JPH02167577A - Color image forming method - Google Patents

Abstract

PURPOSE:To obtain a high definition image, especially color image by developing an image through the use of developer having insulating carriers and without bringing a developer layer into contact with the surface of an image forming body after the second stage of an image developing process. CONSTITUTION:When a compound toner image is formed on the image forming body 1 by repeating image forming stages and transferred onto a transfer material P, the image is developed with the use of the developer having the insulating carriers without bringing the developer layer into contact with the surface of the image forming body 1. Therefore, a recorder is miniaturized and the cost of the device is reduced and the synchronization control of each image exposure can be easily and accurately carried out, and moreover, the image is developed under non-contact jumping developing conditions and a color image having enough developing density and excellent sharpness can be recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an image forming method using electrophotography, and particularly to an image forming method suitable for color image formation.

[Prior art]

Various electrophotographic color image forming methods have been proposed and put into practical use.

One of them is disclosed in Japanese Patent Application Laid-Open No. 144452/1983.

The method described in JP-A-56-144452 is
After the surface of the image forming body is charged by a charger, an electrostatic image is formed on the charged surface by a first exposure means, and developed by a first developer, and then a second image is formed on the same charged surface. An electrostatic image is formed by an exposure means, the electrostatic image is developed by a second developing device, an electrostatic image is further formed on the same charged surface by a third exposing device, and the electrostatic image is developed by a third developing device. This is a method of forming a color image on an image forming body.

In this image forming method, the second, third...
・Developing using a developing device is done using a non-contact developing method.

[Purpose of the invention]

The present invention further improves the image forming method disclosed in the above-mentioned publication, and aims to provide an image forming method capable of obtaining high-quality images, particularly color images.

[Structure of the invention]

The above purpose is to form a composite toner image on the image forming body by repeating an image forming process including electrostatic latent image formation and development on the image forming body, and to transfer the composite toner image to a transfer material. In the image forming method, the image forming step 2
It is distantly related to an image forming method characterized in that, in subsequent image forming steps, development is performed using a developer having an insulating carrier without bringing the developer layer into contact with the surface of the image forming member.

The method described in JP-A-56-144452 is
After the surface of the image forming body is charged by a charger, an electrostatic image is formed on the charged surface by a first exposure means, and developed by a first developer, and then a second image is formed on the same charged surface. An electrostatic image is formed by an exposure means and developed by a second developing device, an electrostatic image is formed on the same charged surface by a third exposing means, and the electrostatic image is developed by a third developing device. This is a method of developing a color image on an image forming body.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to illustrated examples.

FIG. 1 is a schematic diagram of the configuration of a recording device that implements the method of the present invention, FIG. 2 is a schematic diagram of the configuration of a laser beam scanner for image exposure, and FIG. 3 is a portion showing an example of a developing device. The cross-sectional views, FIGS. 4-7, are flowcharts for implementing the method of the present invention.

In the recording apparatus shown in FIG. 1, l is a drum-shaped image forming member having a photoconductive photoreceptor surface layer made of Se or the like and rotating in the direction of the arrow;
2 is a charger that uniformly charges the surface of the image forming body 1; 3 is an exposure lamp that uniformly exposes the surface of the image forming body 1 with weak light;
4 is image exposure for each color of a color image; 5 to 8 are developing units in which toners of different colors such as yellow, magenta, cyan, and black are used as developers; 9 and 10 are on the image forming body L; A pre-transfer charger and a pre-transfer exposure lamp are provided as necessary to facilitate the transfer of a color image formed by polymerizing a plurality of color toner images onto a recording medium P, 11 is a transfer device, and 12 is a recording device. A fixing device for fixing the toner image transferred to the body P; 1-13 a static eliminator consisting of one or a combination of a static-eliminating lamp and a corona discharger for static-eliminating; 14 a static-eliminating device after transferring the color image of the image-forming body 1; This is a cleaning device having a cleaning blade or a fur brush that contacts the surface of the image forming member I to remove residual toner on the surface and leaves the surface of the image forming member I by the time the first development has been performed. .

Here, the charger 2 has a charger like the one shown in the figure, which can provide stable charging with less influence from the previous charging, especially when charging the surface of the image forming body l which is already charged. It is preferable to use a scorotron corona discharger. Also, like this recording device, a drum-shaped image forming body l
, the image exposure 4 may be a slit exposure that is filtered for each color using a filter, as in a normal monochrome electrophotographic copying machine, but in order to record a clear color image, Preferably, a laser beam scanner as shown in FIG. 2 is used.

