JP3327106B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, etc., and more particularly, to a developer which is not transferred onto a transfer material such as paper and remains on an image carrier. The present invention relates to a so-called cleaner-less type image forming apparatus that collects by another device without using the cleaner.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, an electrostatic latent image formed by exposure on a surface of an image carrier charged by a charging brush which is in contact while rotating is visualized with a developer. At the same time, there has been known a cleaner-less type image forming apparatus provided with a developing and cleaning unit for collecting a developer remaining on an image carrier without being transferred to a transfer target body during a previous transfer.

In this type of image forming apparatus, the developer remaining on the surface of the image carrier after transferring the developer image to the material to be transferred is not removed by using a dedicated cleaner, but by a developer cleaning means. It is removed by utilizing the potential difference between the developing bias voltage applied to the carrier and the surface potential of the image carrier. Specifically, after being uniformly charged by the charging brush, the image portion on the surface of the image carrier whose potential has been attenuated by exposure includes:
As in the case of normal reversal development, the developer is electrostatically supplied from the developing cleaning unit and developed. At the same time, the developer remaining on the image carrier after the previous transfer and located in the non-image portion that has not been exposed is based on the potential difference between the surface potential of the uniformly charged image carrier and the developing bias. The developer is electrostatically attracted to the developer carrying member of the developing cleaning means and collected.

[0004]

However, in recent years, various transfer papers have been provided as sheets for use in copying machines and printers. Among them, the transfer paper is made of a special material that affects the image carrier and its peripheral devices, has glue attached, or has a large amount of paper dust attached to the surface of the transfer paper. There is something. When this type of transfer paper is used repeatedly, a foreign material such as a special material, glue, or paper dust adheres to the image carrier, and black spots or white spots appear on the resulting image.
This is because, due to the presence of foreign matter between the developing cleaning means and the image carrier, the portion of the image carrier to which the foreign matter has adhered is not charged, and is developed by the developing cleaning means despite the non-image area. Or, even though it is an area that should be developed, the toner is not transferred to the image carrier, resulting in white spots.
This is because the surrounding area appears as a white spot.

On the other hand, in a contact charging device, particularly a charging device using a brush, the charging ability is deteriorated when used for a long period of time or when continuously used for forming a large amount of images. And image noise such as background fogging is likely to occur.

The present invention achieves the maintenance of charging performance over a long period of time in a contact charging system, and removes only foreign matters adhering from a transfer sheet by passing residual toner to form a desired appropriate image. As an issue.

[0007]

In order to solve the above-mentioned problems, an image forming apparatus according to the present invention comprises: a charging unit for charging a surface of an image carrier by contacting the image carrier; Developing means for developing the electrostatic latent image formed by the exposure with a developer and simultaneously recovering the developer remaining on the image carrier after the previous transfer; As an auxiliary charging means, a conductive elastic body made of a foam having a plurality of foam cells each having a diameter of 0.1 to 1 mm is pressed against the image carrier near the charging means, It has a configuration in which a voltage is applied to the body.

In the image forming apparatus of the present invention having the above structure, the surface of the image carrier is uniformly charged by the charging means and the auxiliary charging means comprising an elastic body, and the charged surface of the image carrier is exposed to static electricity. After the electrostatic latent image is formed, the latent image is developed by a developing / cleaning unit and transferred to a transfer sheet. Foreign matter, such as paper dust, adhered to the image carrier from the transfer sheet after the transfer is conveyed as the image carrier travels, and the conveyance is stopped and recovered by the elastic body at the pressure contact position between the elastic body and the image carrier. Is done. On the other hand, as described above, the developer remaining on the image carrier is also conveyed to the pressure contact position between the elastic body and the image carrier. The elastic body is formed of a foam, and the developer passes through without being blocked by the elastic body because of its small particle size, and is collected by the developing cleaning means.

Therefore, the image carrier can be appropriately charged for a long period of time or even when used for a long period of time, and the image may be disturbed without being appropriately charged or exposed while the foreign matter is adhered, or the developer may be damaged. It is possible to prevent the image from being disturbed due to the entry of foreign matter.

