JPH06161252A - Developing device - Google Patents

Abstract

PURPOSE:To attain manufacture at low cost and miniaturization and simultaneously to obtain the image of high quality by constituting a developing roll without using a sleeve, so as to constitute a developing device at the low cost. CONSTITUTION:The developing roll 4 is cylindrically formed by a permanent magnet, magnetic poles extending in the axial direction are provided on the surface so that an unlike pole alternately appears in the circumferential direction, and the developing roller 4 is opposed to an image carrier 3 via a developing gap and provided so as to rotate counterclockwise. A peeling roll 9 is made of a porous elastic member like a cylinder, in contact with the developing roll 4 in a developer tank 1 and provided so as to rotate clockwise. In other words, a magnetic developer 2 is attracted to the surface of the developing roll 4, carried and brought into contact with the surface of the image carrier 3, so that an electrostatic charge image formed on the surface of the image carrier 3 is made visualizable. Therefore, the magnetic developer 2 after development is peeled/removed from the surface of the developing roll 4 by the peeling roll 9 and a fresh magnetic developer 2 is supplied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for visualizing an electrostatic charge image formed on the surface of an image carrier in electrophotography, electrostatic recording and the like, and particularly to a magnetic carrier and a magnetic toner. The present invention relates to a developing device that uses a magnetic developer obtained by mixing the above-described materials and that can be manufactured at low cost.

[0002]

2. Description of the Related Art In electrophotography, an electrostatic charge image formed on the surface of an image carrier is rubbed and developed by, for example, a magnetic brush method, and the obtained toner image is directly fixed, or this toner image is fixed. Is an image forming process configured to obtain a final image by transferring the image onto a transfer member and then fixing the image.

The developer used in the above magnetic brush development method is a mixed powder of a magnetic carrier such as iron powder and ferrite powder and a non-magnetic toner in which a colorant is dispersed in a resin. Component developers are often used. In the magnetic brush development method using such a two-component developer, the carrier and the toner are mixed so that the toner concentration is usually 3 to 5% by weight, and the toner is triboelectrically charged to a predetermined amount. It is charged in polarity and only the toner is attached to the electrostatic image formed on the surface of the image carrier.

In the above developing method, since the toner has a clear electrostatic charge, it is easy to obtain a faithful image.
In order to carry out stable development, it is necessary to strictly control the toner concentration and to provide a developing device with a mixing means of carrier and toner.

On the other hand, a means of using a one-component developer consisting of a resin and a magnetic toner containing magnetic powder as a main component without using a carrier has been proposed, and in recent years, from the viewpoint of transferability, The mainstream is a means of using an insulating magnetic toner and charging it for development. However, in the case of an uncharged magnetic toner as disclosed in, for example, JP-A-53-31136, since the toner is difficult to be charged, it is necessary to set the surface potential of the image carrier to a higher potential than a normal one. As a result, there is a problem that the life of the image carrier is shortened.

Therefore, in order to promote the charging of the toner,
Charge type magnetic toners to which a charge control agent is added have been proposed. This charged magnetic toner is charged to the same extent as the toner constituting the two-component developer by contact with a sleeve or a doctor blade constituting the developing means and mutual contact of the toner, and therefore, the level of that of an ordinary image carrier is obtained. It can be developed at the surface potential. However, when the charged magnetic toner as described above is used, the toner is likely to be electrically charged and aggregated on the sleeve, and the agglomerated toner is accumulated on the doctor blade, resulting in a shortage of the toner on the sleeve. Development failure may occur.

In order to solve the above-mentioned problems, for example, a developer containing a mixture of a magnetic carrier and a chargeable magnetic toner as disclosed in Japanese Patent Publication Nos. 2-331383 and 4-31583 is proposed. Proposed and put to practical use. When developing an electrostatic charge image by the magnetic brush method using such a developer, a carrier mainly composed of iron oxide such as ferrite or magnetite is used from the viewpoint of reproducibility of a halftone image. Further, it is confirmed that the toner concentration is preferably in the range of 10 to 90% because the toner is likely to be scattered when the toner concentration in the developer is high, and the carrier is easily attached to the surface of the image carrier when the carrier amount is high. Has been done.

[0008]

Use of the developer obtained by mixing the magnetic carrier and the magnetic toner as described above has an effect that both the two-component developer and the one-component developer have the advantages. In recent years, particular attention has been paid. On the other hand, in a developing device using such a developer, a developing roll that is used to convey the developer to the surface of the image carrier and to develop an electrostatic charge image by forming a magnetic brush is, for example, a non-magnetic material. A magnetic field generating member is contained in a sleeve formed into a hollow cylinder so that both can be rotated relative to each other.

FIG. 3 is a cross-sectional explanatory view of an essential part showing an example of a conventional developing device. In FIG. 3, reference numeral 1 denotes a developer tank, which contains a developer 2 formed by mixing a magnetic carrier and a magnetic toner, and at the lower end portion of the developer tank 1, a developing roll 4 facing the image carrier 3. Is rotatably provided. The developing roll 4 is a sleeve 5 made of a non-magnetic material and formed into a hollow cylinder.
A magnetic field generating member 6 having a cylindrical shape made of a permanent magnet and having a plurality of magnetic poles extending in the axial direction on the surface at equal intervals so that different poles alternately appear in the circumferential direction is built in. In addition, the sleeve 5 and the magnetic field generating member 6 are configured to be rotatable relative to each other. Reference numeral 7 is a doctor member, and 8 is a bias voltage source.

