JPH03209488A - Magnetic brush developing device - Google Patents

Abstract

PURPOSE:To obtain a high-definition image by setting the maximum magnetic flux density of a first magnetic field generating means larger than that of a second magnetic field generating means, and simultaneously the magnetic flux density distribution of the second magnetic field generating means so as to have an inflection point on the upstream side than the position of its maxi mum magnetic flux density. CONSTITUTION:A magnet 13 has a developing magnetic pole S1 as the first magnetic field generating means, a carrier magnetic pole N1 as the second magnetic field generating means of its downstream side, a second carrier mag netic pole S2 as the three magnetic field generating means of its down-stream side, and a magnetic pole N2. The maximum magnetic flux density of the first magnetic field generating means S1 is set larger than that of the second mag netic field generating means N1, and simultaneously the magnetic flux density distribution of the second magnetic field generating means N1 is set so as to have the inflexion point on the upstream side than the position of its maximum magnetic flux density. Thus, the carrying properties of a developer 8 are im proved, and a high-definition image is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) The present invention relates to a developing device used in image forming apparatuses such as electrophotographic copying machines, electrostatic recording machines, magnetic recording machines, etc., and particularly relates to a magnetic brush developing device.

2. Description of the Related Art Magnetic brush developing devices are widely used as means for developing latent images in image forming apparatuses such as electrophotographic copying machines, electrostatic recording machines, and magnetic recording machines.

Various configurations of magnetic brush developing devices have been proposed;
As a typical example, a non-magnetic cylinder (hereinafter referred to as a "sleeve") serving as a developer support means is rotatably arranged in a developer container containing developer, and inside this sleeve,
There is a developing device having a structure in which a plurality of magnetic field generating means, that is, a magnet roller having magnets arranged thereon is fixedly arranged. The developing device conveys the developer from inside the developer container to the developing position approximately opposite to the image bearing member carrying the latent image by rotation of the sleeve. A magnet (hereinafter referred to as a "developing magnetic pole") is disposed, and another magnet (hereinafter referred to as a "first conveying magnetic pole") is disposed downstream of the developing magnetic pole in order to convey the developer to a developing position. It is set up.

Furthermore, if the first transport magnetic pole is disposed in an open position from the developer container, the developer that has stood up on the first transport magnetic pole is likely to scatter. Alternatively, attempts have been made to cover it with a guide member.

In addition, in order to improve image quality such as preventing fogging, the magnetic flux density at the development position is increased (in addition, in two-component magnetic brush development using a two-component developer, carrier adhesion is prevented. For this reason, efforts have been made to increase the magnetic flux density of the developing magnetic pole.

In addition, in recent years, the demand for high-quality images has increased, and for example, in two-component magnetic brush development, there have been attempts to obtain high-resolution and high-definition images by reducing the toner particle size. If the particle size of the toner is reduced only, the toner supply ability will be reduced, so it is necessary to reduce the particle size of the carrier. When the particle size of the carrier is reduced, the carrier tends to adhere to the image bearing member, so in order to prevent this, the magnetic flux density of the developing magnetic pole is increased, and the magnetic flux density on the sleeve is 900 Gauss or more. Some are even larger than 1000 Gauss.For this reason, the magnetic flux density of the first transport magnetic pole must be relatively smaller than the magnetic flux density of the developing magnetic pole.

However, in the above-mentioned conventional device, the maximum magnetic flux density of the first transport magnetic pole is smaller than the maximum magnetic flux density of the developing magnetic pole, so that the developer transportability at the first transport magnetic pole portion deteriorates.
The developer may stagnate or overflow from the developer container, resulting in image defects or problems such as scattering.

This is particularly noticeable when the maximum density of the first transport magnetic pole is greater than the second transport magnetic flux density, and is more likely to occur when a two-component developer consisting of a small particle diameter carrier and toner is used. This tends to occur when covered with a guide member that is a transport magnetic pole.

