JPH0552857U - Charging roller - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a charging roller which can easily obtain uniform pressure contact force in the longitudinal direction with respect to the surface of a photoreceptor and can perform uniform charging. [Structure] The charging roller 12 is provided in contact with the surface of the photoconductor 20 at a predetermined pressure, and its voltage application shaft 14
Has a shape in which the central portion in the longitudinal direction is swollen. Further, the voltage application shaft 14 of the charging roller 12 is provided with a power source 22 capable of applying a voltage in which DC or AC is superimposed.

Description

[Detailed description of the device]

[0001]

[Industrial application]

 The present invention relates to a charging roller.

[0002]

[Prior Art]

 Conventionally, in an electrophotographic apparatus, a device called a scorotron charger has been put into practical use as a charging device that charges a photoconductor for carrying an electrostatic latent image to a predetermined initial potential. This scorotron charger is composed of a wire having a diameter of 100 μm or less, a grid provided so as to face the photoconductor, and a case that integrally holds them. When a high voltage of about -5 kV is applied to the wire in this charger, corona discharge is generated around the wire. By controlling the electric charges generated by this discharge with a voltage of about -500 V applied to the grid, it is possible to uniformly charge the surface of the photoconductor to a voltage almost equal to the voltage applied to the grid.

As described above, the scorotron charger has a feature that the charging potential can be controlled by the voltage applied to the grid and that the charging potential is excellent in uniformity, but a high voltage is applied to the wire. Ozone is generated because it causes corona discharge. This ozone not only emits a peculiar odor and makes the user of the electrophotographic apparatus uncomfortable, but due to its rich chemical activity, it also damages organic substances such as rubber and adversely affects the human body.

Therefore, in order to further suppress the amount of ozone generated, a contact charging method has been proposed and put into practical use. As a typical example of the contact charging method, there is a charging method using a roller having conductivity, that is, a so-called charging roller, as disclosed in JP-A-63-149669. Therefore, the structure and operation of the charging roller will be described below with reference to FIG.

The charging roller 40 has a cylindrical shape with a diameter of about 20 mm as a whole, and carbon particles are dispersed around a stainless rod 42 as a core metal so that the volume resistance value is about 10 ⁵ Ω · cm. The urethane foam rubber layer 44 is covered. Further, the stainless rod 42 is provided with a voltage applying device 46 for applying a bias voltage in which an AC voltage having a peak-to-peak voltage of about 1 to 2 kV is superimposed.

Next, the operation of the charging roller 40 will be described. The charging roller 40 is in contact with the surface of the photosensitive drum 48 having a photosensitive layer 48b made of an organic photosensitive body or amorphous silicon on a conductive substrate 48a such as aluminum under a predetermined pressure. The photosensitive drum 48 rotates in the arrow X direction, and the charging roller 40 rotates in the arrow Y direction as the photosensitive drum 48 rotates. At this time, a bias voltage in which the above-mentioned AC voltage is superimposed is applied to the charging roller 40 by the voltage application device 46, and the surface of the photosensitive drum 48 is uniformly charged to a predetermined potential.

The charging process of the surface of the photosensitive drum 48 by the charging roller 40 at this time includes frictional charging between the roller and the surface of the photosensitive member, charge injection from the surface of the charging roller to the photosensitive member, and charging roller. And an air discharge phenomenon in a minute gap between the photoconductor surface and the photoconductor surface when they contact and dissociate. Of these, the largest contribution to the charging of the surface of the photoconductor is the air discharge phenomenon, so that ozone is also generated in the contact charging method using a charging roller. However, the amount of ozone generated is considerably smaller than the amount generated from a charger using a scorotron wire.

[0008]

[Problems to be solved by the device]

 However, in the charging roller having the above structure, since the pressure contact force to the photoconductor is applied at both ends of the stainless steel rod which is the central axis, the pressure contact force at the center part in the longitudinal direction of the charging roller becomes weaker than at both ends. However, there is a tendency that charging tends to be insufficient in the central portion of the image as a result.

The present invention has been made in order to solve the above-mentioned problems, and the pressing force in the longitudinal direction can be made uniform without adding any special device, and as a result, uniform charging can be performed. An object of the present invention is to provide a charging roller that can be used.

[0010]

[Means for Solving the Problems]

 In order to achieve the above-mentioned object, the charging roller of the present invention comprises a central shaft rotatably supported at both ends and an elastic body provided in a substantially cylindrical shape around the central shaft. Has a diameter at the central portion in the longitudinal direction larger than the diameter at both ends thereof.

[0011]

[Action]

 The charging roller of the present invention having the above structure is applied with a voltage, contacts and rotates the charged body, and charges the charged body to a predetermined potential. At this time, since the central axis of the charging roller is bulged in the central portion, it is easy to obtain a uniform pressure contact force in the longitudinal direction of the charging roller, and the surface of the body to be charged can be uniformly charged. .

