JPH05289486A - Electrostatic recording method - Google Patents

Abstract

PURPOSE:To make image density appropriate by controlling the charged amount of toner in the case that the image density becomes low or high though toner concentration shows nearly a specified value. CONSTITUTION:In the case that the reflection density(image density) of a standard toner image which is measured by an optical image density measuring means P5 becomes lower or higher than a specified level though the toner concentration shown nearly the specified value, a 2nd CPU 70 makes the image density appropriate by decreasing the charged amount of toner by rubbing a member which has the same direction of triboelectrification line as that of the toner in two-component developer and whose triboelectrified amount is larger, against the two-component developer or adding particulates on an opposite side to the toner in the two-component developer on a triboelectrification system to the two-component developer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording apparatus adopting a developing method for developing an electrostatic latent image by using a two-component developer composed of a toner and a carrier of a copying machine, and particularly suitable for the image recording apparatus. The present invention relates to an electrostatic recording method in which the amount of toner charge is controlled to obtain various image densities.

[0002]

2. Description of the Related Art In a developing device for visualizing an electrostatic latent image on an image bearing member such as a photosensitive drum by using a two-component developer consisting of a toner and a carrier, the toner in the two-component developer is The mixing ratio by weight with the carrier (hereinafter referred to as toner concentration T _C ) greatly affects the developability. For example, if the toner density of the two-component developer is lower than the proper value, the density of the developed image will be low. On the contrary, when the toner density becomes too high, the density of the developed image becomes too high and the so-called fog increases. Therefore, the recorded image on the transfer material transferred from the image carrier becomes unsuitable.

Therefore, in order to always obtain an image having a preferable density, the toner density of the two-component developer is set to an appropriate level,
At the same time, it is necessary to keep the appropriate level constant during development. Therefore, conventionally, there has been proposed a two-component developer concentration control system in which the toner concentration of the two-component developer is kept constant by controlling the toner supply amount. This density control method detects change events such as magnetic permeability change and volume change of two-component developer, change of image density after development, and color change of two-component developer due to toner and carrier having different colors. By doing so, the toner concentration is detected, and the toner replenishment amount is controlled based on the detected toner concentration to maintain the proper toner concentration.

However, in the method of detecting a change event as described above, stable operation for a long period of time has been difficult due to reasons such as erroneous detection and difficulty in compensating for deterioration of the surface of the photosensitive member over time.

As a solution to this problem, Japanese Patent Laid-Open No. 57-1366 has been proposed.
No. 69 “Two-component developer concentration control device” is introduced. This "two-component developer concentration control device" is a detection level that should detect the volume of the two-component developer in the developing device so that the developing effect in the recording device can be stably and appropriately maintained for a long period of time. In addition to the above, the density of the developed image of the reference image formed on the surface of the photoconductor or the density of the recorded image is optically detected separately in order to detect the development performance, and the plurality of detections are performed accordingly. The toner concentration of the two-component developer is controlled in order to avoid carrier replenishment as much as possible and to keep the developing performance as constant as possible by switching and setting the level by the central processing unit. For the time being, the above-mentioned object was achieved.

[0006]

However, the contents of the original document to be image-recorded often have variations in blackening rate due to differences in image density and image density, and blackening of line drawings, character images, low-density originals, etc. When a developing operation is executed to continuously form an image of original contents having a low rate, a predetermined image density corresponding to the toner density cannot be obtained even though the toner density is constant, and the toner density is low. -The phenomenon that the correspondence between the density and the image density is broken has occurred. It was also found that this phenomenon is likely to occur in the case of a color electrostatic recording device in which a color image can be reproduced by using a two-component developer of various colors.

Then, when the cause of occurrence of such a phenomenon was considered, the following findings were found.

That is, as a result of analyzing the phenomenon common to the above two examples, the developing sleeve and the stirring means in the developing device are continuously driven to rotate within the developing time during the image forming process in the electrostatic recording apparatus. However, it has been found that this stirring time, in other words, the residence time of the two-component developer in the toner hopper, is commonly related. That is, in the former example, since the original is of low density, the toner consumption amount per unit time is smaller than usual, and the toner retention time becomes longer accordingly. In the latter example, the toner consumption amount of the two-component developer for each color is different, and the residence time of the toner is also different for each color.

Considering that the phenomenon in the above example occurs even when the toner concentration is constant, it is presumed that the phenomenon does not result from a so-called spent toner, which is a state in which toner components are attached around the carrier and the toner charge amount is reduced. However, since it is related to the toner retention time, that is, if the toner retention time becomes long, the chances of friction between the toner and the carrier increase, and it is expected that the toner charge amount will continue to increase. It is considered that the toner charge amount outside the predetermined range affects the image density. Therefore, the relationship between the toner charge amount and the image density was examined.

