JPH07168417A - Electrifier - Google Patents

Abstract

PURPOSE:To uniformly electrify a photoreceptor by providing a roller-like electrode member freely turnably supported in a state where the surface part is abutted on the surface of an electrifying member. CONSTITUTION:An electrifying roller 2 is arranged in close proximity to the surface of the photoreceptor 1 and further, a power feeding roller 3 is arranged in the contact position with the surface of the electrifying roller 2. The gap between the surfaces of the photoreceptor 1 and the electrifying roller 2 is kept 3-1000mum by a spacer 4, so that when the surface layer of the electrifying roller 2 is electrified to a high potential, a discharge occurs in the very small gap between this surface layer and the surface layer (photoreceptive layer) of the photoreceptor 1 and it is electrified. When the photoreceptor 1 is rotated/ driven, the drive force is transmitted to the electrifying roller 2 via the spacer 4, to rotate the electrifying roller 2 as well. Further, when it is rotated, the paper feeding roller 3 is rotated in accordance with the rotation of the electrifying roller 2, as well. Therefore, it is electrified with a uniform voltage distribution all around the periphery of the surface layer of the roller 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for an image forming apparatus, and can be used in, for example, a copying machine, a facsimile, a laser printer and the like.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, corona discharge has been widely used as a charging means for uniformly charging the entire surface of a photoconductor. The corona discharge method is effective as a means for uniformly charging the photoconductor to a certain voltage, but it requires a high-voltage power source, and ozone is generated with the discharge. Generation of a large amount of ozone not only adversely affects the environment, but also involves the problem that ozone deteriorates the charging member, the photoconductor, and the like.

Therefore, as described below, various types of charging devices have been proposed in which the photosensitive member is charged by means other than corona discharge.

For example, a charging roller provided with an elastic conductive layer (or an elastic semiconductive layer) on a core metal is brought into pressure contact with the surface of the photoconductor, and in that state, an electric current is caused to flow from the charging roller to the photoconductor.
A charging device that charges a photoconductor has been proposed. However, in the case of this type of charging device, if the same portion of the charging roller and the photoconductor is kept in contact with each other for a long time, the charging characteristic of that portion is easily deteriorated. Therefore, when a halftone image is formed, white or black line image defects occur on the image corresponding to the deteriorated portion at the circumferential pitch of the photosensitive drum.

In order to solve this problem, for example, in the technique disclosed in Japanese Patent Laid-Open No. 4-157485, the charging member is pressed against the photosensitive member only when the charging operation is performed, and the charging member is not pressed against the photosensitive member when the charging is not performed. I am trying to move it to the position. However, in this apparatus, it is necessary to provide a complicated mechanism for moving the charging member, and control becomes complicated.

Further, when the charging roller is in contact with the photosensitive member, even a small amount of toner remaining on the photosensitive member is transferred to the charging roller side. Therefore, a cleaning blade or a cleaning brush is used to clean the toner. It must be attached to the charging roller.

In order to solve the above-mentioned problems caused by the contact between the charging device and the photosensitive member, for example, Japanese Patent Laid-Open No. 62-62160.
In JP-A-296174, the volume resistance is 10 ⁶ to 10 ¹³
It has been proposed to perform non-contact charging by a charging device including a solid electrode made of a high electric resistance of Ωcm and a voltage applying electrode formed on one side surface thereof. However, with such a configuration, it was difficult to uniformly charge. In particular, if there are projections or pinholes on the charging member or the photoreceptor, lightning strikes often occur and uniform charging characteristics cannot be obtained.

Further, in order to make the surface characteristics of the charging roller medium resistance, it is preferable to use a surface layer material composed of a high resistance paint in which conductive powder is dispersed or a conductive paint is mixed and dispersed. However, due to the influence of dispersion and mixed state,
When a halftone image is formed, a pattern of uneven dispersion or uneven mixing tends to appear as uneven density on the image as it is, and uniform density cannot be obtained.

In order to improve the uniformity of charging, Japanese Patent Application Laid-Open No. Sho 6-96
In the "contact charging method" of JP-A-3-149668, it is proposed to improve the uniformity of charging by superimposing an AC voltage having a peak-to-peak voltage that is at least twice the charging start voltage when a DC voltage is applied. ing. However, in this method, since a high-voltage AC voltage is superimposed, an AC power source is provided separately from the DC power source.
A power source is required, which increases the cost of the device itself. Furthermore, since a large amount of AC current is consumed, a large amount of ozone is generated, resulting in deterioration of the charging member and the photoconductor.

[0010]

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to solve the above-mentioned various problems and to realize uniform charging of a photoconductor.

