JPH07104557A - Image forming device - Google Patents

Abstract

PURPOSE:To make the durability of a device high, to prolong the life of the device and to obtain an excellent image by providing a high-resistance layer or an insulating layer on the outside of the image forming area of an elastic electrostatic charging member. CONSTITUTION:The high-resistance layer or the insulating layer 20 is provided at both ends of the elastic layer 2a of an electrostatic charging roller 2 being the elastic electrostatic charging member. The roller 2 is obtained by providing a conductive rubber layer such as EPOM, etc., as the elastic layer 2a provided on the upper layer of a core bar 2b, a middle resistance layer consisting of epichlorohydrin rubber on the layer 2a, and a blocking layer consisting of nylon- based substance as the surface layer on the middle resistance layer. The high- resistance layer 20 consists of the same nylon-based substance as the surface layer 3 and is applied to the outside of the image forming area. By making resistance at the end of the electrostatic charging roller larger than that in other part so that a current hardly flows at the end of the electrostatic charging roller, a photoreceptor drum is prevented from being shaved because of the concentration of the current at the end of the electrostatic charging roller.

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 or a printer, which is characterized by a charging device for uniformly charging an image carrier.

[0002]

2. Description of the Related Art FIG. 12 shows a schematic structure of a conventional image forming apparatus. In the figure, the image forming apparatus includes a photosensitive drum 1 which is an image carrier at the center thereof, and a charging roller 2 which is an elastic charging member, a developing device 4, a transfer roller 5, a cleaner 7 and a fixing device 9 around the photosensitive drum 1. I have it. The photosensitive drum 1 is composed of a metal conductive base material 1b and a photoconductor layer 1a provided thereon.

The charging roller 2 is composed of a conductive cored bar 2b and an elastic layer 2a provided on the surface layer of the conductive cored bar 2b.
Are pressed against the photosensitive drum 1 by spring members and the like attached to both ends of the photosensitive drum 1. Also, conductive core metal 2b
A charging roller bias power supply 11 is connected to the charging roller bias power supply 11, and an AC bias (AC) superimposed on the DC bias (DC) is applied.

Further, the developing device 4 has a developing sleeve 4a provided so as to face the photosensitive drum 1, and the developing sleeve 4
The developing bias power source 12 is connected to a.

The transfer roller 5 is composed of a cored bar 5b and a medium resistance elastic layer 5a provided on the surface layer thereof, and a bias power source 13 is connected to the cored bar 5b. The cleaner 7 has a cleaning blade 7a, which removes toner and paper dust remaining on the photosensitive drum 1. The fixing device 9 is composed of a fixing roller 9a and a pressure roller 9b.

In the image forming apparatus constructed as described above, the photosensitive drum 1 rotates in a fixed direction around its axis, and its surface is uniformly charged by the charging roller 2 and then exposed by the exposure light 3. An electrostatic latent image is formed.
The electrostatic latent image is transferred from the developing bias power source 12 to the developing sleeve 4a.
The developing bias applied to the toner makes the developer (toner) visible. The toner image visualized on the photosensitive drum 1 is transferred to a transfer material (not shown) guided between the photosensitive drum 1 and the transfer roller 5 by a transfer guide 6, and the transfer material is fixed by a conveyance guide 8 to a fixing device. After being transported to 9, the toner image is fixed on the transfer material by heating under pressure to obtain a permanent image.

In the above image forming apparatus, using a contact charging member such as a charging roller to charge the photosensitive drum makes it easier to lower the power supply voltage than using a corona charger. In addition, there are advantages such as less generation of unpleasant corona products such as ozone.

[0008]

However, in the conventional charging roller, a convex portion 2c is formed at the end of the charging roller by dipping such as a multi-layer roller, as shown in an exaggerated manner in FIG. As shown exaggeratedly in FIG. 14, the edge rising portion 2d is formed when the edge portion is cut, and as a result, at the portion of the charging roller that abuts the edge portion having the convex portion 2c or the edge rising portion 2d. There was a problem that the amount of abrasion of the photosensitive drum was extremely large compared to the amount of abrasion of the photosensitive drum in other parts.

