JPH1031362A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent reduction in density and fogging caused by the returning of a developer after development to a developing sleeve, before the developer is sufficiently stirred/mixed with the supplied developer. SOLUTION: The developing device is provided with the developing sleeve 21 for carrying a two-component developer, a first magnetic pole and a second magnetic pole in a part nearer to the downstream side in the rotational direction of the sleeve than the first magnetic pole, which are provided in the sleeve 21 and form a repulsing magnetic field and carrying screws 23 and 24 which carry the developer dropped from between the first and second magnetic poles and are provided with center shafts consisting of ferromagnetic bodies. The center shaft is in a horizontal direction and the whole of the center shaft exists between the center position of a region where both of the strength of a magnetic field in the normal direction of the surface of the developing sleeve 21 between the first and second magnetic poles and the strength of the magnetic field in a tangential direction are <=50G and a position where the strength of the magnetic field in the normal direction of the surface of the developing sleeve in the vicinity of the second magnetic pole is a maximal value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a developing device for developing an electrostatic image on an image carrier with a two-component developer.

[0002]

2. Description of the Related Art As image forming apparatuses have been downsized, developing apparatuses have also been required to be downsized.

In particular, in a four-drum system having four photosensitive drums, a developed image is generally formed on four drums generally arranged on a belt, and transferred to a recording material conveyed on the belt to form an image. In this method, the developing device is required to be of a small type such that the developing device is disposed laterally with respect to the drum and the lowermost portion of the developing device is higher than the lowermost portion of the drum so as not to contact the belt.

The mainstream development methods of this type are a one-component development method using a one-component ratio magnetic toner and a two-component magnetic brush developer method using a two-component developer in which magnetic particles and a toner are mixed. Has become.

The one-component developing method is simple and does not require a means for maintaining a constant developer concentration unlike the two-component developing method. On the other hand, transferability, halftone reproducibility, stability of developing characteristics with respect to temperature and humidity are improved. It is not suitable for forming a full-color stable image.

[0006] On the other hand, the two-component magnetic brush developing method is a simple developing method capable of stable development and suitable for non-black or full-color development. However, developer deterioration due to a change in the surface of magnetic particles (spent toner, etc.) There is a problem.

As a means for solving the above-mentioned problem of the two-component magnetic brush developing method, the present applicant has disclosed Japanese Patent Application Laid-Open No. 62-153.
No. 882 has proposed the invention.

The invention disclosed in Japanese Patent Application Laid-Open No. Sho 62-153882 is a developing device for developing an electrostatic latent image on an electrostatic latent image carrier as exemplified in FIG. And a developer container 2 containing a developer having
Forming a developing unit for supplying the toner particles 128 to the electrostatic latent image carrier 1, facing the electrostatic latent image carrier 1, and carrying the developer from the container 2 to the developing unit. A developer regulating member 9 having a developer carrying member 21 and a regulation portion tip located upstream of the developing section in the rotation direction of the developer carrying member 21 and separated from the surface of the developer carrying member.
Receiving the developer conveyed on the developer carrying member 21 after passing through the portion of the developer regulating member 9 and further passing through the developing portion, downstream of the developing portion, and transferring the developer to the developing portion. The developing device includes transport stirring members (screw) 23 and 24 for transporting the developer into the developer container 2 and mixing the developer with the developer inverted into the developer container 21 by the developer regulating member 9.

[0009]

However, in the above-mentioned prior art, since the developer is prevented from being deteriorated by the developer naturally circulating in the developing container 21, the repulsion poles S ₂ and S ₃ are required. Even when the toner is provided, the circulation of the agent in the S ₂ and S ₃ parts is not effectively used, so that the conveyance and agitation in the axial direction cannot be sufficiently performed, and the toner concentration in the developer is biased. It is difficult to stably produce a uniform image because it causes density unevenness and density gradient. Further, when a toner containing a sharp-melt resin such as a polyester resin is used for obtaining a high-quality full-color image, the developer deteriorates particularly when a toner having a volume average particle diameter of less than 12 μm is used for the purpose of improving image quality. As a result, there has been a problem that when image formation is performed for a long period of time, density reduction and fogging occur.

