JPS62141581A - Developing device - Google Patents

Abstract

PURPOSE:To obtain a developed image which has small edge effect and sufficient solid-black density by providing a means which produces an alternating electric field for transferring toner particles from a layer of toner particles formed on the surface of a developer carrier member to an electrostatic latent image carrier at a development part. CONSTITUTION:A power source 34 applies a voltage to between a photosensitive drum 1 and a sleeve 22 to produce the alternating electric field and toner particles are transferred from a developer on the sleeve 22 to the toner photosensitive drum 1. The development part transfers toner from the surface of the sleeve 22 and surfaces of magnetic particles onto the latent image with the alternating electric field applied to between the photosensitive drum 1 and sleeve 22 to develop the latent image. Toner particles which are not consumed for the development are recovered through the subsequent rotation of the sleeve 22 and applied onto the sleeve 22 again repeatedly by circulation. A repulsive magnetic field is established at the development part, so magnetic particles are agitated and then only toner having sufficient triboelectricity is used for the development, so that sufficient solid-black density is obtained during solid- black development.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing device for developing a latent image formed by an electrophotographic method, an electrostatic two-pot method, or the like.

LLI! Conventionally, as one type of developing device, insulating non-magnetic toner is thinly applied on the surface of a developer carrier, and a gap is formed between the surface of this thin layer of developer and the upper surface of the latent image carrier in the developing section. JP-A-55-18656 discloses a method for developing an electrostatic latent image on a latent image carrier by applying an alternating electric field to this developing section and causing the toner to fly from above the developer carrier. has been done.

This developing device has the following problems. That is,
It removes toner particles on the surface of the developer carrier.

If you try to ensure that each toner is charged to the desired polarity, the thickness of the toner layer on the surface of the developer carrier becomes smaller, and when developing a 0-character latent image where the development density in the solid space is insufficient. Since not only the toner in the area facing this latent image but also the toner in one periphery of the character latent image gathers together due to the alternating electric field, a developed image with a sufficiently high density can be obtained. On the other hand, when an electrostatic latent image with solid spaces or thick lines is developed, the thin layer of toner on the developer carrier surface tends to be insufficient to obtain a high density, and the ,
Toner collects in the dark areas, resulting in image quality that lacks toner in the solid black areas.

This lack of toner density in the case of solid black is a more important problem when performing color development than monochrome development. Particularly when high-quality full-color development is required, edge effects and insufficient density in solid black areas become serious problems.

Therefore, if the thickness of each toner layer on the developer carrier surface F is increased, each toner becomes difficult to be charged to the desired polarity. Therefore, not only excess toner adheres to non-image areas, but also the obtained toner image is of low quality.

Therefore, an object of the present invention is to provide a developing device capable of obtaining a developed image with sufficient solid black density and less edge effect.

According to the present invention, there is provided a developing device for developing an electrostatic latent image on an electrostatic latent image bearing member, which comprises: a developer container containing a developer having toner particles and magnetic particles; a developer supporting member that faces the electrostatic latent image carrier and forms a developing section that supplies toner particles to the electrostatic latent image carrier, and carries and conveys developer from the container to the developing section; A first member provided on the side of the developer carrying member opposite to the latent image carrier, and located upstream of the developing section in the rotational direction of the developer carrier.
and a magnetic field generating means provided on the opposite side of the regulating member of the developer supporting member, located downstream from the developing section with respect to the rotational direction of the developer carrier, and identical to the first magnetic field generating means. a second magnetic field generating means that is polar and forms a repulsive magnetic field with the first magnetic field generating means to form a layer of non-magnetic toner particles on the developer carrier therebetween;
A developing device characterized by comprising: alternating electric field forming means for forming in the developing section a mating electric field that transfers toner particles from a layer of toner particles formed on the surface of the developing member to the electrostatic latent image bearing member. , it is possible to obtain a developed image with sufficient solid black density with little edge effect.
A stable developer state can be formed in the developing section.

1mu1 The figure is a sectional view of a developing device according to an embodiment of the present invention.

In the figure, reference numeral 1 denotes an electrostatic latent image carrier that carries an electrostatic latent image to be developed, and specifically, it is an endlessly movable photosensitive drum, a belt, a dielectric drum, a belt, or the like. It's quiet on top of this! The method of forming the image is not the gist of the present invention, and any known method may be used. In this embodiment, the electrostatic latent image carrier is a photosensitive drum on which an electrostatic latent image is formed by electrophotography, and It can be rotated in any direction.

