JP2000206762A - Charging roller, process cartridge and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent charging noise from being produced in the case of charging an electrophotographic photoreceptor in a state where an charging roller abuts on the surface of the electrophotogrpahic photoreceptor. SOLUTION: The charging noise is prevented by using a crown-shaped charging roller 2 satisfying D2-(D1+D3)/2<=60 μm and (E1+E3)/2-E2>=10 μm when it is assumed that the deflection of the outer peripheral surface of the roller 2 with respect to the surface of the photoreceptor is <=150 μm, and further the outside diameter on either end side in the longitudinal direction of the roller 2 is D1 (μm), the outside diameter at the center part in the longitudinal direction of the roller 2 is D2 (μm), the outside diameter on the other end side in the longitudinal direction of the roller 2 is D3 (μm), the distance from a straight measurement reference 30 arranged separately from the outer peripheral surface of the roller 2 nearly in parallel therewith along the longitudinal direction of the roller 2 is E1 (μm) at the part D1, E2 (μm) at the part D2 and E3 (μm) at the part D3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging roller for contacting the surface of an image carrier and charging the surface of the image carrier to a predetermined potential, a process cartridge provided with the charging roller, and the charging roller. And an image forming apparatus having the same.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic system, for example, a contact charging type charging member is used as a charging means for charging an electrophotographic photosensitive member. Such contact charging has advantages such as the ability to use a lower applied voltage and extremely low generation of ozone, as compared with a corona charging device. For example, image forming such as an electrophotographic copying machine, a laser beam printer, an electrostatic recording device, etc. In a forming apparatus, it is practically used as a charging unit for a chargeable member such as an image carrier such as an electrophotographic photosensitive member and an electrostatic recording dielectric and other transfer materials.

As shown in FIG. 7, for example, as shown in FIG. 7, a contact charging member (hereinafter referred to as a charging roller) 200 having a roller body in general is brought into contact with an electrophotographic photosensitive member 100 in the form of a drum. The surface of the electrophotographic photosensitive member 100 is charged to a required polarity and potential (including static elimination, the same applies hereinafter) by applying a charging bias from a bias power source 206 to the bias power source 200.

The charging roller 200 has a base metal roller 201 (conductive rubber layer) made of a solid low-resistance elastic member and formed concentrically around a metal rod 201 as a conductive material. The outer peripheral surface of the rubber roller layer 202 may be formed as one or a plurality of coating layers, for example, by thinly coating a medium resistance or high resistance rubber material.
Is formed.

Further, both ends of the core 201 of the charging roller 200 are rotatably held by bearings 204, respectively, and the bearings 204 are urged in the direction of the electrophotographic photosensitive member 100 by pressing springs 205 to thereby charge the charging roller 200. To the electrophotographic photoreceptor 100
Are pressed against each other with a predetermined pressing force. The charging roller 200 rotates following the rotation of the electrophotographic photosensitive member 100. The application of the charging bias from the bias power source 206 to the charging roller 200 is performed by the pressing spring 205, the bearing 204,
This is performed via the cored bar 201.

[0006] From the bias power source 206, the charging roller 200
There are two types of charging bias application: a DC application method that uses only a DC voltage, and an AC application method that applies an oscillating voltage (a voltage whose voltage value changes periodically with time) due to superposition of a DC voltage and an AC voltage. is there.

[0007] In the AC application method, for example,
As described in Japanese Patent No. 49669, charging is performed by applying to the charging roller 200 a vibration voltage having a peak-to-peak voltage that is twice or more the charging start voltage of the electrophotographic photosensitive member 100 when a DC voltage is applied. Thereby, a uniform charging process can be performed, which is effective.

[0008]

The above-mentioned A
In the C application method, it is necessary to increase the frequency of the AC bias in order to obtain a uniform charged surface even if the rotation speed of the electrophotographic photosensitive member 100 is increased in order to increase the efficiency of image formation. Is exceeded, so-called charging noise caused by vibration of the electrophotographic photosensitive member 100 and the charging roller 200 increases.

That is, when an AC voltage is applied to the charging roller 200, an electrostatic force acts between the electrophotographic photosensitive member 100 and the charging roller 200. Attraction force increases, and in the middle, this force decreases.

Since the charging roller 200 is formed of an elastic member, the charging roller 200 is elastically deformed and attracted to the electrophotographic photosensitive member 100 when the above-mentioned attracting force is strong. As a result, the charging roller 200 tries to move away from the electrophotographic photosensitive member 100. Therefore, both vibrate at twice the frequency of the applied AC voltage.

Further, the charging roller 200 rotates while rubbing between the charging roller 200 and the electrophotographic photosensitive member 100. The vibration of the charging roller 200 causes the charging roller 200 to abut on the electrophotographic photosensitive member 100 as described above. Changes, the frictional force between the two fluctuates in response to the change, and vibration due to stick-slip occurs. In this case as well, as in the case described above, the vibration occurs at twice the frequency of the applied AC voltage.

The charging noise generated by the above-described causes is generated directly from the contact portion between the electrophotographic photosensitive member 100 and the charging roller 200.
In the case of a so-called cartridge type device in which a plurality of members such as a developing device and a cleaning device arranged around the image forming member are integrally formed, the vibration of the electrophotographic photosensitive member 100 causes the process cartridge or other image forming device to receive the vibration. In some cases, the sound is transmitted to members and converted to those sounds.

In order to reduce the charging noise as described above, an anti-vibration material is provided inside the electrophotographic photosensitive member 100, an appropriate member is press-fitted, or an aluminum cylinder which is a core of the electrophotographic photosensitive member 100 is used. From a normal 1 mm thickness to 3
Means such as a thickness of about mm or more have been proposed.

However, in a configuration in which an anti-vibration member is provided inside or an appropriate member is press-fitted, the electrophotographic photosensitive member 1
00 may be caused, and when the core of the electrophotographic photosensitive member 100 is thickened, the weight increases and the cost increases.

Means have been proposed in which the electrophotographic photoreceptor 100 is made of a solid material such as a resin and has the same effect as that of mounting a vibration damping material. Doing so adds weight and increases cost.

Accordingly, the present invention provides a charging roller, a process cartridge, and an image forming apparatus capable of preventing the generation of charging noise when charging the electrophotographic photosensitive member by contacting the charging roller. The purpose is.

[0017]

In order to achieve the above object, a rotatable charging roller for contacting the surface of an image carrier and charging the surface of the image carrier to a predetermined potential is provided.
The deflection of the outer peripheral surface of the charging roller in the axial direction of the charging roller is 150 μm or less, the outer diameter at _one end of the charging roller in the longitudinal direction is D ₁ , and the center of the charging roller in the longitudinal direction is D ₁ . The outer diameter of the charging roller is D ₂ , and the outer diameter of the other end of the charging roller in the longitudinal direction is D _3. the distance from the arranged straight metrics, the D ₁ part E _1, wherein D ₂ part E _2, the D
When the E _{3 3 moiety, D 2 - (D 1 +} D 3) / 2 ≦
60 (μm) and (E ₁ + E ₃ ) / 2−E ₂
It is characterized by a crown shape satisfying ≧ 10 (μm).

The charging roller includes a rotatable conductive shaft member, a conductive elastic layer formed along the longitudinal direction around the shaft member, and a conductive elastic layer formed along the longitudinal direction around the elastic layer. And a resistance layer formed along the shaft, wherein the shaft member is formed of metal, and the elastic layer is formed of a conductive foam member.

Further, the invention is characterized in that a charging bias voltage in which an AC voltage is superimposed on a DC voltage is applied as the voltage applied to the charging roller.

A process cartridge which includes at least an electrophotographic photosensitive member and a charging roller for contacting the surface of the electrophotographic photosensitive member and charging the surface to a predetermined potential, wherein the process cartridge is detachable from an image forming apparatus. The charging roller is the charging roller according to claim 1, 2 or 3.

Further, in an image forming apparatus comprising an image carrier and a charging roller for contacting the surface of the image carrier and charging the surface to a predetermined potential, the charging roller is
A charging roller according to claim 1, 2 or 3.

[0022]

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

<First Embodiment> FIG. 1 is a schematic structural view showing an image forming apparatus according to the present embodiment. The image forming apparatus according to the present embodiment is an electrophotographic laser beam printer or copier, and uses a charging roller that is a roller-type contact charging unit as a charging unit for the image carrier.

This image forming apparatus includes a drum-shaped electrophotographic photosensitive member (hereinafter, referred to as a photosensitive member) 1 as an image carrier, and a charging roller 2 as a contact charging means, a developing device 3 and a transfer roller 4 around the photosensitive member. , A cleaning device 5 and the like.

In the present embodiment, the photosensitive member 1 is a negatively charged organic photosensitive member, has a photosensitive layer on a drum substrate made of aluminum, and is driven to rotate at a predetermined process speed in the direction of arrow a.

The charging roller 2 is a primary charging means for uniformly charging the peripheral surface of the photoreceptor 1 to a predetermined polarity and potential. Both ends of the roller-shaped core 8 are movable bearings 7. The bearing 7 is rotatably held by the
, The charging roller 2 is pressed against the photosensitive member 1 with a predetermined pressing force, and the charging roller 2 is driven to rotate in the direction of the arrow c with the rotation of the photosensitive member 1 (the charging roller 2). Will be described later in detail).

The charging roller 2 has a charging bias power source 10
Are connected to each other, and a predetermined bias voltage is applied to the charging roller 2 from the charging bias power supply 10 (in the present embodiment,
Oscillating voltage which superimposed AC voltage on DC voltage)
The photoreceptor 1 is charged to a predetermined polarity and potential.

The developing device 3 has a developing sleeve 11 which is driven to rotate in the direction of arrow b. A predetermined developing bias voltage is applied to the developing sleeve 11 from a developing bias power supply 13. The developing device 3 includes a developing sleeve 11.
An elastic blade 12 for regulating the coat thickness of the toner carried thereon is provided.

The transfer roller 5 rotates while being pressed against the surface of the photoreceptor 1, and a predetermined transfer bias voltage is applied from a transfer bias power supply 14.

The cleaning device 5 includes a cleaning blade 15 supported by a support member 16 for scraping off transfer residual toner remaining on the surface of the photoreceptor 1, and a squeeze sheet 17 for collecting scraped transfer residual toner and the like. Have been.

In the image forming apparatus of the present embodiment,
The four process devices of the photoreceptor 1, the charging roller 2, the developing device 3, and the cleaning device 5 are integrated into a process cartridge 19 that can be detachably attached to an image forming apparatus main body (not shown). Reference numeral 18 denotes a cartridge housing in which the above four process devices (photoconductor 1, charging roller 2, developing device 3, and cleaning device 5) are installed in a predetermined arrangement.

As described above, in the image forming apparatus of the present embodiment, the process cartridge 1 is attached to the image forming apparatus main body.
When the cartridge 9 is mounted in a predetermined state, the process cartridge 19 and the image forming apparatus main body are mechanically and electrically coupled to each other, and the lower surface of the photoconductor 1 on the process cartridge 19 side is connected to the image forming apparatus main body. The transfer roller 10 is brought into contact with the transfer roller 10 in a predetermined manner, and the image formation is enabled.

The process cartridge includes at least one of a charging unit (charging roller 2), a developing unit (developing device 3), and a cleaning unit (cleaning device 5) and an electrophotographic photosensitive member (photosensitive member 1). A cartridge which can be attached to and detached from the image forming apparatus main body.

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

At the time of image formation, the photosensitive member 1 is rotationally driven at a predetermined process speed in the direction of arrow a by a driving means (not shown). At this time, a bias voltage obtained by superimposing a DC voltage on an AC voltage is applied to the charging roller 2 from the charging bias power supply 10 to charge the surface of the photoconductor 1 to a negative polarity.

Then, an image exposure L by a laser beam is given to the charged surface of the photoreceptor 1 from an exposure device (not shown), and the electrostatic charge in the form of removing the charge of the image portion in accordance with the input image information. A latent image is formed. The electrostatic latent image formed on the surface of the photoreceptor 1 is negatively charged with the same polarity as that of the electrostatic latent image by a reversal developing method in a developing device 3 from a developing sleeve 11 and is developed as a toner image. You.

When the toner image on the surface of the photosensitive member 1 reaches the transfer nip portion between the transfer roller 4 and the photosensitive member 1, a transfer material P such as paper is conveyed to the transfer nip portion at this timing, and is transferred. The transfer roller 4 to which the transfer bias voltage (DC voltage) is applied from the bias power supply 14 applies a positive charge to the back side of the transfer material P, and the toner image on the surface of the photoconductor 1 is transferred to the front side. The transfer material P on which the toner image has been transferred is conveyed to a fixing device (not shown), and the toner image is fixed as a fixed image on the transfer material P by pressure and heating by the fixing device (not shown), and is discharged.

On the other hand, the untransferred toner remaining on the photoreceptor 1 after the above-mentioned transfer is scraped off by the cleaning blade 15 of the cleaning device 5, and is repeatedly used for image formation. The scraped transfer residual toner etc.
Collected at 7 and collected.

Next, the configuration of the charging roller 2 according to the present embodiment will be described in detail. FIG. 2 is a vertical sectional view of the charging roller 2.

The core 8 of the charging roller 2 of the present embodiment is
An iron shaft having a diameter of 8 mm and a length of 354 mm, a conductive sponge layer 21 which is a concentrically foamed layer is formed around the shaft, and a plurality of resistance layers 22 are formed on the outer peripheral surface of the conductive sponge layer 21. , 23 are formed to have an effective length of 311 mm and a diameter of 14 mm.

