i.e., a state in which no external force is acting on the brush member 11. Figure 5(b) is a cross-sectional view of the brush member 11 in contact with the photosensitive drum 1.

As shown in Figures 5(a) and 5(b), the brush member 11 has a base fabric 11b as a base and conductive threads 11a as bristles supported by the base fabric 11b. The base fabric 11b is made of synthetic resin fibers containing carbon as a conductive agent. The conductive threads 11a are made of, for example, nylon fibers (pile yarns) mixed with a conductive agent, and are woven into the base fabric 11b for implantation. The material of the conductive threads 11a is not limited to nylon; rayon, acrylic, polyester, or other synthetic resin fibers may also be used.

The brush member 11 is a member in which the base fabric 11b extends in an elongated manner in a predetermined direction. Hereinafter, the extension direction of the base fabric 11b will be referred to as the longitudinal direction LD of the brush member 11 (see also Figure 4(a)), and the direction along the base fabric 11b that is perpendicular to the longitudinal direction will be referred to as the lateral direction SD of the brush member 11. When the brush member 11 is in a standalone state (Figure 5(a)) with no external force acting on it, the conductive threads 11a protrude in a direction approximately perpendicular to both the longitudinal direction LD and the lateral direction SD (the normal direction of the base fabric 11b).

As shown in Figure 5(a), the distance from the base fabric 11b to the tip of the conductive thread 11a in the brush member 11 in its standalone state is defined as bristle length L1. In this embodiment, the bristle length L1 of the brush member 11 is 5.75 mm. The base fabric 11b of the brush member 11 is fixed to the frame body 14 (Figure 4(b)) of the latent image unit 1A by a fixing means such as double-sided tape. The seat surface 14a of the brush member 11 on the frame body 14 is set so that the tip of the conductive thread 11a penetrates the photosensitive drum 1. Therefore, the brush member 11 is bent with the tip of the conductive thread 11a pressed against the surface of the photosensitive drum 1.

As shown in Figure 4(c), the brush member 11 is positioned so that its longitudinal direction LD is approximately parallel to the rotational axis of the photosensitive drum 1.

On the other hand, while Figure 4(b) shows a schematic diagram in which the brush member 11 is installed with its short side direction SD approximately parallel to the surface of the photosensitive drum 1, the installation angle of the brush member 11 is not limited to this. In this embodiment, the brush member 11 is arranged at an angle relative to the surface of the photosensitive drum 1. That is, the seating surface 14a of the brush member 11 (and the base fabric 11b supported by the seating surface 14a) is arranged at an angle relative to the tangent direction of the photosensitive drum 1 so that it moves further away from the surface of the photosensitive drum 1 the further downstream in the rotation direction R1 of the photosensitive drum 1. The definition and range of the angle of inclination of the brush member 11 will be described later.

The shortest distance from the base fabric 11b of the brush member 11 fixed to the seat surface 14a to the photosensitive drum 1 is defined as L2. The difference between L2 and L1 (L1 - L2) is the maximum penetration amount of the brush member 11 into the photosensitive drum 1. However, L2 < L1.

In this embodiment, the maximum penetration amount of the brush member 11 into the photosensitive drum 1 is, for example, 1.58 mm. Furthermore, in this embodiment, as shown in Figures 4(b) and 5(a), the lateral width L3, which is the length in the lateral direction SD of the brush member 11 in its standalone state (the length of the area in which the conductive threads 11a are grafted), is 4 mm in this embodiment. The lateral width L3 is preferably 3 mm or more to maintain the performance of the brush member 11 over a long period of time. As shown in Figure 5(b), when pressed against the photosensitive drum 1, the width occupied by the conductive threads 11a in the lateral direction SD increases slightly.

In this embodiment, the brush member 11 has a longitudinal width L4 (FIG. 4C), which is the length in the longitudinal direction LD, of 216 mm. The longitudinal width L4 is set so that the brush member 11 can contact the entire image formation area (the area where a toner image can be formed, the maximum area of the latent image formed by the exposure device 3) on the photosensitive drum 1 in the longitudinal direction (the direction of the rotation axis of the photosensitive drum 1). In this embodiment, the conductive threads 11a have a thickness of 2 denier and a density of 240 kF/ ^inch² . 1 kF/ ^inch² is a density of 1,000 threads per square inch. The thickness and density of the conductive threads 11a can be changed as long as the brush member 11 satisfies the required functions. For example, the conductive threads 11a preferably have a thickness of 1 denier to 6 denier and a density of 150 kF/ ^inch² to 350 kF/ ^inch² . Note that 1 kF/inch ² represents a planting density of 1,000 fibers per square inch.

In the case of the nylon conductive thread 11a used in this embodiment, the constant length unit of 1 to 6 denier is converted to a fiber diameter of approximately 10 μm to approximately 30 μm. Therefore, when using bristle materials other than nylon for the brush member, bristle materials with a constant length unit of 1 to 6 denier or a fiber diameter of 10 to 30 μm can be used.

"1 denier or more and 6 denier or less" can be rephrased as "1.1 dtex or more and 6.7 dtex or less." Also, since 1 ^inch2 is approximately 6.45 ^cm2 , "150 kF/ ^inch2 or more and 350 kF/ ^inch2 or less" can be rephrased as "23 kF/ ^mm2 or more and 54 kF/ ^mm2 or less."

In this embodiment, the brush member 11 is configured to allow the remaining toner adhering to the surface of the photosensitive drum 1 that has passed through the transfer portion P5 to pass through while scattering the remaining toner. Therefore, if the conductive threads 11a are too thick, the remaining toner cannot be uniformly scattered, and the remaining toner may pass through the brush contact area in a streak-like pattern, potentially resulting in streak-like contamination of the charging roller 2. Furthermore, if the conductive threads 11a are too dense, the remaining toner may be blocked at the brush contact area, not only hindering the development roller 41 from collecting the remaining toner, but also potentially contaminating the inside of the image forming apparatus by falling or scattering from the photosensitive drum 1. Furthermore, the brush member 11 in this embodiment functions to triboelectrically charge the remaining toner at the brush contact area. Therefore, if the conductive threads 11a are too thin, the conductive threads 11a may easily bend and escape from the toner particles when they come into contact with the conductive threads 11a, preventing the toner particles from rolling, potentially preventing the remaining toner from being sufficiently triboelectrically charged. Furthermore, if the density of the conductive threads 11a is too low, the frequency with which the residual toner collides with the conductive threads 11a will decrease, which may result in the residual toner not being sufficiently triboelectrically charged.

The above explanation describes the preferred ranges for the thickness and density of the conductive threads 11a from the perspective of the function of dispersing residual toner and the function of frictionally charging the residual toner, but the details of the conductive threads 11a, such as the thickness, density, material, and bristle length, can be changed as appropriate depending on the function required of the brush member 11. The brush member 11 of this embodiment may also have the function of blocking foreign matter other than residual toner (e.g., paper dust) at the brush contact portion.

(Developer)
In this embodiment, toner T, which is a one-component developer having a negative normal polarity (normal charging polarity), is used as the developer. Therefore, in the description of this embodiment, unless otherwise specified, "negative polarity" is synonymous with the normal polarity of toner T, and "positive polarity" is synonymous with the non-normal polarity of toner T.

Toner T contains a binder resin and a colorant, and may also contain a release agent, charge control agent, and external additives as needed. Styrene-acrylic resin or polyester resin, which is lower in the triboelectric series (negative polarity) than the nylon and rayon that make up the conductive threads 11a of the brush member 11, can be suitably used as the binder resin. In other words, it is desirable for the main component (binder resin) of toner T to be located on the normal polarity side (lower) of the triboelectric series relative to the material of the bristle material of the brush member 11. In this embodiment, styrene-acrylic resin is used as the binder resin for toner T.

Known colorants can be used, such as dyes and pigments. Known release agents can be used, such as hydrocarbon waxes and ester waxes. Known charge control agents can be used, such as charge control agents that have an acid value and a hydroxyl value, and preferably have a negative polarity equal to or greater than that of the binder resin. Known external additives can be used, such as silica, alumina, titania, and titanium composite oxides. It is preferable that the colorants and release agents be encapsulated in the binder resin so as not to affect the charge polarity of the toner particle surface.

The toner T can be a polymerized toner produced by polymerization. A particle size (volume average particle size) of 4 to 10 μm, more preferably 6 to 8 μm, is preferably used. In this embodiment, spherical toner with a particle size of 7 μm prepared by polymerization is used. The toner T of this embodiment is a non-magnetic single-component developer that does not contain a magnetic component and is supported on the developing roller 41 primarily by intermolecular forces and electrostatic forces (image forces). However, a single-component developer made of toner containing a magnetic component may also be used. Alternatively, a two-component developer made of non-magnetic toner and magnetic carrier may also be used. When a magnetic developer is used, a cylindrical developing sleeve with a magnet disposed inside is used as the developer support. In addition to the toner or carrier, the developer may contain additives (e.g., wax or silica particles) to adjust the fluidity and charging performance of the toner.

(Photosensitive drum)
The photosensitive drum 1 has a cylindrical or columnar conductive support (metal core) as the bottom layer, on which an undercoat layer, a charge generation layer, and a charge transport layer are sequentially laminated. The charge transport layer is formed by applying and drying a coating material in which a charge transport material and a binder resin are mixed in a solvent. Known charge transport materials can be used as the main charge transport material. Examples include various triarylamine compounds and hydrazone compounds. Examples of binder resins include polycarbonate resins and polyarylate resins.

The surface (outermost) charge transport layer, and in particular the binder resin that makes up the majority of it, are the dominant factors in triboelectric charging with toner. The polycarbonate resins and polyarylate resins listed here are on the non-regular polarity side (higher) of the triboelectric series relative to the styrene acrylic that is the binder resin of toner T. In other words, it is preferable that the outermost layer of the image carrier be made of a material that can triboelectrically charge the toner to the regular polarity when rubbed against the resin that is the main component of the toner. In this embodiment, polycarbonate was selected as the binder resin for the outermost layer.

