JP2005164951A - Electrifying apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the holding property of conductive particles and to secure the physical contact of the bristles of a brush with the surface of a photoreceptor drum in an electrifying apparatus having a fur brush roller to which the conductive particles are stuck. <P>SOLUTION: In the fur brush 40 to which the conductive particles 50 are stuck, conductive fibers 48 are worked from an erected state which is extended in a straight line in the diameter direction of a core bar 44 to an inclined state which is curved in the peripheral direction of the core bar 44 and in a direction opposite to the rotational direction (arrow F or R) of the fur brush roller 40 , and when it is defined that the height of the erected state in the diameter direction of the conductive fibers 48 is H1 and the height of the inclined state is H2, the value of an inclination degree expressed by (H1-H2)/H1 is ≥0.05. The rotational direction and peripheral speed of the fur brush roller 40 are set so that the conductive fibers 48 slide on the surface of the photoreceptor drum 12 in the direction opposite to the direction of the inclination. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a charging device and an image forming apparatus for charging a surface of a member to be charged such as a photosensitive drum, and more particularly to a brush charging type charging device and an image forming apparatus including the charging device.

The first step of image formation in the image forming apparatus using the electrophotographic process is a step of charging the surface of the photosensitive drum as a member to be charged. In this step, the surface of the photosensitive member is uniformly charged to a constant potential. It is important to do.
Conventionally, as a device for charging the surface of a photosensitive drum, a non-contact charging device using corona charging, such as a corotron charging device or a scorotron charging device, is often used because of its simplicity of construction. In corona charging, a high voltage is applied to the discharge wire that is stretched apart from the surface of the photoreceptor at a constant interval, causing corona discharge between the surface of the photoreceptor and positive or negative generated in the air. This is a non-contact charging method in which ions are given to the photosensitive drum. However, in the above-described non-contact charging method, a slight amount of ozone that is harmful to the human body is generated with the air discharge.

In view of this, recently, the interest in a clean office environment has been increased, and a contact-type charging device with much less air discharge compared to the non-contact method described above has been reviewed.
As one of the contact-type charging devices, a charging device including a fur brush roller is known (see, for example, Patent Document 1). FIG. 5A shows a schematic configuration of the charging device 100. The charging device 100 includes a fur brush roller 102 and a DC power source 104. The fur brush roller 102 includes a metal mandrel 102a also serving as an electrode, and a brush part 102b formed by winding a tape having conductive rayon fibers piled around the mandrel 102a in a spiral shape. Then, with the bristles 102c of the brush portion 102b in contact with the surface of the photosensitive drum 106 that rotates in the direction of the arrow X, the fur brush roller 102 is also rotated in the direction of the arrow Y while the mandrel 102a is rotated from the DC power source 104. A predetermined voltage is applied to the surface of the photosensitive drum 106 to charge the surface. At this time, the charge on the surface of the photosensitive drum 106 is dominated by charge (charge injection charge) by direct charge transfer from the contact portion with the bristles 102c, and the charge by corona discharge (air discharge charge) is very small. Thus, generation of ozone can be reduced.

By the way, in the above-described charging device of the conductive brush charging system, various devices for improving the uniformity of charging have been made.
In the charging device 100 described in Patent Document 1, the bristles 102c are processed into a state in which they are curved and inclined in the same direction with respect to the rotation direction of the fur brush roller 102 (hereinafter, the bristles are inclined and inclined). 5), the fur brush roller 102 is rotated in the direction in which the brush hair 102c is raised (the direction of the arrow Y), as shown in FIG. By doing so, as shown in FIG. 5B, the bristles 102c are randomly deformed, and the brush portion 102b is physically and uniformly in contact with the surface of the photosensitive drum 106. The charging uniformity of the photosensitive drum 106 can be improved.

Furthermore, in the charging device described in Patent Document 1, as shown in FIG. 5C, conductive particles 108 are attached to the brush portion 102b as charge accelerating particles for the purpose of charging assistance. The conductive particles 108 increase the electrical contact area between the brush bristles 102c and the surface of the photosensitive drum 106, thereby improving the charging uniformity of the surface of the photosensitive drum 106.
JP-A-11-149202

  However, in the charging device 100 described above, as the fur brush roller 102 rotates, the brush bristles 102c that come into contact with the surface of the photosensitive drum 106 and are greatly deformed (raised) in the direction opposite to the oblique hair direction are photosensitive. At the same time as it passes through the surface of the body drum 106, it is restored vigorously. At this time, the conductive particles 108 attached to the brush hairs 102c are easily blown off and easily fall off from the brush hairs 102c. For this reason, in the conventional charging device 100, the above-described effect due to the conductive particles 108 attached with great effort is reduced in a relatively short time. As a result, it becomes difficult to uniformly charge the surface of the photosensitive drum 106 over a long period of time.

