JP2000066493A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device made possible to obtain the excellent image being supreme in development property and the development stability preventing the occurrence of absorption or void arising at the non- contact development, at the time of forming image on the image carrier, and to obtain the image of excellent hue, furnished with the second color enable inconspicuously changing. SOLUTION: This image forming device, provided with a photoreceptor 1, and the developing device 4 equipped with a developing sleeve 41 carrying the developer held in a state of non-contact with respect to the photoreceptor 1, for developing the electrostatic latent image carried on the developing sleeve 41 by the developer, is allowed to apply voltage consisting of DC component superimposed by non-centrosymmetry AC component being intermittently suspended with regard, to the developing sleeve 41 carrying the developer, and moreover, the image forming device is composed so as to satisfy the next numerical formula, (Vs/Vp)>=2. In the formular, Vs: standing for peripheral speed of developing sleeve 41, and Vp: peripheral speed of photoreceptor 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, such as a copying machine, a printer, a facsimile, etc., which has a developing device for developing an electrostatic latent image on an image carrier to form a visible image and forms an image. Things.

[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.

[0008] The mechanism of 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.

Further, there is a problem that the toner adhesion amount is uneven at the leading end and the trailing end of the latent image formed on the image carrier in the developing area in the sub-scanning direction.

According to the present invention, high resolution and high gradation can be prevented by preventing the above-mentioned sucking and white spots generated in the non-contact development, and preventing the lowering of the developing property (toner adhesion) and the unevenness of the toner adhesion amount. It is an object of the present invention to provide a developing device capable of stably obtaining a high-quality image having the following.

[0020]

An image forming apparatus according to the present invention for achieving the above object has an image carrier and a developer carrier for carrying a developer in a non-contact state with the image carrier. An image forming apparatus having a developing device and developing an electrostatic latent image formed on the image carrier with a developer, wherein an alternating current component that is intermittently paused with astigmatism is superimposed on a direct current component. A voltage is applied to a developer carrying member for carrying a developer, and the following relational expression is satisfied.

(Vs / Vp) ≧ 2 In the formula, Vs: the peripheral speed of the developer carrier, Vp: the peripheral speed of the image carrier. An image forming apparatus for forming a plurality of color images by superimposing the plurality of development devices described above for each color of the plurality of color images, and for each color of the plurality of color images, By forming an electrostatic latent image on, and by developing the electrostatic latent image by the developing device,
It is characterized in that a superimposed image of a plurality of colors is formed.

[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 photosensitive drum (photosensitive member) serving as an image bearing member, which is formed by applying an OPC photosensitive member (organic photosensitive member) on a drum base, and is grounded in a clockwise direction shown in the figure. Rotate. 2 is a scorotron charger (hereinafter, referred to as a charger), a uniform charging of the photosensitive member charge potential V _H on the high potential to the peripheral surface of the photosensitive member 1, and the grid, which is the potential held at grid potential V _G Provided by corona discharge with corona discharge wire. Prior to charging by the charger 2,
In order to eliminate the history of the photoreceptor 1 up to now, the peripheral surface of the photoreceptor 1 is discharged by performing exposure by a pre-charging static eliminator (PCL) 8 using a light emitting diode or the like. 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, image exposure based on an image signal is performed by the image exposing means 3, and the photosensitive member 1 is charged.
An electrostatic latent image is formed on the upper surface. The image exposure means 3 performs a main scan through a polygon mirror, an fθ lens, a cylindrical lens, and a reflection mirror which rotate by using a laser diode (not shown) as a light emitting light source. The latent image is formed by the rotation (sub-scan) of the photoconductor 1. It is formed. 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. An inverted latent image having a potential lower than the absolute potential of the potential V _H is formed (│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, the first color yellow is developed 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 consists of a carrier with magnetite as the core and an insulating resin coated around it, and a toner with a pigment and a charge control agent according to the color with polyester as the main material, silica, titanium oxide, etc.
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
Toner given the opportunity to leave from the carrier by did not attach to the high portion of the photosensitive member charge potential V _H absolute potential than the DC voltage V _DC, low image portion of the DC voltage V _{D C} than the absolute potential (exposure And the latent image potential _VL of the portion (image portion), and visualization (reversal development) is performed.