[0011]

In order to solve the above problems, according to the present invention, in a charging device for charging a body (1) to be charged, at least a surface portion thereof is made of an electrically insulating material and is rotated. A roller-shaped charging member (2) that is freely supported; a gap holding member (4) that supports the charging member in a non-contact state with the member to be charged and holds the gap between the two members constant. A roller-shaped electrode member (3), at least the surface portion of which is made of a conductive material, and which is rotatably supported while the surface portion is in contact with the surface of the charging member.
And a power transmission means (4) for applying a rotational force to the charging member and the electrode member, and by applying a voltage to the electrode member, the charged body is charged through the charging member.

In the second aspect, the gap between the member to be charged and the charging member is set within the range of 3 to 1000 μm.

The symbols shown in parentheses are the reference numerals of corresponding elements in the embodiments described later, but each constituent element of the present invention is a concrete element in the embodiments. It is not limited to only.

[0014]

In the present invention, the roller-shaped charging member (2) and roller
When the electrode member (3) is constantly in contact with the electrode member (3) and a high voltage (much lower than corona discharge) is applied to the electrode member (3), its potential is changed from the surface of the electrode member (3). It is transferred to the surface of the charging member (2). At this time, on the surface of the electrode member (3), due to the protrusions and pinholes,
The voltage distribution may be non-uniform, but when transferred to the charging member (2), the voltage distribution on the surface of the charging member (2) becomes substantially uniform due to the characteristics of the charging member (2). Become. Further, since the charging member and the electrode member are rotated by the power transmission means (4), the entire peripheral surface of the charging member (2) is uniformly charged. Since the charging member (2) is arranged in a position that is in non-contact with and close to the photoconductor by the gap holding member (4), the charging member (2) and the photoconductor are separated by the charging potential of the charging member (2). Discharge occurs between the gaps, and the photoreceptor is charged.

Therefore, uniform charging of the photosensitive member can be realized,
Moreover, since the photoconductor and the charging member (2) are not in contact with each other,
It is not necessary to clean the charging member (2), and it is possible to prevent deterioration of the charging characteristics due to contact.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the structure of the main part of a charging device embodying the present invention. This will be described with reference to FIG. The photoconductor 1 is formed in a drum shape and is used for forming an image in a copying machine or a laser printer. That is, the photoconductor 1
After uniformly charging the surface of the sheet to a predetermined high potential, the photoreceptor 1 is irradiated with light corresponding to the image to be recorded,
A potential distribution corresponding to an image, that is, an electrostatic latent image is formed on the photoconductor 1. When this electrostatic latent image is passed through a predetermined developing device, the toner in the developing device adheres to the photosensitive member according to the potential distribution,
A visible image of the toner is formed. By transferring this toner image onto a predetermined transfer paper, an image can be recorded on the transfer paper.

As shown in FIG. 1, a charging roller 2 is arranged close to the surface of the photosensitive member 1, and the charging roller 2 is further provided.
The power feeding roller 3 is arranged at a position in contact with the surface of the.
As shown in FIG. 2, the charging roller 2 includes a metal core bar 21.
And an electrically insulating surface layer 22 formed on the surface thereof. Further, the charging roller 2 is formed integrally with the spacers 4 attached to both ends 21a and 21b of the cored bar 21, respectively. Further, the charging roller 2 is rotatably supported by a frame of the apparatus by a bearing (not shown). With this bearing, the charging roller 2 has a spacer 4 on the surface of the photoconductor 1 as shown in FIG. It is positioned so as to always come into contact with.

Since the diameter of the spacer 4 is slightly larger than the diameter of the charging roller 2, the charging roller 2 and the photoconductor 1 are not in contact with each other, and the gap between them is kept constant by the spacer 4. Has been done. Further, in order to make this gap constant, the circumferential surface of the cored bar 21 is finished with high accuracy. Although the surface of the charging roller 2 and the surface of the photoconductor 1 are not in contact with each other, since the spacer 4 is in contact with the surface of the photoconductor 1, the spacer 4 and the photoconductor 1 contact with each other due to friction between them. I am fit. That is, when the photoconductor 1 is rotationally driven, the spacer 4 is driven around along with it, and the charging roller 2 integrated with the spacer 4 is rotated.

Although the surface layer 22 of the charging roller 2 is a single layer in FIG. 2, a multilayer structure of two or more layers is also possible. When the charging roller 2 is made of resin, the surface layer 22 may be omitted.

On the other hand, the power feeding roller 3 is constructed as shown in FIG. That is, an elastic material is wound on the circumference of a metal cored bar 31 to form an elastic layer 32, and a surface layer 33 is coated on the elastic layer 32. The elastic layer 32 is provided to increase the area of the contact portion with the charging roller 2. The surface layer 33 is formed of a conductive material and has sufficient durability and life as a surface layer film.