The apparatus of this embodiment has a developer container 21. It includes a developing sleeve 22 (hereinafter simply referred to as a sleeve) which is a developer holding member, a magnet 23, a power source 34 which is an alternating electric field forming means, and the like.

This magnet 23 has a magnetic pole S1 as a first magnetic field generating means, a magnetic pole 52 as a second magnetic field generating means, and the like. Each configuration will be explained below.

The container 21 contains a developer containing a mixture of magnetic particles 27 and toner particles 2B. In this embodiment, the toner particles are non-magnetic toner particles having a particle size of 1 to 20 m and mainly composed of, for example, 10 parts of carbon and 90 parts of polystyrene. The container 21 has an opening at the lower left in the figure.

The sleeve 22 is made of a non-magnetic material such as aluminum, and is provided at the opening of the container 21, with a part of its surface exposed and the other surface protruding into the container 21. The sleeve 22 is rotatably supported around an axis perpendicular to the drawing, and is rotationally driven in the direction indicated by the arrow. In this embodiment, the sleeve 22 is a cylindrical sleeve, but it may also be an endless belt. .

The sleeve 22 has a minute gap with respect to the photosensitive drum l, 20~
800 h m, preferably 100 to 600 gm, and form a developing section facing each other. Here, "developing section"
is a portion where toner is transferred or supplied from the sleeve 22 to the photosensitive drum 1. Only the non-magnetic toner is conveyed to this developing section by the rotation of the sleeve 22 and the action of the magnetic poles Sl and S2, and is subjected to development. This point will be discussed later.

The magnet 23 is fixed statically inside the sleeve 22, and includes, in addition to the above S-polarity, Sl and S2 poles, an S3 pole that attracts and transports the developer, an Nl pole that attracts and transports magnetic particles together with the S3 pole, and It has an N2 pole.

In this example, the magnetic flux densities on the sleeve surface of the S1 pole and the S2 pole are 900 Gauss and 300 Gauss, respectively, and the magnetic flux density is 900 Gauss and 300 Gauss, respectively.
2 is 140", these numbers are not limited to those mentioned above, but the angle between
And S2 is preferably 200 Gauss or more in order to ensure a restraining force on the magnetic particles and prevent the magnetic particles from being transported to the developing section.The S pole and N pole may be reversed.This magnet is used in this embodiment. In the example, one magnet is magnetized to these polarities, but separate magnets may be used.

The power supply 34 applies a voltage between the photosensitive drum 1 and the sleeve 22 to form an alternating electric field in the gap therebetween, thereby transferring the toner from the developer on the sleeve 22 to the photosensitive drum 1. The voltage from the power supply 34 may be a symmetrical alternating voltage in which the peak voltages on the positive side and the negative side are the same, or an asymmetrical alternating voltage in which a DC voltage is superimposed on such an alternating voltage. Peak value is 200V~4K
V, the frequency is preferably l0OHz to 6KHz.

The lower part of the container 21 extends in the direction of the photosensitive drum 1 to form an extension, and prevents the developer (particularly toner particles) from leaking to the outside.

At the top of the container 21 is a hopper 3 for storing non-magnetic toner.
0, and a toner replenishment roller 31 is rotatably provided at the bottom thereof, and the replenishment roller 31 slowly rotates as the sleeve 22 engaged with the drive gear of the photosensitive drum 1 rotates.

The non-magnetic toner in the flopper 30 is supplied into the container 21 located below it to replenish the toner consumed by the developing action.

Next, the operation of the developing device of this embodiment will be explained. First, magnetic particles 27 are put into the container 21 . The introduced magnetic particles are restrained on the sleeve surface near the toner outlet of the container 21 by the magnetic field of the magnetic pole S1, and on the sleeve surface near the toner return port of the container 21 by the magnetic field of the magnetic pole S2.

Thereafter, the toner 28 is put into the container 21.

It is preferable that the magnetic particles 27 initially introduced include toner in an amount of 2 to 70% (ffi-1i) based on the magnetic particles, but it is also possible to include only magnetic particles. If the device is held by suction as described above, no substantial flow or inclination will occur even if the device is vibrated or tilted considerably.

Next, when the sleeve 22 is rotated in the direction of the arrow, the developer moves (circulates) within the container and the toner is frictionally charged.

Near the toner outlet of the container 21, the magnetic particles 27 have a magnetic pole S.
It is attracted to the surface of the sleeve 22 by the action of the magnetic pole St and the magnetic pole N1, and is held in this vicinity by the action of the repelling magnetic field formed between the magnetic pole St and the magnetic pole N1, and even if the sleeve 22 rotates, it does not come out of the container and develop. Furthermore, the ears of magnetic particles formed by the magnetic pole S1 or S2 do not come into contact with the surface of the photoreceptor l.

