JP2722973B2 - Developing method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing method and an apparatus for use in an image forming apparatus such as an electrophotographic copying machine or a printer for forming a monochromatic or multicolor image, and more particularly, to a developing method for forming an image on a developer carrier. The present invention relates to a developing method and an apparatus for forming a thin layer of a magnetic brush made of a component developer and developing an electrostatic latent image on an electrostatic latent image carrier.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine, an electrostatic latent image formed on an electrostatic latent image carrier is developed by a developing means, and the developed image is transferred onto a recording sheet. The image is copied. At this time, as a developing device for developing the electrostatic latent image formed on the electrostatic latent image carrier, a two-component developer including a toner and a magnetic carrier is brought into contact with the surface of the electrostatic latent image carrier, There have been proposed many methods employing a so-called contact type two-component magnetic brush developing method for visualizing an electrostatic latent image.
This development method requires control of toner concentration,
However, the developing method has become mainstream from the viewpoints of image quality characteristics and maintainability.

However, in the above-described contact type two-component magnetic brush developing method, since the magnetic brush mechanically rubs the surface of the electrostatic latent image carrier, image defects such as so-called brush brushing and sweeping by the magnetic brush occur. There is a disadvantage that it is easy to do. Therefore, in order to avoid this, a number of so-called non-contact developing methods have been proposed in which development is performed without bringing the developer into contact with the surface of the electrostatic latent image carrier.

As a non-contact developing method of this kind, for example, as disclosed in Japanese Patent Application Laid-Open No. Sho 56-144452, a thin layer of a two-component developer comprising a toner and a magnetic carrier (developing magnetic layer) is provided on a developing roll. A developing brush which forms a non-contact state between the surface of the electrostatic latent image carrier and the developing magnetic brush, and further develops the developer layer by giving a disturbance effect by a magnetic, electrical or mechanical element. Have been.

Further, as disclosed in Japanese Patent Application Laid-Open No. 60-176069, a magnetic pole is arranged so as to avoid a position where a developing roll and an electrostatic latent image carrier are closest to each other, and a horizontal magnetic field component is added to a developer layer. Which is developed under an oscillating electric field while acting.

According to these methods, since the magnetic brush is not in contact with the surface of the electrostatic latent image carrier, an image without brushing or sweeping can be reproduced.

[0007]

However, the prior art described above has the following problems. That is, in the developing device disclosed in Japanese Patent Application Laid-Open No. 56-144452, when an image having a high spatial frequency such as a kanji having a large number of strokes is developed, carrier particles adhere to a peripheral portion or a line portion of the line image. There is a problem that so-called carrier adhesion easily occurs. As shown in FIG. 9, in the case of an image having a large number of strokes and a high spatial frequency such as a kanji, as shown in FIG. Since an electrostatic latent image exists, the surface of the latent image carrier is
As shown in FIG. 0, a so-called fringe electric field is generated in which electric fields reinforce each other at the boundary (edge) between the image portion and the background portion.
This occurs because carrier particles charged in a polarity opposite to that of the toner adhere to the peripheral portion or the line portion of the line image.

As described above, when the carrier adheres, the carrier transferred onto the electrostatic latent image carrier comes into contact with the recording paper in the transfer area together with the toner image, so that chipping or missing of the toner image occurs. And the image quality is deteriorated such that the carrier is transferred onto the recording paper and becomes a black spot. Further, when the carrier adheres, the carrier flows out little by little from the inside of the developing device, so that there is a problem that the life of the developer is shortened.

On the other hand, in the developing device disclosed in Japanese Patent Application Laid-Open No. 60-176069, it is necessary to increase the intensity of the oscillating electric field in order to obtain a sufficient developing density. For this reason,
There is also a problem that carrier adhesion is likely to occur due to the action of the oscillating electric field.

As means for avoiding the carrier adhesion, as disclosed in Japanese Patent Application Laid-Open No. 61-160664, the content of the magnetic powder in the magnetic carrier is increased to 40 wt% or more, For setting the strength of the magnetic field in the tangential direction to 200 gauss or more
As disclosed in JP-A-92759, the average particle size of the magnetic carrier is in the range of about 50 μm to 90 μm, and about 2.0 / 100000 to 1.0 / 10,000.
A method in which the magnetic field lines are magnetized within the range of the electromagnetic unit and the intensity of the magnetic field lines in the development area is set to about 200 gauss or more, as disclosed in JP-A-1-177056,
The average particle size of the magnetic carrier is in the range of 30 to 90 μm, and the charge amount per one carrier is 5.0 × 10 ^−13.
A method of ^producing particles having a size of not less than Coulomb and not more than 2.5 × 10 ^-12 Coulomb has been proposed.