The cause of this is that an alternating current bias (A) superposed on a direct current bias (DC) from the charging roller bias power source.
C) is applied to the charging roller, current concentrates on the convex portion 2c or the rising portion 2d at the end of the charging roller, and the current flows intensively, whereby the abrasion of the photosensitive drum is rapidly promoted. It has been clarified by the study by the inventors of the present application.

As a problem due to the abrasion of the photosensitive drum, for example, in the case of a reversal developing system, when the edge of the charging roller is in the sheet passing area and the abrasion of the photosensitive drum occurs in the sheet passing area, the photosensitive drum of the charging roller is damaged. In some cases, the charging cannot be performed to a predetermined potential, a charging failure occurs, and the end portion of the transfer material is soiled. Also. Even if the edge of the charging roller is outside the paper passing area and the photoconductor drum is scraped in the non-paper passing area, the photoconductor layer of the photoconductor drum is scraped, and in the case of the charging method by constant current control, the AC bias If V _PP (peak-to-peak voltage) cannot be sufficiently output and charging failure occurs, or if the photosensitive drum is further scraped, a leak occurs between the charging roller and the conductive base material of the photosensitive drum, causing charging failure. Then, a black belt image may appear.

The abrasion of the photosensitive drum greatly affects the life of the photosensitive drum. Particularly, in the contact charging method in which an AC bias is applied to the charging roller, the abrasion of the photosensitive drum is large and the durability is high, and the charging, developing, cleaning device, etc. This has been a problem that hinders the high durability of the integrated process cartridge.

In recent years, a DC contact charging method has been used in which only a DC bias is applied to the charging roller 2 from the charging roller bias power source 14 as shown in FIG.
Even in the charging method that applies only the DC bias without applying the AC bias, the photosensitive drum is less scraped compared to the system that applies the AC bias, but the uniform charging ability is low and the charging failure is likely to occur. Problems such as defective charging due to abrasion of the photosensitive drum at the end portion of the charging roller due to current concentration in the area are the same as above.

Further, the charging roller is constructed so as to rotate following the photosensitive drum, and the charging roller is caused to adhere to the charging roller by adhesion of toner, paper powder or the like, or the friction coefficient of the charging roller surface decreases. The toner is embedded on the photosensitive drum and adheres to it, which appears as black sesame in the case of reversal development and white sesame as in the case of regular development. Sometimes there was a problem.

Therefore, an object of the present invention is to prevent the abrasion of the image bearing member by the elastic charging member and prevent the occurrence of fusion due to the driven roller rotation of the charging roller against the image bearing member. Is to provide.

[0015]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, the present invention is
In an image forming apparatus including a rotatable image carrier, an elastic charging member that is in pressure contact with the image carrier, and a bias power supply for applying a charging bias to the elastic charging member, an image is formed by the elastic charging member. The image forming apparatus is provided with a high resistance layer or an insulating layer outside the region.

Preferably, the elastic charging member is a rotary elastic body, and the coefficient of friction of the surface of the high resistance layer or the insulating layer of the elastic charging member is larger than the coefficient of friction of the surface of the elastic charging member.

Further, preferably, the elastic charging member is a plate-like elastic body, and the friction coefficient of the surface of the high resistance layer or the insulating layer at the end of the elastic charging member is higher than the friction coefficient of the surface of the elastic charging member. small.

According to another aspect of the present invention, a charging bias is applied to a rotatable image carrier, an elastic charging member that is in pressure contact with the image carrier, and a conductive cored bar of the elastic charging member. An image forming apparatus including a bias power supply for providing a high resistance layer or an insulating layer on a joint surface between the conductive cored bar and the elastic charging member outside the image forming area of the elastic charging member. A characteristic image forming apparatus is provided.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus according to the present invention will be described below in more detail with reference to the drawings. In the embodiments described below, the image forming apparatus of FIG. 12 or 15 is embodied, and the same members as those described above are designated by the same reference numerals, and particularly, the elastic member which is a characteristic part of the present invention. The charging member will be described.