FIG. 7 is a diagram showing a change in the image density CD with respect to a change in the toner charge amount Q / m (μC / g) when the toner density in the two-component developer is constant.

FIG. 7 shows that the image density CD decreases as the toner charge amount Q / m increases. Specifically, the toner charge amount Q / m is -19.5 (μC /
g), the image density CD is 1.28, and when the toner charge amount Q / m is -22.0 (μC / g), the image density CD is 1.2 and the toner charge amount Q / m. m is -3
When 1.0 (μC / g), the image density CD is 0.8.

Such image density CD and toner charge amount Q
The relationship with / m is that the toner in the two-component developer magnetically carried by the developing sleeve containing a permanent magnet receives the force in the developing area for developing the electrostatic latent image (hereinafter referred to as developing force). I can explain.

That is, when the developing force is F _t , the developing force F _t is approximately

[0014]

[Number 1] _{F t = q t · E -} k (q t · q c / r 2) -q t (V B / R) { However, q _t is the toner charge amount, E is the electric field by the electrostatic latent image (Hereinafter referred to as latent image electric field), q _c is the carrier charge amount,
r is the distance between the toner and the carrier, V _B is the voltage applied to the developing sleeve (hereinafter referred to as developing bias), and R is the distance between the photosensitive drum surface and the developing sleeve surface}. .

Formula 1 shows that the developing force F _t is the force due to the latent image electric field E, and the adhesion force between toner and carrier (this is called Coulomb force) and the developing bias force acting on the toner. It shows that it has been reduced. Here, it should be noted that the force that determines the developing force F _t is the toner charge amount q.
_Although it is proportional to _t (Q / m), the Coulomb force, which is a force that reduces the developing force F _t , increases the carrier charge amount q _c as the toner charge amount q _t (Q / m) increases. Therefore, it tends to increase more than other forces. Therefore,
Increase in the toner charge amount q _t (Q / m) is appears as a decrease in the developing force F _t, toner - of reduced charge amount q _t (Q / m) appears as a rise in the developing force F _t It is a point.

FIG. 8 is a graph showing changes in the image density CD with respect to the toner concentration (wt%: weight mixing ratio) in the two-component developer loaded in the developing device.

Here, the two-component developer has an average particle size of 20 to
100 μm insulating magnetic carrier (resin coating,
Magnetic particle resin dispersion type) and a toner having an average particle diameter of 5 to 15 μm.

In FIG. 8, the solid line A indicates the developing bias V.
The case where _B is 200 V is shown, and the toner concentration is 1
The image density CD is about 0.4 at about wt%, and the image density CD is about 1.0 at the toner concentration of 5 wt%. When the toner concentration exceeds 5 wt%, the image density CD is about 1.2. It shows that it saturates in the vicinity. This solid line A
The image density CD is about 0.4 to about 1.2, the contrast is sufficiently wide, and the adhesive force between the photosensitive drum, which is the latent image carrier, and the toner is good on the locus of No. Since the image shift is reduced, it is usually desired to control the image density CD on the locus of the solid line A.

The alternate long and short dash line B is, as in the above two examples,
The two-component developer time increases to stir, in the case where the toner charge amount q _t (Q / m) is too large as compared with the solid line A toner - density T _C (wt%) and the relationship between the image density CD Is shown. The other conditions such as the developing bias V _B are all the same as the solid line A. In this case, as is clear from Equation 1, the Coulomb force increases as compared with the other electrostatic forces, so that the force of attracting the toner to the photosensitive drum is relatively reduced, and the image density is reduced. ing. Specifically, the alternate long and short dash line B indicates that the toner density is saturated from 5 wt% to around image density 0.5. Therefore, there is a problem that a sufficient image density CD corresponding to the original image on the locus B cannot be obtained, and further a sufficient contrast cannot be obtained.

The dotted line C indicates the toner density T _C (wt%) and the image density CD when the toner charge amount becomes smaller than the solid line A due to environmental changes such as an increase in relative humidity. Shows the relationship with. In this case, it is shown that the adhesive force (Coulomb force) between the toner and the carrier becomes insufficient and the image density CD rises as compared with the solid line A. Specifically, the image density CD is a toner density of 1 wt /
%, It reaches about 0.7, and as the toner concentration (wt%) rises, it is saturated at about 1.4. Therefore, in the development on the dotted line C, the contrast width has a sufficient width, but a large amount of toner is scattered and too much toner adheres to the latent image, so that the original image is faithfully reproduced. There is a problem that it cannot be put to practical use in terms of reproduction. Further, since the adhesive force between the photoconductor drum and the toner is not sufficient, there is a problem that image shift easily occurs.

