JP2000035709A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent suction and void and to stably form a high-quality image by applying the developing bias voltage obtained by superposing AC voltage on DC voltage between a developer carrier and an image carrier. SOLUTION: A gap between a developing sleeve and a photoreceptor in a developing area is made larger than the thickness of a developer layer, and the AC voltage VAC is superposed on the DC voltage VDC and applied between the developing sleeve and the photoreceptor. The DC voltage VDC, the electrification potential VH of the photoreceptor and the electrification potential of toner have the same polarity, and the toner, to which a chance to separate from carrier at the AC voltage VAC is given, does not adhere to the electrification potential VH part of the photoreceptor where absolute potential is high but adheres to a latent image potential VL part where it is low, so that an image is developed. In the case of applying a blank pulse to the developing sleeve, the attenuation of toner flying speed is a little and hardly goes along the bent line of electric force in a blank part, and the toner easily adheres even to a low density part, then the suction is prevented and the bound of the toner on the image carrier is restrained, so that the void is prevented.

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. 10 is an enlarged schematic view showing the movement of toner in a development 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 attached 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. In some cases, white spots may occur (hereinafter, this phenomenon is referred to as "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 direction of movement of the toner t changes attenuates, the toner t easily follows the lines of electric force shown in FIG. 10, the amount of toner attached to the high-density portion side of the edge increases, and suction occurs. 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]

In order to achieve the above object, an image forming apparatus according to the present invention comprises a charging device for charging at least the surface of an image carrier around the image carrier, and a charged surface of the image carrier. Exposure device for exposing to form an electrostatic latent image, a developing device having a developer carrying member for carrying a developer for developing the electrostatic latent image, and transferring the developed image developed by the developing device An image forming apparatus having a transfer device for transferring to a material, wherein the developing device includes a bias voltage for applying a developing bias voltage obtained by superimposing an AC voltage and a DC voltage between the developer carrier and the image carrier. The AC voltage has an asymmetry waveform in one cycle of the AC voltage, and is applied intermittently.

[0022]

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 color image is formed. 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 (hereinafter, referred to as a photoreceptor) serving as an image bearing member, which is formed by coating an organic photoreceptor layer on a drum base, and is grounded to be clockwise in the drawing. Rotate. 2 is a charging device (scorotron 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 charging device 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 to eliminate the peripheral surface of the photoconductor 1. 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 containing a two-component developer composed of a toner such as yellow (Y), magenta (M), cyan (C), and black (K) and a carrier are provided at the periphery of the photosensitive member 1. 4Y, 4M, 4C, 4K developing device 4
Is provided.

First, for developing the first color of yellow, a developer carrier (hereinafter referred to as a developing sleeve) which contains a magnetic field generating means 42 composed of a plurality of magnets and holds and rotates the developer.
41. The particle size of the developer is magnetite core with insulating resin coating around it.
A carrier having a particle size of 4 to 10 μm including a carrier having a particle size of 0 to 80 μm, a pigment corresponding to a color, a charge control agent, silica, titanium oxide and the like with polyester as a main material,
The developer is regulated to a developer layer thickness of 100 to 600 μm on the developing sleeve 41 by a later-described developer layer regulating member 43, 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. 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.

[0030] 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 a 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 devices 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, reference numeral 40 denotes a developer accommodating portion for accommodating a two-component developer composed of toner and carrier; 41, a developer carrying member (hereinafter, referred to as a developing sleeve) for carrying and transporting the developer; Numeral 43 denotes a magnetic field generating means (hereinafter, referred to as a magnet roll) in which a plurality of fixed magnets are arranged inside the developing sleeve 41. Numeral 43 denotes a magnetic round bar for regulating the thickness of the developer layer on the developing sleeve 41 to a predetermined amount. A developer layer regulating member (a member that regulates the rising of the developer). 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. Agent transport roller, 46
Is a paddle wheel-shaped developer supply roller for replenishing the developer to the developing sleeve 41 from the developer stirring portion;
47B is a developer stirring screw for stirring the developer in the developer stirring section. The illustrated arrows indicate the direction of rotation of each roller. It should be noted that a scraper 44 that is pressed against the developing sleeve 41
Instead of the developing sleeve 41,
The magnets may be arranged close to each other without contacting the outer periphery of the magnet.

