JP2007079378A - Image forming apparatus, process cartridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus having a plurality of charging means for one photosensitive member, capable of preventing leakage between charging means and performing stable image formation. To do.
SOLUTION: Two charging means of a first charger 21 and a second charger 22 are provided for a photosensitive member 1 which is a latent image carrier, and between the first charger 21 and the second charger 22 is provided. By providing the partition member 24 made of an insulator, leakage between the chargers due to the potential difference between the chargers is prevented even when a potential difference occurs between the chargers.
[Selection] Figure 2

Description

  The present invention relates to an image forming apparatus such as a copying machine, a fax machine, and a printer, and a process cartridge used therefor.

Conventionally, in an image forming apparatus, the surface of a photosensitive member as a latent image carrier is uniformly charged by a charging unit, and light is emitted based on image information by a light writing unit including an LED or the like on the uniformly charged surface of the photosensitive member. Irradiation forms a latent image on the photoreceptor.
The photosensitive member may have a low chargeability due to electrostatic fatigue, wear, etc. over time, resulting in a delay in the rise of charging. When the charging rise delay occurs, the potential of the portion charged in the first round of the photoconductor at the start of the image forming operation becomes low, and the first round of the photoconductor becomes in a state where an image cannot be formed.
As a method for solving such a problem, in Japanese Patent Laid-Open No. 2004-228561, the rising of charging is performed on the upstream side in the moving direction of the photosensitive member surface of a charger (hereinafter referred to as a main charger) that uniformly charges the photosensitive member to a desired potential. It has been proposed to provide a charger (hereinafter referred to as a precharger) that applies a potential corresponding to a delay. By providing the precharger, even if the chargeability of the photosensitive member is lowered, the main charger can be charged uniformly at a stable potential.

JP-A-2-193163

However, when charging is performed by providing two chargers for one photoconductor, the chargers often have to be close to each other due to the limitation of layout space. The following problems occur in an image forming apparatus in which two chargers are installed close to each other to charge the surface of the photoreceptor.
When a potential difference occurs between the two chargers, the chargers are close to each other, so that leakage occurs at the position of the conductive member having the smallest distance between the chargers. When a leak occurs, it becomes impossible to apply a desired charge to the photoconductor, the potential on the surface of the photoconductor becomes uneven or the potential becomes insufficient, and the surface of the photoconductor can be uniformly charged to a stable potential. There is a risk of disappearing.
If the potential on the surface of the photoconductor is uneven or the potential is insufficient, the image is uneven or the background is soiled, and stable image formation cannot be performed.
Note that the leakage between the chargers as described above is not limited to a configuration in which a pre-charger and a main charger are provided for one photoconductor as in Patent Document 1, but a single photoconductor. This is a problem that may occur if a plurality of chargers are provided for the body and they are close to each other.

  The present invention has been made in view of the above problems, and an object of the present invention is an image forming apparatus provided with a plurality of charging units for one photosensitive member, and leakage between the charging units. An object of the present invention is to provide an image forming apparatus capable of preventing occurrence and performing stable image formation.

In order to achieve the above object, according to the first aspect of the present invention, in the image forming apparatus provided with a plurality of charging means for one latent image carrier, a partition member made of an insulator is provided between the charging means. It is characterized by that.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, a concave portion is provided on the surface of the partition member.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the charging means uses a non-contact type charging member.
According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the charging means uses a contact-type charging member.
According to a fifth aspect of the present invention, in the image forming apparatus according to the first, second, third, or fourth aspect, at least the latent image carrier, the charging unit, and the partition member are instructed as a unit, and the main body of the image forming apparatus is provided. On the other hand, it has a process cartridge that can be attached and detached.
According to a sixth aspect of the present invention, in the process cartridge detachable from the image forming apparatus main body, at least the latent image carrier, the charging unit, and the partition member according to the first, second, third, or fourth aspect. Is integrally supported.

  In the first to sixth aspects of the present invention, by providing a partition member made of an insulator between the charging units, it is possible to prevent leakage between the charging units.

  According to the first to sixth aspects of the present invention, it is possible to uniformly charge the surface of the photosensitive member to a stable potential by preventing leakage between a plurality of charging means, and to perform stable image formation. There is an excellent effect of being able to.

An embodiment in which the present invention is applied to an electrophotographic printer (hereinafter simply referred to as “printer 100”) as an image forming apparatus will be described below.
FIG. 1 is a schematic configuration diagram of the printer 100. The printer 100 includes a charging device 2, an optical writing device 3, a developing device 4, a transfer device 5, a drum cleaning device 6, and a charge eliminating device 7 around a drum-shaped photoconductor 1 that is a latent image carrier. ing. In addition, a fixing device 8 is provided on the left side of the transfer device 5 in the drawing.