In the image forming apparatus of the present invention, the number of foam cells of the elastic body may be 1 to 10 per 1 mm. With this configuration, it is possible to reliably prevent foreign matter and allow the developer to pass through.

It is desirable that the pressing force between the elastic body and the image carrier is 0.1 to 1 kg / cm ² .
With this configuration, the foreign matter can be reliably prevented without damaging the image carrier without excessively applying it.
Further, the developer can pass through.

Further, the hardness of the elastic body is desirably greater than 0 and 1 kg / cm ² or less. If the elastic body has such hardness, foreign matter can be reliably prevented, and the image carrier is hardly damaged. Note that the hardness in the present case is represented by a force per unit area required to compress a unit volume of an elastic body by 25%.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a schematic configuration of a laser beam printer 1 which is an image forming apparatus according to the present invention. In the laser beam printer 1, an image carrier, that is, a drum-shaped photoconductor 2 having a thin film layer made of an organic photoconductive material (OPC) formed on the outer peripheral surface of a cylindrical body at a substantially central portion of the main body 1 It is provided rotatably. Around the photoreceptor 2, the auxiliary charging member 2
A charging device 30 including a charging brush 2 and a charging brush 3, a developing cleaning device 4, and a transfer charger 5 are sequentially disposed. A laser device 6 is disposed obliquely above the photoreceptor 2 and above the main body 1. .

A paper feed cassette 7 is provided below the developing and cleaning device 4.
And the transfer paper P stored in the paper cassette 7
The paper feed roller 8 is pressed against the sheet. A paper passage is formed from the paper feed cassette 7 along the guides 9 a and 9 b and passing through a transfer area 12 sandwiched between the photosensitive member 2 and the transfer charger 5, and is attached to the main body 1 via a fixing roller pair 10. The transfer paper P is discharged onto the discharged paper discharge tray 11. Further, a power supply 13 is provided below the main body 1.

As shown in FIG. 2, the charging device 30 includes a charging brush 3 serving as a main contact charging device for the photoconductor and an auxiliary charging device serving as an auxiliary charging device for performing preliminary charging on the upstream side in the rotation direction of the photoconductor 2. It has a member 22. The charging brush 3
For example, a fiber formed by dispersing carbon, which is conductive particles, in rayon is formed in a base tube having conductivity by 10,
It is configured by planting hairs at a density of about 000 to 150,000 lines / inch, and a predetermined amount of the photoconductor 2 inserted into the charging brush 3 (for example, , About 1 to 3 mm) and are arranged along the axial direction of the photoreceptor 2 so as to make contact. In this state, the photosensitive member 2 rotates in the direction of arrow B at a peripheral speed of 1 to 5 times the peripheral speed. The periphery of the charging brush 3 is covered by a cover 18 that opens toward the photoreceptor 2, and a scraping member 19 protruding from the inside of the cover 18 extends along the axial direction of the charging brush 3 and contacts the photoreceptor 2. The charging brush 3 is disposed in the charging brush 3 with a predetermined penetration amount (for example, about 1 to 3 mm) on the upstream side in the brush rotation direction (the direction of the arrow B) with respect to the contact portion.

The auxiliary charging member 22 is a cover 18 extending upstream of the charging brush 3 with respect to the rotation direction of the photosensitive member 2.
Are provided on the projection 18a. This auxiliary charging member 2
2 is a conductive support plate 2 attached to the protrusion 18a.
3 and an elastic body 24 supported by this and pressed against the outer peripheral surface of the photoreceptor 2 and having a plurality of foam cells. The elastic body 24 is formed of a conductive ether-based polyurethane foam which is a foam, and has a thickness of 3 m.
m. The size of the foam cells existing in the elastic body 24 is larger than the particle size of the toner T and smaller than the foreign matter D, and the average size is 0.3 mm. Further, the hardness of the elastic body 24 is 0.15 kg / cm ^2.
belongs to. The elastic body 24 is in pressure contact with the photoreceptor 2 with a pressure contact force of 0.1 kg / cm ² and a contact width of the photoreceptor 2 in the rotation direction of 25 mm. Since the elastic body 24 is a foam having a large number of cells (voids), the elastic body 24 is in pressure contact with the photoreceptor 2 at countless points on the pressure contact surface with the photoreceptor 2.

