JPH11212346A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device where the replenishment of a new magnetic carrier is effectively and also efficiently executed and by which high image quality is maintained over a long period despite of the use environment of the consumption state of toner. SOLUTION: Developer carrier 4 consisting of a developing sleeve 4 and a permanent 5 carries developer consisting of the toner and a magnetic carrier on a surface and transports it, and receives the developer after being passed through a developing area D and a developer stirring part 2 having screw augers 7 and 8 stirs it together with the developer remaining at inside. The magnetic carrier is replenished to the developer stirring part 1 by a carrier replenishing device 9 in response to the measured result of a toner concentration sensor 14 that toner concentration is lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used for an image forming apparatus such as an electrophotographic printer or copier.

[0002]

2. Description of the Related Art Conventionally, as a two-component developing device used in an electrophotographic image forming apparatus, a fixed magnet having a plurality of magnetic poles inside, which is disposed so as to be close to or in contact with an image carrier, is used. A two-component developer comprising a toner and a magnetic carrier is supplied to a rotatable developer carrier to form a magnetic brush of the developer on the developer carrier, and the magnetic brush is rotated by rotation of the developer carrier. Is transported to a developing area, and the electrostatic latent image on the image carrier is developed by the action of a bias voltage applied to the image carrier. In such a developing device,
A layer thickness regulating member for adjusting the amount of the developer conveyed to the opposite portion between the image carrier and the developer carrier is disposed with a predetermined gap from the developer carrier.

In the developing device described above, the developer is excessively filled on the upstream side of the layer thickness regulating member, so that a strong compressive force acts on the developer. Further, by the compressive force, the developer that passes through the gap between the layer thickness regulating member and the developer carrier and is transported to the developing section where the image carrier and the developer carrier are opposed to each other, and an upstream portion of the layer thickness regulating member. A strong frictional force acts between the charged developer. Due to the compressive force and frictional force applied to the developer, the external additives and the toner itself, which have been treated to improve the chargeability and fluidity of the toner surface, adhere to the surface of the magnetic carrier, and the deterioration of the magnetic carrier is reduced. Occurs. When a magnetic carrier having a coating layer on the surface is used, abrasion or peeling of the coating layer also causes deterioration of the magnetic carrier. Deterioration of the magnetic carrier causes a decrease in toner charge, thereby deteriorating image quality.

In order to prevent the deterioration of the magnetic carrier, Japanese Patent Publication No. 2-15991 discloses a method of sequentially replenishing a new magnetic carrier into the developing device and discharging the deteriorated magnetic carrier to the outside. A developing device has been proposed which keeps toner charging characteristics of a magnetic carrier in a developing device constant and prevents image quality deterioration. In general, when the amount of consumed toner is large, a large amount of new toner is supplied to make up for the consumed toner. Therefore, the probability that the magnetic carrier encounters a new toner increases, and the adhesion of the external additive and the toner increases, and the deterioration is accelerated. The developing device proposed in Japanese Patent Publication No. 2-15991 has a problem that if the toner consumption is large, the replenishment of a new magnetic carrier cannot catch up with the deterioration of the existing magnetic carrier, and the image quality deteriorates. Conversely, if the toner consumption is small, the magnetic carrier is replaced with a new magnetic carrier before the magnetic carrier is deteriorated. Therefore, there is a problem that the magnetic carrier exchange efficiency is low, running costs are increased, and resources are wasted. Therefore, JP-A-9-204105 discloses that
The deterioration of the magnetic carrier, that is, the decrease of the toner charge amount, has a large relationship not only with the operation time of the developing device but also with the toner consumption amount. From the viewpoint that the larger the toner consumption amount, the faster the deterioration, the higher the toner consumption amount. Alternatively, a developing device has been proposed in which the amount of magnetic carrier supplied is controlled in accordance with the toner consumption and the operating time of the developing device.

[0005]

However, in the conventional developing device as described above, even if the toner consumption and the operating time of the developing device are the same, an image forming apparatus incorporating the developing device is used. If the temperature and humidity environment is different,
There is a problem that the degree of deterioration of the magnetic carrier varies.

