JP2002055510A - Electrostatic charging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic charging device of a contact type capable of stably performing the uniform charge over a long period, and hardly causing the wear or damage on a body to be charged. SOLUTION: This electrostatic charging device standing for the electrostatic charging device provided with the static charging member 2 of a cylindrical shape being held rotatably in contact with a rotary body to be charged 5, and a power source 3 applying a voltage on the charging member 2 of the cylindrical shape, holds the charging member 2 of the cylindrical shape at an assigned position so as to become the specified position with regard to the body to be charged 5, and then supports the member 2 so that the member 2 is rotated while coming into contact with the body to be charged 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact-type charging device for charging a surface of an object to be charged to a desired potential (including substantially eliminating OV) by bringing a cylindrical charging member into contact therewith. In particular, a charging device (or static eliminator) for charging an image carrier or the like to a desired potential in an image forming apparatus typified by a copier, a printer, a facsimile, a multifunction machine, or the like using an electrophotographic method or an electrostatic recording method. As a charging device.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus utilizing an electrophotographic method, an image carrier such as a photoreceptor rotating in a certain direction is uniformly charged to a desired potential by a charging device and then charged. The surface of the image carrier is exposed to light corresponding to image information to form an electrostatic latent image, and the electrostatic latent image is developed with a developer to form a toner image. By directly transferring the toner image to a recording medium such as recording paper or via an intermediate transfer member, and fixing the toner image.
An image is formed.

As a charging device used in such an image forming apparatus, for example, a roll-shaped, brush-shaped or blade-shaped charging member to which a charging voltage is applied is contacted while applying a constant load to the image carrier. 2. Description of the Related Art There is known a contact-type charging device that is disposed in a state where the charging member is in contact with the charging member and generates an electric discharge in a minute gap in the vicinity of a contact portion between the charging member and the image carrier.

Other examples of such a contact-type charging device include a conductive member to which a voltage is applied, and a rotatable, thin, tube-shaped resistance layer member which is fitted around the conductive member. There is also known a charging device in which a charging member of a composite form is disposed such that its conductive member comes into contact with a member to be charged such as a photoreceptor via a tubular resistance layer member (JP-A-4-268584). No.).

[0005]

However, the conventional contact-type charging device has the following problems.

First, in order to uniformly contact the charging member with the rotating member to be charged, any of the charging devices applies a constant load to the charging member by a pressing mechanism using a pressing spring or the like while applying a constant load. Since the support structure for rotatably supporting the surface of the member to be charged is employed, there is a problem that the surface of the member to be charged is easily accelerated with time due to wear and damage. For example, when the object to be charged is an image carrier such as a photoconductor in an electrophotographic image forming apparatus, the image carrier is worn or damaged by the load contact of the charging member, and the photosensitive layer or the like is damaged. Causes the problem that the image quality deteriorates due to the fluctuation of the characteristics.

In addition, the charging member is deformed (distorted) by the load of the pressing mechanism, and as a result, the position and shape of the gap near the contact portion between the charging member and the member to be charged fluctuate, resulting in uniformity. It is difficult to perform charging stably. Moreover, in the charging member having a composite form of the conductive member and the tube-shaped resistance layer member, the tube-shaped resistance layer member meanders and rotates due to the deformation as described above. The end of the tubular resistance layer member buckles or cracks, resulting in poor durability.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to provide a contact-type charging device which is less likely to cause wear and damage to a member to be charged, and has a uniform charging property. Is to provide a charging device capable of performing the charging stably for a long period of time.

[0009]

A charging device according to the present invention which can achieve the above object has a cylindrical charging member rotatably in contact with a rotating member to be charged, and a voltage applied to the cylindrical charging member. A charging device for charging the surface of the member to be charged by applying a voltage to the charging member and generating a discharge in a minute gap near a contact portion between the member and the member to be charged. And holding the cylindrical charging member in a fixed position so as to be at a fixed position with respect to the member to be charged, and supporting the member to rotate in contact with the member to be charged. is there.

Here, the cylindrical charging member is supported by:
A support structure in which the distance between the rotation axis (center) of the charging member and the rotation axis (center) of the member to be charged is constant, wherein at least the charging member is in contact with the surface of the member to be charged. It is a support structure that can rotate. Also, the cylindrical charging member may be configured to rotate at least following the rotation of the member to be charged by contact with the member to be charged only by being rotatably supported. The charging member may be configured to be connected to the driving means and driven to rotate.

According to such a charging device, the cylindrical charging member is rotatably supported in a state of being constantly in contact with the member to be charged in a fixed position (distance) relationship. Is applied, the charging member mainly rotates by following the rotation of the member to be charged basically due to the electrostatic force generated between the member and the member to be charged (strictly speaking, the contact frictional force also acts. However, the force (government) relationship is “electrostatic attraction ≧ contact frictional force”). At this time, a substantially uniform minute gap is obtained between the charging member and the member to be charged, and the discharge is generated to perform charging. In addition, since the charging member is not subjected to a load by the pressing mechanism as in the related art, the charging member is not easily deformed by that amount and does not apply an unnecessary load to the charged member. The position and the shape of the minute gap in the vicinity of the contact portion with the surface are stabilized, whereby uniform charging is stably performed.