The present invention has been made in view of the above problems, and an object of the present invention is to reduce the image density when the toner density is lowered, although the toner density is kept substantially constant at a predetermined value. An object of the present invention is to provide an electrostatic recording method capable of reproducing an image at an appropriate image density by detecting this and controlling the toner charge amount to a predetermined value.

[0022]

In order to achieve the above object, an electrostatic recording method according to the present invention is a method in which an electrostatic latent image on an image carrier is developed with a two-component developer consisting of a carrier and a toner. In the electrostatic recording method for forming an image, the toner density of the two-component developer is substantially constant, and the toner adhesion amount of the reference toner image developed with the toner on the image carrier is below a predetermined value. A member in which the direction of the triboelectrification column of the toner is the same as that of the triboelectrification column and the triboelectrification amount is larger, or the two-component developer is rubbed against the two-component developer, The toner image is formed after the amount of toner charge in the two-component developer is reduced by adding fine particles on the opposite side of the charging column.

[0023]

The member in which the direction of the triboelectrification sequence of the toner in the two-component developer is the same as that of the triboelectrification sequence and the triboelectrification amount is larger is rubbed against the two-component developer, or When the toner and the particles on the opposite side of the triboelectric charging line are added to the toner, the toner charge amount decreases, and the toner adhesion amount of the toner image developed with the toner on the image bearing member such as the photoconductor drum increases, and A decrease in concentration is prevented.

[0024]

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

FIG. 1 is a block diagram of an image recording apparatus to which an electrostatic recording method according to an embodiment of the present invention is applied. The image recording apparatus 100 includes a photosensitive drum 1, a developing device 20, a developing bias circuit 31, and a developing bias circuit 31. Hopper drive circuit 32, toner concentration detection means TS, high voltage power supply circuit 40, transfer device 41, charger 4
2, first CPU 50, reading optical system 61, scanning optical system 6
2. It has a reading and scanning optical system drive 63, a second CPU 70, and an optical density measuring means PS. When a copy button (not shown) is pressed, the scanning optical system 62 emits a light source with an image signal corresponding to the image density of the original image based on a timing signal from the first CPU 50 to irradiate the photoconductor drum 1 with light. An electrostatic latent image is formed on the photosensitive surface of the body drum 1, and the electrostatic latent image formed on the surface is developed by the developing device 20.
To develop the toner image into a toner image, and the transfer device 41 is discharge-driven based on the registration signal to transfer the toner image onto a transfer sheet. After that, the transfer paper is fixed to form a reproducible image that can be stored.

As the photosensitive drum 1, an aluminum drum-shaped conductive support having a diameter of 80 mm is used, and an ethylene vinyl acetate copolymer having a thickness of 0.1 μm is formed on the support.
Is an OPC photosensitive member including a photosensitive layer having a film thickness of 35 μm provided on the intermediate layer, and the surface potential decreases when the photosensitive layer is irradiated with light. Therefore, if the photosensitive drum 1 is previously uniformly charged to a predetermined potential and then the light based on the density of the original image is irradiated, the surface potential of the photosensitive drum 1 becomes non-uniform and a portion with a lowered potential is formed. be able to.
This is what is called an electrostatic latent image. The photoconductor drum 1 is not limited to this, and may be a photoconductor made of, for example, amorphous silicon or TeSe. Further, the shape is not limited to the drum shape and may be a belt shape, but here, an example of the OPC photosensitive member will be described.

The developing device 20 includes a developing sleeve 21 containing a magnet roller having N and S poles in a developing tank formed by a lower casing and an upper casing, and a developer from the developing sleeve 21. A scraper 22 for scraping and first and second screw-shaped stirring rollers 23, 24 are provided, and a thin layer forming means 25 composed of a magnetic rod is provided above the developing sleeve 21. Further, the developing device 20 includes a toner hopper 27 that replenishes the developing tank with new toner and an external additive hopper 28 that adds an external additive. A toner replenishing roller 27R and an external additive adding roller are respectively provided at lower opening portions of the toner hopper 27 and the external additive hopper 28.
La 28R is provided.

The first agitating roller 23 is shaped so as to convey the developer toward the front side of the recording paper, and the second agitating roller 24 is shaped so as to convey it toward the back side of the recording paper. Further, the developing device 20 is provided with a partition wall between the first and second agitating rollers 23 and 24 so that the two-component developer is smoothly circulated and is not locally retained.

