JPH0743554B2 - Development device - Google Patents

Description

The present invention relates to a developing device that visualizes an electrostatic charge image formed on the surface of an image carrier by using a developer containing a magnetic carrier and a magnetic toner. Is.

[Conventional technology]

When developing the electrostatic image formed on the surface of the image carrier,
Generally, the magnetic brush method is used. Thus, most of the developers used for magnetic brush development are two-component developers in which a magnetic carrier and a non-magnetic toner are mixed. On the other hand, there is also a method of using a one-component developer composed of a resin and a toner mainly containing magnetic powder as a developer.

The former developing device using a two-component developer is composed of an independent toner hopper and a developer tank containing the developer, and detects the toner concentration in the developer in the developer tank. Then, the toner replenishing roll provided in the toner hopper is driven to replenish the insufficient toner. However, in the device of this configuration,
In addition to the complicated structure, the toner supply is intermittent and the toner supply timing is delayed, resulting in low reliability. There is also a drawback that the price of the entire apparatus is high and that the replenished toner and the magnetic carrier existing in the developer tank are not sufficiently mixed.

On the other hand, when using the latter one-component developer,
Since no carrier particles are used to give the toner an electric charge of a predetermined polarity, the charging of the toner becomes unstable and the image quality deteriorates. Further, since the toner has an electric charge due to contact with a toner conveying member such as a sleeve, it is difficult to control the amount of charge and there is a limit. As means for solving these problems, for example, JP-A-59-162563 and 59-162
182464 and 59-216149 have proposed a developer in which a magnetic carrier and a magnetic toner are mixed as described in JP-A Nos. 182464 and 59-216149. The advantages of both the conventional two-component developer and the one-component developer described above are proposed. It is supposed to have both.

FIG. 3 is a cross-sectional view of essential parts showing an example of a developing device using a developer obtained by mixing the magnetic carrier and the magnetic toner. In the figure, 1 is a carrier, which carries an electrostatic image (not shown) on its surface and rotates in the direction of the arrow. Next, a developer tank 2 is formed so that the toner cartridge 3 can be mounted thereon and a developing roll 4 is provided at the lower end.
The developing roll 4 is provided so as to face the carrier 1, and
In a hollow cylindrical sleeve 5 made of a non-magnetic material, a magnet roll 6 having a plurality of magnetic poles extending in the axial direction is coaxially and relatively rotatable. FIG. 3 shows an example in which the sleeve 5 is fixed and the magnet roll 6 is formed to rotate counterclockwise. Reference numeral 7 denotes a doctor blade, which is provided in the developer tank 2 and has its tip end faced to the surface of the developing roll 4 and formed so as to be freely retractable. Next, a toner recovery roll 8 is provided so as to face the developing roll 4.
The toner collecting roll 8 is made of a conductive material such as aluminum and its alloy or metal such as stainless steel and has a circular cross section. The toner collecting roll 8 is rotatably provided in the vicinity of the developing roll 4 in the developer tank 2, and the toner collecting roll 8 is provided. The scraper 9 is tangentially and slidably provided on the surface of the. With the above configuration, when the developing roll 4 is driven, the developer 10 composed of the magnetic toner and the magnetic carrier is adsorbed and moved on the surface of the developing roll 4, and the electrostatic charge image carried on the surface of the carrier 1 is developed. The surplus developer 10a returns to the developer tank 2 again. In this case, if the toner concentration measured by the toner concentration sensor (not shown) is high, the bias voltage of the toner recovery roll 8 is raised by the electric signal via the control means, and the toner recovery roll 8 causes the developing roll 4 to rise. The magnetic toner in the developer 10 that is adsorbed and moved on the surface of the toner is electrostatically absorbed and removed, and the toner concentration is controlled within the optimum range.

In the above conventional developing device, since the developing roll 4 is driven in a state where a relatively large amount of the developer 10 is accommodated in the developer tank 2, the contact area between the developing roll 4 and the developer 10 is large. However, since the developing roll 4 is buried in the developer 10, there is a problem that the rotation torque is large.
Further, also in adjusting the concentration of the magnetic toner in the developer 10, there is a problem that a large amount of the magnetic carrier to be supplied into the developer tank 2 is required and the adjustment is extremely complicated and takes time. .