In this embodiment, the photosensitive drum 1 is cylindrical and has an outer diameter of 24 mm. The way in which the brush member 11 is applied (for example, the penetration amount described above and the angle described in the third embodiment) is changed appropriately depending on the outer diameter of the photosensitive drum 1.

(Charging roller)
The charging roller 2 according to this embodiment will now be described. The charging roller 2 has a core metal as a conductive support, a 2 mm elastic layer provided on the outer periphery of the core metal, and a 25 μm resin layer as a surface layer provided on the outer periphery of the elastic layer. The surface of the surface layer comes into contact with the photosensitive drum 1 and serves as a surface that discharges electricity to the photosensitive drum 1.

The elastic layer is made of an electronically conductive rubber material. Electronically conductive rubber materials are, for example, binder polymers that are not themselves electrically conductive, with carbon black dispersed as conductive particles (electronically conductive agents) to adjust the electrical resistance. Known binder polymers used in the conductive elastic layers of charging rollers for electrophotographic devices can be used. Examples include hydrin rubber and butadiene rubber. In this embodiment, hydrin rubber was selected.

The type of carbon black to be compounded in the elastic layer is not particularly limited, as long as it is a conductive carbon black that can impart conductivity to the elastic layer. Furthermore, if necessary, fillers, processing aids, crosslinking aids, crosslinking accelerators, crosslinking accelerator aids, crosslinking retarders, softeners, dispersants, colorants, and other additives commonly used as compounding agents in rubber may also be added to the elastic layer.

The resin for the surface layer of the charging roller 2 is a resin material that is on the non-regular polarity side (higher) of the toner T's main component (binder resin) in the charging series. For example, the surface layer is formed by coating the outer periphery of the elastic layer with a conductive resin such as polycarbonate urethane. By forming the surface layers of the charging roller 2 and photosensitive drum 1 from the above materials and setting a peripheral speed difference between the charging roller 2 and photosensitive drum 1 as described above, the remaining toner can be frictionally charged to the regular polarity at the charging section P2.

Furthermore, roughening particles of a polarity that does not impair frictional charging can be added to the surface layer of the charging roller 2. For example, one method is to disperse the same polycarbonate urethane material as the surface layer in a particulate form. In other words, the charging roller 2 does not need to be in close contact with the surface of the photosensitive drum 1 at the charging section P2, but can be configured so that the peaks of the roughening particles form contact with the surface of the photosensitive drum 1.

(Transfer roller)
The transfer roller 5 is a roller-type transfer member disposed opposite the photosensitive drum 1. The transfer roller 5 is pressed against the photosensitive drum 1 at a predetermined pressure. The transfer roller 5 in this embodiment is an elastic roller with an outer diameter of 12 mm, in which an elastic layer made of conductive nitrile butadiene rubber-hydrin sponge rubber is formed around a core metal.

(Contact conditions of brush members)
In this embodiment, the brush member 11 applies an electric charge to the remaining toner by frictional charging while scattering the remaining toner on the photosensitive drum 1. At this time, the material of the bristles (conductive threads 11a) of the brush member 11 is one that is on the positive side (higher) of the triboelectric series relative to the main component of the toner T so that a negative charge is applied to the remaining toner by frictional charging. In addition, the contact pressure between the brush member 11 and the photosensitive drum 1 at the brush contact portion is ensured so that the conductive threads 11a can rub the remaining toner with sufficient force.

In terms of the triboelectric series, the main component of the toner T in this embodiment is styrene-acrylic resin. The bristle material of the brush member 11 is preferably a material such as nylon or rayon, in which styrene-acrylic is on the negative (lower) side of the triboelectric series and the triboelectric series difference is large. In this embodiment, as described above, nylon resin was selected as the main component of the conductive thread 11a. Polyester and acrylic fibers are not desirable materials for the conductive thread 11a, as styrene-acrylic is on the positive side of the triboelectric series and the triboelectric series difference is small. However, if the main component of the toner T is different, polyester or acrylic fibers may be used for the conductive thread 11a.

The surface layer of the photosensitive drum 1 can also affect the frictional charging of the toner T at the brush contact area. Therefore, it is preferable that the main component of the surface layer of the photosensitive drum 1 be a material that is on the positive side of the triboelectric series relative to the main component of the toner T. In this embodiment, as described above, the main component of the surface layer of the photosensitive drum 1 is polycarbonate.

The contact conditions of the brush member 11 at the brush contact area are described below. To examine the physical properties (parameters) that indicate the contact conditions of the brush member 11, four samples with different bristle thicknesses and densities were prepared. Sample 1 is a brush member 11 with thick bristles and low density. Sample 2 is a brush member 11 with thin bristles and medium density. Sample 3 is a brush member 11 with thin bristles and high density. Sample 4 is a brush member 11 with medium bristle thickness and low density. The brush member 11 of each sample was then brought into contact with the photosensitive drum 1, and the peak pressure and maximum contact area ratio at the brush contact area were calculated using the following method. Note that the peak pressure is the maximum value of the average contact pressure within a 1 mm width in the short direction of the brush contact area, and the maximum contact area ratio is the contact area ratio between the brush member 11 and the photosensitive drum 1 in a 1 mm wide region where the peak pressure is obtained.

The peak pressure was calculated as follows. As shown in Figure 7(a), a compression test fixture for a Shimadzu EZTest compact benchtop testing machine was used to measure the normal force when a pressure plate 71 was pressed against the brush member 11 while aligning the bristles of the brush member 11, which was placed horizontally. This determined the relationship between the penetration amount and the normal force. Meanwhile, a glass plate 72, as shown in Figure 7(b), was moved in the horizontal direction D and pressed against the brush member 11 to align the bristles. The brush contact area was observed under a microscope from the opposite side of the glass plate 72 to measure the contact width 73 in the short direction SD. The horizontal direction D is one side of the short direction SD, which corresponds to the rotation direction R1 of the photosensitive drum 1.

When the density and thickness of the bristles of the brush member 11 are uniform, the peak pressure can be calculated using the following formulas (1) to (3). First, when an object is pressed against the brush member 11 with a given penetration amount, the average value of the contact pressure (average pressure) at the brush contact point can be expressed by the following formula: Note that the normal force and contact width in the formula are values measured when the pressure plate 71 or glass plate 72 is pressed against the brush member 11 with a given penetration amount.
(Formula 1) Average pressure = normal force / (contact width x longitudinal width) (gf/mm ² )

In an actual brush contact portion between the brush member 11 and the photosensitive drum 1, the contact pressure is greatest at the portion where the brush member 11 penetrates the photosensitive drum 1 to the greatest extent. This maximum value of contact pressure is called the peak pressure. The peak pressure is calculated by (Equation 3) using the average penetration amount (Equation 2) obtained from the maximum and minimum penetration amounts of the brush member 11.
(Formula 2) Average penetration amount = (Maximum penetration amount + Minimum penetration amount)/2 (mm)
(Equation 3) Peak pressure = average pressure x maximum penetration amount / average penetration amount (gf/mm ² )

The above calculation method actually means linearly approximating the contact pressure acting on the surface of the photosensitive drum 1, which describes an arc as shown in Figure 14. Specifically, suppose a brush member 11 with a lateral width L3 of 4 mm is brought into contact with a photosensitive drum 1 with an outer diameter of 24 mm, from directly above the photosensitive drum 1, so that the penetration depth is 1.2 mm at the center in the lateral direction SD. In this case, the maximum penetration depth is 1.2 mm, the minimum penetration depth is 1.03 mm, and the average penetration depth is 1.115 mm, and the peak pressure can be calculated using (Equation 3).

If the density, thickness, etc. of the brush member 11 is not uniform in the short direction SD, the brush member 11 is cut at unit lengths (e.g., 1 mm) in the short direction SD, the normal force is measured, and the contact pressure for each unit length region is obtained. The average of these contact pressures is then taken as the average pressure, and the maximum value is taken as the peak pressure.

To calculate the contact area ratio, the brush member 11 was brought into contact with the glass plate g as shown in Figure 8(a), and the areas where the bristles of the brush member 11 were in contact (contact areas) and areas where they were not in contact (non-contact areas) were distinguished by color. Figure 8(b) is an actual photograph observed under a microscope, and Figure 8(c) is an image of Figure 8(b) that has been binarized so that contact areas are white and non-contact areas are black. The contact area ratio is the ratio of the area of the contact areas to the area of the object being observed. Typically, the contact area ratio is at its maximum value (maximum contact area ratio) at the position in the short direction SD where the peak pressure is obtained.

To summarize the above explanation, for an image forming apparatus having the brush member 11 as in this embodiment, the peak pressure and the maximum contact area ratio can be confirmed by the following procedure.
1) The outer diameter of the photosensitive drum 1, the bristle length L1 of the brush member 11, the short width L3, the long width L4, and the shortest distance L2 from the base fabric 11b of the brush member 11 to the surface of the photosensitive drum 1 are measured, and the maximum penetration amount (L1-L2) is calculated (see Figures 3(b) and 3(c)).
2) The minimum intrusion amount is calculated from the outer diameter of the photosensitive drum 1, the width L3 of the brush member 11, and the maximum intrusion amount measured in 1) above, based on the geometric relationship shown in FIG.
3) The average intrusion amount is calculated based on the maximum intrusion amount and the minimum intrusion amount obtained in 1) and 2) above, using (Equation 2).
4) Using the average intrusion calculated in 3) above, a compression test is performed on the brush member 11 using the method of FIGS. 7(a) and 7(b), and the average pressure is obtained based on (Equation 1).
5) Using the maximum intrusion amount, average intrusion amount, and average pressure obtained in 1), 3), and 4), the peak pressure is calculated based on (Equation 3).
6) Using the maximum penetration amount obtained in 1), the brush member 11 is pressed against the glass plate by the method shown in Figures 8(a) to 8(c), and the contact surface is observed to calculate the maximum contact area ratio.

