JP2004069780A - Image forming apparatus and process cartridge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which suppresses scraping due to rubbing of a charging member and an image carrier and prolongs the service life of the image carrier and to provide a process cartridge. <P>SOLUTION: A magnetic brush charger 3 is disposed on the downstream side from a charging roller 2 in the rotating direction of a photosensitive drum 1, comes into contact with the drum 1 and electrifies the drum 1. The magnetic brush charger 3 rotates for at least a definite period of time when an image is not formed with a smaller difference in circumferential speeds than a prescribed difference in circumferential speeds between the charger 3 and the drum 1 in image formation. The distance in which the drum 1 is rubbed by magnetic particles is thereby shortened and scraping of the drum can be suppressed. <P>COPYRIGHT: (C)2004,JPO

Description

【００６０】
表１から、帯電スリーブ３３の周速差を極力小さくし、帯電用磁性粒子３４と感光ドラム１との摺擦を極力減らすことによって、磁性粒子によるドラム削れを低減できることがわかった。特に、画像形成の前後回転の総数が多くなる少量画像出力時において大きな効果が得られた。
【００６１】
（第２の実施の形態）
本実施の形態は、上記第１の実施の形態の電子写真複写機において、画像形成の前後回転時に帯電スリーブ３３を回転させずに停止させ、フローティングスイッチ４３を切断したものであり、その構成を図２，図５に示す。
【００６２】
ここで、磁気ブラシ帯電器３を電気的にフロート状態にした時の効果を説明する。
【００６３】
例えば、図２のように感光ドラム１に対して帯電ローラ２および磁気ブラシ帯電器３を配置し、バイアス装置４１，４２を接続した場合、バイアス装置４１および帯電ローラ２により感光ドラム１表面に帯電を施しても、バイアス装置４２の出力がオフの場合磁気ブラシ帯電器３の帯電用磁性粒子３４を介して感光ドラム１の表面電位を落としてしまう。
【００６４】
これに対して、図５のように感光ドラム１に対して帯電ローラ２および磁気ブラシ帯電器３を配置し、バイアス装置４１を接続し、フローティングスイッチ４３を切断することによって、磁気ブラシ帯電器３を電気的にフロート状態にした場合、バイアス装置４１および帯電ローラ２で帯電された感光ドラム１表面の電位は、磁気ブラシ帯電器３の帯電用磁性粒子３４と接触しても落ちることなく、保持される。
【００６５】
上記のように、磁気ブラシ帯電器３を電気的にフロート状態にすることによって、帯電ローラ２のみで感光ドラム１への帯電を実現することができる。
【００６６】
次に、（１）画像形成時、非画像形成時ともに帯電スリーブ３３が周速２００ｍｍ／ｓｅｃ（周速差５００ｍｍ／ｓｅｃ）で回転し帯電を行うモードと、（２）画像形成時は帯電スリーブ３３が周速２００ｍｍ／ｓｅｃで、非画像形成時はフローティングスイッチ４３を切断（図５参照）し、帯電スリーブ３３を停止させるモードの二つのモードについて、１０００枚連続画像出力を２０セット（１０００枚間欠）、１０枚連続画像出力を２０００セット（１０枚間欠）の、それぞれ合計２万枚の画像出力を行い、そのときの耐久前後の膜厚を測定し、ドラム表層の削れ量を調べた。
【００６７】
上記耐久時の帯電条件は第１の実施の形態と同様であり、帯電ローラ２にはバイアス装置４１によって直流電圧＋１．２ｋＶの帯電バイアスを印加した。磁気ブラシ帯電器３にはバイアス装置４２によって直流電圧＋６５０Ｖ、交流電圧３００Ｖｐｐ，１ｋＨｚの帯電バイアスを印加した。
【００６８】
表２は、非画像形成時に帯電スリーブが停止している場合について、それぞれ２万枚画像出力耐久によるドラム表層削れ量の結果を示すものである。
【００６９】
【表２】

【００７０】
表２から、帯電スリーブ３３を停止させ、帯電用磁性粒子３４と感光ドラム１との摺擦を極力減らすことによって、磁性粒子によるドラム削れを低減することができることがわかった。特に、画像形成の前後回転が多くなる少量画像出力時において大きな効果が得られ、また帯電スリーブ３３を停止させなかった第１の実施の形態よりも効果が大きいことがわかった。
【００７１】
【発明の効果】
以上説明したように、本発明による画像形成装置は、複数の帯電手段を具備し、電子写真感光体の回転方向に対して最下流の帯電手段が磁気ブラシ帯電器のような接触帯電部材である電子写真画像形成装置について、非画像形成時に感光体に対する接触帯電部材の周速差を小さくする、もしくは接触帯電部材を停止させることによって、接触帯電部材によるドラム削れの発生を低減し、感光体の寿命を延ばすことができる。
【図面の簡単な説明】
【図１】本実施の形態に係る画像形成装置の概略構成図である。
【図２】本実施の形態に係る帯電装置の概略構成図である。
【図３】ａ−Ｓｉ系感光体の層構成の一例を示した断面図である。
【図４】本実施の形態に係る画像形成装置の動作過程を説明する図である。
【図５】本実施の形態に係る帯電装置の概略構成図である。
【図６】従来例の説明に用いた画像形成装置の模式図である。
【符号の説明】