In order to solve the above problems, the present applicant has already applied for an improved developing device (Japanese Patent Application No. 63-99004).
issue). FIG. 2 is a sectional view of an essential part showing an embodiment of the improved developing device, and the same parts are designated by the same reference numerals as those in FIG. In FIG. 2, reference numeral 11 denotes a support plate, which is formed of a non-magnetic material into a flat plate shape or a gutter shape, and is provided below the developing roll 4 with a gap d. This gap d
Is set in the magnetic attraction region (inside the chain line A) where the magnetic powder is attracted toward the magnet roll 6 by the magnetic attraction force of the magnet roll 6. A doctor blade 7 is mounted on an edge 11a formed at one end of the support plate 11, and a magnetic carrier accommodating area 11b is formed between the edge 11a and the vicinity of a vertical surface 4a including the axis of the developing roll 4. To do. Next, the other end of the support plate 11, that is, the free end 11d is formed by extending the vertical plane 4a including the axis of the developing roll 4 to a distance L, and the vicinity of the vertical plane including the axis of the developing roll 4 and the supporting plate. 11 free ends 11
A magnetic carrier supply region 11c is formed between this and d. The distance L is within the rotation region (inside the chain line B) in which the magnetic powder is rotated by the rotating magnetic field of the magnet roll 6 to move to the outside.
Position the tip of the. Next, reference numeral 12 is a supply paddle, which is provided with rod-shaped permanent magnets 13 magnetized in the radial direction (thickness direction) at both ends and is rotatably counterclockwise in the developer tank 2. The trajectories of the permanent magnets 13 provided at both ends of the supply paddle 12 are provided near the free end 11d of the support plate 11.

With the above configuration, the operation will be described next. First, the magnetic toner is placed in the developer tank 2 via the toner cartridge 3.
Supply 2a. Next, when the magnetic carrier is supplied to the magnetic carrier accommodating area 11b and the magnet roll 6 is rotated counterclockwise, the magnetic carrier in the magnetic carrier accommodating area 11b moves rightward as indicated by an arrow on the support plate 11. To the magnetic carrier supply area 11c. The magnetic carrier staying in this way is generated by the magnetic attraction force of the magnet roll 6.
As indicated by the arrow, it is adsorbed on the surface of the sleeve 5, and is conveyed clockwise while rotating by the clockwise rotation of the sleeve 5 and the counterclockwise rotation of the magnet roll 6. When the supply paddle 12 is rotated counterclockwise, the magnetic toner 2a attracted by the permanent magnet 13 reaches the free end 11d of the support plate 11 and reaches the surface of the sleeve 5 by the action of the magnetic attraction force of the magnet roll 6. Adsorbed. As described above, the magnetic carrier is adsorbed on the surface of the sleeve 5 and is conveyed clockwise while rotating by the rotation of the magnet roll 6, so that the magnetic toner 2a and the magnetic carrier are uniformly mixed by rotation. Form a magnetic brush. Since the magnetic toner 2a is also affected by the magnetic attraction force of the magnet roll 6, the magnetic brush 2a has a form in which the magnetic toner 2a is concentrated and attached in the vicinity of the contact portion between the magnetic carrier particles. Here, when the excess magnetic toner 2a is supplied onto the sleeve 5, even if the excess magnetic toner 2a is temporarily held on the sleeve 5, the magnetic carrier is absorbed according to the amount of the magnetic carrier adsorbed on the sleeve 5. Since the amount of the magnetic toner 2a that can be held is determined by the rotating magnetic field of the magnet roll 6, the excess magnetic toner 2a is immediately separated from the magnetic brush and returned to the developer tank 2. Therefore, since the magnetic toner concentration in the developer adsorbed on the sleeve 5 is always maintained at a constant value, good development can be performed.

Next, the gap d forming the magnetic carrier accommodating region 11b formed on the support plate 11 is set within the range where the magnetic attraction force of the magnet roll 6 constituting the developing roll 4 acts and near the limit. It depends on the diameter of the magnet roll 6, the surface magnetic flux density on the sleeve 5, the characteristics of the magnetic carrier and the magnetic toner, and the like. Then, the distance L forming the magnetic carrier supply area 11c is obtained from the developer moving distance determined based on the value of the gap d.

For example, the outer diameter of the sleeve 5 is 31mm, the outer diameter of the magnet roll is 29.3mm,
When the number of magnetic poles is 16 and the surface magnetic flux density on the sleeve 5 is 600 G, when the gap d = 7 mm, the distance L is in the range of 4 to 13 mm, and it is particularly preferable that L = 11 mm. The magnetic carrier used in this case is KBN-100 (particle size 74
~ 149μm), magnetic toner has an average particle size of 12μm, DC4000V / c
Volume resistance in the electric field of m 10 ¹⁵ Ωcm, blow-off charge
It has a content of 10 μc / g and a magnetite content of 60% by weight.