The developing roll 4 having the above-described structure maintains coaxiality with the magnetic field generating member 6 in order to make the surface magnetic flux density on the sleeve 5 uniform, and the developing gap between the image carrier 3 and the developing roll 4 has a fixed size. In order to hold the surface of the sleeve 5, it is necessary to form the deflection of the surface of the sleeve 5 as small as possible. Therefore, the sleeve 5
The processing of 1 requires high accuracy, and it is necessary to interpose a bearing so as to be rotatable relative to the magnetic field generating member 6. Therefore, there is a problem that the cost required for processing and assembling the developing roll 4 becomes high.

On the other hand, the sleeve 5 is omitted and the magnetic field generating member 6 is provided.
A developing device has been proposed in which the developer 2 is directly adsorbed on the surface of the sheet and conveyed to the image carrier 3 (see, for example, JP-B-54-39139 and JP-A-60-113127). With such a configuration, the developing device can be downsized and the manufacturing cost of the developing roll can be reduced.

However, the developer 2 adsorbed on the surface of the magnetic field generating member 6 without the sleeve 5 in FIG.
Does not roll on the surface of the magnetic field generation member 6, unlike the case where it is attracted onto the sleeve 5. Therefore the image carrier 3
After consuming the magnetic toner by rubbing the electrostatic charge image on the surface of
Even when the toner is moved into the developer tank 1, there is a problem that the replenishment of new magnetic toner is not smoothly performed, and the magnetic toner having an electrostatic charge remains, resulting in uneven development and deterioration of image quality. .

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems existing in the prior art and to provide a developing device which can be manufactured at a small size and at low cost and which can obtain a high quality image.

[0014]

In order to achieve the above object, in the first aspect of the invention, first, a magnetic developer is contained so as to face an image carrier that carries an electrostatic charge image on its surface and moves. In a developing device, a developing roll is rotatably provided in a developer tank, and the electrostatic charge image is visualized by bringing the magnetic developer close to or in contact with the image carrier by the developing roll. Is made of a permanent magnet material in a cylindrical shape, and a plurality of magnetic poles extending in the axial direction are provided at equal intervals on the surface so that different poles alternate in the circumferential direction, and made of a porous elastic material in a cylindrical shape. A technical means was adopted in which a peeling roll is provided in the developer tank so as to be in contact with the developing roll and rotatable in the same direction.

Next, in the second aspect of the invention, a developing roll is rotatably provided in a developer tank containing a magnetic developer so as to face an image carrier that carries an electrostatic charge image on its surface and moves.
In a developing device configured to visualize an electrostatic charge image by bringing the magnetic developer close to or in contact with the image carrier by the developing roll, the developing roll is formed of a permanent magnet material into a cylindrical shape, and A plurality of magnetic poles extending in the axial direction on the surface are provided at equal intervals so that different poles appear alternately in the circumferential direction, and a peeling roll formed in a cylindrical shape by a ferromagnetic material is provided in the developer tank with the developing roll. We adopted the technical means of providing them close to each other and rotatably in the opposite direction.

In the above invention, as a constituent material of the developing roll, a sintered magnet such as a ferrite magnet and a resin magnet in which a ferromagnetic powder material and a conductive material are dispersed in a resin material can be used. . When the developing roll is composed of a sintered magnet, a thin layer or thin film made of a conductive material is plated, vapor-deposited, etc. on the surface in order to prevent ground fog or to apply a bias voltage for reversal development. It is preferable to form by means of

However, even if the surface is insulative, it is also possible to substitute it by applying a bias voltage to a conductive member that comes into contact with or contacts the magnetic developer, such as a doctor blade. When applying a bias voltage to the doctor blade, the resin magnet may be insulative. The magnetic pole to be provided on the surface of the developing roll has an outer diameter of, for example, 20 mm in order to prevent uneven development.
In this case, the number of poles is preferably 16 or more, and more preferably 32 or more.

[0018]

With the above construction, the magnetic developer adsorbed on the surface of the developing roll is conveyed to the surface of the image carrier, and the magnetic developer is adhered to the electrostatic charge image formed on the surface of the image carrier for development. You can After completion of development, the magnetic developer on the surface of the developing roll is peeled off by the peeling roll provided in the developer tank, and the new magnetic developer in the developer tank is adsorbed again on the surface of the developing roll. Is used for development.

[0019]

FIG. 1 is a cross-sectional explanatory view of an essential part showing an embodiment of the present invention, in which the same parts are designated by the same reference numerals as in FIG.
In FIG. 1, the developing roll 4 is formed in a cylindrical shape by a ferrite magnet, and for example, 18 magnetic poles extending in the axial direction are provided so that different poles appear alternately in the circumferential direction, and the image carrier 3 and the developing gap are formed. They are opposed to each other and are rotatably provided counterclockwise. A peeling roll 9 is formed into a cylindrical shape from a porous elastic material such as sponge, and is provided in the developer tank 1 so as to be in contact with the developing roll 4 and rotatable counterclockwise.