In the laser beam scanner shown in FIG. 2, a laser beam emitted from a laser 21 such as a He-Ne laser is 0N10FFed by an acousto-optic modulator 22, and then deflected by a mirror scanner 23 consisting of an octahedral rotating polygon mirror to form an image. Image exposure 4 is formed by scanning the surface of the image forming body 1 at a constant speed through the f-theta lens 24.

Note that 25 and 26 are mirrors, and 27 is a lens for enlarging the diameter of the beam incident on the imaging r-θ lens 24 in order to reduce the diameter of the beam on the image forming body 1.

If a laser beam scanner as shown in FIG. 2 is used to form the image exposure 4, electrostatic images for different colors can be easily formed with shifts as described later, and therefore clear color images can be recorded. I can do it. However, image exposure 4 is
It is not limited to the above-mentioned slit exposure or dot exposure using a laser beam; for example, it can be applied to LED or CRT.
It may also be obtained using a liquid crystal or an optical fiber transmission body. In a recording apparatus in which the image forming body can be in a flat state such as a belt, the image exposure can be set to 7 lashes.

Further, as the developing units 5 to 8, those having a structure as shown in FIG. 3 are preferably used.

In FIG. 3, 31 is a developing sleeve made of a non-magnetic material such as aluminum or stainless steel, 32 is a magnet body provided inside the developing sleeve 31 and has a plurality of magnetic poles in the circumferential direction, and 33 is a magnet body formed on the developing sleeve 31. A layer thickness regulation blade 34 regulates the thickness of the developer layer formed; 34 is a scraper blade that removes the developed developer layer from above the developing sleeve 31; 35 is a stirring blade 35 that stirs the developer in the developer reservoir 36; 37 is a rotating body; 37 is a toner bar; 38 is a toner replenishment roller that has a recess on its surface into which toner enters; and supplies toner from the toner hopper 37 to the developer reservoir 36; A bias voltage including an oscillating voltage component is applied to the developing sleeve 3.
This is a power source for forming an electric field to control the movement of toner between the developing sleeve 31 and the image forming body L.
and the magnet body 32 rotate in the directions of the arrows, but even if the developing sleeve 31 is fixed, the magnet body 32 is fixed, or the developing sleeve 31 and the magnet body 32 are They may also rotate in the same direction. When the magnet body 32 is fixed, usually, in order to make the magnetic flux density of the magnetic pole facing the image forming body l larger than the magnetic flux density of other magnetic poles, the magnetization is strengthened or a magnetic pole of the same or different polarity is attached thereto. The two magnetic poles may be placed close to each other.

In such a developing device, the magnetic pole of the magnet body 32 is usually 500 to 500.
It is magnetized to a magnetic flux density of 1200 Gauss, and the developer in the developer reservoir 36 is attracted to the surface of the developing sleeve 31 by the magnetic force, and the attracted developer is transferred to the layer thickness regulating blade 3.
3 to form a developer layer, and the developer layer moves in the same direction or in the opposite direction (the same direction in the figure) to the direction of the rotation arrow of the image forming body 1, and forms a developer layer on the surface of the developing sleeve 31. develops the electrostatic image of the image forming body 1 in a developing area facing the surface of the image forming body 1, and the remaining portion is developed by the scraper blade 3.
4, the developer sleeve 31 is removed from the surface of the developer sleeve 31 and returned to the developer reservoir 36. The development is repeated in order to superimpose the color toner images, at least for the second and subsequent development, so that the toner attached to the image forming body 1 in the previous development will not be displaced in the subsequent development. It is preferable to use non-contact jumping development conditions. FIG. 3 shows a state in which development is performed under non-contact jumping development conditions.

Furthermore, the developing units 5 to 8 use non-magnetic toner, which does not require the inclusion of a black or brown magnetic substance in the toner and can provide a toner with a clear color, and can easily control the charging of the toner. It is preferred to use so-called two-component developers, which are removed from mixing with a magnetic carrier. In particular, when magnetic carriers are used in resins such as styrene resins, vinyl resins, ethyl resins, rosin-modified resins, acrylic resins, polyamide resins, epoxy resins, and polyester resins, triiron tetroxide, γ-ferric oxide, and Chromium, manganese oxide, ferrite,
A material containing fine particles of a ferromagnetic or paramagnetic material such as a manganese-copper alloy, or a material whose surface is coated with the above-mentioned resin, and has a resistivity of 108 Ωcm or more. , preferably an insulating carrier with a thickness of 10"0 cm or more. If this resistivity is low, when a bias voltage is applied to the developing sleeve 31, charges are injected into the carrier particles, and the surface of the image forming body 1 is Problems arise in that carrier particles tend to adhere to the image forming member 1 and that a sufficient bias voltage is not applied.In particular, when carrier particles adhere to the image forming member 1, the tone of the color image is adversely affected.

The resistivity is determined by placing the particles in a container with a cross-sectional area of O-50-5O, tapping the particles, and then applying l on the packed particles.
Apply a load of Kg/cm2, and place 1 between the load and the bottom electrode.
00OV This value is obtained by reading the current value when applying a voltage that generates an electric field of 7 cm.

Furthermore, if the average particle size of the carrier is less than 5 μm, the magnetization will be too weak, and if it exceeds 50 μm, the image will not be improved, breakdown or discharge will easily occur, and high voltage will not be able to be applied. Diameter is 5μm or more and 40μm
The following is preferable, and if necessary, a fluidizing agent such as hydrophobic silica may be appropriately added as an additive.

The toner preferably has an average particle size of 1 to 2011 m, and has an average charge amount of 3 to 300 μc/gs, especially 1
0 to 1.00 μc/g is preferred. When the average particle size of the toner is less than 1 μm, it becomes difficult to separate from the carrier, and when it exceeds 20 μm, the resolution of the image decreases.

When a developer made of a mixture of an insulating carrier and toner as shown below is used, the bias voltage applied to the developing sleeve 31 shown in FIG. This makes it easy to configure without worrying about leaks. In order to more effectively control the movement of toner development by applying such a voltage, the toner may contain a magnetic material such as that used in magnetic carriers to the extent that color clarity is not impaired. You can.

The above is the structure of the developing device and developer preferably used in the method of the present invention, but the present invention is not limited to this.
- No. 18659, No. 56-144452, No. 58-1
Developing devices and developers as described in each of the publications No. 1.6553 to No. 116554 may be used. More preferably, Japanese Patent Application Nos. 58-57446, 5896900 to 96903, and 58-9797 previously filed by the applicant of the present application.
It is preferable to use non-contact jumping development conditions using a two-component developer as described in each specification of No. 3.

The method of the present invention as shown in FIGS. 4 to 7 can be carried out using the recording apparatus as described above. still,
4 to 7 all show the stage up to the stage where the development shown in FIG. 2 has been carried out.

FIG. 4 shows that an electrostatic image is formed by an electrostatic image forming method in which the exposed part pH becomes the background part and the non-exposed part DA becomes the electrostatic image.
An embodiment of the present invention is shown in which development is carried out by depositing oppositely charged toner on the electrostatic image. In the recording apparatus shown in FIG. 1, the static electricity is removed by the static eliminator 13
It is cleaned by the cleaning device 14 and the potential becomes O.
The surface of the image forming body l in the initial state is uniformly charged for the first time by the charger 2 in the first rotation, and the charged surface is subjected to color-specific image exposure 4 to remove areas other than the electrostatic image area. The potential is approximately O
A first image exposure is carried out, and an electrostatic image whose potential is approximately equal to the potential of the first charge is generated using a developer of a color toner corresponding to image exposure 4 of the developing devices 5 to 8. The electrostatic image has been developed 11 times using the developing device in use, and the potential of the electrostatic image, which has decreased due to the adhesion of the toner T charged with the opposite polarity, is still higher than the background potential, so the static eliminator 13 (using only the static eliminator lamp) is used. ), the surface potential of the image forming body l is set to O again, and in the second rotation, a second charge is uniformly applied again by the charger 2, so that the charged surface has a different color from the previous one. Similarly, by image exposure 4, the potential other than the electrostatic image area becomes approximately 0.
A second image exposure is carried out, and the obtained electrostatic image is developed a second time with toner T' by another developer using a developer of a corresponding color toner. The 4th electrostatic image formation and development are repeated, and when the 4th development is performed and a color image in which the color toner images are superimposed is formed, the pre-transfer charge is applied until the color image passes through. 9 and the pre-transfer exposure lamp 10 are activated, and then the color image is transferred by the transfer device 11 to the recording medium P that is fed in synchronization with one rotation of the image forming body 1, and the transferred color image is transferred by the fixing device 12. The surface of the image forming body 1, which has been fixed on the recording body P and has transferred the color image, is neutralized by the static eliminator B, and returned to the initial state by being cleaned by the cleaning device 14, thereby completing one cycle of color image recording. This is an example of the present invention. That is, each time the electrostatic image forming body is charged, the charger 2 performs the charging, and the image exposure is also the same, for example, by the same slit exposure device equipped with filter switching means or by the laser beam scanner shown in FIG. Because it is performed by the device, there is no need for a separate image exposure device for each electrostatic image forming body.
The recording apparatus can be constructed in a small size and at low cost, and the electrostatic image forming body can be easily synchronously controlled each time. Note that the charge removal by the charge remover 13 between the previous development and the next charge can be omitted.

