JP2002148907A - Electrostatic charting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic charging device which can prevent the generation of an abnormal image diffusing a dense electric discharge produce generated during electric discharge simultaneously with its generation to sup press the deposition of the electric discharge product on a photoreceptor. SOLUTION: Aspirating holes 23 are bored on the whole surface of an electrostatic charging roller 20 which is a hollow roller. A ventilation pipe 25 is connected to one end 24 of the electrostatic charging roller 20, an exhaust fan 26 is arranged at the tip part to enable exhaust of air inside the electrostatic charging roller 20. The air is sucked in the roller 20 from the hole 23, and NOx which is the electric discharge product in the vicinity of the electrostatic charging roller 20 is sucked by its suction force.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device used in an image forming apparatus such as a copy machine, a printer, and a facsimile by an electrophotographic system, and more particularly, to a charging device used in an image forming apparatus performing a charging process using discharge of a photosensitive member. About.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, a corona discharge is often used in each part such as a charging device for uniformly charging a photosensitive member. Discharge products such as ozone and nitrogen oxides are produced. When ozone stays in the image forming apparatus at a high concentration, it oxidizes the surface of the photoreceptor, causing a reduction in photoreceptor photosensitivity and a deterioration in charging ability, thereby deteriorating the formed image. Development of Corona Charger for Reducing Photoconductor Deterioration by Ozone ": Journal of the Society of Electrophotography, 31, 31, 1992). In addition, there is a problem that deterioration of members other than the photoreceptor is promoted, and the life of parts is shortened.

Therefore, in recent years, a contact charging device has been proposed in which a charging member is brought into direct contact with a photosensitive member to charge the photosensitive member. For example, there has been known a roller-shaped charging member that is driven to contact a photosensitive member to charge the photosensitive member. This contact charging method has a lower applied voltage and lower power supply cost than the conventionally used corona charging method.
It has advantages such as easy design of electrical insulation.

However, a small amount of discharge products such as ozone and nitrogen oxides are generated, and these discharge products accelerate the deterioration of the surrounding members and deteriorate the image on the image carrier (so-called image blur). , Image flow).

In particular, nitrogen oxides cause the following problems. That is, it is known that nitrogen oxides are generated when a discharge occurs. Nitrogen oxides react with moisture in the air to produce nitric acid, and also react with metals and the like to produce metal nitrates. These products have a high resistance in a low humidity environment, but react with water in the air in a high humidity environment to have a low resistance. Therefore, when a thin film made of nitric acid or nitrate is formed on the surface of the photoreceptor, an abnormal image appears as if the image had flowed. This is because nitric acid or nitrate absorbs moisture to lower the resistance, thereby destroying the electrostatic latent image on the surface of the photoreceptor.
Also, since the nitrogen oxides remain in place without being decomposed in the air even after discharge, the attachment of the compound generated from the nitrogen oxides to the surface of the photoreceptor, when not charged,
That is, it occurs even during the pause of the process. Then, this compound permeates from the surface of the photoreceptor to the inside over time, and further accelerates the deterioration of the photoreceptor.

[0006] Specifically, the following problems have occurred. That is, when a copying machine that has been idle for a while is used, a phenomenon called image deletion occurs on the surface of the photoconductor near the charger at the time of idle. A method has been adopted in which deposits on the surface of the photoconductor are removed by scraping the photoconductor little by little during cleaning. However, the problem of deterioration due to cost increase and aging occurs, and is not an essential solution.

In a charging process using discharge, as a conventional example for removing nitrogen oxides, which are discharge products, (a) As disclosed in Japanese Patent Application Laid-Open No. 5-303244, the heat exhausted from a fixing unit is removed. (B) As described in Japanese Patent Application Laid-Open No. Hei 9-114191, a surface glow discharge is generated on the surface of the charger separately from the charging of the photoreceptor. Decomposes nitrogen oxides,
(C) As disclosed in Japanese Examined Patent Publication No. Hei 8-23715, a catalyst is coated on the inside of the discharger to neutralize nitrogen oxides and prevent deterioration of the photoconductor. However, these conventional image forming apparatuses and methods for reducing discharge products are not perfect, and there is still room for improvement.

Further, as a conventional example of removing discharge products from the air near the charging roller using a fan or the like, for example, Japanese Patent Application Laid-Open Nos. 8-202126 and 11-161.
There is a technique disclosed in, for example, Japanese Patent Publication No. 120-120. However, according to these techniques, nitrogen oxides, which are discharge products, cannot be completely removed from the vicinity of the photoconductor due to a loss in the flow of air. Further, since the suction port is separated from the discharge region, there is a possibility that the discharge product may be diffused in the device depending on the power of the fan or a small amount, or depending on the direction of the airflow. According to the technology disclosed in Japanese Patent Application Laid-Open No. 8-202126, a member of an airflow generating device is arranged right beside a charging roller. It is impossible to place them.