１　感光ドラム
２　帯電ローラ
３　磁気ブラシ帯電器
５　レーザー露光手段
６　現像器
７　転写装置
８　定着器
９　クリーナー
１０　前露光手段
１１　導電性支持体
１２　電荷注入阻止層
１３　光導電層
１４　表面層
１５　感光層
２１　表面層
２２　弾性体層
２３　導電性芯金
３１　磁性粒子規制手段
３２　固定マグネット
３３　帯電スリーブ
３４　磁性粒子
４１　バイアス装置
４２　バイアス装置
４３　フローティングスイッチ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus that develops an electrostatic latent image formed on an image carrier corresponding to an image to be recorded with a developer and records the image on paper or the like, and a process cartridge that can be attached to and detached from the image forming apparatus. is there.
[0002]
[Prior art]
Conventionally, many image forming apparatuses using an electrophotographic method or an electrostatic recording method have been devised. FIG. 6 is a cross-sectional configuration diagram for explaining an outline of a conventional image forming apparatus. The schematic configuration and operation will be briefly described below with reference to FIG.
[0003]
In the image forming apparatus shown in FIG. 6, when an image output start signal is input, the photosensitive drum 1 rotates, and the surface of the photosensitive drum 1 is charged by the charging roller 2 to a predetermined potential.
[0004]
Next, the charged surface of the photosensitive drum 1 is subjected to laser beam scanning exposure of the target image information by the laser exposure means 5 to form an electrostatic latent image of the target image information on the surface of the photosensitive drum 1. Is done.
[0005]
Next, the electrostatic latent image is developed by the developing device 6 containing the toner particles, and a toner image according to the electrostatic latent image is obtained on the photosensitive drum 1.
[0006]
The toner image thus formed on the photosensitive drum 1 is electrostatically transferred onto a transfer material by the transfer device 7. Thereafter, the transfer material is electrostatically separated and conveyed to the fixing device 8, where it is thermally fixed and an image is output.
[0007]
On the other hand, the surface of the photosensitive drum 1 after the transfer of the toner image is subjected to exposure by a pre-exposure unit 10 for removing adhered contaminants such as untransferred toner by a cleaner 9 and, if necessary, an optical memory for image exposure, to repeatedly form an image. Used for forming.
[0008]
As the electrophotographic photoreceptor used for the above-described image formation, an organic photoreceptor is often used, and in recent years, high surface hardness, high sensitivity to a semiconductor laser, etc., and deterioration due to repeated use have been almost recognized. For this reason, amorphous silicon photoconductors (hereinafter, referred to as “a-Si based photoconductors”) are often used.