Embodiment 1 With reference to FIGS. 1 and 2, a first embodiment of the elastic charging member according to the present invention will be described.

As shown in FIG. 1, this embodiment is characterized in that a high resistance layer or an insulating layer 20 is provided at both ends of the elastic layer 2a of the charging roller 2 which is an elastic charging member.

In the charging roller 2, as the elastic layer 2a provided on the core metal 2b, 10 ⁴ to 10 ⁵ such as EPDM is used.
A conductive rubber layer of Ωcm is provided, a medium resistance layer of about 10 ⁷ to 10 ⁹ Ωcm made of hydrin rubber or the like is provided on the conductive rubber layer, and a blocking layer of 10 ⁷ to 10 ¹⁰ Ωcm made of a nylon material is provided thereon as a surface layer. In addition, hardness is Asker
It is about 40 to 70 degrees in -C measurement.

The high-resistance layer 20 is actually made of a nylon-based material similar to that of the surface layer, has a thickness of 10 ¹⁰ Ωcm or more, and has a thickness of 100 μm, and is applied outside the image forming area as shown in FIG.

As described above, the resistance of the end portion of the charging roller is made larger than the resistance of the other portions to make it difficult for the current to flow at the end portion of the charging roller. It was possible to prevent scraping. The high resistance layer applied to the end portion is preferably an insulating layer, but if the resistance is higher than the other portions, the effect of reducing the abrasion of the photosensitive drum by the end portion of the charging roller is exhibited.

When the charging roller has a straight shape, as shown in FIG. 2, by applying a high resistance layer or an insulating layer 20 to the convex portion 2c formed at the end of the charging roller 2, Although the diameter of the end portion is larger than the diameter of the central portion of the charging roller, since the charging roller 2 has elasticity, it is possible to form a nip, and the charging roller 2 and the photosensitive drum 1 can be securely connected. If the shape of the charging roller is a crown shape with a large diameter at the center so that it abuts, the contact nip can be made the same as before by adjusting the crown amount (center diameter-end diameter). The thickness of the high resistance layer or the insulating layer 20 in the part does not matter.

The convex portion of the end portion of the multi-layer charging roller by the dip method has been described above. Regarding the charging roller 2 having an edge-like portion 2d at the end when cutting the end portion as shown in FIG. Can be said as above. Further, as shown in FIGS. 4 and 5, the high resistance layer or the insulating layer 20 is applied also to the side surface portion (non-contact surface with the photosensitive drum) 2e of the multilayer elastic layer 2a, so that the dip type liquid It is possible to prevent dripping, uneven coating, leakage from the base layer in the cutting method, and oil seepage.

Embodiment 2 In this embodiment, the friction coefficient of the surface of the high resistance layer or the insulating layer 20 applied to the end portion of the charging roller 2 in the first embodiment is more than the friction coefficient of the surface layer of the charging roller 2. It is characterized by making it larger. As a result, slipping of the charging roller 2 with respect to the photosensitive drum 1 can be prevented, and fusion can be reduced.

The surface layer of the elastic layer 2a of the charging roller has resistance, hardness, permanent deformation prevention, exudation of internal oil and the like,
It must have many functions such as prevention of sticking to the drum and prevention of fusion, and the materials are limited. However, it is sufficient that the end portion has a high resistance or an insulating material and has a large friction coefficient. Therefore, in the charging roller of this embodiment, the surface of the elastic layer 2a has the charging performance, and the high resistance at the end or the insulating layer 20 has the function of preventing current concentration and gripping the photosensitive drum. Therefore, there is an advantage that the degree of freedom can be given to the design.

Third Embodiment Next, a third embodiment of the elastic charging member according to the present invention will be described with reference to FIGS. 6 and 7.

In the first and second embodiments, the charging roller has been described as the elastic charging member. However, as shown in FIG. 6, the elastic charging member of this embodiment has a high resistance layer or an end portion of the charging blade. It is characterized in that an insulating layer is applied. As a result, it is possible to prevent abrasion of the photosensitive drum due to current concentration at the charging blade end portion.

