JPS6159358A - Formation of image - Google Patents

Abstract

PURPOSE:To improve color balance and the eliminate image disorder by increasing the transmissivity of the 1st toner sufficiently to the 2nd irradiation light for the image exposure of latent image formed with the 1st toner. CONSTITUTION:A photosensitive body 1 is charged electrostatically by an electrostatic charger 2 and exposed to laser light L modulated with the output signal of an image pickup element which scans an original through image information processing part 10, transmit signal from another equipment, data in a storage device, etc. An electrostatic latent image is developed by a developing device A and the 1st toner image is charged electrostatically by the electrostatic charger 2 without being transferred to expose the photosensitive body. Then, the 2nd toner image is formed by a developing device B at this time and the 3rd and the 4th toner images are further formed similarly by using developing devices C and D. The irradiation light used for the 2nd image exposure is sufficiently high in transmissivity to the 1st toner and developing devices A-D use yellow, magenta, cyan, and black toner particles in order. Consequently, the color balance is excellent and image disorder is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Field of Industrial Application The present invention relates to an image forming method, for example, a method for forming images (particularly color images) suitable for electrophotographic copying and the like.

2. Prior Art A color image forming method using electrophotography to form a multicolor image from an electrostatic latent image is known.

According to this conventional method, light from an original document is passed through an optical filter to separate the colors, and the steps of charging, exposing, developing, and transferring are repeated using this separated light. That is, this process is repeated three or four times to form images using colored particles (colored toner) of yellow, magenta, cyan, and, if necessary, black. 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 with 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, they have the following problems.

(1) Each time the development of each color is completed, it is necessary to transfer the image to a transfer member, which increases the size of the machine and increases the time required for image formation.

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

From these things, 1. Attempts have been made to downsize the machine by developing a plurality of toner images on the same photoreceptor and performing the transfer process at once.

In such an image forming method, it is only necessary to repeat the next development several times on a photoconductor on which a toner image has already been formed, but during the subsequent development, the toner image already formed on the photoconductor in the previous stage is Or the toner that has already adhered to the photoreceptor may return to the developer conveying body, and this may mix into the subsequent developing device, which contains a developer of a different color than the preceding developer, causing color problems. There are problems such as the occurrence of smudges.

In order to avoid this, except for the developing device that first forms a toner image on the photoreceptor, the photoreceptor and the developer layer on the developer transporting member are not in contact with each other, and the voltage is applied to the developer transporting member or the photoreceptor. A method has been proposed in which an AC component is superimposed on the developing bias.

The principle of the above image forming method will be explained using FIG.
This figure is a flowchart showing changes in the potential on the photoreceptor.

First, the photoreceptor is charged to a certain potential using a scorotron charger or the like. The explanation will be continued below, taking as an example the case where the charging polarity is positive. When imagewise exposure is performed on the photoreceptor charged as described above (FIG. 1 ■), the potential of the light irradiated portion PH of the photoreceptor becomes low (FIG. 1 ■).
Note that DA is a non-exposed area. Next, by applying a bias whose DC component is approximately equal to the potential of the unexposed area DA to the first stage developing device, the positively charged toner Tt in the developing device is applied.
develops by adhering to the exposed area PH, which has a relatively low potential, and a first visible image is formed (Fig. 1 (■)). Due to the adhesion of the positively charged toner, the potential of this portion increases a little (indicated by DUP in the figure). Next, the photoreceptor is again uniformly charged, including the portion to which the toner T8 is attached, by the charger (FIG. 1 (■)). Next, when a second image exposure is performed (Fig. 1 ■) and development is performed in the same manner as above, another toner T2 adheres to the exposed area PH and a second visible image is formed ( Figure 1 ■). When these steps are repeated, for example, four times, toner images of four colors are formed on the photoreceptor drum. After this toner image is transferred to recording paper, it is fixed and becomes a recorded matter. Additionally, the surface of the photoreceptor is cleaned.

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.

Note that in the above explanation of the image forming method, we take as an example the case where reversal development is used to attach toner to the exposed areas of the photoconductor, but it is also possible to use regular development to attach toner to unexposed areas. It is possible.