In this charging device, the bite amount between the cylindrical charging member and the member to be charged is preferably set within a range of 0 to 0.6 mm. This biting amount is determined by the above-mentioned inter-axis distance (L) between the charging member and the member to be charged in the no-load state, and the inter-axis distance (E) set when actually supporting the charging member.
Is represented by a difference S (= LE). When the bite amount exceeds 0.6 mm, the linear pressure at the contact portion between the charging member and the charged member increases, the load on the charged member increases, and the charged member is easily worn or damaged. Also, there is a problem that residual toner or the like adhering to the member to be charged easily adheres strongly to the charging member. Also, this biting amount is determined by a structure in which the charging member is harder (for example, ASK).
If the hardness is such that the ER-C hardness is about 50 to 60 °, it is preferable to set the thickness to about 0 to 0.2 mm.

The cylindrical charging member may be a known charging roll or charging brush, but is preferably a cylindrical film electrode and a rotatable roller in the internal space of the film electrode. And a cylindrical electrode supporting member to be arranged. In this case, the film-shaped electrode comes into contact with the member to be charged and is pulled by the electrostatic force, whereby the contact with the member to be charged is stabilized and the driven rotation with respect to the member to be charged is also stabilized. When the electrode support member is conductive, it also serves as a power supply member to supply a voltage to the film-shaped electrode, and when non-conductive, the power supply member uses another power supply member. What is necessary is just to supply a voltage from a member to a film-shaped electrode.

The cylindrical electrode support member may be a rigid member, but from the viewpoint of reducing the load at the time of contact with the member to be charged, an elastic roll capable of being elastically deformed at the time of the contact. Or a roll-shaped brush is preferable. Further, the cylindrical electrode supporting member may be simply rotatably supported, but if necessary, the electrode supporting member is connected to a driving means to be driven and rotated. For example, the bite amount is 0.01
When the distance is set to be equal to or less than mm, the electrode support member and, by extension, the charging member are driven and rotated by the driving force of the driving means so as to rotate stably without slip. As a result, the electrode support member and, consequently, the charging member rotate stably, so that poor charging due to poor rotation does not occur.

In the case where the cylindrical electrode supporting member is connected to the driving means and driven to rotate, the electrode supporting member is driven to rotate at a constant speed with no difference in peripheral speed with respect to the rotation of the member to be charged. However, it is also possible to perform driving rotation with a peripheral speed difference that is faster or slower than the rotation of the member to be charged. In the case where the drive rotation is performed with this peripheral speed difference, toner or the like adhering to the surface of the film-shaped electrode at the contact portion with the member to be charged can be removed due to the peripheral speed difference,
The toner and the like can be hardly adhered. In this case, in order to stabilize the rotation (peripheral speed) of the driving means of the cylindrical electrode supporting member by the driving force, the cylindrical film electrode and the cylindrical electrode supporting member are bonded and integrated. A more effective effect can be obtained by using a charged charging member. However, regarding the above-mentioned difference in peripheral speed, if the difference in peripheral speed is too large, the film-shaped electrode may be stained or wrinkled.
It is preferable to set within the range of 15%.

Further, this charging device can be widely used as a charging device for charging a surface of a member to be charged by bringing a cylindrical charging member into contact with the member to be charged. Among them, a photoconductor on which a toner image is formed in a conventionally known single-color or color image forming apparatus employing an electrophotographic method or the like,
It is effective when used as a charging device for an image carrier (a body to be charged) such as a dielectric. Furthermore, if the image carrier is used as a charging device for an image carrier not provided with a cleaning device (especially a blade-type cleaning device), since the cleaning device is not provided, the charging device is not provided. Even if there is an attached matter such as residual toner adhering to the image carrier in the above, since the load on the member to be charged (image carrier) of the charging member is small, the residual toner and the like hardly adhere to the charging member. In addition, non-uniform charging due to the adhesion of the residual toner and the like hardly occurs, which is more effective.

On the other hand, in such a charging device, the voltage applied from the power source to the charging member can be set so that the surface potential of the member to be charged becomes substantially 0V. In this case, the charging device functions as a static eliminator for removing the surface charge of the member to be charged. When the charge is removed by the charging device in this way, as described above, the charged member is less likely to be worn or deteriorated due to the contact of the charging member due to a low load, and the charged member is charged to a negative polarity. In this case, even a portion (charge) charged to a positive polarity can be reliably charged to almost 0V.

From this point of view, this charging device is used as a charge removing device for an image carrier on which a toner image is formed by electrophotography and a charge removing device for an intermediate transfer member to which the toner image is temporarily transferred. Is possible and effective.

[0019]

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

[First Embodiment] FIG. 1 is a schematic configuration diagram showing a charging device according to a first embodiment of the present invention. The charging device 1 has a cylindrical charging member 2 rotatably in contact with a drum-shaped charged member 5 that rotates in a fixed direction (the direction of arrow A), and applies a voltage to the cylindrical charging member 2. The power supply 3 is provided. Of these, the cylindrical charging member 2
Is composed of a cylindrical film electrode 21 and a cylindrical electrode support member 22 rotatably disposed in the internal space of the film electrode 21.