More specifically, referring to FIG. 6, both ends of the non-image forming area of the charging blade 31 supported by the conductive support 30 for applying the charging bias are coated with the high resistance layer or the insulating layer 32. As a result, as shown in the enlarged view of FIG. 7, the end portion of the charging blade is configured to increase the electric resistance of the ear rise portion 32d due to burrs and the like at the time of blade formation and prevent current from flowing. It is possible to prevent abrasion of the photosensitive drum.

Further, by making the friction coefficient of the high resistance layer or the insulating layer 32 at the end of the charging blade smaller than that of the other blades 31, it is possible to prevent abrasion of the photosensitive drum due to the side angle of the charging blade 31.

Fourth Embodiment Next, a fourth embodiment of the elastic charging member according to the present invention will be described with reference to FIGS. 8, 9 and 10.

The charging roller, which is the elastic charging member of this embodiment, is characterized in that cap rollers composed of high resistance or insulating members are provided at both ends thereof. As a result, it is possible to prevent current concentration at the end of the charging roller and prevent abrasion of the photosensitive drum.

In this embodiment, as shown in FIG.
Conventional charging roller 2 with an outer diameter of 16 mm and a core metal of 6 mm
Is used to cover the end portion of the elastic layer 2a with the cap roller 40.

As is apparent from FIG. 9, the cap roller 40 is composed of a circumferential portion 40a that covers the end peripheral surface of the elastic layer 2a and a disc portion 40b that covers the end side surface, and the disc portion 40b.
A through hole 40 that penetrates the charging roller core metal 2b is formed at the center of the
c is provided. The material used was POM (Delrin DE850) having an insulating property.

By using such a cap roller 40, abrasion of the photosensitive drum at the end of the charging roller could be prevented.

Further, as shown in FIG. 10, the thickness t1 of the contact surface of the cap roller 40 with the photosensitive drum is set to 150 μm in the present embodiment, but depending on the hardness and durability of the charging roller, The thickness can be arbitrarily set as long as the nip width of the photosensitive drum is sufficiently large.

Further, the nip width between the charging roller and the photosensitive drum and the crush amount of the charging roller elastic layer 2a are uniquely determined by the distance t2 to the core metal 2b on the side surface of the cap roller 40. Regardless of the fluctuation of the pressing pressure to the drum or the fluctuation of the hardness of the charging roller,
Since the nip width is determined, stable charging performance can be maintained. Further, even if the elastic charging member is permanently deformed by being left for a long period of time, a load over a certain level is not applied, so that the amount of crushing is constant and the amount of permanent deformation is small.

Particularly, in order to reduce the charging noise, the base layer is made of foamed EPDM and the hardness is 10 to 40 degrees (Asker C
In the case of a charging roller with a hardness meter (measured by a hardness meter) and a smaller charging roller, the resistance change due to permanent deformation also increases, so the cap roller method is effective.

Fifth Embodiment Next, a fifth embodiment of the elastic charging member according to the present invention will be described with reference to FIG.

The charging roller of this embodiment is characterized in that a high resistance layer or an insulating layer is provided on the cored bar located outside the image forming area at the end of the charging roller. by this,
It becomes difficult for an electric current to flow to the end of the charging roller, and abrasion of the photosensitive drum at the end of the charging roller can be prevented.

As shown in FIG. 11, the thickness t of the elastic layer 2a is obtained by applying or capping the insulating layer 50 on the portion of the conductive cored bar 2b located at the end of the elastic layer 2a.
The distance t4 of the cored bar 2b from the uncoated portion of the insulating layer 50 to the end of the elastic layer is larger than 3. Therefore, the volume resistance at the end portion increases, and the amount of current flowing through the end portion can be reduced.