FIG. 8 is a view showing the results of an experiment on the toner charge retention in a temperature and humidity environment of an image forming apparatus incorporating a conventional developing device. FIG. 8 shows the relationship between the number of printed sheets and the toner charge amount when the toner is consumed at 50 mg / sheet. As is clear from FIG. 8, under a high temperature and high humidity environment (28 ° C./85% RH), a low temperature and low humidity environment (1
0 ° C./15% RH), it can be seen that the charge amount of the toner decreases, that is, the magnetic carrier deteriorates faster. Since the toner charge is affected by the temperature and humidity environment and the degree of deterioration of the toner itself, in this experiment, toner charge is measured by measuring the amount of developer in a high-temperature, high-humidity environment and a low-temperature, low-humidity environment. Take it out under normal temperature and normal humidity environment (2
At 2 ° C./55% RH), only the magnetic carrier was left by a blow-off method, 8 wt% of new toner was added thereto, and the mixture was stirred and measured.

[0007] The degree of deterioration of the magnetic carrier also varies depending on the state in which the toner is consumed. For example, in a certain developing device, the total consumption of the toner is determined in a case where the toner is consumed on average during the operation time of the developing device, and a case where the state where the toner is consumed in a large amount and the state where the toner is consumed in a small amount are mixed. Even if the amounts are the same, the degree of deterioration of the magnetic carrier, that is, the toner charge amount differs. Therefore, in the technology of controlling the replenishment amount of the magnetic carrier based on the total amount of the consumed toner, the replenishment of the new magnetic carrier cannot catch up with the deterioration of the internal magnetic carrier depending on the use environment and the consumption state of the toner, thereby deteriorating the image quality. It is not enough to solve the problem that the magnetic carrier is replaced with a new magnetic carrier before the magnetic carrier deteriorates, which leads to poor magnetic carrier exchange efficiency, increasing running cost and wasting resources. .

The present invention has been made in view of the above-mentioned problems, and it is effective and effective to replenish a new magnetic carrier regardless of the use environment or the toner consumption state. It is an object of the present invention to provide a developing device capable of maintaining high image quality for a long time.

[0009]

According to the present invention, there is provided a developing apparatus for carrying out the above-mentioned object, such that the developing device approaches or comes into contact with an image carrier which moves in a predetermined direction while holding an electrostatic latent image in a predetermined development area. A developer carrier that carries a developer composed of a toner and a magnetic carrier on the surface and transports the developer along a transport path that passes through the development area; and develops the developer that has passed through the development area with the developer. A current agent stirring section that receives from the agent carrier and stirs together with the developer remaining inside, a toner concentration measuring unit that measures the concentration of toner in the internal developer, and a toner concentration measured by the toner concentration measuring unit. A carrier replenishing means for replenishing the magnetic agent stirring section with a magnetic carrier in response to a measurement result indicating that the developer has decreased, and a discharge port for discharging the developer inside are provided.

[0010]

Embodiments of the present invention will be described below. FIG. 1 is a schematic configuration diagram of a first embodiment of a developing device of the present invention. The developing device 100 shown in FIG. 1 includes a developer carrier 3, a developer stirring section 1, a toner density sensor 14 disposed on a bottom wall of the developing device 100, and a developing device 1.
00, a magnetic carrier replenishing device 9, a discharge port 10 provided on a side wall of the developing device 100, a layer thickness regulating member 6 made of a magnetic material and adjusting a developer to a predetermined thickness. It has.

The developer carrier 3, which will be described in detail later, is arranged so as to be close to the latent image carrier 2 which carries the electrostatic latent image and moves in the arrow direction A in a predetermined developing area D, And a developer composed of a magnetic carrier and carried on the surface, and transported along a transport path via the development area D. The developer agitating section 1 has a pair of rotating shafts arranged in a horizontal direction and arranged with a partition wall 15 interposed therebetween. The pair of agitating the developer by transporting the developer in the rotating shaft direction and in the opposite direction to each other. Screw augers 7 and 8 are provided.

The toner density sensor 14 includes a developing device 100
Is arranged on the screw auger 7 side of the bottom wall of the developing device 100, and measures the concentration of toner in the developer inside the developing device 100. The magnetic carrier replenishing device 9 replenishes the magnetic agent stirring section 1 with a magnetic carrier in response to the measurement result of the toner concentration sensor 14 indicating that the toner concentration has decreased. The configuration of the magnetic carrier supply device 9 will be described later.