[0009]
As a method of manufacturing the a-Si based photoreceptor, gas is converted into plasma by high frequency or microwave, solidified and deposited on an aluminum cylinder to form a film. Composition unevenness is caused.
[0010]
In addition, when an a-Si-based photoconductor is used, the potential attenuation after charging is very large even in a dark state compared to the organic photoconductor, and the potential attenuation due to the optical memory for image exposure increases. Pre-exposure means before charging for erasing is required. For this reason, the potential decay between charging and development becomes very large, and a potential decay of about 100 to 200 V occurs. At this time, potential unevenness of about 10 to 20 V may occur in the circumferential direction due to the thickness unevenness described above.
[0011]
When such potential non-uniformity occurs, the a-Si based photoreceptor having a large capacitance has a smaller contrast than the organic photoreceptor, so that it is more affected and the density non-uniformity becomes remarkable.
[0012]
To address such a problem, for example, a method of performing charging a plurality of times is effective. The increase in dark decay due to the optical memory described above can be greatly reduced by the first charging by performing a plurality of chargings, so that the dark decay can be reduced after the second charging. Accordingly, potential ghosts and potential unevenness are significantly improved.
[0013]
As a method for charging the a-Si photosensitive member, a corona charging method using corona discharge, a roller charging method in which charging is performed by direct discharge using a conductive roller, a sufficient contact area is obtained by magnetic particles, etc. There is a magnetic brush injection charging method in which charging is performed by directly injecting the photosensitive material into the surface of the photoreceptor.
[0014]
However, the corona charging method and the roller charging method use electric discharge, so that discharge products easily adhere to the surface of the photoreceptor, and in addition, the a-Si type photoreceptor has a very high surface hardness and is hard to be abraded. Discharge products attached to the body surface are likely to remain. For this reason, there is a problem that the electric charge on the surface of the photoconductor on which the electrostatic latent image is formed moves in the surface direction due to the adsorption of moisture or the like in a high humidity environment or the like, and the accompanying image deletion phenomenon easily occurs.
[0015]
On the other hand, the magnetic brush injection charging method is a charging method in which electric charges are directly injected from a portion in contact with the surface of the photoreceptor without actively using discharge, so that the phenomenon such as image deletion occurs. It has the characteristic that it is difficult to do.
[0016]
Furthermore, the magnetic brush injection charging method has good contact stability between the magnetic particles and the photoreceptor, does not generate ozone during charging, and consumes less power than the corona charging method and the roller charging method. Because of its characteristics, it is preferably used as a charging unit.
[0017]
[Problems to be solved by the invention]
However, in the above-described conventional charging method, a plurality of charging units are arranged on the photoconductor with respect to uniformity of charging of the a-Si photoconductor, and image flow and charging stability are not determined. However, a system using a magnetic brush injection charging method as the most downstream charging means for the photoreceptor is advantageous, but a contact charging method such as a magnetic brush injection charging method has a problem that the wear amount of the photoreceptor surface layer is large, In order to extend the life of the photoconductor, it is necessary to reduce friction between the charging unit and the photoconductor as much as possible.
[0018]
In particular, in a series of processes of image output, in addition to the time for forming an image on the photosensitive drum, non-image forming time such as pre-rotation for warming-up, paper interval, and post-rotation after image output is completed is not short. In order to extend the life of the photoreceptor, it is necessary to reduce as much as possible the rubbing between the charging means and the photoreceptor during the period, for example, in the magnetic brush injection charging method, the scraping between the magnetic particles and the photoreceptor is minimized. It becomes.
[0019]
SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-described problems of the related art, and has as its object to provide an image forming apparatus and a process cartridge for improving the life of an image carrier.
[0020]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention,
An image carrier on which an electrostatic latent image is formed;
A first charging unit disposed around the image carrier and charging the image carrier,
A second charging unit that is disposed downstream of the first charging unit in the rotation direction of the image carrier, and contacts and charges the image carrier.