However, the methods disclosed in JP-A-61-160664 and JP-A-1-92759 are effective when the carrier particles have a relatively large particle size. When the diameter is small, for example, when the average particle diameter is 50 μm or less, there is a problem that occurrence of carrier adhesion cannot be avoided. Therefore, there is a problem in that when carrier particles are reduced in size in order to obtain a finer image, carrier adhesion occurs.

Further, even when the carrier has a relatively large particle diameter, when the process speed is increased and the rotation speed of the developing roll is increased, the centrifugal force acting on the carrier increases, so that the carrier is likely to adhere. Therefore, it has a problem that it is not suitable for a high-speed process.

Further, when the saturation magnetization of the carrier is increased to increase the magnetic restraining force acting on the carrier, the carrier is less likely to adhere, but the chain structure of the developer that forms the magnetic brush on the developing roll has a problem. Long and coarse, it is difficult to form a uniform thin layer of developer,
There is a new problem that poor uniformity of the image and poor edge reproduction of the line image are likely to occur.

On the other hand, the method disclosed in Japanese Patent Application Laid-Open No. 14177056 has a problem that when the charge amount of the carrier particles increases due to a change in the toner concentration or the environment, the carrier is likely to adhere. .

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art. It is an object of the present invention to suppress the occurrence of carrier adhesion and achieve a sufficient image quality. And to provide a novel developing method and apparatus for obtaining the same.

[0016]

Means for Solving the Problems Claim 1 of the present invention
In the developing method described in the paragraph, a developer carrier having a magnetic pole provided inside is separated from an electrostatic latent image carrier on which an electrostatic latent image is carried, and toner and magnetic material are provided on the developer carrier. In a developing method for developing an electrostatic latent image on a latent image carrier with toner after carrying and transporting a two-component developer composed of a carrier, the developing bias voltage is an AC voltage on which a DC voltage is superimposed. The time required for the AC voltage to change from the voltage at which the electric field for moving the carrier to the electrostatic latent image carrier becomes maximum to the voltage at which the electric field for moving the carrier to the electrostatic latent image carrier becomes minimum is defined as one of the AC components. It consists of a voltage that is less than half of the cycle, and the height of the developer
Set it smaller than the gap between the image carrier and the developer carrier.
Is constructed sea urchin.

[0017]

For example, a magnetic carrier having a saturation magnetization of not less than 20 emu / g and not more than 60 emu / g is used.

Further, for example, the arrangement of the magnetic poles inside the developer carrier at a portion facing the electrostatic latent image carrier is set substantially in the middle of the adjacent magnetic poles.

On the other hand, according to the invention described in claim 4 of the present invention, a developer carrying member provided with a magnetic pole therein is spaced apart from an electrostatic latent image carrying member carrying an electrostatic latent image. After a two-component developer composed of a toner and a magnetic carrier is carried and conveyed on the developer carrying member, the developing device develops the electrostatic latent image on the latent image carrying member with toner. Developing bias applying means for applying a developing bias generates an AC voltage on which a DC voltage is superimposed, and the AC voltage changes the carrier from the voltage at which the electric field for moving the carrier toward the electrostatic latent image carrier becomes maximum. Tomo time field to move to the latent image bearing member is changed to a voltage becomes minimum, the following one period of the half of the AC component was to consist of voltage
In addition, the height of the spike of the developer is
It is configured to be set smaller than the gap between the holding bodies .

[0021]

For example, a magnetic carrier having a saturation magnetization of 20 emu / g or more and 60 emu / g or less is used.

Further, for example, the arrangement of the magnetic poles inside the developer carrier at a portion facing the electrostatic latent image carrier is set substantially at the center of the adjacent magnetic poles.

[0024]

In the developing method according to the first aspect of the present invention, the AC voltage of the developing bias voltage is changed from the voltage at which the electric field for moving the carrier toward the electrostatic latent image carrier becomes maximum.
The time required for the electric field to move the carrier to the electrostatic latent image carrier side to a voltage at which the electric field is minimized is configured to be a voltage that is equal to or less than half of one cycle of the AC component. The time required for the acceleration in the direction of moving toward the carrier to change from the maximum to the minimum is reduced. Therefore, it is difficult for the carrier to reach the electrostatic latent image carrier, and the occurrence of carrier adhesion can be prevented. Further, at this time, the toner is charged to the opposite polarity to the magnetic carrier, so that the toner easily reaches the electrostatic latent image carrier opposite to the carrier. Therefore, sufficient image density can be obtained while preventing carrier adhesion.

Further, a developing device according to a fourth aspect of the present invention has the same function as the above-mentioned developing method.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the illustrated embodiment.

FIG. 1 shows an embodiment of an image recording apparatus to which the developing method according to the present invention is applied.

