JPS60154270A - Image forming method - Google Patents

Abstract

PURPOSE:To obtain a sharp image having no disorder by repeating the process wherein a latent image is formed on an image carrier and developed by impressing an electric field containing an AC component between the image carrier and a developer conveying body, and increasing the frequency of the AC component successively on every developing operation. CONSTITUTION:The photosensitive drum 1 which is charged electrostatically uniformly by a scorotron electrifier 30 is exposed to a light image from a laser light source through an image forming lens 32 to form an electrostatic latent image. The electrostatic latent image is developed by a developing device 13A. The formed toner image is no transferred to recording paper, and the 2nd electrostatic latent image is formed by the electrostatic charge of the electrifier 30 and image exposure. Then, the 2nd image is developed by a developing device 13B, and development is carried out repeatedly by a developing device 13C. The devices 13A-13C contains toner particles of yellow, magenta, and cyan, and the frequency of the AC component of the electric field impressed during development is set to 1.2, 1.5, and 2.0kHz in the order of development. Thus, a sharp polychromatic image having no disorder is formed.

Description

[Detailed description of the invention] 1. Industrial application field The present invention relates to an image forming method.

2. Prior Art First, an image forming method in which development is repeated a plurality of times will be explained using a color copying machine shown in FIG. 1 as an example.

In the case of a color copying machine, a filter is required to separate the light reflected from the original and extract a single color of light.The copying machine requires a filter bag with three built-in filters of different colors. It is provided. For example, if an electrostatic latent image is first formed on the original with a green gilter and then developed with the developing device 3B in which magenta toner is stored in the developing device 3, magenta toner will be deposited on the photoreceptor drum 1. An image is formed. This toner image is conveyed from a paper feed box 8 and is transferred onto a copy paper 7, which is a transfer body, wrapped around a copying drum 4, by a transfer pole 10. Thereafter, the photosensitive drum 1 is neutralized by the removing electrode 11, and after the excess four toners are removed by the cleaning device 5, it is charged again by the charging electrode 9. This time, the image exposure is destroyed by the light transmitted through the blue filter, and a yellow toner image is formed on the photoreceptor drum i by the developing device 3A. The image is superimposed and transferred onto the copy paper 7 that has been transferred. Similarly, after the cyan toner image is superimposed and transferred onto the copy paper 7, the copy paper 7 is separated from the transfer drum 4, fixed by the fixing device 6, and then discharged outside the machine. Although this image forming method is desirable because it can add color information compared to information obtained from only black and white images, it has the following problems.

(1) Each time the development of each color is completed, a transfer drum 4 must be provided to transfer the image onto copy paper, which increases the size of the machine and increases the time required for image formation.

(2) It is necessary to repeat the developing process and the transferring process several times, and it is necessary to ensure the accuracy of positional deviation.For these reasons, it is necessary to transfer the toner image to the copy paper 7 after each development. Instead, an image forming method has been proposed in which the toner images of all colors are formed on the photoreceptor drum 1 and then transferred to the copy paper 7 at the same time, thereby solving the above-mentioned problems. According to this image forming method, a toner image of a different color is again formed in an image area where a toner image has already been formed on the photoreceptor drum 1. (disturbing the toner image formed on the photoreceptor drum 1), the toner that has already formed an image on the photoreceptor drum 1 returns to the developer conveying body in the developing device, and this causes toner of a different color to the toner in the previous stage. There is a problem in that it invades the later stage developing device that is housed, causing color mixing. For this purpose, except for the developing device that initially forms a toner image on the photoreceptor drum 1, the photoreceptor drum 1 and the developer layer of the developer transporting member that develops this electrostatic latent image are not in contact with each other.
A means for superimposing an alternating current component as a developing bias is disclosed, for example, in Japanese Patent Application Laid-Open No. 144452/1982, but sufficient image density could not be obtained depending on the developing conditions.
There is a problem that image distortion and color mixing cannot be eliminated.3.Object of the InventionThe present invention has been made to solve the above problems.
The object of the present invention is to provide an image forming method that allows recording with desirable density and without image disturbance or color mixture.

