JP2000066490A - Developing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device and the image forming device capable of stably obtaining the excellent image by preventing the absorption or the void caused by the non-contact development, and particularly restraining the suck or the void remarkably caused when the toner grain size is small. SOLUTION: This developing device, provided with a developing sleeve carrying the developer held in a state of non-contact with respect to a photoreceptor, capable of developing the electrostatic latent image formed on the photoreceptor by the developer, is allowed to apply a voltage superimposing the intermittently suspended AC component over the DC component, on the developing sleeve, and to satisfy the relational expression shown as under, TP/(TP+TB)>($4 Emax)+11.3+0.4(f-4), 0.1<TP/(TP+TB)<0.9, Emax=(1/2.VAC+VDC-VL)/(d), in the above expression, the maximum electric field is expressed as Emax, AC voltage as VAC, DC voltage as VDC, latent image potential as VL, pulse part time as TP, blank part time as TB, pulse part frequency as (f), and minimum proximity distance between developing sleeve and photoreceptor as (d).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for forming a visible image by developing an electrostatic latent image on an image carrier, and a copying machine, a printer, a facsimile machine, etc., having the developing device for forming an image. The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, a developer is carried on the surface of a developer carrier, and the developer is conveyed to a development area facing an image carrier carrying an electrostatic latent image. 2. Description of the Related Art There is known an image forming apparatus that develops an electrostatic latent image to form a visible image while continuously superimposing an AC voltage on a voltage and applying the AC voltage.

In developing an electrostatic latent image, contact development such as magnetic brush development in which a developer layer carried on a developer carrier is rubbed against the image carrier to develop the toner, and toner in a development area is developed. 2. Description of the Related Art Non-contact development is known in which particles are caused to fly from a developer carrier to an image carrier in an air layer to develop an electrostatic latent image.

[0004]

FIG. 6 is an enlarged schematic view showing the movement of toner in a developing area where an image carrier and a developer carrier are opposed to each other.

For example, when non-contact development is performed in the above-described developing area, at the edge portion where there is a gap in the latent image potential on the image carrier, the toner near the edge portion on the opposite developer carrier (developing sleeve) is used. t is sucked into the high-density portion (potential difference large region), and the toner adhesion amount near the boundary increases more than expected, and the image density increases. In addition, the area to which a large amount of the toner t adheres has been widened (hereinafter, this phenomenon is referred to as “suction”).

Conversely, the toner t adhering to the low density portion (small potential difference area) adjacent to the high density portion is sucked into the high density portion as shown by the broken line in FIG. And became white in some cases.
This phenomenon is called "white spots").

[0007] These problems of suction and white spots occur remarkably in the non-contact developing method.

The mechanism of the occurrence of the suction and white spots will be further described with reference to the schematic diagram of FIG.

In the air layer from when the toner separates from the developer carrying member (developing sleeve) and adheres to the image carrying member (photosensitive member), the area (space) on the low-density portion changes from the region (space) on the high-density portion. ) Have lines of electric force (arrows shown). These lines of electric force act perpendicular to the equipotential lines in the figure.

Normally, the amount of toner adhering to an electrostatic latent image on an image carrier is uniquely determined by the latent image potential. However, in actuality, the toner t on the developer carrier opposed to the low-density portion flies along the lines of electric force, so that the amount of toner adhering to the high-density portion of the edge portion is determined based on the toner potential estimated from the latent image potential. It is considered that the amount of toner adhering more than the adhering amount and the amount of toner adhering to the low density portion side of the edge portion becomes smaller than the amount of toner adhering expected from the latent image potential.

That is, when an AC continuous wave is applied to the developer carrier, the direction of the electric field due to the AC voltage changes every half cycle, and the direction in which the toner t moves changes each time.
The flying speed of the toner near the point where the moving direction of the toner t changes attenuates, the toner t easily follows the lines of electric force shown in FIG. 6, the amount of adhered toner on the high-density portion side of the edge portion increases, appear. Due to this suction, the amount of toner adhered to the low density portion side of the edge portion decreases, and white spots occur.