The second charging means rotates at least for a certain period of time during non-image formation with a peripheral speed difference smaller than a predetermined peripheral speed difference that operates on the image carrier during image formation. .
[0021]
Alternatively, an image carrier on which an electrostatic latent image is formed;
A first charging unit disposed around the image carrier and charging the image carrier,
A second charging unit that is disposed downstream of the first charging unit in the rotation direction of the image carrier and contacts and charges the image carrier.
The second charging unit stops the rotation for a certain time at least during non-image formation.
[0022]
In another embodiment of the present invention,
A process cartridge detachable from an image forming apparatus that forms an image by transferring a toner image to a transfer material,
An image carrier on which an electrostatic latent image is formed;
A first charging unit disposed around the image carrier and charging the image carrier,
A second charging unit that is disposed downstream of the first charging unit in the rotation direction of the image carrier, and contacts and charges the image carrier.
The second charging means rotates at least for a certain period of time during non-image formation with a peripheral speed difference smaller than a predetermined peripheral speed difference that operates on the image carrier during image formation. .
[0023]
Alternatively, a process cartridge detachable from an image forming apparatus that forms an image by transferring a toner image to a transfer material,
An image carrier on which an electrostatic latent image is formed;
A first charging unit disposed around the image carrier and charging the image carrier,
A second charging unit that is disposed downstream of the first charging unit in the rotation direction of the image carrier, and contacts and charges the image carrier.
The second charging unit stops the rotation for a certain time at least during non-image formation.
[0024]
It is preferable that the second charging unit is a magnetic brush charger having magnetic particles.
[0025]
It is preferable that the image carrier is a layer containing amorphous silicon.
[0026]
It is preferable that the second charging unit is in an electrically floating state when a non-image is formed.
[0027]
A voltage applying unit that applies a voltage to the first charging unit and / or the second charging unit;
It is preferable that the voltage application unit applies a voltage to the first charging unit and the second charging unit during non-image creation.
[0028]
According to this configuration, at the time of image formation, a predetermined charging bias is applied to the plurality of charging units, and the contact charging member on the downstream side in the rotation direction of the image carrier has a sufficient peripheral speed difference with respect to the image carrier. The surface of the image carrier is uniformly charged by increasing the number of contact points between the charging means and the image carrier.
[0029]
On the other hand, at the time of non-image formation, that is, during the rotation period before and after image formation or between sheets, in order to prevent toner from adhering from the developing device, only the first charging unit is used to charge the surface of the image carrier at the timing of charging. The second charging means on the downstream side, for example, a contact charging means such as a magnetic brush charger, stops the charging sleeve or rotates so as to have a smaller peripheral speed difference than at the time of image formation, the charging unit Thus, the charged state of the image carrier can be maintained to some extent without lowering the potential of the surface of the image carrier, and at the same time, the amount of friction between the magnetic particles and the image carrier can be reduced, and the life of the image carrier can be improved. .
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention thereto unless otherwise specified. Absent. The materials, shapes, and the like of the members once described in the following description are the same as those in the first description unless otherwise specified.
[0031]
(First Embodiment)
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention. The image forming apparatus of the present embodiment is a double charging type electrophotographic copying machine using a transfer type electrophotographic process and using a roller charger and a magnetic brush charger as a charging unit. This is a configuration similar to that of FIG. The developing system was a two-component contact developing system, and an LED having a wavelength of 660 nm was used as a pre-exposure unit.
[0032]
FIG. 2 is a diagram schematically illustrating a charging process portion of the image forming apparatus according to the present embodiment. In the present embodiment, a conductive charging roller 2 is used as a first charging unit and an injection charging type magnetic brush charger 3 is used as a second charging unit for an a-Si photosensitive drum 1 having a diameter of 80 mm. Using.
[0033]
FIG. 3 is a schematic cross-sectional view showing the layer structure of the positively chargeable a-Si photosensitive member used in the present embodiment.