The charging brush 3 is connected to the power supply 13 to apply a DC voltage (for example, -1200 V), a voltage obtained by switching the DC voltage, or a voltage obtained by superimposing an AC component on the DC voltage. As a result, discharge occurs at the brush tip of the charging brush 3, and the surface of the photoconductor 2 is charged. The support plate 23 of the auxiliary charging member 22 is similarly connected to the power supply 13 via the diode 25. The elastic body 24 is in pressure contact with the photoreceptor 2 at countless points. At each of the pressure contacts, a charge injection phenomenon occurs due to a potential difference between the photoreceptor 2 and, in the vicinity of the pressure contact, Since there is a space defined by the cells, a discharge phenomenon occurs in a minute space, and the surface potential of the photoconductor 2 increases. By this operation, the photoconductor 2 is pre-charged. The photoreceptor 2 is charged by the preliminary charging by the auxiliary charging member 22 and the charging by the charging brush 3 with, for example, -600 v to -900 v.
Is almost uniformly charged.

The laser device 6 irradiates a laser beam 14 on the surface of the photosensitive member 2 located between the charging brush 3 and the developing / cleaning device 4 according to image information, and uniformly charges the photosensitive member 2.
To form an electrostatic latent image on the surface of the substrate.

The developing / cleaning device 4 has a casing 15 for accommodating a non-magnetic one-component toner T having triboelectricity. This casing 15 opens toward the photoreceptor 2,
In this opening, a developing sleeve 16 is provided rotatably in the direction of arrow C while making surface contact with the photoconductor 2. The developing sleeve 16 is formed of a conductive elastic material, and is connected to the power supply 13 so that a developing bias is applied. As a result, the toner T held in a layer state on the peripheral surface of the developing sleeve 16 is transported to the developing area according to the rotation thereof, and
Based on the developing bias (−300 V), the toner adheres to the electrostatic latent image on the photoconductor 2 and is visualized. In the casing 15,
The toner T is rotated in the direction opposite to the
There is provided a stirring blade 17 which plays a role of preventing aggregation of the toner and supplying the toner T to the developing sleeve 16.

The transfer charger 5 applies a voltage having a polarity opposite to the charging polarity of the toner T to the transfer paper P sent from the paper feed cassette 7 to the transfer area 12 in synchronization with the rotation of the photosensitive member 2 from the back surface thereof. Then, the toner T is electrostatically attracted to transfer the toner T image on the surface of the photoconductor 2 to the transfer paper P.

Next, the operation of the charging device 30 of the present embodiment having the above-described configuration and the operation of the laser beam printer will be described, assuming that the charging polarity of the toner T is minus. In FIG. 3, the photoconductor 2 is shown in a plan view for convenience of explanation.

First, in a region where an image is formed, as shown in FIG. 3, the changeover switch of the power supply 13 is switched as shown by a solid line to switch a DC voltage (-1200 V) by the switching element 27, or The changeover switch is switched as shown by a broken line, and a voltage in which an AC component is superimposed on a DC voltage is applied. The reason why the voltage having the waveform is applied is that the surface of the photoconductor can be uniformly charged and the charging unevenness can be remarkably reduced as compared with the case where only a DC voltage is applied.

The toner T remaining on the photoreceptor 2 without being transferred to the transfer paper P at the time of the previous transfer and paper powder adhering to the transfer paper P, special coating material or glue applied to the surface of the transfer paper, etc. Foreign matter D adheres to photoconductor 2 at the transfer position. The residual toner T and the foreign matter D are both conveyed along with the rotation of the photoconductor 2 and reach the auxiliary charging member 22. Here, the elastic member 24 and the photosensitive member 2 are in pressure contact with each other, and the elastic member 24 is a foam in which a large number of cells having an average of about 0.6 mm are collected. Therefore, the residual toner T whose particle diameter is very small (approximately 1/50 or less) with respect to the cell diameter passes through the elastic member 24, but the particle diameter is several tens times as large as that of the toner T. The foreign matter D is blocked and captured by the elastic member 24. The situation at this time is shown in FIG. Here, the elastic member 2
4 is connected to the power supply 13 and a voltage of -1200 V is applied, so that the residual toner T passing therethrough is
It will be negatively charged. Further, the electrostatic latent image slightly remaining on the surface of the photoreceptor 2 is also discharged or charged to remove the potential difference, and the electrostatic latent image is substantially removed.

