JPH10312105A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device capable of always preventing toner scattering by setting the upper limit concentration of toner with which a developer carrier is replenished in accordance with carrier particle size and toner particle size. SOLUTION: The developer carrier 4 having plural magnetic poles on its surface, turning while carrying developer by magnetic force and developing an electrostatic latent image on the surface of an image carrier 1 is used in this developing device, which is provided with a developer regulating member 6 regulating the quantity of the developer 3 fed while being carried on the carrier 4 and a developer stirring chamber 5 having an aperture on the upstream side of the member 6; is provided with a toner concentration sensor 8 and an agitator 7 for stirring the magnetic carrier and the toner in the stirring chamber 5; and provided with a toner storing part 10 having a toner replenishing aperture 11a communicating with the stirring chamber 5 and an agitator 12 for replenishing the toner in the storing part 10. Then, the toner concentration in the stirring chamber 5 is set so that carrier coating rate Tn may be <=130% so as to control the toner concentration in the stirring chamber 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in an electrophotographic image forming apparatus such as a copying machine, a facsimile, a printer, etc., and carries a two-component developer containing a toner and a magnetic carrier on a developer carrier. And more particularly to a developing device that transports a developer to an area of an image forming apparatus that faces an image carrier (photoconductor or the like) and develops an electrostatic latent image formed on the image carrier. And a developing device using a developer carrier (sleeveless magnet roll developing roller) that rotates and directly carries a two-component developer on the surface thereof with a magnetic force to develop an electrostatic latent image on the surface of the image carrier. It is about.

[0002]

2. Description of the Related Art Conventionally, when an electrostatic latent image formed on an image carrier such as a photoreceptor is developed using a dry developer, a magnetic brush method is employed. In the magnetic brush method, a developing roller provided with a magnet roll inside a non-magnetic sleeve is used, and the developer held on the sleeve is transported by relative rotation of the sleeve and the magnet roll.

In recent years, there has been a demand for miniaturization and cost reduction of electrophotographic copying machines, facsimile machines, printers, etc., and a cylinder having a plurality of magnetic poles on its surface as disclosed in Japanese Patent Application Laid-Open No. 62-201463. The magnetic roll is arranged rotatably, the magnetic developer is supplied to the surface of the magnet roll, and the magnetic developer is conveyed to the image carrier surface by the rotation of the magnet roll,
A sleeveless two-component developing method for developing has been proposed.
Since this method does not require a sleeve as compared with the conventional magnetic brush method, a small-sized and low-cost developing device can be provided.

In the conventional magnetic brush method, a magnet is fixed inside, and the magnet and the sleeve move relative to each other. Therefore, the magnetic brush always moves on the sleeve, and the magnetic brush moves on the sleeve for reasons such as toner scattering. Cannot be increased, and is about 3 to 6% by weight. On the other hand, in the sleeveless two-component development method, since the magnet roll itself rotates, the
This is possible up to about 0% by weight, and the problem that the image density decreases due to the toner density decrease can be avoided. However, on the other hand, since the developing device is not provided with a mechanism for controlling the toner concentration, the toner is excessively adsorbed and the toner concentration is increased, and consequently the background may be easily stained. Further, in terms of image quality, a two-component developer, which is said to have a relatively wide allowable range of toner density, has a more appropriate density range among such allowable ranges when pursuing higher image quality. There is a strong demand for a device capable of adjusting the toner concentration to an appropriate range. Therefore, for example, as in a developing device described in JP-A-8-22177, a developer supply chamber for containing a two-component developer and a toner replenishment chamber for containing toner are connected through a toner supply hole. There has been proposed an image forming apparatus which is capable of always forming an image in an optimum density range by supplying a predetermined amount of toner.

