JP2000056538A - Charging brush - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging brush brought into contact with the body to be charged and rotated in order to charge the body to be charged, capable of restraining generation of image noises as it can uniformly and stably charge the body to be charged. SOLUTION: A charging brush 12 brought into contact with a photoreceptor (body to be charged) and rotated in order to charge the photoreceptor includes a conducting core 121 (core rod) and strips of conducting brush base material 122 spirally wound around the core 121. The strips of brush base material 122 comprise conducting brush bristles 122b studed into strips of base substance 122a and are wound around the core 121 in such a manner that the adjacent side edges of the strips of conducting brush base material overlap one another on the core 121, so that the density of the brush bristles on each strip of brush base material 122 and the density of the brush bristles at the joint T between the adjacent side edges of the strips of brush base material on the core 121 are made uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for use in an image forming apparatus such as a copying machine or a printer, and more particularly to a charging brush which is rotated in contact with a charged object in order to charge the charged object.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a printer, a surface of an electrostatic latent image carrier such as a photoreceptor is generally charged, and the charged area is exposed to an image based on image information. Forming a latent image, developing the latent image into a visible toner image,
This toner image is directly transferred to a recording material such as paper,
Alternatively, the image is firstly transferred to an intermediate transfer member, and then secondarily transferred to a recording material and fixed.

In such an image forming apparatus, a charging device is used to charge an object to be charged. For example, it is used as a main charging device for uniformly charging the surface of an image carrier prior to image exposure for forming an electrostatic latent image on the image carrier (an example of a charged object). Further, when transferring the toner image formed on the image carrier to a recording material (an example of a charged body), or before transferring the toner image onto the recording material in a color image forming apparatus or the like, Transfer body (1 of charged body)
For example, when the transfer is performed, the transfer material is used as a transfer charging device that applies a transfer voltage from the back side of the recording material or the intermediate transfer body for the transfer. Further, it may be used as a static eliminator for applying a static elimination voltage in order to eliminate charges remaining on an electrostatic latent image carrier or the like after transfer of a toner image.

Conventionally, such charging or voltage application is performed using various charging devices such as a corona charger, a charging roller, and a charging brush. Of these, a charging brush, which is a charging brush that is rotated in contact with a charged object, is generally formed of a conductive core material having a belt-like conductive brush base in which conductive brush bristles are implanted. It is wound in a shape.

FIG. 7 shows a state in which a conductive brush base material B is wound around a conductive core metal S for a charging brush of this type. As shown in FIG. 7, the conductive brush base material B is wound around the cored bar S such that the gap between the side edges (ears) joints T of the conductive brush base materials B adjacent to each other is minimized.
For example, the width W of the conductive brush base material B is 15 mm, and the line X orthogonal to the axial direction of the conductive brush base material B and the conductive core metal S.
(The so-called winding angle) θ is 44.6 degrees, and the diameter D of the conductive cored bar is 6.8 mm.
The width (lead) L in the axial direction of the metal core on the metal core is L = 15.
mm / COS (44.6 degrees) ≒ 21 mm, and the gap at the joint T is calculated to be 0 mm.

[0006]

However, in practice, the gap at the joint T is often larger than 0 mm due to variations in the width and the like of the conductive brush base material B. In addition, the conductive brush base material B usually has a conductive bristle K easily removed at a side edge (ear end) of the brush base material B. In order to prevent the brush bristle K from coming off, the brush bristle K is a brush. It is planted slightly inside the side edge (ear end) of the base material B.

[0007] Therefore, in the conductive brush base material B wound around the conductive core metal S, the density of the brush bristles K at the joints T becomes low, and due to the existence of such a portion, the charged material is charged to the charged object at the time of charging. It tends to cause unevenness. For example, when such a charging brush is used as a main charging brush, uneven charging of the electrostatic latent image carrier is likely to occur, and a portion having a low surface potential due to the uneven charging appears as image noise (so-called image noise due to uneven winding). There is.

