JPS6339714Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a developing sleeve in an electrophotographic magnetic brush developing machine that utilizes a conductive carrier.

Conductive carriers have advantages such as increasing the developing electric field strength, enabling uniform and high-density development, and having a longer lifespan than conventional carriers coated with insulating materials. However, if there are defects such as pinholes or scratches on the surface of the photoreceptor, when the developer comes into contact with the defect, there is a gap between the grounded substrate supporting the photoreceptor and the conductive developing sleeve to which a developing bias is applied. A short circuit occurs through the carrier, and the potential of the sleeve drops to near ground potential due to discharge, resulting in low bias development across the entire sleeve, resulting in a black horizontal pattern on the background of the copy.

In order to prevent such a horizontal step pattern, an insulating sleeve may be used, but it has the disadvantage that the effect of the developing bias is reduced and the characteristics of the conductive carrier are lost. Such drawbacks can be solved by covering the surface of the developing sleeve with a member having a certain resistance value. Examples of this method include covering the surface of the metal sleeve with an oxide film and covering the surface of the metal sleeve with a resistive layer of resin or the like.
For example, Japanese Patent Application Laid-Open No. 51-98033 is known as a method implementing method b, but the carrier has poor conveyance properties, the strength of the coating film on the metal sleeve is limited, and scratches etc. occur on the roll surface. In this case, there is a disadvantage that the conductive member in that part is easily exposed.

The object of the present invention is to provide a magnetic brush developing sleeve which eliminates the above-mentioned drawbacks.

The magnetic brush developing sleeve of this invention is 10 ⁷ ~
It has a resistivity of 10 ¹⁰ Ωcm and is made of a cylindrical member molded from a resin material. The resin material mentioned above can be molded into a pipe shape, and includes phenol resin, epoxy resin, polyethylene resin, and the like. The cylindrical member used in this invention is hollow and cylindrical by lamination or extrusion molding, and when used in a laminated manner, the laminated material may be paper or cloth in the case of phenol resin, glass cloth, etc. in the case of epoxy resin or polyethylene resin. used.

The cylindrical member used in this invention has a resistivity of ¹⁰⁷ to ¹⁰¹⁰ Ω.
It is necessary that the resistivity be in the range of ¹⁰⁷ to 1010 Ωcm. If it is not possible to achieve a resistivity in this range using resin materials or molding methods, it is sufficient to dope the material with a conductive material such as carbon so that the resistivity is in the range of 107 to ¹⁰¹⁰ Ωcm. The appropriate thickness of the sleeve is 1.5 to 5 mm.

In order to perform good development, it is effective to provide a conductive material layer 3 on the inner peripheral surface of the cylindrical member as shown in FIG. This conductive member layer is obtained by applying a conductive paint or pasting a conductive film on the inner peripheral surface of the cylindrical portion. The conductive paint may be a commonly known conductive paint, such as Lowtite (manufactured by Fujikura Kasei), or it may not be a particularly conductive paint; it may be made conductive by adding a conductive material such as carbon to the paint. Anything is fine. As the conductive film, there is a film made of metal or the like.

In this way, the present invention has a small resistance value (10 ⁷ ~
10 ¹⁰ Ω・cm) A developing sleeve made of a resin material is characterized by a conductive material layer provided on the inner circumferential surface thereof. By configuring the developing sleeve in this way, even if defects such as pinholes and scratches occur on the outer peripheral surface of the developing sleeve, a developing bias can be applied more uniformly to the developing sleeve than the conductive material layer on its inner surface. Therefore, there is no possibility that a short circuit will occur between the grounding substrate supporting the photoreceptor and the developing sleeve through the carrier, and the voltage of the entire sleeve will not discharge and drop to near the ground potential.

It is effective to provide unevenness on the outer peripheral surface of the cylindrical member in order to improve the conveyance of the developer, especially the carrier. For example, as shown in the embodiment in FIG. 2, a sleeve in which a large number of grooves 4 are cut along the axial direction on the outer peripheral surface of the sleeve,
Alternatively, there are those in which the outer peripheral surface is randomly roughened by surface roughening treatment using sandblasting or the like.

Further, as a method of utilizing the magnetic field more effectively, it is also possible to use a sleeve in which ferromagnetic particles are scattered and fixed on the sleeve surface or a ferromagnetic material is mixed in the resin of the cylindrical member.

FIG. 3 is an explanatory diagram when the sleeve of the present invention is applied to a developing machine. 8 is a resistor of about 1 MΩ for restricting the discharge current, but it is not necessary when the sleeve of the present invention is applied.

FIG. 4 is a diagram for explaining the action when the developer comes into contact with the peeled portion of the photoreceptor. The carrier forms a carrier chain 10 between the photoreceptor 11 and the sleeve 1 under the force of the magnetic field, and when the photoreceptor peels off and contacts the exposed portion 13 of the ground substrate 12,
Electric discharge occurs in the part where the carrier chain is formed, but the resistivity of the cylindrical member 2 of the developing sleeve 1
10 ⁷ to ^{10 10} Ω·cm, and since a stable developing bias voltage 9 is applied to this cylindrical member by the conductive member layer 3, the potential of the entire developing sleeve 1 and the conductive member layer does not change. There isn't. Therefore, a black horizontal pattern or the like does not appear on the background portion of the copy.

Although the present invention is intended to prevent defects on copies due to short circuit phenomena that occur when using conductive carriers, it can also be applied when using insulating carriers.

Further, it is also possible to apply to a development method known as one-component development. In the case of a one-component development method using magnetic toner, a method in which the sleeve is fixed and an internal magnet rotates is mainstream, but in this case, the sleeve surface may remain smooth. It also suppresses eddy currents caused by alternating magnetic fields and helps prevent heat generation in the sleeve.

[Brief explanation of drawings]

FIG. 1 is a sectional view of one embodiment of the developing sleeve according to the present invention, FIG. 2 is a perspective view of another embodiment of the developing sleeve according to the present invention, and FIG. 3 is a diagram showing how the developing sleeve according to the present invention actually works. FIG. 4, which is a schematic view of the developing sleeve in use, is a diagram illustrating the operation of the developing sleeve according to the present invention. Code in the figure, 1...magnetic brush developing sleeve,
2... Cylindrical member, 3... Conductive member layer, 4...
Groove, 5... Internal fixed magnet, 6... Photosensitive drum, 7
...Conductive developer, 8...Discharge current limiting resistance, 9
... Phenomenon bias voltage, 10 ... Carrier chain, 11 ... Photoreceptor, 12 ... Ground substrate, 13 ...
...Photoreceptor peeling part.

Claims (1)

[Scope of utility model registration request] In the electrophotographic magnetic brush developing sleeve,
A sleeve for magnetic brush development, characterized in that a conductive material layer is provided on the inner peripheral surface of a cylindrical member molded from a resin material having a resistivity in the range of 10 ⁷ to ^{10 10} Ω·cm.