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 section) 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 from 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 onto the rotatable developing sleeve 41 containing the magnet roll 42 has its developer layer thickness regulated by the developer layer regulating member 43, and is conveyed to a development area facing the photoconductor 1, and is contactless. Development takes place.

In FIG. 3, 48 is an AC power source E1, D
A bias voltage applying means 49 including a C power source E2 and the like are a waveform control circuit 49. The waveform control circuit 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 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. 10. 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. 10, the amount of toner attached on 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.

In the case of a continuous wave, the toner t frequently bounces on the image carrier, so that white spots are more likely to occur.

When a blank pulse indicated 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, in the blank portion, it is difficult 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.

This sucking and white spotting occurs remarkably when the toner particle size is small, ie, 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 toner diameter is large (for example, a particle diameter of 15 μm).
In the case of m), the latent image potential in the image area is likely to be saturated due to the toner adhering to the latent image in the development area. When the latent image potential is saturated, no more toner adheres,
Since there is no difference in the amount of toner adhered between the inside of the high-density area where the latent image potential is large and the edge, suction is unlikely to occur. Further, a specified amount of toner adheres to the edge portion of the low-density portion where the latent image potential is small, and white spots are less likely to occur.

As described above, it was found that suction and white spots could be prevented by applying the blank pulse. However, in the blank portion where the application of the AC voltage was stopped, the AC voltage which caused the toner to separate from the surface of the developing sleeve was obtained. Is not applied, there is a problem that the detachment amount of the toner is reduced and the developability (toner adhesion) is reduced as a whole (10 to 20% lower) as compared with the continuous waveform portion having no blank portion.

Therefore, the present inventor has studied a measure for preventing the developing property of the blank pulse from lowering.

FIG. 5 is a diagram showing a conventional developing bias voltage waveform and image defects.

[0059] FIG. 5 (a), yellow toner Yt on the developing sleeve 41Y is in the developing area, an AC voltage V _AC and the DC voltage V _DC and flying to the peripheral of the photosensitive member 1 by being applied to the developing sleeve 41Y It is a schematic diagram which shows that it adheres to a surface.

[0060] The developing sleeve 41Y, and an AC voltage V _AC and DC voltage V _DC is superimposed applied. An AC voltage V _AC 28
Assuming that 00 V and the DC voltage _VDC are −600 V, the superimposed applied voltage is +800 V [(+1400 V) + (− 600 V).
V)] to -2000V [(-1400V) + (-60
0V)].

The latent image potential _VL of the image area on the photosensitive member 1 is -5.
In the case of a high density of 0 V, during development by the developing device 4Y, the yellow toner Yt is applied with a DC voltage _VDC of -600V to a developing sleeve 41Y having a sleeve potential of -2000V.
Photoconductor 1 having latent image potential V _L (−50 V) of image portion from above
Fly over the surface (in the direction of the arrow shown).

[0062] To increase the amount of toner adhered onto the photoreceptor 1, an AC voltage V _AC during the application of the AC bias voltage, further from said 2800V 3800V~480
By increasing the voltage to 0 V, the force for peeling the toner from the carrier is increased, and the amount of toner attached to the developing sleeve 41 can be increased. However, in this case, the potential difference between the developing sleeve 41 and the photoconductor 1 periodically increases, and the latent image potential V _L (−50)
V), a discharge breakdown (lightning phenomena) occurs between the developing sleeve 41Y and the photoconductor 1, and a so-called ring mark that generates a ring-shaped crater on the photoconductor 1 is generated. Therefore, there is a limit in increasing the toner adhesion amount by increasing the _AC voltage value VAC.

FIG. 5B shows that the yellow toner Yt previously formed on the photoreceptor 1 is applied to the photoreceptor 1 in a developing area when a plurality of toner images are superimposed on the photoreceptor 1.
FIG. 4 is a schematic view showing that the toner is peeled off from the top and re-attached to a developing sleeve.

When a magenta image is developed by the developing unit 4M, a yellow toner Yt is adhered onto the photoreceptor 1 by a preceding yellow image forming process including charging, exposure and development. The magenta image by the developing device 4M during development, increasing the AC voltage V _AC as described above, the yellow toner Yt adhering on the photosensitive member 1 of the re-charged photoreceptor potential (-750 V) photosensitive power take off from on the body 1 also will be increased, and the AC voltage V _AC applied to the developing sleeve 41M, the DC voltage V _DC, a yellow toner Yt is stripped from the developing sleeve 41Y, further sleeve potential (+ 800 V ) Developing sleeve 4
In some cases, the yellow toner Yt flies toward 1M and mixes with the magenta toner Mt on the developing sleeve 41M (hereinafter, this phenomenon is referred to as peeling).

[0065] In summary, increasing the AC voltage V _AC, the toner adhesion amount (developability) is increased, and generation exceeds a certain voltage value, the discharge breakdown (lightning phenomena), the photosensitive member 1 In an image forming apparatus that damages the toner or superimposes a plurality of toner images on the photoconductor 1,
The peeling is caused to cause the mixing of different color toners. Therefore, in order to improve the toner adhesion amount (developability), it is necessary to devise a method of preventing discharge breakdown and suppressing occurrence of peeling.

Thus, the present inventors have conducted intensive studies and as a result,
By making the waveform of the AC voltage application part of the blank pulse waveform an asymmetric waveform in one cycle of the AC voltage,
It has been found that a decrease in developability in the blank pulse portion can be prevented.

FIG. 6 is a diagram showing an astigmatically symmetric waveform of the developing bias voltage. In the figure, the broken line indicates a symmetric waveform,
The solid line shows an astigmatic waveform according to the invention. This waveform
In one cycle of the AC voltage, the waveform has no symmetry point, that is, an asymmetry waveform. Preferably, the astigmatism symmetrical waveform includes an integral value on the developing drive side (area of a hatched portion on the upper side in the drawing) in which toner moves from the developing sleeve 41 onto the photosensitive member 1 and a developing sleeve 41 from the photosensitive member 1. The integral value on the return side where the toner moves to the side (the area of the hatched portion on the lower side in the figure) is equal to a constant value (effective voltage level is constant), and the peak value of the asymmetry waveform is effectively applied. The absolute value of the difference from the DC voltage value is different between the high and low DC voltage values. The ratio between the applied voltage and time is changed.

T _{1 in the} figure is the application time on the developing drive side, and T ₂ is the application time on the return side. The waveform shown is Dut.
y ratio: T ₂ / (T ₁ + T ₂ ) is set to 0.6 (T ₂ > T ₁ ). Further, it is desired that the effectively applied DC voltage V ′ _DC is equal to the actually applied DC potential difference V _DC .

As shown in FIG. 6, by making the AC voltage of the developing bias voltage an asymmetry waveform, the absolute value of the applied voltage on the developing drive side increases as compared with the symmetric waveform, so that the developing voltage decreases in the blank portion. This can be compensated for by the AC voltage applying unit, and the amount of toner adhering to the photoreceptor 1 from the developing sleeve 41 increases as a whole, thereby improving the developing property. In addition, since the absolute value of the applied voltage on the return side also becomes small, the above-described stripping can be suppressed.

The following is a comparison of the developability of the symmetric blank pulse waveform and the astigmatic symmetric blank pulse waveform. Note that the charging potential V _{H of} the photoconductor 1 is −750 V, the latent image potential V _L on the photoconductor 1 is −50 V, the DC voltage _{VDC is} −600 V, and the closest distance d between the photoconductor 1 and the developing sleeve 41 is d = 0.57m
m, developer transport amount DWS of the developing sleeve 41 = 9 mg /
cm ² and frequency f = 6 kHz. Further, two wavelengths of the pulse portion and then a portion corresponding to two wavelengths of the blank portion were applied.

(1) Symmetric blank pulse waveform development: At this time, the maximum AC voltage at which peeling does not occur is V _AC =
At 2.4 kV, the toner adhesion amount (M / A) on the photoconductor 1 was 0.56 mg / cm ² .

(2) Duty ratio: Astigmatic symmetric blank pulse waveform development in which T ₂ / (T ₁ + T ₂ ) is set to 0.6: The maximum AC voltage at which peeling does not occur is V _AC =
It is improved to 2.6 kV, and the toner adhesion amount on the photoreceptor 1 is 0.3 kV.
Increased to 78 mg / cm ² .

By making the pulse portion waveform of the blank pulse shown in FIG. 4 a non-point symmetric waveform (a non-point symmetric blank pulse), it is possible to suppress a decrease in developability which is a problem with the blank pulse, and By suppressing the decrease in the property, the potential of the high-density portion is likely to be saturated, so that there is also an effect that the above-described suction and white spots are hard to occur.

