JPS60129760A - Picture forming method - Google Patents

Abstract

PURPOSE:To attain recording having required density and prevented from the disturbance of a picture and the mixture of colors by using a developer consisting of one component by satisfying the amplitude and frequency of an AC component of a developing bias with prescribed conditions in a developing process. CONSTITUTION:A DC power supply 45 for applying a developing bias is arranged between the sleeve 42 of a magnetic roll 43 and a photosensitive drum 9 to execute inversed development, and an AC power supply 46 is connected in series to the DC power supply 45 to vibrate a developer D in a developing area E and sufficiently supply the developer D to the photosensitive drum 9. In the developing process, 0.2<=VAC/d.f<=1.6 is satisfied when the amplitude of an AC component of the developing bias is VAC, its frequency is f and the gap between the photosensitive drum 9 and the sleeve 42 is d(mm.), so that an image already formed on the photosensitive drum 9 is not disturbed and the succeeding development is executed with proper density.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Industrial Application Field The present invention provides a method for repeating a step of forming a latent image on an image carrier and a step of developing the latent image using a -component developer multiple times. The present invention also relates to an image forming method for forming an image on the image carrier.

2. Prior Art A typical example of representing an electrostatic latent image as a multicolor image is related to a color image using an electrophotographic method. In this conventional method, the original document is passed through an optical filter to separate the colors, and the separated light is used to perform the charging, exposure, development, and transfer steps. That is, this step is repeated four times to form images of yellow, magenta, cyan, and black colored particles. There is also a so-called two-color development method in which electrostatic latent images of different polarities are formed on the same photoreceptor (image carrier) and developed using black and red colored particles. Although these multicolor image forming methods are desirable because they can add color information compared to the information obtained from monochrome images only, they have the following problems.

(1) It is necessary to transfer to the transfer body every time the development of each color is completed.
However, the machine becomes larger and the time required to form an image becomes longer.

(2) It is necessary to guarantee positional deviation accuracy through repeated operations.

For these reasons, attempts have been made to downsize the machine by superimposing and developing multiple toner images on the same photoreceptor so that the transfer process can be completed only once. Examples of the developer include a two-component developer composed of toner and a carrier, and a one-component developer composed only of toner. -Although component developers have some problems in toner charge control,
It has the advantage that there is no need to pay attention to the composition ratio of toner and carrier or agitation, and that the machine can be made smaller.

By the way, in the above-mentioned superposition development, it is sufficient to repeat the development several times on the photoconductor on which the toner image has already been formed, but when developing the toner image in the subsequent stage, the toner image formed on the photoconductor in the previous stage can be repeated several times. If the toner image is disturbed, the toner that has already adhered to the photoconductor will return to the developing sleeve, which is a developer conveying member, and this will cause the toner in the latter stage, which contains developer of a different color than the developer in the previous stage, to flow back into the developing sleeve. There is a problem that it invades the developing device and causes color mixing. In order to avoid this, except for the developing device that first forms a toner image on the photoreceptor, the developer material on the photoreceptor and the developing sleeve that develops this electrostatic latent image is shown, but depending on the developing conditions, However, there are problems in that image distortion and color mixture cannot be eliminated.

3. Purpose of the Invention The present invention has been made in consideration of the above points, and has the following objectives: - Image formation using component developers, having a desired density, and recording without image disturbance or color mixture. The purpose is to provide a method.

4. Structure of the invention - That is, the present invention includes a step of forming a latent image on an image bearing member, and -
In an image forming method in which an image is formed on the image carrier by repeating the step of developing the latent image multiple times using a component developer, in each developing step, the amplitude of the AC component of the developing bias is VAC(v), 0.2≦VAC/d-child≦
The present invention relates to an image forming method characterized by satisfying 1.6.

As a result of research into a method for developing and forming images by superimposing an alternating current component on the developing bias, the present inventors found that
We have discovered that there are areas in which high-quality images can be obtained without image disturbance or color mixing by selecting developing conditions such as AC bias and frequency.

The present invention provides a novel developing method based on this discovery.

5. Examples Hereinafter, the present invention will be explained in detail with reference to examples shown in the drawings.