[Problems to be Solved by the Invention]

According to the above-described improved invention, only a predetermined amount of the magnetic carrier is first adsorbed on the sleeve 5 constituting the developing roll 4, and then a small amount of the magnetic toner 2a is supplied onto the sleeve 5, so that the magnetic toner concentration with higher accuracy can be obtained. Can be controlled or adjusted. However, depending on the developing device, the magnetic toner 2a tends to be slightly over-supplied, and a so-called tailing phenomenon may occur. On the other hand, in recent years, the toner density has been made lower than the conventional one,
For example, 35 ± 5% by weight (particle size of magnetic carrier is 74-105μ
In the case of m, it is better to use the magnetic brush in the state of the spikes (most of the magnetic toner adheres to the magnetic carrier,
It will be carried together with the magnetic carrier). The optimum toner concentration depends not only on the particle size and resistance of the magnetic carrier but also on the characteristics of the toner.

The present invention solves some of the points required for improvement in the above-mentioned improved invention, and provides a developing device with higher performance capable of easily and quickly controlling or adjusting the magnetic toner concentration by using a relatively small amount of magnetic carrier. The purpose is to do.

[Means for Solving the Problems]

In order to achieve the above object, in the present invention, a magnet roll having a plurality of magnetic poles extending in the axial direction is formed in a hollow cylindrical sleeve made of a non-magnetic material, facing a carrier for an electrostatic charge image. In a developing device provided with a developing roll provided so as to be rotatable relative to the developer, the developer comprising a magnetic carrier and a magnetic toner is supplied to the carrier through the developing roll to develop the electrostatic image. A support plate is provided below the developing roll with a gap, and a doctor blade is provided at the edge of the support plate on the side of the carrier, and the position of the free end of the support plate opposite to the carrier is set. The first regulating member is provided in the rotation region outside the range where the magnetic attraction force of the developing roll acts, and on the supporting plate in the vicinity of the vertical plane including the axis of the developing roll with a gap between the developing roll surface and the first regulating member. This Thereby forming a magnetic carrier contained area between the first regulating member and said free end of said support plate,
A second restricting member that restricts the amount of magnetic toner supplied is provided between the free end of the support plate and the surface of the developing roll via a gap so that the magnetic toner can be supplied to the surface of the developing roll. , Was adopted as the technical means.

In addition to the above configuration, a third restriction member for restricting the amount of magnetic toner may be provided in the vicinity of the moving path of the support plate upstream.

[Action]

With the above-described structure, only a predetermined amount of the magnetic carrier can be first adsorbed on the sleeve forming the developing roll, and then a small amount of the magnetic toner can be supplied onto the sleeve, and the magnetic carrier accommodating area is kept within the effective range by the regulating member. In addition, the amount of magnetic toner supplied can be regulated within a predetermined range, and the magnetic toner concentration can be controlled with extremely high accuracy.

〔Example〕

FIG. 1 is a sectional view of an essential part showing an embodiment of the present invention, in which the same parts are designated by the same reference numerals as those in FIGS. 2 and 3. In FIG. 1, reference numeral 14 is a first restricting member, which has a substantially L-shaped cross section and is provided on the support plate 11 so as to project from the surface of the developing roller 4 with a gap δ ₁ . The installation position of the first regulating member 14 is preferably provided near the vertical surface including the axis of the developing roll 4. A magnetic carrier accommodating region 11e is formed on the support plate 11 between the free end 11d of the support plate 11 and the first restriction member 14. Next, reference numeral 15 is a second regulating member, which has a cross section formed in an arc shape and is arranged outside the developing roll 4, and the lower end portion of which is a free end 11 of the support plate 11.
Provided through d and a gap δ ₂ . 16 is a supply port, a support plate
It is formed in a groove shape by the free end 11d of 11 and the second regulating member 15. Reference numeral 17 denotes a third regulating member, which is formed in a flat plate shape and has a gap δ ₃ with the permanent magnet 13 provided at the end of the supply paddle 12.
Provided through.