The residual toner T is further non-patterned by the charging brush 3 and is charged together with the photosensitive member 2. At this time, the surface of the photoconductor 2 is −600 to −90.
It is almost uniformly charged at 0V. Some of the residual toner T adheres to the charging brush 3 and is taken in. However, the toner T taken into the charging brush 3 is conveyed in accordance with the rotation of the charging brush 3, is scraped off by the scraping member 19, and is returned to the photosensitive member 2 upstream of the charging brush 3 again. Then, the photosensitive drum 2 and the charging brush 3 are transported together with the newly transported residual toner T.

After passing through the charging device 30 and removing the foreign matter D and dispersing the residual toner T, the laser device 6
Irradiates a laser beam 14 corresponding to the image information. The potential of a portion irradiated with the laser (hereinafter, referred to as an image portion) is attenuated with respect to a portion not irradiated with the laser (hereinafter, referred to as a non-image portion), whereby a new electrostatic latent image is formed.

When the newly formed electrostatic latent image comes into contact with the developing sleeve 16 as the photosensitive member 2 rotates, the toner T held on the peripheral surface of the developing sleeve 16 is biased under the above-described conditions. Based on the electric field formed by the voltage, the toner is electrostatically adhered to the image area and development is performed, and at the same time, the residual toner T charged by the charging device 30 located in the non-image area is charged in the non-image area. Is electrostatically attracted to the developing sleeve 16 which has a relatively high potential, and is reliably collected.

The toner image developed as described above is
The photosensitive member 2 moves to the transfer area 12 according to the rotation. Here, a positive voltage is applied by the transfer charger 5 from the back surface of the transfer paper P conveyed from the paper supply cassette 7. As a result, the negatively charged toner T is transferred to the transfer paper P
, And the toner image is transferred from the photoconductor 2 to the transfer paper P. After the toner image is fixed on the transferred transfer paper P by the fixing roller pair 10, the transfer paper P
It is discharged on 1.

On the other hand, toner T remaining on the photoreceptor 2 without being transferred to the transfer paper P and foreign matter D such as paper dust adhering to the photoreceptor 2 from the transfer paper P are caused by the rotation of the photoreceptor 2. After being conveyed, the operation described above is repeated.

In the above-described embodiment, the charging brush 3 and the auxiliary charging member 22 are integrally formed. However, as shown in FIG. 5, the charging brush 3 is moved with respect to the moving direction of the photosensitive member 2 (the direction of arrow A). A separate auxiliary charging member 22 is provided on the upstream side,
Thus, the above-described foreign matter D such as the attached matter and paper dust may be collected and auxiliary charging may be performed. For each member,
The same reference numerals as in the above-described embodiment denote the same parts, and a description thereof will be omitted.

In any of the embodiments, the elastic member 24 of the auxiliary charging member 22 is formed by firing a material obtained by mixing a conductive material such as carbon with polyurethane, polyethylene, or rubber, in addition to the above-described materials. Are preferably used. The resistance value of the elastic body 24 is about 10 ³ to 10 ⁹ Ω.
/ Cm is appropriate. Furthermore, hardness is 0-1.
It is appropriate to use one of 0 kg / cm ² . This is because the lower the hardness, the smaller the wear on the surface of the photoreceptor 2 is, and the more preferable.
The upper limit is set, and the auxiliary charging member 22
The lower limit may be any value as long as it can be in contact with the photoreceptor 2 as a solid for a long period of time.