The discharge port 10 discharges the developer inside.
The developer carrier 3 is a rotatably supported developing sleeve 4 made of a conductive non-magnetic material, for example, aluminum.
And a permanent magnet 5 housed inside the developing sleeve 4.
It consists of. The surface of the developing sleeve 4 is formed with minute irregularities of about several microns in ten-point average roughness RZ by blasting. The permanent magnet 5 includes the latent image carrier 2
And a developing magnetic pole S for forming a spike of the developer.
1 and the same polarity magnetic pole for removing the developer from the surface of the developing sleeve 4 after passing the developing region D where the latent image carrier 2 and the developer carrier 3 are opposed to each other, and eliminating the image history. The separated magnetic poles N3 and N4 and the developer mixed and stirred by the rotations C and C 'of the screw augers 7 and 8 in different directions in the developer stirring section 1 are magnetically applied to the surface of the developing sleeve 4. Magnetic pole S3 for attracting the developer, a layer-forming magnetic pole S2 for forming a spike of the developer in the vicinity of the layer thickness regulating member 6 for adjusting the developer to a predetermined thickness, and developing the surface of the developing sleeve 4. And transport magnetic poles N1 and N2 for transporting the agent. On the surface of the developing sleeve 4, the magnetic pole S1 is 950 gauss, the magnetic pole N1 is 700 gauss, the magnetic pole S2 is 800 gauss, and the magnetic pole N is
2 is 600 gauss, magnetic pole N3 is 600 gauss, magnetic pole S3
Is set to 650 gauss and the magnetic pole N4 is set to a magnetic flux density of 500 gauss.

The developing sleeve 4 includes a layer thickness regulating member 6.
Are arranged with a gap of 0.7 mm between them and at a surface speed of 300 mm / sec in a counterclockwise direction (arrow B direction).
Is rotating. Further, a developing bias is applied to the developing sleeve 4 from a power supply (not shown) as Vp-p = 1.5K.
V, AC component of frequency f = 6 KHz, and Vdc = −50
A voltage on which a DC component of 0 V is superimposed is applied.

The latent image carrier 2 is disposed opposite to the developing sleeve 4 in the developing area D with a gap of 0.5 mm, and has a surface speed of 150 mm / sec in a clockwise direction (direction of arrow A). ) Is rotating. The latent image carrier 2 is exposed on the exposed portion potential -20 by a normal electrophotographic process.
A latent image of 0 V and a non-exposed portion potential of -650 V is formed. A-Color 63 manufactured by Fuji Xerox Co., Ltd. is used as a developer.
5 toner and a magnetic carrier are used. The toner is a non-magnetic toner having an average particle diameter of 7 μm and using polyester as a binder, and SiO ₂ and TiO ₂ are added as external additives. The magnetic carrier is a ferrite carrier having an average particle size of 50 μm.

The magnetic carrier replenishing device 9 transports the magnetic carrier accommodated in the magnetic carrier accommodating unit 11 to the developer agitating unit 1 by transferring the magnetic carrier accommodated in the magnetic carrier accommodating unit 11 to the developer agitating unit 1. And a magnetic carrier transport section 12 for supplying a new magnetic carrier. The magnetic carrier transport section 12 has a cylindrical shape in which a screw auger 13 is disposed.
The screw auger 13 is driven to rotate in accordance with the output of a toner density sensor 14 disposed below the screw auger 7 and on the bottom wall of the developing device 100.

Next, the operation of the developing device 100 having the above configuration will be described. The developer mixed and stirred by the rotation of the screw augers 7 and 8 is attracted to the surface of the developing sleeve 4 by the action of the attracting magnetic pole S3, and is conveyed to the layer forming area E with the rotation of the developing sleeve 4 in the arrow direction B. Is done.
In the layer forming area E, the developer adjusted to a predetermined amount by the layer forming member 6 is transported to the developing area D where the latent image carrier 2 and the developer carrier 3 are opposed to each other, and is developed by the action of the developing bias. The toner in the developer adheres to the image portion of the electrostatic latent image on the latent image carrier 2 and development is performed. After the development is completed, the developer layer of the developing sleeve 4 is conveyed from the developing region D toward the developer stirring unit 1 and is separated from the developing sleeve 4 by the action of the separation magnetic poles N3 and N4. Returned to augers 7 and 8. By repeating such an operation, the developer gradually deteriorates, and the charge amount of the toner decreases.