On the other hand, since non-magnetic toner particles are not directly affected by the magnetic field, the toner adhering to the surface of the sleeve 22 due to reflection force passes under the magnetic particles, passes through the outlet of the container, and is transported on the sleeve 22. It is broken and reaches the developing section. In this way, a layer of only toner particles is formed on the sleeve 22. The thickness of this toner layer is 20 to 4QO7im. The presence of the above-mentioned repulsive magnetic field in the vicinity of the development area has the effect of excluding magnetic particles from this area, thus ensuring that only toner particles are present in the development area.

In the developing section, toner is transferred from the surface of the sleeve 22 and the surface of the magnetic particles onto the latent image by an alternating electric field applied between the photosensitive drum 1 and the sleeve 22, and the latent image is developed. The principle of this development is the same as that described in Japanese Patent Publication No. 55-18658, so a detailed explanation will be omitted.

As the sleeve 22 continues to rotate, the toner particles not consumed in development pass through the lower part of the magnetic particles (on the sleeve surface side) near the toner return port of the container 21 and are returned to the container 2.
The process of collecting the liquid in the container 21 and applying it again onto the sleeve 22 by the above-mentioned circulation action in the container 21 is repeated.

Similarly to the exit, the magnetic particles near the return port are attracted to the surface of the sleeve 22 by the action of the magnetic aiS2 and the magnetic pole N2, and are held near this area by the action of the repulsive magnetic field formed between the magnetic poles 51 and 32. A sealing action is performed at the lower part of the container 21, so that the toner inside the container 21 is prevented from leaking out of the container.

Next, a specific example will be explained.

When the latent image potential was +000 V and the background potential was Ov, development was carried out by superimposing a DC voltage of +150 V on an AC voltage with a peak peak value of 1800 VPP and a frequency of 1.6 KHz as a developing bias voltage. The non-magnetic developer used is a toner containing thermoplastic resin (polyethylene) as a main component and having a number average particle size of 8 pm, and is a toner that is negatively charged with respect to magnetic particles. Reversal development is also possible if positively charged toner is used and the DC voltage is appropriately selected. The magnetic particles used were particles having a number average particle diameter of 501 Lm, which were produced by mixing 75% by weight of magnetite in a resin mainly composed of styrene-acrylic Φ aminoacrylic copolymer resin and pulverizing the mixture.

The magnetic flux density on the sleeve surface of the Sl pole and the S2 pole is 900 Gauss and 300 Gauss, respectively, and the angle between the magnetic pole 51 and the magnetic pole S2 as seen from the rotation center of the sleeve 22 is 14
It was set as 00.

The resulting developed image was free from edge effects and blur, and had sufficient solid black density. In addition, 1 to 3% of silica particles, which are located between the charging series of magnetic particles and non-magnetic toner in terms of charging series, are superimposed.
I used it mixed and got a better image.

In the above-mentioned embodiment of the present invention, since a repulsive magnetic field is formed in the developing section, only the toner having a sufficient amount of toner particles due to stirring with the magnetic particles contributes to the development, which results in solid black development. A sufficient concentration can also be obtained. The edge effect is also reduced.

As explained above, according to the present invention, a good developing device with high image density and no edge effect is provided.

[Brief explanation of drawings]

The figure is a sectional view of a developing device according to an embodiment of the present invention. Explanation of symbols l...Latent image carrier (photosensitive drum) 21...Developer container (container) 22-φ developer holding member (sleeve) 23・φ magnetic field generating means (magnet) 27.-Magnetic particles 28・-toner particles (toner)

Claims (1)

[Scope of Claims] A developing device for developing an electrostatic latent image on an electrostatic latent image carrier, comprising: a developer container containing a developer having toner particles and magnetic particles; and the electrostatic latent image. a developer carrying member that faces the carrier and forms a developing section that supplies toner particles to the electrostatic latent image carrier, and carries and conveys developer from the container to the developing section; a first magnetic field generating means provided on a side of the member opposite to the latent image carrier and located upstream of the developing section in the direction of rotation of the developer carrier; and the regulating member of the developer carrier; It is provided on the opposite side, is located downstream of the developing section with respect to the rotational direction of the developer carrier, has the same polarity as the first magnetic field generating means, and has repulsion between it and the first magnetic field generating means. a second magnetic field generating means for forming a layer of non-magnetic toner particles on the developer carrier between them by forming a magnetic field; A developing device comprising: alternating electric field forming means for forming in the developing section an alternating electric field that is transferred to the latent image bearing member.