4. Structure of the Invention That is, the present invention includes the step of forming a latent image on an image carrier and the step of supplying the developer on the developer conveying member to the image carrier and developing the latent image multiple times. Repeatedly, a visible image is formed on the image carrier! An image forming method comprising: generating an electric field containing an alternating current component between the image carrier and the developer transporting member; and increasing the frequency of the alternating current component sequentially for each development. The invention relates to an image forming method.

5. Examples Hereinafter, examples of the present invention will be explained in detail using the drawings.

First, the process by which the present inventor came to make this invention will be explained. An image forming method in which a process of forming a latent image on an image carrier and a process of developing the latent image are repeated, and a visible toner image is sequentially superimposed on the image carrier. It is necessary to perform development at an appropriate density without disturbing the toner image already formed on the image carrier in the preceding stage.

As a result of inspection, in order to satisfy this condition, the gap d(-) (hereinafter sometimes simply referred to as gap d) between the image bearing member and the developer conveying member in the developing area, the amplitude vAc of the AC component of the developing bias ( It has become clear that v) and frequency/(Hz) are the parameters when forming a toner image in the subsequent stage at an appropriate density without disturbing the toner image formed in the previous stage.

Therefore, while changing parameters such as the frequency and voltage of the alternating current component of the developing bias, the material is sufficiently charged to either positive or negative polarity as shown in FIG. Here, when the sleeve and/or magnetic roll 21 serving as a developer conveying body rotates, the developer is conveyed through the sleeve. FIG. 2 shows that as the magnetic roll 21 rotates in the direction of arrow A and the sleeve member rotates in the direction of arrow B, the developer is conveyed on the circumferential surface of the sleeve member in the direction of arrow B. There is.

The thickness of this developer layer is regulated by the spike control plate 17, and forms a uniform layer on the photoreceptor drum 1, which is an image carrier.
heading in the direction of When the developer reaches the development area U, the toner in the developer is moved according to the potential of the electrostatic latent image formed on the photoreceptor drum 1 and the electric field generated by the AC and DC voltages as the development bias. An electrostatic force acts on the toner, causing the toner to fly from the sleeve 20 and adhere to the surface of the photoreceptor drum 1, thereby forming a toner image.

Here, developer residue on the four circumferential surfaces of the sleeve containing toner that has not been subjected to development is scraped off by a cleaning blade 26. The AC power supply 22 and the DC power supply 23 are power supplies for applying a developing bias to the sleeve 20.
R is a protective resistance. When the developer reservoir 19 is used for development and there is insufficient toner in the developer reservoir 19,
By rotating the supply p-216), the toner hoch 1
Toner T is replenished from 4 onwards.

Here, a toner image is formed on the photoreceptor drum 1 in advance, and when developing the toner image by superimposing it on the photoreceptor drum 1, experiments are carried out by changing the parameters variously. As a result of measuring the disturbance and the image density of the toner images to be superimposed, the results shown in FIGS. 3 and 4 were obtained.

Note that a two-component developer in which the toner is positively charged was used as the developer.

FIG. 3 shows that the gap d between the photosensitive drum 1 and the sleeve 4 is 1
, o (''), the developer layer thickness is 0.5 (■), the charging potential of the photoreceptor drum 1 is 600 (V), the DC component of the developing bias is 500 (V), and the frequency of the AC component is 1 (KHz).
) shows the relationship between the amplitude VAC of the AC component and the image density of the toner image developed on the exposed portion (potential is 0 (V)) on the photoreceptor drum l. The amplitude EAC of the alternating current electric field is the value obtained by dividing the amplitude of the alternating current component of the developing bias (ie, 1/2 times the peak-to-peak value) AC by the gap d.