By the way, you can change any color to yellow, magenta, cyan (3
In principle, it is possible to express the primary color using toner, and there is no need to add black. However, in ordinary recorded materials, black often needs to be particularly emphasized compared to other colors, as it represents sharp parts such as characters and lines.

In general, expressing black with three primary colors requires strict alignment of the three types of toner images and close to ideal spectral transmittance of each toner, but these are technically difficult. be. Furthermore, recorded images consisting of only three primary colors tend to lack density. In order to solve this problem, the image forming method described above is often equipped with a developing device that stores black toner in addition to the three primary colors.

When expressing various colors using the method explained above,
There are two methods:

■A method that does not directly overlap toners of different colors.

■A method in which toners of different colors are layered on top of each other.

(2) is to generate a pseudo color mixture on the recording paper by distributing multicolored toners T1 and T2 on the photoreceptor 1 without overlapping them as shown in FIG. 2(4).

In method (2), toner of a different color is superimposed on a toner image of a certain color and developed by controlling the latent image potential and developing bias.

However, in case (2), it is necessary to precisely align the image exposure so that the toner images of each color do not overlap at the same position, and if the image exposure is incomplete as shown in Figure 2 (B), the previous stage The toner image T8 partially blocks the image exposure,
There is a problem that the adhering amount of toner T2 developed in the latter stage becomes extremely small as shown in FIG. 2 (0).
It is not possible to produce the desired color mixture. In addition, in case (2), even if light is irradiated onto the previously developed toner T1, it will be absorbed by the toner T1 and will not reach the photosensitive layer sufficiently, and a latent image will not be completely formed.
As shown in the figure, the amount of toner T2 that was developed later is significantly reduced.

3. OBJECT OF THE INVENTION An object of the present invention is to provide a method that can easily form an image with good color balance and no image disturbance.

4. Structure of the invention, that is, the image forming method according to the present invention, a latent image formed by subjecting an image bearing member having a photoconductive layer to a first image exposure to a first image.
In the image forming method, the latent image formed by performing a second imagewise exposure is developed with a second toner. It is characterized by a sufficiently high transmittance.

Note that the irradiation light used for the first and second image exposures may be from the same light source, or may be from different light sources.

5. Example Hereinafter, the actual gun ρ0 of the present invention will be explained in detail with reference to FIGS. 5 to 11.

FIG. 5 is a schematic diagram of main parts of a color image forming apparatus to which the present invention is applied.

The photoreceptor 1 is uniformly charged by a scorotron charger 2. Then, in the image information processing section 10, the output signal of the image sensor that scanned the document, the transmission signal from other equipment, the data in the storage device, etc. are used as image data, and the image data is modulated (for example, by an acousto-optic modulator). )
The He-Ne laser beam is transmitted to the photoreceptor 1 via the imaging lens 3.
is exposed to light, and an electrostatic latent image is formed. This electrostatic latent image is
The toner image is developed by the first developing device A, and a first toner image is formed on the photosensitive drum 1. This toner image is then charged again by the scorotron charger 2 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 B.

Further, third and fourth toner images are formed in the same manner using the developing devices C and De. That is, the steps of charging (not necessarily necessary from the second time), exposure, and development are repeated four times including the transfer step.

After all toner images are formed on the photoreceptor drum 1, pre-charging is performed by the pre-transfer charger 9, whereby the toner on the photoreceptor drum 1 is uniformly charged again, and the toner is charged by the transfer device 4. This toner image is transferred onto the recording paper P fed from the paper feeding device.

The recording paper is separated from the photoconductor by a separator 5, and a fixing device 6 comprising at least one heated roller.
The image is heated and fixed, and the paper is ejected outside the machine.

On the other hand, the photosensitive drum 1 after the transfer has been neutralized by the static eliminator 7, which was not in use during the toner image formation, and the remaining toner on the surface is removed by the cleaning device, which had been deactivated during the toner image formation. 8.

