JPH0862928A - Charging device and image forming device using the same - Google Patents

Abstract

PURPOSE: To provide an image forming device capable of inexpensively providing an excellent image over a long term. CONSTITUTION: The image forming device is provided with a charging sheet 52a arranged on the surface of a photoreceptor drum 50, faced to a downstream side in the rotating direction of the photoreceptor 50 and set at <=3.7g/cm press- contact force with the photoreceptor 50 and at an angle within the range of 0 to 0.7 [rad] to the photoreceptor 50. The sheet 52a includes a conductive foamed sheet incorporated with a conductive material and plural gaps of air bubbles each having <150μm average diameter. The conductive foamed sheet is formed into a thin plate and then cut in a thickness direction at least with a surface layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image on a photosensitive member by an electrostatic photography process, developing the image with toner, and then outputting the image on a sheet.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrostatic photography process, a photoconductor having photoconductivity and a developer containing toner are used, and an image is formed on the photoconductor charged to a predetermined potential. An image is formed by developing an electrostatic latent image obtained by providing light with toner.

Generally, a predetermined potential is provided to a photoreceptor by corona charging by a corona charging device such as a corotron or a scorotron. In corona charging, it is known that the structure of the main body of the charging device can be simplified, and stable charging can be performed based on the past results. On the other hand, since it is necessary to provide a high voltage of 4 to 8 kilovolts to the charging device main body, it is known that the power supply device is expensive and large. Further, it is known that in corona charging, ozone is generated during corona discharge, and an undesired product is generated due to corona discharge. For this reason, it is known that peripheral devices and mechanisms such as an ozone filter and a catalyst device are required, which increases the size and cost of the entire charging device.

Therefore, in recent years, contact charging has attracted attention as a charging method instead of corona charging. The contact charging is to charge the photosensitive member to a predetermined potential by bringing the contact charging member, to which a voltage of 0.5 to 2 kilovolts is applied, into contact with the photosensitive member. Depending on the shape of the contact charging member, roller charging or brush charging is performed. And blade charging.

As roller charging, for example, Japanese Patent Publication No.
As disclosed in Japanese Patent Laid-Open No. 52058, there is an example in which a conductive shaft is wound around a roller with a conductive rubber and then a roller having a surface layer of a dielectric material is further contacted with the photosensitive member.

[0006] As the brush charging, for example, Japanese Patent Publication No. 6
As disclosed in Japanese Patent Publication No. 4-6459, a brush in which conductive fibers formed by dispersing a conductive material such as carbon are planted in a pile weave shape or a brush obtained by molding similar fibers into a brush shape. There is an example in which is contacted with the photoconductor.

As the blade charging, for example, JP-A-3-217873 or JP-A-1-93762 is used.
As can be seen in the publication, with a thickness of 1-2 mm,
EPDM (Ethylene-
Applying a DC electric field (voltage) to a thin plate, that is, a charging blade, such as an elastic body containing propylene trimer) or urethane rubber, and the free end (of the charging blade) to the upstream side in the rotation direction of the photoconductor. There is a method (hereinafter referred to as a counter method) of contacting the photoconductor so as to face it.

In Japanese Patent Laid-Open No. 3-217873, the free length is 5 to 15 mm, the thickness is 1 to 2 mm, the contact angle is 8 to 25 °, and the contact pressure is 4 to 40 g / cm. An example in which the charging blade is brought into contact with the photoconductor is shown. Further, JP-A-1-93762 discloses an example of a charging blade in which the contact pressure is regulated to 5 to 20 g / cm.

[0009]

The charging roller for charging the roller not only has a complicated roller structure,
Since the pressing mechanism for bringing the roller into close contact with the photosensitive member and the power feeding mechanism for applying the electric potential to the roller are complicated and large-scaled, there is a problem that the cost is increased as compared with the corona charging device and the power supply device.

On the other hand, the charging brush for charging the brush is
Due to its structure, there is a problem that streaky charging unevenness is likely to occur in the potential provided to the photoconductor, and unevenness in image density or blurring or streaks occurs in a halftone image.
Further, not only is it difficult to maintain the shape of the brush (especially the tip of the brush) in a constant shape, but there is also the problem that, like the charging roller, the cost cannot be reduced compared to the corona charging device and the power supply device.

On the other hand, the blade charging is widely used at present as the lowest-cost and compact charging device, especially in a low-end image forming device having a low image forming speed and a relatively low image forming speed. However, like other contact charging, it has many problems as described below.

In the method disclosed in Japanese Patent Laid-Open No. 3-217873, the contact surface with the photosensitive member is narrow (for example,
Nip width is 1 mm or less), and the hardness is higher (harder than the similar blade, cleaning blade).
For example, since it is a 65 degree, JIS-A) counter method, fine powder of toner that has slipped through the contact between the cleaning blade and the photoconductor or dirt such as paper powder from the transfer paper conveyed through the photoconductor contacts. A portion, that is, a charging blade, may be caught in a charging position where the photosensitive member is in contact with the photosensitive member. This causes a change in the gap between the blade and the photoconductor due to partial floating at the contact portion between the charging blade and the photoconductor, resulting in partial charging failure. This partial charging failure causes white or black streaks in the image.

Further, dimensional tolerances such as straightness of the charging blade itself, accuracy of assembling with the holder and mounting accuracy when assembled in the unit are strict, and if any or all of the tolerances and accuracy exceed a predetermined control range, This may cause a charge potential gradient (high or low) in the longitudinal direction with respect to the photoconductor, or cause poor charging. In this case, white stripes or black stripes are similarly generated.

Further, such a charging blade is usually made of urethane and EP containing a conductive filler such as carbon.
Since the blade edge (ridge line) becomes rougher than that of an insulating blade due to being manufactured by DM or the like, uneven charging is caused due to the roughness of the edge. This similarly causes white lines or black lines.

On the other hand, a method has been proposed in which the pressure contact force of the charging blade with respect to the photosensitive member is increased so that dirt does not enter between the charging blade and the photosensitive member. However, arranging the charging blade having high hardness (hard) in the counter method facilitates the curling of the charging blade. The curling of the charging blade is more remarkable as compared with a cleaning blade having a similar structure,
Moreover, it is known that the cleaning blade can be avoided by a lubricant such as kainer even in the unused state, but in the case of the charging blade, the kainer cannot be used due to the influence on the charging characteristic.

The method of increasing the pressure contact force of the charging blade with respect to the photosensitive member not only causes the charging blade to be turned up, but also requires a large force as the driving force of the photosensitive member. It is required to be used, resulting in an increase in size and cost of the motor.

Further, by increasing the pressure contact force, the contact resistance between the charging blade and the photoconductor is increased, and the blurring of the image due to the uneven rotation of the photoconductor drum is induced. Further, by increasing the pressure contact force, the abrasion of the photoconductor causes abrasion of the photoconductor surface, that is, a decrease in the image forming ability and a partial change in the charging condition due to the partial wear of the charging blade. , White streaks or black streaks are generated.