Curves A, B, and C shown in Figure 3 are obtained when toners whose average charge amounts are controlled to 30 (μc/r), 20 (pc/r), and 15 (pc/r), respectively, are used. O A1 □ which is the result obtained in
For both curves B and C, the amplitude EAC of the alternating current electric field is 2.
The effect of AC component appears above 0σ (V/-), and 25o
o (V/m) or more, it was observed that the toner image previously formed on the photoreceptor drum 1 was partially destroyed.

Figure 4 shows that the frequency of the AC component of the developing bias is 2.5.
kHz, and shows the change in image density when the amplitude EAe of the AC electric field is changed under the same conditions as in the experiment shown in FIG.

According to this experimental example, the amplitude EAC of the alternating current electric field is 50
If it exceeds 0 (V/■), the image density will be high, and if it exceeds 4 (KV/-) as shown in the figure, a part of the toner image previously formed on the photosensitive drum 1 will be destroyed. It was observed that Furthermore, as can be seen from the experimental results shown in Figures 3 and 4, the density of one image is the amplitude EA of the AC electric field.
Although C changes significantly after a certain value, this value does not depend too much on the average charge amount of the toner. The reason for this is thought to be as follows. In other words, in a two-component developer, the toner is charged by friction with the carrier and mutual friction between the toners, and the amount of charge on the toner is distributed over a certain range. is considered to be preferentially developed.

Even if the average charge profile is controlled by the charge control agent, there is no difference in the average charge amount of the toner actually developed, and the difference in the resulting image characteristics is observed to be small. it is conceivable that.

Now, when we conducted experiments similar to those shown in Figures 3' and 4 while changing the conditions, we found that the alternating current electric field jlIjI1. amplitude EA of
We were able to sort out the relationship between C and frequency f, and obtained the results shown in Figure 5. In FIG. 5, the areas marked ■ are areas where uneven development is likely to occur, the areas marked ■ are areas where the effect of the alternating current component does not appear and the density remains insufficient, and the areas marked ■ are those that have been deposited on the photoreceptor drum 1 in advance. In the areas (2) and (2) where toner tends to return from the photoreceptor drum 1 to the sleeve 20, the effect of the alternating current component appears and a high concentration is obtained, and the toner previously attached to the photoreceptor drum 1 is transferred to the sleeve 20. In the surface area of returning, ■ is a particularly preferable area.

These regions are divided by straight lines G and HXI. Among these, H and I each indicate conditions that give equal concentrations.

As a result, in order to develop the next (later stage) toner image with an appropriate density without destroying the toner image that has already been formed on the photosensitive drum 1 in the previous stage, the amplitude EAC of the alternating current electric field is required. This shows that there is an appropriate range for the frequency f, and the reason for this is considered to be the reason described below.

In a region where the image density tends to increase with respect to the amplitude EAc of the alternating electric field, for example, in the density curve A in FIG. 3, the amplitude EAc of the alternating electric field
In the region where Ae is 0.2 to 1.2 (KV/m), due to the alternating current component of the developing bias, there is a large contribution of force acting on the toner in the direction exceeding the threshold for flying from the sleeve 20, and the alternating current component As the components become stronger, toners with smaller charges are successively used for development. Therefore, as the amplitude EAC of the AC electric field increases, the image density increases.

On the other hand, in the region where the image density is saturated with respect to the amplitude EAC of the AC electric field, curve A in FIG. 3, the amplitude EAC of the AC electric field is 1.
For a region of 2 (KV/■) or more, this phenomenon can be explained as follows.

That is, in the region , the toner vibrates strongly as the amplitude EAC of the alternating current electric field increases, the aggregated toner clusters are destroyed, and only the highly charged toner selectively adheres to the photoreceptor drum 1 . In such a situation, since the amount of toner supplied to the development area in a certain period of time is finite, the image density is considered to be saturated with respect to the amplitude EAC of the alternating current electric field. Furthermore, when the amplitude EAC of the alternating current electric field becomes large, the charge on the surface of the photoreceptor drum 1 leaks, and a phenomenon occurs in which it becomes difficult to develop the toner.