Each of the above-mentioned developing units has a configuration as shown in FIG. 6, for example, regarding developing unit A. B.C.

D also has the same basic configuration. The developer De is conveyed in the direction of arrow G as the magnetic roll 12 rotates in the direction of arrow F and the sleeve 11 rotates in the direction of arrow G.

The thickness of the developer De is regulated by the bristling regulating blade 13 during transportation. In the developer reservoir 19, there are stirring blocks J and 14 to sufficiently stir the developer De.
is provided, and when the developer De in the developer reservoir 19 is consumed, toner T is replenished from the toner hopper 16 by rotating the toner supply roller 15. A DC power supply 17, an AC power supply 18, and a protective resistor R are connected in series for applying a developing bias to the sleeve 11. Further, the sleeve 11 and the drum 1 are arranged facing each other with a distance d between them, and the toner is held in a non-contact state with respect to the drum 1 in the developing area E.

The present inventor has proposed that when forming a color image using the above-mentioned apparatus, the irradiation light L for image exposure (in this example, He-
We focused on the fact that each type of toner has a different light transmittance with respect to Ne laser light). That is, the seventh
The figure shows the spectral transmittance of yellow, magenta, and cyan toners. On the other hand, the oscillation wavelength of He-Ne laser is 6
It is 32.8 nm.

Therefore, laser light is easily transmitted in the order of yellow, magenta, and cyan. That is, a magenta or cyan latent image can be relatively freely formed even on a photoreceptor to which yellow toner is attached by imagewise exposure.

For this reason, if you develop yellow, magenta, and cyan in that order, it is easy to create overlapping spots between the toners, and the above-mentioned
This method is advantageous when trying to express colors using this method. Furthermore, since black toner easily absorbs all visible light, it is desirable to develop it last.

In the method (2) as well, colors can be expressed relatively freely without requiring strict alignment. These will be explained in detail below.

FIG. 8 shows the process of developing with toner of each color based on the method (2) above. First, as shown in FIG. 8(5), after the first exposure, first development is performed using yellow toner Tl', for example, by the above-mentioned developer A. Then again 2
After the first exposure, as shown in FIG. 8 (03), a second development is performed using the magenta toner T2', for example, using the above-mentioned developer B. Furthermore, after the third exposure L' in the same manner,
As shown in FIG. 8C, a third development is performed using cyan toner Ts', for example, using the above-mentioned developing device C.

However, in the process shown in Fig. 8, Fig. 8 (A
) may be exposed at an incomplete position and may be exposed partially overlapping with the previous toner T□'.

However, since the toner Tl' is a rotary toner with high light transmittance as shown in FIG. is sufficiently formed.

Therefore, the next magenta toner T2' is yellow toner T2'.
Even if some portions overlap with +', a sufficient amount will adhere. In this way, a desired color image can be obtained with high density, high contrast, and good reproducibility by the combination of toners T1', T2', and Ts', and the alignment of each exposure is not so strict (i.e., as described above). It is possible to always express the desired color even if the image is misaligned.

FIG. 9 shows an image forming process according to method (2) above. That is, first, as shown in FIG. 9(5), the yellow toner TI' is attached during the first development, and then, after exposure, the previous toner T is attached during the second development as shown in FIG. 9(B).
Apply magenta toner T2' on top of □'.
Furthermore, in the same manner, an electrostatic latent image for cyan is formed in the third exposure L', and cyan toner Ta' is developed and adhered as shown in FIG. 9 (0).

In such superimposed development, especially during the second and third exposures, since the first toner Tl' has excellent light transmittance, the adhesion amount of toner T2' is sufficient, and the second toner T2' also has a sufficient amount of adhesion. Toner T has good light transmittance.
The amount of adhesion of a' becomes sufficient. As a result, desired color expression is always possible.

Further, the above-mentioned relationship between the transmittance of the toner to the irradiation light and the order of development is applied to the case where each latent image is formed with irradiation light having a different wavelength. That is, the toner to be developed first is selected so that its transmittance to the light to be irradiated later is greater than that of other combinations of toner and irradiation light.

