JPH0451831B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing device such as a copying machine or an electrostatic recording device using a one-component developer.

A developing device using one-component development uses a developing sleeve in which a large number of magnetic substances are distributed on the outer circumferential surface, and a magnet provided inside the developing sleeve and having a large number of magnetic poles in which N poles and S poles are arranged alternately. A developing device that forms a developer layer, such as a toner layer, on the circumferential surface of the rotating developing sleeve and brings the developer layer into contact with a latent image carrier on which an electrostatic latent image has been formed to visualize the latent image. It has been known.

In the above-mentioned known developing device, an attempt has been made to make the developer layer as thick as possible in order to improve the conveyance of the developer. However, in order to improve the development effect, it is better to have a large amount of charge on the developer, but when the thickness of the developer layer on the developing sleeve is increased, the electric field near the developing sleeve becomes larger and the charge is reduced. There was a problem in that the amount of charge of the developer could not be increased too much because run-off would occur.

The present invention provides a developing device that can thin the developer layer of a developer carrier, such as a developing sleeve, in order to increase the amount of charge of the developer. The object of the present invention is to provide a developing device capable of performing development.

The present invention focuses on development in which a magnetic material placed in a magnetic field moves toward the direction of higher magnetic flux density, and the developer made of the magnetic material is moved outward in the radial direction of the developing sleeve by the action of the magnetic field on the circumferential surface of the developing sleeve. The above objective was achieved by creating a developing device that made it possible to make a jump, and moreover, make the jump as large as possible.

When a magnetic material is magnetized by induction of a magnetic field, a linear range is formed in which the magnetic susceptibility is proportional to the strength of the magnetic field until the strength of the magnetic field reaches a predetermined value, and above a predetermined value, the change in magnetic susceptibility decreases. It gradually becomes saturated. In the above linear range, the magnetic body receives a force proportional to (H→·H→), so the magnetic body moves in the direction of higher magnetic flux density.
As shown in Fig. 1, when the magnetic body 12 is placed above the magnetic pole 11, the lines of magnetic force are concentrated on the magnetic body 12, and the magnetic flux density changes between the part with the magnetic body and the part without it. becomes uneven. By providing the magnetic body 12, the same effect as providing a large number of magnetic poles can be obtained using one magnetic pole. If there is a fine magnetic material such as iron powder at locations A and B in FIG. 1, the magnetic material at location A will receive a force directed downward in the diagram toward the magnetic material 12, which has a higher magnetic flux density. The magnetic body at location B will receive a force directed upward in the figure. If you move the magnetic body 12 to the left or right in the figure, or move the magnetic pole 11 to the left or right in the figure, the magnetic field at locations A and B will change with respect to a fine magnetic body such as iron powder, so the fine magnetic body will jump up and down in the figure. will be carried out.

In FIG. 2, a developer carrier, for example, a developing sleeve 1, is arranged so as to include therein a magnet 5 having multiple poles in which north poles and south poles are alternately arranged. The developer sleeve 1 is advantageously formed as a hollow cylinder with an inner conductive part 4 and an outer dielectric part 3 of non-magnetic material. A large number of magnetic bodies 2 are embedded in the outer peripheral surface of the dielectric portion 3 while being insulated from each other, and the outer periphery of the developing sleeve 1 is processed into a cylindrical surface with the magnetic bodies 2 embedded therein.

A latent image carrier 6, such as a photosensitive drum, is provided opposite the developing sleeve 1 with a slight gap.

A magnetic field is formed around the outer periphery of the developing sleeve 1 by the magnet 5, and the magnetic body 2 of the developing sleeve 1 corresponds to the magnetic body 12 shown in FIG. 1, and the magnet 5 corresponds to the magnetic pole 1 shown in FIG.
Magnetic flux is formed in a form corresponding to 1, and is formed as a magnetic field with non-uniform magnetic flux density depending on the presence or absence of the magnetic body 2.

By rotating the developing sleeve 1 in the direction of arrow A and, if necessary, rotating the magnet 5 in the direction of arrow B, a layer of developer 7, for example, magnetic toner, is formed on the outer peripheral surface of the developing sleeve 1, and the developer is exposed to light. It is transported to a portion facing the body 6 and subjected to a developing action. A magnetic leveling plate 8 whose tip portion is close to the outer peripheral surface of the developing sleeve 1 and which regulates the thickness of the developer layer of the developing sleeve 1 is provided in a state where it is supported by a support member 9.