Furthermore, to achieve the desired peak pressure and maximum contact area ratio of the brush member 11, parameters such as the outer diameter of the photosensitive drum 1, the bristle length L1 and width L3 of the brush member 11, and the above-mentioned shortest distance L2 can be appropriately changed, and the peak pressure and maximum contact area ratio can be confirmed using the above procedure.

Using the above method, the peak pressure and maximum contact area ratio were calculated for each sample under multiple contact conditions with different maximum penetration amounts. Figure 15 shows a map plotting peak pressure on the vertical axis and maximum contact area ratio on the horizontal axis. In Figure 15, black dots indicate that no image defects occurred, while white dots indicate that image defects occurred.

As shown in Figure 15, image defects occurred when the peak pressure was less than 0.7 gf/ ^mm2 and when the maximum contact area ratio was less than 18%. This is thought to be because when the peak pressure was too low, only a portion of the bristles of the brush member 11 contacted the photosensitive drum 1, resulting in insufficient charging of the residual toner to the normal polarity. Similarly, when the maximum contact area ratio was too low, the frequency with which toner particles came into contact with the bristles of the brush member 11 was reduced, resulting in insufficient charging of the residual toner to the normal polarity. In either case, if the residual toner reached the charging section P2 without being sufficiently charged to the normal polarity at the brush contact point, residual toner charged to the non-normal polarity or toner with a charge amount close to zero would adhere to the charging roller 2, causing further contamination of the charging roller 2.

In addition, image defects also occurred when the peak pressure was greater than 3.5 gf/ ^mm2 and the maximum contact area ratio was greater than 74%. This is thought to be because, in both cases where the peak pressure was too high and the maximum contact area ratio was too high, the remaining toner could not pass through some of the brush contact areas, concentrating in areas where it could pass (areas with relatively low contact pressure or bristle density). In this case, the remaining toner adhered to the surface of the photosensitive drum 1 that had passed through the brush contact area in stripes (lines extending in the direction of rotation), causing striped contamination of the charging roller 2. Note that in areas where the peak pressure or maximum contact area ratio was particularly high, the remaining toner was blocked by the brush member 11, which not only hindered the development roller 41 from collecting the remaining toner, but also potentially caused the blocked toner to scatter and contaminate the interior of the image forming apparatus.

Therefore, it is desirable to configure the brush member 11 so that the peak pressure and maximum contact area ratio at the brush contact portion fall within the following region enclosed by the dotted line in FIG.
Peak pressure: 0.7 gf/mm2 or ^more and 3.5 gf/mm2 or ^less Maximum contact area ratio: 18% or more and 74% or less

This allows the charge distribution of the residual toner to be stabilized at a normal polarity in a cleanerless brush system in which the brush member 11 scatters the residual toner adhering to the surface of the photosensitive drum 1 that has passed through the transfer portion P5. In other words, the charge distribution of the residual toner after it leaves the brush contact portion has a peak on the normal polarity side (negative polarity side) of the toner T, and is sharper than the charge distribution of the residual toner before it enters the brush contact portion.

Note that the image defects described above are less likely to occur near the center of the area surrounded by the dotted line in Fig. 15 than near the periphery. Therefore, it is preferable to configure the brush member 11 so that the peak pressure and/or the maximum contact area ratio falls within the following ranges.
Peak pressure: 1.4 gf/mm2 or ^more and 2.8 gf/mm2 or ^less Maximum contact area ratio: 32% or more and 60% or less

Since 1 gf is approximately equal to 9.8 x mN (millinewtons), "0.7 gf/ ^mm2 or more and 3.5 gf/ ^mm2 or less" can be rephrased as "6.9 mN/ ^mm2 or more and 34 mN/ ^mm2 or less." Similarly, "1.4 gf/ ^mm2 or more and 2.8 gf/mm2 or ^less " can be rephrased as "14 mN/ ^mm2 or more and 28 mN/ ^mm2 or less."

Furthermore, in this embodiment, the Clark-Evans Index is introduced as an index that indicates whether the brush member 11 is contacting the photosensitive drum 1 evenly. When multiple points are distributed in a certain planar area, the Clark-Evans Index indicates the tendency of the points to be distributed in a locally concentrated manner or to be distributed at a distance from each other.

The method for calculating the Clark-Evans index will be described below. First, if the distance from point i to the nearest neighbor point is d_i and the number of points is n, the average value of the distance from each point to the nearest point (average nearest neighbor distance) W is expressed by the following equation (Equation 1).

Here, as an evaluation criterion, consider a case where points are randomly distributed (following a uniform Poisson distribution) on a plane of area S. In this case, the expected value E(W) of the average nearest neighbor distance W is expressed by the following equation (Equation 2):

In order to compare cases where the number of points or density is different, the average nearest neighbor distance W is normalized by the above expected value E(W) as expressed in the following equation (Equation 3), and the resulting w is called the Clark-Evans index.

To determine the Clark-Evans index of the brush member 11, the brush member 11 is pressed against a glass surface as shown in Figure 6(a), and the brush contact area is observed from the glass surface opposite to where the brush member 11 is pressed. If the tips of the bristles in a certain area (100 ^mm2 ) at the brush contact area are represented by points, a distribution of points as shown in Figure 6(b) is obtained. The Clark-Evans index is calculated from this distribution of points using the above equations (Equation 1) to (Equation 3).

Note that some bristles are in contact with the glass surface at the base rather than the tip. It is believed that the effect of such bristles in frictionally charging the toner T is largely due to the contribution of the point where the bristles are in strongest contact with the glass surface (the most pressured point). However, the distribution of the most pressured points of the bristles is largely the same as the distribution of the bristles' tips, and the properties of the distribution are almost the same. Therefore, in this embodiment, the Clark-Evans index is calculated from the distribution of the tips of each bristle in contact with the glass surface.

The Clark-Evans index is w=1 for a random distribution, w<1 for a clustered distribution, and w>1 for a regular distribution. An extreme example of a regular distribution is a grid-like distribution that covers the entire area of the object being observed. An extreme example of a clustered distribution is a distribution in which points are densely concentrated in one or a few places within the area of the object being observed.

The Clark-Evans index was calculated for an actual sample of the brush member 11 and the results are as follows:
Sample 1 w = 1.01
Sample 2 w = 1.13
Sample 3 w = 1.15
Sample 4 w = 1.07
Sample 2 was intentionally twisted into a bundle w=0.7

The properties of the Clark-Evans index indicate that if w>1, the tips of the bristles of the brush member 11 are loose and not bundled; conversely, if w<1, it suggests that the bristles of the brush member 11 are bundled (clusters, clumps) for some reason.

For the brush member 11 to function properly, it is preferable that the bristles of the brush member 11 contact the photosensitive drum 1 in a loose state, rather than in a bundle. In this embodiment, the brush member 11 is configured so that the Clark-Evans index is 1 or greater (w≧1). This condition can also be said to be a condition that ensures that the bristles are not bundled for some reason.

Note that depending on the configuration of the brush member 11, the Clark-Evans index value may differ depending on the location of the brush contact area. In such cases, the Clark-Evans index at the point where the brush member 11 penetrates the most (the point where the contact pressure reaches its peak) is assumed to be 1 or greater. This is because at the point where the penetration is greatest, the force applied to the bristles makes it easier for the bristles to clump together.

(Arrangement of Brush Members)
Next, the arrangement of the brush member 11 relative to the photosensitive drum 1 in this embodiment will be described. In this embodiment, the brush member 11 is arranged at an angle so that the contact pressure of the brush member 11 with respect to the photosensitive drum 1 is higher at the front end of the brush than at the rear end of the brush. Here, the "front end of the brush" refers to the upstream end of the brush member 11 in the rotation direction R1 of the photosensitive drum 1, and the "rear end of the brush" refers to the downstream end of the brush member 11 in the rotation direction R1 of the photosensitive drum 1.

The arrangement of the brush member 11 will be explained in detail below using Figure 1. Figure 1 is a schematic diagram showing the arrangement of the brush member 11 relative to the photosensitive drum 1. Figure 1 shows the brush member 11 and photosensitive drum 1 as viewed in the direction of the rotational axis of the photosensitive drum 1 (the longitudinal direction LD of the brush member 11). Note that the bristles (conductive threads 11a) of the brush member 11 are virtually illustrated in an extended state (single state) without interfering with the photosensitive drum 1.

In the diagram, the rotation axis of the photosensitive drum 1 is designated as O. The line (first line) extending from the rotation axis O through the center of the base fabric 11b of the brush member 11 in the short direction SD is designated as m. The line (second line) perpendicular to line m is designated as Lt. Line Lt is parallel to the tangent line t to the surface of the photosensitive drum 1 at the intersection p between line m and the surface of the photosensitive drum 1. Furthermore, the line (third line extending in the short direction SD) drawn along the base fabric 11b is designated as n.

In this embodiment, the brush member 11 is positioned so that the straight line n drawn along the base fabric 11b is inclined toward the surface of the photosensitive drum 1 toward the upstream side of the rotation direction R1 of the photosensitive drum 1, relative to the straight line Lt extending tangent to the surface of the photosensitive drum 1.

The angle β (°) between the lines n and Lt represents the inclination angle of the brush member 11. β is preferably set in the range of 8° to 16°, for example. If β is too large, the difference between the penetration amount at the front end of the brush and the penetration amount at the rear end of the brush will be large, which may result in excessive penetration at the front end of the brush, blocking toner, or the penetration amount at the rear end of the brush becoming negative (non-contact). If β is too small, it will be difficult to achieve an appropriate difference in contact pressure and contact area ratio between the front end of the brush and the rear end of the brush, as explained below.

In this embodiment, β was set to 12°. In this case, the amount of penetration of the brush member 11 into the photosensitive drum 1 is greatest at the front end of the brush, with this value (maximum penetration) being 1.58 mm.