On the other hand, the developer used in such an image forming method includes a two-component developer composed of toner and a carrier, and a one-component developer composed only of toner. Two-component developers require control of the amount of toner relative to carrier, but have the advantage that triboelectric charging of toner particles can be easily controlled.

In addition, especially with two-component developers consisting of a magnetic carrier and non-magnetic toner, it is not necessary to contain a large amount of black magnetic material in the toner particles, so it is possible to use color toner that does not cause color turbidity due to magnetic material. It is possible to form clear color images.

In such a two-component developer, the toner composition consists of the usual methods (1) to (6).

(11 Thermoplastic resin (binder) 80-90wt% Examples: polystyrene, styrene-acrylic copolymer, polyester, polyvinyl butyral, epoxy resin, polyamide resin, polyethylene, ethylene-vinyl acetate copolymer,
Or a mixture of these.

(2) Pigment (coloring material) 15wt or less Example: Black: Carbon plack.

Blue: Copper phthalocyanine, sulfonamide dielectric dye.

Yellow: benzine derivative.

Magenta: polytungstophosphoric acid, rotamine B lake, carmine 6B, etc.

(3) Charge control agent 5wt or less Positive polarity toner: Contains a large amount of nigrosine-based electron-donating dye,
In addition, metal salts of naphthenic acid or higher fatty acids, alkoxylated amines, alkylamides, chelates, pigments,
Fluorinated surfactant, quaternary ammonium salt.

Negative polarity toner: Electron-accepting organic complexes are effective, and others include chlorinated paraffin, chlorinated polyester, polyester with excess acid groups, and sulfonylamine of copper phthalocyanine.

(4) Examples of fluidizing agents: Representative examples include colloidal silica and hydrophobic silica.
Other examples include silicon face, metal soap, and nonionic surfactants.0 (5) Cleaning agent A substance that prevents toner from 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.

In addition to these materials, a magnetic material may be included to prevent fogging and toner scattering.

As magnetic powder, triiron tetroxide, γ-ferric oxide, chromium dioxide, nickel ferrite, iron alloy powder, etc. with a size of 0.1 to 1 μm have been proposed, but at present, triiron tetroxide is the most common. It is used in an amount of 5 to 70 wt% based on the toner. The resistance of toner varies considerably depending on the type and amount of magnetic powder, but in order to obtain sufficient resistance, the amount of magnetic material must be 55%.
It is preferable to make wt 1 or less. In addition, in order to maintain clear colors as a color toner, the amount of magnetic material must be 3 ow.
It is desirable to make it t% or less.

Other resins suitable for pressure fixing toner include approximately 2
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 0 kg/cm. Capsule toners can also be used.

A toner can be made using the above-mentioned materials by a conventionally known manufacturing method.

In the present invention, in order to obtain a more preferable image, the toner particle size is usually set to an average particle size of 50 p due to the relationship with resolution.
It is desirable that it be about m or less.

In the present invention, there is no theoretical limit to the toner particle size, but it is usually 1 to 30 μm due to resolution, toner scattering, and transportation.
About m is preferably used.

In addition, in order to visualize delicate points and lines or increase gradation, magnetic carrier particles are particles made of magnetic particles and resin (for example, resin dispersion systems of magnetic powder and resin, or resin-coated magnetic particles). ), which are more preferably spherical and have an average particle diameter of preferably 50 μm or less, particularly preferably 30/Jm or less, and 5 μm or more.

In addition, the bias voltage tends to inject charge into the carrier particles, which hinders good image formation, and the carrier tends to adhere to the surface of the image bearing member, and the problem that the bias voltage is not applied sufficiently can be solved. In order to prevent this from occurring, the resistivity of the carrier is 10 8 Ω-m or more, preferably 10 13 Ω-m or more, and more preferably 10 14 Ω-m or more.
It is preferable to have an insulating property of 0 or more, and it is also preferable to use one having the above-mentioned resistivity and particle size.