FIG. 7 is a diagram showing an example of a non-point symmetric blank pulse waveform of the developing bias voltage. In the figure, the broken line indicates the above-mentioned continuous waveform, and the solid line indicates the non-point symmetric blank pulse waveform.

The charging potential V _H , latent image potential V _L , DC voltage V _DC , distance dmm, developer conveyance amount DWS, and frequency f are the same as the above-mentioned set values.

By employing the astigmatic symmetric blank pulse, the toner adhesion amount (M / A) on the photoreceptor 1 is increased by increasing the ratio of the AC voltage application time to the blank time. For example, when the time of the pulse portion is set from 1 to 2 with respect to the time 1 of the blank portion, the toner adhesion amount (M / A) is 0.7 mg / cm ² to 0.8 m.
g / cm ² . The evaluation of the toner adhesion amount (M / A) on the photoconductor 1 is obtained by measuring the amount of toner (weight, mg) per unit area (cm ² ) adhering to the photoconductor 1 with a balance. .

[0077] 1 time of the blank portion, when the time of the pulse portion T _P was 2-3, the suction of the foregoing, 150LP
For one I (line / inch) line (170 μmm)
It was as follows.

The developer transport amount DWS [mg / c
It is desirable that the ratio of m 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 transport (DWS) refers to the amount of developer transported by the developing sleeve 41 to the developing area. The agent was collected by a unit area using a tape, and the weight per unit area of the developer was measured using a balance.

Further, the present inventor has found that the maximum electric field Emax (=) 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.
(1 / 2V _AC + | V _DC | − | V _L |) / 2) and the pulse portion time T _P due to the asymmetry blank pulse,
Pulse portion ratio T _P / (T when changing the resting portion at T _B
A plurality of images are formed under various variable conditions in combination with the change of ( _P + T _B ), and these images are evaluated to achieve an increase in toner adhesion amount and a reduction in a suction phenomenon due to an asymmetry blank pulse. The development appropriate area was experimentally confirmed.

FIG. 8 shows a suitable 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 frequency f of the pulse portion is set to a predetermined value. FIG. 6 is a characteristic diagram showing a limit of the graph.

Note that the image forming apparatus according to the present invention
The outer diameter of the photoreceptor 1 is φ100 mm, and the outer diameter of the developing sleeve 41 is φ18 mm, using an onica KL-2010 color laser printer (manufactured by Konica Corporation).

In the experiment shown in FIG.
The closest distance d between the photoconductor 1 and the photoconductor 1 is 0.5 mm, and the DC voltage V
_DC = −600 V, photoconductor charging potential V _H = −750 V, and latent image potential V _L of the image area were set to −50 V.

Incidentally, DWS = 11.6 mg / cm ² , d
= O. (DWS / d) is 23.
2.

[0085] First of all, set to the frequency f = 4kHz of the pulse part, Duty, while changing the V _AC, Emax and T _P /
(T _P + T _B ) was selected and developed as appropriate, and development was performed. As a result of the above-described evaluation of suction occurring in the main scanning direction, white spots occurring in the sub-scanning direction, and the amount of adhered toner, FIG.
As shown in (a), all were good in the area on the right side of the drawing from the line segment A.

For example, V _AC = 2600 V, Duty =
When it is set to 0.6, the maximum electric field Emax is Emax = (2
(600 × 0.6 + 600−50) /0.5=4.22
[MV / m].

Setting Emax = 2.6 [MV / m],
The change in V _AC obtained while variously changing the Duty in the range of 0.5 to 0.9 below.

[0088] Duty: time of 0.5, V _AC = 1500V Duty: time of 0.6, V _AC = 1250V Duty: time of 0.7, V _AC = 1071V Duty: time of 0.8, V _AC = 938V Duty: when 0.9 V _AC = 833V namely, when the pulse unit ratio that the V _AC = 833V when 0.9 is Emax = 2.6 [MV / m] . Further, when Duty is 0.5, when V _AC = 1500 V, Emax = 2.6 [MV / m].

The above-mentioned evaluation of the suction was carried out for the photosensitive member 1
At the boundary between the upper exposure amount of 20% and 100%, 1
One 50 LPI (line / inch) line (17
0 .mu.m) If it was missing, it was judged 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.