  In view of the above-described problems, the present invention improves the retention of conductive particles, thereby maintaining the charging uniformity over a long period of time and ensuring the physical contact of the brush portion to the surface of the photosensitive drum. It is an object of the present invention to provide a charging device that can contribute to improvement in charging uniformity and an image forming apparatus including the charging device.

  In order to achieve the above object, a charging device according to the present invention includes a fur brush roller formed by winding a pile ground formed by implanting conductive fibers on a base fabric around a mandrel, and a conductive material attached to the conductive fibers. While the fur brush roller is rotated with respect to the object to be charged, the surface of the object to be charged that is moved in one direction by the conductive fiber is rubbed to charge the surface of the object to be charged. In the charging device, the conductive fiber is bent from a straight hair state extending straight in a radial direction of the mandrel to a circumferential direction of the mandrel and in a direction opposite to the rotation direction of the fur brush roller. When the height of the straight hair state in the radial direction of the conductive fiber is H1 and the height of the oblique hair state is H2, the conductive fiber is processed into an inclined oblique hair state (H1-H2) / The value of the degree of bevel shown by H1 is 0.05 or more The fur brush roller has a rotation direction and a peripheral speed set with respect to the member to be charged so that the conductive fiber rubs the surface of the member to be charged in a direction opposite to the inclination direction. It is characterized by. In addition, the value of the oblique hair may be 0.1 or more.

  Further, the moving direction of the outer periphery of the fur brush roller at the rubbing position of the surface of the charged body by the fur brush roller is set to be opposite to the moving direction of the surface of the charged body, and the moving speed of the surface of the charged body The peripheral speed of the fur brush roller can also be set so that the value of the speed ratio θ obtained by dividing the absolute value of the above by the absolute value of the peripheral speed of the fur brush roller is in the range of 1 ≦ θ ≦ 5. In this case, the peripheral speed of the fur brush roller can be set so that the value of the speed ratio θ is in the range of 1.5 ≦ θ ≦ 4.

  Alternatively, the movement direction of the outer periphery of the fur brush roller at the rubbing position of the surface of the charged body by the fur brush roller is set to the same direction as the moving direction of the surface of the charged body, and the moving speed of the surface of the charged body The peripheral speed of the fur brush roller can also be set so that the value of the speed ratio θ obtained by dividing the absolute value of the above by the absolute value of the peripheral speed of the fur brush roller is in the range of 1.5 ≦ θ ≦ 5. In this case, the peripheral speed of the fur brush roller can be set so that the value of the speed ratio θ is in the range of 2 ≦ θ ≦ 4.

  Further, the fur brush roller may be moved from a position where the conductive fiber is lightly in contact with the opposite surface of the object to be charged in a free state and further closer to the object to be charged. The distance D to be arranged is set in a range of 0.2 mm ≦ D ≦ 1 mm. In this case, the distance D can be set in a range of 0.3 mm ≦ D ≦ 0.8 mm.

  In order to achieve the above object, an image forming apparatus according to the present invention is an image forming apparatus that has a photosensitive drum as a member to be charged and forms an image by an electrophotographic method, and charges the photosensitive drum. As the charging device, the above-described charging device is provided.

  In the charging device according to the present invention, a fur brush roller having conductive fibers curved and inclined in a circumferential direction of a mandrel and opposite to a rotation direction of the fur brush roller, the conductive fibers are the Since the surface of the object to be charged is rubbed in the direction opposite to the inclination direction, the retention of the conductive particles attached to the conductive fibers is improved, so that the charging uniformity can be maintained over a long period of time. It becomes. Also, the conductive material processed from a straight hair state extending straight in the radial direction of the mandrel to a slanted hair state that is curved and inclined in the circumferential direction of the mandrel and opposite to the direction of rotation of the fur brush roller. When the height of the straight hair state in the radial direction of the synthetic fiber is H1, and the height of the oblique hair state is H2, the value of the oblique hair degree represented by (H1-H2) / H1 is 0.05. As described above, the contact property of the conductive fiber to the surface of the member to be charged can be secured, and the charging uniformity can be improved.