A cylindrical film-shaped charging device in the charging member 2
The pole 21 has flexibility with a thickness of about 30 to 200 μm.
Is formed by molding a semiconductive member into a cylindrical shape. this
Such semiconductive members are, for example, polyester, poly
Amide, polyethylene, polycarbonate, polyolefin
Plastics, polyurethane, polyvinylidene fluoride, acrylic
Conductive film such as carbon black
The semi-conductive member mixed with
It is formed into a cylindrical shape. Also, this file
The lumped electrode (semiconductive member) 21 has a volume resistivity
Is 10^Three -10 ^TenΩ · cm
Is adjusted. Volume resistivity is 10^ThreeΩ ・ cm not yet
When it is full, spark discharge is likely to occur.^TenΩ
cm, dot-shaped charging failure and abnormal discharge may occur.
It will be easier. Further, the film-shaped electrode 21 is
In consideration of direct contact with No. 5, its tensile modulus is 1
0-280 kg / mm^TwoSet to be about
Is preferred.

The cylindrical electrode supporting member 22 of the charging member 2 is a member for lightly supporting the cylindrical film electrode 21 from the inside of the film electrode 21 so that the cylindrical film electrode 21 comes into contact with the member 5 to be charged. In this embodiment, a roll-shaped electrode support member is used in this embodiment. As shown in FIGS. 1 and 2, the electrode support member 22 is supported and fixed so that the electrode support member 22 can be brought into contact with the charged object 5 at a predetermined position and rotated. Axis of rotation 2
It is supported by a support structure in which the distance between (the center O _{22 of} ) 2a and (the center O _{5 of} ) the rotating shaft 5a of the charged body 5 is constant. In FIG. 2, reference numeral 6 denotes a support frame, and 7 denotes a bearing for each of the rotating shafts 22a and 5a.

The rotation shaft 2 of the electrode support member 22 before being supported by this support structure (with no load).
The distance (L) between the axis 2a and the rotation axis 5a of the charged body 5 is the radius r22 of the electrode support member ₂₂ and the thickness d of the film-shaped electrode.
And the total length of the charged object and the radius r ₅ (= r ₂₂ + d +
r ₅ ), on the other hand, in this support structure, the distance E between the axes is set to be equal to or slightly shorter than the distance L between the axes (E ≦ L). Then, the difference S (= L)
-E) is the bite amount between the cylindrical charging member 2 and the charged member 5. This biting amount (S) is at least 0 mm because the charging electrode 2 (actually, the film-like electrode 21 and the electrode support member 22) needs to contact the member 5 to be charged.
This is set as above (that is, the distance L between the shafts in the no-load state and the distance E between the shafts in the supported state are equivalent). On the other hand, if the biting amount S is too large, the linear pressure at the contact portion with the member to be charged 5 is increased, so that the member to be charged 5 is easily worn or damaged. The deposit is desirably set to 0.2 mm or less because the attached matter is easily transferred and adheres firmly.

The electrode support member 22 is formed of a conductive material to serve also as a power supply member for the film-shaped electrode 21. Specifically, for example, polyester, polyamide, polyethylene, polycarbonate, polyolefin, polyurethane, polyvinylidene fluoride, acrylic, POM, phenol, polyimide, P
EN, PEK, PES, PPS, PFA, PVdF, E
TFE, synthetic resin such as CTFE, or silicone rubber,
Ethylene propylene rubber, butyl rubber, acrylic rubber,
It is formed into a roll of a conductive material provided with conductivity by mixing conductive powder such as carbon black or metal powder into synthetic rubber such as urethane rubber or nitrile rubber. In this case, when a conductive material that cannot maintain the roll shape is used, the roll shape is used together with the roll core material.
Further, a semi-conductive inorganic material such as a polar rubber such as epichlorohydrin rubber, chloroprene rubber, EPDM rubber, or amorphous silicon, or a semi-conductive inorganic material such as amorphous silicon is vapor-deposited on an insulating substrate in a thin film or thick film form. Furthermore, it is formed in a roll shape using a metal material such as stainless steel or aluminum. The electrode support member 22 may be formed of an insulating material, but in this case, a function as a power supply member cannot be obtained. It is necessary to install a power supply member.

Further, the electrode supporting member 22 is usually
Although the outer diameter is smaller than the inner diameter of the cylindrical film electrode 21, the outer diameter may be the same as or slightly larger than the inner diameter of the film electrode 21. In particular, when the outer diameter is made larger than the inner diameter of the film-shaped electrode 21, it is preferable to use an electrode supporting member 22 having elasticity.
In this case, the rotation of the film-shaped electrode 21 tends to meander, and it is desirable to provide a mechanism for preventing the meandering. Conversely, if the outer diameter is smaller than the inner diameter of the film electrode 21, if it is too small, the film electrode 21 will flutter and the charging potential will tend to be non-uniform. In this case, in order to suppress the fluttering of the film-shaped electrode 21, it is desirable to additionally provide a contact member that comes into contact with the outer peripheral surface of the film-shaped electrode 21 to stabilize the rotating state. From such a viewpoint, the outer diameter of the electrode support member 22 is preferably set to be about 0.8 to 1.3 times the inner diameter of the film-shaped electrode 21.

The power supply 3 is capable of applying a DC voltage to the charging member 2 (the film electrode 21 via the electrode support member 22) in the charging step of the member 5 to be charged. The power supply 3 may be set so as to apply a DC voltage on which an AC is superimposed to the charging member 2.

Next, the operation of the charging device 1 will be described.

First, in such a charging device 1, the power supply 3
When no voltage is applied from the charging member 2, the cylindrical film-shaped electrode 21 of the charging member 2
2 is lightly in contact with the member to be charged 5 by the support from the inner surface side (light pressing force), but a predetermined voltage is applied to the film-shaped electrode 21 from the power supply 3 via the conductive electrode support member 22. The film-shaped electrode 21 is pulled and adhered to the member to be charged 5 by an electrostatic attraction force generated between the member to be charged 5 and slightly moved in the moving direction with the rotation of the member to be charged 5. The shape is bent to be pulled.