  A photosensitive member 1 that is rotated in the clockwise direction in the drawing by a driving means (not shown) has an organic photosensitive layer formed on the surface of a raw tube made of aluminum or the like, and is positively or negatively charged by the charging device 2 as it rotates. Is uniformly charged. Then, the potential of the exposure unit is attenuated by the scanning of the laser light L emitted from the optical writing device 3 that constructs the optical scanning information based on image information sent from a personal computer (not shown) or the like. As a result, an electrostatic latent image having a lower potential than the background portion around the exposed portion is carried. The electrostatic latent image contains toner and a magnetic carrier carried on the developing sleeve 41 of the developing device 4 when passing through the developing position that is opposite to the developing device 4 as the photosensitive member 1 rotates. Is rubbed against the developing developer. Then, for example, negative polarity toner contained in the developer is electrostatically adhered to be developed into a toner image.

A transfer position where the transfer roller 51 of the transfer device 5 and the photoconductor 1 are opposed to each other is formed downstream of the developing position in the rotation direction of the photoconductor 1. When the toner image developed on the photosensitive member 1 enters this transfer position with the rotation of the photosensitive member 1, the toner image is conveyed in time by a sheet feeding unit (not shown) and conveyed on the transfer belt 52. It is superimposed on the sheet-like transfer paper P. Then, it is electrostatically transferred onto the recording medium P under the influence of a transfer electric field formed between the exposed portion of the photoreceptor 1 and the transfer device 5. The transfer paper P electrostatically attached to the photoconductor 1 during this transfer is separated from the photoconductor by the action of paper weight, rigidity, paper and members for separating and conveying (not shown), and the like. . The recording material P on which the toner image is electrostatically transferred in this way is sent from the transfer position to the fixing device 8.
The fixing device 8 forms a fixing nip by contact between a heating roller 8a having a heat source (not shown) inside and a pressing roller 8b pressed against the heating roller 8a. These rollers are rotationally driven so as to move the respective surfaces in the same direction at the mutual contact portions. The recording material P sent to the fixing device 8 having such a configuration is sandwiched in the fixing nip and conveyed in the roller surface moving direction. At this time, the toner image is fixed by the influence of nip pressure and heating. The fixing transfer paper P is discharged out of the apparatus via a paper discharge means (not shown).
On the other hand, when the surface of the photoreceptor 1 that has passed the transfer position passes through a position facing the drum cleaning device 6 provided with the fur brush 6a and the cleaning blade 6b as the rotation proceeds, the transfer residual toner is cleaned. The Then, after the residual charge is removed by the static eliminator 7, it is uniformly charged by the charging device 2 and returns to the initial state.

In addition, although the example which provided the optical writing device 3 which forms an electrostatic latent image by irradiation of a laser beam was shown, what performs optical writing with the LED light from an LED array may be used. Further, as the transfer device 5, a belt contact type in which the transfer belt 52 is brought into contact with the photosensitive member 1 at a portion facing the transfer roller 51 to which a transfer bias is applied is shown. Alternatively, a non-contact method such as a transfer charger may be used. In addition, the drum cleaning device 6 has a cleaning blade 6b and a fur brush 6a. However, an electrostatic recovery system that contacts a roller to which a cleaning bias is applied may be used.
Further, although an example in which the drum-shaped photoconductor 1 is provided as the latent image carrier has been described, a belt-shaped photoconductor may be used.

The charging device 2 includes two chargers, that is, a first charger 21 and a second charger 22 as charging means.
As described above, the two chargers are provided for one photoconductor 1 in order to prevent the charging from being delayed in the first round of the photoconductor 1 at the start of the image forming operation and the rise of the charge from being delayed. It is.
Possible causes for the rise delay are as follows.

The cause of the rise delay described in Patent Document 1 is due to charge and light fatigue of the photoreceptor.
This is because the excessive potential generated by light irradiation is trapped in the photosensitive layer, that is, the charge amount corresponding to the rising delay of charging (the charging polarity is reversed) is trapped in the photosensitive layer bulk. to cause. As a result, trap charges (holes) generated by repeated use of the photoreceptor are formed in the photosensitive layer bulk, and they are released in the first charging cycle, so that the surface charge when uniformly charged is canceled. The phenomenon appears only in the first charging cycle because it takes time to recover (re-trap) the holes emitted from the trap.