  Since the image forming apparatus according to the present invention includes the above-described charging device as a charging device for charging the photosensitive drum, a stable image can be formed over a long period of time.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram schematically illustrating a schematic configuration of an image forming apparatus 10 according to an embodiment.
The image forming apparatus 10 is an image forming apparatus that forms an image by an electrophotographic method, and a contact-type charging device 14 and an exposure device are provided around a photosensitive drum 12 that is a cylindrical member to be charged. 16, a developing device 18, an intermediate transfer device 20, and a cleaning device 24 having a cleaning blade 22 are arranged in this order. The photosensitive drum 12 has a diameter of 30 mm and is rotated in the direction of arrow A at a peripheral speed (system speed) of 160 mm / sec (rotation speed: about 100 rpm).

The intermediate transfer device 20 includes an endless transfer belt (hereinafter simply referred to as a “transfer belt”) 30 that is stretched horizontally by a driving roller 26 and a driven roller 28. A primary transfer roller 32 is disposed opposite to the photosensitive drum 12.
A secondary transfer roller 34 is provided at a position facing the driven roller 28 via a transfer belt 30, and a fixing device 38 having a fixing roller pair 36 below the secondary transfer roller 34. Is provided.

  In the image forming apparatus 10 having the above-described configuration, the surface of the photosensitive drum 12 that is rotated clockwise (in the direction of arrow A) at a constant system speed by a driving unit (not shown) is uniformly applied by the charging device 14. The charged area is exposed to light modulated laser light LB from the exposure device 16. The electrostatic latent image formed on the surface of the photosensitive drum 12 by exposure is visualized as a toner image by the developing device 18. The toner image formed on the photosensitive drum 12 is transferred to the transfer belt 30 that is driven to run in the direction of arrow B by the action of the primary transfer roller 32. On the other hand, the recording sheet S supplied from a sheet feeding device (not shown) is conveyed to a position where the transfer belt 30 and the secondary transfer roller 34 face each other, and is subjected to the action of the secondary transfer roller 34, so The toner image is transferred to the recording sheet S. The toner image transferred to the recording sheet S is heated and fixed to the recording sheet S while being heated by the fixing roller pair 36 of the fixing device 38. The recording sheet S on which the toner image is fixed is discharged to a tray (not shown). The toner remaining on the surface of the photosensitive drum 12 without being transferred to the transfer belt 30 is scraped off by the cleaning blade 22 provided in contact with the surface of the photosensitive drum 12 to clean the surface.

As described above, the first step in the above-described electrophotographic process is a step of charging the surface of the photoconductor. In this step, it is important how to uniformly charge the surface of the photoconductor to a constant potential.
The charging device 14 used in the process includes a fur brush roller 40 that is a contact charging member and a DC power supply device 42.

  FIG. 2A shows a schematic configuration of the fur brush roller 40. The fur brush roller 40 has a brush portion 46 formed on the outer periphery of a cylindrical metal mandrel (hereinafter simply referred to as “mandrel”) 44 having a diameter of φ6 mm that also serves as an electrode. The brush portion 46 is formed by winding a pile fabric (hereinafter referred to as “pile belt”) in which conductive fibers are planted on the surface of a belt-like base fabric around the outer periphery of the mandrel 44 in a spiral shape.

As the conductive fiber, conductive nylon obtained by dispersing carbon black as a conductive material in nylon 6 is used. In the present embodiment, UUN manufactured by Unitika Ltd. was used as the conductive nylon. The conductive nylon (UUN) used has a denier value of 2 denier (about 15 μm in terms of fiber diameter) and a volume resistivity of 3.6 × 10 ⁴ Ω · cm.
Moreover, the flocking density of the pile band is 525 / mm ² . Here, the flocking density is the number of conductive fibers per unit area (mm ² ) in the base fabric. In addition, the optimal range of the flock density in the fur brush roller 40 will be described later.

  Each of the bristle portions (conductive fibers) constituting the brush portion 46 is curved and inclined in the same direction in the circumferential direction of the mandrel 44. The direction of inclination is opposite to the direction of rotation of the fur brush roller 40 (arrow F) during image formation. In the present specification, the straight brush hair is referred to as “straight hair”, whereas the curved brush hair as described above is referred to as “oblique hair”. If the pile band is simply wound around the outer periphery of the mandrel 44 as described above, the brush hair 48 is in a straight hair state as shown in FIG. Need to be processed. That is, the mandrel with the pile band wound is inserted into a metal tube while rotating in one direction, and the tube is heated from the outside. By doing in this way, a bristle is addicted to a curved state and will be in a slanted state. Here, as shown in FIG. 3 (a), the length of the straight bristle (the height in the radial direction) extending in the radial direction of the mandrel 44 is H1, and the oblique hair as shown in FIG. 3 (b). When the height of the brush hair in the radial direction later is H2, the value of (H1−H2) / H1 is the skewness of the brush hair. The optimum range of the skewness in the fur brush roller 40 will be described later. Note that the outer diameter φP1 of the fur brush roller indicated by the alternate long and short dash line before the oblique hair processing shown in FIG. 3A is 13.8 mm. Needless to say, the outer diameter φP2 of the fur brush roller after the oblique hair processing shown in FIG. 3B varies depending on the degree of oblique hair (degree of processing). For example, the outer diameter φP2 when processed so as to have a skewness of 0.21 is 12.2 mm.