In this state, when the member to be charged 5 rotates in the direction of the arrow, the cylindrical film-shaped electrode 21
Due to the self-weight, the contact friction caused by the support, and the electrostatic attraction force, the rotating member follows the charged member 5 and rotates.

In addition, application of a voltage from the power supply 3 causes ionization of air in a minute gap formed near a contact portion between the cylindrical film-shaped electrode 21 and the member 5 to be charged. For example, when the negative polarity side of the power supply 3 is connected to the electrode support member 22, negative ions or electrons flow toward the member to be charged 5 to charge the same, and positive ions toward the film electrode 21. Reached and neutralized. Further, in the charging device 1, the film-shaped electrode 21 is pulled in the moving direction of the charged body 5 by the electrostatic attraction force as described above, so that the contact of the film-shaped electrode 21 with the charged body 5 is stabilized. The charged object 5 is uniformly and stably charged. In addition, since the film-shaped electrode 21 is semi-conductive, an excessive current is prevented from flowing through any part of the gap, whereby the charged object 5 is uniformly charged.

Further, the roll-shaped electrode support member 22 of the charging member 2 is supported on the charged member 5 with a constant distance between the axes, and the bite amount S (for example, 0.02
mm) is set to be small, the charging member 2 comes into contact with the charged member 5 with a low load, and therefore, the charged member 5 is worn or damaged by the contact of the charging member 2 for a long time. There is almost no. This also stably charges the member 5 to be charged.

Next, the results of the charging test of the charging device 1 (charging member 2) using the charging test device as shown in FIG. 3 will be described.

The charging test apparatus shown in FIG. 3 includes a drum-shaped charged object 5 rotating in the direction of an arrow,
A surface potential sensor 90 for detecting the surface potential of the object 5 and a charge elimination lamp 91 for removing the surface charge of the charged object 5. A surface voltmeter 92 is connected to the surface potential sensor 90. The charging device 2 is disposed on the upstream side of the surface potential sensor 90 in the rotation direction of the charged object 5, and the tip of the conductive brush bristles 23 of the brush charging roll 20 contacts the surface of the charged object 5. And is supported via a conductive support roll core 22. In addition, support roll core 2
A DC power supply 93 is connected to 2 so that a DC charging voltage is applied. The DC power supply 93 is capable of arbitrarily changing the output voltage. The DC power supply 93 measures the surface potential of the charged body 5 that changes with the increase or decrease of the applied voltage.
2 is to be measured. Here, the charged object 5
A photosensitive drum 50 having a photosensitive layer (charge receiving layer) described later was used.

The charging member 2 of the charging device 1 to be subjected to the charging test is a film of either polyvinylidene fluoride or nylon as the cylindrical film-shaped electrode 21 and has a volume resistivity of 10 ⁵ Ω · cm,
10 ⁷ Ω · cm and the thickness is 30μ
m, 50 μm, and 500 μm, each of which was formed into a tube and used as a tube electrode having an inner diameter of 14.0 mm (a total of 12 types), and a urethane sponge (ASKER-C hardness 7 °) was used as the electrode support member 22. ), An elastic roll having an outer diameter of 13.0 mm was used, and each charging member 2 obtained by combining these was used as a test object. At this time, the bite amount S between the charging member 2 and the charged member 5 was set to 0.03 mm.

FIG. 4 shows the results of the charging test. The relationship between the applied voltage when a DC voltage is applied to each charging member 2 and the surface potential of the photosensitive drum 50 as the member 5 to be charged is shown in FIG. FIG. As is clear from the results shown in FIG. 3, the surface potential of the photosensitive drum 1 when a DC voltage of 0 V to -2000 V was applied from the DC power supply 93 was measured. Is about-
When a voltage of 550 V is applied, the voltage starts to decrease sharply,
It was confirmed that the voltage reached about -1450 V when a voltage of -2000 V was applied. This result was almost the same even when the material, volume resistivity, and thickness of the film electrode 21 of the charging electrode 2 were different. During this period, no abnormal discharge was generated by each charging member 2 in any case. As a result, it has been verified that the charging device 1 using such a charging member 2 has a characteristic that can be used as a charging device for the charged object 5 (and, consequently, the photosensitive drum 50) without practical problems. did it.

Next, a performance comparison test was performed on the charging device 1.

In this performance comparison test, a charging device 1 having a charging member 2 having the following configuration was prepared, and the amount of change in the charging potential for each charging device and the amount of foreign matter attached to the charging member 2 were examined. Things. At this time, the charging device firstly uses a polyvinylidene fluoride film (volume resistivity of 10 ⁷ Ω · c) having a thickness of 50 μm as the charging member 2.
m) was formed into a tube shape, and a tube electrode having an inner diameter of 14.0 mm and an elastic roll used for the charging test and having an hardness set to the hardness (ASKER-C hardness) shown in Table 1 were used. . Further, the biting amount S between the charging member 2 and the charged member 5 (photosensitive drum) was set to a value as shown in Table 1. In Table 1, "load" is a load of the charging member 2 (the tube electrode 22) on the member 5 to be charged, and was measured using a load cell in this test.