In view of the foregoing, the present invention is to prevent the occurrence of an abnormal image by preventing the discharge products from depositing on the photoreceptor and simultaneously dispersing the dense discharge products generated at the time of discharge, and to reduce the size of the photoreceptor drum. It is an object of the present invention to provide a charging device that can be used even when the charging device is used.

[0010]

According to a first aspect of the present invention, there is provided a charging device using a charging method for charging an image carrier by discharging, the charging device comprising: An airflow generating means for generating a flow of air is provided near the member.

According to a second aspect of the present invention, in order to achieve the above-mentioned object, in the charging device according to the first aspect, the airflow generating means moves from the surface of the charging member to the inside of the charging member around the charging member. It is characterized by sucking air.

According to a third aspect of the present invention, in order to achieve the above object, in the charging device of the first or second aspect, the charging member has an opening for connecting to the airflow generating means and an air surface. And the opening and the hole communicate with each other so that air can flow in and out of the charging member.

According to a fourth aspect of the present invention, in order to achieve the above object, in the charging device according to any one of the first to third aspects, the charging member is not in contact with the image carrier. I do.

According to a fifth aspect of the present invention, there is provided a charging device according to any one of the first to fourth aspects, wherein the charging member is rotatable in accordance with the movement of the image carrier. It is characterized in that it has a shape and the rotational speed of the surface is different from the moving speed of the image carrier.

According to a sixth aspect of the present invention, in order to achieve the above object, in the charging device according to any one of the first to fifth aspects, it is preferable that the airflow generating means generates an airflow even after the discharge is completed. Features.

[0016]

Embodiments and examples of the present invention will be described below with reference to the drawings. FIG. 1 shows a main configuration of an image forming apparatus to which the present invention is applied. In the image forming apparatus 1, a photoconductor 2 that is driven to rotate clockwise in FIG.
Around the photoconductor 2, a charging unit 3, a writing unit 4, a developing unit 5,
A transfer unit 6, a paper separation unit 14, a cleaning unit 7, a charge removing unit 8, and the like are provided.

The image forming apparatus 1 includes a paper feed cassette (not shown) for accommodating a plurality of recording papers, and the recording paper in the paper feed cassette is fed by a paper feed roller (not shown).
After the timing is adjusted by a pair of registration rollers (not shown) one by one, the sheet is sent out between the transfer unit 6 and the photoconductor 2. The photoreceptor 2 is driven to rotate clockwise in FIG. 1 to be uniformly charged by a charging unit 3, and then irradiated with a laser modulated by image data by a writing unit 4 to form an electrostatic latent image. The developing unit 5 applies toner to the photoreceptor 2 on which the electrostatic latent image is formed, and develops the image. Further, the toner image formed by attaching the toner in the developing unit 5 is transferred to the recording paper 15 conveyed between the photosensitive member 2 and the transfer unit 6 in the transfer unit 6, and the recording paper on which the toner image is transferred is formed. To the fixing unit 10.

The fixing unit 10 includes a fixing roller 11 heated to a predetermined fixing temperature by a built-in heater, and a fixing roller 11.
And a pressure roller 12 pressed by a predetermined pressure. The recording paper conveyed from the transfer unit 6 is heated and pressed to fix the toner image on the recording paper to the recording paper, and then discharged (not shown). Discharge on tray.

Then, the photoreceptor 2 on which the toner image has been transferred to the recording paper in the transfer unit 6 is further rotated, and the cleaning unit 7 is rotated.
Then, the toner remaining on the surface of the photoreceptor 2 is scraped off by the blade 13 and removed. After the photosensitive member 2 having been neutralized by the neutralization unit 8 is again charged uniformly by the charging unit 3, the next image is formed by the same process as described above.

The cleaning unit 7 includes a blade 13
There are various known types, such as a device for scraping off residual toner on the photoconductor 2 and a device for scraping residual toner on the photoconductor 2 with a fur brush.

The charging section 3 uses a roller-shaped charging member as a charging member, and is arranged in a state of not contacting the photosensitive member 2.

FIG. 2 is a view showing an embodiment of the charging device according to the present invention. The illustrated embodiment relates to a charging roller, and the charging roller 20 includes a conductive base 21 and a resistance layer 22 around the conductive base 21. The conductive substrate 21 has a diameter of 1
It is a hollow cylinder made of aluminum having a thickness of about 0 to 50 mm and a thickness of about 2 to 5 mm. The resistance layer 22 includes an epichlorohydrin rubber layer and a resin surface layer covering the surface thereof.
The surface layer has a thickness of 30 to 100 μm and a surface roughness Rz of 0.1 to 100 μm, which is mainly composed of a fluororesin such as a tetrafluoroethylene copolymer, a polyvinylidene fluoride and a tetrafluoroethylene perfluoroalkylvinyl ether copolymer. A resin tube of about 2 to 2 μm may be used, or another material capable of performing uniform charging may be used. In addition, a roller cleaning member 27 is disposed close to the surface of the charging roller 20 to remove toner, paper dust, and the like attached to the surface of the charging roller 20, so that uniform charging without uneven charging can be performed. It is like that.