Further, even if the toner t flies to the low density portion of the image carrier, it also absorbs that the toner t finally landed on the high density portion when the bouncing is repeated on the image carrier, resulting in white spots. It is considered the cause.

In non-contact development, in order to maintain the developer layer on the developer carrier and the image carrier surface in a non-contact state, the distance between the developer carrier surface and the image carrier surface is increased by contact development. It needs to be set longer than in the case. With this distance setting, the bending of the lines of electric force became large, and suction and white spots became conspicuous.

The phenomenon of suction and white spots is not so noticeable as in non-contact development, but also occurs in contact development.

A blank portion for intermittently stopping an AC component is provided in a voltage waveform in which a bias voltage obtained by superimposing a DC voltage on an AC voltage is applied to the sucking and white spots. It has recently been discovered that the problem can be solved by applying an applied voltage having a waveform (blank pulse waveform) for applying only the component to the developer carrying member.

A known example of a conventional developing method using a blank pulse waveform as a developing bias voltage will be described below. JP 7
JP-A-311497, JP-A-8-160725, JP-A-5-35063, JP-A-60-134262, JP-A-60-53968, JP-A-7-295373, JP-A-6-348117, JP-A-6-348117 No. 7-92786.

However, while the developing methods shown in these known examples are effective against suction and white spots,
In the blank portion where the application of the AC voltage is stopped, since the AC voltage that triggers the toner to separate from the surface of the developer carrying member is not applied, the amount of the separated toner is reduced, compared to the continuous waveform portion that is not the blank portion. There is a problem that the developability (toner adhesion) is reduced as a whole.

An object of the present invention is to provide an image forming apparatus which prevents the above-mentioned sucking and white spots and prevents a decrease in developability (toner adhesion).

In recent years, a toner having a small particle size has been employed to improve image quality. However, a toner having a small particle diameter is easily affected by the above-mentioned line of electric force.

Accordingly, the present invention provides an image forming method for stably forming a high-quality image having high resolution and high gradation by preventing suction and white spots which occur remarkably when the toner particle size is small. It is intended to provide a device.

[0021]

A developing device according to the present invention for achieving the above object has a developer carrying member for carrying a developer in a non-contact state with respect to an image carrying member. A developing device for developing a formed electrostatic latent image with a developer, wherein a voltage obtained by superimposing an intermittently resting AC component on a DC component is applied to the developer carrier, and the following relational expression: Is satisfied.

T _P / (T _P + T _B )> (− 4Emax) +
During 11.3 + 0.4 (f-4) 0.1 <T P / (T P + T B) <0.9 Emax = (1 / 2V AC + │V DC │-│V L │) / d wherein emax [MV / m]: toner direction of maximum electric field V _AC that moves toward the image bearing member from the developer carrying member [V]: AC voltage V _DC applied to the developer bearing member [V]: the developer carrying member applying direct current voltage V _L [V]: image portion latent image potential T _P on the image bearing member [msec]: pulse portion of the AC component applied to the developer carrier time T _B [msec]: a developer carrying member The pause time of the applied AC component f [kHz]: The frequency of the pulse portion of the AC component applied to the developer carrier d [mm]: The closest distance between the developer carrier and the image carrier The above object is also achieved. The image forming apparatus according to the present invention is applied to an image forming apparatus that forms an image of a plurality of colors by superimposing them on an image carrier. And a developing device according to any one of claims 1 to 3 for each color of the plurality of color images, and an electrostatic latent image on the image carrier for each color of the plurality of color images. And developing the electrostatic latent image by the developing device to form a superimposed image of a plurality of colors.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of an embodiment of the present invention, the structure of a color printer as an example of the image forming apparatus of the present invention and its operation will be described with reference to the sectional view of FIG.

In this color printer, after each color toner image sequentially formed on the image carrier is superimposed, the color image is formed on the recording paper by a transfer unit once, and then the image is formed by a separating unit. This is a color image forming apparatus that separates recording paper from the surface of a carrier.