The photosensitive member 1 contacting the charging roller 2 has a photosensitive layer formed on the outer peripheral surface of an aluminum hollow cylindrical drum base having a length of 357.5 mm, an inner diameter of 28.5 mm, and an outer diameter of 29.92 mm. A mold gear (not shown) is attached to both ends of the cylinder so as to close the cylinder, and a shaft (not shown) having a diameter of 7 mm fixed to the cartridge housing 18 penetrates the center of the gear. At least at the time of image formation, a core bar 8, which is the axis of the charging roller 2, is pressed against the photoreceptor 1 by a pressure spring 9 at 500 to 1000 g to bring the charging roller 2 into contact with the photosensitive drum 1, and is charged via the core bar 8. A charging bias voltage is applied from a bias power supply 10 to charge the photoconductor 1.

The conductive sponge layer 21 of the charging roller 2
It is formed in a crown shape in which both ends are smaller in diameter than the center portion in the longitudinal direction of the roller. The crown amount is 60 μm or less, and the runout of the core metal 8 on the roller surface in the longitudinal direction is 15 mm.
The thickness is set to 0 μm or less.

Here, a method of measuring the runout of the surface of the charging roller 2 and the crown amount will be described.

FIG. 3 is a diagram showing a method of measuring the deflection of the core 8 on the surface of the charging roller 2 in the longitudinal direction.
With reference to the AB surface in the drawing of the front surface, three points of 115 mm each are measured from the center in the longitudinal direction of the surface of the charging roller 2 and both ends from the center. Here, the maximum value of the three measured values is defined as the roller runout.

FIG. 4 is a diagram showing a method of measuring the crown amount of the charging roller 2, wherein the crown amount D is represented by D = (D ₂ −
(D ₁ + D ₃ ) / 2) and the charging roller 2
The distance E from the straight measurement reference 30 corresponding to
It was defined as _{(E 1 + E 3) /} 2-E 2. These measurements were performed as shown in FIG.
8 locations. Note that the measurement reference 30 is arranged substantially parallel to the cored bar 8 along the longitudinal direction of the cored bar 8 apart from the outer peripheral surface of the charging roller 2.

FIG. 6 shows the charging sound and the audibility judgment when the deflection and the crown amount of the charging roller 2 are set to be different in Examples 1 to 4 of the present embodiment and Comparative Examples 1 to 3, respectively. These are evaluation results.

The measurement of the charging noise is performed by a dedicated device in order to eliminate the influence of the driving noise of the image forming apparatus, and a microphone is installed at a position 30 cm from the contact surface between the charging roller 2 and the photosensitive member 1. Was. Note that the ripple in this figure is the amplitude of the sound pressure, and the sound pressure is the center value of the amplitude of the charging sound. In FIG. 6, the measured value of the charging noise is a value measured when a pressing force of about 600 g is applied to both ends of the cored bar 8 of the charging roller 2. "X", sound that does not cause discomfort was marked "O".

As is clear from the results shown in FIG. 6, the audibility is related to the magnitude of the ripple rather than the magnitude of the sound pressure (average value). This is because the ripple gives an unpleasant sensation as a sound undulation, and when actually driven in the image forming apparatus, the charging sound undulation is distinguished from other driving sounds to make the charging sound stand out.

Further, with respect to the charging roller 2 of Comparative Example 2,
When 800 g of pressing force is applied to both ends of the core bar 8, the ripple of the charging noise is reduced to about 4 dB, and when 1000 g is added, the ripple of the charging noise is reduced to about 3 dB. Was.

However, when 1000 g of pressing force was applied to both ends of the cored bar 8 to the charging roller 2 of Comparative Example 1, the ripple of the charging noise was about 4.5 dB, which was a sound accompanied by discomfort. there were.

If the pressing force on both ends of the core bar 8 is excessively large, there is a possibility that the frictional force between the core bar 8 of the charging roller 2 and the bearing 7 is increased, thereby increasing the torque. The generation of abrasion powder also increases, which may cause a further increase in torque.

If the crown amount D in the drawing is too large, it is necessary to increase the pressing force for contacting the entire region in the longitudinal direction to which the crown should originally contact, which may increase the torque as described above. There is. On the other hand, if the crown amount D is excessively large, stick-slip is likely to occur near the center in the longitudinal direction, which causes an increase in charging noise.