In this embodiment, the nylon-based insulating layer 50 is provided outside the image forming area and on the charging roller elastic layer 2.
The distance t5 from the end surface of a or the apex of the convex portion to the inside of the elastic layer 2a is 4 mm or more, the distance t6 from the end surface of the elastic layer 2a to the outside of the elastic layer 2a is 1 mm or more, and the thickness is 10 μm.
It was applied on the cored bar in the range of ˜2 mm. As a result, it was possible to prevent abrasion of the photosensitive drum at the end portion of the charging roller and leakage at the end surface.

Further, since the current flowing on the side surface of the elastic layer 2a can be reduced, it is possible to prevent the leak from the core metal 2b which occurs when the surface resistance is small, and the surface resistance of the charging roller. Is not necessary, and there is an advantage that the degree of freedom in design is increased. Incidentally, t
The values of 5 and t6 may be appropriately changed depending on the resistance value of the elastic layer 2a.

[0046]

As is apparent from the above description, the image forming apparatus according to the present invention has the structure in which the high resistance layer or the insulating layer is provided outside the image forming area of the elastic charging member. It is possible to prevent the abrasion of the image carrier due to the above, and it is possible to prevent the occurrence of fusion due to the driven rotation of the charging roller which is the elastic charging member with respect to the image carrier. Thereby, high durability and long life of the apparatus can be achieved, and a good image can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a first embodiment of an elastic charging member according to the present invention.

FIG. 2 is an enlarged explanatory view of a main part of the elastic charging member of FIG.

FIG. 3 is a first modification of the first embodiment.

FIG. 4 is a second modification of the first embodiment.

FIG. 5 is a third modification of the first embodiment.

FIG. 6 is an explanatory view showing a third embodiment of the elastic charging member according to the present invention.

FIG. 7 is an enlarged explanatory view of a main part of the elastic charging member of FIG.

FIG. 8 is an explanatory view showing a fourth embodiment of the elastic charging member according to the present invention.

9 is an enlarged explanatory view of a main part of the elastic charging member of FIG.

10 is a cross-sectional view of the cap roller of FIG.

FIG. 11 is an explanatory view showing a fifth embodiment of the elastic charging member according to the present invention.

FIG. 12 is a schematic configuration diagram showing a conventional image forming apparatus.

13 is an enlarged explanatory view of a main part of an elastic charging member used in the image forming apparatus of FIG.

FIG. 14 is an enlarged explanatory view of a main part of another elastic charging member used in the image forming apparatus of FIG.

FIG. 15 is a schematic configuration diagram showing another conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum (image bearing member) 2 Charging roller (elastic charging member) 2a Elastic layer 2b Conductive core metal 11 Bias power source 14 Bias power source 20 High resistance layer or insulating layer 30 Conductive support 31 Charging blade 32 High resistance layer or Insulation layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Norio Hashimoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Masaharu Okubo 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Co., Ltd. (72) Inventor Takayasu Yuminochi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Hiroto Hasegawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (4)

[Claims] 1. An image forming apparatus comprising: a rotatable image carrier, an elastic charging member that is in pressure contact with the image carrier, and a bias power supply for applying a charging bias to the elastic charging member, Outside the image forming area of the charging member,
An image forming apparatus comprising a high resistance layer or an insulating layer. 2. The elastic charging member is a rotary elastic body, and the friction coefficient of the surface of the high resistance layer or the insulating layer of the elastic charging member is larger than the friction coefficient of the surface of the elastic charging member. The image forming apparatus according to claim 1. 3. The elastic charging member is a plate-like elastic body, and the friction coefficient of the surface of the high resistance layer or the insulating layer at the end of the elastic charging member is smaller than the friction coefficient of the surface of the elastic charging member. The image forming apparatus according to claim 1, wherein 4. An image forming apparatus comprising: a rotatable image bearing member; an elastic charging member that is in pressure contact with the image bearing member; and a bias power source for applying a charging bias to a conductive cored bar of the elastic charging member. The image forming apparatus according to claim 1, further comprising a high resistance layer or an insulating layer on a joint surface between the conductive cored bar and the elastic charging member outside the image forming area of the elastic charging member.