Therefore, an object of the present invention is to prevent the developer from scattering, improve the developer conveyance by the conveying magnetic pole, especially the second conveying magnetic pole, prevent developer stagnation and developer overflow, and achieve high quality. It is an object of the present invention to provide a developing device, particularly a magnetic brush developing device, capable of obtaining images of 1000 yen.

The above-mentioned object is achieved by the developing device according to the present invention. To summarize, the present invention provides a developer support provided opposite to an image carrier, and a plurality of magnetic field generating means disposed inside the developer support to support the developer on the outer surface of the developer support. In a magnetic brush developing device, the latent image on the image carrier is conveyed and visualized by a developer at a development position opposite to the image carrier, the developer comprising a first magnetic field generating means at the development position and the developer. the second located downstream in the direction of movement of the support;
The magnetic field generating means have different polarities, and the second magnetic field generating means and the third magnetic field generating means located further downstream have different polarities, and the maximum magnetic flux density of the first magnetic field generating means is higher than the second magnetic field generating means. The magnetic flux density is set to be larger than the maximum magnetic flux density of the magnetic field generating means, and the magnetic flux density distribution of the second magnetic field generating means is set to have an inflection point upstream of the position of the maximum magnetic flux density. This is a magnetic brush developing device.

Preferably, at least a pole position of the second magnetic field generating means is covered with a developer container, and the magnetic pole position of the second magnetic field generating means is
It is located downstream of the center of the second magnetic field generating means section.

Further, the developer is a two-component developer having magnetic particles with a weight average particle size of 20 to 65 μm and a non-magnetic toner with a volume average particle size of 8 μm or less, and preferably, the maximum magnetic flux of the second magnetic field generating means is The density is made larger than the maximum magnetic flux density of the third magnetic field generating means.

EMBODIMENT OF THE INVENTION Next, one embodiment of the magnetic brush developing device according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of a first embodiment in which the present invention is applied to a copying machine using a drum type photoreceptor.

In this embodiment, the magnetic brush developing device is used in an electrophotographic copying machine having a drum-shaped electrophotographic photosensitive member, that is, a photosensitive drum 1, as an image carrier.

A charging mechanism, an image exposure mechanism, a transfer mechanism, a cleaning mechanism, a static elimination mechanism, etc., which are well-known electrophotographic processes, are arranged around the photosensitive drum 1, but are omitted in FIG. 1.

The developing device of this embodiment is for developing a latent image formed on the photosensitive drum l by the above electrophotographic process,
A developing container 2 containing a developer 8, a developing sleeve 3 serving as a developer support, and a blade 4 serving as a developer layer regulating member.
etc.

That is, an opening is formed in the developing container 2 at a position close to the photosensitive drum 1, and the developing sleeve 3 is rotatably provided in this opening. Further, a blade 4 is attached above the developing sleeve 3 with a predetermined gap therebetween.

The developing sleeve 3 is made of a non-magnetic material, rotates in the direction of the arrow shown in the figure during the developing operation, and has a magnet 13 fixed therein as a magnetic field generating means. The magnet 13 is
A developing magnetic pole S as a first magnetic field generating means, a conveying magnetic pole N1 as a second magnetic field generating means downstream thereof, a second conveying magnetic pole S2 as a third magnetic field generating means downstream thereof, and the blade 4 Magnetic pole N that works with the developer to make a thin and uniform layer of developer
2.

Further, the blade 4 is made of a non-magnetic material such as aluminum (Aβ), and as described above, the blade 4 is made of a non-magnetic material such as aluminum (Aβ).
The surface of the developer sleeve 3 is attached with a predetermined gap between the surface of the developer sleeve 3 and the surface of the developer sleeve 3. to regulate the

Therefore, in this embodiment, since the developer 8 is a two-component developer having a non-magnetic toner 81 and magnetic particles (carrier) 82, there is a gap between the tip of the blade 4 and the surface of the developing sleeve 3. Both non-magnetic toner and magnetic particles pass through and are sent to the developing section.

