JPH04140778A - Developing device - Google Patents

Abstract

PURPOSE:To hold toner concentration on a sleeve in a developing area within a proper range by providing a partition member made of ferromagnetic material on an upstream side in the developer moving direction of a doctor member and within the magnetic field acting range of a permanent magnet member. CONSTITUTION:The partition member 15 made of the ferromagnetic material such as soft iron is provided close to the sleeve 10 in a mixing chamber 7. Therefore, magnetic fluxes by the S polarity of the permanent magnet member 11 are concentrated to prevent magnetic toner 2 from passing and reflux one part of the toner 2 to the upstream side in the moving direction. Therefore, the toner concentration of the developer 14 carried to the developing area Z is controlled to be 25-40 wt.%. The toner 2 consumed by a developing operation is successively supplied to the sleeve 10 via a communicating port 9 provided under the partition plate 8, but one part of the toner 2 is returned to the upstream side as the above, so that the toner concentration is prevented from becoming excessive.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a developing device in electrophotography that visualizes an electrostatic image formed on the surface of an image carrier using an insulating magnetic toner. In particular, the present invention relates to a developing device configured to carry out development by conveying a developer made of a mixture of magnetic carrier and magnetic toner to a developing area by a magnetic conveying means.

[Conventional technology]

In electrophotography, an electrostatic charge image is formed on the surface of a photoreceptor, this electrostatic charge image is made visible using colored particles called toner, and the visualized toner image is transferred onto a transfer member using thermal means, etc. A typical example is the one that is fixed and hard copies are obtained.

Various developing methods for this electrophotographic method have been proposed so far.

The mainstream methods are a magnetic brush method using a two-component developer, which is a mixed powder of non-magnetic toner and a magnetic carrier, or a method using only magnetic toner. Conventionally, when using these powder developers, a non-magnetic metal sleeve and a magnet roll disposed inside the non-magnetic metal sleeve are rotated relative to each other, and the developer adsorbed on the surface of the non-magnetic metal sleeve is transferred to a developing device. A method is adopted in which the material is transported from inside to the developing area and then collected back into the developing device.

- When fishing on a boat, the conveyance speed of these developers is set at a relatively high speed in order to improve image quality or increase image density. This tendency is particularly strong in the -component method, and one typical known example is a developing method using an insulating magnetic toner described in U.S. Pat. No. 4,121,931.

However, in the above method, since the developer is conveyed at high speed, there are problems such as the toner scattering outside the developing device, and in the -component method, the force applied to the toner becomes large, which tends to cause toner agglomeration. Furthermore, the two-component method has the problem of promoting adhesion of the resin component constituting the toner to the carrier surface, shortening the life of the developer. Therefore,
Considering reliability, it is ideal to set the developer transport speed as low as possible, but in order to obtain sufficient image density, that is, sufficient developability, it is necessary to transport the developer at a relatively high speed. It has become.

In recent years, it has also been proposed to use a mixture of a magnetic carrier and an insulating triboelectric magnetic toner as a developer, as described in Japanese Patent Publication No. 2-31383, for example, and the two-component method and the two-component method described above have been proposed. It is said that they share the advantages of

[Problem to be solved by the invention]

In the method of using a mixture of a magnetic carrier and a magnetic toner as a developer as described above, a method in which both a metal sleeve and a magnet roll constituting a magnetic conveyance means for the developer rotate has been the mainstream.

In addition, as the magnetic carrier constituting the developer used in this method, one with relatively good conductivity (for example, a semiconductive ferrite carrier) is used, and in order to simplify the structure of the developing device, the toner concentration is In particular, the control means is not set up. Therefore, the toner concentration in the development area is often as high as 60% by weight or more. Therefore, since the amount of toner components with high electrical resistance increases, the electrical resistance of the developing side as a whole increases, and it is necessary to increase the developer transport speed in order to efficiently develop an electrostatic image. As a result, the metal sleeve and magnet roll, which are the means for transporting the developer, rotate at high speed.2 In such a developing device, not only does it have a negative effect on the developer, but the drive system also makes a lot of noise, making it difficult to work in the office environment. In addition to worsening the situation, there were other problems such as making the 41 structure complicated. Furthermore, as described above, in this method, there is no particular means for controlling the toner concentration in the developer, so the toner concentration in the development area may vary greatly. This results in a decrease in image quality, or in causing dust and other image defects. In order to form a good image, the toner concentration in the development area on the metal sleeve should be 10 to 50%, preferably 25%.
It is necessary to control the amount to ~40% by weight (appropriate toner and
- The density varies somewhat depending on the magnetic properties of the developer, especially the coercivity of the carrier and the saturation magnetization of the toner). However, in conventional devices that use a developer made by mixing magnetic carrier and magnetic toner, the toner density cannot be maintained properly because the toner temperature control means is not provided as described above. There is a problem in that it may be difficult to stably obtain good images.