Accordingly, the present invention relates to a charging brush which is rotated in contact with a charged object in order to charge the charged object. The charged brush can uniformly and stably charge the charged object, thereby suppressing the generation of image noise. It is an object to provide a charging brush that can be used.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a charging brush which is rotated in contact with a charged object to charge the charged object, comprising: a conductive core rod;
A belt-shaped conductive brush substrate spirally wound around the core rod, wherein the conductive brush substrate is obtained by implanting conductive brush bristles in a band-shaped substrate; The conductive brushes adjacent to each other on the core rod so as to equalize the brush bristle density at the seam portion and the brush bristle density at the joint of the adjacent conductive brush base material side edges on the core rod. Provided is a charging brush, wherein the base material side edges are wound around the core bar so as to overlap each other.

According to the charging brush of the present invention, the belt-shaped conductive brush substrate spirally wound around the conductive core rod has the conductive brush bristles implanted in the belt-shaped substrate. The conductive brush base material is formed such that the brush bristle density and the brush bristle density at the joint portion between the adjacent conductive brush base material side edges on the core bar are uniformized. The adjacent conductive brush base material side edges are wound around the core bar so as to overlap each other. Therefore, the charged object can be charged uniformly and stably. For example, even when the charged object is used as a main charging device for charging the surface of the electrostatic latent image carrier prior to image exposure, image noise (so-called image noise due to uneven winding) is reduced. Generation can be suppressed.

The overlapping width of the conductive brush base material on the core rod is set to an optimum size so as to make the brush bristle density of the brush base material and the brush bristle density at the joint portion uniform. Just set it. If the overlapping width is too large, the length of the free end of the conductive brush bristle at the overlapping portion is shortened, thereby preventing uniformity of the brush bristle density at that portion. The size must be within the range that does not exist.

The charging brush according to the present invention is a charging brush for charging an electrostatic latent image carrier in an image forming apparatus such as a copying machine or a printer prior to image exposure, and is formed on the image carrier. A transfer brush used when transferring a toner image to a recording material made of paper or the like, or when transferring the toner image to an intermediate transfer member prior to transferring the toner image onto the recording material in a color image forming apparatus, etc. It can be used for a charge removing brush for removing charges remaining on an electrostatic latent image carrier or the like.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side view showing a schematic configuration of a drum cartridge type image forming apparatus employing a charging brush for charging the surface of a photosensitive member prior to image exposure, which is an example of a charging brush according to the present invention. FIG. 2 is a schematic sectional view of a drum cartridge provided with the charging brush shown in FIG.

The image forming apparatus shown in FIG. 1 is an electrophotographic image forming apparatus, and includes a drum cartridge 1, a laser exposure device 2, a developing device 3, and a transfer charger 4. The drum cartridge 1 includes a drum-shaped photoconductor 1.
1 (an example of a charged object) is provided. The transfer charger 4 faces the photoreceptor 11 and forms a transfer portion P in the figure. A guide plate 5 and a pair of timing rollers 6 are sequentially provided on the right side of the transfer unit P in the drawing, and a sheet feeding unit (not shown) is further provided. Further, a guide plate 7 and a fixing roller pair 8 are sequentially provided on the left side, and a discharge roller pair and a paper discharge tray (not shown) are further provided.

The exposure device 2 can irradiate the photosensitive member 11 with a laser beam m based on image information sent from an image reading device or the like (not shown), thereby forming an electrostatic latent image on the photosensitive member 11. The developing device 3 includes a developing roller 31, a toner supply roller 32, a toner regulating blade 33, and the like. These are provided in a developing device case 300. The device case 300 contains the toner t. The developing roller 31 is driven to rotate in a counterclockwise direction b in the drawing. The toner regulating blade 31 is in contact with the developing roller 31, and a toner supply roller 32 is disposed behind the toner regulating blade 31.

The toner supply roller 32 is driven to rotate,
The toner t can be supplied to the developing roller 31. Developing roller 3
1 carries the toner t supplied to the surface of the roller 31 by the roller 32 to the toner regulating blade 33 by the rotation thereof,
It is made thinner with the blade 33 and further transported to the developing area. Further, a developing bias voltage can be applied from the power supply PW2. Thereby, the electrostatic latent image on the photoconductor 11 can be developed in the development area.