As the developer deteriorates, the screw auger 13 rotates in accordance with the output value of the toner density sensor 14, and a fixed amount of new magnetic carrier is supplied to the developer stirring section 1. An amount of the deteriorated developer corresponding to the amount of the replenished new magnetic carrier passes over the partition wall 15 and reaches the discharge port 1.
Emitted from 0. The newly supplied magnetic carrier is
By the rotation of the screw augers 7, 8, the developer is mixed with the developer remaining therein and is made uniform, thereby recovering the toner charge amount. By repeating this operation, the toner charge amount is maintained at a certain value, and high image quality is maintained for a long time.

Here, the image density is determined by a so-called development contrast determined by a difference between an image portion potential of the latent image carrier 2 and a developing bias, and a toner charge amount. The development contrast forms an electric field that acts in a direction in which the toner adheres to the image portion of the electrostatic latent image on the latent image carrier 2. As the development is performed, the electric field of the toner gradually weakens due to the electric charge of the toner, and the development ends when the electric field in the developing direction due to the development contrast and the electric field in the opposite direction due to the developed toner are balanced. That is, if the development contrast is constant, the development is terminated when the total charge amount of the developed toner reaches a certain value.

Generally, in an image forming apparatus, even if the magnetic carrier is deteriorated and the toner charge is reduced, the toner density is controlled in order to keep the image density, that is, the toner charge, constant. When the toner charge amount is kept constant, it is known that there is a relationship represented by the following equation between the toner charge ability of the magnetic carrier and the toner density (Ro)
bert J. et al. Nash Adv Print Pap
Summ 4th Int Cong Adv No
n-Impact Print Tecnol 1988
page 84-88).

[0021] _{A t = (TC t + C} o) * TV where, A _t: Numerical some showing a toner charging performance at time TC _t: toner concentration at a certain time C _o: constants determined by the carrier and toner TV: This is the toner charge. Numerical A _t is becomes smaller with the deterioration of the magnetic carrier, but in the image forming apparatus to which the toner charge amount TV is controlled to be constant, the values directly A _t that indicates the degree of deterioration of the magnetic carrier by measuring the toner concentration TC _t You can know. In the developing device 100 of the present embodiment, it is possible to know the in numerical A _t by measuring the toner concentration TC _t by the toner density sensor 14 directly, it becomes possible to know directly the degree of deterioration of the magnetic carrier, conventional of,
The magnetic carrier can be replenished more effectively and efficiently as compared with the technique of indirectly estimating the deterioration of the magnetic carrier by measuring the toner consumption. Therefore, in the image forming apparatus in which the developing device 100 of the present embodiment is incorporated, a stable image density can be obtained.

Next, an experiment conducted to confirm the performance of the developing device 100 shown in FIG. 1 will be described. <Experiment 1> The initial toner concentration was 8 wt%, and when the toner concentration was reduced to 5 wt%, a new magnetic carrier was set to be supplied. The printing density is 10%, and the printing density is high (28 ° C./85% RH) and low temperature and low humidity (10 ° C./85%).
The experiment was performed at 15% RH). As a comparative example, a similar experiment was performed with a developing device of the related art that replenishes a magnetic carrier by toner consumption. The toner consumption was detected based on the rotation time of the screw auger for toner supply.

FIG. 2 is a graph showing the measurement results of the image density and the total amount of discharged developer when printing is performed under high temperature and high humidity in both the developing device shown in FIG. 1 and the developing device of the comparative example. . As is clear from FIG. 2, in the case of the comparative example in which the supply of the magnetic carrier is controlled by the toner consumption,
Under high temperature and high humidity, the deterioration of the magnetic carrier is accelerated, so that the supply cannot keep up with the deterioration of the magnetic carrier, and the image density is reduced. In contrast, in the present embodiment, replenishment of the magnetic carrier is controlled by directly knowing the degree of deterioration of the magnetic carrier based on the toner concentration measured by the toner concentration sensor 14, so that deterioration under high temperature and high humidity is accelerated. In some situations, the supply amount, that is, the discharge amount increases, and a stable image density is obtained.