In reality, it is considered that these factors combine to keep the image density constant as the amplitude EAC of the alternating current electric field increases.

Furthermore, the amplitude EAC of the alternating current electric field is increased, for example,
Under the conditions for obtaining curve A in the figure, if the amplitude is set to 2.5 (KV/■) or more, the photoreceptor (as described above)
LC formed above, f-image, 8 fractured, (It was found that the larger 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 1 is pulled back to the sleeve by the alternating current component. When toner images of different colors are superimposed and developed on the photoreceptor drum 1 to form a color image, it is fatal to destroy the toner images that have already been formed.

Based on the above experimental results, the present inventor set the amplitude of the AC component of the developing bias to VAC (V), the frequency to f (Hz), and the gap between the photoreceptor drum 1 and the sleeve to d (- ), then if development is carried out under the conditions satisfying 0.2≦vAc/(d-f) ((VAc/d)-15oo) / f≦1.0, then a It was concluded that subsequent development can be performed at an appropriate density without destroying the toner image that has been formed.
In order to obtain sufficient image density, it is desirable to satisfy the following conditions: 0.8≦vAc/(dllf), and further satisfy the following condition: 1.0≦VAc/(dllf).

Here, a method of setting the frequency f of the alternating current component applied as the developing bias will be explained using FIG.
As mentioned above, the line is a straight line indicating the boundary between ■, ■, ■, and ■, and increases as the frequency f becomes higher. For example, a point J where the amplitude EAC of the alternating current electric field is 2.5 (KV/m) and the frequency f is IKHz is on the straight line G. Also,
The point where the amplitude 11Ac of the AC electric field is 2.5 (KV/wm) and the frequency f is 3 KHz means that the toner is separated from the photoreceptor and drum 1 more easily when the frequency is high than when the frequency is low. , it has been shown that it is effective in preventing the sleeve from slipping back into place.

By the way, as the frequency becomes higher, the vibration range of the toner particles is narrowed, and the amount of toner that adheres to the photoreceptor drum 1 decreases, but it is not necessarily necessary that the same amount of toner of each color adheres to the photoreceptor drum 1 during each development. do not have. Color correction for color images is performed using other development conditions, such as the DC component of the development bias,
This can be done by adjusting the latent image potential, toner supply amount, etc.

From the above, if the frequency f of the AC component of the developing bias is increased sequentially each time development is performed, toner particles that have already been developed in the previous stage and are attached to the photoreceptor drum 1 can be removed from the sleeve 2.
They came to the conclusion that it is possible to perform the subsequent development without causing a reversion to 0. By doing the above, the subsequent development can be carried out without disturbing the already formed toner image or causing color mixing problems.

The frequency of the AC component applied as a developing bias was set at 200 (Hz) to prevent uneven development due to the AC component.
) When the developer cup is supplied to the photosensitive drum 1 by the rotation of the magnetic roller 21 shown in FIG. , 500 (H2) or more is more desirable.

Furthermore, the subsequent toner images are sequentially transferred to the photoreceptor drum 1 without destroying the toner images formed on the photoreceptor drum 1.
In order to develop the image, the frequency is increased in sequence, and (1) toners with a sequentially larger charge amount are used.

■ Gradually reduce the amplitude of the electric field induced by the AC component of the developing bias.

■ Gradually increase the amount of developer supplied to the development area.

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

That is, the toner particle phase has a large amount of charge and is easily affected by the electric field. Therefore, if highly charged toner particles adhere to the photoreceptor drum 1 during initial development, these toner particles may return to the sleeve 2o during subsequent development. For this reason, the above-mentioned point 9 is a good idea to use toner particles with a small amount of charge in the initial development. , ga. @Niichi? fl
H'if2) Kawaii, 8. (This is to prevent the process from returning to Leap 20.) Item □ is especially effective if the amplitude EAC of the alternating current electric field is made smaller as the development progresses to later stages.
This method prevents toner particles already attached to the photosensitive drum 1 from returning. As for the specific method of jin,
There is a method in which the voltage of the alternating current component is gradually lowered as the developing stage progresses, and a method in which the gap d between the photosensitive drum 1 and the sleeve is made wider as the developing stage progresses. On the other hand, method (2) takes advantage of the fact that the larger the amount of toner supplied to the development area, the easier it is to develop.In the subsequent development, along with these methods, the DC voltage of the development bias is adjusted for each development. ], it is possible to maintain appropriate surface image density or color balance.

A specific example carried out using the configuration described above is described in the sixth section.
This will be explained using figures.

Embodiment 1 FIG. 6 is a schematic diagram of the main parts of a color image forming apparatus. A photosensitive drum 1 uniformly charged by a scorotron charger 30 is charged by a He-Ne laser light source (not shown). The image is exposed to light sent through the rotating polygon mirror 31 and the imaging lens 32, and an electrostatic latent image is formed. This electrostatic latent image is developed by the first developing device 13A, and a first toner image is formed on the photosensitive drum 1. Then, this toner image is electrostatically charged again by the scorotron charger 30 without being transferred to the recording paper, and imagewise exposed in the same manner to form a second electrostatic latent image. Then, a second toner image is formed by the developing device 13B.

Similar steps are repeated until a third toner image is formed. In other words, the steps of charging (not necessarily required from the second time onwards), exposure, and development are repeated three times. Thereafter, the pre-transfer exposure lamp 33 irradiates the area of the photoreceptor drum 1 where the toner image is formed, and the transfer device 34
Recording paper (not shown) fed from a paper feeder (not shown)
This toner image is transferred along the path indicated by a broken line 35). The recording paper is heated and fixed by a fixing device 36 (which includes at least one heated roller) and then discharged outside the machine.

On the other hand, after the transfer has been completed, the photosensitive drum 1 is neutralized by the static eliminator 37, which was not used during the toner image formation, and the excess toner remaining on the surface is removed during the toner image formation. Removed by cleaning equipment.
This color image forming apparatus repeats the above operation every time the operation button is operated.

Each developing device used in this color image forming apparatus is
It has the same configuration as the developing device 13 shown in FIG.
The developing device 13A stores yellow toner, the developing device 13B stores magenta toner, and the developing device 13C stores cyan toner. The amplitude VAC of the AC component of the developing bias applied during development is IK■ for each developing device, and the frequency f is 1.2 (KH2) and 1.5 for each developing order.
(KHz), 2.0 (KHz). These developing biases are applied only to the developing device that performs development, and the developing devices that do not participate in development are grounded.
Further, the amount of charge of each toner is 20 (μc/f), the charging potential of photoreceptor drum 1 is 600 (V), the gap d between photoreceptor drum 1 and sleeve 4 is 0.5 (-), and the sleeve The thickness of the developer layer on the 20 circumferential surface was 0.3 (■), and the DC voltage of the developing bias was 500 (V) applied to each developing device.

When a multicolor image is formed using the above configuration, during the subsequent development stage, the toner image already formed on the photoreceptor drum 1 is destroyed, and toners of other colors are mixed into each developing device. A visible image of sufficient density was obtained without any

Example 2 In the color image forming apparatus shown in FIG. 6, which is the same as Example 1, the charging potential of the photoreceptor drum 1 was set to 500 (V) for both development and development.
), 600 M, and 700 (V), and developed
7 sO DC voltage 4400Ql)s ”0 (V), 60
When a multicolor image was formed under the same conditions as in Example 1 except for maintaining the density balance of each color toner image, the toner image that had already been formed on the photoreceptor drum 1 during the subsequent development was ] A visible image of sufficient density was obtained without any toners of other colors being mixed into each developing device.