With respect to the variation amount of the charged potential, the surface of the charged object 5 when the charging and discharging of the charged object 5 is repeated by three or more cycles using the charging test apparatus (FIG. 3). The potential was measured, and the amplitude of the surface potential at that time (the potential difference between the maximum potential and the minimum potential) was examined. The permissible level of the variation amount is 10 in a color image forming apparatus (particularly, a high quality color image is required).
V or less. Regarding the amount of foreign matter attached, charging is performed with a fixed amount of toner attached to the surface of the charged object 5 (without cleaning), and then the surface of the charging member 2 (tube electrode 21) ( The weight of the toner adhering to (unit area) was measured and evaluated based on the following criteria. Table 1 shows the results at this time. ：: when the adhesion amount is 0.1 g or less, Δ: when the adhesion amount exceeds 0.1 g, ×: when the adhesion amount exceeds 0.2 g.

[0039]

[Table 1]

As is clear from the results shown in Table 1,
When the hardness of the elastic roll 22 is small, good results are obtained with respect to the amount of potential fluctuation and the amount of adhered foreign matter irrespective of the magnitude of the bite amount (Test Examples 5 and 6). Conversely, when the hardness of the elastic roll 22 is large, the potential variation increases when the bite amount is reduced (Test Example 1), and conversely, when the bite amount is increased (Test Example 2), the adhesion of foreign substances increases. Therefore, from these facts, when an elastic roll having a small hardness is used for the charging member, it is necessary to perform uniform and stable charging by the charging member even when the bite amount is reduced and the load is reduced. It was confirmed that adhesion of foreign matters could be reduced.

[Embodiment 2] FIGS. 5 and 6 show Embodiment 2 of the present invention. FIG. 5 is a schematic diagram showing an image forming apparatus to which the charging device 1 of the present invention is applied. 6 is a schematic side view and a front view showing a support structure of a charging member in the charging device.

This image forming apparatus, as shown in FIG.
A photosensitive drum (charged member) 5 as a charged member 5 having a photosensitive layer (charge acceptor) on which an electrostatic latent image is formed by irradiating light based on image information after being uniformly charged.
In addition to the charging device 1 according to the present embodiment for charging the surface of the photosensitive drum 50 around the photosensitive drum 50, an electrostatic latent image is formed by irradiating the photosensitive drum 50 with light. Image forming apparatus 51, and developing apparatus 5 which develops the electrostatic latent image with toner as a developer to form a toner image
2. Roll-type transfer device 53, cleaning device 54,
And a lamp-type static elimination device 55. In addition, the image forming apparatus includes a sheet cassette 56 that stores a recording medium P such as a recording sheet or an OHP sheet, and a sheet feeding unit that feeds the recording medium P from the sheet cassette 56 one by one to a transfer position at a predetermined timing. Feed rollers 57a and 57b of the mechanism, and a fixing device 58 for fixing the transferred toner image to the recording medium P
Etc. The transfer device 53 includes a transfer roll 53 a rotating in contact with the photosensitive drum 1 and the transfer roll 53.
and a transfer bias power supply 53b for applying a transfer bias to a.

Charging device 1 used in this image forming apparatus
Has the same configuration as that of the charging device according to the first embodiment except that the configuration shown in FIG. 6 is employed as a supporting structure of the charging member 2 (the biting amount S is 0.3 mm). It is. That is, the charging member 2 in the charging device 1 is mounted on the support frame 60 on which the photosensitive drum 50 is mounted, with the distance E between the shaft and the photosensitive drum 50 being fixed.
Is fixed so as to be constant. First, the rotation axis 50a of the photosensitive drum 50 is
And is fixedly attached to the support frame 60 via the. On the other hand, the electrode support member (elastic roll) 22 of the charging member 2 has a bearing 62 of the rotating shaft 22 a locked by a bearing fixing arm 64 fixed to a mounting plate 63 mounted on the holding frame 60. At this time, the bearing fixing arm 64 locks and fixes the bearing 62 so that the shaft interval E is maintained at a set value.
In practice, the bearing fixing arm 64 is mounted on the mounting plate 6.
3, the positioning pins 65 projecting from one end of the mounting plate 63 are attached to the support frame 60.
The bearing 62 can be fixed by the bearing fixing arm 64 by accurately inserting it into the positioning hole and locking it.

In the image forming apparatus using such a charging device 1, after the photosensitive drum 50 is charged to a predetermined potential by the charging device 1, the latent image forming device 21 irradiates a laser beam corresponding to image information. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 50. This electrostatic latent image is developed by the developing device 52 to become a toner image. Next, the recording medium P is fed from the paper cassette 56 to the paper feed roll 57 of the paper feed mechanism.
And the transfer device (transfer roll) 53
And the toner image on the photosensitive drum 50 is transferred onto the recording medium P. The transferred toner image is fixed on the recording medium P by the fixing device 58.
Thus, a basic image is formed on one recording medium P. On the other hand, on the photosensitive drum 50 after the transfer, after the residual toner adhering to the surface thereof is cleaned by the cleaning device 54, the surface thereof is neutralized by the neutralization device 55,
In order to perform the next image forming step, the charging step by the charging device 1 is started again.

In this image forming apparatus, a DC voltage of -900 V or an AC component of a peak-to-peak voltage of 1500 V is applied to the charging member 2 of the charging device 1 from the power supply 3 via the elastic roll 22. The superposed voltage is set to be applied, whereby the photosensitive drum 50 is charged so that its charged (surface) potential is about -350V.