The transfer charger 4 can apply a transfer voltage from the power supply PW3, and can transfer the toner image on the photosensitive member 11 to a recording paper s described later. Drum cartridge 1
The charging brush 12 (an example of a charging brush) and the cleaning blade 1 as shown in FIG.
3, including a toner collecting roller 14 and a driving gear 15, which are disposed in the cartridge case 100. The photoconductor 11 is driven to rotate in the clockwise direction a in the figure. A charging brush 12 and a cleaning blade 13 are arranged around the photoconductor 11.

The cleaning blade 13 has a blade shape and is cantilevered at one end of a blade holding plate 131. The blade holding plate 131 is rotatably supported by a fulcrum shaft 131a. The other end of the blade holding plate 131 is a spring support 131b, which is connected to one end of the pressure spring 132. The other end of the spring 132 is hooked on the spring supporting portion 101a of the cartridge case 100, and thus the blade holding plate 131 is always pulled in the direction of arrow c in the figure. As a result, the blade 13 is pressed against the photoconductor 11, and the recording paper s adhered to the photoconductor 11.
The transfer residual toner remaining without being transferred to the toner can be removed.

The toner collecting roller 14 is driven to rotate in the direction a in FIG. Thereby, the cleaning blade 1
Transfer residual toner removed in step 3
00 waste toner collecting section 101.
The drive gear 15 is connected to drive transmission means of a main motor (not shown). The main motor is provided in the image forming apparatus and drives the entire image forming apparatus. The gear 15 transmits the drive from the main motor to the photoreceptor 11, the charging brush 12, the toner collecting roller 14, and the like via a gear or the like (not shown) of the cartridge 1, and rotates these.

The charging brush 12 is brought into contact with the photoconductor 11 to charge the photoconductor 11, and is driven to rotate in the direction b in the drawing. The peripheral speed of the charging brush 12 and the peripheral speed of the photoconductor 11 have a constant speed difference. In this example, the peripheral speed ratio between the charging brush 12 and the photoconductor 11 is charged brush: photoconductor = 3. .72: 1. In addition, the charging brush 1
It is conceivable that the peripheral speed of the photoconductor 11 and that of the photoconductor 11 are the same. However, if the peripheral speed ratio is set to 1: 1, uneven charging of the surface of the photoconductor 11 by the charging brush 12 becomes conspicuous, and a necessary charging potential cannot be secured. In order to avoid such a situation, the peripheral speed of the charging brush / the peripheral speed of the photosensitive member may be set to be larger than 1. In this example, the surface movement direction of the charging brush 12 at the mutual contact portion between the charging brush 12 and the photoconductor 11 is a direction that follows the surface movement direction of the photoconductor 11. It is conceivable that the direction is opposite to the above direction. However, when the direction is opposite to the above, the torque of the drive system increases, and
In order to avoid such a situation, the photosensitive layer should be set in the direction as described above.

FIG. 3A is a side view of the charging brush 12, and FIG. 3B is a charging brush 1 for explaining a state of winding the conductive brush base 122 around the conductive core 121.
2 is a front view of the left end. The charging brush 12 includes a conductive core 121 (an example of a conductive core rod) and the conductive brush substrate 1.
22.

The conductive core 121 is made of metal.
Roller shafts 121a protrude from both ends (FIG. 3).
In (B), the right end is not shown). Each roller shaft 121
a is in contact with a conductive leaf spring (not shown) via conductive grease. This conductive leaf spring is connected to the power supply PW1 shown in FIG. Thereby, the power supply P
A charging voltage can be applied to the conductive core 121 from W1.

As shown in FIG. 3A and FIG.
The conductive brush base 122 includes a base 122a and conductive brush bristles 122b. The base 122a is made of a band-shaped cloth, and the conductive brush bristles 122b are made of a conductive resin. The conductive brush base material 122 is
2a, conductive brush bristles 122b are implanted perpendicular to the base 122a. Also, this brush substrate 1
In 22, the brush bristles 122b are planted slightly inside the side edges (ear ends) of the base 122a to prevent the brush bristles 122b from coming off. As shown in FIG. 3B, the conductive brush base 122 is spirally wound around the conductive cored bar 121, and is bonded with a conductive adhesive. Thus, the conductive brush bristles 122b are electrically connected to the conductive cored bar 121.