FIG. 3 is a graph showing the measurement results of the image density and the total amount of discharged developer when printing is performed under low temperature and low humidity in both the developing device shown in FIG. 1 and the developing device of the comparative example. Under low temperature and low humidity, the deterioration of the magnetic carrier is suppressed, so the replenishment amount is small.However, in the comparative example, the same amount of magnetic carrier is replenished as under high temperature and high humidity, and the replenishment is performed effectively. Absent. On the other hand, in the present embodiment, in a situation where deterioration under low temperature and low humidity is suppressed,
It can be seen that the replenishment carrier amount has decreased, and that effective magnetic carrier replenishment has been performed.

Next, a second embodiment of the present invention will be described. FIG. 4 is a schematic configuration diagram of a second embodiment of the developing device of the present invention. The same components as those of the developing device 100 shown in FIG. 1 are denoted by the same reference numerals, and the description thereof will not be repeated. The developing device 200 includes a permanent magnet 2 disposed therein.
5 and a developer carrier 23 comprising a developing sleeve 24 rotatably supported. Further, the developing device 200 is provided with a developer stirring section 30 disposed above the developer carrying member 23. Further, the developing device 200 receives the developer separated from the developer carrier 23 and passed through the developing region D by magnetically attracting the developer and transporting the developer to the developer stirring unit 30 as a pumping mechanism. Rolls 36 and 37 are provided. Further, the developing device 200 is provided with a developer discharging device 40 in a region surrounded by the developer stirring section 30, the transport rolls 36 and 37, and the guide member 38.

The developer stirring section 30 is provided with a pair of screw augers 27 and 28. The rotation direction of the screw auger 27 is clockwise C, and the rotation direction of the screw auger 28 is counterclockwise C ′. The direction of the fin is such that the developer receives a force inward. The amount of the developer pumped up to the developer stirring section 30 by the transport rolls 36 and 37 increases, and the side wall 30 of the developer stirring section 30 increases.
When the height is equal to or larger than a, the developer falls over the side wall 30a. In a normal use state, the developer stirring section 3
At 0, a certain amount of the developer is stored, and approximately the same amount of the developer as the drawn-up developer falls, and a steady state is formed. The dropped developer is guided upstream of the layer thickness regulating member 26 along the guide member 38, and a stagnant portion made of the developer is formed in the layer forming region E. This developer is regulated to a predetermined layer thickness by the layer thickness regulating member 26 and the developing region D
Are transported to the developer agitating section 30 via the transport rolls 37 and attracted to the transport rolls 36 by magnetic force. After the developer conveyed to the developing area D is subjected to the development, the developer is separated from the developer carrier 23, further adsorbed by the conveyance roll 36, and returned to the developer stirring section 30 via the conveyance roll 37. A toner concentration sensor 34 is disposed at an opening provided at the bottom of the developer stirring section 30. The screw auger 13 of the magnetic carrier replenishing device 19 is driven to rotate in accordance with the output value of the toner density sensor 34, and new magnetic carriers are sequentially replenished to the developer stirring section 30.

In the developer discharging device 40, a screw auger 43 is disposed in a cylindrical sleeve 42 having an opening 41 extending in the axial direction of the developer discharging device 40.
When the developer is not discharged, the opening 41 faces downward. When the developer is discharged, the cylindrical sleeve 42 rotates, and the opening 41 faces upward. Layer thickness regulating member 2 along guide member 38
When the opening 41 faces downward, the developer guided upstream of 6 cannot enter the cylindrical sleeve 42. When the opening 41 faces upward, a part of the developer remaining in the layer forming area E or a part of the developer falling along the guide member 26 enters the cylindrical sleeve 42,
The developer is conveyed by the rotation of the screw auger 43 and discharged out of the developing device 200. This is performed sequentially so that the toner charge is kept constant.

In recent years, in a full-color digital image forming apparatus, a so-called tandem type image forming apparatus in which a plurality of latent image carriers and developing apparatuses are arranged in parallel to sequentially form an image in order to respond to a demand for higher speed. Although the apparatus is employed, since the plurality of latent image carriers and the developing device are arranged in parallel, there is a problem that the apparatus is increased in size. In order to cope with this problem, there has been proposed an apparatus in which the developer peeled off from the developer carrier is once pumped upward to make the developing apparatus a vertical structure to reduce the size of the apparatus. Developing device 20 of the present embodiment
In the case of No. 0, since such a vertical structure is adopted, the magnetic carrier can be effectively and efficiently replenished, and the size of the image forming apparatus can be reduced. <Experiment 2> Experiment 1 to confirm the performance of the developing device 200
When an environmental experiment similar to that described above was performed, FIGS.
The result is almost the same as the result shown in FIG. 7, and it is shown that high image quality can be maintained for a long time even in the developing device 200 employing the vertical structure for downsizing the image forming apparatus.