[0034]
The a-Si-based photoconductor shown in FIG. 3 includes a conductive support 11 made of Al or the like, and a photosensitive layer 15 (a charge injection blocking layer 12 and a photoconductive layer) sequentially deposited on the surface of the conductive support 11. The photoconductive layer 13) shown in FIG. Here, the charge injection blocking layer 12 is for preventing charge injection from the conductive support 11 to the photoconductive layer 13, and is provided as necessary. The photoconductive layer 13 is made of an amorphous material containing at least silicon atoms, and has photoconductivity. Further, the surface layer 14 contains silicon atoms and carbon atoms (and, if necessary, hydrogen atoms and / or halogen atoms) and has a capability of retaining a latent image in an electrophotographic apparatus.
[0035]
The magnetic brush charger 3 used in the present embodiment has a fixed magnet 32 provided therein, and a charging magnetic particle 34 regulated by the magnetic particle regulating means 31 is provided on a rotatable non-magnetic charging sleeve 33. The magnetic particles 34 are formed in a brush shape by a magnetic field, and the charging magnetic particles 34 are transported as the charging sleeve 33 rotates.
[0036]
The charging sleeve 33 rotates in the counter direction with respect to the photosensitive drum 1, and during image formation, the rotating speed of the photosensitive drum 1 is 300 mm / sec and the charging sleeve 33 is rotating at 200 mm / sec. By applying a charging voltage to the charging sleeve 33, charges are given from the charging magnetic particles 34 onto the photosensitive drum 1 and charged to a value close to the potential corresponding to the charging voltage. Further, in order to improve the stirring property of the magnetic particles, a repulsive pole is adopted for the fixed magnet 32.
[0037]
The magnetic brush charger 3 can reduce the rubbing force and extend the life of the photoreceptor by reducing the distance between the magnetic particle regulating means 31 and the charging sleeve 33 and reducing the coating amount of the magnetic particles. At the same time, the contact point between the magnetic particles and the photoreceptor decreases, so that the charging ability of the charger also decreases. However, the decrease in the charging ability can be compensated for by performing charging a plurality of times.
[0038]
In the present embodiment, the distance between the photosensitive drum 1 and the charging sleeve 33 is set to 400 μm, and the distance between the magnetic particle regulating means 31 and the charging sleeve 33 is set to 500 μm.
[0039]
The charging magnetic particles, an average particle diameter of 10 to 100 [mu] m, a saturation magnetization 20~250emu / cm ^3, preferably it has a resistance of ^{1~10 8 Ω · m (10 2} ~10 10 Ω · cm), a photosensitive In consideration of the existence of insulation defects such as pinholes in the drum, it is preferable to use a material having a resistivity of 10 ⁴ Ω · m (10 ⁶ Ω · cm) or more.
[0040]
In order to improve the charging performance, it is better to use one having as small a resistance as possible. However, in this embodiment, the charging magnetic particles are subjected to oxidation and reduction treatment of the ferrite surface to adjust the resistance, and the average particle diameter is 25 μm. The saturation magnetization was 200 emu / cm ³ , and the resistance was 5 × 10 ⁴ Ω · m (5 × 10 ⁶ Ω · cm).
[0041]
The charging magnetic particles 34 used in this embodiment have a resistance value of 6.47 × 10 ⁵ N / m ² (6) after 2 g of the charging magnetic particles is placed in a metal cell having a bottom area of 228 mm ^3. 0.6 kg / cm ² ), and measured by applying a voltage of 100 V.
[0042]
The charging roller 2 used in the present embodiment includes a conductive core 23, an elastic layer 22, and a surface layer 21. The core metal 23 is made of iron, aluminum, stainless steel, or the like. The elastic layer 22 is formed by adding a metal oxide such as TiO ₂ or ZnO to a solid or foamed solid elastic body such as urethane, silicone rubber, EPDM (terpolymer of ethylene propylene diene), and the like. The resistivity is 10 ² to 10 ¹¹ Ω · m (10 ⁴ to 10 ¹³ Ω · cm).
[0043]
The surface layer 21 is a nylon-based resin such as resin (trade name) or a synthetic resin film made of polyethylene, polyester, fluororesin, polypropylene, or the like. It is desirable that the resistance value is larger than the resistance of the inner elastic body. As a result, even if there is a pinhole on the surface of the electrophotographic photosensitive member, current does not concentrate and flow. In the present embodiment, the charging roller 2 is used in which a surface layer of a synthetic resin film in which a nylon resin is made conductive is provided on an elastic layer in which resistance is adjusted by dispersing carbon in urethane.
[0044]
The charging roller 2 does not include a driving device, and rotates following the photosensitive drum 1 to perform charging.
[0045]
Next, an operation process of the image forming apparatus according to the present embodiment will be described with reference to FIG.
[0046]
[Previous multi-turn period]
When the main power switch of the image forming apparatus is turned on, the main motor of the image forming apparatus is driven to rotate the photosensitive drum 1, and the heater of the fixing unit 8 is energized to heat up the apparatus. This is a start-up (start-up) operation period (warming period) of the image forming apparatus in which the start-up operation is performed.
[0047]
[Standby period]
When the pre-multi-rotation period ends, the driving of the main motor is temporarily stopped, the rotation of the photosensitive drum 1 is stopped, and the image forming apparatus is kept in a standby state until an image forming start signal is input. During this time, the temperature of the fixing device 8 is adjusted to a predetermined temperature.
[0048]
[Previous rotation period]
In response to the input of the image formation start signal, the main motor is driven again to rotate the photosensitive drum 1 again, and the image forming apparatus performs a predetermined pre-image forming operation for a while.
[0049]
[Previous multi-rotation period]
If the image formation start signal has already been input at the end point, the process shifts to the pre-rotation period without the standby period.
[0050]
[Image formation period]
When the predetermined pre-rotation period is completed, an image forming process (image forming process) of a predetermined sequence of charging, image exposure, development, transfer, and the like for the rotating photosensitive drum is subsequently performed, and the first image forming (printing) is performed. Is performed.
[0051]
In the case of the continuous image forming mode, the image forming process for a predetermined number n is repeatedly executed. FIG. 4 shows an example in which image formation is performed continuously on two sheets. In the continuous image forming mode, the non-sheet passing state period of the transfer material in the transfer unit is between the time when the rear end of one transfer material passes through the transfer unit and the time when the front end of the next transfer material reaches the transfer unit. Yes, referred to as a sheet interval.
[0052]
[Post-rotation period]
After the image forming period for the last or n-th sheet in the single-sheet or continuous image forming mode is completed, the main motor continues to be driven for a while to rotate the photosensitive drum 1 to perform a predetermined post-operation of the image forming apparatus. Is a period during which the process is executed.
[0053]
When the predetermined post-rotation period ends, the drive of the main motor is stopped, the rotation of the photosensitive drum 1 is stopped, and the image forming apparatus is again kept in the standby state until the next image formation start signal is input.
[0054]
In the above description, the image forming period is the time of image formation, and the previous multi-rotation period, the previous rotation period, the sheet interval, and the post-rotation period are non-image formation in the printer driving state.
[0055]
Next, in the above-described image forming apparatus, an image was output under the following conditions.
[0056]
(1) a mode in which the charging sleeve 33 rotates at a peripheral speed of 200 mm / sec (peripheral speed difference 500 mm / sec) to perform charging in both image forming and non-image forming; and (2) a charging sleeve 33 rotates in image forming. In the two modes of charging at a peripheral speed of 30 mm / sec (peripheral speed difference of 330 mm / sec) and charging at a peripheral speed of 30 mm / sec (a peripheral speed difference of 330 mm / sec) at the speed of 200 mm / sec during non-image formation, a continuous image output of 1000 sheets is performed. A total of 20,000 images were output for each of 2000 sets (intermittent of 10 sheets) and 2000 sets of 10 continuous images (intermittent of 10 sheets). The film thickness before and after the endurance was measured at that time, and the shaving amount of the drum surface layer was measured. Was examined.