The nonmagnetic toner 81 used had a volume average particle size of 8 μm or less. Volume average particle size was measured using a Coulter Counter ~TA-II using a 100 μm aperture. That is, a Coulter Counter Model TA-II (manufactured by Coulter Co., Ltd.) was used as the measuring device, and an interface (
A CX-1 personal computer (manufactured by Canon) was connected, and a 1% NaCJ2 aqueous solution was prepared using primary sodium chloride as an electrolyte.

In the measurement, 0.1 to 5 mβ of a surfactant, preferably an alkylbenzene sulfonate, was added as a dispersant to 100 to 150 ml of the electrolytic aqueous solution, and 0.5 to 50 mg of the measurement sample was added. The electrolytic solution in which the sample was suspended was dispersed for about 1 to 3 minutes using an ultrasonic disperser, and then dispersed to 2 to 40 μm using a 100 μm aperture using the Coulter Counter TA-n type.
The particle size distribution of the particles of m was measured to determine the volume average distribution.

One volume average particle diameter is obtained from the volume average distribution thus determined.

When using the above-mentioned toner 81, the magnetic particles 82 preferably have a weight average particle diameter of 20 to 65 μm, but in this example, those with a weight average particle diameter of about 504 cm were used.

The weight average particle size was measured by mesh and was 300/400.
80% passed the mesh, and 75% passed the 300/350 mesh. The magnetic particles used were ferrite particles coated with a resin, and the relative magnetic permeability was 5.0.

The developer 8 is carried by the developing sleeve 3 and conveyed to the developing section, that is, the developing magnetic pole S, and further conveyed to the conveying magnetic pole N while being held by the developing sleeve 3.

The developing device is further provided with a guide member 14,
It extends upstream of the transport magnetic pole N with a predetermined gap from the developing sleeve 3. In this embodiment, the length β of the guide member 14 from the upstream end of the transport magnetic pole N1 to the portion facing the transport magnetic pole N1 is 7 mm.

The developer 8 sent to the developing section is transported to the transport magnetic pole N while being held by the developing sleeve 3.
Since the developer that has stood up in spikes is sufficiently covered by the guide member 14, the developer is prevented from scattering out of the developer container.

Incidentally, the inside of the developing container 2 is divided into a developing chamber (first chamber) S-1 and a stirring chamber (second chamber) S-8 by a partition wall 5 extending perpendicularly to the paper surface of FIG. A toner storage chamber S-1 is formed above the chamber S-O with a partition wall 6 in between.
Replenishment toner (non-magnetic toner) 81 is stored in the toner storage chamber S-3. In addition, the bulkhead 6 has a supply port 6a.
is open, and an amount of replenishment toner 81 commensurate with the amount of consumed toner is dropped and replenished into the stirring chamber S-z through the replenishment port 6a. Moreover, the above-mentioned developing chamber S-1 and stirring chamber S-
A developer 8 is accommodated in the container 2 . Note that the partition wall 5 is not formed at the front and back ends of the developer container 2 in FIG.
An opening (not shown) is formed to allow communication between the stirring chamber S-1 and the stirring chamber S-2.

The developer chamber S-1 is located at the inner bottom of the developer container 2 near the developer sleeve 3 and rotates in the direction of the arrow shown in the figure (counterclockwise) to move the developer 8 from the back side to the front side in FIG. 1, and a first conveying means 9, which is located above the first conveying means 9 and rotates in the direction of the arrow shown (counterclockwise), and conveys the developer 8 from the front side to the back side in FIG. 2 conveying means 10 are provided. Further, the first conveying means 9 is provided in the stirring chamber S-3.
A third conveying means 11 is provided which is located at approximately the same horizontal position as the third conveying means 11 and rotates in the direction of the arrow shown in the figure (clockwise) to convey the developer 8 from the front side to the rear side in FIG.