On the other hand, an example has been proposed in which the charging blade is brought into contact with the photoconductor so that the free end (of the charging blade) faces the downstream side in the rotational direction of the photoconductor (hereinafter referred to as the trail system). The method has a new problem that the charging blade is likely to vibrate and the tolerance for the roughness of the blade edge is more severe than that of the counter method. This is likely to cause white lines or black lines, as in the example described above.

Aside from this, considering the occupation ratio of the charging blade around the photosensitive member, that is, the size of the charging blade with respect to the size of the photosensitive member, for example, JP-A-3-2178 is used.
As disclosed in Japanese Patent Publication No. 73-73, since the contact angle is as small as 8 ° to 25 ° and the free length is required to be 5 to 15 mm, the size of the charging blade including the supporting member is necessarily It will be about 10 to 20 mm. This makes it difficult to arrange a small-diameter photosensitive member around the photosensitive member, and limits the usable photosensitive member diameter to a large photosensitive member drum of substantially about 30 mm.

By the way, in order to reduce the white stripes and the black stripes, which have already been explained, a method of using an electric field (generally a DC electric field) applied to the charging blade, in which a DC electric field and an alternating electric field are superposed is used. Proposed. For example,
Japanese Examined Patent Publication No. 3-52058 discloses an example in which the peak-to-peak voltage (peak-peak) of an alternating electric field is at least twice the charging start voltage, and US Pat. No. 4,851,960 discloses a peak. -Each example is disclosed in which the peak voltage is about 1.2 kilovolts or more and the frequency is 200 hertz or more.

However, when the alternating electric field is superposed on the direct current electric field, an unpleasant oscillating sound is generated, which causes a problem that the user feels uncomfortable. This oscillating sound is reduced by lowering the frequency of the alternating electric field below 200 Hz, or by lowering the voltage of the alternating voltage, but when the frequency is lowered, density unevenness corresponding to the pulse of alternating current occurs, On the other hand, when the voltage is lowered, it becomes impossible to completely remove the white stripes or the black stripes. In addition, this density unevenness is
In particular, a halftone image such as a halftone image may be prominent and a striped image may be formed.

In addition to the oscillating sound generated by superposing the alternating electric field, when the charging blade is used, a sound often called a blade squeal, which is often experienced with the cleaning blade, is recognized. This is one of the characteristics of rubber materials that are usually used as blades, and the impact resilience is about 3
5 to 60% (JISK7311) is 35% or less in a rubber member containing a conductive filler such as carbon, so that it becomes particularly remarkable at low temperatures. Although it has been reduced today by optimizing the contact condition and the thickness of the blade, it is practically difficult to suppress the generation of sound.

Apart from this, it is known that in the method of applying a predetermined electric potential to the photosensitive member by the charging blade, the phenomenon that the toner adheres to the peripheral surface of the photosensitive member, that is, filming occurs.

This filming is a phenomenon which often occurs even in an image forming apparatus using a cleaning blade in a general electrophotographic process which does not use contact charging, and more particularly in a charging blade having a relatively high friction coefficient. It becomes remarkable. Incidentally, in the method of applying the alternating electric field which has already been explained, particularly in the method shown in US Pat. No. 4,851,960, the effective value of the alternating current is about 20 μA.
/ Cm or more, Joule heat easily causes filming.

When such filming occurs, it goes without saying that the light radiated on the photosensitive member, that is, the image information is not converted into an electrostatic latent image, so that the white stripes already described occur.

An object of the present invention is to provide an image having no density unevenness, which can supply a uniform and stable potential over a long period of time, and has a simple structure and a low manufacturing cost. To provide the charging device.

[0027]

SUMMARY OF THE INVENTION The present invention has been made based on the above-mentioned problems, and is 0.7 [ra] for a photosensitive member formed in a thin plate shape and movable in a predetermined direction.
The present invention provides a charging device, characterized in that one end of itself is in contact with the photoconductor so as to be directed to the downstream side in the direction in which the photoconductor is moved, with a limit of d].

Further, according to the present invention, the angle formed by the free end and the photoconductor is 0 from a vertical angle with respect to the photoconductor which is formed in a thin plate shape having a free end and is movable in a predetermined direction. It is arranged in the range of 0.7 [rad] toward the downstream side in the moving direction of the photoconductor, and the pressure contact force between the free end and the photoconductor is 3.7 g / cm or less. A charging device is provided.

Further, according to the present invention, the conductive material and the plurality of voids each having an average diameter of less than 150 μm are formed into a thin plate shape and then cut in the thickness direction together with at least the surface layer. The conductive foam sheet is formed by the above-mentioned method, and the angle formed by the free end of the photoconductor and the photoconductor is 0.04 to 0.49 [rad]. Within the range of [5], the pressure contact force between the free end and the photoconductor is 3.7 g / cm.
There is provided a charging device characterized by being arranged as follows.

Furthermore, according to the present invention, a photosensitive member capable of holding an electrostatic image by being irradiated with light while being charged to a predetermined potential, and a thin plate having a free end are formed. With respect to the photoconductor, the angle between the free end and the photoconductor is set within a range of 0.7 [rad] from a vertical direction, and the photoconductor is directed to the downstream side in the moving direction of the photoconductor. The pressure contact force between the edge and the photoconductor is 3.7g.
An image forming apparatus including: a charging device, which is arranged so as to be equal to or less than / cm.

[0031]

According to the present invention, with respect to the movably formed photoconductor, one end of the photoconductor is directed to the downstream side in the moving direction of the photoconductor with a limit of 0.7 [rad]. A charging device that is contacted with is provided. Therefore, a stable charging potential is provided to the photoreceptor.

The charging device is arranged so that the pressure contact force between the free end of the charging device and the photoconductor is 3.7 g / cm or less. Therefore, a uniform charging potential is provided to the photoreceptor.

Further, the charging device includes a conductive material and a plurality of voids having an average diameter of less than 150 μm, is formed into a thin plate, and is cut in the thickness direction together with at least the surface layer. Since the conductive foamed sheet formed in (1) is included, a uniform charging potential can be provided to the photoconductor even when the temperature or humidity changes.

[0034]

Embodiments of the present invention will be described below with reference to the drawings. According to FIG. 1, an image forming apparatus, that is, a laser beam printer type digital copying apparatus 2 includes an image forming section, that is, a digital copying apparatus main body 10 for copying image information corresponding to an image of an original onto a recording sheet, and a main body of the digital copying apparatus. An automatic feeder (hereinafter, referred to as ADF) 100, which will be described later, is provided on the upper part of (hereinafter, referred to as DPPC) 10 to feed the documents D to be copied on a document table one by one. .

The DPPC 10 includes a document reading section 12 for reading the image information of the document D, an image forming section 14 for forming an image based on the image data read by the document reading section 12 or the image data supplied from the outside. A paper feeding unit 16 for feeding the recording paper holding the image formed by the unit 14, a paper feeding unit 18 for feeding the paper on which the image formed by the image forming unit 14 is transferred in a predetermined direction, and the like. Contains.

The upper part of the DPPC 10 and the ADF 10
A document table (document table) 20 on which a document D to be copied is placed, that is, a document table (document table) 20 for holding the document D is arranged at a position facing the transport belt 0 described later.