The foam cells contained in the elastic body 24 are as follows:
A size that allows the toner T to pass through and blocks the foreign matter D, in other words, a size larger than the particle size of the toner T and smaller than the foreign matter D, about 100 μm to 1 mm
And the number of cells is preferably 1 to 10 cells / mm.
This is because the smaller the cell diameter and the larger the number of cells, the more the photoconductor 2
The number of the pressure contact points increases, the number of charge injection and discharge locations increases, and the charging performance is improved. Even if the residual toner T or the foreign matter D adheres and stays, the charging performance is easily maintained. Moreover,
Regarding the partial wear of the surface of the photoreceptor 2, since there are many abutting portions, the surface of the photoreceptor 2 is easily abraded uniformly and hardly affects the image. However, a size that allows the residual toner T to sufficiently pass through is required, and the above-described value is preferable.

The pressing force between the elastic member 24 and the photosensitive member 2 is controlled by the pressing of the elastic member 24 to restrict the movement of the residual toner T,
It is necessary to adjust so as not to rub the foreign matter D on the surface of the photoreceptor 2 or to damage the surface of the photoreceptor 2 and to prevent the foreign matter D. The pressing force is 0.1 to 1 kg /
It is appropriate to press the elastic body 24 against the photosensitive body 2 in cm ² . This is because a certain or more pressing force is required to keep the elastic body 24 in stable pressure contact with the surface of the photoreceptor 2, and the lower limit is set. On the other hand, in order to reduce the abrasion of the photoconductor 2, it is preferable that the pressing force is small, and the upper limit is set as a value that can maintain the charging performance without causing the abrasion of the photoconductor 2 locally.

Further, the length of the pressure contact portion (nip portion) between the elastic member 24 and the photosensitive member 2 in the rotation direction of the photosensitive member 2 has the same purpose as described above and the space is required to ensure the preliminary charging. If so, it is desirable to have a certain length. At least, in order to maintain charging performance and to ensure pressure contact with the photoreceptor, the minimum pressure contact width is 1
mm is required.

Further, the resistance value of the elastic body 24 itself is 1
It is appropriate to set it to 0 ³ to 10 ⁹ Ω / cm, and the voltage to be applied to the elastic body 24 is suitably about −500 V to −2000 V. It is preferable that the voltage applied to the elastic body 24 has a periodically changing value, for example, a pulsating flow in which alternating current is superimposed on direct current. The reason is that the adhesive force between the photosensitive member 2 and the foreign matter D is weakened by the periodic change of the voltage, and the efficiency of collecting the foreign matter D is improved. As a result, the pressure contact force between the elastic body 24 and the photoconductor 2 can be reduced, and damage to the photoconductor 2 can be reduced.

In each of the embodiments, an auxiliary charging member 22 is provided upstream of the charging brush 3 to perform preliminary charging. Although it is preferable to configure in this way,
The auxiliary charging member 22 is provided between the charging brush 3 and the developing cleaning means 4 on the downstream side of the charging brush 3 for reasons such as space reasons.
May be provided.

Next, a modified example in which the elastic body 24 is pressed against the photosensitive member 2 will be described. 6 shows that the elastic body 24 is inclined such that the pressing force on the upstream side becomes stronger than the pressing force on the downstream side when the elastic body 24 is pressed against the rotating direction of the photoconductor 2. It is designed to be pressed. With this configuration, the foreign matter D can be effectively captured on the upstream side of the press contact surface, and the downstream side is kept in a state where the foreign matter D is small even during long-term use, and the charging performance is maintained for a long time. .

FIG. 7 shows a structure in which the elastic member 24 is pressed against the rotating direction of the photosensitive member 2 such that the pressing force on the downstream side becomes stronger than the pressing force on the upstream side when the elastic member 24 is pressed. It is designed to be inclined and pressed. With this configuration, the pressing force of the pressing surface between the elastic body 24 and the photosensitive member 2 gradually increases from the upstream side to the downstream side, and the foreign matter D and the like are wider on the surface than that shown in FIG. Is removed, the foreign matter D is easily removed, and the possibility that the captured foreign matter D falls from the elastic body 24 and contaminates the inside of the machine is small.