[0012]

【Example】

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, the structure of the charging roller of the present invention used as a charging device in an electrophotographic apparatus will be described with reference to FIG. This charging roller is used in an electrophotographic apparatus for the purpose of uniformly and initially charging the surface of a photoconductor, which is an electrostatic latent image carrier, before exposure of image information.

The charging roller 12 includes a voltage application shaft 14 made of stainless steel and an elastic rubber 16 having conductivity and elasticity around the voltage application shaft 14, and its shape is a substantially columnar shape with the voltage application shaft 14 as a central axis. Is. The voltage application shaft 14 has different shaft diameters in the longitudinal direction, and has a slightly swollen shape at the center. Therefore, the layer thickness of the elastic rubber 16 is relatively thin in the central portion.

As the material of the elastic rubber 16, specifically, a rubber material having elasticity such as urethane foam rubber, in which carbon black is dispersed in order to have conductivity, or the like is used. The volume resistance value is adjusted to about 10 ⁵ Ω · cm.

The surface of the elastic rubber 16 is covered with a high resistance layer 18. The material of the high resistance layer 18 is selected from nylon-based materials, polyurethane rubber, polyurethane elastomer, nitryl butyl rubber (NBR), chloroprene rubber, polyethylene terephthalate (PET), among which tin oxide particles, aluminum particles, A small amount of conductive fine particles such as indium oxide particles and titanium oxide particles are dispersed. The layer thickness is as small as 100 μm to 500 μm, and the volume resistance value is about 10 ¹⁰ Ω · cm.

Further, the voltage application shaft 14 of the charging roller 12 is provided with a power supply 22 as a voltage application means, and a DC voltage of a predetermined polarity or a voltage obtained by superimposing an AC voltage on a DC voltage is applied. As the value of the DC voltage, a positive or negative value of about 700 V is selected, and as the value of the AC voltage, a value of about 2 kV between peaks and a frequency of about 1 kHz is selected.

Next, the operation will be described. Since the charging roller 12 is pressed against the photoconductor 20 with a predetermined pressure and is rotatably supported at both ends, the charging roller 12 is rotated by the rotation of the photoconductor 20. Since the voltage having the above-mentioned value is applied to the voltage applying shaft 14, the surface of the photoconductor 20 is injected with charge at the contact portion with the charging roller 12, or before and after the contact / dissociation with the charging roller 12. It is uniformly charged by the mechanism such as charging by minute discharge at

As described above, the charging roller 12 is formed such that the thickness of the voltage applying shaft 14 becomes larger toward the central portion, and therefore, even when a pressure contact force is applied to both ends of the voltage applying shaft 14. The pressing force is easily applied in the central part. Therefore, the pressing force from both ends is uniformly applied in the longitudinal direction, so that the charging is uniformly performed. Therefore, the pressure contact force to be applied to both ends may be small as compared with the conventional charging roller having a cylindrical central axis with the same axial diameter in the longitudinal direction. As a result, not only the rotational torque of the photoconductor 20 is reduced and the burden on the electrophotographic apparatus main body is reduced, but also the degree of wear of the surface of the photoconductor 20 is reduced, which is effective for extending the life of the photoconductor. You can say that.

As is apparent from the above description, in the charging roller 12 of the present embodiment, the voltage applying shaft 14, which is the central axis, has a bulged shape in the central portion, so that the length of the charging roller 12 is long. It is easy to obtain a uniform pressure contact force in the direction, and as a result, the surface of the photoconductor 20 can be uniformly charged.

Besides, the present invention is not limited to the examples described in detail above, and modifications can be made without departing from the spirit of the invention. For example, a charging roller having a two-layer structure in which an elastic rubber layer such as ethylene propylene rubber (EPDM) / nitrile butyl rubber (NBR) is provided on the voltage application shaft and a urethane rubber layer in which carbon black is dispersed is provided on the peripheral surface thereof. good.

[0021]

[Effect of the device]

 As is clear from the above description, in the charging roller of the present invention, the central axis is bulged in the central portion, so that it is easy to obtain a uniform pressure contact force in the longitudinal direction of the charging roller. As a result, the surface of the body to be charged can be uniformly charged.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a charging roller according to the present exemplary embodiment.

FIG. 2 is a configuration diagram of a conventional charging roller.

[Explanation of symbols]

 12 Charging roller 14 Voltage application shaft 16 Elastic rubber

Claims (1)

[Scope of utility model registration request] 1. A charging roller comprising a central shaft rotatably supported at both ends and an elastic body provided in a substantially columnar shape around the central shaft, wherein a diameter of the central shaft at a central portion in a longitudinal direction. However, the charging roller is characterized in that it is larger in diameter than both ends thereof.