By tilting the brush member 11 as described above, the contact pressure and contact area ratio at the front end of the brush are higher than those at the rear end of the brush. That is, the contact pressure at a first position within the brush contact area (the contact area between the brush member and the image carrier) is higher than the contact pressure at a second position within the brush contact area that is downstream of the first position in the rotation direction R1 of the image carrier. Furthermore, the contact area ratio between the brush member and the image carrier at the first position is greater than the contact area ratio between the brush member and the image carrier at the second position.

In this example of the present embodiment, the contact pressure at the front end of the brush is 2 gf/ ^mm2 and at the rear end of the brush is 1 gf/ ^mm2 . The contact area ratio is 50% at the front end of the brush and 20% at the rear end of the brush. The relationship between the lateral position of the brush member 11 and the contact pressure in this example is shown in Figure 9(a), the relationship between the lateral position of the brush member 11 and the contact area ratio is shown in Figure 9(b), and the relationship between the contact pressure and the contact area ratio is shown in Figure 9(c). Here, the lateral position of the brush member 11 refers to the position in the lateral direction SD, with the front end of the brush as the reference (0).

The embodiment shown in Figures 9 (a) and 9 (b) is an example of a configuration in which the contact pressure and contact area ratio at a first position near the front end of the brush are higher than the contact pressure and contact area ratio at a second position closer to the rear end of the brush than the first position, and the curves drawn by the contact pressure and contact area ratio may be different. As in this embodiment, it is preferable for the contact pressure and contact area ratio to be maximum at the front end of the brush. It is also preferable for the contact pressure and contact area ratio to decrease monotonically from the front end of the brush toward the rear end of the brush, but it is sufficient if the contact pressure and contact area ratio at the front end of the brush are at least greater than the contact pressure and contact area ratio at the rear end of the brush.

The difference between the contact pressure (maximum value) at the front end of the brush and the contact pressure (minimum value) at the rear end of the brush is preferably 0.6 gf/ ^mm2 or more and 1.5 gf/ ^mm2 or less. In addition, the difference between the contact area ratio (maximum value) at the front end of the brush and the contact area ratio (minimum value) at the rear end of the brush is preferably 15% or more and 40% or less.

Furthermore, as will be explained in detail in the fourth embodiment, this embodiment is an example of a configuration in which the penetration amount δ1 (mm) of the front end of the brush against the photosensitive drum 1 and the penetration amount δ2 (mm) of the rear end of the brush against the photosensitive drum 1 satisfy the relationship δ1 > δ2 > 0.

(Brush applied bias)
The brush member 11 is also connected to a brush power supply E11 (FIG. 3) as a voltage application means. During image formation, a predetermined brush voltage (brush bias) is applied to the brush member 11 by the brush power supply E11. In this embodiment, a negative DC voltage is applied to the brush member 11 as the brush voltage during image formation. In this embodiment, the brush voltage during image formation is −350 V. Meanwhile, the surface potential of the surface area of the photosensitive drum 1 that moves through the transfer portion P5 toward the brush contact portion is 0 to −200 V. Therefore, the brush voltage is set so that the surface of the photosensitive drum 1 at the brush contact portion is the normal toner polarity side, and the brush member 11 is the abnormal toner polarity side. With this brush voltage setting, toner charged to the normal polarity is attracted toward the photosensitive drum 1, and toner charged to the abnormal polarity is attracted toward the brush member 11.

(Behavior of toner at brush contact point)
Residual toner that has not been transferred from the photosensitive drum 1 to the sheet by the transfer roller 5 is sent to the brush contact portion by the rotation of the photosensitive drum 1. At this time, the higher the contact pressure at the brush contact portion, the easier it is for the toner particles to roll due to the sliding between the brush member 11 and the surface of the photosensitive drum 1, and the easier it is for the residual toner to be charged with the normal polarity.

However, if the contact pressure is too high, toner will be unable to pass through areas of the brush contact area where the contact pressure is higher than the surrounding area or the bristle density is higher than the surrounding area, while toner will concentrate and escape in areas where the contact pressure or density is lower than the surrounding area. As a result, as shown in Figure 10(a), toner T that has escaped from the brush contact area will be distributed in a streaky pattern. Figure 10(a) shows the area around the brush member 11 as viewed from the outer periphery of the photosensitive drum 1, with remaining toner shown in gray (dot pattern) and areas with no remaining toner remaining shown uncolored.

The state in which toner T that has passed through the brush contact area is distributed in a streak-like pattern will be explained using Figure 10(b). Figure 10(b) is a schematic diagram showing a cross section taken along the longitudinal direction of the surface of the photosensitive drum 1 that has passed through the brush contact area. The toner T that has passed through the brush contact area contains toner particles with irregular polarity (+). Furthermore, when toner T passes through the brush contact area in a streak-like pattern, the brush member 11 does not come into contact with some of the toner particles at the points where the toner passes through, and there is a tendency for many toner particles to pass through the brush contact area without being frictionally charged by the brush member 11 and retaining their irregular polarity.

At charging section P2, a charging voltage of the same polarity as the normal polarity of toner T is applied to charging roller 2. Therefore, as shown in Figure 10(c), normal polarity toner T is pressed against the surface of photosensitive drum 1 by the charging voltage and passes through charging section P2 without adhering to charging roller 2. On the other hand, when non-normal polarity toner T reaches charging section P2 for the reasons described above, it is attracted to and adheres to charging roller 2 by the charging voltage. If toner adhesion to charging roller 2 accumulates, image defects may occur due to improper charging. Therefore, toner that has passed through brush member 11 in a streak-like manner as described above causes streak-like contamination of charging roller 2, which ultimately manifests as streak-like image defects caused by improper charging that appear at certain positions in the main scanning direction of the image.

In contrast, in this embodiment, the contact pressure and contact area ratio of the brush contact portion at the front end of the brush are higher than those at the rear end of the brush. This allows the toner T to be charged with the correct polarity while preventing the toner T from coming off in streaks (dispersing it evenly).

Figure 11(a) is a conceptual diagram showing the state in which the brush member 11 contacts the photosensitive drum 1 in this embodiment. Figure 11(b) is a cross-sectional view of the surface of the photosensitive drum 1 along the longitudinal direction of the photosensitive drum 1 at the front end of the brush. Figure 11(c) is a cross-sectional view of the surface of the photosensitive drum 1 along the longitudinal direction of the photosensitive drum 1 at the center of the brush. Figure 11(d) is a cross-sectional view of the surface of the photosensitive drum 1 along the longitudinal direction of the photosensitive drum 1 at the rear end of the brush.

As shown in Figure 11(a), the contact pressure and contact area ratio at the front end of the brush are high, so a large amount of toner rolls at the front end of the brush and is given a charge of normal polarity through frictional charging. However, the toner passing through the front end of the brush is concentrated in a certain area in the longitudinal direction.

Then, as the photosensitive drum 1 rotates, the bristles of the brush member 11 randomly come into contact with the toner T as it moves toward the rear end of the brush within the brush contact area, as shown in Figures 11(b) and 11(c). Furthermore, because the contact pressure and contact area ratio decrease toward the rear end of the brush, the toner T moves more freely in the longitudinal direction. By mitigating the concentration of toner T, the bristles of the brush member 11 come into even contact with the toner T, allowing more toner T to be converted to the regular polarity. Furthermore, because a brush voltage is applied to the brush member 11, some of the toner with irregular polarity is attracted to the brush member 11.

In this way, with the configuration of this embodiment, the brush member 11 applies a charge of the normal polarity to the toner T, preventing the toner T from falling out in streaks and dispersing it evenly, thereby suppressing the occurrence of poor charging over a long period of time.

(Verification experiment)
In order to verify that the configuration of this embodiment can prevent charging defects, experiments were conducted to confirm whether charging defects occur in several configuration examples with different configurations of the brush member 11 and different contact conditions with the photosensitive drum 1. Table 1 below shows the main contact conditions and whether charging defects occur in each configuration example, and Table 2 shows the detailed configuration of each configuration example.

The configuration described as an example of this embodiment is referred to as configuration example 1-1.
In the configuration example 1-2, the contact pressure and the contact area ratio are substantially constant from the front end side of the brush to the rear end side of the brush.
In configuration example 1-3, the contact pressure and contact area ratio decrease from the front end of the brush to the rear end of the brush to the same extent as in configuration example 1-1, and the bristles of the brush member 11 are thicker and have a lower density than in configuration example 1-1.
In configuration example 1-4, the contact pressure and contact area ratio decrease from the front end of the brush to the rear end of the brush to the same extent as in configuration example 1-1, and the bristle density of the brush member 11 is higher than in configuration example 1-1.
In configuration example 1-5, the contact pressure and contact area ratio decrease from the front end side of the brush to the rear end side of the brush to the same extent as in configuration example 1-1, and the lateral width of the brush member 11 is shorter than in configuration example 1-1.
In Configuration Example 1-6, the contact pressure and contact area ratio decrease from the front end side of the brush to the rear end side of the brush, but the amount of change in the contact pressure and contact area ratio is smaller than in Configuration Example 1-1.
In configuration example 1-7, the contact pressure and contact area ratio decrease from the front end of the brush to the rear end of the brush to the same extent as in configuration example 1-1, and the lateral width of the brush member 11 is intermediate between configuration examples 1-1 and 1-5.
In the configuration example 1-8, the contact pressure and the contact area ratio decrease from the front end side of the brush to the rear end side of the brush, and the amount of change is intermediate between the configuration examples 1-1 and 1-6.

The experimental environment was a low-temperature, low-humidity environment (15°C/10%) where charging defects are likely to occur. In the experiment, 10,000 images were output by intermittently outputting two images at a time with a printing rate (coverage, image ratio) of 3%, and the occurrence of black spots (dot-shaped image defects) was confirmed when a solid white sample image was output. In Table 1, the occurrence of charging defects is recorded as "occurrence" when black spots are observed, and the absence of charging defects is recorded as "absence." The change in contact pressure is the difference between the contact pressure at the front end of the brush and the contact pressure at the rear end of the brush. The change in contact area ratio is the difference between the contact area ratio at the front end of the brush and the contact area ratio at the rear end of the brush. Furthermore, configurations not specifically mentioned in Configuration Examples 1-2 to 1-8 are the same as Configuration Example 1-1.