As shown in FIG. 2B, conductive particles 50 made of conductive zinc oxide doped with aluminum are attached to the brush portion 46 of the fur brush roller 40 as charge promoting particles for the purpose of charging assistance. ing. The primary particle diameter of the conductive particles 50 is 0.05 μm, the volume average particle diameter is 1 μm, and the volume resistivity is 1 × 10 ³ Ω · cm. In addition, the conductive particles 50 are attached with an average attached amount of 11.8 mg / cm ³ . Here, the adhesion amount is a value obtained by dividing the total weight (mg) of the conductive particles 50 adhered to the brush portion 46 by the volume (cm ³ ) of the space occupied by the brush hair.

The conductive particles 50 increase the electrical contact area between the brush bristles and the surface of the photosensitive drum, thereby exhibiting the effect of improving the charging uniformity on the surface of the photosensitive drum. Therefore, if the amount of the conductive particles 50 attached is too small, the above effect is not exhibited so much. On the other hand, if the amount is too large, the conductive particles 50 aggregate and the aggregate adheres to the surface of the photosensitive drum and causes image noise. It will cause the occurrence of. From this viewpoint, the average adhesion amount of the conductive particles 50 is preferably in the range of 0.3 to 20 mg / cm ³ , and more preferably in the range of 0.6 to 15 mg / cm ³ .

  The fur brush roller 40 to which the conductive particles 50 are attached is arranged with a predetermined pressing amount with respect to the photosensitive drum 12. Here, the push-in amount is the shape when the fur brush roller 40 is brought close to the photosensitive drum 12 while the axial center of the fur brush roller 40 is maintained parallel to the axial center of the photosensitive drum 12. This is the distance from which the fur brush roller 40 is brought closer to the photosensitive drum 12 from the position where the brush hair in a free state holding the lightly contacts the surface of the photosensitive drum. The optimum range of the pressing amount for installing the fur brush roller 40 will be described later.

  As shown in FIG. 1, the fur brush roller 40 configured as described above is applied with a DC bias voltage of −600 V from the DC power source 42 to the mandrel 44 while being rotated in the direction of the arrow F. As a result, the surface of the photosensitive drum 12 is charged to substantially the same potential as the applied voltage. At this time, as shown in FIG. 4A, the bristles 48 rub against the surface of the photosensitive drum 12 in the direction opposite to the inclination direction (hereinafter, this direction is referred to as “forward direction”). And rubbing in the forward direction is referred to as “forward rubbing”). The forward direction is referred to as the surface of the photosensitive drum is rubbed in the inclined direction (hereinafter, this direction is referred to as “reverse direction”, and the reverse direction is referred to as “reverse direction”). This is because, as described above, when the bristle brushed in contact with the surface of the photosensitive drum is restored, the conductive particles are easily detached from the bristle and scattered. On the other hand, if the direction is reversed, the load applied to the brush bristles becomes larger than that in the normal direction, and brush hair removal and breakage become severe.

  In the above example, as shown in FIG. 4A, the bristles 48 are inclined in the direction opposite to the rotation direction of the fur brush roller 40 (arrow F), and the fur brush roller 40 is connected to the photosensitive drum 12. By rotating in the same direction, that is, at the positions where they are opposed (the rubbing position of the photosensitive drum 12 by the fur brush roller 40), the outer peripheral portions are moved in opposite directions (passing each other). Therefore, it was decided to realize rubbing. However, even if the fur brush roller is rotated in the opposite direction to the photosensitive drum, it is possible to realize the rubbing in order. Even in this case, as shown in FIG. 4B, the bristles 48 are inclined and inclined in the direction opposite to the rotation direction of the fur brush roller 40 (arrow R). Then, the peripheral speed of the fur brush roller is set to be larger than the peripheral speed of the photosensitive drum 12. By doing so, the outer peripheral portions move in the same direction at the opposing positions, but the moving speed of the outer peripheral portion of the fur brush roller is higher than the outer peripheral portion of the photosensitive drum. This is faster than the moving speed, so it becomes rubbing in order.

