JPH068600Y2 - Charger - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a charger provided facing a photoconductor which is an image forming carrier in an electrostatic electrophotographic copying machine or a facsimile.

(Prior Art) Such a charger usually utilizes a corona discharge action, and is a main charger that charges a photoconductor or a separation (static elimination) for electrostatically separating a sheet after transfer from the photoconductor. There are chargers.

Such a charger is generally composed of a shield case whose surface facing the photoconductor is open, and a wire stretched inside the shield case to which a voltage is applied. It is provided so as to face the photoconductor with only the gap, without the intervening.

By the way, in a charger such as a transfer corona discharger in which a direct current (DC) voltage is applied to a stretched wire, the discharge surface has a high resistance so that the photosensitive body is not directly exposed to the transfer corona. A structure in which the body paper is masked is adopted (Japanese Patent Laid-Open No. 172668/58). In such a transfer corona discharger, if a mask material having a large relative permittivity, that is, a large capacitance component is adopted, the corona discharge is weakened and cannot function, so that a suitable transfer operation is ensured. An insulating material with a smaller capacity component is used.

(Problems to be solved by the invention) On the other hand, in the case of a separation charger or the like in which the power applied to the wire is alternating current (AC), the intensity distribution of corona discharge is substantially constant in the length direction during positive discharge. In contrast,
At the time of negative discharge, a so-called "blind" phenomenon that is strong and weak occurs at certain intervals in the lengthwise direction, and therefore the discharge phenomenon on the photoconductor may not be homogenized.

As a measure to eliminate such inhomogeneity, a method of providing a mask material as used in the above transfer corona discharger on the discharge surface is conceivable, but a material having a material with a low capacity component is preferable from the viewpoint of transfer performance. Is used in a separation charger to which an AC voltage is applied, the phenomenon that the discharge state of the photoconductor is not homogenized still remains.

The present invention has been made in view of the above, and by covering the opening surface of the shield case with an insulator having a large relative permittivity, that is, a large capacitance component, the discharge state of the photoconductor can be obtained regardless of the AC voltage application. Can be homogenized,
It is an object of the present invention to provide a charger capable of obtaining a good charge removal (separation) action.

(Means for Solving the Problem) The present invention provides a charger including a shield case arranged to face the surface of a photoreceptor and a wire stretched in the shield case and to which an AC voltage is applied. It is characterized in that the opening surface of the shield case facing the photoconductor is covered with an insulator having a large relative dielectric constant.

(Operation) According to the present invention, when an AC voltage is applied to the wire, a desired relative induced current can flow in the photoconductor due to the large relative permittivity of the insulator provided on the opening surface, and when the positive discharge occurs. And the component ratio at the time of negative discharge become almost equal to each other, the "blind" phenomenon of strength and weakness in the length direction at the time of negative discharge is suppressed, and the discharge phenomenon to the photoconductor is homogenized.

(Embodiment) First, an electrostatic electrophotographic copying machine to which the present invention is applied will be described with reference to FIG.

In the figure, 1 is a main body of a copying machine, 2 is a contact glass on which an original is placed on the main body 1, 3 is an original holder, 4 is an optical system for exposing and scanning the original, and 5 is an original image. On the photosensitive drum to be irradiated, the main charger 6, the developing device 7, and the developing device 7 are sequentially opposed to the periphery of the photosensitive drum 5.
A process unit including a transfer charger 8, a separation (static elimination) charger 9 and a cleaning device 10 is provided.

Reference numerals 11 and 12 denote a paper feed cassette in which transfer sheets are accommodated, 13 a paper feed roller, 14 a conveyance roller, 15 a registration roller, 16 a conveyance belt, 17 a fixing device, 18 a paper ejection roller, and 19 a paper ejection. It's a tray.

The present invention is applied to the main charger 6 to which an AC voltage is applied, the separation (static elimination) charger 9 and the like. Hereinafter, an example of application to the separation charger 9 will be described with reference to FIGS. 1 and 2. Explain.