Such a finely divided carrier is produced by coating the surface of the magnetic body with the resin by using the above-mentioned magnetic substance and thermoplastic resin that can be used for toner, or by coating the particles with a resin containing fine magnetic particles dispersed therein. It can be obtained by preparing particles and selecting the particle size using a conventionally known average particle size selection means.

In addition, in order to improve the agitation performance of the toner and carrier and the transportability of the developer, and also to improve the charge control performance of the toner and make it difficult for toner particles to aggregate with each other or between toner particles and carrier particles, the carrier is added. It is desirable to make it spherical. In order to produce spherical magnetic carrier particles, for resin-coated carrier particles, select magnetic particles as spherical as possible and coat them with resin; Methods such as forming dispersed resin particles using fine particles and then subjecting them to a spheroidizing treatment using hot air or hot water; or directly forming spherical dispersed resin particles using a spray drying method are employed.

In the image forming method of the present invention, U.S. Pat.
Nos. 6 to 18659, Japanese Patent Application Laid-open No. 125753/1983, and Japanese Patent Application No. 57446/1987 using a one-two component developer;
Japanese Patent Application No. 58-97973, Japanese Patent Application No. 59-4563,
Patent application No. 1987-10699, patent application No. F18-23829
No. 5, Patent Application No. 1982-238296, Patent Application No. 1982-10
The developing method shown in No. 700 or the like may be adopted.

In particular, according to the development method using a two-component developer disclosed in Japanese Patent Application No. 58-238296, the amplitude of the AC component of the development bias is changed to vAc (
v), when the frequency is f (H2) and the gap between the image bearing member and the developer conveying body that conveys the developer is d (-), 02≦vAc/(d@f) ((VAC/d) -1500)/f≦1.0.

In this manner, by selecting the viewing conditions such as the AC bias voltage and its frequency, it is possible to obtain a high-quality image without causing image disturbance or color mixture. below,
The reason will be explained based on the results of experiments conducted by the present inventors.

The experimental conditions set were as follows. A two-component developer consisting of a magnetic carrier and a non-magnetic toner is used as the developer. The carrier has an average particle size of 30 μm (the average particle size is a weight average particle size measured with Omniconi Alpha (manufactured by Poshrom) or Coal Counter (manufactured by Coulter)), magnetization of 5 oemu/gs, and resistivity of 1014 Ω-m or more. It is a spherical carrier in which fine ferrite particles are dispersed in a resin, and the resistivity is as follows: After the particles are placed in a container with a cross-sectional area of 0.506n2 and tapped, 1.
kg/l:m'' is applied, the carrier particles at this time have a thickness of about 1 W, and a voltage is applied that generates an electric field of 1000 V 7 cm between the load and the bottom electrode. This is the value obtained by reading the value.The toner contains 9 owtq6 thermoplastic resin and 10 W pigment.
A small amount of charge control agent is added to each, cross-milled, and the average particle size is 1.
The thickness of 0 μm was used.

The toner was mixed at a ratio of 2wt% to the carrier sowt% to prepare a developer. Note that the toner is positively charged due to friction with the carrier. In addition, a toner image was formed on the photoreceptor drum in advance, the gap d between the photoreceptor drum and the sleeve was 1.0 mm, the developer layer thickness was 0.5 mm, the charging potential of the photo conductor was 600 mm, The DC component of the developing bias is 5
00■, set the frequency of the AC component to IKHz.

Under the following conditions, the relationship between the amplitude of the AC component and the image density of a toner image formed by reversal development on the exposed area (potential: OV) on the photoreceptor drum was measured. As a result, the following phenomenon was revealed. Average charge amount of toner is 30μc/gs20μc/g115μc/g
In both cases, when the charge control is applied, the effect of the alternating current component appears when the amplitude of the alternating current component of the electric field is 200 V/W or more, and when it is more than 112,500 V/W, the effect of the alternating current component appears, and when the amplitude is more than 112,500 V/W, the effect of the alternating current component appears. A toner image was observed to be partially destroyed.

In addition, the frequency of the AC component of the developing bias was set to 2.5 KHz.
When we measured the change in image density when changing the alternating current electric field strength EAC under the same conditions as in the above experiment, we found that the amplitude EAC of the alternating current electric field strength was 500 V/w.
When it exceeds 4Kv/W, the image density becomes high, and when it exceeds 4Kv/W, a part of the toner image previously formed on the photoreceptor drum is destroyed.

As can be seen from these results, the image density changes greatly after a certain amplitude, but the value of this certain amplitude can be obtained without much dependence on the average charge amount of the toner. The reason may 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 expected to be distributed over a wide range, and toner with a large amount of charge is given priority. It is thought that it will be developed. Even if the average charge amount is controlled using a charge control agent, the proportion of toner with a large charge amount will change significantly.As a result, although changes in development characteristics may be observed, it is thought that they will not be observed to a large extent. .

Now, when an experiment similar to the above was conducted with a woman under different conditions, the relationship between the amplitude EAC of the alternating current electric field strength and the frequency f was able to be sorted out, and the results shown in FIG. 10 were obtained.
In FIG. 10, the area indicated by ■ is an area where uneven development is likely to occur, the area indicated by ■ is an area where the effect of the AC component does not appear, the area indicated by @ is an area where toner backflow is likely to occur, (2) and (2) are regions where the effect of the alternating current component appears and toner backflow does not occur, and (2) is a particularly preferable region.

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

For areas where the image density tends to increase with respect to the amplitude EAC of the AC field strength, the amplitude EAc of the AC field strength is 0.
．． In the region of 77 m from 2 to 12, the alternating current component of the developing bias acts to make it easier to exceed the threshold for toner flying from the sleeve, and even toner with a small amount of charge adheres to the photoreceptor drum and is subjected to development. . Therefore, as the alternating current electric field strength increases, the image density increases.

On the other hand, in a region where the image density is saturated with respect to the amplitude EAC of the AC electric field strength, the amplitude EAC of the AC electric field strength is 1.2 KV.
For areas larger than /wa, this phenomenon can be explained as follows. In other words, in this region, as the amplitude of the alternating current electric field strength increases, the toner vibrates more strongly, and the clusters formed by toner aggregation become more likely to break, causing only toner with a large charge to selectively adhere to the photoreceptor drum. Toner particles with a small charge are difficult to develop. Toner that still has a small charge is
Even if it adheres to the photoreceptor drum, the mirror image force is weak, so it is easy to return to the sleeve due to AC bias. Furthermore, if the electric field strength of the alternating current component is too large, the electric charge on the surface of the photoreceptor drum leaks, making it difficult to develop the toner. In reality, it is considered that these factors overlap and the image density remains constant despite the increase in the AC component.

Furthermore, if the AC electric field strength is increased, for example, under the above conditions,
As mentioned above, when the amplitude is set to 2.5KV/■ or more,
It was found that the toner image previously formed on the photoreceptor drum was destroyed, and the greater the alternating current component, the greater the degree of destruction. The reason for this is thought to be that the AC component exerts a force on the toner adhering to the photoreceptor drum to pull it back toward the sleeve.

When toner images are sequentially developed on a photoreceptor drum, it is a fatal problem that the already formed toner images are destroyed during subsequent development.

Also, as can be seen by comparing the above results, when we experimented by changing the frequency of the AC component, the higher the frequency, the lower the image density, but this is because the toner particles follow the changes in the electric field. This is because the vibrating range is narrowed, making it difficult for the particles to adhere to the photoreceptor drum.

Based on the above experimental results, in each development process, the amplitude of the AC component of the development bias is set to VA c (V), and the frequency is set to f (H
z), when the gap between the photosensitive drum and the sleeve is d (w), 0.2≦■Ac/(d-f) ((VAC/d) - t500) / f≦1
．． It was concluded that if development is performed under conditions that satisfy 0, subsequent development can be performed at an appropriate density without disturbing the toner image already formed on the photoreceptor drum. In order to obtain sufficient image density and not disturb the toner image formed up to the previous stage, among the above conditions, 0.5≦■Ac/(d-f) ((VAC/d) -1500) It is preferable to satisfy /1≦1.0. Furthermore, especially when 0.5≦vAc/(d-f) ((VAC/d) -1500) / f≦0.8 is satisfied, a clear multicolor image with no color turbidity can be obtained, and many Even if the toner is rotated, it is possible to prevent toner of a different color from entering the developing device.