The scraper 22 is provided so as to be in pressure contact with the sleeve 21, and scrapes the two-component developer, which has passed through the developing area and consumed toner, from the sleeve 21. As a result, the two-component developer conveyed to the developing area can be replaced, and the developing conditions are stabilized.

To the developing sleeve 21, a developing bias circuit 31 for applying a DC bias component and a voltage having a DC bias component via a protective resistor in order to prevent image fogging.
Is provided.

The developing bias circuit 31 includes an AC power source for applying an AC bias for causing toner to vibrate between the sleeve and the photosensitive drum 1 in the developing area, and a high voltage DC power source for applying a DC bias.

The hopper drive circuit 32 is a circuit for rotationally driving the toner replenishment roller 27R and the external additive addition roller 28R based on the replenishment signal from the second CPU 70, whereby the toner to the developing unit 20 is supplied. Replenishment or addition of the external additive G to the two-component developer in the developing device 20 is performed.

Here, the external additive G is a toner charge amount control member for controlling the toner charge amount, and is a fine particle on the opposite side of the toner on the triboelectric charge train. For example, titanium oxide T
iO ₂ particles are used. Other examples are metals such as gold or copper, semiconductor materials such as silicon, germanium or carbon black, magnetite, reduced titanium oxide, doped antimony oxide, tin oxide and yttrium oxide, There are conductive metal oxides such as reduced zirconium oxide, conductive organic polymers such as reduced polyacetylene, and semi-metals such as carbon. Examples of preferred materials used in this example are Regal 330 carbon black, and Raven 420 carbon black, and Raven 420 carbon black. , Yttrium oxide and zirconium oxide solid solutions (ZYP powders) are available, and these materials can positively withstand electricity against common resins, particularly styrene and vinyl chloride based resins. Generally, any material that can be made into particles of about 1 micron or less can be used.

Another example is silica particles treated with hexamethyldisilazane as a fluidity improver.
The chromium-containing organic complex can be used not only for black toner but also for yellow toner, magenta toner, and cyan toner.

When the above-mentioned external additive G is added to the two-component developer, only a part, that is, a relatively small number of particles, is required, and it is stirred by the first stirring roller 23 and the second stirring roller 24. The amount of charge on the toner can be controlled by adhering the particles to the toner or contacting the toner during the mixing with the component developer. The external additive G may be added once, for example, by 0.1 to 10%, preferably about 0.5% of the total amount of toner in the two-component developer in the developing device 20.

The toner charge control member is the external additive G.
Other toner charge amount control members that are not limited to the above will be described later.

The toner density detecting means TS detects the toner density by detecting the change in the magnetic permeability of the two-component developer loaded in the developing device 20. The toner density detecting means TS is not limited to this, and the developing device 20
The toner concentration may be detected by another method such as detecting the volume level of the two-component developer in the inside. Here, for convenience of explanation, a high voltage power supply circuit 40 will be described as a toner density detecting means for detecting a toner density by a change in magnetic permeability.
Is a circuit for applying a predetermined high voltage to the transfer device 41 and the charging device 42. The charging device 42 and the transfer device 41 are preferably so-called corona electrification and corona transfer devices that perform corona discharge, but are not limited thereto as long as the discharge efficiency is uniform.

The reading optical system 61 is composed of an illumination lamp (not shown) integrally formed with the first scanning mirror, a second mirror (V mirror) which moves at a speed ratio of 1/2 of that of the first mirror, and the like. The original is scanned while the optical path length in front of is always kept constant. As a result, the reading optical system 61
Forms an image of the reflected light from the document image on the platen glass on the light receiving portion of the solid-state image sensor. The reading optical system 61 reads an output signal from the solid-state image sensor and drives the scanning optical system 63.
To send to.

The scanning optical system 62 is a laser scanning system including a polygon mirror for rotating and scanning a laser from a semiconductor laser modulated by an image signal, a fixed scanning system using an LED array and liquid crystal. The scanning optical system 62 includes an intensity modulation method and a pulse width modulation method as a light modulation method of a laser emitted from the scanning optical system 62. In this case, image data corresponding to the light image from the standard density plate (this is called standard density data)
Is stored in advance in the ROM. In this embodiment, standard density data corresponding to an image density of about 1.0 is stored.

Note that the above description describes a so-called digital scanning optical system, but the present invention is not limited to this, and in the case of an analog system, a known scanning system is used. For example, although not shown, it comprises an illumination lamp integrally formed with the first scanning mirror, a second mirror (V mirror) which moves at a speed ratio of 1/2 of the first mirror, etc., and the optical path length in front of the lens is always The document is scanned while keeping it constant. A standard density plate having an optical reflection density of, for example, 1.0 is provided at one lower end of the platen glass, and a standard latent image is formed on the photosensitive drum 1 after being irradiated with the irradiation lamp to develop the standard latent image with toner. Is done.