As shown in FIG. 4B to be described later, the conductive brush base 122 has a brush core density of the conductive brush base 122 and a brush density adjacent to each other on the core 121. In order to equalize the brush bristle density at the joint T portion of the edge of the base material 122, the core metal so that the adjacent edges of the conductive brush base material 122 on the core metal 121 overlap each other. 121.

The charging brush 12 is connected to the power supply P shown in FIG.
A high voltage can be applied from W1, and the photoconductor 11 can be charged. In this example, the photoconductor 11,
Although the charging brush 12 and the cleaning blade 13 are provided integrally with the drum cartridge 1, they may be provided separately at similar positions without employing a cartridge configuration. The photoconductor 11 is a drum-shaped photoconductor drum, but may be a belt-shaped photoconductor belt or the like.

According to the image forming apparatus described above, FIG.
The photosensitive member 11 is driven to rotate as shown in FIG.
2 is uniformly charged. The operation and effect of the charging brush 12 will be described later. The laser beam m emitted from the exposure device 2 exposes the charged area to form an electrostatic latent image. This electrostatic latent image is transferred to the developing device 3 as the photoconductor 11 rotates.

In the developing device 3, the toner t in the device case 300 is developed by the toner supply roller 32 by the developing roller 31.
Supplied to The toner t supplied to the developing roller 31 is regulated by the regulating blade 33 by the rotation of the roller 31 and then moves to a developing region formed between the developing roller 31 and the photoconductor 11. The toner t that has moved to the development area is
The electrostatic latent image on the photoconductor 11 is developed under the application of the developing bias voltage from Step 2. Thus, a visible toner image is formed on the photoconductor 11.

The visible toner image on the photoreceptor 11 moves to the transfer portion P with its rotation. The toner image transferred to the transfer section P is transferred to the recording paper s. The recording paper s is sent out from a paper feed tray (not shown) by a paper feed roller (not shown), and is sent to a timing roller pair 6. The timing roller pair 6 sends out the recording paper s in synchronization with the toner image on the photoconductor 11. The recording sheet s is supported by the guide plate 5 and moves to the transfer section P, where the toner image is transferred onto the recording sheet s by the transfer charger 4.

After the transfer of the toner image, the recording paper s is carried by the fixing roller pair 8 while being supported by the guide plate 7. Here, the toner image is fixed on the recording paper s. Thereafter, the sheet is discharged to a sheet discharge tray by a sheet discharge roller pair (not shown). FIG. 4A is a sectional view of the left end in the axial direction of the conventional charging brush, and FIG. 4B is a sectional view of the left end in the axial direction of the charging brush 12 of the present invention. The charging brush shown in FIG. 4A is obtained by forming the conductive brush base 122 into a conventional type in the charging brush 12 of the present invention shown in FIG. 4B. The other points are the same, and parts having the same configuration and operation are denoted by the same reference numerals.

According to the charging brush 12 of the present invention, FIG.
As shown in (B), the belt-shaped conductive brush base 122 spirally wound around the conductive cored bar 121 has conductive brush bristles 122 slightly inside the side edges of the band-shaped base 122a.
b is implanted. This conductive brush substrate 122
Are set on the cored bar 121 so as to equalize the brush bristle density and the brush bristle density at the joint T of the adjacent brush base material side edge on the conductive cored bar 121. The adjacent conductive brush base material side edges are wound around the metal core 121 so as to overlap each other. This makes it difficult to open the gap at the joint T. In addition, core metal 1
Seam T of each adjacent brush base material side edge on the surface 21
In the portion, the lower one of the stacked base material side ends is compressed and inclined, so that the brush bristles 122 there are
Since the tip of b ′ is more likely to approach the portion N of the upper part where the brush bristles are not implanted, the brush bristle density at the joint T is increased. In addition, the photosensitive member 11 can be uniformly and stably charged, and the occurrence of image noise (so-called image noise due to uneven winding) can be suppressed accordingly.