The charging roller 20 has a hole 23 for suction on the entire surface. The size of the hole 23 is φ50
About 500 μm. This is because the diameter is preferably about 50 to 100 μm in order not to impair the uniformity of charging. If the hole 23 is too small, suspended particles such as toner and carrier will close the hole 23, and the suction efficiency will be reduced.

The charging roller 20 is a hollow roller. An exhaust pipe 25 is connected to one end 24 of the charging roller 20. An exhaust fan 26 is disposed at the end of the exhaust pipe 25 to exhaust air inside the charging roller 20. Thereby, air is sucked into the roller 20 from the holes 23, and nitrogen oxides, which are discharge products, are sucked by this suction force. Before discharging the sucked air out of the apparatus, it is preferable to control the exhaust gas using an ozone filter or the like. Of course, the exhaust fan 26 may also be used as another fan (for example, a fan for cooling the fixing roller).

The surface of the charging roller 20 moves or rotates at a speed 2 to 5 times that of the surface of the photosensitive drum 1, that is, the length of the charging roller 20 in the longitudinal direction (axial direction) is the maximum image width A4.
It is set slightly longer than the width (about 290 mm). The charging roller 20 is provided with spacers (not shown) at both ends in the longitudinal direction. The spacers are brought into contact with the non-image forming areas at both ends of the photosensitive drum 2 so that the photosensitive drum 2
The gap H between the charged surface on the surface and the charged surface on the charging roller 20 is maintained such that the distance at the nearest portion is 5 to 100 μm. This closest distance is more preferably set to 5 to 50 μm.

A power supply for charging is connected to the charging roller 20, and the charged surface is discharged by a gap H between the charged surface of the photosensitive drum 2 and the charged surface of the charging roller 20. Charges uniformly. The gap H is formed in a band shape along the generatrix on the surface of the photosensitive drum 2. The applied voltage is
A DC voltage or a DC voltage with an AC voltage superimposed is used. Since the amount of generated discharge products is smaller when a DC voltage is applied, it is preferable to perform charging by applying a DC voltage.

The hardness of the charging roller is, for example, about 60 to 70 degrees according to JIS-A. However, since it is not necessary to bring the charging roller into contact with the photosensitive drum, a higher hardness may be used in consideration of its durability.

Next, an experiment performed by the present inventors will be described. <Experiment 1> Copying machine installed in a high-temperature, high-humidity environment (manufactured by Ricoh Co., Ltd .: remodeled imageioMF-200,
(Charging method: DC charging roller), about 10,000 copies were made. After creation, the copier was stopped, suspended overnight in a high-temperature, high-humidity environment, and resumed operation the next morning.
What was called image bleeding was observed in the copied image. This is because the NOx in the machine falls on the photoreceptor and the NOx
Is considered to have reacted with high-humidity moisture in the air on the photoreceptor and changed to a nitric acid or nitrate compound. This compound lowers the resistance of the photoreceptor surface. In other words, even if a charge is applied to the surface of the photoreceptor, the surface of the photoreceptor cannot maintain the charge at that location, so that the electrostatic latent image is destroyed, and it is considered that an image flow occurs. <Experiment 2> On the other hand, the result when the charging device with the suction mechanism of the present invention is used in a copying machine will be described. Outer diameter Φ1
A charging roller in which a 0.5 mm thick epichlorohydrin rubber layer and a resin layer are sequentially formed in a 6 mm hollow cylinder,
The photosensitive member was arranged with a gap of about 50 μm. Then, the suction port of the charging roller was connected to an external fan through a resin tube to enable suction. Further, a motor is connected to the charging roller, and the number of rotations of the charging roller can be changed. Hereinafter, experiments 1 to 3 were performed. (1) Roller rotation speed While changing the rotation speed of the charging roller, the appearance of the copied image was visually checked. When the roller speed was set so that the roller surface moved at the same speed as the photosensitive member surface, small black circles appeared on the copy image. This is because the suction holes on the surface of the charging roller cause charging unevenness and appear on the copy image. However, when the rotation speed of the roller was increased and the speed of the roller surface was about twice as high as the speed of the photoreceptor surface, the copy image did not show any image defects considered to be due to charging. Further, in a state where the roller was stopped without rotating, a defect appeared to be caused by charging unevenness due to the suction hole in the copy image. (2) Comparative experiment A copying machine (image MF- manufactured by Ricoh Co., Ltd.) equipped with the charging roller of the present invention installed in a high-temperature, high-humidity environment.
200 remodeled machine) and made about 10,000 copies. Of course, the fan connected to the charging roller is operating and sucking air. After the creation, the copier was stopped (the fan stopped at the same time as the process was completed), suspended overnight in a high-temperature, high-humidity environment, and resumed operation the next morning. Was done. The portion where this streak occurred was the surface where the photoconductor stopped near the charging roller when the copying machine was stopped. (3) Fan stop timing This is an experiment similar to the above experiment (2), but the process stop 1
After a minute, the fan was stopped. Then, even when the same experiment was performed, the image deletion phenomenon did not appear. This is presumably because most of the discharge products were discharged out of the apparatus through the suction holes on the surface of the charging roller, so that image blurring and image deletion did not occur.