With the above structure, the magnetic developer 2 formed by mixing the magnetic carrier and the magnetic toner is adsorbed on the surface of the developing roll 4 and conveyed, and comes into contact with the surface of the image carrier 3 to thereby contact the image carrier 3. The electrostatic charge image formed on the surface of the can be visualized. Magnetic developer 2 after development
Is adsorbed on the surface of the developing roll 4 and returned to the developer tank 1, but is peeled off from the surface of the developing roll 4 by the peeling roll 9 which rotates in contact with the developing roll 4. Then, the new magnetic developer 2 is adsorbed and conveyed to the developing roll 4 above the peeling roll 9. The peeled magnetic developer 2 is mixed in the developer tank 1, and the toner concentration is recovered so as to maintain a predetermined value. In this case, the mixing action is promoted by the rotation of the peeling roll 9.

FIG. 2 is a cross-sectional explanatory view of an essential part showing another embodiment of the present invention, and the same parts are designated by the same reference numerals as those in FIG. In FIG. 2, reference numeral 10 denotes a peeling roll, which is formed in a cylindrical shape from a soft magnetic material such as soft iron, is provided in the developer tank 1 close to the developing roll 4, and is rotatable in the clockwise direction.

With the above construction, the magnetic developer 2 after development is adsorbed by the developing roll 4 and returned to the developer tank 1, but at the position of the peeling roll 10, the developing roll 4 is placed.
By the action of the magnetic poles having the opposite polarities generated on the peeling roll 10 by the magnetic induction by, the toner is peeled from the surface of the developing roll 4. That is, an induction magnetic pole having a polarity different from that of the developing roll 4 is generated on the peeling roll 10 provided so as to face the developing roll 4, and the magnetic developer 2 is adsorbed in a brush shape between the magnetic poles.
The developing roll 4 and the peeling roll 10 rotate to move to the downstream side.

Since the distance between the magnetic poles of the developing roll 4 and the peeling roll 10 increases with this movement, the brush-like magnetic developer is divided from the middle and transferred to the peeling roll 10 as shown in FIG. The magnetic developer 2 and the magnetic developer 2 moving together with the developing roll 4 generate two streams,
Mixed rapidly. When the peeling roll 10 is rotated in the same direction as the developing roll 4 as shown in FIG. 1, such action does not occur. Further, a mode in which the new magnetic developer 2 is adsorbed by the developing roll 4 and conveyed above the peeling roll 10 is the same as in the above-described embodiment.

In the above embodiments, an example of a magnetic developer prepared by mixing a magnetic carrier and a magnetic toner has been described, but in the case of a one-component magnetic toner and a two-component magnetic toner using a non-magnetic toner and a magnetic carrier. Of course, it can be applied to a developer.

[0025]

Since the present invention has the structure and operation as described above, by constructing the developing roll without using a sleeve, the developing roll can be manufactured at low cost and can be downsized. Further, since the magnetic developer after development can be peeled off and removed from the surface of the developing roll by the peeling roll and a new magnetic developer can be supplied, there is an effect that a high quality image can be stably formed.

[Brief description of drawings]

FIG. 1 is an explanatory cross-sectional view of a main part showing an embodiment of the present invention.

FIG. 2 is a cross-sectional explanatory view of essential parts showing another embodiment of the present invention.

FIG. 3 is a cross-sectional explanatory view of a main part showing an example of a conventional developing device.

[Explanation of symbols]

 4 Development roll 9,10 Release roll

Claims (2)

[Claims] 1. A developing roll is rotatably provided in a developer tank containing a magnetic developer so as to face an image carrier that carries an electrostatic charge image on its surface and moves, and the magnetic developer is held by the developing roll. In a developing device configured to visualize an electrostatic charge image by approaching or contacting the image carrier, a developing roll is formed of a permanent magnet material in a cylindrical shape, and a plurality of axially extending surfaces are formed on the surface. The magnetic poles are provided at equal intervals so that different poles appear alternately in the circumferential direction, and a peeling roll formed in a cylindrical shape by a porous elastic material is brought into contact with the developing roll in the developer tank and rotatable in the same direction. A developing device provided. 2. A developing roll is rotatably provided in a developer tank containing a magnetic developer so as to face an image carrier which carries an electrostatic charge image on its surface and moves, and the magnetic developer is held by the developing roll. In a developing device configured to visualize an electrostatic charge image by approaching or contacting the image carrier, a developing roll is formed of a permanent magnet material in a cylindrical shape, and a plurality of axially extending surfaces are formed on the surface. The magnetic poles are provided at equal intervals so that different poles appear alternately in the circumferential direction, and a peeling roll formed in a cylindrical shape by a ferromagnetic material is placed in the developer tank in proximity to the developing roll and rotatable in the opposite direction. A developing device provided.