As described above, in this embodiment, the conductive particles attached to the brush hairs (conductive fibers) are detached by sequentially rubbing the surface of the photosensitive drum by the fur brush roller. Thus, the charging uniformity of the photosensitive drum is achieved.
In addition, the present inventor conducted tests on various other factors involved in charging uniformity in order to find the optimum range for each factor. The tested factors were (1) the skewness, (2) the peripheral speed ratio between the fur brush roller and the photosensitive drum, (3) the pushing amount, and (4) the flocking density.

  Here, a value obtained by dividing the absolute value of the peripheral speed of the photosensitive drum, which is the moving speed of the surface of the photosensitive drum, by the absolute value of the peripheral speed of the fur brush roller is defined as a speed ratio θ. In addition, when the fur brush roller is rotated in the same direction as the photosensitive drum (see FIG. 4A), a sign “−” is added to the speed ratio θ, and the fur brush roller is rotated in the opposite direction to the photosensitive drum. It is distinguished from the speed ratio θ in the case of making it (see FIG. 4B).

The test machine was based on a laser printer “magicolor 2200 DeskLaser” manufactured by Minolta QMS Co., Ltd. That is, the laser printer is equipped with a scorotron charger, but instead, it is equipped with the charging device 14 according to the embodiment and used for the test.
In the test, unevenness of the charged potential on the surface of the photosensitive drum 12 (hereinafter referred to as “initial charge uniformity”) at the start of use of a new fur brush roller 40, and B / The measurement was performed by measuring unevenness of the charged potential on the surface of the photosensitive drum 12 (hereinafter referred to as “long-term charging uniformity”) after printing 10,000 images of a W ratio 5% chart.

  A surface potential meter MODEL344 and a probe 6000B-16 manufactured by Trek Japan Co., Ltd. were used to measure the charged potential on the surface of the photosensitive drum 12. The surface potential measurement position is the center of the photosensitive drum 12 in the longitudinal direction and the mounting position of the developing device 18 (FIG. 1) in the circumferential direction. At the time of measurement, the developing device 18 is removed, the probe is arranged, the surface of the photosensitive drum 12 is charged with the fur brush roller 40, and the state is left as it is (without exposure by the exposure device 16). The potential on the surface of the photosensitive drum 12 was measured for a predetermined time. Then, the difference between the maximum value and the minimum value of the surface potential measured during that time was defined as charging potential unevenness δV.

According to the range of the charged potential unevenness δV, the measurement results were evaluated in four stages as follows, and each classification was represented by symbols “◎”, “◯”, “Δ”, “×”.
A: 0 ≦ δV <20
○: 20 ≦ δV <50
Δ: 50 ≦ δV <100
×: 100 ≦ δV
Here, in the image formation, the evaluations “」 ”,“ ◯ ”,“ Δ ”are allowable ranges, and the evaluation“ × ”is an unacceptable range.
Hereinafter, each factor will be described with reference to test results.

  In the case of straight hair that is not beveled, that is, in the state where the brush hairs are radially extended with respect to the rotation axis of the fur brush roller, the direction of the centrifugal force acting on the conductive particles attached to the brush hairs and the brush The direction in which the hair extends is substantially the same. As a result, even the conductive particles adhering to the base or middle of the brush hair are easily transferred to the tip of the brush hair by centrifugal force and are easily detached from the brush hair. On the other hand, when inclined, the direction of the brush hair intersects the direction of the centrifugal force acting on the conductive particles, so that the conductive particles move to the brush tip compared to the case of straight hair. Becomes slower. For this reason, in the case of oblique hair, even if a larger amount of conductive particles are attached to the brush hair, the conductive particles will not be released at a stretch, so that the generation of image noise due to this can be prevented. On the contrary, if a large amount of conductive particles are attached in advance, the conductive particles will gradually move to the tip of the bristle, so the conductive particles at the tip of the bristle contacting the photosensitive drum. Can be replenished, and stable charging can be realized over a long period of time.

Further, in the case of rubbing, the abdomen of the brush hair curved like a bow comes into contact with the surface of the photosensitive drum, so that the contact area is larger than in the case of straight hair. Therefore, it is possible to improve the charging uniformity.
In order to obtain the above effect, it is necessary to process with a certain degree of bevel, not just beveling. Here, Table 1 shows the results of tests performed to define at least the necessary degree of bevel. In this test, the degree of oblique hair was changed under the conditions of speed ratio θ = −2, flocking density: 524 [lines / mm ² ] and indentation amount D = 0.5 mm. The charging uniformity and long-term charging uniformity were evaluated.