With the above configuration, the operation will be described next. By operating the developing roll 4 and the supply paddle 12, as described with reference to FIG. 2, magnetic toner (not shown) can be sequentially supplied to the magnetic carrier storage area 11e. In this case, the magnetic toner is first adsorbed to the outside of the permanent magnet 13 constituting the supply paddle 12, but when it passes under the third regulating member 17, the magnetic toner has a layer thickness of δ ₃ (for example, 2.0 mm). ) And the excess magnetic toner falls into the developer tank 2,
Only a predetermined amount of magnetic toner set in advance is used for the developing roll 4
Can be supplied to the outside. Next, the magnetic toner is supplied to the magnetic carrier accommodating region 11e formed on the support plate 11, and in this case, the supply port 16 is the support plate.
Due to the free end 11d of 11 and the second regulating member 15, a gap δ
_Since it is set to ₂ (for example, 3.0 mm), the permanent magnet
Even if the layer thickness of the magnetic toner adsorbed on 13 is partially increased during the movement, it is supplied to the magnetic carrier accommodating area 11e with a predetermined thickness δ ₂ . Therefore, magnetic carrier accommodation area 1
It is possible to eliminate the obstacle to the mixing action of the developer, which is being uniformly mixed by rotation within 1e, and to prevent the large fluctuation of the magnetic toner concentration. On the other hand, the left end of the magnetic carrier accommodating area 11e is partitioned by the first restricting member 14, and the rotation of the magnetic carrier and the magnetic toner accompanying the rotation of the magnet roll 6 constituting the developing roll 4 and the action of the mixing and suction force are in an optimum state. Can be held at. Further, since the gap δ ₁ (for example, 2.0 mm) is set between the first regulating member 14 and the surface of the developing roll 4, it is possible to prevent an adverse effect that an excessive amount of developer is conveyed and to prevent the magnetic carrier. It is ensured that the mixing action of the magnetic carrier and the magnetic toner in the containing area 11e is performed uniformly.

In this way, the magnetic toner in the developer tank 2 is supplied to the developing roll 4 after being adjusted to a certain amount by the second regulating member 15 and the third regulating member 17 and then supplied onto the developing roll 4. It is possible to maintain the toner concentration of the developer held in the proper value. Therefore, a high quality image without tailing can be obtained.

In this embodiment, a sleeve constituting a developing roll,
Although the example in which the magnet roll is rotated has been shown, only the magnet roll may be rotated, that is, any configuration may be adopted as long as the rotating magnetic field of the magnet roll exists. The shape of the support plate is not limited to the flat plate shown in the present embodiment,
The cross-section may be arcuate, and any shape is acceptable as long as it can form the magnetic carrier accommodation area. Further, the magnetic toner replenishing means has the same operation even if it is replaced with a known powder replenishing means other than this embodiment. Although the restricting member in this embodiment has an L-shaped cross section, an arc shape, and a flat plate shape, the restricting member may be formed in a circular, rectangular, or other geometrical cross section. Are the same. Further, the value of the gap formed by the regulating member can be appropriately selected in consideration of the specifications, characteristics, etc. of the developing device, the magnetic carrier, the magnetic toner and the like. Further, the third regulating member which is provided outside the magnetic toner replenishing means and regulates the supply amount of the magnetic toner may be omitted in some cases.

〔The invention's effect〕

Since the present invention has the configuration and operation as described above,
There is an effect that the control or adjustment of the magnetic toner concentration in the developer is extremely easy and quick, and further high precision and high performance can be achieved. Further, since the amount of the developer that comes into contact with the developing roll is small, the rotating torque is small and the driving member can be downsized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an essential part showing an embodiment of the present invention, FIG. 2 is a cross-sectional view of an essential part of an improved developing device, and FIG. 3 is a cross-sectional view of an essential part of a conventional developing device. It is a figure. 4: Developing roll, 5: Sleeve, 6: Magnet roll, 11: Support plate, 11
b, 11e: magnetic carrier accommodating area, 12: supply paddle, 14, 15, 17: regulating member.

Claims (2)

[Claims] 1. A development comprising a magnet roll having a plurality of magnetic poles extending in an axial direction, which is provided in a sleeve formed of a non-magnetic material in the shape of a hollow cylinder so as to be rotatable relative to the electrostatic image carrier. In a developing device that is provided with a roll and supplies the developer consisting of a magnetic carrier and magnetic toner to the carrier through the developing roll to develop the electrostatic image, a gap is provided below the developing roll. A support plate is provided through the support plate, a doctor blade is provided at the edge of the support plate on the side of the carrier, and the magnetic attraction force of the developing roller is set at the position of the free end of the support plate opposite to the carrier. A first regulating member is provided on the supporting plate near the vertical surface including the axis of the developing roll and outside the working range, and the first regulating member is projected with a gap from the surface of the developing roll. And in front of the support plate A magnetic carrier accommodating area is formed between the free end and a second restricting member that restricts the magnetic toner supply amount via a gap between the free end of the support plate and the surface of the developing roll. A developing device characterized in that magnetic toner can be supplied to the surface of the developing roll. 2. The developing device according to claim 1, wherein a third regulating member for regulating the amount of magnetic toner is provided in the vicinity of the moving path upstream of the support plate.