Further, as shown in FIG.
A seal member 26 may be provided on the upstream and downstream sides of the charging device 30 so as to cover around the charging device 30. With such a configuration, the foreign matter D to be captured by the elastic body 24 falls, or the residual toner T
Can be prevented from being contaminated inside the aircraft by scattering.

Further, as shown in FIG. 9, a multi-stage auxiliary charging member 22 having a plurality of elastic bodies 24 may be used. With this configuration, the upstream elastic body 24 mainly plays a role of capturing, and the downstream elastic body 24 mainly plays a role of charging, so that stable charging performance can be maintained. .

As described above, when the auxiliary charging member 22 is used, foreign matter D such as paper dust adhered to the photosensitive member 2 is captured by the foamed cells of the elastic member 24 at the pressure contact portion between the elastic member 24 and the photosensitive member 2. Is done. However, the toner T passes through the pressure contact portion with the elastic body 24 and is transported to the contact area of the charging brush 3. Therefore, a blank pattern does not appear on the created image. In addition, the elastic member 24 is pressed against the photosensitive member 2 with the rotation of the photosensitive member 2, whereby an effect of suppressing a so-called filming phenomenon due to the toner T can be obtained.

Further, in the present invention, the charging device 30
By using the charging brush 3 and the auxiliary charging member 22 having the elastic body 24 composed of a large number of foam cells in combination,
The charging characteristics for the photoreceptor 2 are ensured by use over a long period of time or by continuous printing. This can be either one of the charging brush 3 or the elastic body 2
If only 4) is used, the foreign matter D or the residual toner T adheres, and the charging characteristics deteriorate over a long period of use. However, in the present case, the auxiliary charging member 22 (elastic body 2)
Since 4) is used, the charging brush 3 can maintain sufficient charging performance even if the auxiliary charging member 22 has deteriorated charging performance due to the attachment of foreign matter or the like, and can uniformly charge the photosensitive member 2. it can. Conversely, when the auxiliary charging member 22 is located on the downstream side of the charging brush 3, even if the charging brush 3 is deteriorated, the photosensitive member 2 is
The surface can be charged uniformly.

In the above embodiment, the case where the surface of the photosensitive member 2 is negatively charged has been described. However, the present invention can be applied to the case where the surface of the photosensitive member 2 is positively charged. Also, the case where the contact cleaning method is used for the developing cleaning device 4 has been described, but the present invention is not limited to this. The developing cleaning device 4 can be applied using other known developing device.

The results of experiments conducted to confirm the effects of the present invention will be described below. The graphs shown in FIGS. 10 to 13 show the surface roughness (roughness) Ra of the photoconductor 2 when 3,000 images are recorded under each set condition.
Conditions not particularly described are the same as the conditions described in the above embodiment. Surface roughness Ra of photoreceptor 2
Is preferably as small as possible, and if it is 0.5 μm or more, it will affect an image to be formed, which is not practically suitable.

In the graph shown in FIG. 10, the vertical axis represents the surface roughness of the photosensitive member 2, and the horizontal axis represents the number of cells, that is, the number of cells included in the elastic body 24 having a width of 25 mm.
As is apparent from this graph, considering the surface roughness of the photoconductor 2 when used for a long period, it is preferable that the number of cells is preferably about 25 or more.

In the graph shown in FIG. 11, the vertical axis represents the surface roughness of the photosensitive member 2 and the horizontal axis represents the cell diameter.
As is clear from this graph, considering the surface roughness of the photoconductor 2 when used for a long time, the cell diameter is 1 mm.
If it exceeds, the shaving amount increases and the surface of the photoreceptor 2 becomes rough and unsuitable for use. Therefore, the cell diameter is preferably 1 mm or less.

In the graph shown in FIG. 12, the vertical axis represents the surface roughness of the photosensitive member 2, and the horizontal axis represents the pressure contact force between the elastic member 24 and the photosensitive member 2. As is apparent from this graph, considering the surface roughness of the photoconductor 2 when used for a long period of time, if the pressure contact force with the elastic body 24 exceeds 1.0 kg / cm ² , the shaving amount increases, and 2 is considered to be unsuitable for use due to the rough surface, so that the pressure contact force between the elastic body 24 and the photoconductor ² is preferably 1.0 kg / cm ² or less.