After the visualization of the first color is completed, a magenta image forming process for the second color is started, and the scorotron charger 2 is again turned on.
, And a latent image based on the image data of the second color is formed by the image exposure unit 3. 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 in the vicinity of the registration sensor position via the intermediate sheet feeding roller pairs 22A and 22B, and is fed to the transfer area by the rotation operation of the registration roller pair 23 of the sheet feeding unit when the transfer timing is adjusted. You.

In the transfer area, a transfer roller 6 for applying a voltage for transferring a toner image to the peripheral surface of the photosensitive member 1 is pressed against the peripheral surface of the photosensitive member 1 in synchronization with the transfer timing, and the fed recording medium P is pinched. Then, the four color toner images are collectively transferred 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 roller 6 is retracted from the peripheral surface of the photoreceptor 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 section for accommodating a two-component developer composed of toner and carrier; 41, a developer carrying member (developing sleeve) for carrying and transporting the developer; A magnetic field generating means (hereinafter, referred to as a magnet roll) having a plurality of fixed magnets disposed therein, and a developer layer 43 formed of a non-magnetic round bar for regulating the thickness of the developer layer on the developing sleeve 41 to a predetermined amount A regulating member (a member that regulates the rising of the developer). 44 is a scraper for removing the developer adhered on the developing sleeve 41 after development, and 45 is a scraper for removing the developing sleeve 4 from the developing sleeve 41.
A paddle wheel-shaped developer conveying roller for conveying the developer removed from the peripheral surface of the developing device 1 to the developer stirring section, and a paddle wheel-shaped developer 46 for supplying the developer to the developing sleeve 41 from the developer stirring section Supply roller, 47A, 47
B 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.
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 of the scraper 44 is pressed against the peripheral surface of the developing sleeve 41 near the intermediate position Nu 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 image forming apparatus according to the present invention includes:
A modified Konica KL-2010 color printer (manufactured by Konica Corporation) was used. The outer diameter of the developing sleeve 41 was 18 mm and the outer diameter of the photoconductor 1 was 100 mm.

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 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 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 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 has been found that suction and white spots can be prevented by applying the blank pulse. However, in the blank portion where the application of the AC voltage is stopped, the AC voltage which triggers the toner to separate from the surface of the developing sleeve is 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 measures 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.

[0060] 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.

[0061] 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).

[0063] 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~48
By increasing the voltage to 00 V, the force for peeling the toner from the carrier increases, and the amount of toner adhered on 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 the yellow toner Yt formed on the photosensitive member 1 in the developing area when a plurality of toner images are formed on the photosensitive member 1 in a superimposed manner.
FIG. 4 is a schematic view showing that the toner is peeled off from the top and re-attached to a developing sleeve.

When the magenta image is developed by the developing device 4M, the 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).

[0066] 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.

The inventor of the present invention has conducted intensive studies and has found that
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 astigmatism 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.

In the figure, T ₁ 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, the DC voltage (V ′ _DC ) that is effectively applied is equal to the DC voltage V _DC that is actually applied.
Is desired.

As shown in FIG. 6, by making the AC voltage of the developing bias voltage an astigmatically symmetrical waveform, the absolute value of the applied voltage on the developing drive side increases as compared with the symmetrical waveform. 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) Symmetrical blank pulse waveform development: At this time, the maximum AC voltage at which stripping 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: At this time, 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 waveform of the pulse portion of the blank pulse shown in FIG. 4 a non-point symmetric waveform (a non-point symmetric blank pulse), it is possible to suppress the deterioration of the developing property which has been a problem with the blank pulse. 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 , closest distance d, developer transport amount DWS, frequency f
Is the same as the above set value.

By adopting the asymmetry blank pulse, the toner adhesion amount (M / A) on the photosensitive member 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. .

[0078] 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 transported (DWS) refers to the amount of developer transported by the developing sleeve 41 to the development 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.

The present inventor has further studied toner bias in the sub-scanning direction when a voltage is superimposed on a DC component in which an AC component that is intermittently halted with astigmatism is applied.

Considering the traveling direction, speed, etc. of the image carrier and the developer carrier in the developing area, the developer carrying direction of the developer carrier and the traveling direction of the image carrier are the same, and Are the same, there is no difference in toner adhesion amount between the leading end of the latent image and the trailing end of the latent image even when there is a gap in the latent image potential in the traveling direction.

However, it is difficult to obtain a predetermined reflection density because the absolute amount of toner adhesion is small.

FIG. 8A is a schematic diagram showing toner adhesion in a development area where the image carrier and the developer carrier are close to each other.
FIG. 8B is a diagram schematically showing the toner adhered to the image carrier when the development area is divided into five and the latent image data on the image carrier is also divided into five at the same interval as the development area division. is there.

As shown in FIG. 8, the peripheral speed Vp of the image carrier
On the other hand, when the peripheral speed Vs of the developer carrier is high (Vs>
Vp), the reflection density of the toner image can be increased, but the toner t adheres by a predetermined amount or more to the rear end portion of the latent image in a region where the latent image potential is large. This is because toner consumption of the developer generally occurs in the development area, but the unconsumed developer enters the rear end portion of the latent image, so that the supply amount of the toner t increases. .

The amount of toner adhered from the trailing end of the latent image to the leading end of the latent image sharply decreased, so that the color change was particularly noticeable especially when the secondary colors were superimposed.

Further, toner does not easily adhere to the rear end portion (highlight portion) of the latent image in the region where the latent image potential is small.

This is because the developer on the developer carrier has already consumed the toner where the latent image potential is large and then enters the region where the latent image potential is small.

FIG. 9 is a schematic cross-sectional view and a schematic plan view showing a state in which a yellow toner Yt and a magenta toner Mt are superimposed on an image carrier to form a two-color toner image.

The central portion where the primary yellow toner Yt and the secondary magenta toner Mt are evenly superposed has a uniform red color.

However, as described above, the trailing end of the yellow toner Yt formed first on the developer carrier in the sub-scanning direction has a large amount of adhered yellow toner Yt and a high toner layer potential. The adhesion amount of the magenta toner Mt laminated on the yellow toner Yt decreases.

Accordingly, at the rear end, the density of the yellow toner Yt is high, the density of the magenta toner Mt is low, and the yellow color changes to a strong red color.

The color change portion of the secondary color having less secondary color magenta toner Mt is called a secondary deviation width and is represented by δ in the drawing.

As described above, it is necessary to reduce the variation in the amount of adhered toner in the latent image potential gap between the leading end portion of the latent image and the trailing end portion of the latent image, and to make the color change of the secondary color less noticeable.

Therefore, the present inventor has determined that the peripheral speed Vs
And the peripheral velocity Vs of the developing sleeve 41 were examined.

When the rotation direction of the photosensitive member 1 and the rotation direction of the developing sleeve 41 are the same in the developing area, the larger the value of Vs / Vp, the smaller the adhesion amount ratio between the central portion and the edge portion where the latent image potential is large. In addition, the area to which a large amount of the developer adhered increased, and the tendency of the increase in the amount of adhesion from the center to the edge became slower and became less noticeable as a change in the density of the developed image.

Similarly, when the traveling direction of the image carrier and that of the developer carrier are opposite to each other, as Vs / Vp is further increased, the adhesion amount ratio between the central portion and the edge portion where the potential of the latent image is large becomes smaller.

When Vs / Vp is increased, the amount of adhesion also increases, which is equivalent to the fact that the potential of the latent image is easily saturated.

Accordingly, the developability is improved.

It was confirmed through experiments that in which range Vs / Vp should be set.

The results are shown below.

[0102]

Next, the present invention will be described with reference to the following examples.

In the experiment, image development was performed by developing under the following developing conditions. The image forming apparatus shown in FIG. 1 is used for image formation, and the developing apparatus shown in FIGS. 2 and 3 is used for development. The image was developed by the following operation, and the image was evaluated.

The image forming apparatus according to the present invention includes:
Using a modified Konica KL-2010 color printer (manufactured by Konica Corporation) shown in FIG.
1 has an outer diameter of 18 mm, and the outer diameter of the photoconductor 1 has a diameter of 100 mm.
It is.

The setting conditions for the development processing are as follows.

The closest distance d between the photosensitive member 1 and the developing sleeve 41 is d = 0.55 [mm]. The photosensitive member charging potential V _H : -750 [V] DC voltage V _DC applied to the developing sleeve 41: -600
[V] the latent image potential on the photosensitive member 1 V _L: -50 [V] AC voltage applied to the developing sleeve 41 V _AC p-p:
[2.5 kV] Yellow latent image PWM: 50%, magenta latent image PWM: 1
Table 1 shows the evaluation of the secondary deviation width δ, the hue change, and the reflection density of the edge portion.

[0107]

[Table 1]

In Table 1, No. In each of 1 to 6, a voltage having a non-point symmetrical blank pulse waveform (see FIG. 9) is applied to the developing sleeve 41. In addition, No. In Nos. 1 to 3, the rotating direction of the developing sleeve 41 in the developing area is the same direction (normal rotation) as the rotating direction of the photoconductor 1 (see FIG. 8). No. 4 to 6, the rotation direction of the developing sleeve 41 in the developing area is the opposite direction (reverse rotation) to the rotation direction of the photoconductor 1. No. At 7, a voltage having a symmetrical continuous waveform is applied to the developing sleeve 41.

The duty in Table 1 is as shown in FIG.
o. The astigmatism waveforms 1 to 6 have T ₂ / (T ₁ + T ₂ ) = 6.
0%, that is, T ₂ > T ₁ . No. In the symmetric continuous waveform of _No. 7, 50%, that is, T ₁ = T ₂ .

The B / P ratio in Table 1 is represented by T _P / (T _P + T _B ) as shown in the blank pulse of FIG.
o. The point-asymmetrical waveform of _{1~6, T P / (T P} + T B) =
0.5, ie, T _P = T _B. No. In the symmetric continuous waveform of 7, T _B = 0 and the B / P ratio is 1.

The speed ratio Vs / Vp in Table 1 represents the ratio between the peripheral speed Vs [mm / sec] of the developing sleeve 41 and the peripheral speed Vp [mm / sec] of the photosensitive member 1. No. The speed ratio 3 of No. 1 corresponds to the case of the normal rotation of the developing sleeve. The speed ratio 3 of 4 indicates the case of the reverse rotation of the developing sleeve. No. The speed ratio 2 of No. 2 corresponds to No. The speed ratio 2 of 5 indicates the case of the reverse rotation of the developing sleeve. No. Three
The speed ratio 1 of No. corresponds to the case of the forward rotation of the developing sleeve. The speed ratio 1 of 6 indicates the case of the reverse rotation of the developing sleeve. N
o. The speed ratio 2 of 7 is the case of the reverse rotation of the developing sleeve.

The secondary deviation width δ in Table 1 means that the secondary color magenta toner M is placed on the primary color yellow toner Yt shown in FIG.
The color change portion of the secondary color where t is small is referred to.

The hue change at the edge portion in Table 1 is a change in hue due to a change in the amount of toner attached to the boundary portion (edge portion) of the portion where the yellow toner Yt and the magenta toner Mt overlap each other as shown in FIG. Say.

As shown in Table 1, Duty, B / P ratio,
The developing process was performed while setting the speed ratio Vs / Vp, and the hue change of the formed color image was evaluated.

In a developing device having a developing sleeve 41 to which a blank pulse voltage having an astigmatically symmetric waveform is applied and which rotates in the reverse direction, no. As shown in Nos. 4 to 6, the secondary deviation width δ appeared widely in a width of 5 mm at the front end of the image. A blank pulse voltage having a non-point symmetric waveform is applied, and the developing sleeve 41 having the normal rotation is provided. In the developing devices of Nos. 1 to 3, the secondary deviation width δ is smaller than this. As shown in FIGS. 1 and 2, the secondary deviation width δ
Appeared at a width of 2 mm at the tip of the image. No. 3, the secondary deviation width δ is even smaller, and 0.5 mm to 2.5 mm
mm width.

The change in hue at the edge portion is visually determined.
A good image with no hue change was rated as ◎, an image with little hue change was rated as ○, an image with a little hue change as Δ, and an image with many hue changes as x.

The developing bias voltage of the astigmatic symmetric blank pulse waveform, the reverse rotation of the developing sleeve, and the speed ratio Vs / Vp = 3
No. which adopted The developing device of No. 4 of the present invention did not change the hue at the edge portion, and an image having the best hue was obtained. In addition, no. In No. 4, suction and white spots were prevented from being generated, a sufficient density was obtained, and excellent developer properties and development stability were obtained, and a high-quality image was obtained.

Next, No. 1, No. 3, No. Sample No. 5 showed little change in hue at the edge. No. 2, No. 7
Is an image having a little change in hue. No. In No. 6, a significant change in hue occurred.

The reflection densities shown in Table 1 are obtained by measuring a toner image formed by the developing device according to the present invention with a reflection densitometer. Images less than 4 were judged as x. As a result, in the case of No. 1 in which the speed ratio (Vs / Vp)> 2 was adopted. 1-2, N
o. 4 to 5 were good.

When these evaluations are combined, Duty 60
%, A blank pulse with a B / P ratio of 0.5 (see FIG. 7), a reverse rotation of the developing sleeve, and a speed ratio (Vs / Vp)> 2. 1, 2, 4, and 5 are good, and in particular, N in which the speed ratio (Vs / Vp) = 3 is adopted.
o. 4 was excellent.

The larger the (Vs / Vp) is 2 or more, the higher the secondary deviation width, the change in the hue of the edge portion, and the reflection density. However, if this ratio is too large, the rotational speed of the developing sleeve increases. Causes a problem in mechanical durability. Therefore, (V
The upper limit of s / Vp) is suitably about 5.

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 including a tandem type color image forming apparatus and the like.

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

[0124]

According to the image forming apparatus of the present invention, the occurrence of suction and white spots is prevented, a sufficient density is obtained, and a high quality image with excellent developer properties and development stability is obtained. . In addition, by setting the speed ratio (Vs / Vp) between the developer carrier and the image carrier in the developing area to 2 or more, the change in the secondary color in the latent image potential gap is hardly conspicuous and sufficient reflection is achieved. A density was obtained, and an image having a good hue was 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 blank pulse voltage waveform.

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 schematic diagram illustrating toner adhesion in a development region where an image carrier and a developer carrier are close to each other, and a diagram schematically illustrating toner adhered on the image carrier.

FIG. 9 is a schematic cross-sectional view and a schematic plan view of a two-color toner image formed on a photoconductor.

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

[Explanation of symbols]

Reference Signs List 1 image carrier (photosensitive drum, photosensitive body) 2 scorotron charger (charger) 4 developing device 4Y, 4M, 4C, 4K developing device 40 developing device housing (developer accommodating portion) 41, 41Y, 41M, 41C, 41K Developer carrier (developing sleeve) 42 Magnetic field generating means (magnet roll) 43 Developer layer regulating member 45 Developer transport roller 46 Developer supply rollers 47A, 47B Developer stirring screw 48 Bias voltage applying means 49 Waveform control means Vs Circumferential speed of developing sleeve Vp Circumferential speed of photoconductor V _AC voltage applied to _AC developing sleeve _VDC Voltage applied to _DC developing sleeve _VL Image latent image potential on photoconductor (latent image potential of exposed portion) _VH photoconductor charge potential T _P pulse unit time of the AC component applied to the developing sleeve T _B resting part time of the AC component applied to the developing sleeve f The closest distance [delta] 2-order deviation width of the pulse unit frequency d developing sleeve of the AC component applied to the image sleeve and the photosensitive member

Claims (2)

[Claims] An image forming apparatus comprising: an image carrier; and a developing device having a developer carrier for carrying a developer in a non-contact state with respect to the image carrier. An image forming apparatus that develops a latent image with a developer, applying a voltage obtained by superimposing an AC component that intermittently pauses at an astigmatic symmetry on a DC component to a developer carrier that carries the developer, And an image forming apparatus satisfying the following relational expression. (Vs / Vp) ≧ 2, where: Vs: peripheral speed of developer carrier [mm / sec] Vp: peripheral speed of image carrier [mm / sec] 2. An image forming apparatus for superimposing and forming a plurality of color images on an image carrier, comprising a plurality of developing devices according to claim 1 for each color of said plurality of color images, Forming an electrostatic latent image on the image carrier for each color of the image, and developing the electrostatic latent image by the developing device to form a superimposed image of a plurality of colors. Characteristic image forming apparatus.