The reading / scanning optical system drive circuit 63 is a circuit including a circuit for controlling a mechanical system such as a polygon mirror and an image processing circuit for color-processing the image signal from the reading optical system 61. Standard image density data that changes stepwise or continuously from 0 to 1.0 is stored in the ROM, and this data is used to form a standard latent image based on this data. In the present embodiment, the standard image density data corresponds to the optical reflection density of 1.0, but the invention is not limited to this, and may correspond to 1.0 or more to 0.

The optical density measuring means PS uses LE as a light source.
D is used to convert the light reflected from the reference toner image on the photosensitive drum 1 into an electric signal by photoelectric conversion and output the electric signal to the second CPU 70. For example, a tungsten lamp is used as a light source, It is composed of a light-receiving portion composed of a single photo sensor.

The first CPU 50 is for controlling the sequence of the image forming process, and has an image forming program for executing the image forming process therein, and the image forming process is executed by a start signal issued in response to the pressing of the copy button. The program is started to execute the image forming process.

The second CPU 70 makes a one-to-one correspondence between the data of the image density CD and the data of the toner density T _C on the loci of the solid line A, the chain line B and the broken line C shown in FIG. A look-up table T and an image density control program including a toner density determination program and a toner charge amount control program are stored in the built-in ROM 70a.

The toner density determination program determines whether or not the toner density detected by the toner density detecting means TS is below a predetermined value, and when the toner density is below a predetermined value, a toner density NG signal is output. , When the toner density is not lower than the predetermined value, the toner density OK signal is sent to the first CP.
It is a program transmitted to U50. The first CPU
Reference numeral 50 has a toner density determination result register R1 for setting the toner density NG signal or the toner density OK signal received from the second CPU 70. The signal in the toner density determination result register R1 is the toner density NG signal. In this case, the toner supply roller 2 is controlled by controlling the hopper drive circuit 32.
By rotating 7R, the toner in the toner hopper 27 is replenished to the developing tank to maintain the toner density constant.

The toner charge amount control program, when the detection signal from the optical density measuring means PS indicates a decrease / increase in the image density, even though the toner density is kept substantially constant at a predetermined value, This is detected and the hopper drive circuit 3
2 is a program for controlling the external additive replenishing roller 28R to add the external additive G in the external additive hopper 28 to the two-component developer in the developing tank 20 to reduce the toner charge amount. Is.

Here, the decrease or increase of the image density is detected by detecting the reflected image density of the toner image on the photosensitive drum 1 corresponding to the standard density plate, and the image density CD which is the reference for comparison read from the look-up table T. = About 1.0 [toner concentration T _C = 5 (wt%)]. At this time, the reference image density is set in the reference image density register R2.

The first CPU 50 has a first counter CT1 for counting the number of copies and a second counter CT2.
The first counter CT1 counts the number of continuous copies at the time of continuous copying, and the second counter CT2 indicates the timing for executing the toner charge amount control program in response to a detection signal from a paper discharge sensor or the like. The number of copies, that is, the total number of copies after the previous toner charge amount control is performed, is counted. Specifically, copy 1
The toner charge amount control program is executed every 000 sheets. This is because the toner charge amount control can be practically sufficiently dealt with by intermittent control, and the toner on which the reference toner image is formed is the same as the photosensitive drum 1.
This is to save toner because it is removed by a cleaner that cannot be used for normal copying.

Next, the image recording operation of the image recording apparatus will be described with reference to the flow charts of FIGS. In addition,
2 is a main flow executed by the first CPU 50, and FIG. 3 is a toner charge amount control flow executed by the second CPU 70.

The power is turned on by pressing the main switch (not shown). As a result, the first CPU 5
0 and the second CPU 70 are activated (step F-1 in FIG. 2).

The first CPU 50 is the first motor driver 1
By driving 0, the main motor is started, and the drive system is connected to the first and second agitating rollers 20e, 2 of the developing device 20.
0f is connected to stir the two-component developer. Further, the heater of the fixing device is heated to a predetermined temperature. Also, the first CP
The U50 connects the photoconductor drum 1 to the drive system of the main motor to rotate and drive it, and the charger 41 and the static eliminator (not shown)
As a result, pretreatment such as charging the photosensitive drum 1 and adjusting the image forming process conditions by repeating static elimination is performed. Further, in the pre-processing, the number of continuous copies A set by the user by a predetermined button operation is set in the first counter CT1 (step F-2).