The developing sleeve 1 is formed into a thin layer by the leveling plate 8.
In the layer of toner 7 formed on the outer peripheral surface of the first
Due to the phenomenon shown in the figure, due to the rotation of the developing sleeve 1 and, in some cases, the rotation of the magnet 5, the toner, which is a magnetic substance, jumps in the radial direction of the phenomenon sleeve 1 to a position facing the photoreceptor 6. transported. Even if there is some gap between the surface of the developer layer of the developing sleeve 1 and the photoreceptor 6 due to the jump of the toner particles, the toner particles 7 having a true charge are easily moved and attached to the photoreceptor 6 due to frictional charging. be able to.

In order to be able to sufficiently adhere the developer to the photoreceptor 6 even in a relatively wide gap, it is necessary to make the jump development of the developer noticeable. For this purpose, it is necessary to increase the interaction between the developer, that is, the powdery magnetic material, and the magnetic field formed by the magnetic material in the developing sleeve. The magnetic field caused by the magnetic material of the developing sleeve is generated by the magnet 5 in the developing sleeve 1.
is formed by the relationship between the magnetic _field of You can change the strength of the magnetic field caused by your body. On the other hand, the magnetic permeability μ and saturation magnetic flux density B _S of the magnetic material constituting the developer
One method is to increase the interaction between the developer and the magnetic field by increasing the squareness ratio of the saturation curve or by making the squareness ratio of the saturation curve close to 1, that is, close to square.

Since the magnetic material inside the developing sleeve is fixed, when the coercive force H _C is large, the area surrounded by the hysteresis loop becomes large, causing energy loss when rotating the developing sleeve 1 to form a rotating magnetic field. On the other hand, since the developer can move freely to some extent, energy loss is not a problem even if the hysteresis loop is large to some extent.

For the above-mentioned reasons, in order for the developer to cause a large jump phenomenon, as shown in Figure 3, if the magnetic material constituting the developer has the properties shown by the saturation curve A, then the magnetic field that magnetizes the developer must be In the range of strength H _O , the relationship shown by straight line B holds between magnetic field strength H and magnetic flux density B, and a magnetic material with a property that prevents the magnetic flux density from reaching a saturated state is embedded in the developing sleeve. is desirable. In this preferred state, soft iron or permalloy can be used as the magnetic material of the developing sleeve, and iron tetroxide can be used as the magnetic material of the developer. The material should be selected in consideration of the magnetic field suitable for development. In this way, in the developing device according to the present invention, good image quality was obtained with the developer layer having a thickness of about 20 μm and a developing gap of 0.2 to 0.3 mm. As a result, compared to conventional developing sleeves in which the thickness of the developer layer is approximately 0.5 mm and the surface of the developer layer is brought into contact with the surface of the photoreceptor, the present invention allows the developer layer to be made extremely thin.
Moreover, good image quality could be obtained even with a large development gap.

The same effect can be obtained even if the magnet 5 in the example of FIG. 2 is omitted, the magnet 5 and the magnetic material of the developing sleeve are integrated, and the magnetic pole is embedded in the developing sleeve.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the principle of the present invention, Fig. 2 is an explanatory diagram of the developing device according to the invention, and Fig. 3 is a diagram showing the relationship between the magnetization curves of the magnetic material of the developing sleeve and the magnetic material of the developer. be. 1...Developing sleeve (developer carrier), 2...
Magnetic material, 3... Dielectric material, 5... Magnet, 6... Photoreceptor (latent image carrier).

Claims (1)

[Claims] 1. A developer carrier having a dielectric layer formed on its surface and a magnetic material finely divided insulated from each other on the surface of the dielectric layer, and a developer carrier provided inside the developer carrier. The magnet has a large number of magnetic poles in which north poles and south poles are arranged alternately, and a developer made of a magnetic material. In a developing device that develops a latent image by moving a developer sleeve and a developer carrier relatively to face an electrostatic latent image carrier at a development position, the magnetic material between the magnetic material of the developing sleeve and the magnetic material constituting the developer is A developing device characterized in that properties are adjusted by each squareness ratio of a saturation curve of the magnetic material, and the magnetic material constituting the developer is formed to have a shape closer to a square than the magnetic material of the developing sleeve.