A document stopper 20a for defining the leading end position of the document D is arranged at one end of the document table 20. The rear surface of the document stopper 20a, that is, the lower surface facing the illumination lamp described later is defined to have a predetermined whiteness (brightness) in order to generate white light for correcting the threshold level of the CCD sensor described later. It is formed in white.

Below the document table 20, it is arranged substantially parallel to the document table 20 and movably along the document table 20, and the information written on the document D is read out optically. A second carriage 4 that follows the carriage 30 and the first carriage 30 and transmits the information read by the carriage 30 to an information recording medium described later.
Contains 0.

The first carriage 30 has an illumination lamp 32 for illuminating the original document D, a reflector 34 for converging light from the illumination lamp 32 on the original document D and increasing illumination efficiency, and second reflection light from the original document D. A first mirror 36 that reflects the light toward the carriage 40 is arranged.

On the second carriage 40, the first mirror 36
A second mirror 42 for returning the reflected light reflected from the mirror 90 by 90 ° and a third mirror 44 for returning the reflected light from the document D reflected by the second mirror 42 by 90 ° are arranged.

Below the first carriage 30 and within the plane including the optical axis of the third mirror 44 of the second carriage 40, an image forming lens 46 for converging the reflected light from the document D is provided. , And a CCD sensor 48 for photoelectrically converting the reflected light from the document D at a predetermined threshold level.

The image forming unit 14 includes a drum-shaped photosensitive member, that is, a photosensitive drum 50 as a photosensitive member arranged in the center of the main body 10. Around the photosensitive drum 50, a charging device 52 that applies a predetermined surface potential to the photosensitive drum 50, and a latent image corresponding to image data are exposed on the photosensitive drum 50 that is charged to a predetermined potential by the charging device 52. The laser exposure device 54, the developing device 56 that develops the latent image formed by the laser exposure device 54 on the photosensitive drum 50 by supplying toner (not shown), and the toner remaining on the photosensitive drum 50 are removed. Excluding,
A cleaning device 58 for removing the electric charge remaining on the photoconductor drum 50 is arranged. In addition, between the developing device 56 and the cleaning device 58, a latent image, that is, a toner image developed on the photosensitive drum 50 via the developing device 56 is supplied with a transfer target material such as a copy sheet P supplied from a cassette described later. A transfer roller 60 for transferring the image is arranged.

On the right side of the image forming unit 14, a paper cassette 62a for accommodating the paper P for holding the image formed via the image forming unit 14 and an upper part of the paper cassette 62a are integrally formed with the cassette 62a. The bypass tray 62b is arranged. Below the cassette 62a, for example, 2000 sheets of paper P
A large-capacity cassette (hereinafter, referred to as large capacity cassette, LCC) 62c capable of accommodating the above is arranged.

Between the paper cassette 62a and the large-capacity cassette 62c and the photosensitive drum 50, the cassette 62 is provided.
The upper paper feed roller 64a and the upper paper feed guide 66 that guide the paper P supplied from a toward the photoconductor drum 50.
a and a lower paper feed roller 64b and a lower paper feed guide 66b for guiding the paper P supplied from the LCC 62c toward the photoconductor drum 50, respectively.
The bypass tray 62b is provided with a bypass feed roller 68 for guiding the paper P placed on the tray 62b to the upper paper feed roller 64a.

Between the paper feed guides 66a and 66b and the photosensitive drum 50, the paper P fed from the cassette 62a or the bypass tray 62b and the LCC 62c is temporarily stopped to correct the inclination of the paper P, and A registration roller 70 that is formed on the surface of the photosensitive drum 50 and that aligns the leading end positions of the image, that is, the toner image and the toner image that is conveyed toward the transfer roller 60 with the rotation of the photosensitive drum 50, is arranged.

On the left side of the image forming unit 14, there are a fixing device 72 and a fixing device 72 for fixing the image transferred on the paper P to the paper P on which the toner image is transferred from the photosensitive drum 50 by the transfer roller 60. The sheet P on which the toner image is transferred is disposed between the transfer roller 60 and the fixing device 7
The branch gate 76 and the branch gate 76 for guiding the sheet P, on which the image has been fixed through the conveying device 74 and the fixing device 72, to the outside of the DPPC main body 10 or a sheet reversing part described later, by the branch gate 76. A discharge roller 78 for sending the paper P guided toward the outside of the DPPC 10 to the outside of the DPPC 10 and a tray 80 for holding the discharged paper P are arranged.

Below the image forming unit 14, a sheet reversing section 90 is provided for reversing the front and back of the sheet P branched by the branch gate 76 and then guiding it to the registration roller 70 again.

The paper reversing section 90 guides the paper P having the image already copied on one side thereof, and a reversing guide 91 and a reversing guide 9.
1 is a storage space for temporarily accommodating a transport roller 92, a reversing guide 91, and a sheet P guided by the transport roller 92, which are disposed at a predetermined spacing, that is, a spacing defined depending on the size of the reversible sheet P. The sheet P accommodated in the area portion 93 and the storage area portion 93 is guided by the reverse sheet feeding roller 94 for conveying the sheet P toward the registration roller 70, and the sheet P pulled out from the rear end side by the reverse sheet feeding roller 94. The reverse paper feed guide 95 and the intermediate conveyance roller 96 for propelling the paper P passing through the reverse paper feed guide 95 toward the registration rollers 70 and the like.

The ADF 100 includes an original tray 120 on which originals D to be fed are placed, an original take-out section 130 for taking out the originals D placed on the original tray 120 one by one, and
A document transport for feeding the document D taken out through the document taking-out unit 130 to a predetermined position of the document reading unit 12, that is, a position on the document table 20 where one end of the document comes into contact with the document stopper 20a. The document table 20 including the portion 140 is provided above the DPPC 10 by a fixing mechanism (not shown).
It is fixed so that it can be opened and closed freely.

The document tray 120 has a tray body 122 on which, for example, about 50 documents D can be placed, and a pickup roller 132 of the document take-out section 130.
The originals D taken out one by one are held by. The document D taken out via the pickup roller 132 is guided to the document feeding path 134.

An aligning roller 136 for correcting the inclination of the document D and aligning the supply timing is arranged at the downstream side of the document feeding path 134. The document conveying unit 140 has a conveyance belt 142 that covers the upper surface of the document table of the document reading unit 12 and conveys the document D fed from the document extracting unit 130 along the document table 20 of the document reading unit 12. ing. Conveyor belt 142
Is a wide belt having a white outer surface and formed in a ring shape, which is seamless and has a first belt roller 144 that supports an end portion adjacent to the document conveying portion 140 and a second belt roller that supports the other end portion. And is rotated in both forward and reverse directions via a drive motor (not described in detail).