Further, for the purpose of solving the drawbacks of the above conventional example, a configuration shown in FIG. 4 has been proposed in Japanese Patent Laid-Open Publication No. Hei 3-4267. This configuration defines the relationship between the center position of the zero gauss of the repelling pole, the position of the center of the screw as the stirring member, the position of the developer pumping pole, and the distance between the surface A extending vertically from the center of the developing area. Things. The distance between the center position of zero Gauss and the above-described surface A is L ₁ , the distance between the center of the screw and the surface A is L ₂ , the developer pumping pole and the surface A
Agents related to development after development is dropped from the position of the zero gauss rebound machining gap by the distance to the L ₃ relationship L ₁ <L ₂ <L ₃ and is conveyed further by the rotation of the screw, the screw After being sufficiently mixed with the developer, the developer is supplied to the developer carrier by the action of the pumping pole. However, since this configuration defines only the relationship between the center of the stirring member and the developer carrier, when the amount of the developer is small, the conveyance and stirring are performed stably. When control is performed, charge-up occurs at low humidity, and when the T / _{T + C} ratio is increased in order to obtain the same image density, the fluidity of the agent changes due to environmental fluctuations, etc., and the agent circulation balance When the developer changes and the developer in the developing chamber increases, when the surface of the developer rises to the vicinity of the uppermost surface of the screw shaft, the agent dropped by the repulsion pole is conveyed on the screw with the rotation of the screw. Before being mixed with the developer, it is supplied to the developer carrier again by the action of the pumping pole, and as a result, there is a problem that the concentration of the developer is reduced and fogging due to poor stirring is caused. Was . As described above, it is extremely difficult to obtain a stable developer circulation over a long period of time with the conventional configuration.

[0011]

According to the present invention, there is provided a developer carrier for carrying a developer having a toner and a carrier, and a first magnetic pole provided in the developer carrier to form a repulsive magnetic field. A second magnetic pole downstream of the first magnetic pole in the direction of movement of the developer carrier, and a transport screw for transporting the developer dropped from between the first and second magnetic poles. A central axis made of a magnetic material, and the central axis is horizontal, and the strength of the magnetic field in the direction normal to the surface of the developer carrier between the first and second magnetic poles and the strength of the magnetic field in the tangential direction are reduced. Both are characterized by being present between the center position of the region of 50 gauss or less and the position where the strength of the magnetic field in the direction normal to the surface of the developer carrier near the second magnetic pole has a maximum value.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a longitudinal sectional view of a developing device according to the present invention,
FIG. 2 is a diagram supplementarily explaining the principle of agent circulation in FIG.

The developing device is for developing a latent image formed on a latent image carrier 1 such as a photoreceptor or a dielectric by an electrophotographic method, an electrostatic recording method or the like. 2. A developing sleeve 21 as a developer carrier and a blade 9 as a developer layer regulating member. That is, an opening is formed in the developing container 2 at a position close to the latent image carrier 1, and the developing sleeve 2 is formed in this opening.
The blade 9 is rotatably provided, and the blade 9 is attached above the developing sleeve 21 with a predetermined gap.

The developing sleeve 21 is made of a non-magnetic material, rotates during the developing operation in the direction indicated by the arrow in the drawing, and has a magnet 3 serving as a magnetic field generating means fixed therein.
Pole N ₁ N ₃ magnet 3 conveys the developing magnetic pole S ₁ below the developer 4, the magnetic pole S ₂ for regulating has a pole N ₂ for pumping, the N ₂ N ₃ with the used developer recovered agent Provides a rebound action that is peeled off once from the sleeve. The blade 9
Is made of a magnetic material such as SUS, aluminum or the like, and is provided with a predetermined gap between the developing sleeve 21 and the surface of the developing sleeve 21 as described above. The amount of the developer 4 to be applied, specifically, the thickness of the developer on the developing sleeve 21 is regulated. Therefore, in this embodiment, both the non-magnetic toner and the magnetic particles pass between the tip of the blade 9 and the surface of the developing sleeve 21 and are sent to the developing unit.

By the way, FIG.
Are separated into a developing chamber B and a stirring chamber A by a partition wall 14 and an opening 8 formed between the partition walls 14 in a direction perpendicular to the paper surface of FIG. An opening is formed, and an amount of toner corresponding to the amount of toner consumed through the supply port is dropped and supplied into the stirring chamber A. The developer 4 is contained in the developing chamber B and the stirring chamber A. The developer 4 used was a non-magnetic toner and had an average volume particle size of 8 μm.