As shown in Table 1, it was confirmed that configuration examples 1-1, 1-7, and 1-8 did not produce black spots and prevented poor charging. On the other hand, poor charging occurred in configuration examples 1-2 to 1-6.

The reason why poor charging occurred in configuration example 1-2, where the contact pressure and contact area ratio do not decrease from the front end of the brush to the rear end of the brush, is thought to be because the contact pressure and contact area ratio are high even at the rear end of the brush, causing the toner to come off in streaks. This shows that a configuration like configuration example 1-1, where the contact pressure and contact area ratio decrease from the front end of the brush to the rear end of the brush, is effective in preventing poor charging.

Furthermore, poor charging occurred in Configuration Example 1-6, where the change in contact pressure and contact area ratio was small, while poor charging did not occur in Configuration Example 1-8, where the change in contact pressure and contact area ratio was greater than in Configuration Example 1-6 but smaller than in Configuration Example 1-1. This indicates that a greater change in contact pressure and contact area ratio can more effectively suppress the occurrence of poor charging. Specifically, a change in contact pressure of 0.6 gf/mm² or ^more and a change in contact area ratio of 15% or more (more preferably, 18% or more as in Configuration Example 1-8) are preferred, with 1.0 gf/ ^mm² or more and 30% or more being even more preferred. However, since the timing at which poor charging occurs in Configuration Example 1-6 is later than in Configuration Example 1-2, where the contact pressure and contact area ratio do not decrease, poor charging may also be suppressed in Configuration Example 1-6 depending on the specific configuration of the image forming apparatus (e.g., the life setting of the charging roller 2).

Specifically, the differences between Configuration Example 1-2 and Configuration Example 1-6 will be explained. While Configuration Example 1-2 has the same penetration amount at the upstream and downstream ends of the brush, Configuration Example 1-6 has a greater penetration amount at the upstream end of the brush than at the downstream end. Therefore, in Configuration Example 1-6, the contact pressure and contact area ratio at the upstream end of the brush contact area are higher than at least the contact pressure and contact area ratio at the downstream end of the brush contact area. Therefore, the timing at which poor charging occurs in Configuration Example 1-6 is later than in Configuration Example 1-2, where the contact pressure and contact area ratio do not decrease. Therefore, it can be said that Configuration Example 1-6 has a certain degree of effectiveness in suppressing poor charging. However, as can be seen from Table 2, in both Configuration Example 1-2 and Configuration Example 1-6, the maximum penetration amount occurs near the center of the brush rather than the upstream end, which may result in insufficient toner scattering from the upstream end to the rear end of the brush.

The reason poor charging occurred in configuration example 1-5 is because the brush member 11, which has an extremely short width, is unable to sufficiently scatter toner at the rear end of the brush. On the other hand, poor charging did not occur in configuration example 1-7, where the brush member 11 has a width of 3 mm. Therefore, it is clear that a width of 3 mm or more for the brush member 11 is preferable.

The reason why poor charging occurred in Configuration Example 1-3 is thought to be that the minimum value of the contact pressure of the brush member 11 (contact pressure at the rear end of the brush) was too high, causing the toner to pass through the brush member 11 in a streaky manner. Therefore, it is preferable to set the contact pressure at the rear end of the brush to 1.5 gf/ ^mm² or less (more preferably, 1.4 gf/ ^mm² or less in Configuration Example 1-8).

The reason for the poor charging in Configuration Example 1-4 is thought to be that the contact area ratio at the rear end of the brush was too high, causing the toner to pass through the brush member 11 in a streaky manner. Therefore, it is preferable to set the contact area ratio at the rear end of the brush to, for example, 40% or less (more preferably, 32% or less as in Configuration Example 1-8). In addition, it is preferable to set the density of the bristle material of the brush member 11 to the above-mentioned 350 kF/ ^inch2 or less.

As explained above, in this embodiment, the contact pressure and contact area ratio at the front end of the brush are higher than those at the rear end of the brush, making it possible to suppress the occurrence of poor charging over a long period of time.

(Modification)
In this embodiment, a configuration is realized in which the contact pressure and contact area ratio on the front end side of the brush are higher than those on the rear end side of the brush by arranging the brush member 11, which has a constant bristle length, at an angle with respect to the tangential direction of the photosensitive drum 1. Without being limited to this, for example, a configuration in which the contact pressure and contact area ratio are reduced by providing a difference in bristle length between the front end side and the rear end side of the brush may be adopted.

Second Embodiment
In this embodiment, the bristle density of the brush member 11 varies depending on the location so that the contact pressure and contact area ratio at the front end of the brush are higher than those at the rear end of the brush. Hereinafter, elements with the same reference numerals as those in the first embodiment will be considered to have substantially the same configurations and functions as those described in the first embodiment, and differences from the first embodiment will be mainly described.

In this embodiment, the brush member 11 has a higher bristle density at the front end than at the rear end. In this example, conductive yarn 11a with a thickness of 2 denier is used as the bristle material, and the density decreases in three stages of 240, 200, and 160 (all in kF/ ^inch2 ) every 2 mm from the front end to the rear end of the brush. The lateral width of the brush member 11 in this example is 6 mm.

Figures 12(a) and 12(b) are schematic diagrams of the brush member 11 observed from the tip of the bristles. Figure 12(a) shows this embodiment, in which the density of the bristles (conductive threads 11a) decreases toward the rear end of the brush (downstream in the rotation direction R1 of the photosensitive drum 1). In contrast, in the first embodiment shown in Figure 12(b), the density of the bristles (conductive threads 11a) is constant.

In this way, in this embodiment, the bristle density at the first position on the front end of the brush is higher than the bristle density at the second position, which is closer to the rear end of the brush than the first position. This embodiment is an example of a configuration in which the contact pressure and contact area ratio at the first position on the front end of the brush are higher than the contact pressure and contact area ratio at the second position.

In this embodiment, it is also desirable that the Clark-Evans index w of the brush member 11 be w≧1.

In this embodiment, unlike the first embodiment, it is not necessary to position the brush member 11 at an angle relative to the photosensitive drum 1. In the example of this embodiment, β = 0 in Figure 1. In this example, the penetration amount (maximum penetration amount) of the brush member 11 into the photosensitive drum 1 was set to 1 mm.

In this embodiment, the contact pressure of the brush member 11 against the photosensitive drum 1 is 2 gf/mm ² at the front end of the brush and 1 gf/mm ² at the rear end of the brush. The contact area ratio is 50% at the front end of the brush and 20% at the rear end of the brush.

In this embodiment, it is also preferable to apply a brush voltage to the brush member 11. The brush voltage is set to, for example, -350 V, as in the first embodiment.

(Verification experiment)
In order to verify that the configuration of this embodiment can prevent charging defects, experiments were conducted to confirm whether charging defects occur in several configuration examples with different brush member 11 configurations and different contact conditions with the photosensitive drum 1. Table 3 below shows the main contact conditions and whether charging defects occur in each configuration example, and Table 4 shows the detailed configuration of each configuration example. The experimental environment, output image, sample image, and charging defect evaluation method are the same as those in the first embodiment.

The configuration described as an example of this embodiment is referred to as configuration example 2-1.
In configuration example 2-2, the contact pressure and the contact area ratio are substantially constant from the front end side of the brush to the rear end side of the brush.
In configuration example 2-3, the contact pressure and contact area ratio decrease from the front end of the brush to the rear end of the brush to the same extent as in configuration example 2-1, and the bristles of the brush member 11 are thicker and have a lower density than in configuration example 2-1.
In configuration example 2-4, the contact pressure and contact area ratio decrease from the front end of the brush to the rear end of the brush to the same extent as in configuration example 2-1, and the bristle density of the brush member 11 is higher overall compared to configuration example 2-1.
In configuration example 2-5, the contact pressure and contact area ratio decrease from the front end side of the brush to the rear end side of the brush, but the amount of change in the contact pressure and contact area ratio is smaller than in configuration example 2-1.
In the configuration example 2-6, the contact pressure and the contact area ratio decrease from the front end side of the brush to the rear end side of the brush, and the amount of change is intermediate between the configuration examples 2-1 and 2-5.

As shown in Table 3, no black spots occurred in Configuration Examples 2-1 and 2-6, confirming that poor charging could be prevented. On the other hand, poor charging occurred in Configuration Examples 2-2 to 2-5.

The reason why poor charging occurred in configuration example 2-2, where the contact pressure and contact area ratio do not decrease from the front end of the brush to the rear end of the brush, is thought to be because the contact pressure and contact area ratio are high even at the rear end of the brush, causing the toner to come off in streaks. This shows that a configuration where the contact pressure and contact area ratio decrease from the front end of the brush to the rear end of the brush, as in configuration example 2-1, is effective in preventing poor charging.

Furthermore, poor charging occurred in Configuration Example 2-5, where the change in contact pressure and contact area ratio was small, while poor charging did not occur in Configuration Example 2-6, where the change in contact pressure and contact area ratio was greater than in Configuration Example 2-5 but smaller than in Configuration Example 2-1. This indicates that a greater change in contact pressure and contact area ratio can more effectively suppress the occurrence of poor charging. Specifically, a change in contact pressure of 0.6 gf/ ^mm² or more and a change in contact area ratio of 15% or more are preferable, with 1.0 gf/ ^mm² or more and 30% or more being more preferable, respectively. However, since the timing at which poor charging occurs in Configuration Example 2-5 is later than in Configuration Example 2-2, where the contact pressure and contact area ratio do not decrease, poor charging may also be suppressed in Configuration Example 2-5 depending on the specific configuration of the image forming apparatus (e.g., the life setting of the charging roller 2).