From the results shown in Table 1, it can be said that the degree of oblique hair is preferably 0.05 or more, more preferably 0.1 or more, and still more preferably 0.21 or more.
It should be noted that the feasible (workable) oblique hair degree is naturally limited by the size of the diameter of one conductive fiber and the flocking density, and does not become “1” which is the maximum by definition. For example, the upper limit in this example is about 0.3.
(2) Speed ratio θ
The purpose of rotating the fur brush roller is to increase the chance of rubbing the surface of the photoreceptor by the brush hairs, thereby improving the charging uniformity. Therefore, a speed ratio θ of a certain level or more is required. That is, the peripheral speed of the photosensitive drum cannot be changed so much because it is constrained by the system speed. Therefore, in order to ensure the necessary speed ratio θ, the peripheral speed (rotation speed) of the fur brush roller is set to a certain level or more. It is necessary to raise. On the other hand, if the peripheral speed (rotational speed) of the fur brush roller is excessively increased, the following problems occur. That is, although the hair is slanted, the centrifugal force acting on the conductive particles becomes large, the separation from the brush hair becomes intense, and stable charging cannot be performed for a long time. In addition, since the impact when the brush bristles come into contact with the surface of the photoconductor increases, the surface of the photoconductor is easily damaged, and as a result, uneven charging occurs. Further, the wear of the brush hair is accelerated, and the life of the fur brush roller is shortened.

Therefore, the present inventor (A) rotates the fur brush roller in the same direction as the photosensitive drum (FIG. 4A) and (B) rotates the fur brush roller in the opposite direction to the photosensitive drum. In each of the cases (FIG. 4 (b)), a test was conducted to define the optimum range of the speed ratio θ. In both tests, the speed ratio θ was changed under the conditions of the oblique hair degree: 0.21, the flocking density: 524 [lines / mm ² ], and the indentation amount D = 0.5 mm. Initial charging uniformity and long-term charging uniformity were evaluated.
(A) When the fur brush roller is rotated in the same direction as the photosensitive drum Table 2 shows the test results in this case.

From the results shown in Table 2, it can be said that the speed ratio θ is preferably in the range of 1 ≦ θ ≦ 5, more preferably in the range of 1.5 ≦ θ ≦ 4, and further preferably θ = 2.
(B) When the fur brush roller is rotated in the opposite direction to the photosensitive drum Table 3 shows the test results in this case.

From the results shown in Table 3, it can be said that the speed ratio θ is preferably in the range of 1.5 ≦ θ ≦ 5, more preferably in the range of 2 ≦ θ ≦ 4, and further preferably θ = 3.
(3) Indentation amount If the indentation amount is too small, the brush portion of the fur brush roller cannot sufficiently and stably contact the surface of the photosensitive drum, and the contact pressure is reduced, resulting in brush hairs and conductive particles. Contact resistance between the photosensitive drum and the photosensitive drum increases, and uneven charging occurs. On the other hand, if the pushing amount is too large, the following problems occur. That is, the pressing force on the surface of the photosensitive drum due to the brush bristles becomes excessive, and the surface of the photosensitive drum is easily scratched by the friction acting between them. As a result, uneven charging occurs. Further, the wear of the brush bristles and the photosensitive drum is accelerated, and the lifetime of both is shortened.

Therefore, the present inventor conducted a test to define an optimum range of the pushing amount. In the test, the indentation amount D was changed under the conditions of oblique hair degree: 0.21, speed ratio θ = −2, flocking density: 524 [lines / mm ² ], and initial charging at each indentation amount D was performed. Uniformity and long-term charging uniformity were evaluated. The test results are shown in Table 4.

From the results shown in Table 4, the indentation amount D is preferably in the range of 0.2 ≦ D ≦ 1, more preferably in the range of 0.3 ≦ D ≦ 0.8, and even more preferably D = 0.5. You can say that.
(4) Flocking Density If the flocking density is too low, the contact of the conductive fibers (brush hairs) with the surface of the photoreceptor becomes rough and the charging uniformity decreases.

  Here, Table 5 shows the results of tests conducted to define at least the required hair density. In this test, the hair density was changed under the conditions of the oblique hair degree: 0.21, the speed ratio θ = −2, and the indentation amount D = 0.5 mm, and the initial charging uniformity and long-term at each hair density were changed. The charging uniformity was evaluated.

From the results shown in Table 5, the flocking density is preferably 155 [lines / mm ² ] or more, more preferably 217 [lines / mm ² ] or more, and further preferably 524 [lines / mm ² ] or more. I can say that.
In addition, the upper limit of the flocking density is naturally determined from the size of the diameter of one conductive fiber. In this example, the upper limit is 10,000 [lines / mm ² ]. This is a value that is geometrically determined when two denier conductive nylon (UUN) is arranged as densely as possible (when flocking is attempted).