In FIG. 2, the photosensitive drum 50 and the charging device 5 are shown.
The image forming unit 14 is shown in an enlarged manner centering on 2. Referring to FIG. 2, the photosensitive drum 50 is, for example, an aluminum cylinder having an outer diameter of 15, 96 mm and a thickness of 0.7 mm, and a thickness of 0.1 μm including a phthalocyanine pigment. Sano carrier generation layer (CG
L layer), a 19 μm-thick carrier transport layer (CTL layer) containing hydrazone and resin, and a resin material (protective material) of a predetermined thickness that can transmit light are negatively charged. An organic photoconductor (OPC) drum having an organic photoconductor layer having an outer diameter of about 16 mm. In this embodiment, the photosensitive drum 50 is provided with a length of 320 mm so that the lateral direction of A4 size paper is the transport direction.

The photosensitive drum 50 is rotated in the direction of arrow A at a predetermined peripheral speed (moving speed of the outer peripheral surface, that is, process speed), for example, 17 mm / sec. At a predetermined position on the outer circumference of the photoconductor drum 50, a charging sheet 52 whose free end is directed to the downstream side in the rotation direction of the photoconductor drum 50.
The charging device 52 having a has the free end of the photosensitive drum 50.
Is arranged so as to be in contact with a predetermined amount of the surface.

The charging sheet 52a is supported by a supporting member 52b and is electrically connected to the charging power source device 152 via the supporting member 52b, and a predetermined charging voltage is applied to the photoconductor by the control of the CPU 102 as a main control device. Serve on the drum 50.

To the developing roller 56a of the developing device 56, a bias power supply device 156 for applying a predetermined developing bias voltage to the toner is connected. The transfer roller 60 is
It is connected to the transfer power supply device 160 and supplies a predetermined transfer voltage to the paper P and the photosensitive drum 50 under the control of the CPU 102.

The registration roller 70 has a CPU 1
A mechanical controller 170 for turning on / off a motor (not shown) or a clutch of the registration roller 70 at a predetermined timing under the control of 02 is connected.

The CPU 102 also stores data for initial operation of the DPPC 10 and the like.
An OM (Read Only Memory) 104, a RAM (Random Access Memory) 10 for temporarily storing data such as copy magnification and the number of copies input from an operation panel (not shown) or input operating conditions.
6. An NVM (nonvolatile memory) 108 for storing initial setting data and time-dependent data relating to the operation of the DPPC 10, for example, the total number of copies (prints) in which the photosensitive drum 50 is used is connected.

The CPU 102 further includes a main motor (not shown) for rotating the photosensitive drum 50, a developing motor (not shown) for rotating the developing roller 56a of the developing device 56,
A scanning motor (not shown) that moves the first and second carriages 30 and 40 of the image reading unit 12 along the original table 20 and a motor drive circuit 110 that rotates many motors arranged in the DPPC main body 10, and Many control circuits such as a lamp regulator 112 for lighting a heater lamp (not shown) incorporated in the illumination lamp 32 and the fixing device 72 are connected.

FIG. 3 shows the positional relationship between the outer peripheral surface (front surface) of the photosensitive drum 50 and the charging sheet 52a of the charging device 52. Referring to FIG. 3, the charging sheet 52a
Are in contact with the surface of the photosensitive drum 50 at an angle φ. It should be noted that FIG. 3 illustrates an example of a counter method that has been widely used in the past (a method of bringing the free end of the charging sheet into contact with the photoconductor so as to face the upstream side in the rotation direction of the photoconductor).

The angle φ indicates an angle between the tangent line of the photosensitive drum 50 and the edge of the charging sheet 52a, that is, an edge angle, at a position where the charging sheet 52a and the photosensitive drum 50 are in contact with each other. The free length of the charging sheet 52a, that is, the sheet-side end of the support member 52b and the charging sheet 52a.
The length between the free end of a is indicated by L.

FIG. 4 shows the charging sheet 52a in a trail system different from the counter system shown in FIG. 3 (the free end of the charging sheet is brought into contact with the photoconductor so as to face the downstream side in the rotational direction of the photoconductor). Method) is shown.

According to FIG. 4, the charging sheet 52a is in contact with the surface of the photosensitive drum 50 at an angle φ.
The angle φ is the same as the counter method shown in FIG.
The angle between the tangent line of the photosensitive drum 50 and the charging sheet 52a at the position a where the edge of the charging sheet 52a contacts the photosensitive drum 50, that is, the edge angle is shown. Similarly, the free length of the charging sheet 52a is indicated by L.

Assuming that the charging sheet 52a is arranged linearly, the amount d of the charging sheet 52a jumping out inside the circle showing the outer periphery of the photosensitive drum 50 (the free end of the sheet when the sheet is replaced as a straight line) The radial distance between the position 52s and the tangent to the surface of the drum 50) is the bite amount. The angle θ is the angle at which the charging sheet 52a is fixed with respect to the tangent to the surface of the photoconductor drum 50, and is called the support angle.

With respect to the trail system shown in FIG. 4, the free length L of the charging sheet 52a (the distance from the position of the end of the supporting member 52b to the free end of the sheet 52a protruding) is 5 to 9 mm. Between the sheet 52a and the photosensitive member by changing the support angle θ between 24 and 50 ° and the biting amount into the photosensitive drum 50 within the range of 1.25 to 3.4 mm. Consider the optimum positional relationship with the drum 50.

FIG. 5 shows in detail the relationship between the tip (free end) or edge of the charging sheet 52a and the surface of the photosensitive drum 50. According to FIG. 5A, the tangent line and the edge of the surface of the photoconductor drum 50 at the contact point between the edge (free end) of the sheet 52a and the surface of the photoconductor drum 50 in the arrangement shown in FIG. The edge angle φ is replaced by φ ₁ and φ ₂ , as shown below.

The edge angle φ ₁ is, in detail, the charging sheet 5
In the state where 2a is in contact (contact) with the surface of the photoconductor drum 50, the leading end (free end) of the charging sheet 52a, that is, the position where the edge contacts the photoconductor 50 (contact point) a
It is defined as the angle between the tangent L ₁ and an extension L ₁ 'of abutment edges of the charge sheet 52a of.

The edge angle φ ₁ is calculated by φ ₁ = θ− (3d / 2Lcos θ) [rad = radian].

When the free length L of the sheet 52a is further extended, the edge or free end of the sheet 52a is moved to the position 52a 'shown by the dotted line in FIG.
In this case, the edge (free end) is separated (lifted) from the surface of the photoconductor 50.

The edge angle φ ₂ of the raised edge shown at this position 52a ′ is the virtual contact point between the edge 52a ′ and the drum 50 (ie, the drum 50) obtained by projecting the edge position 52a ′ onto the surface of the photosensitive drum 50. An intersection of a line extending in the radial direction of the drum 50 from the center of the drum 50 toward the edge and the surface of the photosensitive drum 50) A'tangent line L ₂ and an extension line L of the edge position 52a 'of the charging sheet 52a It is defined as the angle formed by ₂ '.

This edge angle φ ₂ is calculated by φ ₂ = θ− (3d / 2Lcos θ) [rad] similarly to φ ₁ already described.

When the free end L of the charging sheet 52a is separated from the surface of the photoconductor 50 by changing the free length L and the support angle θ of the charging sheet 52a, as a result, It is a negative angle (φ ₁ and φ ₂ are opposite signs) with respect to the tangent line of 50.