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

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

From the above results, the optimum development area in which the increase in the amount of adhered toner and the reduction in the suction phenomenon due to the asymmetry blank pulse are determined by the maximum electric field Emax and the pulse portion ratio T _P / (T _P + T _B ). , is represented by an approximate expression in which the frequency f of the pulse portion to the _{parameter, T P / (T P +} T B)> (-
4Emax) + 11.3 + 0.4 (f-4): It was found that this was the formula.

Similarly, FIG. 9 shows the maximum electric field Emax [MV / m] when the pulse frequency f is set to a predetermined value.
When a characteristic diagram showing the limits of developing appropriate region in the correlation between the pulse portion ratio _{T P / (T P + T} B).

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 generated in the main scanning direction are performed. As a result of the evaluation of the white spots generated in the direction and the toner adhesion amount, as shown in FIG.

The above-mentioned evaluation of the suction was carried out for the photosensitive member 1
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.

For example, when the pulse ratio is 0.1,
When V _AC = 2000 V and Duty = 0.9, the maximum electric field Emax is 4.70 [MV / m].

[0098] Emax = 4.70 is set to [MV / m], indicating a change in the V _AC obtained while variously changing the Duty in the range of 0.5 to 0.9 below.

[0099] Duty: time of 0.5, V _AC = 3600V Duty: time of 0.6, V _AC = 3000V Duty: time of 0.7, V _AC = 2571V Duty: time of 0.8, V _AC = When 2250 V Duty: 0.9, V _AC = 2000 V. That is, when Duty is 0.9, when V _AC = 2000 V, Emax = 4.70 [MV / m]. Further, when Duty is 0.5, when V _AC = 3600 V, Emax = 4.70 [MV / m].

Similarly, the frequency f of the pulse section is 6 kHz.
In the case of Z, as shown in FIG. 9 (b), all were good in the region on the left side of the line segment F in the drawing.

When the frequency f of the pulse portion is 8 kHz,
As shown in FIG. 9 (c), all were good in the region on the left side of the drawing from the line segment G.

When the frequency f of the pulse portion was 10 kHz, all were good in the region on the left side of the line H as shown in FIG. 9D.

From the above results, the optimum development area in which the increase in the amount of adhered toner and the reduction in the suction phenomenon due to the asymmetry blank pulse are determined by the maximum electric field Emax and the pulse portion ratio T _P / (T _P + T _B ). , Expressed as an approximate expression using the frequency f of the pulse portion as a parameter, (−4Emax) +18.
9 + 0.4 (f-4) > T P / (T P + T B): it was found to be an expression.

To summarize the above, the AC component (blank pulse) that intermittently pauses is formed asymptotically, and Emax,
T _P, by setting the T _B, is effective in lowering or white spots, and it is also possible to prevent lowering of developability.

The developing device of the present invention and the image forming apparatus provided with the developing device are not limited to the above-described embodiments, 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. Further, the developing device of the present invention is not limited to a two-component developer, but can be applied to a one-component developer.

[0106]

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. In addition, a sufficient density can be obtained, developability and development stability are improved, and a high-quality image can be stably 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 diagram showing a developing bias voltage waveform and an image defect.

FIG. 6 is a diagram showing an asymmetry waveform of a developing bias voltage according to the present invention.

FIG. 7 is a diagram showing an asymptotically symmetric blank pulse waveform of a developing bias voltage according to the present invention.

FIG. 8 is a characteristic diagram showing a relationship between a maximum electric field and a pulse portion ratio.

FIG. 9 is a characteristic diagram showing a relationship between a maximum electric field and a pulse portion ratio.

FIG. 10 is an enlarged schematic diagram illustrating lines of electric force and toner movement in a development area.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Image carrier (photosensitive drum, photosensitive body) 2 Charging device (scorotron charger) 3 Exposure device 4 Developing device 4Y, 4M, 4C, 4K Developing device 6 Transfer device 40 Developing device housing (developer accommodating part) 41 Development 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 circuit Emax The maximum electric field in the direction in which the toner moves from the developing sleeve to the photoconductor V _AC voltage applied to the _AC developing sleeve V _DC voltage applied to the _DC developing sleeve _{VL L L} mark pulse unit time T _B developing sleeve of the AC component applied to the potential) V _H photoreceptor charging potential T _P developing sleeve The closest distance of the pulse portion frequency DWS developer conveying quantity d developing sleeve of the AC component applied to the rest portion time f developing sleeve of the AC component and the photosensitive member

Claims (11)