As described above, from the results of FIG. 6, the fluctuation of the outer peripheral surface of the charging roller 2 with respect to the longitudinal direction of the
m, preferably 148 μm or less, and the crown shape of the charging roller 2 is set to the above-mentioned D (= D ₂ − (D ₁
+ D ₃ ) / 2) is 60 μm or less, preferably 58 μm.
m and the above E (= (E ₁ + E ₃ ) /
By setting the value of 2-E ₂ ) to 10 μm or more, preferably 11 μm or more, the gap between the charging roller 2 and the surface of the photoreceptor 1 is substantially eliminated, so that the ripple of charging noise is reduced and charging is performed. The discomfort caused by the sound could be eliminated, and when incorporated in the image forming apparatus, the charging noise could be almost eliminated.

In the above-described embodiment, the longitudinal dimension of the contact surface of the charging roller 2 has been described as 311 mm covering the width of 297 mm of A3 paper.
It is also applicable to process cartridges and charging rollers.

Further, in the case of a long charging roller, it is particularly effective to average the contact pressure between the photosensitive member and the charging roller when both ends are pressed, in the longitudinal direction as much as possible.

In the above-described embodiment, the image forming apparatus of the process cartridge type has been described. However, it is needless to say that the present invention can be similarly applied to other image forming apparatuses regardless of the process cartridge type.

[0057]

As described above, according to the present invention, the charging roller which comes into contact with the surface of the image carrier can be brought into contact with the longitudinal direction of the image carrier at a substantially uniform pressure without any gap. The charging noise generated in the case of the conventional charging roller can be prevented without providing a vibration isolating member on the image carrier.

Further, since it is not necessary to provide an anti-vibration member or the like for preventing charging noise, the cost of the process cartridge or the image forming apparatus can be reduced and the assembling property can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an image forming apparatus provided with a charging roller according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view showing a charging roller according to the embodiment of the present invention.

FIG. 3 is a view for explaining a method of measuring a deflection of a charging roller.

FIG. 4 is a diagram for explaining a method of measuring a crown amount of a charging roller.

FIG. 5 is a diagram for explaining a position for measuring a crown amount of a charging roller.

FIG. 6 is a diagram showing the evaluation results of charging noise and audibility determination when the deflection and crown amount of the charging roller are set to be different from each other.

FIG. 7 is a longitudinal sectional view showing a charging roller in a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor (image carrier) 2 charging roller 3 developing device 4 transfer roller 5 cleaning device 7 bearing 8 core metal (shaft member) 9 pressurizing spring 10 charging bias power supply 11 developing sleeve 12 elastic blade 13 developing bias power supply 14 transfer bias Power supply 15 Cleaning blade 18 Cartridge housing 19 Process cartridge 21 Conductive sponge layer (elastic layer) 22, 23 Resistance layer

Claims (5)

[Claims] 1. A rotatable charging roller for abutting against the surface of an image carrier and charging the surface of the image carrier to a predetermined potential, wherein a fluctuation of an outer peripheral surface of the charging roller in an axial direction of the charging roller is provided. , 150 μm or less, and the outer diameter at _one end side in the longitudinal direction of the charging roller is D ₁ , the outer diameter at the central portion in the longitudinal direction of the charging roller is D ₂ , the longitudinal direction of the charging roller is The outer diameter at the other end of the charging roller is defined as D _3, and the distance from a straight measurement reference that is disposed substantially parallel to the charging roller outer peripheral surface along the longitudinal direction of the charging roller is referred to as D _3. E ₁ in _one part, D
E ₂ in _two parts, when the E ₃ in the D _{3 moiety, D 2 - (D 1 +} D 3) / 2 ≦ 60 satisfies ([mu] m), and _{(E 1 + E 3) /} 2-E 2 ≧ A charging roller having a crown shape that satisfies 10 μm. 2. The charging roller comprises: a rotatable conductive shaft member; a conductive elastic layer formed along a longitudinal direction around the shaft member; and a conductive elastic layer formed along a longitudinal direction around the elastic layer. The charging roller according to claim 1, further comprising: a resistance layer formed along the shaft, wherein the shaft member is formed of metal, and the elastic layer is formed of a conductive foam member. 3. The charging roller according to claim 1, wherein a charging bias voltage in which an AC voltage is superimposed on a DC voltage is applied as the voltage applied to the charging roller. 4. A process cartridge comprising at least an electrophotographic photosensitive member and a charging roller for abutting on the surface of the electrophotographic photosensitive member and charging the surface to a predetermined potential, wherein the process cartridge is detachable from an image forming apparatus. The process cartridge according to claim 1, wherein the charging roller is the charging roller according to claim 1. 5. An image forming apparatus comprising: an image carrier; and a charging roller that contacts the surface of the image carrier and charges the surface to a predetermined potential. 4. An image forming apparatus, comprising: the charging roller according to 2 or 3.