As a means to solve the above problems, [the content is to form a magnetic brush on a metal sleeve with a developer consisting of a magnetic carrier and a magnetic toner, and to pass this magnetic brush through a concentrated parallel magnetic field region on the sleeve. It has been proposed (for example, see Japanese Unexamined Patent Publication No. 59-75269) that in order to form the above-mentioned concentrated parallel magnetic field region, a spike-promoting mechanism consisting of a plate of magnetic material is placed at a small distance from the surface of the metal sleeve. There is a description that the magnetic plan can be enlarged at the location where the panicle promoting mechanism is placed, and an image with a clear, negative-like and stable density can be formed over the entire development area. It is said to be possible.

However, in the above scheme, since the metal sleeve constituting the magnetic conveying means is constantly in contact with a large amount of magnetic toner, the toner concentration inevitably tends to be high (1).
The problem remains that the above-mentioned problems have not been completely solved.

The present invention solves the problems existing in the above-mentioned prior art, and provides a developing device that can properly control toner concentration and stably form good images despite the slow developer transport speed. The purpose is to provide

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a sleeve formed of a non-magnetic material into a hollow cylindrical shape, and a sleeve provided coaxially within the sleeve and extending axially around the outer periphery. A developer comprising a permanent magnet member provided with a plurality of magnetic poles, a toner tank accommodating magnetic toner, and a mixing chamber holding the sleeve and the permanent magnet member, and mixed with a magnetic carrier and magnetic toner. In a developing device configured to perform development by conveying developer to a developing area using a sleeve, a magnetic toner supply means is provided in a toner tank, and a magnetic toner supply means is provided facing the outer periphery of the sleeve so as to regulate the layer thickness of the developer. A partition member made of a ferromagnetic material is provided on the upstream side of the doctor member in the developer movement direction and in the magnetic field action range of the permanent magnet member,
A portion of the magnetic toner supplied to the mixing chamber via the supply means is formed to flow back to the upstream side of the partition member in the direction of movement of the magnetic toner. A technical method was adopted.

[For production]

With the above configuration, it is possible to prevent a large amount of magnetic toner from coming into direct contact with the sleeve in the toner tank, and to prevent excess magnetic toner from getting stuck on the sleeve. The toner concentration of the developer can be maintained within an appropriate range. The magnetic toner refluxed by the partition member is mixed with the developer returned through the development area and the developer refluxed from the vicinity of the doctor member.

(Example] The figure is a cross-sectional view of a main part showing an embodiment of the present invention.

In the figure, reference numeral 1 denotes a toner tank, which is composed of a storage section 3 for containing magnetic toner 2 and a holding section 5 for holding magnetic conveying means 4 . A supply means 6 for supplying the magnetic toner 2 is provided within the storage portion 3 so as to be rotatable back and forth in the direction of the arrow. The supply means 6 can be formed, for example, by bending a small-diameter round rod into a U-shape.

A toner cartridge (not shown) is provided above the accommodating portion 3, and is configured to be capable of replenishing the magnetic toner 2. Next, a partition plate 8 is provided between the storage section 3 and the holding section 5 to form a mixing chamber 7, and a communication port 9 for supplying the magnetic toner 2 is provided at the bottom. Note that the lower end of the partition plate 8 is provided close to the surface of the magnetic conveyance means 4. The magnetic conveying means 4 includes a sleeve IO formed in a hollow cylindrical shape from a non-magnetic material such as an aluminum alloy or stainless steel, and a plurality of odd number of magnetic poles coaxially provided within the sleeve 10 and extending axially around the outer circumference. A permanent magnet member 11 is provided. It should be noted that the permanent magnet member 11 is arranged so that, for example, a specific N pole of the plurality of magnetic poles faces the image carrier 12 (with a gap of 0.2
~0.6m+a) Fixed, and the sleeve 10 is formed to be freely rotatable in the counterclockwise direction. Next, 13 is a doctor member, which is fixed above the sleeve 10 with a gap (0.2 to 0.6+nm) therebetween, so as to be able to regulate the layer thickness of the developer 14 on the sleeve 10 to a predetermined value. .

Incidentally, two adjacent permanent magnet members 1 are arranged as repelling magnetic poles 1 of the same polarity, for example, S poles, between the lower end of the partition plate 8 and the tip of the doctor member 13. Next, reference numeral 15 denotes a partition member, which is formed of a round bar made of soft iron, for example, and is provided parallel to the sleeve 10 on the upstream side of the doctor member 13 in the direction of rotation of the sleeve 10, with a gap of 0.5 to 5 Ioffl between the doctor member 13 and the sleeve 10.