[0029]

As described above, the charging device according to the first aspect of the present invention generates an airflow from the surface of the charging member by discharging the most densely located discharge products near the surface of the charging member which is the discharge area. As a result, the air can be diffused by the flow of air at the same time as the generation, so that the discharge product does not fall on the photoreceptor, and there is an effect that abnormal images such as image blur and image deletion do not occur. Also,
Since it is not necessary to newly arrange a member around the image carrier, there is also an effect that a mechanism for generating an air flow can be incorporated even when a photosensitive drum having a small diameter is used.

In the charging device according to the second aspect, in addition to the above-mentioned common effect, the discharge products are diffused in the machine by sucking the discharge products from the surface of the charging member, and the floating discharge products are drastically reduced. The discharge products floating on
There is an effect that the deterioration of the member is not accelerated. Further, image blur or image deletion, which is considered to be caused by the diffused discharge products adhering to the photoreceptor, does not occur, and the dense discharge products near the charging member are sucked and efficiently discharged outside the apparatus. There is an effect that can be.

According to the third aspect of the present invention, in addition to the above-described common effects, the discharge products are not diffused into the apparatus by sucking the discharge products from the holes of the charging member using the airflow generating means. There is an effect that the discharge products floating inside the machine do not adhere to the members and accelerate the deterioration of the members.

In the charging device according to the fourth aspect, in addition to the above-mentioned common effects, since there is a gap between the charging roller and the photoreceptor, the flow of air at the time of suction is very good, and there is no place where air is stagnated. There is an effect that discharge products can be exhausted well.

In the charging device according to the fifth aspect, in addition to the above-mentioned common effects, since the moving speed of the moving speed of the surface of the charging roller is different from the moving speed of the surface of the photoreceptor, the suction hole on the surface of the charging roller is provided with respect to the surface of the photoreceptor. Thus, even when a charging roller having holes is used, uniform charging can be performed similarly to the conventional charging roller. Also,
When the charging roller is not in contact with the photoconductor, there is almost no frictional force applied to the charging roller from the photoconductor, so that it is easy to generate a speed difference between the charging roller and the photoconductor.

In the charging device according to the sixth aspect, in addition to the above-mentioned common effects, the fan is operated even after the discharge is completed, so that when the image forming process is stopped, ozone and nitrogen oxides are almost eliminated in the apparatus, and the copying machine is operated for a long time. There is also an effect that the image flow generated on the photoconductor near the charging roller after stopping the operation is not generated.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a main configuration of an image forming apparatus to which the present invention is applied.

FIG. 2 is a diagram showing one embodiment of a charging device according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 image forming apparatus 2 photoreceptor 3 charging unit 4 writing unit 5 developing unit 6 transfer unit 7 cleaning unit 8 static elimination unit 10 fixing unit 11 fixing roller 12 pressure roller 13 blade 14 paper separation unit 15 recording paper 20 charging roller 21 conductive Base 22 Resistance layer 23 Hole 24 One end of charging roller 25 Exhaust pipe 26 Exhaust fan 27 Roller cleaning member

Claims (6)

[Claims] 1. An image forming apparatus comprising: a charging device that uses a charging method for charging an image carrier by discharging; and an air flow generating unit that generates an air flow from a charging member surface to a vicinity of the charging member. 2. The charging device according to claim 1, wherein the airflow generating means sucks air around the charging member from the surface of the charging member to the inside of the charging member. 3. The charging device according to claim 1, wherein
The charging member has an opening for connecting to the airflow generating means and a hole through which air can flow, and the opening and the hole communicate with each other so that air can flow inside the charging member. Charging device. 4. The charging device according to claim 1, wherein said charging member is not in contact with said image bearing member. 5. The charging device according to claim 1, wherein the charging member has a roller shape rotatable in accordance with the movement of the image carrier, and a rotation speed of a surface of the charging member is equal to that of the image carrier. A charging device characterized by having a different moving speed. 6. The charging device according to claim 1, wherein said airflow generating means generates a flow of air even after the discharge is completed.