JPS6180181A - Developing device with magnetic brush - Google Patents

Abstract

PURPOSE:To decrease the load on a driving mechanism and to obtain a developed image having good image quality by conveying a magnetic developer by only the rotational driving of a developing sleeve. CONSTITUTION:The developing sleeve 2 and a toner contg. vessel 8 which is formed to face the peripheral surface of the sleeve 2 are so installed that one magnetic pole of the magnet of the sleeve faces the toner replenishing port 9 of said vessel even if the magnetic developer De is conveyed only by the rotational driving of the sleeve 2. The replenishing of the toner to the magnetic carrier Ca magnetically attracted onto the peripheral surface of the sleeve 2 is assured by such constitution. The magnetic pole position is set in the position deviated from the center of the aperture 9 in the peripheral direction of the sleeve 2, by which the oversupply of the toner to the carrier Ca magnetically attracted onto the peripheral surface of the sleeve 2 is prevented. The developed image having good image quality is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is capable of developing a magnetic carrier by supplying toner stored in a toner storage container to a magnetic carrier magnetically attracted on the circumferential surface of a developing sleeve. This invention relates to a magnetic brush developing device that prepares a magnetic developer made of a mixture of magnetic carrier and toner on the circumferential surface of a sleeve, and develops an electrostatic latent image using this magnetic developer, and is used for electrophotographic copying. It can be used by being incorporated into a machine, etc.

BACKGROUND OF THE INVENTION In recent years, one type of magnetic brush developing device of the above type has been formed to open toward the circumferential surface of a developing sleeve located upstream of a developing area in the developer conveying direction. The present applicant has developed a device equipped with a carrier loading chamber into which a magnetic carrier is loaded (Japanese Patent Application No. 183633).

Problems to be Solved by the Invention Incidentally, in the magnetic brush developing device of the above-mentioned type as well as other types of magnetic brush developing devices, the conveyance of the magnetic developer along the circumferential surface of the developing sleeve is This can be done by rotationally driving a magnet provided within the sleeve and/or the developing sleeve. However, according to the present inventors, when it is attempted to convey the magnetic developer only by rotationally driving the sleeve, the development of the electrostatic latent image itself may be adversely affected in the magnetic brush developing device of the above type. This has been experienced as something that can be done.

That is, in the magnetic brush developing device of the above configuration, in order to reduce the load on the drive mechanism, the magnet in the developing sleeve is fixed in a stationary state, while only the developing sleeve is rotationally driven to convey the magnetic developer. It has already been experienced that when this is done, the quality of the developed image deteriorates, such as fogging occurring in the developed image due to excessive supply of toner to the magnetic carrier.

Means for Solving the Problems An object of the present invention is to provide a magnetic brush developing device of the form described above, in which the magnetic developer is conveyed only by the rotational drive of the developing sleeve, and the image quality is always good. An object of the present invention is to provide a magnetic brush developing device capable of obtaining a developed image.

In order to achieve this object, the magnetic brush developing device according to the present invention has a magnet fixedly fixed inside the developing sleeve in a stationary state. In addition to conveying the magnetic developer along the magnetic developer, one magnetic pole of the magnet is arranged opposite to the toner replenishing opening of the toner storage container. Moreover, the magnetic pole position is set one position away from the center of the toner replenishment opening in the circumferential direction of the developing sleeve.

Function: In the magnetic brush developing device according to the present invention, although the magnetic developer is transported only by the rotational drive of the developing sleeve, one magnetic pole of the magnet faces the circumferential surface of the developing sleeve. By being installed opposite to the toner supply opening of the toner storage container formed by
The supply of toner to the magnetic carrier magnetically attracted on the circumferential surface of the developing sleeve is guaranteed. In addition, since the position of the magnetic pole is set away from the center of the toner replenishment opening in the circumferential direction of the developing sleeve, excess toner may be present on the magnetic carrier magnetically attracted on the circumferential surface of the developing sleeve. Supply is also prevented. As a result, according to the magnetic brush developing device according to the present invention, developed images of good quality can be obtained at all times.

Embodiment FIG. 1 is a diagram showing an internal outline of an embodiment of a magnetic brush developing device according to the present invention, and is shown installed in a powder image transfer type electrophotographic copying machine.