In addition, in order to prevent uneven development due to the AC component, the frequency of the AC component should be 200 Hz or higher, and if a rotating magnetic roll is used as a means for supplying the developer to the photoreceptor drum, the frequency of the AC component and the magnetic roll should be 200 Hz or higher. In order to eliminate the influence of beats caused by rotation, the frequency of the AC component is set to 500.
It is more desirable to set the frequency to Hz or higher.

In the above experimental example, since the developer is conveyed without contacting the image holding member (photoreceptor drum), the toner must be caused to fly toward the latent image surface using an alternating current bias. However, due to the phase of the alternating current, an electric force from the developer toward the image carrier and an electric force in the opposite direction act on the toner particles between the image carrier and the developer. Of these, the latter causes the toner on the image carrier to move to the developing device, causing toner of a different color to mix into the developing device. In order to prevent this situation and develop successive toner images on the photoreceptor drum at a constant density without destroying the toner image formed on the photoreceptor drum, the charge amount must be adjusted sequentially as development is repeated. Use larger toner.

@Sequentially reduce the AC component of the developing bias.

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

It is more preferable to employ these methods individually or in any combination.

That is, toner particles with a larger amount of charge are more easily affected by the electric field. Therefore, if highly charged toner particles adhere to the photoreceptor drum during initial development, they will
These toner particles may return to the sleeve. Therefore, as mentioned above, by using toner particles with a small amount of charge in the initial development, it is possible to prevent the toner particles from returning to the sleeve during the subsequent development. It is something. @
This is a method in which toner particles already attached to the photoreceptor drum are prevented from returning by decreasing the electric field strength sequentially as development is repeated (that is, as development progresses to later stages). 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 and the sleeve is made wider as the developing stage progresses. Moreover, the above-mentioned θ is a method in which the frequency of the alternating current component is gradually increased as development is repeated, thereby preventing the toner particles already attached to the photoreceptor drum from returning.

These ■@O are effective even when used alone, but for example,
It is even more effective to use a combination of, for example, increasing the toner charge amount and decreasing the alternating current bias sequentially as development is repeated. Further, when the above three methods are employed, appropriate image density or color balance can be maintained by adjusting the DC biases respectively.

Further, in addition to the above-mentioned methods (1) to (theta), the following methods O to (2) can also be employed.

O Move the unused developing device away from the image holder.

■ Gradually increase the toner supply amount.

θ　Sequentially increase the latent image potential contrast.

■ Gradually increase the gap between the image carrier and the developer layer.

■ Apply a bias to prevent toner from getting mixed in with unused developing devices.

Next, the present invention will be explained in more detail.

Example 1 Color images were recorded based on the method described above.

The specific conditions were as follows.

Drum Se photoreceptor drum diameter 120■ Tram linear speed 120wa/BeQ Light source He-Ne laser charging
+600V (Scorotron, rechargeable) Sleeve diameter: 30 dew Sleeve rotation Linear speed: 120■/See Number of magnet poles: 6 Magnet rotation: 1000r, p, m - Sleeve surface magnetic flux density: 900G (Maximum) Developer (common to each developer) 2 Component developer toner: Particle size average 10μm Resistivity 1014Ω-m or more Carrier: Particle size average 30μm Magnetization 50e, m, u, /g Resistivity 1014Ω-m or more Toner charge amount (common to each developer) 20μc/g developer Layer thickness: 0.5m between drum and sleeve (common to each developer) 08m Developing bias (common to each developer) AC
1.5 KV (effective value), KHz DC 500 V Image formation was performed according to the method (2) described above (ie, a method in which toners are not overlapped). Development was performed in the order of toner A-+B→C-+D. A developing bias was applied only to the developing device that performs development, and the developing sleeve and magnetic roll were also driven only during development. FIG. 11 shows a time chart of this process.

It was confirmed that various colors could be easily expressed under the above conditions.

Example 2 The differences from Example 1 are as follows.

(1) The charging process is only performed before the first image exposure,
No recharging is performed. The charging potential is +700■.

Due to the dark decay of the photoreceptor, the potential of the non-image area was +650V, 600V, and 550V during each development.

(11) The developing bias was as shown in the table below.

(110 The latent image was formed by the method (2) described above (that is, the method of overlapping toner).

In the above embodiment, He −Ne1/
-Although Boo light is used, the present invention is not limited to this, and any light source may be used. For example, when using a light source with a peak wavelength of 500 nm, development may be performed in the order of cyan→yellow→magenta. The developer used is not limited to a two-component developer.

Furthermore, the present invention can also be applied to an apparatus in which image exposure sections are provided at a plurality of locations. Further, by driving a plurality of developing devices for one type of latent image, any color can be reproduced.

Note that instead of the reversal development employed in each of the above embodiments, regular development may be performed to develop the non-exposed areas. Also, regarding the transfer and fixing method, known methods such as using EF paper, using an adhesive transfer method, or using a pressure fixing method can be used.

Furthermore, the present invention can be applied to non-impact printers that utilize not only electrophotographic recording methods but also electrostatic recording methods and magnetic recording methods.

6. Effects of the Invention As described above, in the present invention, development is performed using a toner that has a sufficiently high transmittance for the irradiation light of the second image exposure, so that the next irradiation light passes through the previous toner sufficiently. can be transmitted through the toner, thus forming a latent image to which the next toner can adhere in sufficient quantity. Therefore, an image with good color balance and less image disturbance can be easily obtained.

[Brief explanation of the drawing]

Figures 1 to 4 show conventional examples. Figure 1 is a flow diagram of the image forming process, Figure 2 (4), 3 and 4 are cross-sectional views showing the state of toner adhesion during other image formation. FIGS. 5 to 11 show embodiments of the present invention. , Fig. 5 is a schematic cross-sectional view of the image forming apparatus, Fig. 6 is a cross-sectional view of the developing device, Fig. 7 is a graph showing the light transmittance of irradiation light for each toner, Fig. 8 (4), Q3) , (0 is each cross-sectional view showing the toner adhesion state during image formation, Fig. 9, CB), (c) is each cross-sectional view showing the toner adhesion state during other image formation, Fig. 10 is each cross-sectional view showing the toner adhesion state during image formation. FIG. 11 is a time chart of the image forming process, which shows the density characteristics when the electric field strength and frequency are changed under various development conditions. In addition, in the symbols shown in the drawings, 1...... Photosensitive drum (image carrier)
11...Development sleeve 12...
・・・・・・・・・McNet Roll 17.18...
...Bias T1, T2, T3, T1, T2,
T3......Toner A, B, C, D...
...Developer, L...Image exposure. Agent: Hiroshi Aisaka, Patent Attorney Figure 2 Figure 3 Figure 5 (Voluntary) Procedural Amendment April 13, 1985] 1. Indication of the case 1988 Patent Application No. 181550 2. Image formation of the name of the invention Method 3: Relationship with the case of the person making the amendment Patent applicant address: 1-26-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Name:
(+27) Roku Konishi Photo Industry Co., Ltd. 4, Agent 6, Number of inventions increased due to amendment (11, ``Image formation'' in the third line from the bottom on page 31 of the specification is 1 - Developing device A, For B, C, and D, respectively,
1-, macenta, n-an, and black toners are stored. "Image formation," he corrected himself. (2), page 31, 2 lines from the bottom], delete ``I. Na''. One or more -

Claims (1)

[Claims] 1. A latent image formed by applying a first image exposure to an image bearing member having a photoconductive layer is developed with a first toner, and then a latent image formed by performing a second image exposure is developed into a second image. An image forming method in which the first toner is developed with the toner, wherein the first toner has a sufficiently high transmittance to the irradiation light used for the second image exposure.