As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described form, and for example, the following form is also possible.
(1) In the above embodiment, UUN (conductive nylon) manufactured by Unitika Co., Ltd. using nylon 6 as the fiber material and carbon black as the conductive material dispersed therein as the conductive fiber (brush hair). Although used, the fiber material, the conductive material, and the conductive fiber are not limited to those described above.

  For example, the fiber material can be selected from nylon, acrylic, polyester, rayon, and the like. In addition, as the conductive material dispersed in this, metal such as aluminum, iron, copper and nickel, conductive oxide such as zinc oxide, tin oxide and titanium oxide, or carbon fine particles such as graphite and carbon nanotube, etc. You can choose. Specific examples of conductive fibers include UUN, GBN (conductive nylon), SUN (conductive nylon), USV (conductive vinylon), REC (conductive rayon, “REC” manufactured by Unitika Ltd. "Can be selected from registered trademarks).

In the above embodiment, the volume resistivity of the conductive fiber is 3.6 × 10 ⁴ Ω · cm, but is not limited thereto. The volume resistivity of the conductive fiber is set in the following range from the following viewpoints. When the photosensitive drum has a defect such as a pinhole, an overcurrent flows from the fur brush roller to the defective portion, resulting in a charging failure in the axial direction of the fur brush roller. Further, the bristle in which the overcurrent flows is deteriorated, and charging failure occurs in the circumferential direction of the photosensitive drum corresponding to the deteriorated bristle. Therefore, in order to prevent the occurrence of the above problem due to overcurrent, the volume resistivity is required to be 1 × 10 Ω · cm or more, preferably 1 × 10 ² Ω · cm or more. Further, in order to flow a blackout current necessary for sufficient charging (in order to inject charges), the volume resistivity is 1 × 10 ⁸ Ω · cm or less, preferably 1 × 10 ⁵ Ω · cm or less. Set by range.

Further, the thickness of the conductive fiber is preferably 1 to 10 denier, more preferably 2 to 5 denier.
(2) In the above embodiment, the conductive zinc oxide doped with aluminum is used as the material of the conductive particles. However, the present invention is not limited to this.
In addition to the above, the conductive particles may be made of metal oxides such as zinc oxide, tin oxide, titanium oxide, iron oxide, aluminum oxide and magnesium oxide, carbon such as carbon black, graphite, fullerene and carbon nanotubes. You can choose from materials.

  Moreover, when using a metal oxide, it is also possible to use a metal oxide containing a metal element different from the main metal element. For example, as in the above embodiment, in addition to zinc oxide containing aluminum, tin oxide containing antimony, or the surface of titanium oxide, aluminum borate, or barium sulfate contains antimony. Those covered with tin oxide can be used.

  Among these, the conductive particles are preferably metal oxides such as zinc oxide, tin oxide and titanium oxide, zinc oxide containing aluminum, tin oxide containing antimony, and fine particles having at least the surface thereof. This is because they exhibit white or a color close to white, so that exposure is not hindered, and the particles are hardly noticeable even when attached on a recording sheet.

Specifically, the conductive zinc oxide is 23K (manufactured by Hakusui Tech Co., Ltd.), the conductive tin oxide is SN-100P (manufactured by Ishihara Sangyo Co., Ltd.), metal covered with conductive tin oxide. The oxide can be selected from ET-300W (manufactured by Ishihara Sangyo Co., Ltd.), Bustran 4310 (manufactured by Mitsui Mining & Smelting Co., Ltd.), and the like.
If the volume average particle size of the conductive particles is too small, the manufacturing cost is increased, and consequently the cost of the entire charging device is also increased. If the volume average particle size is too large, the centrifugal force acting on the conductive particles by the rotation of the fur brush roller. Increases and the amount of detachment from the brush hair increases. From such a viewpoint, the volume average particle size of the conductive particles is preferably in the range of 0.02 μm to 10 μm, and more preferably in the range of 0.1 μm to 5 μm.

If the volume resistivity of the conductive particles is too large, a sufficient charge cannot be supplied from the fur brush roller to the photosensitive drum, so that it is preferably 1 × 10 ¹⁰ Ω · cm or less, more preferably 1 × 10. ⁸ Ω · cm or less.
(3) In the above embodiment, the conductive brush is attached in advance to the brush portion of the fur brush roller, and then the fur brush roller is assembled at a predetermined position. However, after assembling, the conductive particles may be supplied and attached to the fur brush roller (brush portion) using an appropriate conductive particle supply means.

  As the conductive particle supply means, for example, a developing device can be used. That is, conductive particles are mixed in the developer (toner), adhered to the surface of the photosensitive drum, and conveyed to the fur brush roller for supply. In this case, it is desirable to employ a so-called cleanerless system that does not use a cleaning blade. The cleanerless system is a system that recycles residual toner by eliminating the cleaning blade by controlling the charge of the transfer residual toner.