This power feeding roller 3 has both ends 31 of a cored bar 31.
A and 31b are rotatably supported by bearings (not shown), and the surface layer 33 is positioned so as to always contact the surface layer 22 of the charging roller 2. Therefore, the power feeding roller 3 and the charging roller 2 are always engaged by the friction of their contact portions, and when the charging roller 2 rotates, the power feeding roller 3 rotates around accordingly.

An electrode contact (not shown) connected to a predetermined power supply terminal is in contact with the core metal 31 of the power supply roller, and this power supply terminal is not shown when the photoconductor 1 is charged. A voltage is applied from a DC power supply.

When a high voltage is applied to the cored bar 31 from the power supply terminal of the power supply roller 3, the surface layer 33 of the power supply roller 3 becomes equal in voltage to this high voltage. Since the surface layer 22 of the charging roller 2 is in contact with the surface layer 33 of the power feeding roller 3, when a voltage appears on the surface of the former, the voltage is applied to the charging roller 2.
Is transferred to the surface layer 22 of.

At this time, on the surface layer 33 of the power feeding roller 3, unevenness in the voltage distribution often occurs due to the projections and pinholes formed therein. However, it has been confirmed that, when the voltage distribution is transferred onto the surface layer 22 of the charging roller 2, it changes depending on the characteristics of the charging roller 2, and the voltage distribution on the surface layer 22 becomes substantially uniform.

When charging the photoconductor 1,
Since the photoconductor 1 is rotationally driven, its driving force is transmitted to the charging roller 2 via the spacer 4, and the charging roller 2 also rotates. Further, when the charging roller 2 rotates, the power feeding roller 3 is driven to rotate accordingly. Therefore, the charging roller 2 is charged with a uniform voltage distribution over the entire peripheral surface of the surface layer 22.

Since the gap between the surface of the photosensitive member 1 and the surface of the charging roller 2 is kept at 3 to 1000 μm by the spacer 4, when the surface layer 22 of the charging roller 2 is charged to a high potential, the surface layer 22. A discharge is generated in a minute gap between the surface layer 11 of the photoconductor 1 (photosensitive layer) and the photoconductor 1 is charged.

Experiments for measuring the characteristics of various examples and one comparative example, which will be described below, in order to investigate the difference between the conventional example and the characteristic due to the change in the configuration of the charging roller 2 and the power feeding roller 3 Was carried out.

[Structure of Example 1] Charging roller core metal 21: SUS303 Surface layer 22: Fluororesin Lumiflon LF100 manufactured by Asahi Glass Co., Ltd., block isocyanate as a curing agent Power supply roller core metal 31: SUS303 elastic layer 32: Epichlorohydrin rubber (trade name: epichroma) manufactured by Daiso Co., Ltd. (composition per 100 polymers): Tin stearate 1 Active magnesia 5 NA-22 1.5 Anti-aging NBC 2 Extruded into a cylindrical film shape, a metal roll. When la was inserted, it was rolled, steamed and vulcanized.

After that, the surface of the power feeding roller was polished.

Surface layer 33: Lumiflon and epichroma
1: 1 mixed material was spray-painted. Film thickness is 5
μm.

[Structure of Embodiment 2] Charging roller core metal 21: SUS303 Surface layer 22: Fluororesin Lumiflon LF100 manufactured by Asahi Glass Co., Ltd., block isocyanate as a curing agent Power supply roller core metal 31: SUS303 elastic layer 32: Epichlorohydrin rubber (trade name: epichroma) manufactured by Daiso Co., Ltd. (composition per 100 polymers): Tin stearate 1 Active magnesia 5 NA-22 1.5 Anti-aging NBC 2 Extruded into a cylindrical film shape, a metal roll. When la was inserted, it was rolled, steamed and vulcanized.

After that, the surface of the power supply roller was polished.

Surface layer 33: None [Structure of Example 3] Charging roller core metal 21: A5052 Surface layer 22: SR2410 power supply roller core metal 31 manufactured by Toray Dow Corning Silicone Co., Ltd. SUS303 Elastic layer 32: Diso -Epichlorohydrin rubber (trade name: Epichroma) manufactured by Co., Ltd. (per 100 polymer): Tin stearate 1 Active magnesia 5 NA-22 1.5 Anti-aging NBC 2 Extruded into a cylindrical film and inserted with a metal roller. Then, it was rolled and steamed and vulcanized.

After that, the surface of the power feeding roller was polished.

Surface layer 33: Lumiflon and epichroma
1: 1 mixed material was spray-painted. Film thickness is 5
μm.