FIG. 5B shows the leading end of the charging sheet 52a.
It shows the size of the area where the (free end) and the surface of the photosensitive drum 50 contact each other, that is, the nip width N. The leading end (free end) of the charging sheet 52a shown in FIG. 5A is the photosensitive member. The contact area F of the sheet 52a on the downstream side of the photoconductor drum 50 is the front nip, and the contact area R of the sheet 52a on the upstream side of the photoconductor drum 50 is the rear nip with reference to the position (contact point) a of the photoconductor drum 50. Stipulate. Needless to say, the nip width N is obtained by adding the front nip F and the rear nip R together.

Next, the characteristics of the charging sheet 52a will be considered. Table 1 shows the physical characteristics of five types of conductive member samples that can be used as the charging sheet 52a. The electrical resistance value of each sample is controlled to a predetermined resistance value due to carbon dispersion, for example, a value larger than 10 ⁴ Ω which may cause leakage due to pinholes. The resistance values shown in Table 1 are shown in FIG.
After connecting the stainless electrodes 202a and 202b having a width of 10 mm with an insulating material (plastic rod) 204 at intervals of 30 mm with respect to the inside of each electrode, a voltage of 200 V is applied between the electrodes. It is calculated from the value of the electric current flowing in the state.

[0074]

[Table 1]

Sample A is a 70 μm thick polycarbonate film. Sample B is a 70 μm thick polyimide film. Sample C is a conductive urethane foam sheet formed by uniformly kneading carbon black and the like with thermoplastic polyurethane as a main component, and then foaming the mixture into a sheet having a thickness of 0.5 mm. The urethane foam sheet is an independent pore type urethane sheet (brand name "LL rubber" manufacturer, Kyowa Giken Co., Ltd.)
According to the measurement from the scanning electron microscope (SEM) photograph,
It contains pores having an average pore diameter of about 80 μm.

In Sample D, thermoplastic ether polyurethane was used as a main component, carbon black and the like were kneaded, and the average pore diameter was controlled to 40 μm for foaming.
This is a microporous foamed (conductive) urethane sheet molded into a sheet shape (trade name "Rubycell" manufacturer, Toyo Polymer Co., Ltd.). As shown in FIG. 7, this sheet was molded to a thickness of 3.0 mm and then formed to a thickness of 1.0 mm.
Of the three sheets obtained by slicing into mm, the upper and lower two sheets having the skin surface (molding surface) are used. Also, the hardness of each sheet, the rubber hardness,
It is 28 degrees at the measured value of 10 sheets stacked under the ASKER-C scale, and about 63 kg / cm at 100% Md value.
²

Sample E is a solid-state charging sheet that is not a foam type, and has a surface of a 0.2 mm-thick polyurethane resin sheet that is not subjected to a conductive treatment.
The conductive polyurethane coating is applied, dried and then heat treated. In detail, conductive polyurethane paint
(Trade name "Subarex DH20Z313" manufacturer, Nippon Miractolan Co., Ltd.) was mixed with tetrahydrofuran (TH
F) and methyl ethyl ketone (MEK) are diluted at a predetermined ratio with a 1: 1 mixture of diluted solvents, and the diluted paint is thoroughly stirred and then dipping is applied to the surface of the sheet base material that has been washed with the solvent in advance. And apply about 30
After drying in air for 1 minute, it is further heated at 100 ° C for 20 minutes.
Provided by heating for minutes. As a result,
A conductive layer having a film thickness of about 20 μm is obtained.

Next, the voltage applied to the charging sheet 52a will be considered. Charging sheet 52a (support member 52b)
8 is obtained by applying a predetermined DC constant voltage (applied voltage) _VDC (hereinafter referred to as "DC charging") to the charging voltage Vo of the photosensitive drum 50 shown in FIG. ) (Representing the charging characteristic of sample D as a representative example), it shows a generally linear characteristic with respect to the applied voltage VDC, and the applied voltage V of about -1.05 kilovolts.
At DC, a charging potential Vo of -540 volts was obtained.

On the other hand, as already described with reference to FIGS. 4 and 5, by changing the free length L of the charging sheet 52a, the positional relationship between the sheet and the drum (contact condition) is changed. As a maximum between each condition,
A charging voltage difference ΔVo of about 100 volts occurs.

From this, in order to measure the charging voltage characteristic by "DC charging", the DC applied voltage is adjusted by each charging sheet sample and the contact condition, and the applied voltage V _DC determined for each condition is supported. By supplying to the member 52d, the charging potential Vo was standardized to −540 volts.

FIG. 8B shows an applied voltage obtained by superimposing an AC constant voltage on a DC constant voltage (hereinafter referred to as "AC + DC charging").
At -550V and -800V,
Photosensitive drum 5 obtained by superimposing an alternating electric field (AC constant voltage) having a frequency of 416 Hz and a peak-peak voltage in the range of 0 to 1.6 kilovolts on a DC constant voltage of Volt.
6 is a graph showing a charging characteristic Vo of 0.

Referring to FIG. 8B, the peak-peak voltage of the alternating electric field is about 1. regardless of the magnitude of the DC voltage.
When the voltage reaches 2 kilovolts, the charging potential V of the photoconductor 50
O is saturated, and stable charging is possible initially.

However, the AC voltage, that is, the oscillating electric field is too large, and the noise caused by vibrating the charging sheet 52a is large, and the AC current is about 20 μA / c.
It has been confirmed that even a small number of copies cannot be practically used due to a filming phenomenon caused by Joule heat increased by exceeding m. From this, the peak-peak voltage of the alternating electric field was set to 600 V, and the charging potential Vo was unified to −540 V by changing the magnitude of the DC voltage V _DC as in “DC charging”.

In the following, the edge angles φ of the charging members of Samples A to E were changed, and "DC charging" and "AC charging" were performed.
Tables 2 and 3 show the results of evaluating the image formed on the photosensitive drum 50 charged by "+ DC charging" by a predetermined method.

[0085]

[Table 2]

Table 2 shows the results for "DC charging". A4 paper was used between samples A to E, which are charging members.
Using (Toshiba recycled paper P-RS), 50
The result of checking the black stripes in this image evaluation by repeating the copying of 00 sheets and checking the image every 1000 sheets is shown.

Here, the photosensitive drum 50 is rotated at a peripheral speed of 17 mm / sec, and a DC voltage (-) is applied to each charging sheet.
(Approx. , And the fixed image was evaluated. Also, the printing density of laser exposure is 300d.
pi [dots per inch].

As is clear from Table 2, it is common to the charging member samples A to E that the edge angle φ is −0.
04 (including substantially "0") to -0.69 [rad]
In the range of 1, the black streak is not generated at all in the initial stage, which shows that uniform charging is possible as the charging performance.

Furthermore, in sample C or D, 20
This indicates that it is possible to print on 00 or 4000 or more sheets without black stripes. In particular, in Sample D, it is shown that the edge angle φ is in the range of −0.04 to 0.49 [rad], and it is possible to stably charge more than 4000 sheets without black stripes.

The edge angle φ is positive, that is, +0.08
(Substantially larger than “0”) [rad] Above, as the edge angle φ becomes larger, the charging sheet 52 already explained.
Due to the influence of the nip width of the edge of a, the charging characteristics become non-uniform, and locally sharp black stripes are formed in the vertical direction with respect to the paper traveling direction. The nip width is apt to change due to the accuracy of the edge, that is, the straightness of the edge of the charging sheet, or burrs or deviations that may occur when the edge is cut off. It has been confirmed to make the characteristics non-uniform.

Apart from this, the edge angle φ is, for example,
When it is projected to the minus side like −0.93 [rad], the edge of the charging sheet 52a floats (is separated from the surface of the photoconductor drum 50, as already described in FIG. 5A). In addition, the vibration of the charging sheet 52a tends to be remarkable due to the influence of the fluctuation of friction due to the rotational movement of the photosensitive drum 50.

For this reason, it becomes difficult to obtain a stable nip width in the longitudinal direction of the photosensitive drum 50, and a gentle partial charging failure occurs. In this case, fog or black streaks occur in the image due to the relation with the unevenness ΔVo of the charging potential in the longitudinal direction.

[0093]

[Table 3]

Table 3 shows the results for "AC + DC charging", which is the same as "DC charging" shown in Table 2 and 1000
The image is checked for each sheet, and the result of checking the black streak in this image evaluation is shown.

Referring to Table 3, similarly to the "DC charging" shown in Table 2, the edge angle is -0.04 to -0.69 [r.
In the range of [ad], a good image without black streaks was obtained.
In addition, this “AC + DC charging” has an edge angle in the range of −0.19 to −0.49 [rad] as compared with “DC charging”, and for all of the samples A to E, 2000 or more black stripes are formed. It was confirmed that printing without generation was possible.

If the magnitude of the AC voltage superimposed on the DC voltage is in the range of 200 V to 1 KV, the vibration noise of the charging sheet and the filming of the toner on the photosensitive drum are practically used. It can be reduced to the possible range.

By the way, even in "AC + DC charging", if the edge angle φ is positive, "DC charging" is performed.
Similarly to the above, the occurrence of black stripes due to uneven charging is seen,
Further, when the edge angle φ is negative such as −0.93 [rad], the vibration sound peculiar to “AC + DC charging” is increased.

From this, the charging sheet 52a has an edge angle φ of −0.04 with respect to the surface of the photosensitive drum 50.
To -0.69 [rad], more preferably-
By setting the range of 0.19 to −0.49 [rad], optimum charging characteristics can be provided.

Next, the charging sheet of Sample D, which gives the best results from the charging characteristics shown in Tables 2 and 3, will be described in more detail. In FIG. 9, the edge angle φ of the charging sheet and the distance between the end of the supporting member on the free end side of the charging sheet supported by the supporting member and the contact point at which the photosensitive drum and the charging sheet come into contact, that is, the sheet- Drum abutment distance (denoted k in FIGS. 3 and 4),
Also, the relationship between the edge angle φ of the charging sheet and the nip width N of the charging sheet is shown.

As is apparent from FIG. 9, when the edge angle φ of the charging sheet is changed from 0 [rad] to the negative side, the sheet-drum contact distance k is about 6.0 m.
It becomes m and becomes stable.

Similarly, referring to FIG. 9, the nip width N
Is gradually increased as the edge angle φ is changed from the positive side to 0 [rad], and the edge angle φ is negative side,
In particular, it is further increased until it is changed to about −0.4 [rad]. On the other hand, the front nip F is
It takes a maximum value at 0.7 [rad] and becomes 4.5 mm.
It should be noted that the rear nip R is reduced by changing the edge angle φ to the minus side, which is approximately -0.65 [rad].
Thus, the nip width N and the front nip F are matched.

FIG. 10 shows the charging current of “AC + DC charging”, that is, AC for the charging sheet of Sample D.
The magnitude of the AC current I _AC flowing by charging and the DC current I _DC flowing by charging DC and the edge angle φ of the charging sheet
Is shown. The DC current I _DC is represented by a temperature of 10 ° C. and a humidity of 20% or L / L, a temperature of 25 ° C. and a humidity of 55% or N / N, and a temperature of 30 ° C. and a humidity of 85% or H / H. In different measurement environments, the AC current I _{AC also} has a temperature of 10 ° C. and a humidity of 20% or L / L, and a temperature of 30 ° C. and a humidity of 8
5% or H / H, two kinds of measurement environment,
Being tested.

As is apparent from FIG. 10, the DC current I _DC
9 in each environment L / L, N / N and H / H.
It can be seen that it changes corresponding to the nip width N shown in (L / L is substantially a straight line, but no change appears because the amount of current for each edge angle is extremely small. Can be expected).

Further, according to FIG. 10, the AC current I _AC is
It can be seen that when the edge angle φ is changed from 0 [rad] to the minus side, it tends to be saturated, and at the same time, the AC current difference ΔI _AC due to the environmental difference between L / L and H / H also decreases. . Therefore, by setting the edge angle φ in the negative direction, the impedance including various environmental conditions can be stabilized, and the AC current I _AC can be stabilized.

FIG. 11 shows the maximum value V _max and the minimum value V _{min of} the charging potential applied to the photosensitive drum in the various test environments shown in FIGS. 9 and 10.

Referring to FIG. 11, it is recognized that when the edge angle φ is in the negative direction, the charging potential Vo is increased and the fluctuation range ΔVo of the charging potential in each environment is reduced. For example, the edge angle φ is 0.4 [r
In the case of [ad], ΔVo of about 80 volts is recognized, but when the edge angle φ is −0.4 [rad], ΔV
o is reduced to about 40V, which is approximately 1/2.

Judging from all of these, the edge angle φ
Is generally in the negative range, and in particular 0 to -0.7
[rad], more preferably -0.19 to -0.49.
It is recognized that by setting it in the range of [rad], the occurrence of black stripes is small and the change of the charging potential Vo with respect to the change of the environment is reduced.

Further, the edge angle φ of the charging sheet is 0 to −
Setting to the range of 0.7 [rad] means setting the nip width N
Not only can be easily secured, but also the assembly can be facilitated, so that the cost of the charging device can be reduced.

Next, the pressure contact force of the charging sheet with the photosensitive drum will be described. Here, the polycarbonate film of Sample A and the urethane foam sheet of Sample D are shown. Also, here, the edge angle φ is −
It was fixed at 0.36 [rad] (the amount of bite into the photoconductor at this time was 2.75 mm), and about −1 kilovolt was applied by “DC charging”.

The pressure contact force is changed by increasing or decreasing the thickness of the charging sheet. For the polycarbonate film of Sample A, 70 μm, 80 μm, 9 μm.
0 μm, 100 μm, 120 μm, 150 μm and 2
For the urethane foam sheet of 00 μm and sample D, 1.0 mm, 1.5 mm, 1.8 mm, 2.0
It was measured by each sheet having a thickness of mm, 2.5 mm and 3.0 mm.

At this time, the pressure contact force W between each sheet and the photoconductor drum is a [cm] the amount of bite into the photoconductor, E [g / cm] the Young's modulus of each sheet, and the thickness of the charging sheet. t
[cm] and free length L [cm] of the charging sheet, W = dEt ³ / 4L ³ [g / cm ² ]. Here, W is the pressing force, a is the amount of bite into the photoreceptor (cm), E is Young's modulus (g / cm), t is the thickness of the charging sheet, and L is the free length (cm) of the charging sheet. .

Tables 4 and 5 show the results of evaluating the images obtained by the pressure contact forces of the polycarbonate film (Sample A) and the urethane foam sheet (Sample D), respectively.

[0113]

[Table 4]

[0114]

[Table 5]

According to Tables 4 and 5, it was confirmed that black streak was generated from the initial stage when the pressure contact force, that is, the load was 3.7 g / cm or more and which sheet was used. There is.

On the other hand, the pressure contact force, that is, the load is 3.7 g / c.
When the sheet thickness is m or less, no black streak occurs in the initial stage regardless of which sheet is used. Especially, in the urethane foam sheet, no black streak occurs even after 2,000 copies. Is recognized. Presuming the reason for this, firstly, if the pressure contact force is too strong, foreign matter such as toner that has slipped through the cleaning blade is likely to be caught between the charged sheet photoconductors, and charging failure is likely to occur because the charged sheet does not slip through. Secondly, since the edge angle φ is set in the negative direction, when a high pressure contact force is applied, the load in the longitudinal direction of the seat becomes uneven due to the distortion of the seat,
As a result, it is considered that a slight distortion easily causes a partial charging failure.

From this, the pressure contact force between the photosensitive drum and the charging sheet is substantially as small as 3.7 g / cm 3 or less so as to be governed by the electrostatic attraction force acting between them. It will be appreciated that loading is preferred.

As described above, the result that the urethane foam sheet (Sample D) was excellent was obtained in all the tests. Next, urethane foam sheet (Sample D)
The average diameter of the pores contained in will be briefly described.

The urethane foam sheet described so far
The average pore diameter of (Sample D) is approximately 40 μm as described above, but sheets of the same material were used, and the average pore diameter was 80 μm, 150 μm, 300 μm, 500 μm.
m, the image was formed on each sheet under the above-mentioned image forming conditions, and the image was evaluated. As a result, a 500 μm sheet had a printing rate of 1 dot (minimum printing unit) of 25. % Of halftone dot images, white stripes due to uneven charging occurred from the beginning, and
On the sheet of m, white streaks were confirmed when the number of copies reached 5,000.

Therefore, it is recognized that a sheet having a pore diameter of preferably 10 to 300 μm and a small pore diameter provides a more uniform and stable image quality. The reason for this is that since a wide charging nip is obtained and the adhesion to the photoconductor is good, it is unlikely to be affected by the sheet precision and assembly precision, and foreign matter such as toner that is trapped between the sheet photoconductors escapes to the pores. Can be uniformly charged without causing streak images.

The pore diameter is over 300 μm and 500 μm
In the vicinity, a halftone dot image consisting of 1 dot (minimum printing unit) with a printing rate of 25% will appear as white streaks due to uneven charging or black streaks on a white background from the beginning, and film members such as polycarbonate resin It is worse than the initial image when compared with a sheet of polyurethane or solid type.

Next, the characteristics of the operation of the copying apparatus of the present invention will be described. After the document D is placed on the document tray 120 of the ADF 100, a print key (not shown) on the operation panel (not shown) is turned on, so that the above-described charging sheet 52
a (preferably 1.0 mm in thickness, the free length L of the urethane foam sheet (sample D) having one surface formed on the skin side is set to 7 mm by the trail method, and the contact pressure is generally less than 10 g / cm. The surface of the photoconductor drum 50 is pressed against the surface of the photoconductor drum 50 with a direct current electric field of −800 V and an alternating electric field of peak-peak voltage of 600 V is applied. Is supplied, and the surface of the photosensitive drum 50 has a predetermined potential, for example, −550.
It is uniformly charged to the level of a volt.

Subsequently, the illumination lamp 32 is turned on by the lamp regulator 112, the first and second carriages 30 and 40 are moved in parallel with the original table 20, and the original D placed on the original table 20 is read. The image information is guided to the CCD sensor 48.

The image information of the document D guided to the CCD sensor 48 is photoelectrically converted by the CCD sensor 48, and then an image output signal corresponding to the exposure from the laser exposure device 54 by an image processing circuit and an exposure control circuit (not shown). And is supplied to the laser exposure device 54. The image information photoelectrically converted by the CCD sensor 48 may be temporarily stored in the image memory secured in the RAM 106 (or independently prepared).

By exposure from the laser exposure device 54, an electrostatic latent image corresponding to the image of the document D is formed on the photosensitive drum 50. The electrostatic latent image is developed by the toner supplied by the developing roller 56a of the developing device 56.

This toner image is conveyed with the rotation of the photosensitive drum 50, and is released from the registration roller 70 in a state where the front end of the sheet P stopped by the registration roller 70 and the front end of the toner image are aligned. The sheet P is conveyed to the transfer area between the transfer roller 60 and the photoconductor drum 50, and is transferred to the sheet P via the transfer roller 60.

The photosensitive drum 50 to which the toner image is transferred is transferred to the photosensitive drum 5 via the cleaning device 58.
After the toner remaining on the photosensitive drum 5 is removed, the photosensitive drum 5
The charge distribution remaining at 0 is erased and used for the next latent image formation.

The sheet P on which the toner image is transferred is conveyed to the fixing device 72 by the conveying belt 74, the toner image is fixed by the fixing device 72, and the sheet P is ejected to the tray 80 via the ejection roller 78.

This series of operations is sequentially repeated a predetermined number of times in accordance with the number of copies input via the operation panel. Further, the process is repeated in order for all the documents D placed on the document tray 120 of the ADF 100.

In the examples of the present invention, polycarbonate and polyimide were used as the film member, but similar results can be obtained with a polyamide resin such as nylon. In addition, polyethylene naphthalate, polyvinylidene fluoride, ethylene tetrafluoroethylene copolymer, P
It can also be used by dispersing a conductive material in a resin material or applying a conductive coating on the surface of ES alloy, polyether, ether ketone, etc. as a conductive treatment.

As the conductive coating material, lacquer, vinyl type, aminoalkyd, aminoacryl, phenol, alkyd, epoxy, polyester, silicone, acrylic urethane and vinylurethane as binder resin may be used alone or in a mixture of two or more kinds. It can be used.

As the conductive filler, carbon black, a conductive surfactant, a metal oxide semiconductor, graphite, metal fine particles and a composite material in which a metal is attached to the surface of a carrier can be used.

The carbon black is preferably conductive carbon black such as furnace black, acetylene black and Ketjen black, but thermal black, channel black or process black can also be used. As the metal oxide semiconductor, zinc oxide, tin oxide, titanium oxide, barium oxide, antimony oxide, zirconium oxide, aluminum oxide, zinc sulfide, barium sulfide and the like can be used.

Solvents for producing a conductive paint include dimethylformamide, diethylformamide, dimethylacetamide, dimethylsulfoxide, N-methyl-2-pyrrolidone, N, N-tetramethylurea, hexamethylenephosphoamide, Aprotic polar solvent such as tetramethyl sulfone, aromatic hydrocarbon solvent such as benzene, toluene, xylene and ethylbenzene, ester solvent such as methine acetate, ethyl acetate and butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone Ketone solvents such as
Chlorinated hydrocarbon solvents such as trichlene and dichloroethane, alcohol solvents such as isopropanol and butanol, and ether solvents such as tetrahydrofuran and dibutyl ether can be used.

If necessary, additives such as pigments, dyes, fillers, plasticizers, antioxidants, and surfactants can be added to the conductive paint described above. For kneading and dispersing the bander resin and conductive filler, use a 3-roll mill, ball mill, sand grinder, high-speed stone mill, high-speed impact mill, disper, kneader, high-speed mixer, homogenizer, ultrasonic disperser, or other kneading machine or dispersing machine. Machine can be used.

The conductive coating material is applied by hand or continuously or semi-continuously in a line by dipping, spraying, curtain flow or brush coating on the surface of the sheet, followed by drying. As a result, a required conductive layer can be formed.

In addition to the polyurethane rubber used in Samples B to E, silicone rubber, EPDM, CR (chloroprene rubber), NBR (nitrile rubber), SBR (styrene butadiene rubber), natural rubber, polyethylene rubber,
It is possible to use rubber such as polypropylene rubber or foam.

[0138]

As described above, according to the charging device of the image forming apparatus of the present invention, one end portion of the photosensitive member formed movably is limited to 0.7 [rad]. A charging device is provided that is in contact with the photoconductor so as to face the downstream side of the direction in which the photoconductor is moved.

The charging device is arranged so that the pressure contact force between the free end of itself and the photoconductor is 3.7 g / cm or less. Therefore, a uniform charging potential is provided to the photoreceptor.

Furthermore, the charging device includes a conductive material and a plurality of voids having an average diameter of less than 150 μm, is formed into a thin plate shape, and is then cut in the thickness direction together with at least the surface layer. Since the conductive foamed sheet formed in (1) is included, a uniform charging potential can be provided to the photoconductor even when the temperature or humidity changes.

Therefore, the photosensitive member is provided with a uniform charging potential without unevenness. Also, the assembly cost for assembling the charging device is reduced. Therefore, the cost of the image forming apparatus is reduced. Further, the image forming apparatus including the charging device is downsized.

[Brief description of drawings]

FIG. 1 is a schematic view showing an image forming apparatus in which a contact type charging device according to an embodiment of the present invention is incorporated.

FIG. 2 is a schematic block diagram mainly showing a charging device and an image forming unit of the image forming apparatus shown in FIG.

FIG. 3 is a partially enlarged view showing the positional relationship between the charging device and the photosensitive drum shown in FIGS. 1 and 2.

FIG. 4 is a partially enlarged view showing the positional relationship between the charging device and the photosensitive drum shown in FIGS. 1 and 2.

5 is a partially enlarged view showing the positional relationship between the tip of the charging device shown in FIG. 4 and a photosensitive drum, and FIG. 5 (a) is a charging sheet and a photosensitive drum. FIG. 5 is a partially enlarged view showing in detail an edge angle which is an angle formed by
(b) is a partial enlarged view showing in detail the nip width defined between the charging sheet and the photosensitive drum.

FIG. 6 is a schematic view showing a measuring device for measuring the electric resistance value of a charging sheet.

FIG. 7 is a schematic view for explaining a forming method for forming the most suitable foamed electrification sheet of the embodiment of the present invention.

FIG. 8 is a graph showing a relationship between an applied voltage supplied to a charging device and a charging potential charged on a photosensitive drum, and FIG. 8A shows a DC voltage as an applied voltage. FIG. 8B is a graph showing the charging potential, and FIG. 8B is a graph showing the charging potential as an applied voltage by superimposing an AC voltage on a DC voltage.

FIG. 9 is a graph showing the relationship between the edge angle of the charged sheet of Sample D, the distance between the sheet and the drum contact, and the edge angle of the charged sheet and the nip width of the charged sheet.

FIG. 10 is a graph showing changes in the charging current with respect to changes in the edge angle of the charging sheet of Sample D and environmental conditions.

FIG. 11 is a graph showing the maximum value V _max and the minimum value V _min of the charging potential provided to the photosensitive drum in various test environments shown in FIGS. 9 and 10.

[Explanation of symbols]

2 ... Copier (image forming apparatus), 10 ... Digital copying apparatus main body, 12 ... Original reading section, 14 ... Image forming section, 1
6 ... Paper supply unit, 18 ... Paper transport unit, 20 ... Original table, 30 ... First carriage, 32 ... Illumination lamp, 34 ...
Reflector, 36 ... First mirror, 40 ... Second carriage, 42 ... Second mirror, 44 ... Third mirror, 46 ... Imaging lens, 48 ... CCD sensor, 50 ... Photoconductor drum (photoconductor), 52 ... Charging Apparatus, 54 ... Laser exposure apparatus, 56
... developing device, 58 ... cleaning device, 60 ... transfer roller, 62a ... paper cassette, 62b ... bypass tray,
62c ... Large-capacity cassette, 64a and 64b ... Paper feed roller, 66a and 66b ... Conveying roller, 68 ... Bypass feed roller, 70 ... Registration roller, 72 ... Fixing device, 74 ... Conveying device, 76 ... Branch gate, 78 ... Discharge Rollers, 80 ... Tray, 90 ... Paper reversing section.

Claims (4)

[Claims] 1. A photosensitive member which is formed in a thin plate shape and is movable in a predetermined direction. One end of the photosensitive member is downstream of the photosensitive member moving direction within a limit of 0.7 [rad]. A charging device, wherein the charging device is brought into contact with the photoconductor so as to be directed to the side. 2. An angle formed by the free end and the photoconductor is 0.7 [rad] from a vertical angle with respect to the photoconductor which is formed in a thin plate shape having a free end and is movable in a predetermined direction. Within the range, the photoconductor is directed toward the downstream side in the moving direction, and the pressure contact force between the free end and the photoconductor is 3.7 g / cm or less. And charging device. 3. A conductive material and a plurality of bubble-shaped gaps having an average diameter of less than 150 μm, which are formed by being formed into a thin plate shape and then cut in the thickness direction together with at least a surface layer. The angle formed by the free end of the conductive foam sheet and the photosensitive body is 0.04 to 0.49 [ra] with respect to the photosensitive body formed so as to be movable in a predetermined direction.
d] is directed toward the downstream side in the moving direction of the photoconductor and the pressure contact force between the free end and the photoconductor is 3.7 g / cm or less. Characteristic charging device. 4. A photosensitive member capable of holding an electrostatic image by being irradiated with light while being charged to a predetermined potential, and a thin plate-like member having a free end. The angle between the free end and the photoconductor is 0.
Within the range of 7 [rad], the photosensitive member is directed to the downstream side in the moving direction, and the pressure contact force between the free end and the photosensitive member is arranged to be 3.7 g / cm or less. An image forming apparatus comprising: a charging device, comprising: