JPH08137220A - Developing method - Google Patents

Abstract

PURPOSE: To reduce positive fog without lowering developing ability by specifying a shifting method between return voltage and fly voltage. CONSTITUTION: Development is performed by repeating a stage where return voltage V1 returning developer to a developer carrier carrying the developer and opposed to an image carrier carrying an electrostatic image is impressed on the developer carrier for a specified time t1 and a stage where the fly voltage V2 making the developer fly from the developer carrier is impressed on the developer carrier for a specified time t2 . In such a case, the return voltage V1 is shifted to the fly voltage V2 rectangularly in substance, and the fly voltage V2 is shifted to the return voltage V1 in a specified time T3 . Namely, the waveform of developing bias capable of obtaining the sufficient image density at Vpp at which leakage is not caused and preventing the positive fog is shown in figure. The bias is changed from Vmax to Vmin rectangularly in substance and changed from Vmax to Vmin in substance, and the rise to the Vmax side (return side of normal toner) is made slow.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing method for developing an electrostatic image on an image carrier which is used in an electrophotographic system and an electrostatic recording system.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic system, an electrostatic latent image formed on an image carrier is developed by a developing device to be visualized as a toner image. FIG. 6 shows a main part of an example of an image forming apparatus including a conventional developing device.

This image forming apparatus comprises a photosensitive drum 1 coated with a photosensitive layer as an image bearing member. In this example, the photosensitive drum 1 has a diameter of 80 mm and is 320 m / s in the direction of the arrow in the figure.
It is rotated at a speed of m and is uniformly primary-charged to 400V by a primary charger arranged around it. Next, the photosensitive drum 1 is subjected to image exposure through an optical system or exposure based on image information by a light emitting element such as a laser or an LED to form an electrostatic latent image on the photosensitive drum 1. This photosensitive drum 1
The electrostatic latent image formed on the photosensitive drum 1 is developed by a developing device arranged around the photosensitive drum 1.

In this developing device, a developing sleeve 2, a magnet roller 3 and a magnetic blade 4 are provided in a developing container 5 containing a magnetic toner as a developer. The developing sleeve 2 has a diameter of 25 mm and is rotatably arranged in the direction of the arrow in the opening facing the photosensitive drum 1. Inside the developing sleeve 2, a magnet roller 3 is fixedly arranged.

The developing sleeve 2 carries the toner and conveys it to a developing portion facing the photosensitive drum 1. During the conveyance, the toner is regulated in the layer thickness by the magnetic blade 4, and the developing sleeve 2 has a constant thickness. Is applied and formed.

As described above, the toner applied to the thin toner layer on the developing sleeve 2 is rubbed by the magnetic blade 4 and the developing sleeve 2 in the process so far, and the charged charge of −10 μC / g. Is given.

The photosensitive drum 1 and the developing sleeve 2 are arranged in a non-contact manner with a gap of 50 to 500 μm in the developing portion, and the gap between the developing sleeve 2 and the photosensitive drum 1 (SD) in the developing portion. The bias power supply applies a developing bias in which a direct current voltage and an alternating current voltage having a frequency of 1 kHz to 8 kHz, an amplitude of 40 to 3000 V, and an integrated average value Vdc of the waveform of 50 to 300 V are superimposed, and a developing electric field is generated. ing.

The AC voltage may be a sine wave, a triangular wave, a sawtooth wave, a rectangular wave, or a peak-to-wave waveform.
A bias such that the half value of the peak voltage and the integrated average value Vdc have different values (hereinafter, this bias is referred to as a duty bias) is known in the related art.

The charged toner on the developing sleeve 2 is transferred from the surface of the developing sleeve 2 to the surface of the photosensitive drum 1 by the force received from the developing electric field in the developing section, and the electrostatic latent image on the photosensitive drum 1 is transferred. Normal development of the image is performed.

Regarding the above-mentioned bias, at the same peak-to-peak voltage (hereinafter referred to as V _PP ), sin
It is known that image density is improved by changing to a rectangular wave instead of a wave or a triangular wave.

FIG. 5 shows the potential of the photoconductor and each rectangle at the same V _PP . In this example, the SD distance is 200 μm. The image portion V _D has a potential difference 1 between the photoconductor potentials V _D and V _min.
Although the toner is developed by V _D -V _min 1, the toner having the electric potential actually adheres to the developing sleeve by a mirroring force,
When a potential difference of a certain level or more occurs, the mirror image force is overcome to jump out of the sleeve and develop on the drum. The threshold potential is not known exactly, but when the toner tribo is about -10 μC / g, the electric field strength is 1 to 2 V / μ.
Since it flies at m or more, when the gap between SD is about 200 μm, it is about about 200 V or more. Therefore, if this threshold value is set to 250 V here, the developing side is carried out when the difference from V _D is 250 V or more, so that the region B in FIG. 5 receives a force corresponding to this area.

Comparing the areas of the B part, as is clear from FIG. 5, the sin wave / triangular wave / rectangular wave are 2: 1 / 2π: π = 2: 1.57: 3.14, respectively, If the _VPP is the same, the rectangular wave is the largest, so that a sufficient density can be obtained.

[0013]

However, when the above rectangular wave is used, there is a problem that the reversal fog increases.

The reversal fog is a development in which the toner charged to the opposite polarity to the normally charged toner on the developing sleeve is developed in the V _C portion, and the pullback side (V _max for the regular toner of the developing AC bias). Side).

Also here, if the voltage at which the reverse toner starts to fly is set to 250 V, the reverse toner adheres to the V _C portion under the force of this area in the area indicated by A in FIG. Therefore, if the sin wave is a rectangular wave, the density is improved. Similarly, if the sin wave is a rectangular wave, the area of the portion A is increased, and thus the reversal fog is increased.

Of course, if the rectangular wave is returned to the sin wave, the reversal fog is reduced, but the density becomes insufficient. Also, the peak-to-peak potential V of an alternating waveform as a sine wave is maintained.
Even if an attempt was made to up _PP to obtain a concentration, there was a leak particularly when used at a low pressure, and there was a limit to the up of V _PP .
Accordingly, it is an object of the present invention to provide a developing bias AC waveform capable of ensuring sufficient density at V _PP that does not cause leakage even at low pressure and reducing reversal fog.

[0017]

SUMMARY OF THE INVENTION According to the present invention for solving the above-mentioned problems, the developer is pulled back to the developer carrying body which faces the image carrying body carrying the electrostatic image and carries the developer. The step of applying the return voltage V ₁ for a predetermined time t ₁ and the flight voltage V ₂ for flying the developer from the developer carrier for a predetermined time t
_{In the} developing method in which the step of applying ₂ is repeated to perform the development, the return voltage V ₁ changes to a flying voltage V ₂ in a substantially rectangular shape, and a predetermined time t ₃ is changed from the flying voltage V ₂ to the returning voltage V ₁ . The feature is that it is necessary to shift.

According to the present invention, reversal fog can be reduced without lowering the developing ability.

[0019]

EXAMPLES Examples of the present invention will be described below.

The developing device has the same structure as that shown in FIGS. 6 and 7, and an a-Si photosensitive member is used as the image bearing member.

(First Embodiment) FIG. 1 is a view best showing the features of the present invention. In the development, a sufficient image density is obtained with V _PP which does not cause a leak as in the conventional case and a reverse fog is prevented. It is a bias waveform. This bias substantially rectangular manner displaced from V _max to V _min, V from V _max
This is referred to as a "slope bias" because it is displaced in a substantially rectangular shape to _min and the rise to the V _max side (regular toner pull-back side) is made slower.

Similar to FIG. 5, the potential relationship with V _D and V _L is shown, but the abscissa is taken as time to explain the change of the AC bias.

In this embodiment, the developing device used in the conventional example is used.

The change in the developing bias will be described below in time series. First, the developing bias falls from point a, and c
However, because of the falling of the transformer, a
→ c takes some time. ) When the potential becomes lower than the point b, that is, the point b where the potential difference from V _D is about 250 or more, the toner on the sleeve overcomes the mirror image with the sleeve and starts to fly to the drum.

For 25% of one cycle from the point c to the point d, the development is performed while maintaining the potential V _min on the development promoting side, and the potential rises again from the point d.

At this time, the potential rises so that the change to V _max on the pullback side becomes gentle.
Of course, a high-voltage transformer has a rise of bias conventionally, and a normal rectangular wave has a rise time of 10 to 20% of one cycle. In this case, it is important to intentionally increase the rise time rather than the usual square wave,
In this embodiment, 50% of one cycle is taken.

Then, at the point e of 1/2 cycle, the integrated DC value V _DC of the AC component is crossed. Therefore, as shown in the conventional example, it is assumed that development is performed in an area surrounded by bcde, and when this area is compared with sin / triangle wave / rectangle / slope, it is 2: 1 / 2π: π: 3 / 4π = 2: 1.5
It is 7: 3.14: 2.36, and it can be seen that the slope can make the strength of development larger than that of sin. This is c
Depending on what percentage of one cycle is set between ~ d, c ~
If the distance between d is about 15% or more, the area can be made larger than that of the sin wave.

When the developing bias further rises and rises to the point f, the potential difference from V _L becomes about 250 V or more, so the reversal toner starts to fly to the V _L portion. Then, it goes to the h point of V _max through the g point. Points h to i are pullbacks for the regular toner, and the excess toner excessively attached to the V _D portion is pulled back to the sleeve. On the other hand, for the reversal toner, development is performed on the _VL portion. Since the lengths of h to i are the same as those between cd and d, the AC bias waveform is the target waveform. Then, it falls again at point i, and the above is repeated.

Here, considering the area of the area (area higher than the V _L portion by 250 V or more) fhij for developing the reversal toner, the area is surely made smaller than the rectangular wave as compared with FIG. be able to.

This is because the effect becomes more remarkable as the slope is made gentle, and conversely, the effect becomes smaller as the rise is made steeper. Therefore, it is different from the conventional rectangular wave having a steep rise time of about 10 to 20%.

As described above, the strength on the developing side is stronger than that of sin, and the strength of causing reverse fog is smaller than that of the rectangular wave. However, as such a bias waveform, a gradual falling waveform as shown in FIG. 2B also corresponds to this. 2A has the same waveform as that in FIG.

However, the present inventor confirmed the effects shown in the following table by comparing and examining the waveforms of FIGS. 2 (a) and 2 (b).

[0033]

[Table 1]

[0034]

[Table 2]

That is, the slope wave (b) is intermediate between the sin wave and the rectangular wave in terms of density and inversion fog, but both are insufficient, whereas the slope wave (a) is insufficient.
It was found that the density was at the same level as that of the rectangular wave and the inversion fog could be reduced to the level of the sin wave.

The reason for this will be described with reference to FIGS. 2 (c) and 2 (d). In (c) and (d), T is the length of one cycle of the developing bias, b → g or q → ν is the time during which the AC bias is displaced so that the regular toner flies to the V _D portion, and f →
k, m → γ indicates the time during which the reverse toner is displaced so as to fly to the V _L portion.

Referring to FIG. 2C in connection with FIG. 2A, the regular toner overcomes the mirror image of the sleeve at point b and starts to fly to the drum, and as described above, approximately bcde. Is developed by receiving a force corresponding to the area of. After that, the toner receives almost no force between e and f, but the developing bias becomes higher than V _D , and the toner is displaced toward the pullback side.
Up to the point, it continues to fly to the drum due to inertial force (of course, the flight speed is attenuated by air resistance and collision of toner). Therefore, the force received for development substantially corresponds to the area of bcde, but the time of flight in the development direction is between b and g.

Similarly, the time during which the reverse toner continues to fly to V _L is from f to k from f to k when the developing bias is lower than V _L. The slope bias (a) having a slope on the pull-back side of the AC bias can make the developing time of the regular toner larger than 50% of one cycle T, and the time to develop the reverse toner to V _L. Can be less than 50%.

On the other hand, FIG. 2D shows the time q → v on the developing side.
Can only be about 50%, and the time for developing the reversal toner is, on the contrary, longer than 50%. (In addition, s
For in-wave and square-wave, these are all about 50%
Becomes Therefore, in the waveform of FIG. 2B, the force qstu on the developing side is set to be larger than the sin wave and smaller than the rectangular wave, so that the density is in the middle of the re-waveform and the reversal fog is the same.

On the other hand, in the waveform of FIG. 2 (a), bcde is smaller than the rectangular wave and the density is hard to appear, but since it is compensated by making the interval between b and g (developing time) larger than 50%,
A density equivalent to that of a rectangular wave can be obtained.

Also, in the case of reverse fog, the area of fhij is larger than the sin wave, and it is easy to perform reverse fog, but f → k
Since the compensation is performed by setting the interval (reversal fog time) to be less than 50%, there is an effect of preventing reversal fog similar to sin waves.

As described above, by improving the rectangular wave so that the developing AC bias has a relatively large slope toward the pullback side for the normal toner, the sin wave and the rectangular wave are changed as shown in Table 1. It is possible to provide a waveform capable of satisfying both of the drawbacks, that is, the density / inversion fog. Of course, there is no fear of leakage because achievable with conventional level of V _PP.

If the difference from the conventionally known duty bias shown in FIG. 5 (d) is clarified, this is because the B portion is smaller than the rectangular wave, which makes it difficult to obtain the density. There is. However, since V _min is lower, the developing electric field 1V _D −V _min 1 is larger than the rectangular wave, and the developing time is short. Therefore, if the high tribo development that allows the toner to reach the drum in a short time is not performed, the density will not decrease, but if the tribo is the same, the density is also low.

With respect to reversal fog, the area A is smaller than the rectangular wave and it is difficult for reversal fog to occur, but it is canceled by the long development time of the reversal toner, and the effect of preventing reverse fog is small.

Further, the difference from the gentle rising waveform shown in FIG. 5E is as shown in FIG.
In (e), in order to increase the area of the B portion, there is only the point where V _PP is up. In this case, from point c to point d in FIG. 1, V _min continues for at least 15% or more of one cycle. Therefore, if V _PP is the same, this area can be increased to 4/3 times or more of the triangular wave, and the density is improved.

More detailed experimental conditions will be described below.

As the developing device, the one described in FIG. 6 of the conventional example is used.

Experiments were carried out at an average tribo of toner of about −10 μC / g. The triboelectrification amount of the toner was determined by prescription and particle size of the toner, addition of a charge control agent, surface property of the developing sleeve 2, and further. The distance between the regulating member 4 and the developing sleeve 2,
It depends on the strength of toner packing (toner density) and the like. In this embodiment, the average particle size of styrene-acrylic type is 8μ.
The magnetic toner of m was used, and silica was externally used for imparting fluidity.

The developing sleeve 2 was used by blasting the basic surface of a non-magnetic stainless sleeve with glass beads of No. 400. The regulating member 4 was made of magnetic stainless steel and had a thickness of 1.2 mm. The gap between the regulating member 4 and the developing sleeve 2 was 200 μm. At this time, the toner triboelectrification amount is −10 μC / g, and the application amount is about 0.8.
It was ~ 1.2 mg / cm ² .

The magnet roller 3 is magnetized to have four poles, the developing pole located in the developing area faces the photosensitive drum 1, and the developing sleeve 2 has a magnetic force of about 800 to 1200 gauss.
The magnetic toner on top is made to stand. In this state, jumping development is performed by the action of the alternating electric field described above.
The closest distance between the developing sleeve 2 and the photosensitive drum 1 is 200 μm, and the developing sleeve 2 rotates when the photosensitive drum 1 rotates.
In the same direction as the peripheral speed of the photosensitive drum 1 is about 1.5.
Doubled

At this time, the developing bias was set to V _PP = 1000 frequency of 2.2 kHz by using the developing bias described in FIG. 1 (integrated DC value is about 150 V).

Since the actual waveform used is about 30 μsec for shifting from point a to point c in FIG. 1, the actual waveform is shown in FIG. Therefore, b → g
The period is about 62% of one cycle, and the period between f and k is 43%.

When an image is output under these conditions, the image density is about 0.10 higher than that of the sin wave.
1.35, which is almost the same as the rectangular wave, was obtained. The reversal fog was also better than the rectangular wave and equivalent to the sin wave.

The density was measured with a Macbeth RD914 manufactured by Macbeth Co., and the reversal fog was measured with a TC-6DS manufactured by Tokyo Denshoku Co., Ltd. using the reflectance of a blank sheet as a reference. The reflectance of each part was measured, and the difference between the two was taken as the fog. And the slope is 1
When the density and fog were compared with sin wave and rectangular wave with 80%, 70%, 50%, 30% and 20% of the cycle, the results are shown in Table 3 below. This of course keeps V _PP constant.

[0055]

[Table 3]

The rectangular wave used here has a steep rising edge of 10% of one cycle. From this table, it is understood that in order to secure the density of 1.20 or more and the fog to be 2.0% or less, the slope should be 30 to 70%.

In the examination using this bias, it was found that the halftone uniformity was superior to that of the rectangular wave. The reason for this is not clear enough, but it is considered that the effect of slowly pulling back the toner adhering to the drum is made because the change to the developing pullback side is made gentle, and it is difficult to disturb the toner image.

As another experimental example, an example in which a latent image is formed under the same conditions as in FIG. 1, a developing device having the configuration shown in FIG. 7 is used, and a non-magnetic toner (one-component non-magnetic developer) is used It is described below.

A developing device 5'shown in FIG. 6 contains non-magnetic toner therein, the toner is agitated by a stirring blade 7 and supplied to the coating roller 6, and the toner is applied by the coating roller 6 to the developing sleeve 2. ′ Is configured to feed. The toner is charged by friction with the developing sleeve 2'and the elastic blade 4'rotating in the direction of the arrow, and the charged toner rubs through the elastic blade 4'while adhering to the developing sleeve 2'by the mirror image force, and the developing area. Be transported to.

The toner remaining in the developing area without being used for development is returned to the inside of the developing device 5'by the rotation of the developing sleeve 2'and scraped off by friction with the coating roller 6.
The charging polarity of the toner is negative, as in the first embodiment.

The elastic blade 4'is made of silicone rubber, and the elastic blade 4'is applied to the developing sleeve 2'with a linear pressure of 15-.
Counter contact was performed at 20 g / cm. As the toner of the developing unit 5 ', a styrene-acrylic non-magnetic toner having an average particle size of 8 μm colored with carbon black was used, and silica was externally added for imparting fluidity.

At this time, the triboelectric charge amount of the toner is about −15 μm.
C / g, the coating amount was about 0.4 to 0.8 mg / cm ² . This toner charge amount is higher than −10 μC / g which is the charge amount of the magnetic toner in the first embodiment, but this is not a problem because the magnetic toner is attracted to the developing sleeve even by the magnetic force, but in this embodiment. Since the non-magnetic toner adheres to the developing sleeve only due to the mirroring force, unless the charging amount is increased to increase the mirroring force, the non-magnetic toner easily flies to the photosensitive drum and causes fog.

The developing device is arranged with respect to the photosensitive drum with a gap of about 180 μm between the developing sleeve 2'and the photosensitive drum 1, and the developing sleeve is at a peripheral speed of about 1.5 times in the same direction as the photosensitive drum 1. 2'rotated.

The developing bias shown in FIG. 3 is used.

Since the tribo is higher than in the previous experimental example, the image force on the sleeve is large and it is difficult to separate from the developing sleeve. Therefore, the SD distance is reduced to substantially increase the electric field strength. At the same time, pullback will be slightly stronger, so
Fogging does not occur even with non-magnetic toner. Of course, the bias frequency or V _DC may be adjusted for fogging.

When an image was output under such conditions, the image density was about 0.15 as compared with the sin wave.
It was 1.40, which was high and was equivalent to a square wave. Further, the reversal fog was also improved compared to the rectangular wave, and the sin wave was similar.