Next, as a result of performing a test image formation (for 5000 sheets) using such an image forming apparatus and performing a reliability test of the charging device 1, the photosensitive drum 50 always has a constant surface potential. Thus, it was confirmed that no image defect such as fogging or density reduction caused by abrasion or deterioration of the photosensitive drum 50 appeared in the obtained image. Further, as a durability test of the charging device 1, the environment (temperature and humidity) was set to 28 ° C., 85% RH and 10 ° C., 15% R
When the same image formation was performed on 1000 A4 size sheets after setting each to H, it was confirmed that an almost constant image was obtained from the initial sample (printed material) to the final sample. .

From the above, the charging device 1 can be used as a charging device for the above-mentioned image forming apparatus without any practical problems.
It was verified that it was very effective.

Third Embodiment A third embodiment is the same as the second embodiment, except that the cleaning device (54) for the photosensitive drum is not provided. That is, in the third embodiment, the cleaning device (5
This is an example of a case where the charging device 1 according to the first embodiment is used in a so-called cleaner-less image forming apparatus not provided with 4).

In such a cleanerless image forming apparatus, almost 100% of the toner image formed on the photosensitive drum 50 is transferred to the recording medium P by the transfer device 53, but the transfer is not performed to a small extent. The residual toner remains on the body drum 50. When such a residual toner passes through the charging device 1, the charging member 2 (the film-like electrode 21)
Almost pass without sticking to. Further, even if the residual toner adheres, the residual toner can be removed by a simple removing device and does not adhere. This is presumably because the load on the photosensitive drum 50 is extremely small due to the support structure of the charging member 2. Further, even though the residual toner is present, uniform charging is performed by the charging device 1. The residual toner that has passed through the charging device 1 is collected by the developing device 52, or
In the next transfer step, the image is transferred to the recording medium P side.

Further, in this cleanerless image forming apparatus, since foreign matters such as paper dust and discharge products including residual toner adhere to the photosensitive drum 50 after transfer, the charging member 2 in the charging device 1 The film-shaped electrode 21 tends to be easily stained by the adhesion of foreign matter. Further, when the adhesion of the foreign matter increases, there is a tendency that the charging potential decreases and abnormal discharge easily occurs. For this reason, the charging member 2
It is important to reduce the adhesion of foreign matter to the surface.

In view of the above test results (Table 1) on the amount of adhered foreign substances, if the hardness of the electrode support member (elastic roll) 22 of the charging member 2 is high and the same, the bite amount should be reduced. Accordingly, it is possible to keep the amount of adhered foreign matter low (for example, Test Examples 1 and 3), and when the hardness of the electrode support member (elastic roll) 22 is reduced, the amount of adhered foreign matter is small regardless of the amount of penetration. Is clear (Test Examples 5 and 6).
In the cleaner-less image forming apparatus, it was confirmed that the biting amount S of the charging member 2 should be reduced and the electrode support member 22 should be soft. For this reason, the electrode support member 22 includes a soft elastic roll,
It is preferable to use a member having low hardness and excellent elasticity, such as a brush roll, a felt agent, a soft foam, and a nonwoven fabric. Also,
From the viewpoint of increasing the transfer efficiency of the toner and minimizing the amount of residual toner remaining on the photosensitive drum 50 after the transfer to reduce the contamination of the charging member, the spherical particles whose toner particles have a shape factor of 100 to 125 are used as the toner. It is preferable to use a toner having a shape.

Further, as a result of performing a reliability test of the charging device 1 by forming a test image (for 10,000 sheets) using this cleanerless image forming apparatus, the photosensitive drum 50 always has a constant surface potential. Thus, it was confirmed that no image defect such as fogging or density reduction caused by abrasion or deterioration of the photosensitive drum 50 appeared in the obtained image.

Fourth Embodiment FIG. 7 shows a fourth embodiment of the present invention, and is a schematic configuration diagram showing an image forming apparatus using the charging device of the present invention as a charging device and a charge removing device.

First, this image forming apparatus has four image forming units 70Y, 70M, 70C and 70C. The configuration of these image forming units 70 is substantially the same as that of the image forming apparatus shown in FIG. 5 (however, there is no cleaning device 54), but each developing device 52 has yellow (Y), Contains four color toners of magenta (M), cyan (C), and black (K). Also, the photosensitive drum 50 of each image forming unit 70
Is provided with a roll-type charging device 59. The image forming apparatus also includes an intermediate transfer belt 7 stretched around a plurality of rolls 76 as an intermediate transfer body to which each toner image formed by each image forming unit 70 is temporarily transferred.
The intermediate transfer belt 65 extends across the image forming units 70Y, 70M, 70C, and 70C, and is driven to circulate in the direction of arrow B. When a toner image is transferred from the photosensitive drum 50 of each unit 70 to the intermediate transfer belt 167, a transfer voltage is applied to the transfer device 53. Further, the intermediate transfer belt 75 is provided with a roll-type secondary transfer device 77 for secondary-transferring the transferred toner image to the recording medium P.