In FIG. 1, a magnetic brush developing device (MD) is installed on the surface of an electrophotographic photosensitive drum (1) which is rotated in the direction of arrow (a) while carrying an electrostatic latent image to be developed on the surface. They are provided in close opposition to each other, and in the developing area (Al), the surface of the developing sleeve (2) faces the surface of the photoreceptor drum (1) with a small gap maintained therebetween.

The developing sleeve (2) is made of a conductive non-magnetic material formed into a cylindrical shape, and has inside thereof a magnetic roller (3) which is sequentially magnetized to S or N poles on its outer periphery. .

Here, the developing sleeve (2) can be rotationally driven in the direction of the arrow (b1), and by being rotationally driven during development, the developing sleeve (2) is rotated along the circumferential surface of the developing sleeve (2) on the magnetic development side (D
e) in the direction of the arrow (b1).

Incidentally, in order to ensure such conveyance of the magnetic developer (De), minute irregularities are formed on the circumferential surface of the developing sleeve (2). On the other hand, the mI magnetic roller (3) is fixedly installed inside the developing sleeve (2) in a stationary state, and among its plurality of magnetic poles, the magnetic pole (N2) is located at the center of the developing area (5). position, and this magnetic pole (N
Due to the action of 2), a magnetic brush of magnetic developer (De) is formed in the development area (7!).Also, as will be explained in detail later, the magnetic pole (St ) is installed facing a toner replenishment opening (9), which will be described later.

By the way, after the magnetic developer (De) is loaded in advance into a carrier loading empty chamber (7) described later, the magnetic developer (De) is loaded into the developing sleeve (2) at the initial setting stage of the magnetic brush developing device (De).
By supplying insulating toner (TO) contained in the toner tank (8) to the magnetic carrier (Ca) magnetically attracted onto the circumferential surface of the developing sleeve (2).
It is prepared on the circumferential surface of , and consists of a mixture of both. The magnetic carrier (Ca) may be made of a single magnetic material such as ferrite, coated with a resin, or a so-called baying type magnetic carrier. In addition, insulating toner (T
As for (o), either a non-magnetic toner or a magnetic toner can be used as desired.

On the other hand, on the circumferential surface of the developing sleeve (2) located upstream of the developing area (~ in the developer conveying direction, that is, in the arrow b1 direction, there is a front regulating plate (4) and a height regulating plate along the developer conveying direction. Boards (5) are installed facing each other in sequence. This front regulating board (4) is integrated with the upper part/% housing of the toner tank (8) in which insulating toner (To) is stored as replenishment developer. The leading edge of the magnetic developer (De) is formed such that a gap greater than the thickness of the magnetic developer (De) conveyed along the curved surface of the developing sleeve (2) is maintained with respect to the circumferential surface of the developing sleeve (2). The front regulation plate (4) and the hot height regulation plate (
5), a carrier loading cavity +617+1 in which a magnetic carrier (Ca) is loaded in advance is formed.

The empty chamber (6) is opened toward the circumferential surface of the developing sleeve (2) located at the upstream side of the developing area (in the developer transport direction) and located approximately at the top.
This empty chamber (6) contains a certain amount of magnetic carrier (Ca) at the initial setting stage of the magnetic brush developing device (MD).
0) is loaded, but at that time, the magnetic carrier (C
In addition to loading only a), the magnetic carrier (Ca) may be loaded in a state mixed with a certain amount of insulating toner (TO). In order to make it possible to load such a magnetic carrier (Ca 2 ) into the cavity (6), the upper wall of the cavity (6) is constituted by an openable/closeable lid (7).

Further, the toner tank (8) has an opening (9) for toner replenishment formed by the front regulating plate (5), and this opening (9) is formed on the circumferential surface of the developing sleeve (2). is in a state of facing. Therefore, the insulating toner (TO) stored in the toner tank (8) is stored in this opening (
9), the magnetic developer (De) magnetically adsorbed onto the circumferential surface of the developing sleeve (2), so to speak, the magnetic carrier (
It is designed to be supplied to both Ca) and H.

In this toner tank (8), arrows (C1 The stirring blade is rotated in the direction (
10) are provided.

By the way, if we pay attention to the structure near the toner replenishment opening (9) with reference to FIG. 2, we will find that the magnetic roller (
The magnetic pole (Sl) of 3) is installed facing the toner replenishment opening (9), and the position of the magnetic pole (Sz) is in the circumferential direction of the developing sleeve of the toner replenishment opening (9). It is set off-center. in particular,
The width (ω) of the opening (9) in the circumferential direction of the developing sleeve is 1
3m+, and the position of the magnetic pole (Sl) is
It is set at a distance of 9 points (J+) from the edge of the opening (9) formed by the front regulation plate (4).

However, with regard to the magnetic brush developing device (M D ), the supply of insulating toner (To) to the magnetic developer (De ) magnetically attracted on the circumferential surface of the developing sleeve (2) must be maintained at an appropriate rate. Although the above-mentioned settings are necessary to achieve this purpose, the settings to achieve such a purpose do not necessarily need to be prompted only by the above-mentioned settings.

That is, as confirmed by the present inventors, under the condition that the width (ω) of the opening (9) is within the range of lO to 20H, the distance fJl is (1/8 to 3/8).
It has also been revealed that the proper supply of the insulating toner (To) can be maintained as long as the opening width is set to a certain opening width, and the above objective can be sufficiently achieved even with such a setting. In other words, the above objective can be fully achieved as long as it is set in the front device. However, even in such a case, the supply of the insulating toner (TO) itself may be adversely affected by the magnetic poles (N1) and (N3) adjacent to the magnetic pole (Sl), so the distance ( 1)
(5/8 to 7/8)・ω, the distance between the magnetic pole (S+) and the magnetic pole (N1), specifically, the point (Xl) in FIG. It is desirable to set the distance between the point (N2) and the point (N2) to be equal to or greater than ω.

In addition, when the distance (7'l) is set within the range of (1/8 to 3/8)・ω, the magnetic pole (Sl) and the magnetic pole (N
3) is desirably set equal to or larger than ω.

By the way, with the above settings, the developing sleeve (2)
At present, there is no concrete solution to the problem of properly supplying the insulating toner (TO) to the magnetic developer (D, e) that is magnetically attracted on the circumferential surface of the magnetic developer (D, e). Inferred from the behavior of the magnetic developer (De) described below without reference to , the magnetic developer (D
It is considered that the magnetic brush (e) is subject to certain restrictions under the above settings, and as a result, the above-mentioned appropriate supply can be achieved.

Here, FIG. 3 shows the magnetic development when a magnetic brush of magnetic developer (Oe) is formed on the circumferential surface of the developing sleeve (2) without any restrictions in the presence of magnetic poles. This diagram schematically shows the behavior of the agent (De). In this state, the magnetic brushes are in a raised state, and a considerable gap is formed between the magnetic brushes. Therefore, assuming that insulating toner (To) is supplied in this state, in addition to charged toner (cTo) that is charged by frictional contact with magnetic carrier (Ca), there is no contact with magnetic carrier (Ca). Uncharged toner (nTo), which does not hold any charge, also enters the gap and is supplied in large quantities. And, such uncharged toner (
As a result of the oversupply of nTo ), a large number of these uncharged toners (nTo) along with the magnetic developer (De) are transferred to the development area (
It is fully predicted that the image quality of the ring image will be deteriorated, such as fogging occurring in the developed image due to the presence of a large amount of uncharged toner (nTo), which is transported uncharged.

On the other hand, Figure S4 shows the developing sleeve (2) between the magnetic poles.
This diagram schematically shows the behavior of the magnetic developer (De) when it is magnetically adsorbed on the circumferential surface of the magnetic developer (De). In this state, the magnetic brush of the magnetic developer (De) The ears are in a flat state, and the magnetic carrier (Ca) is dense on the circumferential surface of the developing sleeve (2). Therefore, assuming that insulating toner (To) is supplied in this state, only a small amount of charged toner (cTo) is supplied due to frictional contact with the magnetic carrier (Ca).
Most of the insulating toner (To) will not be supplied. As a result, the supply of insulating toner (TO) becomes insufficient, and it is fully predicted that the toner concentration of the magnetic developer (Oe) that is being transported to the developing area will decrease.

However, under the above settings and under certain restrictions, a magnetic brush of magnetic developer (De) is formed on the circumferential surface of the developing sleeve (2) at the toner replenishment opening (9). If so, the uncharged toner (n
Excess supply of To) is suppressed and uncharged toner (nTo)
Moreover, the amount of magnetic carrier (Ca) supplied is suppressed to a small amount, and moreover, the amount of magnetic carrier (Ca) is
The insulating toner (TO) is sufficiently charged due to the frictional contact with the developing sleeve (2), and as a result, the insulating toner (TO) can be properly supplied to the magnetic developer (De) that is magnetically attracted on the circumferential surface of the developing sleeve (2). It can be considered as a thing.

By the way, the magnetic brush developing device shown in FIG.
When attempting to develop an electrostatic latent image using an MD), at the initial setting stage, the opening/closing lid (7) is first opened, a magnetic carrier (Ca) is loaded into the empty chamber (6), and the developing sleeve (2) is loaded.
) is pre-rotated, then insulating toner (TO) is loaded into the toner tank (8).

In this state, the developing sleeve (2) is further pre-rotated to a state in which the electrostatic latent image can be developed, and the initial setting of the magnetic brush developing device (MD) is completed. However, magnetic carrier (Ca) and a fixed amount of insulating toner (TO
) is loaded into the empty chamber (6), the latter preliminary rotation drive of the developing sleeve (2) can be omitted.

During development, as the developing sleeve (2) is rotated in the direction of the arrow (b1), the magnetic developer (De ) Insulating toner (To) supplied to
is conveyed along the circumferential surface of the developing sleeve (2) along the direction of arrow (b) together with the magnetic developer (1)e). During this transportation, the insulating toner (T o ) is mixed and stirred with the magnetic carrier (Ca) when passing through the empty chamber (6), and both are triboelectrically charged. Through such mixing and stirring, the insulating toner (TO) and magnetic carrier (Ca), which are each component of the magnetic developer (De), are constantly integrated at a constant mixing ratio at this point, and the developing area (In ~, a magnetic brush made of magnetic developer (De) is reliably formed. Note that the insulating toner (TO) and magnetic carrier (
The mixing ratio with Ca) is mainly determined by the magnetic pole (
It is determined depending on the position setting of the magnetic carrier (SL) and/or the amount of magnetic carrier (Ca) accumulated in the empty chamber (6), and by changing these, the mixing ratio, that is, the development It is possible to finely adjust the toner concentration of the magnetic developer (De) in the region (A). The magnetic brush formed here rubs the surface of the photoreceptor drum (1), and develops the electrostatic latent image carried on the surface into a visible image.

In addition, at this time, it is common to develop an electrostatic layer (original layer) while a DC developing bias is applied to the developing sleeve (2), but an AC developing bias may also be superimposed on this. Alternatively, the developing sleeper (2) may be grounded.

Further, after being subjected to development, the magnetic developer (De) remaining on the circumferential surface of the developing sleeve (2) is further conveyed in the direction of arrow Cb1, and when it passes through the toner replenishment opening (9). After being supplied with insulating toner (To), it is used for restart development.

By the way, the amount of magnetic developer (De) that reaches the developing area (~) is regulated by the height regulating plate (5), but a The moe regulation gap between the hot height regulation plate (5) and the developer IJ.

Because it is set wider than the height regulation gap formed between the developing sleeve (2) and the developing sleeve (2),
All of the existing magnetic carrier (Ca) passes through the front regulation gear knob and reaches the empty chamber (6). Here, the hot height regulation plate (
The magnetic carrier (Ca) and insulating toner (TO) regulated in 5) accumulate in the empty chamber (6) and are also mixed and stirred in the axial direction of the developing sleeve (2). They, especially the magnetic carrier (Ca 2 ), are stirred only within the empty chamber (6) and are not diffused into the toner tank (8).