[Claims] A charging device for charging at least a surface of the image carrier around the image carrier; an exposure device for exposing the charged surface of the image carrier to form an electrostatic latent image; An image forming apparatus comprising: a developing device having a developer carrier for carrying a developer for developing a latent image; and a transfer device for transferring a developed image developed by the developing device to a transfer material. Has bias voltage applying means for applying a developing bias voltage in which an AC voltage and a DC voltage are superimposed between the developer carrier and the image carrier, and the AC voltage is applied for one cycle of the AC voltage. The image forming apparatus according to any one of claims 1 to 3, wherein the waveform has an astigmatic symmetry and is applied intermittently. 2. The method according to claim 1, wherein an area value of a region sandwiched between the waveform of the AC voltage and the DC voltage that is effectively applied in one cycle of the AC voltage is the DC voltage that is effectively applied. The same value is set on the higher and lower sides than the voltage value, and the absolute value of the difference between the peak of the AC voltage and the DC voltage that is effectively applied is effectively applied. The image forming apparatus according to claim 1, wherein the difference is different between a side higher than the DC voltage and a side lower than the DC voltage. 3. The image forming apparatus according to claim 2, wherein the DC voltage value applied effectively and the DC voltage value applied by the bias voltage applying unit are the same value. . 4. The image forming apparatus according to claim 2, wherein the bias voltage applying unit applies a DC voltage and an AC voltage so as to satisfy the following relational expression. 0.5 <[T ₂ / (T ₁ + T ₂ )] <0.9 In the formula, T ₁ [sec]: The developer is transferred from the developer carrier to the image carrier with respect to the DC voltage that is effectively applied. Time for applying AC voltage to the side moving to the body T ₂ [sec]: Applying AC voltage to the side where the developer moves from the image carrier to the developer carrier with respect to the DC voltage that is effectively applied Time T ₁ + T ₂ : time of one cycle of AC voltage 5. The image forming apparatus according to claim 1, wherein the bias voltage applying unit applies the AC voltage so as to satisfy the following relational expression. 0.1 _{<[T P / (T P + T} B) ] <in 0.9 formula, T _P [msec]: time T _B for applying an AC voltage [msec]: time to pause the application of the AC voltage 6. The apparatus according to claim 1, wherein various conditions of the image forming apparatus are set so as to satisfy the following relational expression.
The image forming apparatus according to any one of claims 1 to 5, wherein [-4Emax + 11.3 + 0.4 (f-4)] <[T
_{P / (T P + T B} ) ] <[- 4Emax + 18.9 + 0.
4 (f-4)] _{Emax = (1/2 · V AC +} | V DC | - | V L |) in / d formula, Emax [MV / m]: developer image bearing member from the developer carrying member V _AC [V]: the voltage value of the AC voltage applied by the bias voltage applying means _VDC [V]: the voltage value of the _DC voltage applied by the bias voltage applying means _VL [V] : minimum potential of the latent image formed on the image bearing member d [mm]: shortest distance T _P between the developer carrying member and the image bearing member [msec]: time T _B for applying an AC voltage [msec]: Time for suspending application of AC voltage f [kHz]: Frequency of AC voltage applied by bias voltage applying means 7. The image forming apparatus according to claim 1, wherein the developer is a two-component developer including a toner and a carrier. 8. The image forming apparatus according to claim 7, wherein the toner has a particle diameter of 10 μm or less. 9. The image carrier according to claim 1, a developing device,
An image forming apparatus, comprising: an exposure device; and a reversal development in which a developer is adhered by the developing device to a latent image portion from which a charge is removed by a light beam from a uniformly charged surface on the image carrier. Item 2. The image forming apparatus according to Item 1. 10. An image bearing member according to claim 1, a developing device, and a bias voltage applying unit, wherein a bias voltage for superimposing an AC voltage on a DC voltage is applied to the developer carrier, and The image forming apparatus according to claim 1, wherein the developer on the developer carrier is visualized by non-contact development in which the developer flies onto an electrostatic latent image on the image carrier. 11. A plurality of developing devices according to claim 1, each containing a developer of a different color, and the developing device according to claim 9 performs the reversal development and the non-contact development according to claim 10. Developing the electrostatic latent image formed on the image carrier, forming a superimposed color developed image of a plurality of colors on the image carrier, and transferring the color developed image onto a transfer material at once by a transfer device The image forming apparatus according to claim 1, wherein the image forming apparatus forms a color image.