Alternatively, a dedicated device (conductive particle supply device) for supplying conductive particles to the fur brush roller may be provided in the fur brush roller.
Even when the conductive particle supply means as described above is used, the conductive particles may be attached in advance to the fur brush roller (brush portion). By doing so, it is possible to replenish the conductive particles that are naturally reduced, and it is possible to realize charging uniformity over a long period of time.
(4) In the above embodiment, a DC voltage is applied to the metal mandrel of the fur brush roller. However, an alternating voltage (AC component) may be applied to the DC voltage in a superimposed manner. For example, the alternating voltage may be a rectangular wave having a peak-to-peak magnitude of 500 V and a frequency of 1 kHz.
(5) In the above embodiment, a photosensitive drum, which is a cylindrical charged body, is used as the charged body. However, a belt-shaped body can also be used as the charged body.

  The charging device and the image forming apparatus according to the present invention can be suitably used for, for example, a printer, a facsimile machine, a copying machine, and a multifunction machine having these functions, which perform image formation by an electrophotographic method.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment. (A) is a perspective view showing a schematic configuration of a fur brush roller constituting a charging device in the image forming apparatus, and (b) is a diagram in which the brush bristles of the fur brush roller are in contact with the surface of the photosensitive drum. It is a schematic diagram which shows a state. It is a figure for demonstrating a skewness. It is a figure which shows the relationship between the rotation direction of a fur brush roller and a photoconductor drum. It is a figure for demonstrating the charging device which concerns on a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Photosensitive drum 40 Fur brush roller 48 Brush hair (conductive fiber)
50 conductive particles

Claims (9)

A fur brush roller formed by winding a pile of conductive fibers on a base fabric and wound around a mandrel; and conductive particles attached to the conductive fibers;
A charging device for charging the surface of the object to be charged by rubbing the surface of the object to be charged that moves in one direction with the conductive fiber while rotating the fur brush roller with respect to the object to be charged,
The conductive fiber changes from a straight hair state that extends straight in the radial direction of the mandrel to a slanted hair state that is curved and inclined in the circumferential direction of the mandrel and opposite to the direction of rotation of the fur brush roller. When the height of the straight hair state in the radial direction of the conductive fiber is H1, and the height of the oblique hair state is H2, the oblique hair represented by (H1-H2) / H1 The degree value is 0.05 or more,
The fur brush roller has a rotation direction and a peripheral speed set with respect to the charged body so that the conductive fiber rubs the surface of the charged body in a direction opposite to the inclination direction. Characteristic charging device.   The charging device according to claim 1, wherein the value of the skewness is 0.1 or more. The movement direction of the outer periphery of the fur brush roller at the rubbing position on the surface of the charged body by the fur brush roller is set to be opposite to the moving direction of the surface of the charged body,
The value of the speed ratio θ obtained by dividing the absolute value of the moving speed of the charged body surface by the absolute value of the peripheral speed of the fur brush roller,
The charging device according to claim 1, wherein the peripheral speed of the fur brush roller is set so as to be in a range of 1 ≦ θ ≦ 5.   4. The charging device according to claim 3, wherein a peripheral speed of the fur brush roller is set so that a value of the speed ratio θ is in a range of 1.5 ≦ θ ≦ 4. The movement direction of the outer periphery of the fur brush roller at the rubbing position on the surface of the member to be charged by the fur brush roller is set in the same direction as the direction of movement of the surface of the member to be charged.
The value of the speed ratio θ obtained by dividing the absolute value of the moving speed of the charged body surface by the absolute value of the peripheral speed of the fur brush roller,
3. The charging device according to claim 1, wherein the peripheral speed of the fur brush roller is set so as to be in a range of 1.5 ≦ θ ≦ 5.   6. The charging device according to claim 5, wherein a peripheral speed of the fur brush roller is set so that a value of the speed ratio θ is in a range of 2 ≦ θ ≦ 4. The fur brush roller is disposed at a position where the conductive fiber is lightly in contact with the opposite surface of the object to be charged while keeping its shape, and further close to the object to be charged. And
3. The charging device according to claim 1, wherein the distance D to be approached is set in a range of 0.2 mm ≦ D ≦ 1 mm.   The charging device according to claim 7, wherein the distance D is set in a range of 0.3 mm ≦ D ≦ 0.8 mm. An image forming apparatus having a photosensitive drum as a charged body and forming an image by an electrophotographic method,
An image forming apparatus comprising the charging device according to claim 1 as a charging device for charging the photosensitive drum.

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