[0057]
Here, the charging conditions during the above-mentioned durability will be described. A charging bias of DC voltage +1.2 kV was applied to the charging roller 2 by the bias device 41. A charging bias of DC voltage +650 V, AC voltage 300 Vpp, 1 kHz was applied to the magnetic brush charger 3 by the bias device 42.
[0058]
Table 1 shows a comparison result of the amount of drum surface layer scraping due to image output durability of 20,000 sheets for each case where the peripheral speed difference is different.
[0059]
[Table 1]

[0060]
From Table 1, it was found that by reducing the peripheral speed difference of the charging sleeve 33 as much as possible and reducing the friction between the charging magnetic particles 34 and the photosensitive drum 1 as much as possible, it is possible to reduce drum scraping due to the magnetic particles. In particular, a great effect was obtained at the time of outputting a small amount of image in which the total number of rotations before and after image formation increased.
[0061]
(Second embodiment)
In the present embodiment, in the electrophotographic copying machine of the first embodiment, the charging sleeve 33 is stopped without rotating and the floating switch 43 is cut off during the rotation before and after the image formation. As shown in FIGS.
[0062]
Here, the effect when the magnetic brush charger 3 is electrically floated will be described.
[0063]
For example, when the charging roller 2 and the magnetic brush charger 3 are arranged on the photosensitive drum 1 as shown in FIG. 2 and the bias devices 41 and 42 are connected, the surface of the photosensitive drum 1 is charged by the bias device 41 and the charging roller 2. However, if the output of the bias device 42 is off, the surface potential of the photosensitive drum 1 drops through the charging magnetic particles 34 of the magnetic brush charger 3.
[0064]
On the other hand, as shown in FIG. 5, the charging roller 2 and the magnetic brush charger 3 are arranged on the photosensitive drum 1, the bias device 41 is connected, and the floating switch 43 is turned off. Is electrically floated, the electric potential on the surface of the photosensitive drum 1 charged by the bias device 41 and the charging roller 2 is maintained without dropping even when it comes into contact with the charging magnetic particles 34 of the magnetic brush charger 3. Is done.
[0065]
As described above, the charging of the photosensitive drum 1 can be realized only by the charging roller 2 by electrically setting the magnetic brush charger 3 to the floating state.
[0066]
Next, (1) a mode in which the charging sleeve 33 rotates at a peripheral speed of 200 mm / sec (peripheral speed difference 500 mm / sec) to perform charging in both image forming and non-image forming, and (2) a charging sleeve in image forming. 33 is a peripheral speed of 200 mm / sec, and when the image is not formed, the floating switch 43 is cut off (see FIG. 5), and in the two modes of stopping the charging sleeve 33, 20 sets of continuous image output of 1000 sheets (1000 sheets) (Intermittent), 2,000 sets of 10 continuous image outputs (intermittent 10 images) were output for a total of 20,000 sheets, and the film thickness before and after the endurance at that time was measured, and the shaving amount of the drum surface layer was examined.
[0067]
The charging conditions at the time of the endurance were the same as in the first embodiment, and a charging bias of DC voltage +1.2 kV was applied to the charging roller 2 by the bias device 41. A charging bias of DC voltage +650 V, AC voltage 300 Vpp, 1 kHz was applied to the magnetic brush charger 3 by the bias device 42.
[0068]
Table 2 shows the results of the drum surface layer scraping amount due to the image output durability of 20,000 sheets for the case where the charging sleeve is stopped during non-image formation.
[0069]
[Table 2]

[0070]
From Table 2, it was found that by stopping the charging sleeve 33 and reducing the friction between the charging magnetic particles 34 and the photosensitive drum 1 as much as possible, it is possible to reduce drum scraping due to the magnetic particles. In particular, it was found that a large effect was obtained when a small amount of image was output, in which the number of rotations before and after the image formation increased, and the effect was larger than in the first embodiment in which the charging sleeve 33 was not stopped.