First, the process by which the present inventors came to make this invention will be explained. As described in the prior art section, the method of sequentially overlapping toner images on an image carrier (for example, a photoreceptor drum) involves disturbing the toner image previously formed on the image carrier during development. This refers not only to forming a toner image multiple times, but also to forming a toner image multiple times in different portions of the image area. As a result of the study, in order to satisfy this condition, the gap d(fi) (hereinafter simply referred to as gap d) between the image bearing member and the developer conveying member in the development area, and the alternating current component of the development bias are required. To JiE
It has become clear that it is not possible to obtain an excellent image even if the values of VAC and frequency + (H-) are determined independently, and that these parameters are closely related to each other. Therefore, we conducted an experiment using the developing device 11 shown in FIG. 1 while changing parameters such as the voltage and frequency of the alternating current component of the developing bias.
The results shown in the figure were obtained. Note that a toner image is formed on the photoreceptor drum 9 in advance. This developing device 11 transports the developer on the circumferential surface of the sleeve 420 in the direction of arrow B as the sleeve 42 and/or the magnetic roll 43 rotates, thereby supplying the developer to the developing area EK. . The developer was a one-component magnetic developer, thermoplastic resin 70 wt%, pigment (carbon black) 10 wt%, magnetic material 20 wt%, and charge control agent were cross-milled to give an average particle size of 10 μm. The following was used. The amount of charge is controlled by a charge control agent. magnetic roll 4
As the sleeve 4 rotates in the direction of arrow A and the sleeve 4 rotates in the direction of arrow B, the developer is conveyed in the direction of arrow B. The thickness of the developer layer is regulated by the spike control blade 40 during transportation. A stirring screw 41 is provided in the developer reservoir 47 to sufficiently stir the developer reservoir, and when the developer reservoir in the developer reservoir 47 is consumed, the toner supply roller 39 As the toner cartridge 38 rotates, developer is replenished from the toner cartridge 38.

A DC power supply 45 is provided between the sleeve 42 and the photosensitive drum 9 to apply a developing bias in order to perform reversal development, and also vibrates the developer in the development area E to vibrate the developer. One AC power source 46 is provided in series with the DC power source 45 so that a sufficient amount of energy is supplied to the photoreceptor drum 9. R is a protective resistance.

In FIG. 2, the gap d between the photosensitive drum 9 and the sleeve 42 is 0.7 mm, the thickness of the developer layer is 0.3+m, the DC component of the developing bias applied to the sleeve 42 is 5 oov, and the frequency of the AC component of the developing bias is 0.7 mm. shows the relationship between the amplitude of the AC component and the image density of the toner image formed on the exposed area (potential is 0 V) on the photoconductor drum 9 when the charging potential of the photoconductor is set to 1 kHz and the charging potential of the photoconductor is 600V. There is. The amplitude EAC of the AC electric field strength is the amplitude VA of the AC voltage for development.
It is the value obtained by dividing C by 1iJd. Curves A and BSC shown in Figure 2 each have an average charge amount of 5 μC of magnetic toner.
These are the results when using 3μc/f and 2μC/l%. The three curves AlB and C are both
The amplitude of the alternating current component of the electric field is 200 V 7 mm or more; 1.
The image density is thick below 5kV/luI (,1,6kV/
+m+ or more, it was observed that the toner image previously formed on the photoreceptor drum 9 was partially destroyed.
kHz, and shows the change in image density when changing the alternating current electric field strength, etc. under the same conditions as in the experiment shown in FIG.

According to this experimental example, the image density is large when the amplitude Etc of the alternating current electric field strength is 5 oov/sw or more and 3.8 kV/lIm (not shown in Figure 2) or less, and 3.2 kV/w (not shown in Figure 2). ), a part of the toner image previously formed on the photoreceptor drum 9 was destroyed.

As can be seen from the results in Figures 2 and 3, the image density changes greatly after a certain amplitude, but the value of this amplitude is the average of the toner, as seen from curves A, B, and C. This can be obtained without depending on the amount of charge.The reason is thought to be as follows.

In other words, it is expected that the charge amount of the -component developer is widely distributed across positive and negative directions due to mutual friction between toner particles. Therefore, although the average charge amount is a small value, it is actually a large charge amount, for example, 2Oμc / 9
It is thought that the above toners are also present in a certain proportion, and such toners are mainly used for development. Even if the average charge amount is controlled by a charge control agent, the proportion occupied by the toner having a large charge amount does not change significantly, and as a result, it is considered that almost no change in development characteristics is observed.

Now, when experiments similar to those shown in FIGS. 2 and 3 were conducted while changing the conditions, the relationship between the amplitude EAC of the alternating current electric field strength and the frequency could be sorted out, and the results shown in FIG. 4 were obtained.

In FIG. 4, the area indicated by a circle is an area where uneven development is likely to occur, the area indicated by a square is an area where the effect of the AC component does not appear, and the area indicated by a circle is an area where toner backflow is likely to occur, that is, color mixing. (2) is a region in which the effect of the alternating current component appears and color mixing does not occur, and (2) is a particularly preferable region.

This result shows that in order to develop the next (later stage) toner image at an appropriate density without destroying the toner image previously (early) K formed on the photoreceptor drum 9, the amplitude of the alternating current electric field strength must be This shows that there is an appropriate range for that frequency, and the reason is considered to be due to the reasons described below.

In a region where the image density tends to increase with respect to the amplitude EAC of the AC electric field strength, that is, for example, regarding the density curve AVc in FIG. 2, the amplitude EAe of the AC electric field strength is 0.2 to 1 kV/
In the region wm, the alternating current component of the developing bias serves to make it easier to exceed the darkness value at which the toner flies from the sleeve, and even a small amount of toner is attached to the photoreceptor drum 9 and development is performed. Therefore, as the amplitude EAC of the alternating current field strength increases, the image density increases.

On the other hand, there are several possible reasons why the image density decreases as the amplitude of the alternating current electric field increases (for example, in the density curve A of FIG. 2, the amplitude EAC of the alternating current electric field strength is in the region of 1 kV or more). As the amplitude EAC of the alternating current electric field strength increases, the toner strongly vibrates, and the clusters formed by toner aggregation are not easily broken, and only toner with a large charge is selectively applied to the photoreceptor drum 9. attached,
Toner with a small charge becomes difficult to develop. Moreover, even if toner with a small charge is attached to the photoreceptor drum 9, its mirror image force is weak, so that it tends to return to the sleeve 42 due to the alternating current bias. Furthermore, if the amplitude of the electric field strength of the alternating current component is too large, the electric charge on the surface of the photoreceptor drum 9 will leak, making it difficult to develop the toner. In reality, it is thought that these factors overlap to reduce image density.

On the other hand, when the amplitude EAC of the alternating current electric field strength is increased, the toner image previously formed on the photoreceptor drum 9 is destroyed, as described above, and the greater the alternating current component, the greater the degree of destruction. The reason for this is thought to be that the toner adhering to the photoreceptor drum 9 is pulled back to the sleeve 42 by the alternating current component. When developing toner images by sequentially overlapping them on the photoreceptor drum 9, it is a fatal problem that the already formed toner images are destroyed during subsequent development.

Also, as can be seen by comparing the results in Figures 2 and 3, when we experimented by changing the frequency of the AC component, the higher the frequency, the lower the image density, but this is because toner particles This is because the vibration range is narrowed because it cannot follow changes in the electric field, making it difficult to be attracted to the photoreceptor drum 9.

Based on the above experimental results, the present inventor has determined that in each development step,
The amplitude of the AC component of the developing bias is VAC (V), 0.2
It was concluded that if development is performed under the conditions satisfying ≦vAc/dIIf≦1.6, subsequent development can be performed at an appropriate density without disturbing the toner image already formed on the photoreceptor drum 9. I got it. In order to obtain sufficient image density and not disturb the toner image formed up to the previous stage, the image density should be 0.4, which is the region in which the image density tends to increase with respect to the alternating current electric field in FIGS. 2 and 3. It is desirable to satisfy the condition ≦vAc/d11f≦1.2. Further, within the region, it is desirable that the electric field is slightly lower than that at which the image density becomes maximum, and satisfies 0.6≦MA c/d @4≦1.0.

In addition, in order to prevent uneven development due to the AC component, the frequency f of the AC component is set to 200 Hz or more, and when a rotating magnetic roll is used as a means for supplying the developer to the photoreceptor drum 9, the AC component and the magnetic port are - In order to eliminate the influence of the eel caused by the rotation of the AC component, the frequency of the AC component is 50
It is more desirable to set the frequency to 0Hz or higher.

The configuration of the present invention is as described above, but in order to sequentially develop subsequent toner images on the photoreceptor drum 9 at a constant density without destroying the toner image formed on the photoreceptor drum 9, As development is repeated.

■Use toners with larger charge amounts in order.

(2) Gradually reduce the amplitude of the electric field strength of the AC component of the developing bias.

■Sequentially increase the frequency of the AC component of the developing bias.

It is more preferable to use these methods alone or in any combination.

In other words, toner particles with a larger amount of charge are more susceptible to the influence of the electric field. Therefore, if toner particles with a larger amount of charge adhere to the photoreceptor drum 9 during initial development, these toner particles may return to the sleeve during subsequent development. There is. Therefore, in the above-mentioned method 90, by using toner particles with a small amount of charge in the initial development, the toner particles are prevented from returning to the sleeve during the subsequent development. ■
By gradually decreasing the electric field strength as development is repeated (i.e. #1, which is the later stage of development, etc.),
This method prevents toner particles already attached to the photoreceptor drum 9 from returning. Specific methods for reducing the electric field strength include a method in which the voltage of the alternating current component is gradually lowered, and a method in which the gap d between the photoreceptor drum 9 and the sleeve 42 is gradually widened.