The reason why poor charging occurred in Configuration Example 2-3 is thought to be that the minimum value of the contact pressure of the brush member 11 (contact pressure at the rear end of the brush) was too high, causing the toner to pass through the brush member 11 in a streaky manner. Therefore, it is preferable that the contact pressure at the rear end of the brush be, for example, 1.5 gf/ ^mm2 or less.

The reason for the poor charging in Configuration Example 2-4 is believed to be that the contact area ratio at the rear end of the brush was too high, causing the toner to pass through the brush member 11 in a streaky manner. Therefore, it is preferable to set the contact area ratio at the rear end of the brush to, for example, 40% or less. The density of the bristle material at the rear end of the brush is preferably 200 kF/ ^inch² or less, and more preferably 180 kF/ ^inch² or less.

As explained above, the configuration of this embodiment can also suppress the occurrence of charging defects over a long period of time.

(Modification)
In this embodiment, the density of the bristle material of the brush member 11 is changed in three stages, but the density may be decreased continuously from the front end of the brush to the rear end of the brush to decrease the contact pressure and the contact area ratio. Also, the density may be decreased in two stages or four or more stages.

Furthermore, the brush member 11 of this embodiment may be arranged at an angle relative to the photosensitive drum 1, as in the first embodiment.

Third Embodiment
In this embodiment, the thickness of the bristles of the brush member 11 varies depending on the location so that the contact pressure and contact area ratio at the front end of the brush are higher than those at the rear end of the brush. Hereinafter, elements with the same reference numerals as those in the first embodiment will be considered to have substantially the same configurations and functions as those described in the first embodiment, and differences from the first embodiment will be mainly described.

In the brush member 11 of this embodiment, the thickness of the bristles at the front end of the brush is greater than the thickness of the bristles at the rear end of the brush. In this example of this embodiment, conductive threads 11a with a density of 240 kF/inch ² are used. The thickness of the conductive threads 11a decreases in three stages of 2, 1.5, and 1 (all in denier) at 2 mm intervals from the front end of the brush to the rear end of the brush. The lateral width of the brush member 11 in this example is 6 mm.

Figures 13(a) and 13(b) are schematic diagrams of the brush member 11 observed from the tip side of the bristles. Figure 13(a) shows this embodiment, in which the bristles (conductive threads 11a) become thinner toward the rear end of the brush (downstream in the rotation direction R1 of the photosensitive drum 1). In contrast, in the first embodiment shown in Figure 13(b), the thickness of the bristles (conductive threads 11a) is constant.

In this way, in this embodiment, the thickness of the bristles at the first position on the front end of the brush is greater (thicker) than the thickness of the bristles at the second position, which is closer to the rear end of the brush than the first position. This embodiment is an example of a configuration in which the contact pressure and contact area ratio at the first position on the front end of the brush are higher than the contact pressure and contact area ratio at the second position.

In this embodiment, it is also desirable that the Clark-Evans index w of the brush member 11 be w≧1.

In this embodiment, unlike the first embodiment, it is not necessary to position the brush member 11 at an angle relative to the photosensitive drum 1. In the example of this embodiment, β = 0 in Figure 1. In this example, the penetration amount (maximum penetration amount) of the brush member 11 into the photosensitive drum 1 was set to 1 mm.

In this embodiment, the contact pressure of the brush member 11 against the photosensitive drum 1 is 2 gf/mm ² at the front end of the brush and 1 gf/mm ² at the rear end of the brush. The contact area ratio is 50% at the front end of the brush and 20% at the rear end of the brush.

In this embodiment, it is also preferable to apply a brush voltage to the brush member 11. The brush voltage is set to, for example, -350 V, as in the first embodiment.

(Verification experiment)
In order to verify that the configuration of this embodiment can prevent charging defects, experiments were conducted to confirm whether charging defects occurred in several configuration examples with different brush member 11 configurations and different contact conditions with the photosensitive drum 1. Table 5 below shows the main contact conditions and whether charging defects occurred in each configuration example, and Table 6 shows the detailed configuration of each configuration example. The experimental environment, output image, sample image, and method for evaluating charging defects are the same as those in the first embodiment.

The configuration described as an example of this embodiment is referred to as configuration example 3-1.
In the configuration example 3-2, the contact pressure and the contact area ratio are substantially constant from the front end side of the brush to the rear end side of the brush.
In configuration example 3-3, the contact pressure and contact area ratio decrease from the front end of the brush to the rear end of the brush to the same extent as in configuration example 3-1, and the bristles of the brush member 11 are thicker overall and have a lower density than in configuration example 3-1.
In configuration example 3-4, the contact pressure and contact area ratio decrease from the front end of the brush to the rear end of the brush to the same extent as in configuration example 3-1, and the bristle density of the brush member 11 is higher overall compared to configuration example 3-1.
In configuration example 3-5, the contact pressure and contact area ratio decrease from the front end side of the brush to the rear end side of the brush, but the amount of change in the contact pressure and contact area ratio is smaller than in configuration example 3-1.
In the configuration example 3-6, the contact pressure and the contact area ratio decrease from the front end side of the brush to the rear end side of the brush, and the amount of change is intermediate between the configuration examples 3-1 and 3-5.

As shown in Table 5, no black spots occurred in Configuration Examples 3-1 and 3-6, confirming that poor charging could be prevented. On the other hand, poor charging occurred in Configuration Examples 3-2 to 3-5.

The reason why poor charging occurred in configuration example 3-2, where the contact pressure and contact area ratio do not decrease from the front end of the brush to the rear end of the brush, is thought to be because the contact pressure and contact area ratio are high even at the rear end of the brush, causing the toner to come out in streaks. This shows that a configuration like configuration example 3-1, where the contact pressure and contact area ratio decrease from the front end of the brush to the rear end of the brush, is effective in preventing poor charging.

Furthermore, in Configuration Example 3-5, where the change in contact pressure and contact area ratio was small, charging defects occurred, while in Configuration Example 3-6, where the change in contact pressure and contact area ratio was greater than in Configuration Example 3-5 but smaller than in Configuration Example 3-1, charging defects did not occur. This indicates that a larger change in contact pressure and contact area ratio can more effectively suppress the occurrence of charging defects. Specifically, a change in contact pressure of 0.6 gf/ ^mm² or more and a change in contact area ratio of 15% or more are preferable, with 1.0 gf/ ^mm² or more and 30% or more being more preferable, respectively. However, since the timing at which charging defects occur in Configuration Example 3-5 is later than in Configuration Example 3-2, where the contact pressure and contact area ratio do not decrease, charging defects may also be suppressed in Configuration Example 3-5 depending on the specific configuration of the image forming apparatus (e.g., the life setting of the charging roller 2).

The reason why poor charging occurred in Configuration Example 3-3 is thought to be that the minimum value of the contact pressure of the brush member 11 (contact pressure at the rear end of the brush) was too high, causing the toner to pass through the brush member 11 in a streaky manner. Therefore, it is preferable that the contact pressure at the rear end of the brush be, for example, 1.5 gf/ ^mm2 or less.

The reason for the poor charging in configuration example 3-4 is thought to be that the contact area ratio at the rear end of the brush was too high, causing the toner to pass through the brush member 11 in a streaky manner. Therefore, it is preferable to set the contact area ratio at the rear end of the brush to, for example, 40% or less.

As explained above, the configuration of this embodiment can also suppress the occurrence of charging defects over a long period of time.

(Modification)
In this embodiment, the thickness of the bristles of the brush member 11 is changed in three stages, but the thickness may be decreased continuously from the front end of the brush to the rear end of the brush to decrease the contact pressure and the contact area ratio. Also, the thickness may be decreased in two stages or four or more stages.

Furthermore, the brush member 11 of this embodiment may be arranged at an angle relative to the photosensitive drum 1, as in the first embodiment.

Fourth Embodiment
In this embodiment, we will consider a configuration and its detailed conditions in which the penetration amount of the brush member 11 into the photosensitive drum 1 decreases from the upstream side (the front end side of the brush) to the downstream side (the rear end side of the brush) in the rotation direction of the photosensitive drum 1. Hereinafter, elements with the same reference numerals as those in the first embodiment will be considered to have substantially the same configurations and functions as those described in the first embodiment, and differences from the first embodiment will be mainly described.

Figure 16 shows the positional relationship between the brush member 11 and the photosensitive drum 1 when the brush member 11 is positioned at an angle relative to the tangent direction of the photosensitive drum 1. Figure 16 is a schematic diagram of the brush member 11 and the photosensitive drum 1 as viewed in the direction of the rotation axis of the photosensitive drum 1.

The brush member 11 used in this embodiment is the same as that described in the example of the first embodiment. That is, the brush member 11 has a constant bristle length L1, density, and thickness, as shown in Figure 5(a). Furthermore, while the brush member 11 is actually bent along the surface of the photosensitive drum 1 as shown in Figure 5(b), Figure 16 shows the bristles inserted into the photosensitive drum 1, ignoring interference with the photosensitive drum 1.

The relationship between the penetration amount (δ) of the brush member 11 into the photosensitive drum 1 is described using Figure 16. In the figure, the rotation axis O of the photosensitive drum 1 is the origin of the coordinate system. The coordinate axis extending parallel to the short direction SD of the brush member 11 is the X axis, and the coordinate axis perpendicular to the X axis (the axis extending parallel to the normal direction of the base fabric 11b) is the Y axis.