With the above configuration, first, a predetermined amount of magnetic carrier is supplied to the magnetic conveyance means 4, and the magnetic toner 2 is supplied into the storage section 3 of the toner tank 1 via a toner cartridge (not shown). Next, the sleeve 10 is rotated so that a magnetic carrier (not shown) is attracted to the surface in a layered manner, and the magnetic toner 2 is supplied from the storage section 3 onto the sleeve 10 through the supply means 6 and the communication port 9 . In this case, since the magnetic toner 2 is intermittently supplied onto the sleeve 10, the toner concentration of the developer 14 may temporarily become high in the conventional configuration. However, in the present invention, the toner concentration of the developer 14 conveyed to the development area Z can be suppressed to a low concentration. That is, since the partition member 15 is provided in the mixing chamber 7 in close proximity to the sleeve 10 and is made of a ferromagnetic material such as soft iron, the lines of magnetic force due to the S pole of the permanent magnet member 11 are concentrate. This prevents the magnetic toner 2 from passing through, and a portion of it is forced to flow back upstream in the moving direction. Therefore, the toner concentration of the developer 14 conveyed to the development area Z can be controlled to 10 to 50% by weight, preferably 25 to 40% by weight. After some time has passed, a developer 14 made of a mixture of magnetic carrier and magnetic toner 2 is formed in a layer on the sleeve 10, and the doctor member]3
As a result of regulating the N thickness of the developer 14, a developer reservoir 14a is formed near the doctor member 13 and on the upstream side in the conveying direction of the developer 14.

When developing work is performed in this state, the magnetic toner 2 in the developer 14 is consumed, but the magnetic toner 2 corresponding to this consumed amount is transferred via the communication port 9 provided below the partition plate 8. Although the magnetic toner 2 is sequentially replenished onto the sleeve 10, a portion of the magnetic toner 2 is returned to the upstream side as described above, thereby preventing the toner concentration from becoming excessive. Note that the development area Z
The developer 14 that has passed through moves as the sleeve 10 rotates, but two same-polarity repelling magnetic poles (S) are arranged adjacently between the lower end of the partition plate 8 and the tip of the doctor member I3. Therefore, the developer 14 on the sleeve 10
A force is applied that causes the material to separate from the material, and some of the material is agitated by falling. Therefore, the charging property is improved, and the magnetic carrier and/or magnetic l.
A phenomenon occurs in which the roller 2 changes its relative position. Therefore, even if the consumption of the magnetic toner 2 is uneven in the development area Z, the insufficient magnetic toner 2 is reliably taken in and the distribution of the magnetic toner 2 in the developer 14 is made uniform. Note that a part of the magnetic carrier separates from the surface of the sleeve 10 due to the repulsive force caused by the S pole.
Since the partition plate 8 is provided close to the surface of the magnetic carrier 0, it is possible to prevent the inconvenience of the magnetic carrier dispersing into the housing part 3.

In this embodiment, an example was shown in which the permanent magnet member provided coaxially with the sleeve was formed into a solid cylindrical shape, but the shape of the permanent magnet member is not limited to this.

For example, a block-shaped permanent magnet may be fixed around the shaft.

Further, the number of magnetic poles to be provided on the permanent magnet member may be an even number, and furthermore, both the permanent magnet member and the sleeve may be rotated, as long as there is relative rotation between them.

Next, the material constituting the partition member is not limited to soft iron, but may also be other ferromagnetic materials such as steel, nickel, cobalt, and magnetic materials, and the cross-sectional shape is not only circular but also square,
It can be any other geometric shape such as rectangle, polygon, etc.

(Effect of the invention) Since the present invention has the structure and operation as described above,
Since the developer can be transported only by rotation of the sleeve at a relatively low speed, the structure of the device is simple, and since no noise is emitted, the office environment can be significantly improved. Furthermore, since the toner density in the development area on the sleeve can be controlled to a low and appropriate density, good images without dust or fog can be stably formed over a long period of time. Furthermore, since the developer and the magnetic carrier and/or the magnetic toner are agitated by the same-polarity repelling magnetic poles, charging performance can be improved, and the magnetic toner can be taken in smoothly and the distribution of the magnetic toner can be made uniform. This has the effect of significantly improving image quality.

[Brief explanation of drawings]

The figure is a cross-sectional view of a main part showing an embodiment of the present invention. 1: toner tank, 8: partition plate, io sleeve 11: permanent magnet member, 13: doctor member, I5: partition member.

Claims (1)

[Claims] A sleeve formed of a non-magnetic material into a hollow cylindrical shape, a permanent magnet member having a plurality of magnetic poles coaxially provided within the sleeve and extending in the axial direction on the outer periphery, and a toner tank containing magnetic toner. , a developing device comprising a mixing chamber that holds the sleeve and a permanent magnet member, and configured to carry a developer formed by mixing a magnetic carrier and a magnetic toner to a developing area by the sleeve to perform development, A magnetic toner supply means is provided in the toner tank, and a doctor member provided facing the outer periphery of the sleeve so as to regulate the layer thickness of the developer is provided on the upstream side in the direction of developer movement and within the magnetic field action range of the permanent magnet member. A developing device comprising: a partition member made of a ferromagnetic material; and a part of the magnetic toner supplied to the mixing chamber via the supply means is refluxed to the upstream side of the partition member in the direction in which the magnetic toner moves. .