On the other hand, in recent years, more durability than ever has been required for organic photoreceptors. In order to increase the durability of the organic photoreceptor, it is necessary to improve the wear resistance.
Techniques for improving the wear resistance include those using a curable binder in the crosslinkable charge transport layer (for example, see JP-A-56-48637), and those using a polymer type charge transport material (for example, JP JP-A 64-1728), and those obtained by dispersing an inorganic filler in a cross-linked charge transport layer (for example, see JP-A-4-281461).
And, by improving the wear resistance, it can be used for a longer time than before, and accordingly, a phenomenon that has not been seen conventionally has occurred. As one of them, a phenomenon of a decrease in the charging potential on the first round of the organic photoreceptor has come to appear.
This phenomenon in which the charge is reduced only in the first round of the organic photoreceptor is similar to the conventional delay in the charge rising.

Further, as a means for achieving high durability, there is a method of using the photosensitive member until the thickness of the photosensitive member becomes thinner. Usually, since the surface potential of the organic photoconductor is kept constant, the electric field strength increases as the photoconductor is shaved, and electric charge leaks locally, causing soiling and resulting in a lifetime.
For this reason, there is a method of extending the life by increasing the breakdown voltage by increasing the thickness of the undercoat layer or by forming a two-layer structure so that it can be used until the film thickness becomes thinner.
In this case as well, there is a problem that the charging potential at the first round with time is low as in the case where a long life is achieved by improving the wear resistance. Also, in this case, if the wear resistance is equivalent to the conventional one, the change in the film thickness increases, which means that the change in the capacitance is larger than the conventional one. .

When the charging rise delay occurs due to the above-described causes, the charging performed in the first round of the photosensitive member at the start of the image forming operation becomes insufficient in potential. If the potential of the first round of the photosensitive member at the time of activation is extremely low, an image cannot be formed in the first round, so it is necessary to delay the start of the first copy.
Even if the start of the first copy is delayed, the developing device may develop the toner on the surface of the photoconductor having a low potential in the first round even when a latent image is not formed. As described above, when toner is developed on the photoreceptor other than at the time of image formation, the photoreceptor is poorly cleaned, and the image is also affected by the poor cleaning. When a contact type transfer device is used, if the cleaning failure of the photosensitive member occurs, the transfer device becomes dirty and the transfer paper becomes dirty. Further, since the toner is developed on the photosensitive member at a timing when image formation is not performed, toner that does not need to be consumed is consumed, and the amount of toner consumption increases.

  In the charging device 2 of the present embodiment, the first charging unit 21 as a main charging unit that uniformly charges the photosensitive member 1 to a desired potential, and the charging rising on the upstream side of the photosensitive member surface moving direction of the first charging unit 21 A second charger 22 is provided as a precharger that applies a potential corresponding to the delay. By providing the second charger 22, even when the chargeability of the photosensitive member is lowered, the first charger 21 can uniformly charge with a stable potential. It can prevent the rise delay that causes it.

Next, the charging device 2 will be described in detail.
FIG. 2 is an enlarged view around the charging device 2 in FIG. As shown in FIG. 2, the charging device 2 covers the first charger 21 and the second charger 22 with a casing 23 that is a charger holding member. And the partition member 24 which consists of an insulator is provided between the 1st charger 21 and the 2nd charger 22 which are arrange | positioned adjacently. The first charger 21 and the second charger 22 are chargers using a non-contact type scorotron.
Since the second charger 22 precharges the surface of the photoreceptor before reaching the portion facing the first charger 21, the second charger 22 is compared with the first charger 21. The potential is low. If a potential difference is generated between two chargers arranged close to each other, a leak may occur between the chargers. However, since the charging device 2 includes the partition member 24, the occurrence of the leak should be prevented. Can do.

Further, since the charging device 2 uses a non-contact type scorotron charger as a charging member, durability can be improved as compared with a charging device using a contact type charging member.
This is because even if some toner remains on the photoconductor, or even if the photoconductor has been scraped away, it is easy to perform uniform charging because it is non-contact. This is because the potential to be charged becomes non-uniform when it is not in contact, but if it is non-contact, it can be uniformly charged.

The potential difference between the chargers may be determined by specifications or may occur due to a failure of any charger. In particular, even when one of the chargers fails due to a failure, no leakage occurs between the chargers, so that copying can be continued. In this case, since the charging performance is lower than when there are two chargers, it is necessary to delay the first copy. However, it is not impossible to copy until one of the failed chargers is repaired by a service person.
In the present embodiment, a charging device including two chargers, ie, a main charger and a precharger, has been described. However, the plurality of chargers is not limited to the relationship between main charge and precharge. Further, the number is not limited to two, and three or more chargers may be provided.

In FIG. 2, the photoconductor 1 and the charging device 2 are provided separately, but a process cartridge in which the photoconductor 1 and the charging device 2 are housed in a common casing may be used.
FIG. 3 shows an example of the process cartridge in the present invention. In the process cartridge 200, the photosensitive member 1, the first charger 21, and the second charger 22 are integrally held by a common casing 23 and can be attached to and detached from the printer 100 main body. This makes it possible to maintain the photosensitive member and the charger at the same time. This makes it possible to easily synchronize the charging performance of the photosensitive member and the charger at the initial time or with time, so that it is possible to always provide an image with stable quality.