Although the above description has been made by using the one-component development as the developing method, the present invention is also applicable to the well-known two-component development in which the alternating bias is applied. At this time, since the developer coating on the developing sleeve becomes thick, it is preferable to set the SD gap to 500 to 1000 μm, and it is well known that the peak-to-peak voltage must be increased accordingly. is there. However, when the two-component development is used, the effect of preventing reversal fogging also becomes the effect of preventing carrier adhesion. Although the normal development has been described so far with the polarity of the toner being negative, reversal development may be used.

It is also applicable to the development of positive polarity toner. In this case, the bias waveforms of FIGS. 3 to 4 may be inverted upside down.

Further, although the photosensitive drum has been described as an α-Si drum, it is of course applicable to a well-known OPC drum, and at this time, the charging potential can be set relatively higher than that of α-Si. Therefore, the difference between V _D and V _L can be made larger than that in this embodiment. Therefore, there is an advantage that the latitude of setting the bias waveform is expanded.

(Second Embodiment) In this embodiment, various developing methods used in the first embodiment were used as the developing method, and the developing bias shown in FIG. 4 was used. V _PP is 1
The frequency was 2.2 kHz V _DL 150 V at 000 V.

The present embodiment is different from the first embodiment in that the way of rising is changed in the middle. Therefore, the circuit configuration of the transformer becomes slightly complicated.

However, t _D is 65% of one cycle and t _L is 40.
%, The effect on density and reversal fog is
It is larger than in the first embodiment. Further, since the pull-back side V _max time is as short as 65 μsec, background fog is likely to occur, and it is necessary to cope with it by, for example, making the gap between the developing device and the drum larger than in the first embodiment. At that time, also in this example, it was confirmed that the ground fog was the same as in Example 1.

[0073]

As described above, according to the present invention,
It is possible to reduce the reversal fog without reducing the developing ability.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a bias used in a first embodiment of the present invention.

FIG. 2 is a diagram for comparatively explaining the effect of the bias of the present invention.

FIG. 3 is a diagram of an actual waveform of a bias waveform used in the first embodiment of the present invention.

FIG. 4 is a diagram of an actual waveform of a bias waveform used in the second embodiment of the present invention.

FIG. 5 is a diagram illustrating a conventional bias waveform.

FIG. 6 is a diagram of a main part of an image forming apparatus used in the present invention.

FIG. 7 is a diagram of a main part of another image forming apparatus used in the present invention.

[Explanation of symbols]

 1 Photosensitive Drum 2 Developing Sleeve 3 Magnet Roller 4 Magnetic Blade 4'Elastic Blade 5, 5'Developing Container 6 Elastic Roller

Claims (6)

[Claims] _1. A step of applying a return voltage V ₁ for returning the developer to the developer carrying member facing the image carrying member carrying an electrostatic image and carrying the developer to the developer carrying member for a predetermined time t ₁ and developing. In a developing method in which development is performed by repeating a step of applying a flight voltage V ₂ that causes the developer to fly from the developer carrier for a predetermined time t ₂ , the return voltage V ₁ shifts to a flight voltage V ₂ in a substantially rectangular shape. , A predetermined time t ₃ from the flying voltage V ₂ to the return voltage V ₁ .
A developing method characterized in that the transfer is required. 2. The predetermined time t ₃ is 30 to 70 of a cycle T.
%, And the developing method according to claim 1. 3. The developing method according to claim ₁ , wherein the time t ₁ and the time t ₂ are substantially equal to each other. 4. The developing method according to claim 1, wherein the time t ₂ is 15% or more of the cycle T. 5. When the image portion potential V _D and the non-image portion potential _VL on the image carrier are V _D , the developer charged to the normal polarity is V _D.
2. The time for developing the portion is more than 50% of the cycle T, and the time for developing the V _L portion by the developer charged to the polarity opposite to the normal polarity is less than 50% of the cycle T.
To 4 development methods. 6. The developing method according to claim 1, wherein the developer is a one-component magnetic toner.