Specifically, the first, second, and third conveying means 9.10.11 are constituted by screws having a spiral shape.

FIG. 2 is a diagram for explaining the form of magnetic flux density distribution, where the vertical direction shows the magnitude [Gauss] of the magnetic flux density on the developing sleeve 3, and the horizontal direction shows the circumferential position of the developing sleeve in angles. It shows.

Next, the meaning of "magnetic pole part" used in this specification will be explained.

Taking the first transport magnetic pole as an example, as shown in FIG.
The transport magnetic pole portion is defined as a region from a position where the magnetic flux density is zero Gauss on the upstream side of the first transport magnetic pole to a position where the magnetic flux density is zero Gauss on the downstream side of the first transport magnetic pole.

That is, the position where the magnetic flux density is zero Gauss becomes the boundary.

In FIG. 2, KA indicates the range of the first carrying magnetic pole section in terms of angle, and K indicates the angle from the upstream boundary of the first carrying magnetic pole section to the first carrying magnetic pole.

Next, to explain the form of the magnetic flux density distribution in the first transport magnetic pole part, the solid line in FIG. 2 is an example where there is an inflection point upstream of the first transport magnetic pole, and the broken line is an example where there is no inflection point. . The existence of an inflection point means that the magnetic flux density Br is differentiated twice (a
” B, )/(a”θ)=0.

The inventor confirmed through experiments that the first transport magnetic pole N
It has been confirmed that when the inflection point is set upstream of , the developer transportability in the first transport magnetic pole portion is improved. The present inventor believes that the reason for this is that the magnetic force in the horizontal direction on the developing sleeve 3 in the first transport magnetic pole portion is related. That is, it is believed that this is because the magnetic force of the first transport magnetic pole portion was displaced in the direction of transporting the developer.

In this embodiment, since the first transporting magnetic pole N immediately downstream of the developing magnetic pole Sl is covered with the guide member 14 for the purpose of preventing scattering, the transportability of the developer is disadvantageous. Furthermore, in order to prevent fogging and carrier adhesion, the magnetic flux density of the developing magnetic pole S1 is increased, so the magnetic flux density of the first transport magnetic pole N1 is considerably smaller than that of the developing magnetic pole.
The developer in the transport magnetic pole portion is configured to be quite difficult to transport.

In such a configuration, the form of the magnetic flux density of the first transport magnetic pole part is particularly important, and although the details will be described later, there is an inflection point of the magnetic flux density upstream of the first transport magnetic pole N1 of the first transport magnetic pole part. By providing this, the developer transportability of the first transport magnetic pole portion can be improved.

Next, the present invention will be described in more detail with reference to examples using the developing device shown in FIG.

In the developing device shown in FIG. 1, a member consisting of the developing sleeve 3 containing the magnet 13 will be referred to as a "developing roller."

Based on the specifications shown in Table 1, Table 2 shows experimental data obtained regarding the developer transportability of the first transport magnetic pole portion on the developing sleeve 3 and the developer scattering state using various developing rollers.

In Example 4 shown in Table 2, a scattering prevention member was provided in the developing device shown in FIG. 1, and the details will be described later.

Table 1 First, Examples 1 to 3 will be explained. Table 2 shows that Comparative Example 1, which does not have an inflection point upstream of the first transporting magnetic pole, has poor developer transportability and is prone to developer overflow due to developer retention. However, in Examples 1 to 3, which had an inflection point upstream of the first transport magnetic pole, the developer transportability was good, and developer overflow did not occur at all. It can be seen that there is almost no scattering of the developer (which is good. In other words, it can be seen that the developer transportability is improved by providing an inflection point of the magnetic flux density upstream of the first transporting magnetic pole.

In addition, as in Examples 1 and 2, the pole position (K,) of the first transport magnetic pole N is set downstream (K,>I KA) from the center (K KA) of the first transport magnetic pole part, and the developing It can be seen that when the position is far from the magnetic pole, there is very little developer scattering.