As described above, according to the present embodiment, the first charging device 21 and the second charging device 22 include the first charging device 21 and the second charging device 22 for the photosensitive member 1 that is a latent image carrier. By providing a partition member 24 made of an insulator between the charger 22 and the charger, even when a potential difference occurs between the chargers, it is possible to prevent leakage between the chargers due to the potential difference between the chargers. it can. Accordingly, the functions of the respective chargers can be distributed such that the first charger 21 is the main charger and the second charger 22 is the precharge. In addition, even if one charger breaks down, leakage between chargers can be prevented, so you can take a copy by delaying the first copy until repair by a service person. Can continue.
Further, by using a non-contact type scorotron charger as the charging member, the durability of the charging member and the photoreceptor can be improved.

[Modification 1]
In the above-described embodiment, the configuration including the flat partition member 24 has been described. Hereinafter, as a first modification, a configuration in which a recess is provided on the surface of the partition member 24 will be described.
FIG. 4 is an enlarged view around the charging device 2 according to the first modification. In the charging device 2 of the first modification shown in FIG. 4, a slit 25 as a concave portion is provided on the surface of the partition member 24 facing the photoreceptor 1.
Since the partition member 24 is formed of an insulator, it is very difficult for electricity to flow. However, the surface of the partition member 24 may be in a state in which electricity can flow due to a decrease in resistance due to deposits. In such a case, the distance along the surface of the partition member 24 between the position closest to the first charger 21 on the surface of the partition member 24 and the position closest to the second charger 22 on the surface of the partition member 24 (hereinafter referred to as “the first charger 21”). If the creepage distance is short, the surface may be energized and the two chargers may leak.
For such a problem, as shown in FIG. 4, by providing a slit 25 in the partition member 24, the creepage distance can be increased, and energization between the chargers by energizing the surface of the partition member 24. Can be prevented. In addition, since the chargers can be brought closer to each other, the opening of the charger can be made large, and the charging performance can be improved.

[Modification 2]
In the above-described embodiment, the configuration of the charging device including the scorotron that is a non-contact charging member has been described. However, the charging device is not limited to the non-contact type. Hereinafter, as a second modification, a configuration including a contact-type charging member will be described.
FIG. 5 is an enlarged view around the charging device 2 according to the second modification. In the charging device 2 of Modification 2 shown in FIG. 5, a first charging roller 210 and a second charging roller 220 are provided as contact-type charging members.
Even in the configuration using two charging rollers, the charging rise delay can be prevented as in the above-described embodiment. Further, by providing the partition member 24 between the first charging roller 210 and the second charging roller 220, it is possible to prevent leakage between the two charging rollers.
Further, since charging is performed in contact with the photosensitive member 1, charging can be performed with a smaller amount of ozone generation than that using a non-contact type charging member.

1 is a schematic diagram of a printer according to an embodiment. FIG. 3 is an enlarged view of the vicinity of the charging device of the printer. FIG. 2 is a schematic diagram illustrating an example of a process cartridge used in the printer. FIG. 9 is an enlarged view around a charging device according to a first modification. FIG. 9 is an enlarged view around a charging device according to a second modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging device 3 Optical writing device 4 Developing device 5 Transfer device 6 Drum cleaning device 6a Fur brush 6b Cleaning blade 7 Static elimination device 8 Fixing device 8a Heating roller 8b Pressing roller 21 First charger 22 Second charger 23 Casing 24 Partition member 25 Slit 41 Developing sleeve 51 Transfer roller 52 Transfer belt 100 Printer 200 Process cartridge 210 First charging roller 220 Second charging roller

Claims (6)

In an image forming apparatus comprising a plurality of charging means for one latent image carrier,
An image forming apparatus comprising a partition member made of an insulator between the charging means. The image forming apparatus according to claim 1.
An image forming apparatus, wherein a recess is provided on a surface of the partition member. The image forming apparatus according to claim 1 or 2,
An image forming apparatus, wherein the charging means uses a non-contact type charging member. The image forming apparatus according to claim 1 or 2,
An image forming apparatus characterized in that the charging means uses a contact-type charging member. The image forming apparatus according to claim 1, 2, 3, or 4.
An image forming apparatus comprising: a process cartridge which instructs at least the latent image carrier, the charging unit, and the partition member as a unit, and is detachable from the main body of the image forming apparatus. In a process cartridge detachable from the image forming apparatus main body,
5. A process cartridge comprising at least the latent image carrier according to claim 1, 2, 3 or 4, the charging means and the partition member supported integrally.

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