The separation charger 9 is composed of a shield case 20 having an opening surface at a portion facing the surface of the photosensitive drum 5, and a wire 21 that is an electrode stretched in the shield case 20 in the length direction. A transfer charger 8 is also formed by partitioning a part of the case 20 with a partition plate 20a, and a wire 22 is also stretched in the transfer charger 8. And the shield case 2
0 has end blocks 23 and 24 at both ends in the length direction, and one end block 23 has wires 21 and 22.
Are provided with electrodes 25 and 26 for applying a voltage, and the other end block 24 is provided with a handle 27 for inserting and removing the separation charger 9 from the main body in the length direction, that is, the axial direction of the photosensitive drum 5. Has been.

Further, in the present invention, the opening surface of the shield case 20 is covered with an insulator 28 such as a polyester film having a large relative dielectric constant, that is, a large capacitance component.

It should be noted that this insulator 28 may be fixed by a method such as sticking to both sides of the shield case 20 in the longitudinal direction, and as shown in the figure, an R shape in which the central portion projects in the circumferential surface direction of the photosensitive drum 5 above the opening. I am trying. By thus forming the R shape, the transfer paper that passes through the gap between the transfer charger 8 and the photosensitive drum 5 located immediately upstream of the separation charger 9 (with respect to the transfer paper conveyance direction A indicated by the arrow) is The photoconductor drum 5 can be set in a position that allows it to approach the photoconductor drum 5 as much as possible, thereby improving transfer efficiency.

Next, the operation of the separation charger 9 having the above configuration will be described.

When an AC voltage power supply is applied to the electrode 25, corona discharge is generated between the wire 21 and the photosensitive drum 5. Here, the alternating current is generated as an induced current due to the electrostatic induction action,
Since the insulator 28 that covers the opening surface of the shield case 20 has a large capacitance component, the current can flow at a required or sufficient level. Due to the presence of the capacitive component of the insulator 28, each current component ratio during positive discharge and negative discharge becomes close to 1: 1, which is suitable for obtaining separation and static elimination action. Moreover, as described above, the dielectric current caused by the capacity component flows, so that the so-called "blind" phenomenon at the time of negative discharge in the corona discharge intensity distribution characteristic is alleviated, and as a result, the homogenization of the discharge state, Can be improved.

The present invention can be applied to any charger other than the separation charger as long as it is a charger to which AC power is applied.
In addition, since the opening surface of the shield case 20 of the charger is covered with the insulator 28, paper dust and toner dust are prevented from entering the shield case 20 or being sucked, and therefore the discharge state changes. It is possible to prevent the deterioration of the performance.

Further, when the insulator 28 is formed into the R shape as described above, if the space a (FIG. 2) on both side surfaces in the length direction due to the R shape is also closed with a polyester film or the like, the inside of the shield case 20 will be closed. The intrusion of dust can be prevented more reliably.

(Effects of the Invention) As described above, the charger to which the AC voltage is applied according to the present invention has an opening surface facing the photosensitive member of the shield case covered with an insulator having a large relative dielectric constant. When the AC voltage is applied to the wire, the ratio of the positive and negative components of the current electrostatically induced in the photoconductor is made constant, and the so-called "blind eye" phenomenon at the time of negative discharge is alleviated. The effect of homogenizing is obtained, and it is suitable for obtaining separation and static elimination action.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an essential part showing an embodiment of the charger of the present invention, FIG. 2 is a perspective view of the charger, and FIG. 3 is a configuration diagram of a copying machine to which the charger is applied. 9 ... Separation charger, 20 ... Shield case, 2
1 ... Wire, 28 ... Insulator.

Claims (1)

[Scope of utility model registration request] 1. A charger comprising a shield case arranged to face a surface of a photoconductor, and a wire stretched in the shield case and to which an AC voltage is applied.
A charger characterized in that an opening surface of the shield case facing the photoconductor is covered with an insulator having a large relative dielectric constant.