By the way, as described above, the second CPU 70
Determines whether the toner concentration detection signal from the toner concentration detecting means TS is always below the set value 5 (wt%) based on the toner concentration determination program.
When it becomes less than (wt%), toner concentration NG signal, 5
When it is not less than (wt%), the toner concentration OK signal is sent to the toner concentration determination result register R1 of the first CPU 50.
Have been sent to.

Therefore, the first CPU 50 reads the signal set in the toner concentration determination result register R1 (step F-3) and determines whether or not it is the toner concentration NG signal (step F-4). As a result, if the toner density signal is NG, the toner is replenished (step F-
5) Go to step (F-6). On the other hand, the toner density O
If it is a K signal, immediately proceed to step (F-6),
By determining whether or not the countdown value in the second counter CT2 is “0”, it is determined whether or not the count value of the total copy number has reached the total copy number of 1000, which is the setting. As a result, if the total number of copies has not reached 1000, the process proceeds to step (F-9). If the total number of copies has reached 1,000, the first CPU 50 sets "1000" as the set value of the total number of copies in the second counter CT2 (step F-7), and the image density control interrupt is generated. Then, a toner charge amount control command signal is output to the second CPU 70 (step F
-8).

Therefore, the second CPU 70 is connected to the first CPU 5
In response to the toner charge amount control command signal from 0, the scanning optical system 62 is activated to turn on the light source, and the standard density plate is irradiated with light, so that the reflected light from the first and second mirrors is reflected. A standard electrostatic latent image is formed by forming an image on the photoconductor drum 1 via (step F- in FIG. 3).
81). Then, the developing device 20 is driven to visualize the standard electrostatic latent image as a toner image to form a standard toner image (step F-82). Next, the second CPU 70
The reference image density CD corresponding to the toner density detection signal from the toner density detecting means TS is read from the lookup table T and set in the reference image density register R2 (step F-83).

Then, the actual optical image density is fetched from the optical image density measuring means PS, and the reference image density register R2
Then, it is determined whether or not they match with each other by comparing with the reference image density held in (step F-84). As a result, if they do not match, it is determined whether or not the addition flag F is set, that is, whether or not the external additive G is currently being added (step F-85). As a result, if the addition flag F is not set and the external additive G is not currently being added, the addition flag F is set (step F-86) and the hopper drive circuit 32 is controlled to replenish the external additive. By rotating the roller 28R a predetermined number of times, a predetermined amount of the external additive G in the external additive hopper 28 is added to the two-component developer in the developing tank 20 (step F-87). In this case, the first stirring roller 23, the second
The stirring roller 24 continues to rotate, and the added external additive G is mixed with the two-component developer, so that the toner charge amount is reduced as shown in FIG. It should be noted that the toner charge amount continues to increase for a while after the addition of the external additive G in FIG. 4 because the mixing of the external additive G and the two-component developer is still insufficient. This is because the amount of increase in the toner charge amount due to stirring is larger than the amount of decrease in the toner charge amount due to the additive G. Therefore, after waiting for the time required for the external additive G to be sufficiently mixed with the two-component developer to elapse (step F-88), the toner charge amount is reduced, and as a result, the actual optical image darkness becomes the reference. The process returns to step (F-81) to check whether the image density has been restored. When it is determined in step (F-85) that the addition flag F is set, as is clear from the above description,
Although the external additive G was added in a predetermined amount unit, it means that the addition amount is insufficient and the actual optical image density has not yet been restored to the reference image density. Therefore, step (F-8
Skip 6) and proceed to step (F-87).

When it is determined in step (F-84) that the actual optical image density and the reference image density match each other, it is determined whether the addition flag F is set (step F). -89). As a result, if the addition flag F is set, it means that the actual optical image density has been restored to the reference image density as a result of adding the external additive G, so the external additive G addition processing is completed. Therefore, the addition flag F is reset (step F-90), and the process returns. On the other hand, if the addition flag F is reset, it means that the actual optical image density matches the reference image density from the beginning, and it is not necessary to add the external additive G. ..

Therefore, the first CPU 50 executes the image forming process based on the image forming program (FIG. 2).
Step F-9). Then, the countdown value of the continuous copy number of the first counter CT1, the second counter CT2
The countdown value of the total number of copies of 1 is subtracted by 1 (step F-10), and it is determined whether or not the countdown value of the number of continuous copies of the first counter CT1 is "0" to determine whether the number of continuous copies relating to the setting is continuous. Number of copies A
(Step F-11), and when the countdown value of the first counter CT1 is "0" and the continuous copy number A has been reached, the process ends. On the other hand, if the number of continuous copies A has not been reached, the process returns to step (F-3) to make continuous copies for that number.