[Structure of Example 4] Charging roller core metal 21: A5052 surface layer 22: SR2410 power supply roller core metal 31 manufactured by Toray Dow Corning Silicone Co., Ltd. SUS303 elastic layer 32: manufactured by Daiso Co., Ltd. Epichlorohydrin rubber (trade name: epichroma) Compounding (per 100 polymer): Tin stearate 1 Active magnesia 5 NA-22 1.5 Anti-aging NBC 2 Cylindrical film extruded and steamed with a metal roller inserted. Vulcanized

After that, the surface of the power supply roller was polished.

Surface layer 33: None [Structure of Example 5] The entire charging roller was made of high-density polyethylene.

Power supply roller Core metal 31: SUS303 Elastic layer 32: Epichlorohydrin rubber (trade name: epichroma) manufactured by Daiso Co., Ltd. Compounding (per 100 polymer): Tin stearate 1 Active magnesia 5 NA-22 1.5 Aging Preventing NBC 2 A film was extruded into a cylindrical film, wound with a metal roller, and then steamed and vulcanized.

After that, the surface of the power supply roller was polished.

Surface layer 33: None [Structure of Comparative Example] The charging roller 2B is shown in FIG.
It was placed close to the photoconductor and a voltage was directly applied to the charging roller 2B. No power supply roller is provided. Charging roller 2B is core metal 2
1B, elastic layer 32B and surface layer 22B.

Core bar 21B: SUS303 Elastic layer 32B: Epichroma Surface layer 22B: A material in which Lumiflon and epichroma were mixed in a ratio of 1: 1 was spray-coated. The film thickness is 5 μm.

The results of the experiment are shown in Table 1 below.

[0044]

[Table 1]

Referring to the results in Table 1 above, Examples 1 to 1
In all cases of 5, the remarkable effectiveness is recognized with respect to the uniformity of charging. Further, in Examples 2, 4 and 5 in which the surface layer does not exist on the power feeding roller, the necessity of cleaning the charging roller is recognized to some extent. Therefore, a cleaning blade or a cleaning pad is provided near the charging roller 2. It is desirable to clean it.

Although the charging device used in the charging process of the image forming apparatus has been described in the above embodiment, the transfer device used in the transferring process of the image forming apparatus basically performs the same charging function. As such, the present invention can also be implemented in a transfer device.

In an experiment in which the gap between the photoconductor 1 and the charging roller 2 was set outside the range of 3 to 1000 μm, good charging performance could not be obtained.

[0048]

As described above, according to the present invention, since the charging roller 2 is not in contact with the photoconductor 1, it is possible to prevent the charging performance from deteriorating due to the influence of the pressure contact, and the rotation cycle of the photoconductor 1 can be prevented. Image defects such as white lines or black lines do not occur. Further, since the charging roller 2 is not in contact with the photoconductor 1, the toner remaining on the photoconductor is difficult to transfer to the charging roller side (especially when the surface layer is provided), and the good charging performance is maintained for a long time. sell.

In the present invention, the charging roller is charged by the power feeding roller. However, in this process, uneven charging on the power feeding roller is made uniform, so that uniform charging characteristics can be obtained. In the conventional charging roller in which the conductive powder is dispersed in the high-resistance paint or the conductive paint is mixed and dispersed to obtain medium resistance, uneven charging occurs due to uneven distribution or mixing, but in the present invention, non-contact Therefore, uneven charging does not occur. In addition, since it is indirectly charged, lightning strikes no longer occur and the occurrence of this abnormal image disappears.

Further, by setting the gap between the photoconductor and the charging roller to 3 to 1000 μm as in the second aspect, preferable charging characteristics can be obtained.

[Brief description of drawings]

1A and 1B show a configuration of a charging device of an embodiment, FIG. 1A is a front view and FIG. 1B is a side view.

FIG. 2 is a front view showing the configuration of the charging roller 2 of FIG.

3 is a front view showing the configuration of a power feeding roller 3 of FIG. 1. FIG.

FIG. 4 is a front view showing a configuration of a charging device of a comparative example.

[Explanation of symbols]

 1: Photoconductor 2: Charging roller 21: Core metal 22: Surface layer 3: Power feeding roller 31: Core metal 32: Elastic layer 33: Surface layer 4: Spacer

Claims (2)

[Claims] 1. A charging device for charging an object to be charged: a roller-shaped charging member, at least a surface portion of which is made of an electrically insulating material and is rotatably supported; A gap holding member that supports the member to be charged in a non-contact state and holds a gap between both members constant; at least a surface portion of the member is made of a conductive material, and the surface portion contacts the surface of the charging member. A roller-shaped electrode member that is rotatably supported in a contact state; and a power transmission unit that applies a rotational force to the charging member and the electrode member; are provided by applying a voltage to the electrode member. A charging device, characterized in that the charging target is charged via a charging member. 2. The charging device according to claim 1, wherein a gap between the member to be charged and the charging member is set within a range of 3 to 1000 μm.