In Example 4, the developing roller of Example 3 was used, the developing device shown in FIG. 3 was used, and a scattering prevention member 12 was further provided. The scattering prevention member 12 has one end connected to the guide member 1.
4, the other end is a free end, and a part of it is in contact with the developer upstream of the transport magnetic pole N. According to this embodiment, even without the scattering prevention member 12, the scattering of the developer was sufficiently tolerable, but by providing the scattering prevention member 12, the scattering was further reduced (and extremely good). Note that the developer transportability was also very good as in Example 3.

In the above embodiment, the non-magnetic toner 8 is used as the developer.
Although a two-component developer having a magnetic particle carrier 82 and a carrier 82 of magnetic particles was used, a one-component developer may also be used.

Further, in the above embodiment, at the development position, the development magnetic pole S
Although the method of pole position development in which the developer is developed with the developer standing up is adopted, the present invention can also be suitably adopted in a developing device that adopts the method of pole-to-pole development in which the developer is developed in a state where it is laid down. obtain. In this case, the relationship between the downstream developing magnetic pole of the developing magnetic pole group and the downstream first and second transporting magnetic poles may be configured as described in the above embodiment.

As detailed above, the present invention applies to a case where the maximum magnetic flux density of the second magnetic field generating means (conveying magnetic pole) is smaller than the maximum magnetic flux density of the first magnetic field generating means (developing magnetic pole), and Even if the second magnetic field generating means and the third magnetic field generating means located downstream thereof have different polarities, the magnetic flux density distribution of the second magnetic field generating means changes upstream from the position of maximum magnetic flux density. Since it is set to have a curved point, it is possible to prevent the developer from scattering, improve the conveyance of the developer by the second and eleventh field generating means, prevent the developer from stagnation and overflow, and obtain a high quality image. It has the advantage of being able to

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional side view showing an embodiment of a magnetic brush developing device according to the present invention. FIG. 2 is a chart showing the magnetic flux density distribution in the developing sleeve. FIG. 3 is a longitudinal sectional side view showing another embodiment of the magnetic brush developing device according to the present invention. : Image carrier: Developing sleeve (developer support) : Developing magnetic pole (first magnetic field generating means) : Transporting magnetic pole (second FI! i field generating means): Transporting magnetic pole (third magnetic field generating means) Fig. 1 figure

Claims (1)

[Scope of Claims] 1) A developer support is provided opposite to the image carrier, and the developer is supported on the outer surface of the developer support by a plurality of magnetic field generating means arranged inside the developer support. , a magnetic brush developing device configured to convey a latent image on the image carrier with a developer at a development position opposite to the image carrier, the magnetic brush developing device comprising: a first magnetic field generating means at the development position; The second magnetic field generating means located downstream in the direction of movement of the agent support have different polarities, and the second magnetic field generating means and the third magnetic field generating means located further downstream have different polarities. , the maximum magnetic flux density of the first magnetic field generating means is set larger than the maximum magnetic flux density of the second magnetic field generating means, and the second
A magnetic brush developing device characterized in that the magnetic flux density distribution of the magnetic field generating means is set to have an inflection point upstream of the position of maximum magnetic flux density. 2) At least a pole position of the second magnetic field generating means is covered with a developer container, and the magnetic pole position of the second magnetic field generating means is located downstream of the center of the second magnetic field generating means section. A magnetic brush developing device according to claim 1. 3) The magnetic brush development according to claim 1, wherein the developer is a two-component developer having magnetic particles having a weight average particle size of 20 to 65 μm and a non-magnetic toner having a volume average particle size of 8 μm or less. Device. 4) The magnetic brush developing device according to claim 1, wherein the maximum magnetic flux density of the second magnetic field generating means is greater than the maximum magnetic flux density of the third magnetic field generating means.