The amount of penetration of the brush member 11 into the imaginary circle C1 representing the surface of the photosensitive drum 1 at the front end (upstream end) of the brush member 11 in the rotation direction R1 of the photosensitive drum 1 is defined as δ1. The amount of penetration of the brush member 11 into the imaginary circle C1 at the rear end (downstream end) of the brush member 11 in the rotation direction R1 is defined as δ2. The amount of penetration of the brush member 11 into the imaginary circle C1 at the center between the front and rear ends of the brush member 11 in the short direction SD is defined as δ3.
, δ2, δ3. In this case, the penetration amounts δ1 to δ3 are expressed by the following (Equation 4) to (Equation 6).
(Formula 4) δ1=r×SIN(90-Θ1)-P
(Formula 5) δ2=r×SIN(90-Θ2)-P
(Formula 6) δ3=r×SIN(90-Θ3)-P
Here, r is the radius of the photosensitive drum 1, and P is the distance in the Y-axis direction from the rotation axis O of the photosensitive drum 1 to the tip of the bristles of the brush member 11. In other words, P is the distance L5 in the Y-axis direction from the rotation axis O to the base fabric of the brush member 11 minus the bristle length L1 of the brush member 11. The first terms on the right-hand sides of (Equation 4) to (Equation 6) represent the Y-coordinates of the intersections A1, A2, and A3 of the bristles located at the front end, rear end, and center of the brush member 11 with the imaginary circle C1.

Furthermore, the angles Θ1, Θ2, Θ3 (°) formed by a line extending from the rotation axis O of the photosensitive drum 1 through the intersections A1, A2, A3 between the brush member 11 and the imaginary circle C1 and a line parallel to the Y-axis direction are expressed by the following equations (7) to (9).
(Formula 7) Θ1=90-ACOS(Q1/r)
(Formula 8) Θ2=90-ACOS(Q2/r)
(Formula 9) Θ3=90-ACOS(Q3/r))
Here, Q1 is the distance in the X-axis direction from the rotation axis O of the photosensitive drum 1 to the front end of the brush member 11. Q2 is the distance in the X-axis direction from the rotation axis O of the photosensitive drum 1 to the rear end of the brush member 11. Q3 is the distance in the X-axis direction from the rotation axis O of the photosensitive drum 1 to the center of the brush member 11. That is, Q3 = (Q1 + Q2)/2. Furthermore, if the short side width of the brush member 11 is L3, then Q2 = Q1 + L3 and Q3 = Q1 + L3/2. Furthermore, ACOS is an inverse trigonometric function (the inverse cosine function).

In this example of the present embodiment, the penetration depth of the brush member 11 was δ1 = 1.6 (mm) at the front end of the brush, δ3 = 1.2 (mm) at the center, and δ2 = 0.45 (mm) at the rear end of the brush. In other words, the penetration depth (δ1) at the upstream end of the brush member 11 in the rotation direction R1 of the photosensitive drum 1 was greater than the penetration depth (δ2) at the downstream end of the brush member 11, and δ2 > 0. The radius r of the photosensitive drum 1 was 12 mm. Θ3 is the contact angle of the brush member 11 with the photosensitive drum 1. In this example of the present embodiment, the contact angle Θ3 was set to 16°.

In this embodiment, it is also preferable to apply a brush voltage to the brush member 11. The brush voltage is set to, for example, -350 V, as in the first embodiment. Also, in this embodiment, it is also preferable that the Clark-Evans index w of the brush member 11 be w≧1.

(Verification experiment)
To verify that the configuration of this embodiment can prevent charging defects, experiments were conducted to confirm whether charging defects occurred in several configuration examples with different brush member 11 configurations and different contact conditions with the photosensitive drum 1. Table 7 below shows the contact conditions and whether charging defects occurred in each configuration example. The experimental environment, output image, sample image, and method for evaluating charging defects were the same as those in the first embodiment.

The configuration described as an example of this embodiment is referred to as configuration example 4-1.
In configuration example 4-2, the amount of penetration is constant from the front end to the rear end of the brush member 11 (δ1=δ3=δ2).
In configuration example 4-3, the amount of penetration increases from the front end to the rear end of the brush member 11 (δ1<δ3<δ2).
In configuration example 4-4, the amount of penetration decreases from the front end to the rear end of the brush member 11, but the rate of decrease is more gradual than in configuration example 4-1.

The difference in penetration amount between each configuration example is set, for example, by dividing the lateral width L3 of the brush member 11 into three equal parts in the lateral direction SD, and setting the bristle length L1 to a different value for each of these three regions (a configuration in which the bristle length changes in three stages). For example, in configuration example 4-3, the bristle length increases from the front end of the brush to the rear end of the brush.

As shown in Table 7, no black spots occurred in Configuration Example 4-1, confirming that poor charging could be prevented. On the other hand, poor charging occurred in Configuration Examples 4-2 and 4-3. Slight poor charging occurred in Configuration Example 4-1.

In configuration examples 4-2 and 4-3, the penetration amount δ2 at the rear end of the brush is equal to or greater than the penetration amount δ1 at the front end of the brush. Poor charging in configuration examples 4-2 and 4-3 is thought to be due to the toner passing through the brush member 11 in a streaky manner because the contact pressure or contact area ratio at the rear end of the brush was too high.

In contrast, in configuration examples 4-1 and 4-4, where the brush rear end penetration amount δ2 is smaller than the brush front end penetration amount δ1, no or only minor charging defects occurred. This is thought to be because the low contact pressure and contact area ratio at the brush rear end allowed the toner to be dispersed.

Furthermore, in configuration example 4-4, where the ratio δ2/δ1 of the penetration amounts δ1 and δ2 at the front and rear ends of the brush was larger than in configuration example 4-1, minor charging defects occurred. For this reason, it is preferable that the ratio δ2/δ1 of the penetration amounts δ1 and δ2 at the front and rear ends of the brush is small. For example, δ2/δ1 < 0.69 is preferable. Furthermore, since minor charging defects occurred in configuration example 4-4, where the difference (δ1 - δ2) between the penetration amounts δ1 and δ2 at the front and rear ends of the brush was smaller than in configuration example 4-1, it is preferable that the difference between δ1 and δ2 (δ1 - δ2) is large. For example, δ1 - δ2 > 0.4 is preferable.

Table 7 shows the ratios between the penetration amounts δ1 to δ3 at the front end, rear end, and center of the brush member 11. When each ratio is less than 1, it indicates that the penetration amount of the brush member 11 decreases from the upstream side to the downstream side in the rotation direction R1 of the photosensitive drum 1. In this case, the closer the ratio is to 1, the more gradual the decrease in penetration amount (the smaller the rate of decrease), and the closer the ratio is to 0, the more rapid the decrease in penetration amount (the larger the rate of decrease).

Since poor charging is suppressed in configuration examples 4-1 and 4-4, it is preferable for the relationship 1 > δ3/δ1 > δ2/δ3 to hold. This relationship means that the rate of decrease in the penetration amount from the front end of the brush to the center of the brush is relatively small, and the rate of decrease in the penetration amount from the center of the brush to the rear end of the brush is relatively large. With this configuration, the toner can be firmly triboelectrically charged and normalized in the area upstream of the center of the brush member 11, where the penetration amount is large. Furthermore, because the penetration amount is smaller in the area downstream of the center of the brush member 11, it is possible to prevent the toner from scattering and coming off in streaks.

As explained above, the configuration of this embodiment can also suppress the occurrence of charging defects over a long period of time.

Fifth Embodiment
In this embodiment, we consider the conditions under which the brush member 11 contacts the photosensitive drum 1 with an appropriate penetration amount even when the outer diameter of the photosensitive drum 1 changes. Hereinafter, elements with the same reference numerals as those in the first and fourth embodiments have substantially the same configurations and functions as those described in the first and fourth embodiments, and the following mainly describes the parts that differ from the first and fourth embodiments.

The brush member 11 used in this embodiment is the same as that described in the examples of the first and fourth embodiments. That is, the brush member 11 has a constant bristle length L1, density, and thickness, as shown in Figure 5(a). The definitions of the penetration amounts δ1 to δ3 of the brush member 11 into the photosensitive drum 1 and the definition of the contact angle Θ3 of the brush member 11 are the same as those described in the fourth embodiment.

In this embodiment, the penetration depth of the brush member 11 was fixed at δ1 = 1.6 (mm) at the front end of the brush and δ3 = 1.2 (mm) at the center, and the penetration depth δ2 at the rear end of the brush was controlled by adjusting the contact angle Θ3 for photosensitive drums 1 with different outer diameters. The radius r of the photosensitive drums 1 examined ranged from 6 mm to 24 mm.

In this embodiment, it is also preferable to apply a brush voltage to the brush member 11. The brush voltage is set to, for example, -350 V, as in the first embodiment. Also, in this embodiment, it is also preferable that the Clark-Evans index w of the brush member 11 be w≧1.

(Verification experiment)
To verify that the configuration of this embodiment can prevent charging defects, experiments were conducted to confirm whether charging defects occurred in several configuration examples with different outer diameters of the photosensitive drum 1. Table 8 below shows the contact conditions and whether charging defects occurred when the brush center penetration δ3 was fixed at 1.2 mm and the contact angle Θ3 was fixed at 16°. Table 9 shows the contact conditions and whether charging defects occurred when the contact angle Θ3 was adjusted to δ1 = 1.6 and δ3 = 1.2. The experimental environment, output image, sample image, and charging defect evaluation method were the same as those in the first embodiment.

As shown in Table 8, when the contact angle Θ3 of the brush member 11 was fixed at 16°, charging defects occurred when the radius r of the photosensitive drum 1 was less than 10 mm, and minor charging defects occurred when the radius r was 10 mm. On the other hand, no charging defects occurred when the radius r of the photosensitive drum 1 was greater than 10 mm.

The smaller the radius r of the photosensitive drum 1, the smaller the penetration amount δ1 of the front end of the brush when the brush member 11 is brought into contact under the conditions of δ3 = 1.2 (mm) and Θ3 = 16 (°). Therefore, the smaller the radius r of the photosensitive drum 1, the greater the ratio (δ3/δ1) of the penetration amount δ3 of the center of the brush to the penetration amount δ1 of the front end of the brush. In other words, the smaller the radius r of the photosensitive drum 1, the closer δ3/δ1 is to 1, and the contact condition (contact pressure, contact area ratio, etc.) of the center of the brush becomes closer to the contact condition of the front end of the brush.