Next, a method for measuring the particle size distribution in the present invention will be described.

As a measuring device, Coulter Counter T
A-II type (manufactured by Coulter), number average distribution,
Interface to output volume average distribution (made by Nikkaki)
And a CX-1 personal computer (manufactured by Canon Inc.), and the electrolyte is 1% Na using primary grade sodium chloride.
Prepare a cl aqueous solution.

The measuring method is as follows.
In 150 ml, 0.1 to 5 ml of a surfactant, preferably an alkylbenzene sulfonate, is added as a dispersant, and 0.5 to 50 mg of a measurement sample is further added.

The electrolyte in which the sample is suspended is subjected to dispersion treatment for about 1 to 3 minutes by an ultrasonic disperser, and the particle size distribution of particles of 2 to 40 μm is measured by the Coulter Counter TA-II using a 100 μm aperture as an aperture. Is measured to determine a volume average distribution. The volume average particle size is obtained from the obtained volume average distribution.

At the front and rear ends of the developing container 2 in FIG. 1, the partition walls 14 are not formed. As can be seen from FIG. 5, the developing chamber B and the stirring chamber A are located at both ends. Are formed so as to communicate with each other.
The circulation of the developer will be described with reference to FIG. 5, which is a schematic sectional view taken in the direction of the arrow in FIG. 1. The toner supplied from the toner supply port 13 is dropped into the stirring chamber A, The developer is agitated by one transport unit 23 (hereinafter referred to as a screw 23) and transported from right to left in the direction of the arrow,
The developer is transferred to the developing chamber B through the opening 25. In the developing chamber B, the developer, which is located at substantially the same horizontal position as the screw 23 and is delivered from the opening 25, is fed from the left to the right (in the direction of the arrow) while being supplied to the sleeve 21. The developer supplied to the sleeve 21 moves in the direction of the arrow along with the rotation of the sleeve 21, and a thin layer is formed at a predetermined height by the cut blade 9. Receiving the toner, the toner is collected as it is in the developing device 2 as the sleeve 21 rotates,
It is conveyed by the screw 24 and contributes to development.

Here, the relationship between the transport screw and the repulsion poles N ₂ N ₃ which is a feature of the present invention will be described.

As a method of solving the conventional problems of inefficient circulation of the agent and a narrow latitude for obtaining a stable circulation, first, if the shaft of the transport screw is magnetic, the circulation is stabilized. We have found. In addition, it was found that various experiments showed that the positional relationship between the magnetic axis and the repulsion poles N ₂ N ₃ is very important, not just magnetic.

One is that the point at which the force acting on the developer on the sleeve surface becomes almost zero is almost the same as the point closest to the surface A extending vertically from the center of the developing area on the magnetic axis of the stirring screw, or That is, it is located at a position close to the surface A. The condition that the force acting on the developer becomes almost zero is that the vertical magnetic flux density on the sleeve surface and the horizontal speed density on the horizontal direction become 50 G or less. Repulsive pole N ₂ N
_{In the} case of configuration ₃ , if the magnetic flux density in the vertical direction is near zero, the horizontal direction is also near zero, so the force acting on the developer is almost zero. FIG. 2 is a diagram in which data of the magnetic flux density in the vertical direction on the sleeve surface is superimposed on the magnet portion of the developing device.

According to the above description, since the force for restraining the developer on the sleeve becomes almost zero at the point 11, the developer drops. The hatched portion 31 is a magnetic portion of the screw shaft, and iron is used in the present invention. The surface layer 31 is provided with a screw blade and a mold 32 formed as one body. As can be seen from the figure, the position of 11 is closer to the surface A extending vertically from the center of the development area than any point on 31, so that the rotation of the screw shaft also helps the action of the magnetic field generated by the screw shaft, The mixture is stirred and taken into the agent being conveyed on the screw without returning to. At this time, the rotation direction of the screw is the C direction which is the same direction as the rotation direction D of the sleeve, and as a result, the opposite portions of the sleeve and the screw move in opposite directions. The next important point is the pumping point. Pumping position is dependent on the position 12 of the repelling poles N ₂ on the sleeve surface, the position is magnetic member
It is important that the point A is farther away from the plane A extending in the vertical direction from the center of the development area than any point of the first point. By arranging the magnetic pole N _{2 at} such a position, even if the developer surface of the developer slightly rises, the developer is sufficiently mixed with the agent being conveyed through the screw 24 with the rotation of the screw shaft. ,
Because pumped by N ₂ after passing through the lower portion of the screw 24 even when the image reproduction was carried out over a long period of time, a stable image can be obtained charge-up and deterioration does not occur. The condition described above means that the distance between the plane A and the point 11 extending in the vertical direction from the center of the development area is L as described above.
_When the distance between points ₁ and 12 is L ₃ and the distance to the axis of the screw 24 is L ₂ , L ₁ <L ₂ <L ₃ ,
In addition, the lengths of L ₂ -L ₁ and L ₃ -L ₂ are substantially equal, and the distance between the magnetic member and the surface A is substantially between L ₁ and L ₃ . When such a condition is satisfied, the developer after the development is surely separated from the sleeve and supplied to the sleeve after being sufficiently mixed with the agent being fed through the screw, so that a stable image is provided for a long time. Obtained.