In FIG. 1, reference numeral 1 denotes a photoreceptor drum (photoreceptor) serving as an image carrier, which is formed by coating an organic photoreceptor layer on a drum base, and is rotated in a clockwise direction as shown in FIG. 2 is a scorotron charger (hereinafter referred to as a charger)
, The photosensitive member charging potential V _{H having a} high potential with respect to the peripheral surface of the photosensitive member 1
The uniform charging of, given by a corona discharge by a grid and the corona discharge wire which is the potential held at grid potential V _G. Prior to the charging by the charger 2, in order to eliminate the history of the photoconductor 1 up to now, exposure is performed by a pre-charging static eliminator (PCL) 8 using a light emitting diode or the like, and the peripheral surface of the photoconductor 1 is neutralized. Keep it. The history on the photoreceptor 1 refers to an electrostatic latent image pattern remaining on the photoreceptor 1 formed by charging and image exposure during preceding image formation.

After the photosensitive member 1 is uniformly charged, an exposure device (image exposing means) 3 performs image exposure based on an image signal to form an electrostatic latent image on the surface of the photosensitive member 1. The exposure device 3 performs main scanning through a rotating polygon mirror, fθ lens, cylindrical lens, and reflection mirror using a laser diode (not shown) as a light emitting light source, and forms a latent image by rotation (sub-scanning) of the photoconductor 1. Is done. In this embodiment, the portion where the toner is to be adhered is exposed, and the absolute potential of the latent image potential _VL of the image portion (exposed portion) on the photoconductor 1 is changed to the photoconductor charge on the photoconductor 1. than the absolute potential of V _H to form a reversal latent image becomes a low potential _{(| V H |> | V} L |).

A plurality of developing devices each including a two-component developer including a toner such as yellow (Y), magenta (M), cyan (C), and black (K) and a carrier are provided on the periphery of the photosensitive member 1. 4Y, 4M, 4C, 4K developing device 4
Is provided.

First, development of yellow of the first color is performed by a developer carrier (developing sleeve) 41 which includes a magnetic field generating means 42 composed of a plurality of magnets and holds and rotates the developer. The developer has a core of magnetite and an insulating resin coated around the core.
And a toner having a particle diameter of 4 to 10 μm obtained by adding a color-dependent pigment, a charge control agent, silica, titanium oxide, etc., using polyester as a main material, and a developer layer regulating member described later. The developer layer 43 regulates the developer layer thickness on the developing sleeve 41 to 100 to 600 μm, and is conveyed to the developing area.

The gap between the developing sleeve 41 and the photosensitive member 1 in the developing area is 0.5 to 1.0, which is larger than the thickness of the developer layer.
As mm, an AC voltage V _AC and the DC voltage V _DC is applied to overlap therebetween. DC voltage V _DC and the photosensitive member charge potential V _H, for charging the toner are the same polarity, the AC voltage V _AC
The toner given the opportunity to leave the carrier does not adhere to the portion of the DC voltage V _DC from the absolute potential high photoconductor charge potential V _H, lower image portion absolute potential than the DC voltage V _DC (exposed portion adhering to a portion of the latent image potential V _L of), visualized (reversal development) is carried out.

After the visualization of the first color is completed, the magenta image forming process of the second color is started, and the charging device 2 performs uniform charging again, and the latent image based on the image data of the second color is exposed by the exposure device 3. It is formed. At this time, the charge elimination by the PCL 8 performed in the image forming process of the first color is not performed because the toner attached to the image portion of the first color scatters due to a sharp decrease in the surrounding potential.

[0031] Among the photosensitive surface which is charged to the charging potential V _H over the entire surface of the photosensitive member 1 the circumferential surface again, one for the portion having no color image similar latent image and the first color is made development However, in the portion where the image of the first color is developed again for the portion where the image of the first color is present, the latent image potential _VL of the exposed portion of the first color is reduced by the influence of the light shielding by the toner attached to the first color and the charge of the toner itself. also a latent image of a slightly higher voltage V _M is formed, developed in accordance with the voltage of the DC bias voltage V _DC and the potential V _M is performed.

For the third color cyan and the fourth color black, an image forming process similar to that for the second color magenta is performed, and four color toner images are formed on the peripheral surface of the photosensitive member 1.

The developing devices 4Y, 4M, 4C, and 4K include:
New toner of each color is supplied from the toner cartridge 5 (Y, M, C, K).

On the other hand, the half-moon roller 2
1 recording medium (transfer paper, etc.) P unloaded through
Is temporarily stopped near the position of a registration sensor (not shown) via the intermediate sheet feeding roller pairs 22A and 22B, and when the transfer timing is adjusted, the registration roller pair 23 of the sheet feeding unit is stopped.
The paper is fed to the transfer area by the rotation of.

In the transfer area, a transfer device 6 such as a transfer roller for applying a voltage for transferring a toner image formed on the peripheral surface of the photoreceptor 1 to the recording medium P in synchronization with the transfer timing is used. The four color toner images are collectively transferred onto the recording medium P while sandwiching the recording medium P pressed against and fed to the recording medium P.

Next, the recording medium P is neutralized by the sawtooth electrode 7 and separated from the peripheral surface of the photoreceptor 1 to form the fixing device 2.
4, and the toner transferred by heating and pressing of the heat roller (upper roller) 241 and the pressure roller (lower roller) 242 is welded, and then the paper discharge roller pair 25A, 25
B and 25C, and are discharged onto a discharge tray 26 outside the apparatus. After passing through the recording medium P, the transfer device 6 is retracted and separated from the peripheral surface of the photoconductor 1 to prepare for the formation of the next toner image.

On the other hand, the photosensitive member 1 from which the recording medium P is separated is
The residual toner is removed and cleaned by the pressure contact of the blade 91 of the cleaning device 9, and is again subjected to the charge removal by the PCL 8 and the charge by the scorotron charger 2 to enter the next image forming process. The blade 91 moves immediately after cleaning the surface of the photoconductor 1 and retracts from the peripheral surface of the photoconductor 1. The waste toner scraped into the cleaning device 9 by the blade 91 is discharged by a screw 92 and then stored in a waste toner collecting container (not shown).

FIG. 2 shows a plurality of sets of developing units 4Y and 4Y according to the present invention.
FIG. 4 is a sectional view of a developing device 4 including 4M, 4C, and 4K.
In these developing units 4Y, 4M, 4C, and 4K, the respective developing sleeves 41Y, 41M, 41C, and 41K are arranged in parallel in the vertical direction so as to face the photosensitive surface of the photosensitive member 1.

These plural sets of developing units 4Y, 4M, 4C,
Since 4K has almost the same structure, the following description will be made on behalf of the developing device 4Y.

FIG. 3 is a sectional view of the developing device 4Y.

In the figure, 40 is a developer accommodating section for accommodating a two-component developer composed of toner and carrier, 41 is a developing sleeve for carrying and transporting the developer, and 42 is a plurality of fixing sleeves inside the developing sleeve 41. A magnetic field generating means (hereinafter, referred to as a magnet roll) having a magnet body, 43 is a developer layer regulating member (a developer ear) formed of a magnetic round bar for regulating the thickness of the developer layer on the developing sleeve 41 to a predetermined amount. (A member that restricts standing). Reference numeral 44 denotes a scraper for removing the developer adhered on the developing sleeve 41 after the development, and reference numeral 45 denotes a paddle wheel-shaped developing device that conveys the developer removed from the peripheral surface of the developing sleeve 41 by the scraper 44 to a developer stirring section. A developer conveying roller 46 is a paddle wheel-shaped developer supply roller for replenishing the developing sleeve 41 with the developer from a developer stirring section, and 47A and 47B are developer stirring screws for stirring the developer in the developer stirring section. The illustrated arrows indicate the direction of rotation of each roller. Note that, instead of the scraper 44 that is in pressure contact with the developing sleeve 41, a magnet may be disposed as a developer removing unit in close proximity without contacting the outer periphery of the developing sleeve 41.