When the radius r of the photosensitive drum 1 is small, it is thought that after the toner becomes unevenly distributed at the front end of the brush, where the penetration amount is large, the uneven distribution of toner becomes difficult to eliminate even at the center of the brush. The rear end of the brush alone is unable to sufficiently distribute the toner, and the toner escapes from the brush member 11 in streaks. As a result, it is thought that poor charging occurs when the radius r of the photosensitive drum 1 is less than 10 mm. On the other hand, when the radius r of the photosensitive drum 1 is greater than 10 mm, δ3/δ1 is relatively small, so the center of the brush contributes to dispersing the toner, making it less likely for the toner to escape in streaks, thereby suppressing poor charging.

From this, it is believed that the ratio of the penetration depth δ3 at the center of the brush to the penetration depth δ1 at the front end of the brush (δ3/δ1) is preferably δ3/δ1≦0.77, and more preferably δ3/δ1≦0.75.

Therefore, as shown in Table 9, when the contact angle Θ3 was set so that δ3/δ1 = 0.75 for each photosensitive drum 1 with a different radius r, no charging defects occurred even when the radius r of the photosensitive drum 1 was 8 mm and 10 mm.

In the case of the brush member used in the verification, which had a short side width L3 of 4 mm, when the radius r of the photosensitive drum 1 was 6 mm and the relationship δ3/δ1≦0.75 was attempted to be satisfied, the rear end of the brush would float above the surface of the photosensitive drum 1. As a result, poor charging occurred when r = 6.

Furthermore, from the results in Table 9, it is preferable that the ratio of the penetration depth δ2 at the rear end of the brush to the penetration depth δ1 at the front end of the brush (δ2/δ1) be in the range of 0.14≦δ2/δ1≦0.38. By making the penetration depth at the rear end of the brush smaller than the penetration depth at the front end so that it is within this range, the toner can be firmly frictionally charged at the front end of the brush member 11 while being evenly dispersed at the rear end, thereby preventing poor charging.

(Other embodiments)
In the above-described embodiments, a direct transfer configuration in which a toner image is directly transferred from the photosensitive drum 1 (image carrier) to a sheet (recording material) as a transfer recipient has been described. However, the present technology may also be applied to an intermediate transfer image forming apparatus. In the intermediate transfer configuration, the transfer member refers to, for example, a transfer roller (primary transfer roller) that primarily transfers the toner image from the photosensitive drum 1 as an image carrier to an intermediate transfer material as a transfer recipient. The intermediate transfer material may be an endless belt member stretched over multiple rollers. The toner image primarily transferred to the intermediate transfer material is then secondarily transferred from the intermediate transfer material to the sheet (recording material) by a secondary transfer means, such as a secondary transfer roller that forms a secondary transfer nip between the intermediate transfer material and the belt. Even in such an intermediate transfer configuration, the same effects as those of the above-described embodiments can be achieved by replacing the transfer roller in the above-described embodiments with a primary transfer roller.

In addition, while each embodiment has been described primarily with regard to charge impartation through frictional charging caused by friction between the brush member and toner, the charge imparting method is not limited to this, and for example, a configuration in which charge is injected into the toner via the brush member may also be used. In other words, regardless of the charge imparting method, any brush member may be used that can bias the charge distribution of the remaining toner after it has passed the brush contact portion and before it reaches the charging portion toward the normal polarity, compared to the charge distribution of the remaining toner carried on the image carrier and before it reaches the brush contact portion.

1... Image carrier (photosensitive drum) / 2... Charging member (charging roller) / 5... Transfer member (transfer roller) / 11... Brush member / 41... Development member (developing roller)

Claims (22)

a rotating image carrier;
a charging member that contacts the image carrier to form a charging section, and that charges the surface of the image carrier to the same polarity as the normal charging polarity of the toner in the charging section;
a developing member that develops the electrostatic latent image formed on the surface of the image carrier using the toner ;
a transfer member that transfers the toner image developed by the developing member from the image carrier to a transfer-receiving member in a transfer section;
a brush member that is disposed so as to come into contact with the surface of the image carrier at a contact portion that is downstream of the transfer portion and upstream of the charging portion in the rotation direction of the image carrier, and that applies a charge of the normal charging polarity to the toner that has not been transferred to the transfer target;
an image forming apparatus comprising: a developing member for recovering toner that has not been transferred to the transfer object;
a contact pressure between the brush member and the image carrier at an upstream end of the brush member at the contact portion in the rotation direction is higher than a contact pressure between the brush member and the image carrier at a downstream end of the brush member at the contact portion in the rotation direction,
a contact area ratio between the brush member and the image carrier at the upstream end of the brush member is greater than a contact area ratio between the brush member and the image carrier at the downstream end of the brush member;
An image forming apparatus characterized by: the contact pressure and the contact area ratio monotonically decrease from the upstream end to the downstream end in the rotation direction.
2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium. the difference between the maximum and minimum values of the contact pressure is 0.6 gf/ ^mm² or more and 1.5 gf/ ^mm² or less,
The difference between the maximum value and the minimum value of the contact area ratio is 15% or more and 40% or less.
3. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium. the maximum value of the contact pressure is 0.7 gf/mm ² or more and 3.5 gf/mm ² or less,
The maximum value of the contact area ratio is 18% or more and 74% or less.
4. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium. the maximum value of the contact pressure is 1.4 gf/mm ² or more and 2.8 gf/mm ² or less,
The maximum value of the contact area ratio is 32% or more and 60% or less.
4. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium. the brush member has a base portion extending in a longitudinal direction parallel to the rotation axis direction of the image carrier and in a lateral direction perpendicular to the longitudinal direction, and bristles supported by the base portion and in contact with the surface of the image carrier,
the brush member is disposed at an angle with respect to the image carrier such that the base portion thereof becomes farther away from the image carrier toward the downstream side in the rotation direction;
6. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium. When viewed in the direction of the rotation axis, a line passing through the rotation axis and the center of the base in the short-side direction is defined as a first line, and an angle between a second line perpendicular to the first line and a third line extending in the short-side direction along the base is equal to or greater than 8° and equal to or less than 16°.
7. The image forming apparatus according to claim 6, wherein the image forming apparatus is a recording medium. the brush member has bristles that come into contact with the surface of the image carrier;
the density of the bristles at the upstream end of the brush member is higher than the density of the bristles at the downstream end of the brush member;
6. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium. the brush member has bristles that come into contact with the surface of the image carrier;
the thickness of the bristles at the upstream end of the brush member is greater than the thickness of the bristles at the downstream end of the brush member;
6. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium. Let δ1 (mm) be the penetration amount of the brush member into the surface of the image carrier at the upstream end of the brush member, and δ2 (mm) be the penetration amount of the brush member at the downstream end of the brush member in the rotation direction,
δ1>δ2>0;
10. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium. a rotating image carrier;
a charging member that contacts the image carrier to form a charging section, and that charges the surface of the image carrier to the same polarity as the normal charging polarity of the toner in the charging section;
a developing member that develops the electrostatic latent image formed on the surface of the image carrier using the toner ;
a transfer member that transfers the toner image developed by the developing member from the image carrier to a transfer-receiving member in a transfer section;
a brush member that is disposed so as to come into contact with the surface of the image carrier at a contact portion that is downstream of the transfer portion and upstream of the charging portion in the rotation direction of the image carrier, and that applies a charge of the normal charging polarity to the toner that has not been transferred to the transfer target;
an image forming apparatus comprising: a developing member for recovering toner that has not been transferred to the transfer object;
Let δ1 (mm) be the penetration amount of the brush member into the surface of the image carrier at the upstream end of the brush member at the contact portion in the rotation direction, and δ2 (mm) be the penetration amount of the brush member at the downstream end of the brush member at the contact portion in the rotation direction,
δ1>δ2>0;
An image forming apparatus characterized by: The penetration amount at the center between the upstream end and the downstream end of the brush member in the short direction of the brush member perpendicular to the rotation axis direction of the image carrier is δ3 (mm),
1>δ3/δ1>δ2/δ3,
12. The image forming apparatus according to claim 10, wherein the image forming apparatus is a recording medium. When the radius of the image carrier is r (mm), in the range of r>6,
0.14≦δ2/δ1≦0.38 and δ3/δ1≦0.75;
13. The image forming apparatus according to claim 10, wherein the image forming apparatus is a recording medium. The penetration amount is configured to monotonically decrease from the upstream end to the downstream end of the brush member.
14. The image forming apparatus according to claim 11, wherein the image forming apparatus is a recording medium. a voltage applying means for applying a voltage having the same polarity as the normal charging polarity to the brush member;
15. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium. a value of the voltage applied to the brush member by the voltage application means is on the same side as the normal charging polarity with respect to the surface potential of the image carrier that reaches the contact portion with the brush member;
16. The image forming apparatus according to claim 15. In the triboelectric series, the toner is located on the same side as the normal charging polarity with respect to the brush member.
17. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium. the peripheral speed of the charging member is faster than the peripheral speed of the image bearing member,
In the triboelectric series, the toner is located on the same side as the normal charging polarity with respect to the material of the surface layer of the charging member and the material of the surface layer of the image bearing member.
18. The image forming apparatus according to claim 17. a Clark-Evans index of the brush member at a contact portion between the brush member and the image carrier is 1 or more;
19. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium. a length of the brush member in a lateral direction of the brush member perpendicular to the rotation axis direction of the image carrier is 3 mm or more;
The bristles of the brush member are synthetic resin fibers having a thickness of 1 denier or more and 6 denier or less,
The density of the bristle material is 150 kF/inch ² or more and 350 kF/inch ² or less,
20. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium. the transfer medium is a recording material,
21. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium. the transfer medium is an intermediate transfer medium,
a secondary transfer unit that transfers the toner image transferred to the intermediate transfer body onto a recording material;
21. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.