In addition, as the development is repeated, the frequency of the alternating current component is increased sequentially to increase the frequency of the photoreceptor drum 9.
There is a method to prevent the toner particles that have already adhered to the toner from returning. These ■■■ are effective when used alone, but they are even more effective when used in combination, for example, by increasing the toner charge amount and gradually decreasing the AC bias as development is repeated. . Furthermore, when the above three methods are employed, appropriate image density or color balance can be maintained by adjusting the DC bias.

Another specific embodiment based on the configuration described above will be described with reference to FIGS. 5 and 7.

Embodiment The photoreceptor drum 9 is exposed to light sent from a He-Ne laser light source (not shown) through a rotating polygonal ljIgsi and an imaging lens 52 to form an electrostatic latent image. be done. This electrostatic latent image is developed by the first developing device 11A, and a first visible image is formed on the photosensitive drum 9. This toner image is then charged again by the scorotron charger 50 and exposed to light without being transferred to the recording paper, and this time a second toner image is formed by the second developing device 11B. . This continues until the fourth toner image is formed. That is, the charging (not necessarily necessary from the second time), exposure, and development steps are repeated four times without including the transfer step. After all the toner images are formed on the photoreceptor drum 9, the pre-transfer exposure lamp 53 irradiates the area on the photoreceptor drum where the toner image is formed, and transfers the image to the transfer device 54 from the paper feeder. Recording paper sent from (not shown) (its route is indicated by a broken line)
Then, the recording paper onto which this toner image is transferred is heated and fixed by a fixing device 57, which includes at least one heated roller, and is discharged outside the machine.

On the other hand, after the photosensitive drum 9 has been transferred, the static electricity is removed by the static eliminator 55, which was not used during the toner image formation, and the excess toner remaining on the surface is removed during the toner image formation. It is removed by a cleaning device 56.
This color image forming apparatus repeats the above operation every time the operation button is operated.

In this embodiment, selenium is used as the photoreceptor, and the photoreceptor drum 9 has a diameter of 120 m and a circumferential speed of 120 w/s.
ee, the charging potential is 600V, and the developing devices 11A, IIB, IIC, and IID used have a DC component of 50V.
ov, the amplitude of the AC component is 500v and its frequency is 1k
A developing bias of Hz is applied, and the gap d between the photosensitive drum 9 and the sleeve of each developing device is set at a constant value of 0.8 mmKm. The composition of the developer is 80 parts by weight of thermoplastic resin;
It contains 20 parts by weight of magnetic material, 5 parts by weight of pigment, and 1 part by weight of charge control agent, and the pigments used are yellow for 11A, magenta for 11B, cyan for 11C, and black for 11D. There is. Also, the average charge amount is 2μc/t in both cases.
s average particle size is 10 μm. Furthermore, in each developing device, the sleeve and the magnetic roll rotate in opposite directions, and the brush height is controlled by a magnetic blade, with a gap of 0.4 tan. The agent layer thickness is 0.4 tm.

With the above configuration, when a multicolor image was formed by sequentially superimposing toner images by superposition development as described above,
During subsequent development, it is possible to form a visible image with sufficient density without destroying the toner image already formed on the photoreceptor drum 9 or without allowing toner of another color to enter each developing device. done.

Example 2 This is carried out using the force/F-1iii image forming apparatus also shown in FIG. The difference from Example 1 is that the photosensitive drum 9
The developing device 11A is different in that the gap d between the sleeve and the developing device and the DC component of the applied developing bias are different from each other.
So, respectively 0.5 tug, 0.7 taxi for 450V%11B, 0.8 wm for 500V, 11C
, 500 V, 1.0 fin and 550 V for 11D. The average charge amount of the toner, the width of the AC via 4, and the frequency are common to each developing device as in Example 1, and are 2 pc/l, 500 V, and 1 kHz, respectively.

In this embodiment, the gap d between the photoreceptor drum 9 and the sleeve of each developing device is configured to widen to the developing layer, thereby preventing the toner from returning on the photoreceptor drum 9, and also preventing the toner from returning to the photoreceptor drum 9. By increasing the size of the developing layer, the density of each color toner image is kept balanced.

According to this example, even clearer images were obtained, and even after recording on multiple sheets of transfer paper, other colors were not mixed into each developing device.

Example 3 Similarly, this example is carried out using a color image forming apparatus shown in FIG. The difference from Example 1 is that the AC component and DC component of the applied developing bias differ depending on the developing device. In the developing device 11A, the amplitude of the AC component and the DC component are 700 V and 450 V, respectively, and in IIB, the amplitude is 600 V and 50 V.
500V1520V at 0V and 11C.

The gap between the drum 9 and the sleeve is the same for each developing device as in Example 1, and is 2 pcit, 1 kHz, and 0.5 pct, respectively.
8 It is darkness.

In this embodiment, the alternating current component is set to be small in the developing layer, thereby preventing the toner from returning on the photoreceptor drum 9, and by increasing the direct current bias sequentially, the toner image of each color is Maintains concentration balance.

A clear multicolor image was also obtained in this example, and even after recording a large number of sheets, other colors were not mixed into each developing device.

Embodiment 4 Similarly, this embodiment is carried out using a color image forming apparatus shown in FIG.

The development conditions were such that the amplitude of the AC component of the development bias was 1 kV for each developing device, and the frequency and DC component were 800 Hz s 400 V, respectively, for IIA.
1 kHz at %1iB, 1 at 450V, 11'C
．． 5 kHz % 500 2 kHz in VllllD
, is set to 550V.

Further, in each developing device, only the sleeve rotates to supply developer, and the magnets inside are fixed. The head height is controlled by a magnetic blade, the gap is 0.5 wm, and the developer layer thickness is 0.2 mK.
It has become. The average charge amount of the toner and the gap between the photoreceptor drum 9 and the sleeve are common to each developing device, and each is 2 μc/
f, 0.8 m, and other developing conditions and developer size were the same as in Example 1.

In Yamamoto's embodiment, the frequency of the alternating current component is set so that water flows into the developing layer to prevent the toner from returning to the photosensitive drum 9, and the direct current bias is gradually increased. The balance of density of each color toner image is maintained.

Also in this example, a clear multicolor image was obtained, and even after recording a large number of sheets, other colors were not mixed into each developing device.

FIG. 6 is a flowchart showing changes in the potential on the photosensitive drum 9 when development is performed by the color image forming apparatus of FIG. 5, where p=H is an exposed area and DA is an unexposed area. When charged by the scorotron charger 50, the photosensitive drum 9 maintains a constant potential, and when image exposure is performed, the potential of the portion irradiated with light becomes low.
Next, by applying a bias whose DC component is approximately equal to the potential of the unexposed area to the developing device, the positively charged toner in the developing device adheres to the exposed area where the potential is relatively low, and development is performed. A visible image is formed.

Due to the adhesion of positively charged toner, the potential of this portion increases slightly (indicated by DUP in the figure).

Next, by being charged again by the charger 50, the potential on the photosensitive drum 9 is uniformly charged so as to rise again to a predetermined potential (indicated by CUP in the figure). Next, a second image exposure is performed, and development is performed in the same manner, toner adheres to the exposed area and a second visible image is formed. By turning the edges four times, visible images of four colors are formed on the photosensitive drum 9 in a superimposed manner.

In the above method, the second and subsequent charging can be omitted. Furthermore, if charging is not omitted, a static elimination step may be performed before charging.

Although the three embodiments described above all use a reversal development method, it goes without saying that a regular development method, that is, a method in which a toner image is formed by depositing toner on non-exposed areas, can also be used. However, when developing using a regular developing method, a charging step is required each time.

Embodiment 5 Next, a description will be given of what happens when development is performed in the power 2-image forming apparatus shown in FIG.

The surface of the photoreceptor drum 9 is covered with an insulating layer. First, the surface of the photoreceptor drum 9 is charged by +1 by a negative charger 58 while the entire surface is exposed to light using a lamp L provided in the charger 58.
Charge to 00OV. This exposure is performed to facilitate charge injection into the photosensitive layer in the photosensitive drum 9.
Then, by the secondary charger 59 having an AC component,
The photosensitive drum 9, which is charged to 100 V and is charged to 0-iov, which reduces the positive charge on the surface of the insulating layer, is imagewise exposed to light reflected from the rotating polygon mirror 51, and the exposed portion is When the potential is positive, the image is developed by the first developing device 11A, and a first visible image is formed.

The photoreceptor drum 9 is uniformly charged to 1100 VK by the secondary charger 59, which acts as a secondary charger, and is exposed to light to form a second developing device 11.
B forms a second visible image.