In the developing sleeve 41, a plurality of N poles,
A magnet roll 42 in which N1, N2, and N3 and a plurality of S poles and S1 and S2 are alternately arranged is fixed (five pole arrangement). Of these plural magnetic poles, two magnetic poles N2 and N3 arranged adjacent to each other have the same polarity, and the adjacent magnetic poles N2 and N3 having the same polarity form a repulsive magnetic field. Of the developer is removed. The magnetic pole S1 faces the developer layer regulating member 43. The tip end of the scraper 44 is pressed against the peripheral surface of the developing sleeve 41 between the magnetic poles N2 and N3 of the same polarity.

The outer diameter of the developing sleeve 41 is preferably not less than φ8 mm and not more than φ60 mm. When the outer diameter is 8 mm or more, it is easy to form the magnet roll 42 having at least five magnetic poles required for image formation.

The outer diameter of the developing sleeve 41 is φ60 m.
m or less, the developing device is easily reduced in size. In particular, in a color printer (see FIG. 1) having a plurality of sets of developing devices (developing units 4Y, 4M, 4C, 4K), the developing device 4
Is smaller, the outer diameter of the photoconductor 1 can be reduced.
After the transfer to the recording medium P and the charge elimination, the recording medium P is
Can be separated from the peripheral surface by the curvature. Further, the image forming apparatus can be made compact by downsizing the developing device 4 and the photoconductor 1.

The developer layer regulating member 43 is formed of a round bar made of a magnetic member such as magnetic stainless steel (SUS).

The developer stirring screw 47A and the developer stirring screw 47B are connected to a first stirring chamber 40b formed on both sides of a partition wall 40a standing upright from the bottom of the developing device housing (developer accommodating portion) 40. Second stirring chamber 4
0c, and rotate in opposite directions to each other. The upper portions of the first stirring chamber 40b and the second stirring chamber 40c are closed by a lid 40A.

The toner replenished from the toner cartridge 5 is fed into a first stirring chamber 40b of the developing device housing 40 through a toner replenishing port (not shown) formed in the lid 40A and replenished. , A developer stirring screw 47 in the first stirring chamber 40b and the second stirring chamber 40c.
A and 47B mix and agitate the developer, and are supplied to the developing sleeve 41 by the developer supply roller 46. The developer supplied on the rotatable developing sleeve 41 containing the magnet roll 42 is regulated in the thickness of the developer layer by the developer layer regulating member, and is conveyed to a development area facing the photoreceptor 1 for non-contact development. Is performed.

In FIG. 3, 48 is an AC power supply E1, D
A bias voltage applying means 49 including a C power source E2 and the like are waveform control means 49. The waveform control means 49 outputs a pause portion (blank portion) time T _B , a pulse portion time T _P , and a time ratio between the pulse portion and the pause portion (T _P / (T _P +
T _B )), the pulse amplitude, the pulse frequency (f) and the like are controlled.

FIG. 4 is a diagram showing a waveform of a blank pulse. The waveform of the blank pulse has a blank portion that intermittently suspends an AC component in a voltage waveform in which a bias voltage obtained by superimposing a DC voltage on an AC voltage is applied,
This blank portion is a waveform for applying only a DC component.

In the above-mentioned problem to be solved by the invention, suction and white spots due to the behavior of the toner have been described with reference to FIG. 6. Here, the behavior of the toner due to the difference between the continuous wave and the blank pulse will be described.

In FIG. 4, when a continuous wave indicated by a solid line and a broken line is applied to the developing sleeve, the direction of the electric field changes every half cycle of the AC voltage. The flying speed of the toner near the point where the moving direction of the toner changes is attenuated, the toner t easily follows the lines of electric force shown in FIG. 6, the amount of toner adhered to the high density portion side of the edge increases, and suction occurs. . Due to this suction, the amount of toner adhered to the low density portion side of the edge portion decreases, and white spots occur.

When a continuous wave is used, an image bearing member (photosensitive member)
1, the toner t frequently bounces, so that white spots are more likely to occur.

When a blank pulse shown by a solid line in FIG. 4 is applied to the developing sleeve, there is no change in the moving direction of the toner t in the blank portion as compared with the continuous wave.
Attenuation of toner flying speed is small.

As a result, it is difficult for the blank portion to follow the curved lines of electric force, and the toner t easily adheres to the low-density portion, and suction can be prevented. Further, in the blank portion, the bounding of the toner t on the image carrier is also suppressed, so that white spots can be prevented.

The sucking and white spotting occur remarkably when the toner particle size is small, that is, 10 μm or less. In an image forming apparatus using such a toner particle size, applying a blank pulse to the developing sleeve is very effective. The present inventor has found that this is the case.

The waveform of the blank pulse is conventionally known (JP-A-7-311497, JP-A-8-1607).
No. 25, JP-A-5-35063, JP-A-60-134
No. 262, JP-A-60-53968, JP-A-7-29
5373, JP-A-6-348117, JP-A-7-9
2786 publications).

However, it does not disclose what kind of blank pulse waveform is good for suction and white spots.

Therefore, the present inventor examined what kind of blank pulse waveform is effective for sucking and white spots.

The maximum electric field Emax (= (1/2 V _AC + V) in the direction in which the developer (toner) moves (flies) from the developing sleeve 41 to the photosensitive member 1 when the _AC voltage VAC is changed.
Combined with changes in the _DC -V _L) / 2), the pulse unit time T _P by blank pulse, and a change of the pulse portion ratio at the time of changing the resting part during the _{T B T P / (T P} + T B) A plurality of images were formed under various variable conditions, and these images were evaluated to experimentally confirm an appropriate development area in which suction and reduction in white spots could be achieved.

FIG. 5 shows the optimum development area in the correlation between the maximum electric field Emax [MV / m] and the pulse portion ratio T _P / (T _P + T _B ) when the pause portion frequency f is set to a predetermined value. It is a characteristic view showing a limit.

In the experiment shown in FIG.
The closest distance d between the photoconductor 1 and the photoconductor 1 was set to 0.57 mm, the DC voltage _VDC was set to -600 V, and the latent image potential _VL of the image portion was set to -50 V.

Further, the developer transport amount DWS = 11.6 mg
/ Cm ² , d = 0.5 mm, (DWS /
d) is 23.2.

First, the frequency f of the pulse portion is set to 4 kHz, Emax and T _P / (T _P + T _B ) are appropriately selected and developed, and the suction and the sub-scan which occur in the main scanning direction are performed. As a result of evaluation of white spots occurring in the direction, as shown in FIG.

The above-mentioned evaluation of suction was carried out by
At the boundary between the upper exposure amount of 20% and 100%, 1
If one line of 50 LPI is missing, it was determined that the image was defective.

Similarly, the frequency f of the pulse section is 6 kHz.
In the case of z, as shown in FIG. 5 (b), all were good in the area on the right side of the line B in the drawing.

When the frequency f of the pulse section is 8 kHz,
As shown in FIG. 5 (c), all were good in the region on the right side of the drawing from the line segment C.

From the above results, the optimum development area in which the suction by the blank pulse and the reduction of the white spots can be achieved is determined by setting the maximum electric field Emax, the pulse portion ratio T _P / (T _P + T _B ), and the pulse portion frequency f as parameters. When expressed by an approximation formula, T _P / (T _P + T _B )> (− 4Emax) +11.3+
0.4 (f-4): It turned out that it is Formula.

In summary, by forming an AC component (blank pulse) that intermittently pauses, and by setting Emax, T _P , and T _B in an appropriate range that satisfies the above equation, suction and white There is an effect on omission.

Experimental values for determining the appropriate development area are shown below.

[0070] _{d: 0.5~0.6mm V DC: -600V V} H: -750V T P / (T P + T B) = 0.5 f = 4~8kHz continuous pulse number: 2 to 4 The developing It is desirable that the ratio of the agent transport amount DWS (mg / cm ² ) to the closest distance d [mm] between the developing sleeve 41 and the photoconductor 1 satisfies the following relationship.

5 <(DWS / d) <40 The amount of developer transported DWS refers to the amount of developer transported by the developing sleeve 41 to the development area.
The developer on the surface of the developing sleeve 41 is sampled for a unit area using a tape, and the weight per unit area of the developer is measured using a balance. Also, d indicates the closest distance [mm] between the developing sleeve 41 and the photoconductor 1.