In addition, in the above configuration, the front regulation gap needs to be wide enough to pass all of the magnetic developer (De) present on the circumferential surface of the developing sleeve (2), and the front regulation plate (4) must partition the empty chamber 6) and the toner tank (8) and prevent the magnetic carrier (Ca) accumulated in the empty chamber (6) from diffusing into the toner tank (8). For example, if the scraping regulation gap is narrow and the amount of magnetic developer (De) passing through is smaller than the height regulation gap, magnetic carrier will accumulate in the front regulation plate (4), causing the toner tank (8) to This also causes diffusion of magnetic carriers (Ca). On the other hand, not only the magnetic carrier (Ca) is accumulated in the empty chamber (6), but also the toner concentration unevenness of the magnetic developer (De) in the axial direction of the developing sleeve (2) is effectively eliminated. Spread.

[Experiment example]

Regarding the magnetic brush developing device (MD) shown in FIG. 1, excellent effects have already been confirmed based on various experimental results. Here, among the experiments conducted by the present inventor, representative ones are shown below, and the above-mentioned excellent effects are specifically clarified as follows.

Experimental Example-1 (Preliminary Experiment) Regarding the magnetic brush developing device (MD) shown in Fig. 1, magnetic roller Magnetic force: 750G Number of poles: 6 poles (asymmetrical) Developing sleeve Outer diameter: 24.5a + rotation speed; 1
0100rP arrow direction) Head height regulation gap; 0.
351111 Front regulation gap; 1.211 Development gap; 0.45N Opening width (ω); 13aw Distance between magnetic pole (St) and magnetic pole (N1); 13 Fighting pole (
Distance between S rim and magnetic pole (N3): 13 mm Magnetic carrier: 100 parts of styrene acrylic resin, 400 parts by weight of Zn-based ferrite fine powder, 2 parts by weight of carbon black, and 1.5 parts by weight of silica were heated and kneaded, cooled, Binder-type magnetic carrier insulating toner with an average particle size of 60 μm obtained by pulverization and classification; polyester resin (weight average molecular weight: 23.300) 1
00 parts by weight of negatively charged dye, 2 parts by weight of carbon black, and 2.5 parts of wax are heated, mixed, cooled, pulverized, and classified, and the insulating toner has an average particle size of 11 μm. , 0.2 ωt% silica fine powder is electrostatically adsorbed on its surface.Amount of magnetic carrier loaded in the empty chamber (6); 40g of insulating toner loaded in the toner tank (8). Jil
i Under the condition of 100 g, the distance (ll) from the edge of the gutter replenishment opening (9) formed by the front regulating plate (4) to the center of the magnetic pole (Sl) of the magnetic roller (3) is 1
As a result of measuring the toner concentration of the magnetic developer (De) in the developing area (~12 mm), the results shown in Figure 5 were obtained. As a specific method, a method was adopted in which the magnetic roller (3) was rotatably supported and fixed at a position corresponding to the distance (1) or the value described above.

As is clear from the results shown in FIG. 5, it can be seen that the toner a change greatly varies depending on the position of the magnetic pole (Sl). and a magnetic developer (De) prepared from the magnetic carrier (Ca) and the insulating toner (To).
Since the appropriate toner concentration of
)@ω, 7/8・0 or more [however, ω is the opening width of the toner replenishing opening (9) in the circumferential direction of the developing sleeve], there will be excess or deficiency in the supply of insulating toner (To). It is predicted that.

Experimental Example 2 (Example) The same conditions as Experimental Example 1 were applied except that the magnetic roller (3) was fixed at a position where the distance (1) was 9 mm, and the process speed (photoreceptor drum peripheral speed) was ) ; 130 thrn/
sec electrostatic latent image potential; +500 V (highest potential)
Development bias: under the conditions of DC + 150V AC 400 VrmS 400 Hz,
A copying experiment was conducted using a powder image transfer type electrophotographic copying machine while gradually replenishing the toner tank (8) with insulating toner (To). As a result, it was confirmed that good copied images could always be stably obtained by the copying machine.

In addition, when we observed the toner concentration of the magnetic developer (De) in the development area formula, the value was 15 ωt% at the beginning of the copying experiment, but it decreased slightly as the copying experiment progressed, and the value decreased slightly as the copying experiment progressed. 10 after copying 100 sheets
It was found that it is stable at ~12ω[%. The range in the stable value of toner density is due to the difference in the black-and-white ratio of the copied originals used in the copying experiment.
[It was stable at a value of %. This level of decrease in toner density had no effect on the quality of the copied image.