Incidentally, as the intermediate transfer belt 65,
Polyimide, polycarbonate, polymer film such as PVdF and silicone rubber, synthetic rubber such as fluorine rubber,
A material formed by adding a conductive filler such as carbon black and made conductive to form a belt shape is used. As the transfer device 53, a transfer roll made conductive by adding a conductive filler such as carbon black to synthetic rubber such as silicone rubber, EPDM, or urethane rubber is used, and the roll diameter is set to about 10 to 30 mm. . A voltage of about +0.5 to 1.5 kV is applied to each transfer roll 53a of the transfer device 53 from a power supply (53b) (not shown). On the other hand, a voltage of about +1.5 to 3.0 kV is applied to the secondary transfer device 77 from a power supply (not shown).

In this image forming apparatus, the charge removing devices 10Y, 10M, 10M, 10M, and 10K of the photosensitive drum 50 in each of the image forming units 70Y, 70M, 70C, and 70K.
The charging device 1 according to the first embodiment is used as each of C and 10K (so as to exhibit a static elimination function). Further, the charging device 1 according to the first embodiment as the charge removing device 15 of the intermediate transfer belt 75 is used (so as to exhibit a charge removing function).

In this image forming apparatus, when a toner image of each color is formed by each of the image forming units 70Y, 70M, 70C, and 70K, the intermediate transfer belt 7 moves in the direction of arrow B.
The primary transfer is performed on the recording medium P from the intermediate transfer belt 75 to the recording medium P by the secondary transfer device 77 at a time. The recording medium P after the secondary transfer is sent to the fixing device 58, and a (color) image is formed on the recording medium P by fixing the toner image. On the other hand, in the image forming unit 70 after the primary transfer, the residual charges on the respective photosensitive drums 50 are removed by the charging devices 10Y, 10M, 10C, and 10K serving as the charge removing device according to the present embodiment, and when the toner enters the charging device. The surface potential of the photosensitive drum 50 at 0 V is made uniform to 0V. At this time, the charging device 10 for static elimination
A voltage of about +200 V to +600 V is applied to a charging member 2 of Y, 10M, 10C, and 10K from a power supply (3) (not shown).

Further, the intermediate transfer belt 65 after the secondary transfer
Before entering the first image forming unit 70Y, the residual charge is removed by the charging device 15 as the charge removing device according to the present embodiment. At this time, the charging device 161e for static elimination
, An AC voltage having a peak-to-peak voltage of about 2.2 kV is applied from an AC power supply (3) not shown.

In general, when a DC voltage is applied to a charging device of an image forming apparatus, there is a disadvantage that the charging potential is liable to fluctuate due to the pattern of the intrusion potential, and image quality defects such as ghosts are likely to occur. In addition, since the intermediate transfer belt is formed of an insulating or high-resistance material, there is a disadvantage that the residual potential increases during repeated transfer, and transfer failure easily occurs. Moreover,
Unlike the photoconductor, the residual potential on the intermediate transfer belt generally fluctuates greatly from plus to minus, and the magnitude sometimes exceeds 2000 V. Therefore, it may be better to use AC discharge instead of DC voltage. Further, the intermediate transfer belt has almost no adverse effect even if the surface energy increases, so that there is no problem even if AC discharge is used. From the above,
By using the charging device 1 according to the first embodiment as a charging device for removing charges on the photosensitive drum 50 and the intermediate transfer belt 75, it is possible to efficiently remove charges with a simple configuration.

Using such an image forming apparatus, a charging test was performed by the above-described charging test apparatus (FIG. 3).
It was confirmed that the invasion potential of the charging device 1 (10) to the charging member 2 was almost uniformly 0 V, and the same result as that of the static elimination lamp was obtained. When a test image was formed using the image forming apparatus according to the fourth embodiment,
It was confirmed that a good color image free from image quality defects such as fog was obtained. From the above results, it has been clarified that the charging device of the present invention is very effective as a charging device for removing charges on the photosensitive drum 50 and the intermediate transfer belt 75.

[Other Embodiments] In the first to fourth embodiments, as the charging member 2 in the charging device 1, a composite charging member composed of a cylindrical film-shaped electrode 21 and an electrode support member 22 has been described. A conventional charging roll may be used. In this case, the charging roll has a support structure in which the distance between the shafts is constant.

In the first to fourth embodiments, the charging device 1
The charging member 2 in (1) is the charged object 5 (photosensitive drum 50)
In the case of the configuration in which the charging member 2 (in the case of the composite form, the cylindrical electrode member 22) is driven by a dedicated rotation driving means (for example, an electric motor and a rotation transmission mechanism), Composed) and the charged object 5
Are connected so that the rotational power of the driving means is transmitted,
You may comprise so that it may drive and rotate by the rotational power. This is particularly effective when the biting amount S of the charging member 2 is set to a small value, so that the charging member 2 rotates reliably and stably, and uniform and stable charging is surely performed.

Further, in the first to fourth embodiments, when the electrode support member 22 is driven by being connected to the driving means, the electrode support member 22 is connected to the photosensitive drum 50 which is a member to be charged.
Can be driven to rotate with a peripheral speed difference in the range of -15% to 15% with respect to the rotation of. At this time, the cylindrical film-shaped electrode 21 and the electrode support member 22 are preferably bonded and integrated. In this case, the outer diameter of the electrode support member 22 is the same as or slightly larger than the inner diameter of the film electrode. When the charging member 2 including the cylindrical film electrode 21 and the electrode support member 22 is configured as described above, the charging member 2 adheres to the surface of the film electrode 21 at the contact portion with the photosensitive drum 50 due to the difference in peripheral speed. Toner and the like can be removed, and the toner and the like hardly adhere. In addition, since the film-shaped electrode 21 and the electrode support member 22 are bonded and integrated, the rotation by the driving force of the driving means of the electrode support member 22 is stabilized. No dirt or wrinkles occur. Even in the case of such a configuration, uniform and stable charging can be performed and good static elimination can be performed, similarly to the case of each of the charging devices or the static elimination devices according to Embodiments 1 to 4. You can also.