This is repeated four times, and the entire visible image is transferred to the photoreceptor drum 9.
After the visible image is formed on the photoreceptor drum, a pre-transfer exposure tamp 53 illuminates the area of the photoreceptor drum where the visible image is formed, and the transfer device 54
Recording paper (not shown) fed from a paper feeder (not shown)
This visible image is transferred to the path shown by the dashed line).
The recording paper is heated and fixed by a fixing device 57, which includes at least one heated roller, and is then discharged from the machine.

On the other hand, after the transfer has been completed, the photosensitive drum 9 is neutralized by a static eliminator 55, and then excess toner remaining on the surface is removed by a cleaning device 56, which is turned off during toner image formation.

This color image forming apparatus repeats the above operation every time the operation button is operated. The development conditions for each development step are that the AC component of the development bias is 1.5 kV, and the frequency is 2 kV.
Hz, the DC bias is ov, and the gap between the photoreceptor trim 9 and the sleeve of each developing device is 0.8 tm.
In each developing device, the sleeve and magnetic roll rotate in opposite directions to convey the developer, and the developer layer thickness is regulated to 0.4 van by a magnetic blade. ing.

Each developer has the same structure as in Example 1 except that the charge control is -2 .mu.c/lK.

When a multicolor image is formed using the above configuration, the toner image already formed on the photoreceptor drum 9 may be destroyed during subsequent development, or if toner of another color gets mixed into each developing device. However, a visible image with sufficient density was obtained.

Example 6 Similarly, the color image forming apparatus shown in FIG. 7 is used.

The difference from Example 5 is that the average charge amount of the developer used and the DC component of the applied developing power differ depending on the developing device.
, -20V, IIB: -1 tic/fs, 11C: -2 μc/f, 20V, 111D: -4 pe/l.

As in Example 5, each developing device has a common cost of 1.5k.
V12 kHz s 0.8 try. Nao, i
The average charge amount of the toner used in the image device i11 AK is Oμc/f, but due to mutual friction of the toner particles, the charge amount distribution spreads over a wide range, and only the toner with the necessary charge is In this embodiment, the toner on the photoreceptor drum 9 is prevented from returning by controlling the charge so that the absolute value of the average charge amount of the developer increases in the order of development. At the same time, the density of each color toner image is maintained in balance by increasing the DC bias value sequentially.

A clear multicolor image was also obtained in this example, and even after recording a large number of sheets, other colors were not mixed into each developing device.

Example 7 Similarly, the color image forming apparatus shown in FIG. 7 is used.

The difference from Example 5 is that the average charge amount of the developer used and the amplitude of the alternating current component of the applied developing bias differ depending on the developing device, and in the developing device 11A, each is 0.
2kV, 11μ in IIB, 1.5 kV, 111
．． Te is -2 pc/f, 1.2 kV, 11 D Te is 2 kHz, r 0.8 m, respectively.

In this embodiment, as development is repeated, charge control is performed so that the absolute value of the average charge amount of the developer increases sequentially, and the alternating current bias is sequentially set to decrease.
This prevents the toner from returning on the photosensitive drum 9, and at the same time maintains the density balance of each color toner image.

According to this example, a clearer multicolor image was obtained, and even after recording a large number of sheets, other colors were not mixed into each developing device.

FIG. 8 shows changes in the potential on the photosensitive drum 9 when the color image forming apparatus shown in FIG. 7 performs development.

After being positively charged by the primary charger 58, the secondary charger 5
9 is negatively charged, and the surface potential of the photosensitive drum 90 is l.
It will be 600■. Next, as image exposure is performed, the potential of the light irradiated area increases, toner negatively charged in the developing device adheres to this area, and the potential of the adhered area decreases.

(Indicated by DDW in the figure) Next, the secondary charger uniformly charges the film to approximately 0V, and image exposure and development are repeated. After the visible images of all colors are repeatedly formed on the photoreceptor drum 9, this toner image is transferred to a recording paper, and the photoreceptor drum 9 is destaticized and cleaned, and the next image forming step is performed. Proceed to.

In the above method, the second and subsequent secondary charging can be omitted. Further, negative and secondary charging may be performed each time, and in that case, a static elimination step may be performed before charging.

In each of the embodiments described above, four-to-four transfer is used as the toner image transfer method, but other methods may also be used. For example, by using the adhesive transfer described in Japanese Patent Publication No. 46-41679, Japanese Patent Publication No. 48-22763, etc., transfer can be performed without considering the polarity of the toner. Furthermore, a method of directly fixing the image on the photoconductor, such as electrofax, can also be adopted.

Further, although magnetic toner is used in each embodiment, it is also possible to use non-magnetic toner.