In FIG. 1, reference numeral 1 denotes a photosensitive drum as an electrostatic latent image carrier.
Is a photoreceptor layer 1b formed in a thin layer on the surface of a cylindrical member 1a made of a conductive material. As the photoconductor layer 1b, for example, a negatively charged organic photoconductor (hereinafter, referred to as OPC) is used. The outer diameter of the photosensitive drum 1 is set to, for example, 100 mm.

By the way, around the photosensitive drum 1, a charger 2 and an exposing means 3 are arranged along the rotation direction thereof.
And an electrophotographic recording means comprising a developing device 4, a pre-transfer corotron 5, a transfer corotron 6, a peeling corotron 7, a cleaner 8, and a photo-static eliminator 9.

In this image recording apparatus, the photosensitive drum 1 is driven to rotate in the direction of the arrow by driving means (not shown). The surface of the photosensitive drum 1 is uniformly charged to a predetermined voltage by the charger 2. Next, exposure corresponding to the image is performed on the surface of the photosensitive drum 1 by the exposure unit 3 to form an electrostatic latent image. The electrostatic latent image formed on the surface of the photosensitive drum 1 is developed by the developing device 4 with toner and visualized. At that time, a predetermined developing bias is applied to the non-magnetic cylindrical sleeve 11 of the developing device 4 by a developing bias power supply 20 as described later. Next, in this way, the photosensitive drum 1
The toner image formed above is charged by the pre-transfer corotron 5 as necessary. Subsequently, after being transferred onto the recording paper 10 by the charging of the transfer corotron 6, the recording paper 10 is separated from the surface of the photosensitive drum 1 by the charging of the separation corotron 7. Thereafter, the recording paper 10 is conveyed to a fixing device (not shown), the toner image is fixed on the recording paper 10, and the image recording is completed.
After the transfer of the toner image and the peeling process of the recording paper 10 are completed, the surface of the photoconductor drum 1 is cleaned by a cleaner 8 to remove residual toner, and then subjected to exposure by an optical neutralizer 9 to remove residual charges. Prepare for the next image recording step.

As the exposure means 3, any exposure means can be used as long as it can perform exposure according to image information. As the exposure means 3, for example, an arbitrary means such as a laser writing device, an LED array, a liquid crystal light valve comprising a uniform light source and a liquid crystal micro shutter can be used according to the purpose. The exposure means 3 may be either one for performing image portion exposure or one for performing non-image portion (background portion) exposure, and is appropriately selected as necessary.

Next, the developing device 4 used in this embodiment will be described with reference to FIG.

The developing device 4 includes a magnet roll 1 inside a rotatable non-magnetic cylindrical sleeve 11 as a developer carrier.
2 are arranged. The magnet roll 12 is fixed such that the photosensitive drum 1 and a substantially intermediate position between the magnetic poles 14 and 15 face each other. In this embodiment, the non-magnetic cylindrical sleeve 1
The developer 16 transported in a state of being attached to the photosensitive drum 1 is regulated to a constant thickness by the layer thickness regulating member 13, and is transported to a developing area facing the photosensitive drum 1 with the rotation of the non-magnetic cylindrical sleeve 11. Is done. In this embodiment, the gap between the photosensitive drum 1 and the non-magnetic cylindrical sleeve 11 is 500 μm.
In addition, the developer layer thickness at the portion facing the photosensitive drum 1 is 35
Each is set to 0 μm. Further, the outer diameter of the non-magnetic cylindrical sleeve 11 is set to 25 mm,
The angle between 4 and the magnetic pole 15 is set to 70 degrees. As described later, a predetermined developing bias is applied to the non-magnetic cylindrical sleeve 11 by a developing bias power supply 20. The developing bias is an AC voltage on which a DC voltage is superimposed.

In the developing device 4, a two-component developer composed of a toner and a magnetic carrier is used as the developer 16.

In this embodiment, the developing bias voltage is an AC voltage on which a DC voltage is superimposed, and the AC voltage is changed from the voltage at which the electric field for moving the carrier to the electrostatic latent image carrier becomes maximum to the carrier voltage. Time to change to a voltage at which the electric field for moving the
It is configured to have a voltage that is equal to or less than half of one cycle of the AC component.

FIG. 4 is a circuit diagram showing a developing bias power supply for applying a developing bias to the nonmagnetic cylindrical sleeve 11 of the developing device 4.

In the drawing, reference numeral 20 denotes this developing bias power supply.
An AC voltage generator 21 for generating an AC voltage and a DC voltage generator 22 for generating a DC voltage are provided. And
The developing bias power supply 20 outputs an AC voltage on which a DC voltage is superimposed as a developing bias.