In the graph shown in FIG. 13, the vertical axis represents the surface roughness of the photosensitive member 2, and the horizontal axis represents the hardness of the elastic body 24. As is apparent from this graph, considering the surface roughness of the photoconductor 2 when used for a long time,
If the hardness of the elastic member 24 exceeds 1.0 kg / cm ² , the shaving amount of the photosensitive member 2 increases, and the surface of the photosensitive member 2 becomes rough and unsuitable for use.
g / cm ² or less.

[0048]

As is apparent from the above description, according to the charging device of the present invention, the diameter of each of the individual charging members is in the vicinity of the contact charging means for charging the surface of the image carrier by contacting the image carrier. By pressing a conductive elastic body made of a foam having a plurality of foam cells of 1 to 1 mm against the image carrier and applying a voltage, foreign matter attached to the image carrier can be removed, and The photosensitive member can be stably charged over a long period of time, and a stable image can be obtained without deteriorating the image quality.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a laser beam printer to which the present embodiment is applied.

FIG. 2 is an enlarged view of a charging device and a photoconductor of the present embodiment.

FIG. 3 is a diagram illustrating an operation of collecting residual toner.

FIG. 4 is a diagram illustrating a state in which an auxiliary charging member allows toner to pass therethrough and blocks foreign matter.

FIG. 5 is a diagram showing an embodiment in which an auxiliary charging member and a main charging member are made independent.

FIG. 6 is a view showing a modification of the shape of the elastic body.

FIG. 7 is a view showing a modification of the shape of the elastic body.

FIG. 8 is a view showing a modification of the auxiliary charging member.

FIG. 9 is a view showing a modification of the auxiliary charging member.

FIG. 10 is a diagram showing a relationship between the density of elastic foam cells and the surface roughness of a photoconductor.

FIG. 11 is a diagram showing a relationship between the size of an elastic foam cell and the surface roughness of a photoconductor.

FIG. 12 is a diagram illustrating a relationship between a pressing force applied to an elastic body and a photosensitive member and a surface roughness of the photosensitive member.

FIG. 13 is a diagram showing the relationship between the hardness of an elastic body and the surface roughness of a photoreceptor.

[Explanation of symbols]

2 ... Photoconductor (image carrier), 3 ... Charging brush, 4 ... Developing cleaning device, 5 ... Transfer charger, 6 ... Laser device, 13 ...
Power supply, 22: auxiliary charging member, 24: elastic body, 30: charging device, P: transfer paper.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-4-20986 (JP, A) JP-A-2-259784 (JP, A) JP-A-7-325461 (JP, A) JP-A-8- 62928 (JP, A) JP-A-5-224506 (JP, A) JP-A-5-6075 (JP, A) JP-A-6-289687 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 21/00 G03G 21/00-21/12 G03G 15/02-15/02 103 G03G 15/08 507

Claims (4)

(57) [Claims] A charging means for charging the surface of the image carrier by contacting the image carrier, and developing an electrostatic latent image formed on the charged surface of the image carrier by exposure with a developer;
And a developing cleaning unit for collecting a developer remaining on the image carrier after the previous transfer. In the image forming apparatus, a plurality of foams each having a diameter of 0.1 to 1 mm are provided as auxiliary charging units of the charging unit. An image forming apparatus, wherein a conductive elastic body made of a foam having cells is pressed against the image carrier near the charging means, and a voltage is applied to the elastic body. 2. The image forming apparatus according to claim 1, wherein the number of foam cells of the elastic body is 1 to 10 per millimeter. 3. A pressing force between the elastic body and the image carrier is:
The image forming apparatus according to claim 1, wherein the pressure is 0.1 to 1 kg / cm ² . 4. The hardness of the elastic body is greater than 0 and 1
4. The image forming apparatus according to claim 1, wherein the pressure is equal to or less than kg / cm ² .