[0064]

As described above, according to the charging device of the present invention, the charging member is supported and fixed so as to be able to contact and rotate at a predetermined position with respect to the member to be charged. On the other hand, the contact pressure of the charging member can be made as small as possible (low load), so that the member to be charged is less likely to be worn or damaged, and uniform charging can be stably performed for a long period of time. Can be. In addition, deposits on the member to be charged are transferred to the charging member and become difficult to adhere to the charging member, thereby reducing the occurrence of abnormal discharge and the like due to the deposits, and suitably used as a charging device in a cleaner-less image forming apparatus. It is possible to Furthermore, this charging device can be used as a static eliminator that charges the surface of a charged object to almost 0 V, and exhibits high performance not only as a charging device but also as a static elimination device that removes electric charges. Can be.

Furthermore, even if the accuracy of the charging member such as the degree of straightness and coaxiality of the electrode supporting member is somewhat poor, especially when the charging member has an independent structure in which a film-shaped electrode and an electrode supporting member are combined. In addition, the film-shaped electrode comes into uniform contact with the member to be charged by the electrostatic attraction force, and a sufficient and uniform charging potential can be obtained, so that the yield can be improved. is there.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a charging device according to a first embodiment of the present invention.

FIG. 2 is a schematic explanatory view showing a support structure of a charging member in the charging device of FIG. 1;

FIG. 3 is a schematic diagram showing a charging test apparatus.

FIG. 4 is a graph showing the results of a charging test.

FIG. 5 is a schematic view of a main part showing an example of an image forming apparatus to which the charging device of the present invention is applied.

FIG. 6 is an explanatory view of a main part showing a support structure of a charging member of the charging device in the image forming apparatus of FIG. 5;

FIG. 7 is a main part schematic diagram showing another example of the image forming apparatus to which the charging device of the present invention is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Charging device, 2 ... Cylindrical charging member, 3 ... Power supply, 5 ...
Object to be charged, 6, 60 support plate, 10, 15 ... static eliminator (charger for static elimination), 21 ... cylindrical film-like electrode, 22 ... cylindrical electrode support member, 50 ... photosensitive drum (image bearing) Body), 64: bearing fixing arm, 75: intermediate transfer belt (intermediate transfer body).

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tatsuo Okuno 430 Green Tech Nakaicho, Nakai-cho, Ashigarakami-gun, Kanagawa Prefecture, inside Fuji Xerox Co., Ltd. Inside Fuji Xerox Co., Ltd. (72) Ryuichi Yamamoto, Inventor 3-7-1, Fuuchi, Iwatsuki City, Saitama Prefecture, Inside Fuji Xerox Co., Ltd. (72) Yusuke Kitagawa, 3-7-1, Fuchu, Iwatsuki City, Saitama Prefecture, Inside Fuji Xerox Co., Ltd. (72) Inventor Koji Miyake 3-7-1, Fuchu, Iwatsuki-shi, Saitama, F-term in Fuji Xerox Co., Ltd. (reference) 2H003 AA12 BB11 BB14 BB16 CC05 2H032 AA05 BA02 BA07 BA23 BA29 2H035 AA15 AZ05 AZ11 2H077 AA37 AC16 AD06 AD31

Claims (10)

[Claims] 1. A charging device comprising: a cylindrical charging member rotatably in contact with a rotating member to be charged; and a power supply for applying a voltage to the cylindrical charging member. In a charging device for charging a surface of a member to be charged by generating discharge in a minute gap near a contact portion between the member and the member to be charged, the cylindrical charging member is fixed to the member to be charged. A charging device characterized in that it is held in a fixed position so as to be in a position, and is supported so as to be able to rotate in contact with the member to be charged. 2. The charging device according to claim 1, wherein the bite amount between the cylindrical charging member and the member to be charged is zero.
A charging device, wherein the charging device is set within a range of 0.6 mm. 3. The charging device according to claim 1, wherein the cylindrical charging member comprises a cylindrical film electrode, and a cylindrical member rotatably disposed in an internal space of the film electrode. And an electrode supporting member. 4. The charging device according to claim 3, wherein the cylindrical film-shaped electrode and the cylindrical electrode support member of the cylindrical charging member are bonded and integrated. . 5. The charging device according to claim 3, wherein said cylindrical electrode support member is an elastic roll or a roll-shaped brush. 6. The charging device according to claim 3, wherein the cylindrical electrode support member is connected to driving means and driven to rotate. 7. The charging device according to claim 6, wherein the cylindrical electrode support member is driven and rotated with a peripheral speed difference with respect to the rotation of the charged object. 8. The charging device according to claim 1, wherein the member to be charged is an image carrier on which a toner image is formed by electrophotography and a cleaning device is not provided. A charging device characterized by the above-mentioned. 9. The charging device according to claim 1, wherein a voltage applied from the power supply to the charging member is set so that a surface potential of the member to be charged becomes substantially 0V. Characteristic charging device. 10. A charge eliminator for an image bearing member on which a toner image is formed by electrophotography and a charge eliminator for an intermediate transfer member to which the toner image is temporarily transferred. A charging device.