Note that the present invention can be further modified based on its technical concept. In the above embodiment, a case was explained in which a two-component developer was used as the developer, but the same effect as described above can be obtained even if a -component developer is used. It can be applied not only to forming a single color image but also to forming a single color image.

In this case, it is also possible to form a toner image with gradation by using one developing device and increasing the frequency of the AC component of the developing bias sequentially for each development.

Further, the present invention can be applied not only to electrophotographic recording methods but also to non-male printers using electrostatic recording methods and magnetic recording methods.

6. Effects of the Invention According to the present invention, by sequentially increasing the frequency of the AC component of the developing bias applied between the image carrier and the developer transporting member for each development, the former stage is already During development, the electrostatic force applied to the developer attached to the image carrier can be reduced.

Therefore, during the subsequent development, the subsequent development can be performed without disturbing the image formed on the image carrier by the previous development. Due to this, even if multiple images are formed by repeating development on the image carrier multiple times, a clear image without any disturbance can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a conventional color image forming apparatus. 2 to 6 show embodiments of the present invention, in which FIG. 2 is a sectional view of the developing device and the photosensitive/photosensitive drum, and FIGS. 3 and 4 show the amplitude of the alternating current electric field. Figure 5 shows the density characteristics when changing the amplitude and frequency of the alternating current electric field. Figure 6 shows color image formation with multiple developing devices. FIG. 3 is a diagram showing the main parts of the device. Regarding the symbols used in the drawings, 1...
...Four...Photoreceptor drums 13.13A, 13B
, 13C...Song...Developing device 14...
・・・・・・−) Naho, Pa17・・・・・・・・・
・・・・・・・・・Hotate regulation mechanism・・・・・・・・・・・・
・・・・・・・・・Sleeve 21-・・・・・・・・・・・・
・・・・・・Magnetic roll 4・・・・・・・・・・・・・・・
・・・・・・AC power supply phantom・・・・・・・・・・・・・・・
・・・DC power supply D・・・・・・・・・・・・・・・・・・
・Developer T: Toner. Agent: Patent Attorney Hiroshi Aisaka (and 1 other person) (Voluntary) Procedure I
IVR official text 1. Indication of the case 1982 Special*mi No. 10701 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 Title
(127) Roku Konishi Photo Industry Co., Ltd. 4, Agent 6, [Number of inventions increased due to the amendment 7, Detailed explanation of the invention in the specification to be amended 8, Contents of the amendment (1) (11 Specification In the seventh line from the bottom of the second page, "extra" is corrected to "remaining." (2) In the third line from the bottom of the seventh page, "here, on the photoreceptor drum 1" is changed to "in accordance with the present invention." (3) "When developing" in line 1 to λ from the bottom of page 7 of the same page should be corrected to "When developing" using the developing device described above.
Developed. At this time," I am corrected. (4) From page 9, line 7 to page 10, line 5, [change in degree...... can be considered. ” is corrected as follows. [Indicates a change in degrees] According to this experimental example, when the amplitude EAC' of the alternating current electric field exceeds 500 (V/W), the image density increases. It was observed that part of the formed toner image was destroyed. In FIGS. 3 and 4, the shapes of curves A1(2)B and C, respectively, are almost the same except that the image density increases as the average charge amount of the toner increases. this is,
This is thought to be related to the fact that toner particles with a high charge amount, which has a distribution centered on the average value, are developed preferentially. ” +51 Delete “redundant” in the 3rd line of page 19. - Above - (3) 502-

Claims (1)

[Claims] 1. The process of cultivating a latent image on the image carrier and the process of supplying the developer on the developer conveying member to the image carrier and developing the latent image are repeated nine times to produce the image carrier. In an image forming method for forming a visible image on an image, an electric field containing an alternating current component is generated between an image carrier and the developer conveying member, and the frequency of the alternating current component is increased sequentially for each development. An image forming method characterized by: