JP2002268326A - Imaging device and process cartridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To move an electrifying roller to a desired position, by optimizing biasing force acting on the charging roller in an imaging device provided with a crossed axes angle between the rotary axial line of a photoreceptor drum and that of the charging roller. SOLUTION: If the crossed axes angle of the rotary axial line of the photoreceptor drum 1 with that of the charging roller 2 is defined as θ( deg.), the pressing force of the roller 2 to the drum 1 by pressure springs 23a and 23b is S(N), the hardness of the roller 2 is R( deg.) and the surface slip factor of the roller 2 is H, index F of the biasing force of the roller 2 expressed by F= tanθ×S×R×H lies in the range of 0.8<F<9.4, whereby the appropriate biasing force acts on the roller 2, and the roller 2 is moved to the desired position and abuts on the drum 1. Therefore, an image is formed properly, while holding stable electrifying width over a long term.

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 such as a copying machine, a printer, a facsimile or the like for forming an image using an electrophotographic system or an electrostatic recording system, and a photoconductor and at least a charging means. The present invention relates to a process cartridge detachably mounted on an image forming apparatus.

[0002]

2. Description of the Related Art FIG. 12 is a schematic diagram showing an example of a conventional image forming apparatus using an electrophotographic system, such as a copying machine, a printer, a facsimile or the like.

In this image forming apparatus, a photosensitive drum 100 is driven to rotate in the direction of an arrow (clockwise), and its surface is uniformly charged by a charging roller 101 to which a charging bias has been applied. Image exposure L is performed according to the input image signal to form an electrostatic latent image. This electrostatic latent image is developed as a toner image by a developing sleeve 102a of a developing device 102 having a thin layer of toner carried on the surface. The toner image formed on the photosensitive drum 100 is transferred to a transfer material P such as paper conveyed to a transfer nip N between the photosensitive drum 100 and the transfer roller 103 by the transfer roller 103 to which a transfer bias is applied. .

That is, at the transfer nip N, the photosensitive drum 10
A transfer bias having a polarity opposite to that of the toner is applied to the transfer roller 103 in contact with the transfer roller P, and a charge having a polarity opposite to that of the toner is applied from the back side of the transfer material P where the toner image is not formed. The upper toner image is the transfer material P
Transferred to the surface.

The transfer material P onto which the toner image has been transferred is conveyed to a fixing device (not shown), where the toner image is thermally fixed on the surface of the transfer material P by this fixing device, and then discharged outside. The transfer residual toner remaining on the photosensitive drum 100 after the transfer is removed by the cleaning blade 104 and collected.

As described above, the charging roller 101 of the contact charging type has been widely used in recent years as a charging means for the photosensitive drum 100 from the viewpoint of charging stability. That is, the contact charging method (the roller charging method) using the charging roller 101 generates a corona discharge by applying a high voltage to the wire and exposes the photosensitive drum to the corona. This is because the applied voltage required to obtain the potential can be reduced, and the amount of ozone generated during the charging process is small.

By the way, the charging roller 101 described above is
The photosensitive drum 100 is brought into contact with the photosensitive drum 100 with a predetermined pressure, and is driven to rotate by the driving rotation of the photosensitive drum 100.

Therefore, as shown in FIG. 13, the rotation axis p of the charging roller 101 and the rotation axis q of the photosensitive drum 100
In other words, in the configuration in which the crossing angle is not provided between the charging roller 101 and the rotation axis p of the charging roller 101 and the direction of the rotation axis q of the photosensitive drum 100 coincide with each other, the charging roller 101 moves in the direction of the rotation axis p. No force is acting.

Therefore, when the core metal 105 of the charging roller 101 is rotatably supported by the bearings 106a and 106b, the charging roller 101 is mounted on the bearing 10a, for example.
6a, the charging roller 1 is supported in this state.
01 contacts the photosensitive drum 100, there is a possibility that a charging failure area may occur in the bearing 106b in the longitudinal direction of the photosensitive drum 100, and it is necessary to take the longitudinal dimension of the charging roller 101 sufficiently in consideration of assembly errors and the like. There is.

It is necessary to take the longitudinal dimension of the charging roller 101 sufficiently in consideration of the influence of tolerance such as play at the longitudinal position of the charging roller 101 which is driven and rotated by the rotation of the photosensitive drum 100.

For this reason, as shown in FIG. 14, in the above-described image forming apparatus, the rotation axis q of the photosensitive drum 100 and the rotation axis p of the charging roller 101 have a predetermined tolerance angle θ so that the charging roller 101 Is brought into contact with the photosensitive drum 100. Note that both ends of the core metal 105 of the charging roller 101 are rotatably supported by bearings 106a and 106b.

As described above, when the intersection angle θ is provided between the rotation axis p of the charging roller 101 and the rotation axis q of the photosensitive drum 100, the charging roller 101 that rotates following the rotation axis p moves in a fixed direction along the rotation axis p. Approach. For example, in FIG. 14, when the photosensitive drum 1 is driven to rotate in the direction of the arrow, a biasing force in the direction of the arrow A (the direction of the rotation axis p) acts on the charging roller 101 that is driven and rotated in the opposite direction. To the bearing 106a side.

As shown in FIG. 14, since the photosensitive drum 100 which is in contact at the intersection angle θ is driven to rotate and the charging roller 101 is driven to rotate, the charging roller 101 receives a rotational driving force Fdr. At this time, since the charging roller 101 rotates around its rotation axis p, the charging roller 10
1, a rotating force Fcr acts on the charging roller 1
01 also receives a force in the direction of arrow A. Therefore,
The charging roller 101 has an arrow A along its rotation axis p direction.
A leaning force in the direction will work.

The biasing force in the direction of the arrow A causes the charging roller 101 to move to a predetermined position and
Can be brought into contact with the vehicle. Therefore, the charging roller 10
1 can be set while minimizing the effects of assembly errors and the like, so that the longitudinal dimension of the charging roller 101 can be shortened as compared with the case where the above-mentioned intersection angle is not provided, and A stable charged area can be maintained.

[0015]

As described above, the rotation axis q of the photosensitive drum 100 and the charging roller 101
In the configuration in which the intersection angle θ is provided with the rotation axis p, if the intersection angle θ is too small, the biasing force (moving force in the direction of arrow A) acting on the charging roller 101 is insufficient, and If the charging roller 101 does not move to a desired position, and if the crossing angle θ is too large, the biasing force (moving force in the direction of arrow A) acting on the charging roller 101 is too large,
There is a possibility that the core metal 105 of the No. 01 may come into contact with the bearing 106a with a large force to damage the bearing 106a, or the surface of the charging roller 101 may be rubbed against the photosensitive drum 100 more than necessary and damaged.

If the charging roller 101 does not move to a desired position, the longitudinal position of the charging roller 101 deviates from the desired position. The charging roller 101 does not contact the
Poor charging occurs at that portion, resulting in poor image quality.

Further, the biasing force of the charging roller 101 in the direction of arrow A is too strong, and the surface of the charging roller 101 is
If it is damaged by rubbing with 0, sufficient charging is not performed at the damaged portion, and poor charging occurs and image failure occurs. In particular, in the configuration in which the surface layer of the charging roller 101 is not adhered to the lower layer and is coated on the lower layer surface, if the moving force in the direction of arrow A is too large, the surface of the charging roller 101 may be twisted, It is easy to break.

Therefore, in the present invention, in a configuration in which a crossing angle is provided between the rotation axis of the photosensitive drum and the rotation axis of the charging roller, the biasing force acting on the charging roller is made appropriate, and the charging roller can move to a desired position. It is an object of the present invention to provide an image forming apparatus capable of performing good charging in this way.

[0019]

In order to achieve the above object, according to the first aspect of the present invention, a rotatable image carrier is brought into contact with the image carrier at a predetermined pressure by a pressurizing means and is charged. A rotatable contact charging member for charging the image carrier by applying a bias, wherein the rotation axis of the contact charging member contacts the rotation axis of the image carrier at a predetermined crossing angle, and The charging member is driven to rotate by the rotation of the image carrier, and the image generated in a state where the contact charging member exerts a biasing force in one direction of the rotation axis of the contact charging member by a force generated by the crossing angle during rotation. In the image forming apparatus to be brought into contact with the carrier, the crossing angle is θ (°), the pressing force applied to the image carrier by the contact charging unit by the pressing unit is S (N), and the hardness of the contact charging member is Is R (°), Assuming that the surface slip coefficient of the contact charging member is H, a deviation index F of the contact charging member represented by F = tan θ × S × R × H is set in a range of 0.8 <F <9.4. It is characterized by being done.

According to a fourth aspect of the present invention, the rotatable image carrier is brought into contact with the image carrier at a predetermined pressure by a pressing means, and the image carrier is charged by applying a charging bias. At least a rotatable contact charging member,
The contact charging member is detachable from the image forming apparatus, and the rotation axis of the contact charging member contacts the rotation axis of the image carrier at a predetermined crossing angle, and the contact charging member rotates the image carrier. In the process cartridge, the contact charging member is brought into contact with the image carrier in a state where the contact charging member exerts a biasing force in one direction of its rotation axis by a force generated by the crossing angle at the time of rotation. The intersection angle is θ (°), and the pressing force of the contact charging unit on the image carrier by the pressing unit is S.
(N), when the hardness of the contact charging member is R (°) and the surface slip coefficient of the contact charging member is H, F = tan θ
The deviation index F of the contact charging member represented by × S × R × H is set in a range of 0.8 <F <9.4.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the illustrated embodiment.

<First Embodiment> FIG. 1 is a schematic configuration diagram showing an image forming apparatus (in this embodiment, an image forming apparatus such as an electrophotographic laser printer) according to a first embodiment of the present invention. is there.

The image forming apparatus 20 includes the photosensitive drum 1 as an image carrier. A charging roller 2, a developing device 3, a transfer roller 4, and a cleaning device 5 are disposed around the photosensitive drum 1 in order along the rotation direction of the photosensitive drum 1. Is provided with an exposure device 6. A transfer guide 7 and a fixing device 8 are disposed downstream of the transfer nip N formed between the photosensitive drum 1 and the transfer roller 4 in the transfer material transfer direction.

In the present embodiment, the photosensitive drum 1 is an organic photosensitive drum that is negatively charged, has an OPC photosensitive layer on a drum base made of aluminum, and has a predetermined peripheral speed (process) by driving means (not shown). (Speed) in the direction indicated by the arrow (clockwise), and receives a uniform negative charge by the charging roller 2 in contact during the rotation process.

The charging roller 2 as a contact charging means is driven by the contact with the surface of the photosensitive drum 1 with a predetermined pressing force,
The photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by a charging bias applied from a charging bias power supply 9 (the charging roller 2 which is a feature of the present invention will be described later in detail).

The developing device 3 includes a rotatable developing sleeve 1 which is substantially in contact with the surface of the photosensitive drum 1 at the opening of the developing container 10.
The developing unit attaches toner t to the electrostatic latent image on the photosensitive drum 1 in the developing unit and visualizes it as a toner image.

A transfer roller 4 as a transfer means contacts the surface of the photosensitive drum 1 with a predetermined pressing force to form a transfer nip N, and the transfer roller 4 is supplied with a transfer bias from a transfer bias power supply (not shown). The toner image on the surface of the photosensitive drum 1 is transferred to a transfer material P such as paper at a transfer nip N between the transfer roller 1 and the transfer roller 4.

The exposure device 6 outputs a laser beam (exposure beam) modulated according to a time-series electric digital image signal of image information input from a personal computer (not shown) from a laser output unit (not shown). The output and charged surface of the photosensitive drum 2 is subjected to scanning exposure L via the reflection mirror 12 to form an electrostatic latent image corresponding to image information.

The fixing device 8 includes a heating roller 8a having a halogen heater (not shown) and a pressure roller 8b, and a transfer material P is formed at a fixing nip between the fixing roller 8a and the pressure roller 8b. While holding the toner image, the toner image transferred onto the surface of the transfer material P is heated and pressed to be thermally fixed.

Next, the image forming operation of the image forming apparatus 20 will be described.

At the time of image formation, the photosensitive drum 1 is driven to rotate at a predetermined peripheral speed in a direction indicated by an arrow (clockwise) by a driving means (not shown), and is driven by the charging roller 2 to which a charging bias is applied from a charging bias power supply 9. In this manner, the negative electrode is charged to a predetermined potential. When the scanning exposure L by the laser beam is applied from the exposure device 6 to the charged photosensitive drum 1 via the reflection mirror 12, the potential on the photosensitive drum 1 is reduced at the portion exposed to the scanning exposure L. Thus, an electrostatic latent image corresponding to image information input from a personal computer (not shown) or the like is formed.

An electrostatic latent image formed on the photosensitive drum 1 by the developing sleeve 11 of the developing device 3 to which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 1 is applied in the developing section. The toner t is adhered to the toner image, and is visualized as a toner image by reversal development.

On the other hand, a transfer material P such as a sheet in the cassette 13 is fed by a pickup roller 14 and conveyed to a pair of registration rollers (not shown) in synchronization with the formation of a toner image on the photosensitive drum 1. . When the toner image on the photosensitive drum 1 reaches the transfer nip N between the photosensitive drum 1 and the transfer roller 4, the transfer material P is conveyed to the transfer nip N by a pair of registration rollers (not shown) at this timing. Is done.

The transfer roller 4 to which a transfer bias of the opposite polarity (positive polarity) is applied to the transfer material P conveyed to the transfer nip N is generated between the photosensitive drum 1 and the transfer roller 4. The toner image on the photosensitive drum 1 is transferred by the electric power. Then, the transfer material P on which the toner image has been transferred is conveyed to the fixing device 8 via the conveyance guide 7, and the toner image is heated and added to the transfer material P by a fixing nip between the heating roller 8a and the pressure roller 8b. Press and heat fix. The transfer material P on which the toner image has been fixed is discharged out of the image forming apparatus main body 30 via the discharge roller pair 15, and a series of image forming operations is completed.

The transfer residual toner remaining on the photosensitive drum 1 after the transfer is removed and collected by the cleaning blade 5a of the cleaning device 5.

Next, the charging roller 2 will be described in detail.

As shown in FIG. 2, both ends of a metal core 21 on which the charging roller 2 is inserted are respectively bearings 22a, 2b.
2b rotatably supported. Bearing 22
a and 22b are urged toward the photosensitive drum 1 by a predetermined spring force (3.5 to 9.5N) S by the pressure springs 23a and 23b. 1, the photosensitive drum 1 is driven to rotate with the driving rotation of the photosensitive drum 1.

The charging roller 2 has a conductive elastic layer on a cored bar 21 and a thin resistive layer coated on the surface thereof without an adhesive member therebetween. Sa2
It is formed in a 50 mm roller shape.

The core 21 is made of SUS rod having a diameter of about 5 mm and plated with nickel. The bearings 22a and 22b are formed of a member such as POM, and one of the bearings 22a is a power supply path of the charging bias from the charging bias power supply 9 to the charging roller 2. The filler is uniformly dispersed, and the resistance is kept at 10 ¹ to 10 ³ Ω.

The charging bias power supply 9 applies an oscillating voltage (Vdc + Vac) obtained by superimposing a DC voltage Vdc and an AC voltage Vac as a charging bias to a pressing spring 23 a and a bearing 22.
a, the voltage is applied to the charging roller 2 through the metal core 21. By applying this oscillating voltage to the charging roller 2, the peripheral surface of the photosensitive drum 1 in contact with the charging roller 2 causes the oscillation center voltage (=
It is charged to a DC voltage Vdc).

In the present embodiment, as shown in FIG. 3, the charging roller 2 is rotated so that the rotation axis q of the photosensitive drum 1 and the rotation axis p of the charging roller 2 abut at a predetermined intersection angle θ. Is installed. As a result, "conventional technology"
As described above, when the photosensitive drum 1 is driven to rotate in the direction of the arrow and the charging roller 2 is driven to rotate in the opposite direction,
The crossing angle θ causes a biasing force (moving force) in the direction of arrow A to act on the charging roller 2 along the direction of the rotation axis p. The intersection angle θ is set in a range of 0 <θ <5 °.

At this time, the intersection angle between the rotation axis q of the photosensitive drum 1 and the rotation axis p of the charging roller 2 is θ (°), and the spring pressing force of the pressure springs 23a, 23b on the bearings 22a, 22b is S ( N), assuming that the hardness of the charging roller 2 is R (°) and the surface slip coefficient of the charging roller 2 is H, the above-described index index F of the charging roller 2 in the direction of arrow A is as follows: F = tan θ × S × R × H ... (1)

The present inventor has examined the experimental results described below and found that the biasing force index F of the charging roller 2 was set within a predetermined range (0.8 <F <9.4 as described below). It has been found that the biasing force of the roller 2 in the direction of arrow A can be properly adjusted. Hereinafter, an experiment for setting a value of the deviation force index F in a predetermined range in the present embodiment will be described.

As shown in FIG. 4, the charging roller 2 is pressed against the photosensitive drum 1 by a predetermined spring pressing force S by each of the pressure springs 23a and 23b. A predetermined intersection angle θ is provided between the rotation axis q of the photosensitive drum 1 and the rotation axis p of the charging roller 2, and the charging roller 2 is driven to rotate in the direction of the arrow by driving and rotating the photosensitive drum 1 in the direction of the arrow. The crossing angle θ causes a biasing force in the direction of arrow A to act on the charging roller 2. The deviation force generated at this time is determined by the intersection angle θ and the pressure spring 23a.
The pressure was measured by the pressure gauge 24 while changing the spring pressure S of 23b.

The photosensitive drum 1 used in this experiment had a diameter of 2
The photosensitive layer is formed by coating a photosensitive layer on the outer surface of a 4 mm aluminum cylinder. The photosensitive layer has a two-layer structure in which a charge generation layer and a charge transport layer are formed on the surface thereof. The photosensitive layer is usually an insulator, but has the property of becoming a conductor when absorbing light of a specific wavelength. In the present embodiment, a charge transport layer in which fluororesin particles are dispersed is used.

The charging roller 2 used in this experiment is:
An elastic layer in which conductive carbon is dispersed in urethane rubber, EPDM, or the like having a thickness of 3 mm is provided on the peripheral surface of a core metal 21 having a diameter of 6 mm, and the surface thereof has a thickness of 100 to 500 without an adhesive member.
It is constituted by coating a high-resistance surface layer such as a μm epichlorohydrin rubber. The roller hardness used was 40 to 60 ° (value at 4.5 N load using Asker C hardness tester).

The surface slip coefficient H of the charging roller 2 is given by
It was measured as follows. That is, as shown in FIG. 5, one end of the charging roller 2 is fixed on the measuring table 25, and urethane rubber 26 having a thickness of 2 mm is pressed against the surface of the charging roller 2 with a load M = 0.29N. Charging roller 2 at this time
And the angle α between the surface and the urethane rubber 26 is 20 °. In this state, the measuring table 25 on which the charging roller 2 is fixed is moved in the direction of arrow B at a speed of 50 mm / min, and the force applied to the urethane rubber 26 at that time is measured by the tensile force measuring device 27.

Then, a roller having the same diameter as that of the charging roller 2 and a Mylar tape adhered to the roller surface is used as a standard sample, and the above measurement is performed for the case of the standard sample and the case of the charging roller 2. The ratio H of the measurement value H ₀ of the standard sample obtained in this measurement and the measurement value H ₁ of the charging roller 2 (= H 1 / _{H 0)} is a surface slip coefficient H of the charging roller 2. The larger the value of the surface slip coefficient H, the harder the surface of the charging roller 2 slips.

In this experiment, each of the charging rollers (charging rollers A, B, and C) shown in FIG. 6 (charging rollers A, B, and C) which were made of the same material and differed only in physical property values (hardness and surface slip coefficient) were used. Each charging roller (charging rollers A, B,
The offset force acting on C) was measured. FIG. 7 shows the measurement results.
Shown in In FIG. 7, the horizontal axis plots the deviation index F of the charging roller, and the vertical axis plots the deviation force. As described above, the charging rollers A, B, and C all had a configuration in which the surface of the elastic layer was covered with the surface layer without the interposition of an adhesive member.

The biasing force acting on the charging roller increases as the hardness R and the surface slip coefficient H increase. This is to transmit the force received from the photosensitive drum without attenuating as the hardness is higher and the surface is less slippery. Further, as will be described later, it was found that the larger the intersection angle θ and the larger the spring pressing force S of the pressure springs 23a and 23b against the charging roller 2, the larger the biasing force.

Therefore, as shown in FIG. 7, the biasing force index F of the charging roller is calculated by the equation (1).
By expressing = tan θ × S × R × H, the leaning force is proportional to the leaning force index F and can be approximated by a straight line.

Next, a durability test as described below was carried out using each of the charging rollers (charging rollers A, B, and C).

(Experiment 1) In this experiment, using the image forming apparatus shown in FIG. 1, 5000 sheets of A4-size paper (transfer material) were used in a normal temperature and normal humidity environment of 25 ° C. and 40% humidity. A continuous durability test was performed. FIG. 8 shows the result. In this experiment, when the charging roller A was used and the intersection angle θ between the rotation axis of the photosensitive drum 1 and the rotation axis of the charging roller A and the spring pressure S of the pressure springs 23a and 23b were changed. Next, whether or not the bearing of the charging roller A (one bearing 22a on which the biasing force shown in FIGS. 3 and 4 acts) was damaged was evaluated by ○.

As is apparent from the test results, the larger the intersection angle θ between the rotation axis of the photosensitive drum 1 and the rotation axis of the charging roller A, the larger the shift force index F becomes. The larger the spring pressure S, the larger the deviation force index F.

As is clear from this durability test, when the crossing angle θ = 0.50 ° and the spring pressing force S = 8.0N, the bearing has a deviation force index F = 10.9 (shown in FIGS. 3 and 4). One of the bearings 22a) on which the biasing force acts is broken. this is,
It is considered that because the biasing force of the charging roller A was too large, a force exceeding the friction durability was applied to the bearing 22a, and the bearing 22a was damaged due to durability. Because the bearing 22a was damaged,
The charging roller A moved beyond the predetermined width in a direction to receive the biasing force, and a defective charging portion was formed on the opposite side, and an image defect occurred at that portion.

In Experiment 1, the charging roller A
When the maximum deviation index F for preventing the bearing of the charging roller A from being damaged was examined by changing the hardness R and the surface slip coefficient H, the deviation index F was 9.4.

(Experiment 2) In this experiment, 5,000 sheets of A4 size paper (transfer material) were used in an image forming apparatus shown in FIG. 1 under a normal temperature and normal humidity environment of a temperature of 25 ° C. and a humidity of 40%. A continuous durability test was performed. FIG. 9 shows the result. In this experiment, when the charging roller B was used and the intersection angle θ between the rotation axis of the photosensitive drum 1 and the rotation axis of the charging roller B and the spring pressure S of the pressure springs 23a and 23b were changed. Then, whether or not the surface of the charging roller B was rubbed against the photosensitive drum 1 was evaluated by ×.

As is clear from the durability test, when the crossing angle θ = 0.50 ° and the spring pressing force S = 9.5N, the surface of the charging roller B was rubbed and damaged with a deviation force index F = 9.74. . This is because, because the biasing force of the charging roller B is too large, a force exceeding the friction durability is applied to the surface of the charging roller B, and the surface layer on the surface of the charging roller B is broken due to the endurance by rubbing against the photosensitive drum 1 and twisting. it is conceivable that.

The damaged portion of the surface layer on the surface of the charging roller B is a scratch that can be visually confirmed, and charging failure occurs at that portion, resulting in black stripes on the image.

In Experiment 2, the charging roller B
When the maximum deviation index F for preventing the surface of the charging roller B from being damaged was examined by changing the hardness R and the surface slip coefficient H, the deviation index F was 9.4.

(Experiment 3) In this experiment, using the image forming apparatus shown in FIG. 1, 5000 sheets of A4 size paper (transfer material) were used in a normal temperature and normal humidity environment of 25 ° C. and 40% humidity. A continuous durability test was performed. FIG. 10 shows the result. In this experiment, when the charging roller C was used and the intersection angle θ between the rotation axis of the photosensitive drum 1 and the rotation axis of the charging roller C and the spring pressure S of the pressure springs 23a and 23b were changed. Next, whether or not the charging roller C moved to a desired position due to a biasing force acting on the charging roller C was evaluated by ×.

As is clear from the durability test, when the intersection angle θ = 0.10 °, the spring pressing force S = 3.5N and 5.0.
At N, the charging roller B did not move to the desired position with the deviation force index F = 0.46 and 0.66. This is because the biasing force of the charging roller C is too small.

As described above, the deviation index F of the charging roller C
However, below this value (0.66), the charging roller C did not move to the desired position.

In Experiment 3, the charging roller C
When the minimum deviation index F for moving the charging roller C to a desired position was examined by changing the hardness R and the surface slip coefficient H, the deviation index F = 0.8.

From the experimental results described above, in the present embodiment, the problem caused by the above-described biasing force is prevented by setting the biasing force index F of the charging roller 2 in the range of 0.8 <F <9.4. Thus, the biasing force in the direction of arrow A with respect to the charging roller 2 shown in FIG.

As described above, in the present embodiment, by setting the deviation force index F of the charging roller 2 in the range of 0.8 <F <9.4, an appropriate deviation force can be applied to the charging roller 2. Therefore, damage to the bearing of the charging roller 2 (one of the bearings 22a on which the biasing force acts as shown in FIGS. 3 and 4), damage to the charging roller 2 due to friction with the photosensitive drum 1,
It is possible to move the charging roller 2 to a desired position by preventing the charging roller 2 from moving poorly.

Therefore, in the charging area where the charging roller 2 and the photosensitive drum are in contact with each other, it is possible to maintain a stable charging width for a long period of time and perform good image formation.

<Embodiment 2> In the present embodiment, FIG.
As shown in FIG. 1, the photosensitive drum 1 in the first embodiment,
The charging roller 2, the developing device 3, and the cleaning device 5 are integrated into a cartridge to form a process cartridge 31.
And can be detachably attached to the image forming apparatus main body 30 shown in FIG. Also in the present embodiment, as described in the first embodiment, the biasing force index F of the charging roller 2 is set in the range of 0.8 <F <9.4. Other configurations and image operations are the same as those in the first embodiment, and a description thereof will be omitted in the present embodiment.

As described above, in this embodiment, in addition to the effects obtained in the first embodiment, the process cartridge 31
The replacement of the photosensitive drum 1, the charging roller 2, the developing device 3, and the cleaning device 5 can be easily and integrally performed by attachment and detachment, so that the maintainability of the image forming apparatus is remarkably improved. By exchanging, the photosensitive drum 1, the charging roller 2, the developing device 3, and the cleaning device 5 can be exchanged for a new one, so that good image formation can always be performed stably.

[0070]

As described above, according to the present invention, the rotation axis of the image bearing member and the rotation axis of the contact charging member have a predetermined intersection angle of θ (°), and the image bearing of the contact charging means by the pressing means. The pressure applied to the body is S (N), and the hardness of the contact charging member is R
(°), when the surface slip coefficient of the contact charging member is H,
By setting the deviation index F of the contact charging member represented by F = tan θ × S × R × H in the range of 0.8 <F <9.4, an appropriate deviation force acts on the contact charging member. Then, the contact charging member moves to a desired position and abuts on the image carrier, thereby maintaining a stable charging width for a long period of time in a charging area where the contact charging member and the image carrier abut, thereby obtaining a good image. The formation can take place.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a photosensitive drum and a charging roller of the image forming apparatus according to the first embodiment.

FIG. 3 is a schematic diagram illustrating a photosensitive drum having a crossing angle and a charging roller of the image forming apparatus according to the first embodiment.

FIG. 4 is a schematic diagram illustrating measurement of a photosensitive drum having an intersection angle and a charging roller biasing force of a charging roller in the image forming apparatus according to the first embodiment.

FIG. 5 is a schematic diagram illustrating measurement of a charging roller surface slip coefficient of a photosensitive drum having a crossing angle and a charging roller in the image forming apparatus according to the first embodiment.

FIG. 6 is a diagram showing hardness and surface slip coefficient of a charging roller used in an experiment in the first embodiment.

FIG. 7 is a diagram illustrating a relationship between a charging roller shift force index and a charging roller shift force according to the first embodiment.

FIG. 8 is a diagram showing a result of an endurance test of Experiment 1 in Embodiment 1.

FIG. 9 is a diagram showing a result of an endurance test of Experiment 2 in Embodiment 1.

FIG. 10 is a diagram showing a result of an endurance test of Experiment 3 in Embodiment 1.

FIG. 11 is a schematic configuration diagram showing a process cartridge according to a second embodiment of the present invention.

FIG. 12 is a schematic configuration diagram showing an image forming apparatus in a conventional example.

FIG. 13 is a schematic diagram illustrating a photosensitive drum and a charging roller having no crossing angle of an image forming apparatus in a conventional example.

FIG. 14 is a schematic diagram showing a photosensitive drum having a crossing angle and a charging roller of an image forming apparatus in a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum (image carrier) 2 charging roller (contact charging member) 3 developing device 4 transfer roller 5 cleaning device 6 exposing device 8 fixing device 9 charging bias power supply 11 developing sleeve 20 image forming device 21 core metal 22a, 22b bearing 23a , 23b Pressurizing spring (pressurizing means) 24 Pressure gauge 27 Tensile force measuring instrument 30 Image forming apparatus main body 31 Process cartridge

Claims (6)

[Claims] 1. A rotatable image carrier and a rotatable contact charging member which is brought into contact with said image carrier by a pressing means at a predetermined pressure and charges said image carrier by applying a charging bias. The rotation axis of the contact charging member is in contact with the rotation axis of the image carrier at a predetermined crossing angle, and the contact charging member is driven to rotate by the rotation of the image carrier, and rotates during rotation. An image forming apparatus in which the contact charging member is brought into contact with the image carrier in a state in which the contact charging member exerts a biasing force in one direction of the rotation axis by a force generated by the crossing angle, wherein the crossing angle is θ (°). When the pressing force of the contact charging means to the image carrier by the pressing means is S (N), the hardness of the contact charging member is R (°), and the surface slip coefficient of the contact charging member is H , F = tan θ × S The deviation index F of the contact charging member represented by × R × H is 0.8 <
An image forming apparatus, wherein F is set in a range of 9.4. 2. The contact charging member has a conductive elastic layer on the surface of a conductive support, and a thin resistive layer is coated on the outer peripheral surface thereof without using an adhesive member. The image forming apparatus according to claim 1, wherein: 3. The image forming apparatus according to claim 1, wherein the intersection angle θ is set in a range of 0 <θ <5 °. 4. A rotatable image carrier, and a rotatable contact charging member which is brought into contact with said image carrier at a predetermined pressure by a pressing means and charges said image carrier by applying a charging bias. At least the image forming apparatus is detachable from the image forming apparatus, and the rotation axis of the contact charging member contacts the rotation axis of the image carrier at a predetermined crossing angle, and the contact charging member is attached to the image carrier. A process in which the contact charging member is brought into contact with the image carrier in a state in which the contact charging member exerts a biasing force in one direction of its rotation axis by a force generated by the crossing angle at the time of rotation. In the cartridge, the crossing angle is θ (°), the pressing force of the contact charging unit to the image carrier by the pressing unit is S (N), the hardness of the contact charging member is R (°), When the surface slip factor of the charging member was H, F = tanθ × S × deviation force index F of the contact charging member represented by R × H 0.8 <
A process cartridge wherein F <9.4 is set. 5. The contact charging member has a conductive elastic layer on the surface of a conductive support, and further has an outer peripheral surface covered with a thin resistive layer without an interposition of an adhesive member. The process cartridge according to claim 4, wherein: 6. The process cartridge according to claim 4, wherein the intersection angle θ is set in a range of 0 <θ <5 °.