As a developing method using non-magnetic toner, for example, Japanese Patent Application Laid-Open No. 50-30537 or Japanese Patent Application Laid-Open No. 52-22926
The one shown in Publication No. 1 is known. Further, in order to easily transfer the visible image on the photosensitive drum 9 to recording paper, it is desirable that the specific resistance of the toner is 1 o Ill Ωd or more. The resistivity was determined by placing the particles in a container with a cross-sectional area of 0.50-, tapping them, applying a load of 1 kf/- on the packed particles, and applying 1000 V/cm between the load and the bottom electrode. This value is obtained by reading the current value when applying the voltage generated by the electric field.

Furthermore, the constituent materials of the developer, excluding the magnetic material, are generally as follows.

(1) Thermoplastic resin: binder 80-90wt% Examples: polystyrene, styrene acrylic polymer, polyester,
Polyvinyl butyral, epoxy resin, polyamide resin, polyethylene, ethylene-vinyl acetate copolymer, etc. are often mixed and used. (2) Pigment: Coloring agent 0-15 wt Example: Black: Carbon plaque Blue: Copper phthalocyanine, Sulfonamide dielectric dye Yellow: benzine derivative Magenta: polytungstophosphoric acid, rotamine B lake, carmine 6B, etc. (3) Charge control agent θ ~ 5 wt% Example Nibras: Nigrosine type (electron donating) Minus: organic complex (electron (4) Examples of fluidizing agents: Colloidal silica (left), hydrophobic silica is a typical example, and others include silicon face, metal soap, and nonionic surfactants.

(5) Cleaning agent Prevent toner filming on the photoreceptor.

Examples: fatty acid metal salts, oxidized silicon acids with organic groups on the surface,
There are fluorine-based surfactants.

(6) Filler The purpose is to improve the surface gloss of images and reduce raw material costs.

Examples: calcium carbonate, clay, talc, pigments, etc.

Triiron tetroxide, γ-ferric oxide, chromium dioxide, nickel ferrite, iron alloy powder, etc. with a particle size of 0.1 to 1 μm have been proposed as magnetic powder, but at present, triiron tetroxide is often used. It is contained in an amount of 5 to 70 parts per toner. The resistance of the toner changes slightly depending on the type and amount of magnetic powder, but in order to obtain sufficient resistance, the amount of magnetic material should be
It is preferable to set it to 5vrt% or less. In addition, in order to maintain clear colors as a color toner, the amount of magnetic material must be increased by 3.
The content is preferably 0 wt% or less.

The above-mentioned materials may be simply mixed and pulverized, but in some cases, some measures may be taken as described below.

1. Adding an insulating substance to the toner or toner surface to control electrical resistance.

2. The surface of the magnetic powder is coated with a surfactant, organic dye, or specific resin in advance, or the surface is activated and then a film is formed through a polymerization reaction, and then mixed with a resin, etc. Make it into toner. The purpose of this is to facilitate uniform dispersion into the resin and to improve images at high humidity.

3. By selecting the magnetic properties such as the shape, axial ratio, and holding force of the magnetic powder, developing performance can be improved and, in some cases, toner scattering can be prevented.

4. Mixing magnetic toners with different particle sizes, amounts of magnetic powder, magnetic properties, and even electrical resistance increases fluidity and improves developability.

In addition, most magnetic powders are black and can also be used as a substitute for black pigment.

Other resins suitable for pressure fixing toner include approximately 20
Adhesive resins such as wax, polyolefins, ethylene-vinyl acetate copolymers, polyurethane, and rubber are selected so that they can be plastically deformed and adhered to paper with a force of about kg/ctn. Capsule toners can also be used.

The average particle size of these toner particles is preferably about 50 microns or less from the viewpoint of resolution. In this method, there is no theoretical limit to the toner particle size, but from the viewpoint of resolution, toner scattering, and conveyance, it is usually preferably about 1 to 30 microns.

Note that the present invention can be further modified based on its technical idea. In the above embodiment, only the development of a color image has been described, but the present invention can also be applied to developing the same color toner in multiple stages.

In this case, a toner image with excellent gradation can be formed on the photoreceptor drum. In addition, the present invention is applicable not only to electrophotographic recording methods but also to non-impact printers using electrostatic recording methods and magnetic recording methods. According to the present invention, the step of forming a latent image on the image carrier and the step of developing the latent image using a -component developer are repeated multiple times. Even if the image is formed in the previous stage, it is possible to form a subsequent image on the image carrier without disturbing the image formed in the previous stage.