On the other hand, in the conventional charging brush of the winding type shown in FIG. 4A, the conductive brush base 122 is spirally wound around the core 121 similarly to FIG. 4B. In addition, the adjacent conductive brush base material side edges on the cored bar 121 do not overlap each other. According to this charging brush, there is a gap at the joint T between the adjacent brush base material side edge portions on the cored bar 121, or the brush base material 122 is wound so as to minimize this gap at the time of winding. Also, the portion N where the brush bristles are not implanted at the brush substrate side edge is exposed. Therefore, the brush bristle density at the joint T becomes low, and charging unevenness is easily generated on the photoconductor at the time of charging, and image noise (so-called image noise due to so-called winding unevenness) is easily generated. As described above, such a problem is solved in the brush 12 according to the present invention.

Next, an experiment for evaluating the charging performance of the charging brush 12 will be described. In this evaluation experiment, the charging brush 12 was provided on the drum cartridge 1 shown in FIGS. 1 and 2, and the drum cartridge 1 was mounted on the image forming apparatus shown in FIG.

In this experiment, the width (W) of the brush base 122 was 15 mm, the conductive brush bristles 1222b were made of conductive rayon fiber, and the brush bristles density was 100,000 / inc.
a h ^2, the diameter of the core 121 (D) is 6 mm (base material 1
Considering the thickness of the charging brush 22a and the thickness of the adhesive, the charging brush 12 having a diameter (D) of 6.8 mm)
The average rank of winding unevenness was evaluated by changing the lead (L) condition of No. 2. The average rank of the winding unevenness was obtained as follows. Arbitrary n (here, 10) charged brushes 12 having different lead lengths L are prepared, images are output for all the brushes, and ranking is performed according to a winding rank sample prepared in advance for each image. Was. The rank was summed for each charging brush of each lead length and divided by n (here, 10), and this was defined as the average rank of the winding of the charging brush of each lead length. The larger the rank value is, the less the image noise due to the winding unevenness is.

The experimental conditions are as follows. Note that FIG.
As shown in (B), the length (lead) of the conductive brush base 122 on the conductive core 121 in the axial direction of the core is L, and a line perpendicular to the axial direction of the brush base 122 and the core 121. X
(Winding angle) is θ, and the width between the side edges of the brush base 122 on the cored bar 121 is W ′.

Lead L 17mm 18mm 19mm 20mm 21mm 22mm Angle θ 38.51 ° 40.12 ° 41.65 ° 43.11 ° 44.51 ° 45.84 ° Width W '13.3mm 13.77mm 14.2mm 14.6mm 15.0mm 15.33mm Gap -1.7mm -1.23mm -0.8mm -0.4 mm 0 mm 0.33 mm In the above table, the “gap” at the bottom is a value obtained by subtracting the width W ′ from the width (W) of the brush base 122 before being wound around the cored bar 121. If this value is less than 0 mm, the absolute value indicates the width at which the edges of the adjacent conductive brush base materials 122 on the cored bar 121 overlap each other, and if the value is 0 mm or more, the gap between the adjacent conductive brush base materials 122. Represents

FIG. 5 shows the experimental results. FIG. 5 is a graph showing the relationship between the lead (L) of the conductive brush base 122 and the average rank of the winding unevenness. As shown in FIG. 5, as the lead (L) of the conductive brush base material 122 becomes smaller from 20 mm to 18 mm, in other words, the end portions of the adjacent conductive brush base material 122 on the metal core 121 become closer to each other. As the overlapping width increased from 0.4 mm to 1.23 mm, the average rank value of the winding unevenness increased, and image noise due to the winding unevenness was suppressed.

However, if the lead (L) is too small as 17 mm, in other words, if the overlap is too large as 1.7 mm, the conductive brush bristles 122 at the joint T portion will not be formed.
As the length of the free end of b 'was shortened, the brush bristle density at that portion was lowered, causing uneven charging. Next, resistance unevenness in the axial direction of the charging brush 12 was evaluated.

In this evaluation experiment, the resistance value of the charging brush 12 removed from the drum cartridge 1 was measured from one end of the brush 12 to another using a resistance measuring device. In this experiment, the lead (L) used in the above experiment was 18
It measured about the charging brush of mm (charging brush of this invention). In addition, as a comparative experiment, measurement was performed on a charging brush having a lead (L) of 21 mm (conventional charging brush).