[0071]
【The invention's effect】
As described above, the image forming apparatus according to the present invention includes a plurality of charging units, and the most downstream charging unit in the rotation direction of the electrophotographic photosensitive member is a contact charging member such as a magnetic brush charger. Regarding the electrophotographic image forming apparatus, by reducing the peripheral speed difference of the contact charging member with respect to the photoconductor during non-image formation, or by stopping the contact charging member, the occurrence of drum scraping by the contact charging member is reduced, and Life can be extended.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment.
FIG. 2 is a schematic configuration diagram of a charging device according to the present embodiment.
FIG. 3 is a cross-sectional view illustrating an example of a layer configuration of an a-Si photoconductor.
FIG. 4 is a diagram illustrating an operation process of the image forming apparatus according to the embodiment.
FIG. 5 is a schematic configuration diagram of a charging device according to the present embodiment.
FIG. 6 is a schematic diagram of an image forming apparatus used for describing a conventional example.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 photosensitive drum 2 charging roller 3 magnetic brush charger 5 laser exposure means 6 developing device 7 transfer device 8 fixing device 9 cleaner 10 pre-exposure means 11 conductive support 12 charge injection blocking layer 13 photoconductive layer 14 surface layer 15 photosensitive layer Reference Signs List 21 surface layer 22 elastic layer 23 conductive core metal 31 magnetic particle regulating means 32 fixed magnet 33 charging sleeve 34 magnetic particles 41 bias device 42 bias device 43 floating switch

Claims (10)

An image carrier on which an electrostatic latent image is formed;
A first charging unit disposed around the image carrier and charging the image carrier,
A second charging unit that is disposed downstream of the first charging unit in the rotation direction of the image carrier, and contacts and charges the image carrier.
The second charging means rotates at least for a certain period of time during non-image formation with a peripheral speed difference smaller than a predetermined peripheral speed difference that operates on the image carrier during image formation. Image forming device. An image carrier on which an electrostatic latent image is formed;
A first charging unit disposed around the image carrier and charging the image carrier,
A second charging unit that is disposed downstream of the first charging unit in the rotation direction of the image carrier and contacts and charges the image carrier.
The image forming apparatus according to claim 1, wherein the second charging unit stops rotating at least for a certain time during non-image formation. The image forming apparatus according to claim 1, wherein the second charging unit is a magnetic brush charger having magnetic particles. 4. The image forming apparatus according to claim 1, wherein the image carrier has a layer containing amorphous silicon. The image forming apparatus according to claim 1, wherein the second charging unit is in an electrically floating state when a non-image is formed. A voltage applying unit that applies a voltage to the first charging unit and / or the second charging unit;
The image forming apparatus according to claim 1, wherein the voltage application unit applies a voltage to the first charging unit and the second charging unit during non-image creation. . A process cartridge detachable from an image forming apparatus that forms an image by transferring a toner image to a transfer material,
An image carrier on which an electrostatic latent image is formed;
A first charging unit disposed around the image carrier and charging the image carrier,
A second charging unit that is disposed downstream of the first charging unit in the rotation direction of the image carrier, and contacts and charges the image carrier.
The second charging means rotates at least for a certain period of time during non-image formation with a peripheral speed difference smaller than a predetermined peripheral speed difference that operates on the image carrier during image formation. Process cartridge. A process cartridge detachable from an image forming apparatus that forms an image by transferring a toner image to a transfer material,
An image carrier on which an electrostatic latent image is formed;
A first charging unit disposed around the image carrier and charging the image carrier,
A second charging unit that is disposed downstream of the first charging unit in the rotation direction of the image carrier, and contacts and charges the image carrier.
The process cartridge according to claim 1, wherein the second charging unit stops rotating at least for a certain time during non-image formation. 9. The process cartridge according to claim 7, wherein the second charging unit is a magnetic brush charger having magnetic particles. The process cartridge according to claim 7, wherein the image carrier has a layer containing amorphous silicon.

Images