Experimental Example-3 (Example) Magnetic roller (3) is placed at the position where the distance (7) is 11 points.
A copying experiment was conducted in the same manner as in Experimental Example 2, except that . As a result, at the beginning of the copying experiment, there was a tendency for the density of the solid copy image to gradually decrease until the completion of copying 100 A4 size sheets, but after that, good copy images were always produced. It was confirmed that it could be obtained stably.

Regarding the toner concentration, at the beginning of the copying experiment, 10
It was found that ω (%) decreased slightly as the copying experiment progressed, and stabilized at 7 to 8 ωt% after copying 100 A4 size sheets. Such a decrease in toner concentration
This is thought to appear as a decrease in the density of the solid copy image.

Experimental Example-4 (Comparative Experimental Example) Magnetic roller (3
) is fixed [In this state, the magnetism (Sl) of the magnetic roller (3)
A copying experiment was conducted in the same manner as in Experimental Example 2, except that the opening (9) for toner replenishment was located at the circumferential center of the developing sleeve. As a result, fogging occurred in the copied images from the beginning of the copying experiment, and the image quality was extremely poor in terms of sharpness, uniformity of halftone reproducibility, etc. In addition, a large amount of insulating toner (To) was observed scattering around the magnetic brush developing device (MD).

Incidentally, the toner concentration is as high as 25ω%, and the appropriate toner concentration of the magnetic developer (De) is 5~
There were also some that deviated from 20 ωt%.

Effects of the Invention According to the magnetic brush developing device according to the present invention, since the magnetic developer is transported only by rotationally driving the developing sleeve, the load on the drive mechanism is reduced. and,
Such a reduction in the load on the drive mechanism can be achieved without deteriorating the quality of the developed image such as fogging in the developed image, so that developed images of good quality can always be obtained.

The above-mentioned advantage is that by supplying the toner stored in the toner storage container to the magnetic carrier magnetically attracted on the circumferential surface of the developing sleeve, the magnetic carrier can be absorbed onto the circumferential surface of the developing sleeve. A magnetic developer is prepared from a mixture of a toner and a toner, and this magnetic developer is used to develop an electrostatic latent image.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an internal outline of an embodiment of the magnetic brush developing device according to the present invention, FIG. 2 is an enlarged view of the main part of FIG. A diagram schematically showing the behavior of magnetic developer on a surface, and Figure 5 shows the correlation between the magnetic pole position of the magnetic roller facing the toner replenishment opening of the toner tank and the toner concentration of the magnetic developer in the development area. It is a drawing showing the relationship. MD...Magnetic brush developing device De...Magnetic developer Ca...Magnetic carrier To...Insulating toner cTo...Charged toner nTo...Uncharged toner A, development area 2...Development sleeve 3 ... Magnetic roller 8 ... Toner tank 9 ... Toner replenishment opening Applicant: Minolta Camera Co., Ltd. D

Claims (1)

[Claims] 1. By supplying the toner stored in the toner storage container to the magnetic carrier magnetically attracted on the circumferential surface of the developing sleeve, the magnetic carrier is formed on the circumferential surface of the developing sleeve. A magnetic brush developing device which prepares a magnetic developer consisting of a mixture of and toner and develops an electrostatic latent image using this magnetic developer, wherein the developing sleeve is fixedly fixed inside in a stationary state. The magnetic developer is conveyed along the circumferential surface of the developing sleeve by being rotationally driven, and furthermore, one magnetic pole of the magnet is opposed to the circumferential surface of the developing sleeve. The developing sleeve is disposed opposite to the toner replenishment opening of the toner storage container, and the magnetic pole position is set at a position away from the center of the toner replenishment opening in the circumferential direction of the developing sleeve. A magnetic brush developing device characterized by: 2. The magnetic brush developing device according to claim 1, wherein the opening width of the toner replenishing opening in the circumferential direction of the developing sleeve is within a range of 10 to 20 mm. 3. A magnetic pole installed opposite to the toner replenishment opening is (1/8 to 3/8) from the center of the toner replenishment opening in the circumferential direction of the developing sleeve [where ω is the toner replenishment opening] 3. The magnetic brush developing device according to claim 1, wherein the opening width in the circumferential direction of the developing sleeve is set at a position different from the opening width in the circumferential direction of the developing sleeve.