However, this always appropriate concentration range,
In particular, the upper limit toner concentration differs depending on the magnetic carrier particle size and the toner particle size, and it is difficult to set it. Also, originally,
The toner is held on the surface of the magnetic carrier by the electrostatic force generated by the friction between the magnetic carrier and the minute toner. However, in such a configuration, the toner and the magnetic carrier are not sufficiently mixed and the toner is not charged. It has been found that stable toner is supplied to the developer carrier, and that the unstable toner causes background contamination.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its first problem (object) is to
An object of the present invention is to provide a developing device in which the upper limit of the toner concentration supplied to the developer carrying member is set in accordance with the carrier particle size and the toner particle size, and the toner does not always scatter. A second object (object) is to provide a developing device capable of controlling density without using a toner sensor.

[0007]

As a means for solving the above-mentioned problems, according to the present invention, a plurality of magnetic poles are provided on a surface, and a two-component developer is directly supported on the surface by magnetic force. In a developing device using a developer carrier (sleeveless magnet roll developing roller) that moves to develop an electrostatic latent image on the surface of an image carrier (photoreceptor, etc.), the developer is carried by the developer carrier and conveyed A developer regulating member that regulates the amount of the developer, a developer stirring chamber having an opening upstream of the developer regulating member, and a toner concentration sensor in the agent stirring chamber;
A toner container having an agitator for agitating the magnetic carrier and the toner, having a toner replenishing opening communicating with the agent agitating chamber, and an agitator for replenishing toner in the toner container; The toner concentration in the chamber was set so that the carrier coverage Tn represented by the following equation was 130% or less, and the toner concentration in the agent stirring chamber was controlled. Tn = 100C√3 / {2π (100−C) · (1 + r / R) ² ·
(r / R) · (ρ _t / ρ _c )} where C is the toner concentration, r is the radius of the toner, R is the radius of the magnetic carrier, ρ _t is the true specific gravity of the toner, and ρ _c is the true of the magnetic carrier. Specific gravity.

According to the second aspect of the present invention, a plurality of magnetic poles are provided on the surface, and the two-component developer is directly supported on the surface by a magnetic force and rotated to rotate the electrostatic latent on the surface of the image carrier (photoreceptor, etc.). In a developing device using a developer carrying member (sleeveless magnet roll developing roller) for developing an image, a developer regulating member for regulating the amount of developer carried and conveyed by the developer carrying member, and a developer regulating member upstream thereof A developer agitating chamber in which the developer removed from the developer carrier and the replenished toner are mixed by the developer regulating member; and above the agent agitating chamber, the developer agitating chamber is communicated. A toner replenishing portion having a toner replenishing port, and opening and closing the toner replenishing port by utilizing a change in the volume of the developer in the developer stirring chamber due to a change in toner concentration on the developer carrying member. Controlling the toner concentration on the developer carrier It was to be performed.

According to a third aspect of the present invention, in the developing device according to the second aspect, the toner concentration on the developer carrying member is set such that the carrier coverage Tn represented by the following equation becomes 130% or less. Then, the amount of the magnetic carrier to be set in the developer was set. Tn = 100C√3 / {2π (100−C) · (1 + r / R) ² ·
(r / R) · (ρ _t / ρ _c )} where C is the toner concentration, r is the radius of the toner, R is the radius of the magnetic carrier, ρ _t is the true specific gravity of the toner, and ρ _c is the true of the magnetic carrier. Specific gravity.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(1) First, the structure and operation of the developing device according to claim 1 will be described. FIG. 1 shows an embodiment of a developing device to which the present invention is applied. This developing device 2 has a plurality of magnetic poles on a surface and directly carries a two-component developer 3 on the surface by magnetic force. A sleeveless multi-pole developing roller (sleeveless magnet roll developing roller) 4 is provided as a developer carrier for rotating and developing an electrostatic latent image on the surface of the image carrier (for example, a photoconductor). It has a developer regulating member 6 for regulating the amount of developer carried and conveyed by the magnetic pole developing roller 4, and a developer stirring chamber 5 having an opening upstream of the developer regulating member 6. Has a toner concentration sensor 8, a toner stirring agitator 7 for stirring the magnetic carrier and toner, a toner storage unit 10 having a toner supply opening 11 a communicating with the agent stirring chamber 5, and a toner storage unit 10. To replenish 3a And a toner accommodating portion for agitator 12. In the figure, reference numeral 9 denotes a seal, 11 denotes a partition wall, and the partition wall 11 is provided with a toner supply opening 11a.