As shown in FIG. 5, the AC voltage generator 21 is configured to output an AC voltage having a different waveform depending on whether the gradient dv / dt of the AC voltage is positive or negative. I have. That is, when the gradient dv / dt of the AC voltage is positive, the AC voltage generation unit 21 determines that V _AC1 = (V _PP / 2) ×
Outputs the AC voltage V _AC in accordance SIN (ω ₁ t), when dv / dt is negative, V _AC2 = (V _PP /
2) × outputs an AC voltage V _AC in accordance with the SIN (ω ₂ t).

Further, as shown in FIG. 5, the AC voltage generating section 21 generates a time T _{1 during} which the voltage rises from the minimum value V _MIN to the maximum value V _MAX and a voltage T from the maximum value V _MAX to the minimum value V _MIN. An AC voltage different from the falling time T ₂
It can be generated at a predetermined frequency. In addition, the AC voltage generation unit 21 determines the time and the AC that change from the voltage at which the electric field for moving the carrier to the photosensitive drum 1 becomes the maximum to the voltage at which the electric field for moving the carrier to the photosensitive drum 1 becomes the minimum. The ratio of the component to one cycle T (hereinafter referred to as duty ratio (DUTY)), that is, DUTY =
_{T 1 / (T 1 + T} 2) or _{DUTY = T 2 / (T 1} + T
₂ ) is variable. Further, the cycle T of the _AC voltage VAC is T = T ₁ + T ₂ = 1 / Freq. = 1
Although it is constant at / 1500, the amplitude V _PP of the _AC voltage VAC is variable.

As described above, the duty ratio (DUT
The reason why Y) is expressed in two different forms is that the direction of the electric field acting on the carrier is reversed depending on the polarity of the developing bias and the polarity of the carrier. That is, FIG.
As shown in (2), when the polarity (minus) of the developing bias and the polarity (minus) of the toner are the same, that is, when reversal development is performed, the voltage at which the electric field for moving the carrier to the photosensitive drum 1 becomes maximum. Is _VMAX shown in FIG. 7, and the voltage at which the electric field for moving the carrier toward the photosensitive drum 1 is minimized is _VMIN . Therefore, the duty ratio (DUTY) in this case is given by T _A / T _B.

On the other hand, the DC voltage generator 22 is a known DC voltage generator.
The DC power supply 23 comprises
23 is the output voltage V_DCIs variable. This output power
Pressure V _DCIs output to the capacitor C2. This capacitor
C2 bypasses the AC output current superimposed on the DC voltage
It fulfills the function of causing Further, the output voltage V
_DCIs the external V_DCControllable by control signal
ing.

Next, the configuration of the AC voltage generating section 21 will be described in more detail. The AC voltage generating section 21 includes a waveform signal generating means 24. There is provided a waveform signal generating means 24 for generating a waveform signal for determining a voltage waveform. The waveform signal generating means 24 has a first binary counter 25, and the first binary counter 25 and the first binary counter 25
Oscillator 26 connected to a binary counter 25
And the gate circuits therearound determine the count-up period of the address output from the second binary counter 29 to the PROM 30 described later, depending on whether the count value of the second binary counter 29 is 00h to 7Fh or 80h to FFh. It is a circuit for changing in.

That is, the first binary counter 2
5, a pulse oscillator 26 is connected via NAND circuits 27 and 28. The pulse oscillator 26 generates a clock pulse of a predetermined frequency (for example, 2.88 MHz). The clock pulse CLK output from the pulse oscillator 26 is supplied to a first binary counter via NAND circuits 27 and 28. 25 CLK DWN and CLK UP terminals. Further, duty control data is input to the first binary counter 25. The duty control data can be appropriately set by a duty control data setting means (not shown).

Then, the first binary counter 25
Is the output of the second binary counter 29 (M
If SB) is FALSE (00h to 7Fh), the FALSE signal is sent to the NOT circuit and the NAND circuit 27.
The operation of counting down one by one from the duty control data every time a clock is input from the pulse oscillator 26 is repeated. O
A clock is output from the (BORROW OUT) terminal every time a series of countdown operations is completed. Therefore, the cycle of the clock (CLKOUTPUT) output from the first binary counter 25 is the cycle of the pulse oscillator 26 multiplied by the duty control data. On the other hand, in the first binary counter 25, the output (MSB) of the second binary counter 29 is TRUE (80h to FF).
h), the TRUE signal is output to the NAND circuit 28.
To the CLKUP terminal via a clock signal, and every time a clock is input from the pulse oscillator 26, the duty control data
The operation of counting up is repeated, and C.I. O (CA
RRY OUT), a clock is output each time a series of count-up operations is completed. Therefore, the clock (CLK) output from the first binary counter 25
The cycle of OUTPUT) is the cycle of the pulse oscillator × (1
5-duty control data).

Next, the clock output (CLK OUTPUT) of the first binary counter 25 is input to the second binary counter 29. The second binary counter 29 repeats the counting operation based on the clock output (CLK OUTPUT) of the first binary counter 25, outputs a signal corresponding to the count value from the output terminal Q, and outputs the other output terminal Q (MSB) to the first binary counter 25 to FALSE (00h to 7h).
A signal for identifying Fh) and TRUE (80h to FFh) is output.

By the way, the second binary counter 2
9 is performed based on the clock output (CLK OUTPUT) of the first binary counter 25. The clock output (CLK OUTPUT) of the first binary counter 25 is, as described above, the FAL.
SE (00h-7Fh) and TRUE (80h-F)
The output cycle of the clock is different from the case of Fh).
Therefore, the count value output from the second binary counter 29 is output at different periods between FALSE (00h to 7Fh) and TRUE (80h to FFh).

The output signal from the second binary counter 29 is input to the PROM 30. This PR
As shown in FIG. 6, the OM 30 stores data corresponding to a sine wave waveform at addresses 0d (00h) to 255d (7
Fh) is stored in advance as data of the ROM.
The PROM 30 sequentially outputs the waveform data corresponding to the sine wave waveform of the corresponding address according to the address signal input from the second binary counter 29. Therefore, when a signal is input at a constant period from the second binary counter 29, the PROM 30 outputs a waveform signal similar to a sine wave waveform as shown in FIG.

However, the second binary counter 2
9 is based on the duty control data as described above, FALSE (00h to 7Fh) and T
RUE (80h to FFh) is output at a different cycle. Therefore, the PROM 30
Outputs data corresponding to the waveform of the sine wave at different periods between the rising portion (the portion where the gradient dv / dt is positive) and the falling portion (the portion where the gradient dv / dt is negative) of the sine wave. Will be.

Further, the output data of the PROM 30 is input to the DAC 31. This DAC 31 is shown in FIG.
A current output of an analog value is output from the output terminal OUT1 according to the output data of the PROM 30 indicated by. DA above
The C31, V _AC control signal is input, the DA
Current output OUT from the C31 is adapted to be modulated linearly by V _AC control signal. Therefore, DAC
The amplitude of the current output OUT from 31 is controllable linearly by V _AC control signal.

Next, the current output OUT of the DAC 31
Is input to the I / V converter 32 and is subjected to I / V (current / voltage) conversion by the I / V converter 32.
The output of the I / V converter 32 is supplied as a waveform signal output to the buffer amplifier 33 via the capacitor C.
Is output to At this time, the I / V converter 32
As desired AC output voltage V _AC control signal is obtained, the gain is made adjustable by a variable resistor R1.

As a result, an AC voltage corresponding to the waveform signal output from the waveform signal generating means 24 is output from the buffer amplifier 33 as described above. The AC voltage output from the buffer amplifier 33 is boosted by the transformer T, superimposed on the DC voltage, and output as a developing bias from the output terminal _Vout to the second developing device 4b.

[0052] Now, the output V _AC of the AC voltage is 1500V, when the output of the buffer amplifier 33 was set to 15V,
The transformer T is designed to have a boost ratio of 100. The buffer amplifier 33 is a power buffer voltage gain 1, the output AC voltage V _AC is a an output voltage waveform of the waveform signal generating means 24 obtained by step-up ratio multiple of the transformer T.

[0053] Thus, the AC voltage V _AC output from the AC voltage generator 21, the duty ratio (DUT
Y = T ₂ / (T ₁ + T ₂ )) can be changed according to the duty control data. That is, as shown in FIG. 5, the AC voltage generating section 21 reduces the electric field for moving the carrier to the photosensitive drum 1 from the voltage at which the electric field for moving the carrier to the photosensitive drum 1 becomes maximum. The time T _{2 at} which the voltage changes is T ₂ = cycle of the pulse oscillator 26 × (15−duty control data) × 1
28, and the remaining T ₁ is T ₁ = cycle of pulse oscillator 26 × duty control data × 128. here,
The number 128 indicates half the number of data for one cycle stored in the PROM 30. Therefore, one cycle T of the AC voltage is T = T ₁ + T ₂ = cycle of the pulse oscillator 26 × 15 × 128, and the duty ratio is DUTY =
Duty control data / 15. Therefore, when the frequency of the pulse oscillator 26 is 2.88 MHz, 150
An output of 0 Hz is obtained, and the duty ratio of the _AC voltage VAC can be controlled as shown in Table 1 according to (15-duty control data) / 15.

[0054]

[Table 1]

Although the AC voltage generator of this embodiment has been described based on the configuration of FIG. 4, the duty ratio of the _AC voltage VAC can be changed by changing the first binary counter 26 and its peripheral circuits. It is clear that higher resolution control is possible. In FIG. 4, the case where the waveform signal generating means 24 is provided inside the power supply 20 has been described.
Needless to say, the power can be easily generated by the converter, and the power supply 20 may be constituted only by the portion after the waveform signal generating means. Further, in this embodiment, the waveform signal generating means 24 is constituted by a digital circuit. However, it is needless to say that the waveform signal may be generated by an analog circuit, and may be replaced with an analog circuit.

In the above configuration, in the image recording apparatus according to this embodiment, development is performed by the developing device as follows. That is, the electrostatic latent image formed on the photosensitive drum 1 is developed by the developing device 4. At this time, a non-magnetic cylindrical sleeve 11 of the developing device is supplied with a developing bias power supply 20 to have a waveform as shown in FIG.
A developing bias voltage in which a predetermined DC voltage is superimposed on an AC voltage is applied. Therefore, the negatively charged toner in the developer flies between the photosensitive drum 1 and the non-magnetic cylindrical sleeve 11 by the electric field formed by the AC component of the developing bias, and the toner on the photosensitive drum 1 Develop the electrostatic latent image.

On the other hand, the positively charged carrier having a polarity opposite to that of the toner is kept magnetically attracted to the surface of the nonmagnetic cylindrical sleeve 11 by the electric field formed by the AC component of the developing bias. Vibrates so as to reciprocate to the photosensitive drum 1 side and the non-magnetic cylindrical sleeve 11 side.

At this time, assuming that the charge amount of the carrier is q, the electric field E formed by the developing bias voltage and the surface potential of the photosensitive drum 1 gives F = qE
A force F acts. Accordingly, the vibration state of the carrier is given by ma = qE ·, where the mass and acceleration of the carrier are m and a, respectively, and the magnetic attraction force acting on the carrier is F _M.
It can be represented by the equation of motion F _M. However,
Force and acceleration are positive in the direction from the non-magnetic cylindrical sleeve 11 toward the photosensitive drum 1.

Here, as shown in FIG. 7, the AC voltage of the developing bias is changed from the voltage V _MAX at which the electric field for moving the carrier to the photosensitive drum 1 becomes maximum, to the carrier being moved to the photosensitive drum 1. The time for changing the electric field to be applied to the minimum voltage V _MIN is set to be equal to or less than half of one cycle of the AC component. Accordingly, the time during which the acceleration a acting on the carrier and moving the magnetic carrier toward the photosensitive drum 1 changes from the maximum to the minimum depends on the acceleration a moving the magnetic carrier toward the non-magnetic cylindrical sleeve 11. Changes from maximum to minimum
The distance that the carrier moves toward the photosensitive drum 1 becomes shorter. As a result, the carrier is less likely to move to the photosensitive drum 1 side, and the occurrence of carrier adhesion on the photosensitive drum 1 can be effectively prevented.

At this time, since the toner is charged to the polarity opposite to that of the carrier, a force opposite to that of the carrier acts and the toner is easily developed on the photosensitive drum 1. Therefore, a sufficient image density can be obtained while preventing carrier adhesion. Moreover, since the carrier is difficult to electrostatically reach the photosensitive drum 1, the average particle diameter is 50%.
Even if a carrier having a small particle diameter of μm or less is used, the occurrence of carrier adhesion can be effectively prevented. Also, even in the high-speed process, even if the rotation speed of the developing roll becomes high,
The occurrence of carrier adhesion can be prevented. further,
Even if a carrier having a small saturation magnetization is used, the occurrence of carrier adhesion can be prevented.

Further, even if the charge amount of the carrier increases due to a change in toner concentration or environment, the occurrence of carrier adhesion can be prevented.

Experimental Example 1 Next, the present inventors conducted an experiment for confirming the effect of preventing carrier adhesion using the image recording apparatus shown in FIG. Exposure was performed by image area exposure, and development was performed by reversal development. The toner is a negatively charged black toner, and the carrier is positively charged. The surface moving linear velocity of the photosensitive drum 1, that is, the process speed is 2
It was set to 00 mm / s.

Hereinafter, the image forming process of Experimental Example 1 will be described with reference to FIG.

The surface of the OPC photosensitive drum 1 was uniformly charged to -600 V by the charger 2 (FIG. 3A). Next, the image area was exposed to laser light to form a negative latent image having an exposed area potential of -100 V (FIG. 3B). Then, the negative latent image was reversal-developed by the developing device 4 (FIG. 3C). Further, in order to transfer the carrier adhered on the photosensitive drum 1 onto the recording paper 10 together with the toner, uniform negative charging was performed by the pre-transfer corotron 5.

A developing bias voltage was applied to the non-magnetic cylindrical sleeve 11 of the developing device 4 by a developing bias power supply 20. The DC component of the developing bias voltage was set to -500 V in order to prevent occurrence of background fog.

As the carrier, a so-called magnetic powder-dispersed resin carrier in which magnetic powder was dispersed in a resin was used. The average particle size of the carrier was 45 μm, the density was 2.2 g / cm ³ , and the saturation magnetization was 40 emu / g.

Here, the relationship between the carrier adhesion and the image density was examined by using a 1500 Hz sine wave as the AC component of the second developing bias and changing the AC voltage V _PP and the duty ratio. FIG. 7 shows a developing bias waveform. The AC voltage V _PP indicates | V _MAX −V _MIN |. As described above, the duty ratio changes from the voltage at which the electric field in the direction of moving the carrier to the photoconductor drum 1 becomes maximum to the voltage at which the electric field in the direction of moving the carrier to the photoconductor drum 1 becomes minimum. Time T _A and one cycle T _{B of the} AC component
Shows the ratio of

In evaluating the results, as shown in FIG. 8, the carrier adhesion was evaluated at a so-called alternating line portion in which a line image and a background portion were arranged at a constant period. The cycle of the alternating line is 2 cycles / mm, and the ratio of the image portion to the background portion is
1: 1. Then, an image analysis device (product name: LUZ)
EX-5000) was used to measure the area ratio of carrier particles on the background. The area ratio of the carrier particles is 1.0
% Or less, there is no practical problem.
○ indicates 1.0% or less, and X indicates 1.0% or more.

The image density was measured using a reflection densitometer (trade name:
X-RITE310) was measured for the solid image. When the image density is 1.3 or more, both the solid image and the line image are sufficient. Table 2 was obtained as a result.

[0070]

[Table 2]

As can be seen from Table 2, when the AC voltage V _PP is the same, the smaller the duty ratio, the smaller the carrier adhesion. That is, the AC component is defined as a time T _A from the voltage at which the electric field in the direction of moving the carrier to the photosensitive drum 1 becomes maximum to the voltage at which the electric field in the direction of moving the carrier to the photosensitive drum 1 becomes minimum. Is set to be equal to or less than half of one cycle T _B , the occurrence level of carrier adhesion is reduced. When the AC voltage V _PP is 0.75 kV or less,
There was a tendency for the image density to decrease. Also, the AC voltage V
_{When the PP} was 2 kV or more, the carrier adhesion amount tended to exceed the allowable level. Therefore, the duty ratio is set as described above, and the AC voltage V _PP is changed from 0.75 kV to 2 kV.
If it is set between V, a sufficient image density can be obtained without the carrier adhesion amount exceeding the allowable level.

Experimental Example 2 The present inventors conducted experiments using the image recording apparatus shown in FIG. 1 while changing the type of carrier.

As the carrier, the same magnetic powder-dispersed resin carrier as in Experimental Example 1 was used, and the average particle diameter and the saturation magnetization were changed. The carrier type is an average particle diameter of 20 μm, a saturation magnetization of 10 emu / g, an average particle diameter of 20 μm, a saturation magnetization of 20 emu / g, an average particle diameter of 60 μm, and a saturation magnetization of 60 emu.
mu / g, average particle diameter 60 μm, saturation magnetization 80 emu /
g) were used. Other conditions were the same as those in Experimental Example 1.

Here, a sine wave of 1500 Hz and V _PP = 1.5 (kV) was used as an AC component of the developing bias voltage. Other conditions were the same as those in Experimental Example 1. The relationship between carrier adhesion, image density, and edge failure of a line image was investigated by changing the duty ratio. The edge defect of the line image was visually evaluated. A state where no jaggedness was visually observed was evaluated as ○, a level where there was a small amount of jaggedness but no practical problem was indicated as Δ, and an unusable level was evaluated as ×. Table 3 was obtained as a result.

[0075]

[Table 3]

From Table 3, it can be seen that when the magnetic binding force acting on the carrier is small, that is, when the carrier particle diameter is small and the saturation magnetization is small, carrier adhesion is more likely to occur.
Also, it can be seen that when the magnetic restraining force acting on the carrier is large, that is, when the carrier particle size is large and the saturation magnetization of the carrier is large, the edge failure of the line image tends to occur.

If the saturation magnetization of the carrier is 20 emu / g or more and 60 emu / g or less and the duty ratio is 0.5 or less, a sufficient image quality can be obtained without the carrier adhesion amount exceeding the allowable level.

In the above embodiment, a sine wave is used as the waveform of the AC component of the developing bias. However, the same effect can be obtained when a triangular wave or another waveform is used.

In the above embodiment, the non-contact developing method using a two-component developer has been described. However, the present invention can be applied to a contact developing method using a two-component developer. Further, the present invention can be applied to a contact magnetic brush developing method using a two-component developer and having a low rubbing force.

Further, in the above-described embodiment, the magnetic pole arrangement inside the developer carrier at a portion facing the electrostatic latent image carrier is substantially intermediate between adjacent magnetic poles of different polarities.
The polarity may be set substantially at the middle between adjacent polarities of the same polarity. Further, the present invention is also applicable to a developing method in which substantially the magnetic pole inside the developer carrier is opposed to the electrostatic latent image carrier.

Further, in the above embodiment, the photosensitive member is used as the electrostatic latent image carrier, but the discharge recording head used in the electrostatic printer is used by using the dielectric material as the electrostatic latent image carrier. Alternatively, an electrostatic latent image may be formed by an ion flow control head or the like disclosed in JP-A-59-190854.

Further, in the above-described embodiment, the description has been given of the monochromatic image recording apparatus. However, the present invention can be similarly applied to a color image recording apparatus.

[0083]

According to the present invention, the developing bias voltage is an AC voltage on which a DC voltage is superimposed, and the AC voltage moves the carrier toward the electrostatic latent image carrier. Since the time required to change from the voltage at which the electric field is maximized to the voltage at which the electric field for moving the carrier to the electrostatic latent image carrier is minimized, the voltage is set to be less than half of one cycle of the AC component, A sufficient image density can be obtained while preventing carrier adhesion.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a main part configuration diagram showing a developing device used in the image forming apparatus.

FIG. 3 is an explanatory diagram of a potential showing an image forming process.

FIG. 4 is a circuit diagram showing a developing bias power supply.

FIG. 5 is a waveform diagram showing an AC component of a developing bias.

FIG. 6 is an explanatory diagram showing waveform data stored in a PROM.

FIG. 7 is a waveform diagram showing a developing bias voltage.

FIG. 8 is an explanatory diagram of an alternation line.

FIG. 9 is an explanatory diagram of a photoconductor potential in an alternating line portion.

FIG. 10 is a waveform diagram showing a developing electric field in an alternating line portion.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Photoreceptor drum, 3 exposure means, 4 developing device, 20
Power supply for developing bias.

Continuation of front page (72) Inventor Taku Aoshima 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd. (56) References JP-A-4-356076 (JP, A)

Claims (6)

(57) [Claims] 1. A developer carrier having a magnetic pole provided therein is spaced apart from an electrostatic latent image carrier on which an electrostatic latent image is carried, and a toner carrier and a magnetic carrier are provided on the developer carrier. After carrying and transporting the two-component developer, the developing method of developing the electrostatic latent image on the latent image carrier with toner,
The developing bias voltage is an AC voltage on which a DC voltage is superimposed, and the AC voltage moves the carrier toward the electrostatic latent image carrier from a voltage at which the electric field for moving the carrier toward the electrostatic latent image carrier becomes maximum. the time varying from voltage electric field is a minimum, it becomes a voltage less than half of one period of the AC component, the bristles height of the developer, the electrostatic latent image bearing
A developing method characterized in that the gap is set smaller than the gap between the developer and the developer carrier . 2. A magnetic carrier having a saturation magnetization of 20 emu.
2. The developing method according to claim 1, wherein the concentration is not less than / emu / g and not more than 60 emu / g. 3. A pole arrangement of the developer bearing body portion in a position facing the latent electrostatic image bearing member, a first claims, characterized in that set in the substantially intermediate adjacent magnetic poles or paragraph 2 Symbol <br/> The developing method described above. 4. A developer carrier having a magnetic pole provided inside the electrostatic latent image carrier on which an electrostatic latent image is carried, and a toner carrier and a magnetic carrier are provided on the developer carrier. After carrying and transporting the two-component developer, the developing device develops the electrostatic latent image on the latent image carrier with toner,
Developing bias applying means for applying a developing bias to the developer carrier generates an AC voltage on which a DC voltage is superimposed, and the AC voltage is changed from a voltage at which the electric field for moving the carrier toward the electrostatic latent image carrier becomes a maximum. , the time for the electric field to move the carrier to the electrostatic latent image bearing member is changed to a voltage becomes minimum, to consist voltage less than half of one period of the AC component
In both cases, the developing height of the developer is
A developing device characterized in that it is set smaller than the gap between the agent carriers . 5. A magnetic carrier having a saturation magnetization of 20 emu.
5. The developing device according to claim 4, wherein the developing ratio is not less than / emu / g and not more than 60 emu / g. 6. The magnetic pole arrangement of the developer bearing body portion in a position facing the latent electrostatic image bearing member, a fourth claims, characterized in that set in the substantially intermediate adjacent magnetic poles or paragraph 5 Symbol developing device.