In the embodiment shown in FIG. 4, development is carried out by a developing method in which an electrostatic image is developed with a toner that is charged with opposite polarity. Therefore, it is easy to increase the development density of each color, and therefore it is easy to produce clear colors. Images can be recorded.

Incidentally, in order to avoid color mixing, it is preferable to set the DC bias during development to higher values in later stages.

Correspondingly, the charging potential may also be set higher in sequence.

Figures 5 to 7 show that an electrostatic image is formed by an electrostatic image forming method in which the pH of the exposed area is lower than that of the background area, and the electrostatic image is developed to have the same polarity as the potential of the foreground area. 3 shows an embodiment of the invention which is carried out by the deposition of electrically charged toner.

In the embodiment shown in FIG. 5 using the recording apparatus shown in FIG. 1, the surface of the image forming body l in the same initial state as shown in FIG. second to
The image exposure 4 for each color is projected by the laser beam scanner shown in the figure, and the first image exposure is performed so that the potential of the electrostatic image area becomes approximately O. A developer using a color toner corresponding to image exposure 4 (however, in this case, unlike the example shown in FIG. 4, the toner is charged to the same polarity as the image forming member 1) is used. After the first development, from the second rotation, without using the charger 2, image exposure 4 of a different color is projected at a position shifted from the projection position of the previous image exposure 4 using the same laser beam scanner. Image exposure is performed twice, and the resulting electrostatic image with a potential of approximately 0 is developed using another developer using a developer of the corresponding color toner, and then the third and fourth exposures are carried out in the same manner. After repeating electrostatic image formation and development, one cycle of color image recording is completed in the same manner as described with reference to FIG. In this example, even if an electrostatic image with a potential of approximately 0 is developed and the toner T charged to the same polarity as that of the image forming member 1 is attached, the potential is changed to a dark background area as shown in the figure. Since the potential is not equal to the potential, during development in which different color toner T' is attached to the electrostatic image formed later,
Toner T' often adheres to the electrostatic image area to which toner T has previously adhered in a piled manner even though exposure, that is, writing has not been performed. However, since a laser beam scanner is used to form the image quality light 4, it is extremely easy to shift the projection position of the image exposure 4 each time, and charging can be done only once. The fact that electrostatic images tend to overlap can be prevented by successively lowering the DC bias in each development, thereby making it possible to obtain color images with excellent clarity.

In the example of FIG. 6, an electrostatic image cannot be actively formed in the position where an electrostatic image was previously formed in the example of FIG. Since there is a high possibility that even a small amount of toner of a different color will adhere to the image area during subsequent development, this is an example in which these points have been improved. That is, in the example shown in FIG. 6, the steps from the initial stage to the first development are the same as those shown in FIG. In the second rotation, the charged surface is uniformly charged for a second time by the charger 2, and the charged surface is subjected to a second image exposure, a second development is performed, and so on. This example differs from the example shown in FIG. 5 in that the third and fourth electrostatic image formation and development are repeated.

In this way, in the example of FIG. 6 in which the surface of the image forming body l is uniformly charged again after the previous development to perform the subsequent electrostatic image formation and development, it is different from that in the example of FIG. 4. Similarly, an electrostatic image can be formed over the position where an electrostatic image was previously formed, and if the subsequent electrostatic image formation position is shifted from the previous one, the previous electrostatic image can be The effect is that there is almost no possibility that later toner of a different color will adhere to the image position.

The example shown in FIG. 7 is an example in which a subsequent different color toner is particularly prevented from adhering to an image position to which a previous toner has adhered. In this example, the steps up to the first development are the same as those shown in FIGS. 5 and 6, but after the first development, the pre-transfer exposure lamp 1o or the static elimination lamp of the static eliminator 12 is used. First, the surface of the image forming body 1 is uniformly exposed, and then a second charge is applied using the charger 2.
Either charging is carried out twice, or the charger 2 is used to uniformly charge the battery, and then the exposure lamp 3 is used to expose the strip to light, and then a second image exposure and a second development are carried out, and so on. The electrostatic image formation and development shown in FIG. 4 are repeated a third time. Here, if uniform exposure is performed first after development, the developed area to which the toner has adhered will not be neutralized and will maintain a high potential, while the other areas will become approximately 0 potential, and then a second charging will be performed. This makes it possible to charge the surface of the image forming member 1 by making the potential of the part to which the toner adheres slightly higher than that of the other part where an electrostatic image is formed. Even if the surface of the image forming body 1 is uniformly charged by applying a second charge to the surface of the image forming body 1, and then subjected to inter-stack exposure, the charged state of the surface of the image forming body 1 will be the same as that of the case where the uniform exposure was performed first. It will be the same as

Therefore, when developing an electrostatic image formed by shifting the next position, the potential of the area to which the previous toner was attached is high, so toner of a different color is effectively prevented from adhering there. .

In any of the above examples, it is preferable to use a developer made of a mixture of toner and an insulating carrier in the developing devices 5 to 8, and to perform the development under non-contact jumping development conditions. As mentioned above, this prevents the mixing of toners of different colors, and also makes it easy to apply an appropriate bias voltage for toner control to the developing sleeve 31 of the developing device, making it easy to apply a bias voltage to the developing sleeve 31 of the developing device. Even when using the electrostatic image forming method or the developing method as shown in the examples of FIGS. 5 to 7, in which an image exposure device such as the one shown in FIG. .

Next, the embodiments shown in FIGS. 4 to 7 will be described in more detail as Examples 1 to 3, respectively.

Example 1 (Example shown in FIG. 4) A recording apparatus as shown in FIG. 1 was used. However, the exposure lamp 3 was not used, the image forming body 1 had a CdS photoreceptor surface layer, and the peripheral speed was 180 mm/sec. The surface of this image forming body 1 was charged to -500 V by a charger 2 using a scorotron corona discharger, and the charged surface was subjected to slit exposure through a blue filter. As a result, the image forming body 1 has a background potential of -50 below the pH of the exposed area.
An electrostatic image was formed in which the potential of the non-exposed area DA was -500V with respect to V. This electrostatic image was first developed using a developing device 5 as shown in FIG.

The developing device 5 contains magnetite dispersed in a resin in an amount of 50 wL%, with an average particle size of 20 μm and magnetization of 30 em μ/g.

A carrier with a resistivity of 1014 Ωcm or more and styrene.
Benzine derivative 10 as yellow pigment in acrylic resin
Average particle size including parts by weight and other charge control agents is 10μ
A developer consisting of m non-magnetic toner was used under conditions such that the ratio of toner to carrier was 25 wt %.

Further, the outer diameter of the developing sleeve 31 is 30 mm, its rotation speed is 1100 rpm, and the magnetic flux density of the N and S magnetic poles of the magnet body 32 is 1.
000 gauss, the rotation speed is looorpm, the thickness of the developer layer in the developing area is 0.7 mm, the gap between the developing sleeve 31 and the image forming body 1 is 0.8 mm, and the developing sleeve 31 has a rotation speed of 1100 gauss.
A non-contact jumping development condition was used in which a superimposed voltage of a DC voltage of V and an AC voltage of 3 kHzXlooOV was applied.

While the electrostatic image is being developed in the developing unit 5, the other
Developing units 6 to 8 as shown in the figure were kept in a non-developing state. This can be done by disconnecting the developing sleeve 31 from the power source 39 and leaving it in a floating state, or by grounding it, or by actively supplying the developing sleeve 31 with a direct current of the same polarity as the charging of the image forming body 1 and the opposite polarity of the charging of the toner. This can be achieved by applying a bias voltage, and it is particularly preferable to apply a DC bias voltage. Since the developing devices 6 to 8 are also designed to perform development under non-contact jumping development conditions like the developing device 5, the developer layer on the developing sleeve 31 does not need to be particularly removed. This developing device 6 uses a developer in which the toner in the developer in the developing device 5 is changed to a toner containing polytan dust phosphoric acid as a magenta pigment instead of a yellow pigment. A developer was used in which the toner was changed to a toner containing copper phthalocyanine as a pigment, and a developer in which the toner was changed to a toner containing carbon black as a black pigment was used in the developing device 8. Of course, other pigments or dyes can be used as the color toner, and the order of the colors to be developed and the order of the developing devices can also be appropriately selected.

The surface of the image forming body 1 that had been subjected to the first development was re-charged to -600 V by operating the static eliminator 13 and the charger 2 (the static eliminator does not need to be operated).

A second image exposure is performed by slit exposure through a green filter on the charged surface, and then the developing sleeve 31
A second development of the magenta toner was carried out using the developing device 6 under non-contact jumping development conditions in which a superimposed voltage of a DC voltage of -200 V and an AC voltage of 3 kHz.times.loooV was applied. Similarly, charging, slit exposure through a red filter, third development of cyan toner by developer 7, and slit exposure without charging and filter, and fourth development of black toner by developer 8 were repeated. .

In the second development and subsequent developments, the amplitude of the DC bias component and AC component of the voltage applied to the developing sleeve 3I is adjusted appropriately according to changes in the surface potential of the image forming member I, development characteristics, and color reproducibility. , frequency, selection time of time selection conversion, etc. can be changed. In particular, increasing the DC bias while increasing the charging potential successively has the effect of preventing color mixing of toners.

After the fourth development is performed and a four-color image is formed on the image forming body L, the image is easily transferred by the pre-transfer electric device 9 and the pre-transfer exposure lamp 10, and then transferred to the recording body P by the transfer device 11. The image is transferred to the printer and fixed by the fixing device 12.

The image forming body l on which the color image has been transferred is neutralized by the static eliminator 13, residual toner is removed from the surface by contact with the cleaning blade or fur brush of the cleaning device 14, and the surface on which the color image has been formed is cleaned. When the image passes through the device 13, one cycle of color image recording is completely completed.

The color image recorded in the above manner was clear with sufficient density for each color, but some color mixing of toners was observed in areas where the toners of each color were closely adhered to each other.

Example 2 (Example shown in FIG. 5) A recording apparatus as shown in FIG. 1 was used. However, the exposure lamp 3 was not used, the image forming body 1 had a Se photoreceptor surface layer, and its peripheral speed was 180 mm/sec. The surface of this image forming body 1 is charged to +500V by a charger 2 using a scorotron corona discharger, and H
A first image exposure was carried out at a density of 16 dots l□/mm using a laser beam scanner shown in FIG. 2 using an e-Ne laser. As a result, the image forming body 1 has a background potential of +5
An electrostatic image was formed in which the potential of the pH of the exposed area was +50V with respect to 00V. This electrostatic image was first developed using a developing device 5 as shown in FIG.

The developing conditions for the developing device 5 are as follows: the average particle diameter of the developer carrier is 30 μm, the ratio of toner to carrier is 20 wt %, and the developing sleeve 31 has a DC voltage of +400 V and an AC voltage of 1.5 kHz, 100 OV superimposed. The procedure was the same as in Example 1 except that a voltage was applied. Further, the conditions of the other developing devices 6 to 8 were the same as in Example 1 except for the bias voltage. However, in this case, the bias voltage that maintains the developing device that does not participate in development in a non-developing state has a polarity opposite to that of toner charging, and also has a polarity opposite to that of image forming body 1.

A pre-transfer charger 9, a pre-transfer exposure lamp 10. Static eliminator 13. without operating the cleaning device 14 and the charger 2,
A second image exposure was performed again using the same laser beam scanner with the dot position shifted without changing the density, and then a second development of magenta toner was performed using the developing device 6. Similarly, the third development of yellow toner by developer 7 and developer 8
A fourth development of the black toner was repeated.

In the development after the second development, the amplitude of the DC bias component and AC component of the voltage applied to the developing sleeve 31 is adjusted appropriately according to the change in the surface potential of the image forming body 1, the development characteristics, and the color reproducibility. Changed the selection time etc. of 1 frequency 9 time selection conversion. In this example, it is particularly effective to gradually reduce the DC bias each time to prevent color mixing of toners.

After the fourth development is performed and a four-color image is formed on the image forming member L, the rest is transferred and fixed onto the recording member P, and the image forming member L is charged and cleaned in the same manner as in Example 1. This completed one cycle of color image recording.

The color image recorded in the above manner was as clear as in Example 1.

Example 3 (Example shown in FIG. 6) Using the same device as in Example 2, the voltage applied to the developing sleeve 31 of the developing device was +400 V DC voltage and 50 V DC voltage.
A superimposed voltage of AC voltage of 0 Hz and 250 V was used, and before each image exposure after the second image exposure, static electricity was removed by the transfer exposure lamp 10, and then the surface potential of the image forming body 1 was reset to +500 V by the charger 2. Color image recording was carried out under the same conditions as in Example 2, except for charging.

The recorded color image is better than that of Example 2.
Color mixing of the toners in areas where the color toners adhered closely to each other was reduced, resulting in a clear layer.

According to this embodiment, as mentioned above, the earlier image exposure position and the later image exposure position can be overlapped, and in that case, the order of developing colors depends on the sharpness of the color image. Since this will have a considerable effect, it is necessary to carefully decide the order of the colors to be developed.

Example 4 (Example shown in FIG. 7) The same apparatus as in Example 2 was used except that the exposure lamp 3 was provided, and the voltage applied to the developing sleeve 31 of the developing device was +450 V DC voltage and 2 kHz 500 V AC voltage. The voltage is a superimposed voltage, and before each image exposure after the second image exposure, charging is performed by a charger 2 to bring the surface potential of the image forming body l to +600 V, and by an exposure lamp 3 to reduce the surface potential to +500 V. Color image recording was carried out under the same conditions as in Example 2, except that single-stock exposure was performed.

The recorded color image was extremely clear, with no color mixing of the toners even in areas where the toners of each color closely adhered to each other.

In this embodiment as well, as in the third embodiment, the previous image exposure position and the subsequent image exposure position can be overlapped.

〔Effect of the invention〕

According to the present invention, the same device is used for repeated electrostatic image formation, and the recording device can be made small and inexpensive, and the synchronization control of each image exposure can be easily and accurately performed. It is also possible to perform each development by controlling the development density or by a relatively easy development method in which a toner charged to the opposite polarity is attached to the electrostatic image, or by using a laser beam scanner as the image exposure device. This can be done by a developing method in which a toner charged with the same polarity is attached to the electrostatic image that is formed.In addition, in any of the developing methods, development is performed under non-contact jumping development conditions to ensure that the developed density is sufficient. It is possible to obtain an excellent effect of being able to record a color image with excellent clarity.

As mentioned above, the present invention is not limited to those in which the image forming body uses a drum-shaped recording device, and is not limited to those in which a color image is transferred to a recording medium. do not have.

That is, the present invention can also be applied to an image forming member mounted on a substrate such as electrofax paper, on which a color image is fixed without being transferred. In this case, a pre-transfer charger, a pre-transfer exposure lamp, a transfer device, and even a cleaning device are not required. Of course, the pre-transfer charger, pre-transfer exposure lamp, or static eliminator can be omitted even when transferring, and the transfer can be either direct pressure transfer or transfer via an intermediate transfer body, and the fixing can be done by heat roller fixing. Of course, it is not limited to.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the configuration of an example of a recording device that implements the method of the present invention, FIG. 2 is a schematic diagram of the configuration of a laser beam scanner for image exposure, and FIG. 3 is a partial cross-section diagram of an example of a developing device. 4 to 7 are flow charts for implementing the method of the present invention. l...image forming body, 2...charger, 3...
Exposure lamp, 4... Image exposure, 5-8... Developing device, 10... Pre-transfer exposure lamp, 11... Transfer device, 12... Fixing device, 13... Static eliminator,
14... Cleaning device, P... Recording body,
21... Laser 22... Acousto-optic modulator,
23... Mirror scanner, lens, 24... f-θ for imaging 25.26... Mirror 31, developing sleeve, 33, layer thickness regulation blade, 34... Scraper blade, 35... Stirring Rotating body, 36・Developer reservoir, 37...L・ner hopper 38...toner replenishment roller, 39...power supply, 40・protective resistor 27...lens', 32...magnet body,

Claims (1)

[Claims] (1) By repeating an image forming process including electrostatic latent image formation and development on the image forming body, a composite toner image is formed on the image forming body, and the composite toner image is transferred to a transfer material. The image forming method is characterized in that in the second and subsequent image forming steps, development is performed using a developer having an insulating carrier without bringing the developer layer into contact with the surface of the image forming body. image forming method.