In a developing device 2 shown in FIG. 1, a developer 3 in a developer stirring chamber 5 stirred by a developer stirring agitator 7 is regulated on a multi-pole developing roller 4 having a plurality of magnetic poles on its surface. It is supplied from upstream of the member (doctor blade) 6. Then, the supplied developer 3 is regulated to a constant developer layer thickness by the developer regulating member 6, and is conveyed to a developing section which is a portion facing the image carrier 1. The toner concentration in the agent stirring chamber 5 is monitored by a toner concentration sensor 8, and when the toner concentration becomes lower than a set value, the toner storage unit agitator 12 in the toner storage unit 10 is rotated to open the toner supply opening. By supplying the toner 3a to the agent stirring chamber 5 from 11a, the toner concentration in the agent stirring chamber 5 is kept constant.

However, even if the same amount of carrier is set, the toner concentration varies depending on the particle size of the carrier, as shown in FIG. The upper limit toner concentration must be set in consideration of the particle size and the like, and setting is difficult.

FIG. 5 shows the relationship between the carrier amount of the developer set in the developer stirring chamber and the upper limit toner concentration TC. The characteristic line a shows the relationship when the carrier particle size is 50 μm. The characteristic line b shows the relationship when the carrier particle size is 60 μm.

Therefore, as a result of experiments and research conducted by the present inventors, the toner concentration in the agent stirring chamber 5 was set so that the carrier coverage Tn represented by the following equation was 130% or less. It was found that by controlling the toner density, an image free from background stains and white spots on solid portions could be obtained.

Therefore, according to the present invention, the toner concentration in the agent stirring chamber 5 of the developing device 2 is changed to the carrier coverage Tn represented by the following equation.
Is set to be 130% or less, and the toner concentration in the agent stirring chamber 5 is controlled. Tn = 100C√3 / {2π (100−C) · (1 + r / R) ² ·
(r / R) · (ρ _t / ρ _c )} where C is the toner concentration, r is the radius of the toner, R is the radius of the magnetic carrier, ρ _t is the true specific gravity of the toner, and ρ _c is the true of the magnetic carrier. Specific gravity.

The process of deriving the above equation will be described below.
First, the carrier coverage Tn is represented by Tn = (sum of areas occupied by n toners / surface area of carrier) × 100, where the area occupied by one toner is 2
(√3) r ² and the surface area of one carrier is 4π (R + r) ² , so the carrier coverage Tn is expressed by the following equation. Tn = {2 (√3) r ² n / 4π (r + R) ² } × 100 (A) The value of toner density (wt%) is expressed by toner weight / (toner weight + carrier) Weight) × 1
It is represented by 00.

Here, in order to have universality, FIG.
As shown in (a) and (b), the carrier and the toner are each considered to be spherical, and the toner density when the carrier surface is covered with the toner in a close-packed oblique arrangement without gaps is considered.
That is, a state in which the surface of one carrier is completely covered with n toner layers in one layer is defined as a coverage of 100%. The number of toners that covers one carrier surface without any gap at this time is hereinafter referred to as a limit toner number. Conventionally, a planar approximation and a spherical approximation have been proposed for the calculation of the carrier coverage. However, in the present embodiment, a planar approximation and a spherical approximation are used within a practical range of the ratio of the radius of the toner and the carrier. Calculate by approximation.

The calculation based on the planar approximation is shown in FIG.
As shown in FIG. 6, the radii of the toner 3a and the carrier 3b are r and R, respectively, and the radius (r + R) as shown in FIG.
Is obtained by dividing the surface area of the sphere by the area of a parallelogram ABCD which is one substantial occupied area.
Is given by the following equation. N = 4π (r + R) 2/2 (√3) r 2 In this approximation method, the surface of the carrier 3b toner 3
A condition R >> r that can be regarded as a plane when viewed from a is required.

Further, when the toner concentration C (wt%) of the developer is represented by using the number n of the toner on the carrier surface, the carrier 1
The weight of each toner is 4πR ³ ρ _c / 3, and the weight of one toner is 4πr
^{Since 3} ρ _t / 3, the following equation is obtained. C = 100 nr ³ ρ _t / (nr ³ ρ _t + R ³ ρ _c ) (B) where r is the radius of the toner particle size (μm), R is the radius of the carrier particle size (μm), ρ _t Is the true specific gravity of the toner (g / c
m ³ ) and ρ _c are the true specific gravity of the carrier (g / cm ³ ).

When n is eliminated from the equations (A) and (B) and rearranged, the following equation for the carrier coverage Tn is obtained. Tn = 100C√3 / {2π (100−C) · (1 + r / R) ² ·
(r / R) ・ (ρ _t / ρ _c )}

Here, FIG. 7A shows that the carrier coverage is 1
FIG. 7 is a diagram illustrating a sketch of an attached state of toner 3a at a toner concentration of 00%. As shown in FIG. 7A, when the carrier coverage is 100%, the toner 3a adheres to the surface of the carrier particles without any gap. on the other hand,
FIG. 7B is a diagram illustrating a sketch of the adhesion state of the toner 3a at the toner concentration when the carrier coverage is 169%. As shown in FIG.
In the case of 9%, the surface of the carrier particles is covered with the toner 3a several times. Thus, the carrier coverage is 100%
It was confirmed that the toner 3a completely covered the surface of the carrier when the ratio exceeded the limit.

By the way, in the state where the carrier coverage exceeds 100%, the developers that have entered the agent retaining portion repeatedly friction with each other. The toner is charged by friction with the carrier. However, when the carrier coverage exceeds 100%, the surface of the carrier is not exposed, so that the toner already covering the carrier is further covered by the toner.
Therefore, the toner rubs against each other, so that a positively charged toner and a negatively charged toner are generated, and the charged state becomes uneven. Here, for example, if the toner is negatively charged due to the friction between the carrier and the toner, the toner positively charged due to the friction between the toners will not normally adhere to the electrostatic latent image, and This causes inconveniences such as the occurrence of a problem. Therefore, in order to prevent problems such as soiling, the carrier coverage must be 100%.
% Is set as the upper limit density.

As described above, according to the present embodiment, the following equation is obtained: Tn = 100C√3 / {2π (100−C) · (1 + r / R) ² ·
Using (r / R) · (ρ _t / ρ _c )}, a toner concentration at which the carrier coverage does not exceed 100% is determined as an upper limit concentration, and a developer having a carrier amount capable of realizing the upper limit toner concentration is determined. By setting the developer in the agent stirring chamber 5, a good developed image can be obtained without causing a problem such as background contamination. However, in practice, the carrier is not perfectly spherical but has irregularities on the surface, and 130% of Tn represented by the above equation is equal to the above-mentioned coverage of 10%.
It corresponds to 0%. Therefore, by setting the upper limit concentration of the toner set in the agent stirring chamber 5 such that Tn in the above equation does not exceed 130%, it is possible to achieve satisfactory development without causing problems such as background contamination. An image can be obtained.

(2) Next, the structure and operation of the developing device according to claim 2 will be described. FIGS. 2, 3 and 4 show an embodiment of the developing device to which the present invention is applied. FIG. 2 shows the structure of the developing device, and FIG. 3 shows the structure of the developing device. FIG. 4 shows a state in which the toner concentration of the developer after toner replenishment is saturated.

In FIG. 2, the developing device 20 has a plurality of magnetic poles on its surface, and rotates while supporting a two-component developer directly on the surface with a magnetic force.
A sleeveless multi-pole developing roller (sleeveless magnet roll developing roller) 21 is provided as a developer carrier for developing an electrostatic latent image on the surface.
And a developer removed from the multi-pole developing roller 21 by the developer regulating member 23 at an upstream portion of the developer regulating member 23. And an agent stirring chamber 22 in which the supplied toner is mixed. A toner container 24 having a toner supply port 25 communicating with the agent agitating chamber 22 is provided above the agent agitating chamber 22. The toner replenishing port 2 uses the fact that the volume of the developer in the
5, the toner density on the multi-pole developing roller 21 is controlled.

Next, a state where toner is actually supplied and a state where toner is not supplied will be described with reference to FIGS. 3 and 4. FIG. As shown in FIG. 3, by providing the agent stirring chamber 22 that is sealed to some extent, when the toner concentration decreases, the volume of the developer (toner + carrier) 3 in the agent stirring chamber 22 decreases, and the upper surface of the developer 3 Is lowered and the toner supply port 25 is opened.
As a result, the toner 3a is replenished from the toner container 24 into the agent stirring chamber 22. When the toner 3a is replenished and the toner and the carrier are mixed, as shown in FIG.
Closes the toner supply port 25, and toner supply is stopped.

Incidentally, Japanese Unexamined Patent Publication No.
In the developing device described in Japanese Patent No. 22177, toner is not supplied to a portion where the developer is actually agitated, so that the developer does not easily rise and soiling is likely to occur. For this reason, the toner concentration was about to run away.

However, in the present invention, since the toner is replenished to the portion where the developer is agitated (the agent agitating chamber 22), the toner is replenished as in the developing device described in JP-A-8-22177. There is no occurrence of background contamination due to poor startup of the developer. Further, the toner concentration can be easily set based on the amount of the carrier initially supplied and the toner concentration in the agent stirring chamber 22. Furthermore, as compared with the configuration of the first aspect, the density can be controlled without the need for a toner density detection mechanism (such as a toner density sensor), so that the configuration is compact and the developing device can be configured at low cost. There is such a merit.

(3) Next, the structure and operation of the developing device according to claim 3 will be described. In the developing device according to claim 3,
3. The developing device having the structure of FIG. 2 shown in FIGS. 2 to 4, wherein the upper limit of the toner concentration on the multi-pole developing roller 21 as a developer carrier is set to a carrier coverage Tn represented by the following equation.
Was set to be 130% or less, and the amount of the magnetic carrier set in the developer was set. Tn = 100C√3 / {2π (100−C) · (1 + r / R) ² ·
(r / R) · (ρ _t / ρ _c )} where C is the toner concentration, r is the radius of the toner, R is the radius of the magnetic carrier, ρ _t is the true specific gravity of the toner, and ρ _c is the true of the magnetic carrier. Specific gravity.

That is, for the same reason as described in the structure and operation of the first aspect, the following equation is obtained: Tn = 100 C√3 / {2π (100−C) · (1 + r / R) ² ·
(r / R) · (ρ _t / ρ _c )}, the toner concentration on the multi-pole developing roller 21 is determined as the upper limit concentration such that the carrier coverage Tn does not exceed 130%. By setting a developer having a carrier amount capable of realizing the upper limit toner concentration in the agent stirring chamber 22, it is possible to obtain a good developed image without causing problems such as background contamination. As described above, in addition to the configuration of claim 2, by setting the upper limit toner concentration on the multi-pole developing roller 21 according to the carrier particle size and the toner particle size as described above, the configuration is compact, and A stain-free developing device can be provided. still,
The reason why the background is not stained has already been described in the configuration and operation of the first aspect, and thus the description thereof is omitted here.

[0032]

As described above, according to the first aspect of the present invention, the upper limit toner concentration can be set according to the carrier particle size and the toner particle size, and a good developed image without toner scattering can be always obtained. Can be provided.

According to the second aspect of the present invention, since the density can be controlled without the need for the toner density detecting mechanism, the configuration can be made compact and an inexpensive developing device can be provided.

According to the third aspect of the present invention, in addition to the configuration of the second aspect, the upper limit toner concentration on the developer carrying member can be set according to the carrier particle size and the toner particle size. It is possible to provide a developing device that is always free from background contamination.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a configuration of a developing device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a configuration of a developing device according to an embodiment of the present invention.

FIG. 3 is an explanatory view of the operation of the developing device shown in FIG. 2,
FIG. 7 is a diagram illustrating a state in which toner has just been replenished from a toner storage unit due to a decrease in toner density.

4 is an explanatory diagram of an operation of the developing device shown in FIG. 2,
FIG. 6 is a diagram illustrating a state in which the toner concentration of the developer after toner replenishment is saturated.

FIG. 5 is an explanatory diagram illustrating a relationship between a carrier amount of a developer and an upper limit toner concentration TC.

FIGS. 6A and 6B are diagrams showing a planar approximation model of a carrier and a toner used for deriving a formula of a carrier coverage. FIG.

FIG. 7A is an explanatory diagram showing a toner attached state to a carrier when the carrier coverage is 100%, and FIG. 7B is an explanatory diagram showing a toner attached state to the carrier when the carrier coverage is 169%. is there.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier 2 Developing device 3 Developer 3a Toner 3b Carrier 4 Multi-pole developing roller (developer carrier) 5 Agent stirring chamber 6 Developer regulating member 7 Agent agitator 8 Toner density sensor 9 Seal 10 Toner container 11 Partition wall 11a Toner supply opening 12 Agitator for toner container 20 Developing device 21 Multi-pole developing roller (developer carrier) 22 Agent stirring chamber 23 Developer regulating member 24 Toner container 25 Toner supply port

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Genki Hanada 1-3-6 Nakamagome, Ota-ku, Tokyo, Ricoh Co., Ltd.

Claims (3)

[Claims] 1. A developer carrier having a plurality of magnetic poles on its surface and rotating to develop an electrostatic latent image on the surface of the image carrier while carrying a two-component developer directly on the surface by magnetic force. In the developing device, a developer regulating member that regulates an amount of the developer carried and conveyed by the developer carrier is provided, and a developer stirring chamber having an opening upstream of the developer regulating member is provided. The chamber has a toner concentration sensor, an agitator for stirring the magnetic carrier and the toner, a toner storage unit having a toner supply opening communicating with the agent stirring chamber, and a toner supply unit for replenishing toner in the toner storage unit. An agitator having a carrier coverage Tn of 13 expressed by
A developing device, wherein the toner concentration is set to be 0% or less and the toner concentration in the agent stirring chamber is controlled. Tn = 100C√3 / {2π (100−C) · (1 + r / R) ² ·
(r / R) · (ρ _t / ρ _c )} where C is the toner concentration, r is the radius of the toner, R is the radius of the magnetic carrier, ρ _t is the true specific gravity of the toner, and ρ _c is the true of the magnetic carrier. Specific gravity. 2. A developer carrier having a plurality of magnetic poles on its surface and rotating to develop an electrostatic latent image on the surface of the image carrier while carrying a two-component developer directly on the surface with a magnetic force. In the developing device, a developer regulating member that regulates an amount of a developer carried and conveyed by the developer carrier, and a developer that is separated from the developer carrier by the developer regulating member upstream of the developer regulating member And a toner replenishing section having a toner replenishing port having a toner replenishing port communicating with the developer agitating chamber above the developer agitating chamber. The toner concentration change on the developer carrier is performed by opening and closing the toner supply port using the change in the volume of the developer in the agent stirring chamber due to the above change in the toner concentration. Characteristic developing device. 3. The developing device according to claim 2, wherein the toner concentration on the developer carrier is set such that the carrier coverage Tn represented by the following formula is 130% or less, and the developer is set in the developer. A developing device wherein the amount of a magnetic carrier is set. Tn = 100C√3 / {2π (100−C) · (1 + r / R) ² ·
(r / R) · (ρ _t / ρ _c )} where C is the toner concentration, r is the radius of the toner, R is the radius of the magnetic carrier, ρ _t is the true specific gravity of the toner, and ρ _c is the true of the magnetic carrier. Specific gravity.