FIG. 6 shows the experimental results. FIG. 6A is a graph (comparison experiment result) showing the resistance value in the axial direction of the charging brush having the lead (L) of 21 mm, and FIG. 6B is the axial direction of the charging brush having the lead (L) of 18 mm. 7 is a graph (results of evaluation experiments) showing the resistance values of the samples. As shown in FIG. 6B, the resistance value of the charging brush in the axial direction is 1.0 × 10 ^8.
Ω to 1.0 × 10 ⁹ Ω, and no extremely high resistance portion appeared. This indicates that the charging brush 12 can uniformly and stably charge the photoconductor 11.

On the other hand, in FIG. 6 (A), it can be seen that the resistance value reaches around 1.0 × 10 ¹¹ Ω at several places and is high. The interval substantially coincides with the lead (L) of the conductive brush base material. From this, it can be said that the brush bristle density is low at those locations, which may cause uneven charging. Although the example in which the charging device according to the present invention is used as the charging brush 12 has been described above, the transfer charging in which a transfer voltage is applied to the recording paper in order to transfer the toner image formed on the photoconductor to the recording paper The present invention can also be applied to an apparatus or a static eliminator that applies a voltage for static elimination in order to eliminate charges remaining on a photoconductor or the like after transfer of a toner image.

[0041]

As described above, according to the present invention, there is provided a charging brush which is rotated in contact with a charged object to charge the charged object, and which can uniformly and stably charge the charged object. Accordingly, it is possible to provide a charging brush capable of suppressing the occurrence of image noise.

[Brief description of the drawings]

FIG. 1 is a schematic side view of an example of a drum cartridge type image forming apparatus employing a charging brush according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view of a drum cartridge provided with the charging brush shown in FIG.

FIG. 3A is a side view of a charging brush, and FIG. 3B is a front view of a left end portion of the charging brush for explaining a state of winding a conductive brush substrate around a conductive core. is there.

FIG. 4A is a cross-sectional view of the left end in the axial direction of a conventional type charging brush, and FIG. 4B is a cross-sectional view of the left end in the axial direction of the charging brush of the present invention.

FIG. 5 is a graph showing a relationship between a lead (L) of a conductive brush base material and an average rank of winding unevenness.

FIG. 6A is a graph showing the resistance value in the axial direction of a charging brush (conventional charging brush) having a lead (L) of 21 mm, and FIG. 5 is a graph showing the resistance value of a brush (the charging brush of the present invention) in the axial direction.

FIG. 7 is a diagram showing a state in which a conductive brush base material is wound around a conductive cored bar.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Drum cartridge 11 Drum-shaped photoreceptor (one example of a charged object) 12 Charging brush (one example of a charged brush) 13 Cleaning blade 14 Toner collecting roller 15 Driving gear 100 Cartridge case 101 Waste toner collecting part 101a Spring support Part 121 Conductive mandrel (one example of a conductive core rod) 122 Conductive brush base 121a Roller shaft 122a Base 122b Conductive brush bristles 122b ′ Brush bristles on the side of the brush base material side of the superposed brush base 131 blade holding plate 131a fulcrum shaft 131b spring support 132 press-contact spring 2 laser exposure device 3 developing device 31 developing roller 32 toner supply roller 33 toner regulating blade 300 developing device case 4 transfer charger 5, 7 guide plate 6 timing roller pair 8 Fixing roller pair m Laser light P Transfer section PW1, PW2, PW3 Power supply t Toner s Recording paper T Joint between adjacent brush base material side edges on core metal N Non-embedded portion of brush bristles at brush base material side edge of seam T '' The width between the side edges of the brush base on the core bar W The width of the conductive brush base B The conductive brush base S The conductive core D The diameter of the conductive core L L On the brush base Width in the axial direction of the metal core (lead) X Line perpendicular to the axial direction of the conductive metal core θ Angle to line X

Claims (1)

[Claims] 1. A charging brush, which is rotated in contact with a charged object to charge the charged object, comprising: a conductive core rod;
A belt-shaped conductive brush substrate spirally wound around the core rod, wherein the conductive brush substrate is obtained by implanting conductive brush bristles in a band-shaped substrate; The conductive brushes adjacent to each other on the core rod so as to equalize the brush bristle density at the seam portion and the brush bristle density at the joint of the adjacent conductive brush base material side edges on the core rod. A charging brush, wherein the base material side edges are wound around the core bar so as to overlap each other.