Further, the developing device of the present invention and the image forming apparatus provided with the developing device are not limited to the above-described embodiment, but may be a color image forming device provided with a belt photoreceptor, or a transparent photoreceptor. The present invention is also applicable to a color image forming apparatus having a color image forming apparatus, a tandem type color image forming apparatus, and other electrostatic type color image forming apparatuses.

The developer used in the developing device of the present invention is not limited to a two-component developer, but can be applied to a one-component developer.

[0074]

According to the developing device and the image forming apparatus of the present invention, suction and white spots which occur during non-contact development are prevented, and suction and white spots which occur particularly when the toner particle size is small are prevented. And high-quality images can be stably obtained.

In particular, suction and white spots which are remarkably generated when the toner particle size is small are prevented, and developability is ensured, and a high-quality image having high resolution and high gradation can be stably formed. Obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a color printer on which a plurality of sets of a developing device of the present invention are mounted.

FIG. 2 is a sectional view of a developing device including a plurality of sets of developing devices according to the present invention.

FIG. 3 is a cross-sectional view of the developing device of the present invention.

FIG. 4 is a diagram showing a waveform of a blank pulse.

FIG. 5 is a characteristic diagram showing a relationship between a maximum electric field and a pulse portion ratio.

FIG. 6 is an enlarged schematic diagram illustrating lines of electric force and toner movement in a developing area.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 image carrier (photoreceptor drum, photoreceptor) 2 scorotron charger (charger) 4 developing device 4Y, 4M, 4C, 4K developing device 40 developer accommodating portion 41 developer carrier (developing sleeve) 42 magnetic field generating means (Magnet roll) 43 Developer layer regulating member 44 Scraper 45 Developer transport roller 46 Developer supply roller 47A, 47B Developer stirring screw 48 Bias voltage applying means 49 Waveform control means Emax Direction of developing toner from developing sleeve to photoconductor Maximum electric field V _AC voltage applied to _AC developing sleeve _VDC Voltage applied to _DC developing sleeve _VL Latent image potential of image area on photoconductor (latent image potential of exposed area) _VH Photoconductor charging potential _TP development mark in the rest part time f developer carrying member of the AC component applied to the pulse unit time T _B developing sleeve of the AC component applied to the sleeve The closest distance of the pulse portion frequency d developing sleeve of the AC component and the photosensitive drum

Claims (4)

[Claims] And a developing device for developing the electrostatic latent image formed on the image carrier with the developer. A developing device, wherein a voltage obtained by superimposing an intermittently resting alternating current component on a direct current component is applied to the developer carrier, and the following relational expression is satisfied. T _P / (T _P + T _B )> (− 4Emax) +11.3+
In 0.4 (f-4) 0.1 < T P / (T P + T B) <0.9 Emax = (1/2 · V AC + │V DC │-│V L │) / d wherein emax [MV / m]: maximum electric field V _AC directions developer to move to the image bearing member from the developer carrying member [V]: AC voltage V _DC applied to the developer bearing member [V]: a developer carrying member applying a DC voltage V _L [V]: latent image potential T _P of the image portion on the image bearing member [msec]: pulse portion of the AC component applied to the developer carrier time T _B [msec]: a developer carrying Pause time of AC component applied to body f [kHz]: Frequency of pulse portion of AC component applied to developer carrier d [mm]: Closest distance between developer carrier and image carrier 2. The developing device according to claim 1, wherein the developer is a two-component developer composed of a toner and a carrier. 3. The developing device according to claim 2, wherein the particle size of the toner is 10 μm or less, and the particle size of the carrier is 35 μm or less. 4. The developing device according to claim 1, wherein the image forming apparatus is configured to superimpose and form a plurality of color images on the image carrier. Forming an electrostatic latent image on the image carrier for each color of the plurality of color images, and developing the electrostatic latent image by the developing device, thereby superimposing a plurality of colors. An image forming apparatus for forming an image.