That is, the relationship between the amplitude vAc1 of the AC component of the developing bias, its frequency a, and the gap d between the developer conveying member and the image carrier satisfies 0.2≦VAc/d''1≦1.6. By setting this, a clear image can be formed on the image carrier.

[Brief explanation of the drawing]

1 to 8 show examples of the present invention, in which FIG. 1 is a sectional view of a developing device and a photosensitive drum, and FIGS. Figure 4 is a diagram showing the density characteristics when changing the electric field strength and frequency. Figures 5 and 7 are color image formation with multiple developing devices. Figure 6 is a diagram showing the main parts of the apparatus; Figure 6 is a diagram showing changes in the surface potential of the photosensitive drum used in the color image forming apparatus shown in Figure 5; Figure 8 is a diagram showing the color image forming apparatus shown in Figure 7. 1 is a diagram showing changes in surface potential of a photoreceptor drum used in the device. Regarding the symbols used in the drawings, 9...
...Photosensitive drum 11, llA111B, IIC, 11D...
...Developing device 14.56, ...Cleaning device 42, Sleeve 43, Magnetic roll 45... ...DC bias power supply 46...
・・・・・・AC bias power supply agent Patent attorney Ai
Hiroshi Saka (and 1 other person) 10th 40th @20 EACEkv/qpckiJ 30th EAt E kv/nrs) 50th 60th 70th/80th (Voluntary) Procedure 11 City Book March 7, 1982 1. Indication of the case 1981 Patent Application No. 238295 2. Name of the invention Image forming method 3. Person making the amendment Relationship to the case Patent applicant address 1-26-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Name Name
(127) Roku Konishi Photo Industry Co., Ltd. 4, Agent 6, Number of inventions increased by amendment 7, Detailed explanation column of the invention in the specification subject to amendment and Figure 6 of the drawings, (1
), "same" on the second line from the bottom of page 6 of the specification is "same position"
I will correct it. (2), "formed in" on page 9, line 5 is corrected to "formed by reversal development." 3) Delete the phrase [i.e., color mixing is likely to occur] on page 11, line 7. (4), ``Color mixture'' on page 11, line 8 is corrected to ``toner backflow.'' (5) In the 6th line of page 13, [Toner ga] is corrected to read ``Toner.'' (6), on page 13, line 7, ``to be pulled back'' is corrected to ``a pulling force acts.'' (7), "combine" on page 15, line 13 is corrected to "adopt in combination." 8), in the third line from the bottom of page 18, "developing bias is applied" has been corrected to "developing bias is applied during each development". (9), page 19, line 6, ``In each developing device, the sleeve'' is corrected to ``In each developing device, the sleeve is used during development.'' (1O), on page 19, line 7, ``while rotating'' is corrected to ``while rotating.'' (11), "and is applied" in the first line of page 20 is corrected to "and is applied during development." (12), ``Applied'' in the first line from the bottom of No. 20 is corrected to ``Applied during development''. (13), "Development bias" in the first line of page 22 is corrected to "Development bias applied during development." (14), page 22, line 6, "sleeves in each developing device" has been corrected to "sleeves in each developing device during development." (16), ``Developing bias'' on the 6th line of page 26 has been corrected to ``developing bias applied during development''. (17), "sleeve" in line 10 of page 26 is corrected to "sleeve during development." (18), page 27, line 3, "applied" is corrected to "applied during development." (19), page 28, line 8, "applied" has been corrected as shown in the attached sheet. One or more Figure 6 Figure 8

Claims (1)

[Scope of Claims] 1. Repeating the steps of forming a latent image on an image carrier and developing the latent image using a -component developer multiple times;
In the image forming method of forming an image on the image carrier, in each developing step, the amplitude of the alternating current component of the developing bias is set to vA.
c(v), the frequency is (H-), and the gap between the image bearing member and the developer transporting member that transports the developer is d (mm), 0.2≦VAC/a-4≦1 .6 An image forming method characterized by satisfying the following. 2. In each developing step, the gap between the image carrier and the developer transporting member is maintained larger than the thickness of the developer layer formed on the developer transporting member. The image forming method described in item 1. 3. The image forming method according to claim 1 or 2, wherein the image is characterized by using 11th developer using a developer having a small absolute value of average charge amount. 4. Any one of claims 1 to 3, wherein the image is characterized by sequentially reducing the amplitude of the AC component of the electric field between the image carrier and the developer transporting member in each developing step. The image forming method described in item 1. 5. Any one of claims 1 to 4, wherein an image is characterized by sequentially increasing the frequency of an alternating current component of an electric field between the image carrier and the developer transporting member in each developing step. The image forming method described in Section 1.