Even if the triboelectric charge polarity of the external additive G added to the developer is the same as that of the toner, the present invention can be applied. In this case, it is necessary that the external additive G is smaller than the toner on the triboelectric charging series. As a specific example, a case where titanium oxide fine powder is used as the external additive G will be described. A two-component developer prepared by adding an appropriate amount of negative (negative) chargeable toner to an insulating carrier coated with resin on the surface of a ferrite core having an average particle diameter of 40 μm is used.
ONICA9028 (product name) was placed in a black developing device to make a running copy. The toner charge amount at the start was -19.5 μC / g, the maximum reflection density on the transfer paper after development was 1.28, and the density of the portion corresponding to the reference density of 1.0 on the photosensitive drum 1 was 1. It was 08. And 30
The toner charge amount after copying 00 sheets increased to about −31 μC / g, and the maximum reflection density decreased to 0.8. Therefore, independently of toner replenishment, the total toner amount of the total two-component developer amount (total two-component developer amount of about 1.5 Kg, total toner amount of about 6
0g, toner concentration about 4wt%), 0.1wt%
60 mg of titanium oxide fine powder corresponding to the above was added twice at intervals with a total of 120 mg. When the two-component developer was stirred for a while and then image formation was carried out again, the toner charge amount decreased to about −22 μC / g and the maximum reflection density was restored to 1.2. After that, when the copying was continued, the developability deteriorated after copying about 1500 to 5000 sheets. Therefore, the developability was recovered by adding 60 mg of titanium oxide fine powder 2 to 3 times each time. We were able to.

Next, a modification of the toner charge amount control member is shown in FIG.
And FIG. 6 will be described. 5 and 6 are sectional views showing a developing device equipped with a modified example of the toner charge amount control member.

The developing device 20X and the developing device 20Z are provided with a toner charge amount control member in place of the scraper 22 in the developing device 20 of FIG. 1, and the external additive hopper 2 for loading the external additive G therein.
8. The external additive-added roller 28R is omitted, and other configurations are substantially the same as those of the developing device 20 described above. Therefore, the same reference numerals and description as those of the members described in FIG. 1 are omitted.

The toner charge amount control member in FIG. 5 is a blade 22X made of silicone rubber. Blade 2
2X is rotatably provided from a position shown by a dotted line to a position shown by a solid line. Specifically, a fixed magnet is arranged inside,
About 0.3 to 20 m of the developing and developing sleeve 21 which is rotated in the counterclockwise direction which is the same direction as the photosensitive drum 1 in the developing area.
It is provided so that it can approach up to m. This makes the development sleeve
It is possible to control the charge amount of the toner in the two-component developer carried on the sleeve 21, and adjust the toner charge amount to an appropriate value. Further, when the material of the blade 22X is silicon rubber or Teflon rubber, it is preferable that the blade 22X is close enough to slightly rub the magnetic brush. The material of the blade 22X is not limited to this, and the direction of the triboelectric charging series is the same as that of the toner triboelectric charging series.
In addition, it may be made of a substance having a large triboelectric charge amount.

In this case, a toner charge amount control member drive circuit for driving the blade 22X based on the control signal of the second CPU 70 is required.

The toner charge amount control member in FIG. 6 is a friction charge roll 22Y. The triboelectric charging roll 22Y preferably has substantially the same curvature as the developing sleeve 21.
The friction charging roll 22Y is rotatably provided from a position shown by a dotted line to a position shown by a solid line, and specifically, is provided so as to be able to approach the developing and developing sleeve 21 to about 0.3 to 2.0 mm. There is. As a result, when the two-component developer carried on the developing sleeve 21 returns to the inside of the developing device 20 after development, the two-component developer is stripped from the developing sleeve 21 and the two components inside the developing device 20Z are removed. By stirring and mixing with the component developer, it becomes possible to control the charge amount of the toner in the two-component developer. The friction charging roll 22Y and the developing sleeve are
Adjusting the distance from the sleeve 21 and the friction charging roll 22
By adjusting the rotation speed and rotation direction of Y, the toner
It is also possible to control the charge amount. In this case, when the decrease in the optical reflection density is large, the developing sleeve 21
The rotation speed of the triboelectric charging roll 22Y may be increased. Further, when the material of the friction charging roll 22Y is silicone rubber or Teflon rubber, it is preferable that the friction brushes 22Y are close enough to slightly rub the magnetic brush. The material of the triboelectrification roll 22Y is not limited to this, but the direction of the triboelectrification series of the toner is the same as that of the triboelectrification series, and the triboelectrification quantity is large and the triboelectrification quantity is the same direction and large. It may be configured with.

As a specific example, a case where running copying is performed using the developing device shown in FIG. 5 will be described. At the start of running copy, the toner charge amount is -19.5.
μC / g, the reflection density of 1.0 part of the reference density on the photosensitive drum 1 was 1.08. The distance between the blade 22X made of fluorine-based silicon rubber and the developing sleeve 21 is 1.
When I started running copy with 8mm,
Toner charge amount after copying 5,000 sheets is -29 μC
/ G, the reflection density at the reference density of 1.0 part decreased to 0.8. Therefore, the blade 22X is attached to the developing sleeve 21 at a rate of 0.
When 100 sheets are continuously copied with a distance of 4 mm, the toner charge amount decreases to about −21 μC / g, and the reference density is 1.
Since the reflection density of the 0th part was restored to about 1.0, the distance between the blade 22X and the developing sleeve 21 was returned to the original 1.8 mm. It should be noted that the reflection density at the reference density of 1.0 copy decreased every time 5,000 to 8,000 copies were made.
It was necessary to perform the same processing as described above every time copying from 1 to 8000 sheets. In this case, a toner charge amount control member drive circuit for driving the friction charging roll 22Y based on the control signal of the second CPU 70 is required.

It has also been found that controlling the rotational speed of the developing sleeve 21 is effective. That is, when the reflection density of the reference density portion decreases, the developing property is improved by increasing the rotation speed of the developing sleeve 21. Furthermore, since the amount of the two-component developer controlled by the triboelectric charging roll also increases, it is presumed that a greater effect will be exhibited. However, this effect is largely influenced by the developing conditions, and therefore may be temporary and may have an adverse effect.

Although not shown, a method of controlling the toner charge amount of the two-component developer on the developing sleeve 21 by discharging is also effective. For example, a system in which corona discharge is performed by a corona discharger arranged so as to face the two-component developer on the developing sleeve 21 may be used. In this case, the corona discharger preferably includes an AC power supply as a power supply, and does not necessarily include a DC power supply.

[0067]

As described above, according to the electrostatic recording method of the present invention, when the density of the image is lowered despite the toner density being maintained substantially constant at a predetermined value, By detecting this and controlling the toner charge amount to a predetermined level,
The image can be reproduced with an appropriate image density.

[Brief description of drawings]

FIG. 1 is a block diagram of an image recording apparatus to which an electrostatic recording method according to an exemplary embodiment of the present invention is applied.

FIG. 2 is a flow chart showing an image recording operation in the electrostatic recording method of the present embodiment.

FIG. 3 is a flowchart showing an image density control operation in the electrostatic recording method of this embodiment.

FIG. 4 is a diagram showing a state where a toner charge amount is reduced by adding an external additive.

FIG. 5 is a configuration diagram of a developing device according to a second embodiment.

FIG. 6 is a configuration diagram of a developing device according to a third embodiment.

FIG. 7 is a toner in a two-component developer loaded in a developing device.
It is a figure which shows the change of the image density with respect to a density.

FIG. 8 is a toner in a two-component developer loaded in the developing device.
FIG. 6 is a diagram showing a change in image density with respect to a change in the charge amount of the image.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum 20, 20X, 20Z Developing device 22X Blade 22Y Friction charging roll 28 External additive hopper 28R External additive adding roller 32 Hopper drive circuit 50 First CPU 70 Second CPU TS Toner density detecting means PS Optical density measuring means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kunihisa Yoshino 2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica Stock Company

Claims (2)

[Claims] 1. An electrostatic recording method for forming a toner image by developing an electrostatic latent image on an image bearing member with a two-component developer comprising a carrier and toner, wherein the toner concentration of the two-component developer is substantially the same. When the toner adhesion amount of the reference toner image developed with the toner on the image carrier is constant and equal to or less than a predetermined value, the direction of the triboelectrification column of the toner is the same as that of the triboelectrification column, and An electrostatic recording method comprising: rubbing a member having a larger amount with the two-component developer to reduce the toner charge amount in the two-component developer, and then forming the toner image. 2. An electrostatic recording method for forming a toner image by developing an electrostatic latent image on an image bearing member with a two-component developer comprising a carrier and toner, wherein the toner density of the two-component developer is almost the same. When the toner adhesion amount of the reference toner image developed with the toner on the image carrier is constant and is less than or equal to a predetermined value, the toner is on the opposite side of the toner in the two-component developer in the triboelectric series. An electrostatic recording method characterized in that the toner image is formed after reducing the toner charge amount in the two-component developer by adding fine particles.