Hereinafter, various conditions in this embodiment will be described.

Photoconductor 1: OPC drum 60φ Sleeve 21: 24.5φ Drum and forward movement 280 mm / sec S ₁ Br 100 Gauss half width 31 ° S ₂ Br 500 Gauss half width 46 ° N ₁ Br 580 Gauss half width 47 ° N ₂ Br500 Gauss half width 33 ° N ₃ Br500 Gauss half width 38 ° Cut blade 9: SUS sleeve-plate distance 800 μm Screw 23: Outer diameter 20φ 360rpm 24mm pitch 24: Outer diameter 20φ 360rpm 24mm pitch Sleeve-drum 500μm

FIG. 6 shows another embodiment.

In the embodiment shown in FIG. 6, a developing device having the same configuration as that of the first embodiment except that the stirring assist member 16 is provided on the shafts of the screws 23 and 24 will be described.

By providing a stirring assisting member, the structure shown in FIG.
It is possible to effectively take in the developer dropped at the point 1 and to pump up the developer to the point 12 in FIG. 2, so that the circulation of the developer, which is the object of the present invention, can be performed more smoothly.

[0031]

As described above, the shaft of the stirring screw is made of a ferromagnetic material, the developer is completely removed from the sleeve before the rotation center of the stirring screw, and the developer is pumped up at the end of the rotation center of the stirring screw. By adopting the configuration of the magnetic poles and screws arranged as described above, sufficient circulation of the agent can be obtained even in a small developing device, and the toner has a small particle size of 8 μm with a sharp melt toner such as a polyester toner. Even in this case, a uniform image without unevenness can be stably obtained over a long period of time.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating the principle of the embodiment of the present invention.

FIG. 3 is a cross-sectional view of a conventional developing device.

FIG. 4 is a sectional view of a conventional developing device.

FIG. 5 is a cross-sectional view of the developing device of FIG. 1 as seen from a direction perpendicular to the paper surface.

FIG. 6 is a diagram showing a screw used in another embodiment.

[Description of Signs] 1 Latent image carrier 3 Magnet 21 Developing sleeve 23, 24 Screw

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Fumitake Hirobe 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Masami Izumizaki 3-30-2 Shimomaruko, Ota-ku, Tokyo (72) Inventor Takao Ogata 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor ▲ Toshinobu Yoshi ▼ 3-2-2 Shimomaruko, Ota-ku, Tokyo Canon Inside (72) Inventor Kunihiko Kitayama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (2)

[Claims] 1. A developer carrier for carrying a developer having a toner and a carrier, a first magnetic pole provided in the developer carrier and forming a repulsive magnetic field, and a downstream of the developer carrier in a movement direction of the developer carrier from the first magnetic pole. A second magnetic pole, and a transport screw that transports the developer dropped from between the first and second magnetic poles. The transport screw has a central axis made of a ferromagnetic material,
This central axis is horizontal, and the center position of the region where the strength of the magnetic field in the direction normal to the surface of the developer carrier between the first and second magnetic poles and the strength of the magnetic field in the tangential direction are both 50 gauss or less. A developing device characterized in that the magnetic field in the direction of the normal to the surface of the developer carrier near the second magnetic pole is all present between the positions where the magnetic field has a maximum value. 2. The developing device according to claim 1, wherein the center of said central axis is located substantially at the center of said center position and the maximum value position in the horizontal direction.