FIG. 5 is a schematic structural view of a developing device according to a third embodiment of the present invention. The same components as those of the developing device 100 shown in FIG. 1 are denoted by the same reference numerals, and the description thereof will not be repeated. The developing device 300 shown in FIG. 5 is different from the developing device 100 shown in FIG. 1 in that the partition wall 15 provided between the screw augers 7 and 8 is omitted, and the toner density sensor 14 is different from the developing device 100 in FIG. Is different from the screw auger 7 in that the screw auger 7 is disposed at an intermediate portion between the screw augers 7 and 8. When the fins of the screw augers 7 and 8 are directed in a direction in which the developer receives an outward force, there is a possibility that the banded developer is generated at the bottom of the developer agitating section 1 between the screw augers 7 and 8. Therefore, arranging a toner density sensor below the screw auger 7 (auger on the developer discharge port side) enables more accurate detection of toner density.

In the developing device 300 of this embodiment, the partition 1
5 is deleted, the replenished new magnetic carrier and the deteriorated magnetic carrier remaining in the developing device 300 are quickly mixed by the screw augers 7 and 8 to be uniform, and a constant toner charge amount is obtained. Obtained quickly. <Experiment 3> Next, the developing device 300 shown in FIG.
When an experiment similar to Experiment 1 was performed, similar results were obtained. Further, in order to examine the image density stability immediately after replenishment of the magnetic carrier, a printing experiment was performed in both the developing device 100 and the developing device 300, and a change in image density was measured.
An experiment was conducted by operating the developing device 100 and the developing device 300 from a state in which 600 g of the developer having a toner concentration of 8 wt% and 50 g of the magnetic carrier were charged. The result is shown in FIG.

FIG. 6 is a diagram showing the results of experiments on the image density stability immediately after the replenishment of the magnetic carrier in both the developing device shown in FIG. 1 and the developing device shown in FIG. In the developing device 300, compared to the developing device 100, the developer is mixed and mixed more quickly over the entire area of the screw augers 7 and 8 in the axial direction.
As a result of the stirring, the replenished magnetic carrier and the magnetic carrier remaining in the apparatus are quickly homogenized, and
Stable image density is obtained from the printing of the first sheet. Accordingly, in the developing device 300, the magnetic carrier is effectively replenished, and a stable image density can be obtained immediately after the replenishment. <Experiment 4> Next, the developing device 100 of the present embodiment that controls the supply of the magnetic carrier by the toner concentration and the conventional developing device that controls by the toner consumption as a comparative example use the magnetic carrier described below. An experiment similar to the experiment 1 was performed using the developer.

The carrier used is a low-resistance magnetic core made of magnetite (MXO30A, manufactured by Fuji Electric Chemical Co., Ltd.) having an average particle size of 50 μm, and a styrene-methacrylate copolymer (copolymerization ratio of 20:80) as a coating resin on the surface. )
And 10% by volume of carbon black (VXC72, manufactured by Cabot Corporation) dispersed as a conductive powder,
It was coated to a thickness of μm.

The carrier and magnetite unit having this structure
Body resistance was measured as follows. Of this embodiment
Developing device 100 is placed between aluminum plate and 0.5 mm gap
And the developing device 100 and the aluminum plate
From the current value when a DC voltage is applied between, the electric field E and the current
A commonly known relationship between density J, LogJ =
E ^1/2 Was determined based on 10^Four V / cm electric field resistance
Anti is 10 as a carrier ⁸ ・ Ωcm, magnetite only
10 in the body^-FiveΩ · cm. Also, on the conductive substrate
Coating a resin layer with conductive powder dispersed to a thickness of 0.8 μm
Then, a metal electrode is deposited on this, and the
The resistance of the coated layer alone under an electric field of 100 V / cm
10^Five Ω · cm. FIG. 7 shows the results.

FIG. 7 is a diagram showing the results of an experiment on the image density stability immediately after replenishment of the magnetic carrier when a conductive magnetic carrier is used in the developing device shown in FIG. 1 and the developing device of the comparative example. In the comparative example, the image density is reduced earlier than when the magnetic carrier used in the developing device 100 of the present embodiment is used. This is probably because the carrier resistance increased due to the deterioration of the magnetic carrier, and the developing electric field became smaller. On the other hand, when the conductive magnetic carrier is used in the developing device 100 of the present embodiment, the carrier replenishment amount is increased, and a uniform image density is obtained.

[0035] Thus, of a magnetic carrier, and electrically conductive core material, coating layer comprising a conductive agent and, 10 ⁸ Ω · cm
In a developing device having the following electric resistance, the position of the virtual developing electrode approaches the latent image carrier, so that the electrostatic latent image on the latent image carrier is developed more faithfully, and high image quality is obtained. However, if the magnetic carrier deteriorates and its resistance increases, faithful development cannot be obtained. Therefore, when a low-resistance magnetic carrier is used, it is more important to efficiently and effectively replenish the new magnetic carrier, and the effect of the developing device 100 of the present embodiment becomes more effective.

[0036]

As described above, in the developing device of the present invention, a sufficient amount of toner charge is maintained over a long period of time, and good image quality can be stably obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of a developing device of the present invention.

FIG. 2 is a graph showing the measurement results of the image density and the total amount of discharged developer when printing is performed under high temperature and high humidity in both the developing device shown in FIG. 1 and the developing device of the comparative example.

3 is a graph showing the measurement results of the image density and the total amount of discharged developer when printing is performed under low temperature and low humidity in both the developing device shown in FIG. 1 and the developing device of the comparative example.

FIG. 4 is a schematic configuration diagram of a second embodiment of the developing device of the present invention.

FIG. 5 is a schematic configuration diagram of a third embodiment of the developing device of the present invention.

FIG. 6 is a diagram showing experimental results on image density stability immediately after magnetic carrier replenishment in both the developing device shown in FIG. 1 and the developing device shown in FIG.

FIG. 7 is a view showing an experimental result on image density stability immediately after replenishment of a magnetic carrier when a conductive magnetic carrier is used in the developing device shown in FIG. 1 and a developing device of a comparative example.

FIG. 8 is a diagram showing the results of an experiment on toner charge retention in a temperature and humidity environment of an image forming apparatus incorporating a conventional developing device.

[Explanation of symbols]

 1,30 Developer stirring section 2 Latent image carrier 3,23 Developer carrier 4,24 Developing sleeve 5,25 Permanent magnet 6,26 Layer thickness regulating member 7,8,13,27,28,43 Screw auger 9 Magnetic carrier replenishing device 10 Discharge port 11 Carrier storage unit 12 Magnetic carrier transport unit 14, 34 Toner density sensor 15 Partition wall 30a Side wall 36, 37 Transport roll 38 Guide member 40 Developer discharge device 41 Opening 42 Cylindrical sleeve 100, 200, 300 Developing device

Claims (4)

[Claims] An image bearing member that carries an electrostatic latent image and moves in a predetermined direction is disposed so as to approach or contact a predetermined developing region, and carries a developer including a toner and a magnetic carrier on a surface thereof. A developer carrier that is transported along a transport path that passes through the development region, and receives the developer that has passed through the development region from the developer carrier and stirs it together with the developer remaining inside. An agent agitating section; a toner concentration measuring means for measuring the concentration of toner in the developer therein; and a toner agent measuring section in response to a measurement result that the toner concentration has decreased by the toner concentration measuring means. A developing device comprising: a carrier replenishing means for replenishing a magnetic carrier; and a discharge port for discharging an internal developer. 2. The developing device according to claim 1, wherein the developer stirring section is disposed above the developer carrier, and receives the developer after passing through the developing region from the developer carrier to receive the developer. 2. The developing device according to claim 1, further comprising a pumping mechanism for pumping the agent. 3. A pair of augers for agitating the developer by transporting the developer in the direction of the rotation axis and in a direction opposite to each other, wherein the developer agitating section is arranged in such a manner that each rotation axis faces in the horizontal direction. The developing device according to claim 1, further comprising: 4. The method according to claim 1, wherein the magnetic carrier comprises a conductive core material,
2. The developing device according to claim 1, comprising a coating layer containing a conductive agent and having an electric resistance of 10 ⁸ Ω · cm or less.