JPH02167576A - Color image forming device - Google Patents

Abstract

PURPOSE:To obtain an image forming device excellent in color reproductivity and sharpness by using a scorotron electrifier as an electrifying means carrying out electrification. CONSTITUTION:The scorotron electrifier is used for the electrifier 2: The scorotron electrifier can carry out stable electrification with less influence of previous electrification when an already electrified image forming body 1 is repeatedly electrified. When the drum-shaped image forming body 1 such as used for this recorder is used, an image exposing light 4 could be a light which slit exposing light is filtrated at every color which is used for an usual monochromatic electrophotographic copying machine, but the light by a laser beam scanner is more preferable in order to record a sharp color image. Thus, a recorder is miniaturized and the cost is reduced and the synchronization control of each image exposure can be easily and accurately carried out, and moreover, a color image having enough developing density and excellent sharpness can be recorded.

Description

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

[Prior art]

Various color image forming methods using electrophotography 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 method, since the image forming process is repeatedly performed on the photoreceptor, there is a problem in that the history of the previous image forming process remains, which deteriorates the image quality.

[Purpose of the invention]

The present invention has been made to solve the problems in the conventional color image forming method described above, and an object of the present invention is to provide an image forming apparatus with excellent color reproducibility and sharpness.

[Structure of the invention]

The above object is to provide an image forming apparatus that forms a composite toner image on a photoreceptor by repeating charging, exposure, and development on the photoreceptor, and transfers the composite toner image to a transfer material. This is achieved by an image forming apparatus characterized in that a scorotron charger is used as a charging means for performing this.

〔Example〕

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

FIG. 1 is a schematic configuration diagram showing an example of a recording apparatus that implements the method of the present invention, FIG. 2 is a schematic configuration diagram of a laser beam scanner for image exposure, and FIG. 3 is a partial cross-section diagram showing an example of a developing device. 4 to 7 are flow charts 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 used in the flowchart example of FIG. 7, which will be described later;
denotes image exposure for each color of a color image; 5 to 8 are developing units each using different color toner or developer such as yellow, magenta, cyan, and black; 9 and 10 are multiple units on the image forming body 1; 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 color toner image onto a recording medium P, 11 is a transfer device, and 12 is a recording medium. A fixing device for fixing the toner image transferred to P; 13 is a static eliminator consisting of one or a combination of a static elimination lamp and a corona discharger for static elimination; This is a cleaning device having a cleaning blade or a fur brush that comes into contact to remove residual toner on the surface and separates from the surface of the image forming member 1 by the time the surface on which the first development has been performed reaches.

Here, the charger 2 may be a charger such as the one shown in the figure, which can provide a stable charge with less influence from the previous charge, especially if the charger 2 superimposes charge on the surface of the image forming body 1 that 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 r-θ 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 f-theta lens 24 in order to reduce the diameter of the beam on the image forming body l. If a laser scanner as shown in FIG. 2 is used to form the image exposure 4, electrostatic images of different colors can be easily formed with shifts as described later, and therefore clear color images can be recorded. be able to. However, the image exposure 4 is not limited to the above-described slit exposure or dot exposure using a laser beam, but may be obtained using, for example, an LED, CRT, liquid crystal, or optical fiber transmission body. In a recording apparatus in which the image forming body can take a flat state such as a belt shape, the image exposure can also be flash exposure.

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; A rotating body 37 is a toner hopper, 38 is a toner replenishment roller having a recess on the surface into which toner enters and replenishes toner from the toner hopper 37 to the developer reservoir 36, and 39 is a toner supply roller that is connected to the developing sleeve 31 via a protective resistor 40 as the case may be. is a power supply for applying a bias voltage including an oscillating voltage component and forming an electric field for controlling the movement of toner between the developing sleeve 31 and the image forming body 1; Although it is shown that the developing sleeve 31 rotates in the direction of the arrow, even if the developing sleeve 31 is fixed, the magnet body 32 is fixed, or the developing sleeve 31 and the magnet body 32 rotate in the same direction. It may be something. When the magnet body 32 is fixed, normally, in order to make the magnetic flux density of the magnetic pole facing the image forming body 1 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-
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 on 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. Preference is given to using so-called two-component developers, which consist of a mixture 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 having a resistance of 1013 Ωcm 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 image forming body 1
Problems arise in that carrier particles tend to adhere to the surface and that a sufficient bias voltage is not applied. In particular, if the carrier adheres to the image forming body 1, it will adversely affect the tone of the color image.

The resistivity is determined by placing the particles in a container with a cross-sectional area of 0.50 cm2, tapping the particles, and then applying l on the packed particles.
Apply a load of Kg7cm2, and place 1 between the load and the bottom electrode.
This value is obtained by reading the current value when applying a voltage that generates an electric field of 00 OV/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 is preferably a resin with various pigments and, if necessary, a charge control agent, etc., with an average particle size of 1 to 20 μm.
The average charge amount is 3 to 300μc/gs, especially 1O-
100 uC/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 20
If it exceeds μm, the resolution of the image will decrease.

When using a developer obtained from a mixture of an insulating carrier and toner as described below, the bias voltage applied to the developing sleeve 31 in FIG. Settings can be easily made without fear of leaks. In order to more effectively control the toner development movement by applying such a bias voltage, it is possible to contain a magnetic material such as that used in a magnetic carrier in the toner to the extent that color clarity is not impaired. good.

The above is the configuration of the developing device and developer preferably used in the method of the present invention, but the present invention is not limited thereto.
- No. 18659, No. 56144452, No. 58-11
A developing device and developer described in each of the publications No. 6553 to No. 116554 may be used. More preferably, non-contact jumping development conditions using a two-component developer as described in Japanese Patent Application Nos. 58-57446, 5896900-96903, and 58-97973 previously filed by the present applicant. Maybe it depends.

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 area pH becomes the background area and the non-exposed area DA becomes the electrostatic image.
1 illustrates an embodiment of the present invention in which development is performed by depositing oppositely charged toner on the electrostatic image. According to the recording apparatus shown in FIG. 1, this static electricity is removed by the static eliminator 13.
It is cleaned by the cleaning device 14 and the potential becomes 0.
The surface of the image forming body 1 in the initial state is uniformly charged for the first time by the charger 2 in the first rotation, and the charged surface is exposed to color-specific image exposure 4 so that areas other than the electrostatic image area are The potential is approximately O
The first image exposure is carried out, and the electrostatic image obtained by this is approximately equal to the potential of the first charging. The potential of the electrostatic image, which has been developed for the first time by the developing device in use and has been lowered due to the adhesion of the toner T charged to the opposite polarity, is still higher than the foreground potential, so the static eliminator 13 (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, and the charged surface is charged differently from the previous one. Image exposure 4 for color also reduces the potential of areas other than the electrostatic image area to approximately O.
A second image exposure is carried out, and the electrostatic image obtained is developed a second time with toner T' using another developer using a developer of the corresponding color toner. The electrostatic image formation and development are repeated 3 times and the 4th time, and when the 4th development is performed and a color image in which the color toner images are superimposed is formed, the process is continued before the transfer until the color image passes through. Charger 9 and pre-transfer exposure lamp 1
o is activated, and then the color image is transferred by the transfer device 11 to the recording medium P which is fed in synchronization with one revolution of the image forming body L, and the transferred color image is transferred to the recording medium P by the fixing device 12.
According to the present invention, the surface of the image forming body 1 on which the color image has been transferred 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. 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. Since this is done by the device, there is no need for a separate image exposure device for each electrostatic image forming body, and the recording device can be made small and inexpensive, and the synchronized control of the electrostatic image forming bodies each time is possible. easily done. 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. 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. 2nd on the side
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 0. A developer using a color developer corresponding to image exposure 4 (however, in this case, unlike the example in FIG. 4, a developer in which the toner is charged to the same polarity as that of the image forming member 1) The image exposure 4 of a different color is projected by the same laser beam scanner at a position parallel to the projection position of the previous image exposure 4, without using the charger 2 from the second rotation. Then, a second image exposure is performed, and the electrostatic image obtained thereby with a potential of approximately 0 is developed by another developer using a developer of a corresponding color toner, and then a third image is exposed in the same manner. ,
Repeat the fourth electrostatic image formation and development, and then
One cycle of color image recording is completed in the same way as described with reference to the figure. In this example, even if the electrostatic image with a potential of approximately O 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, even if the electrostatic image area to which toner T was previously attached is not exposed, that is, written. Regardless, the toner T' often accumulates and adheres. However, since a laser beam scanner is used to form the image exposure 4, each image exposure 4
It is extremely easy to shift the projection position of the image, so charging only needs to be done once.Also, since electrostatic images of different colors tend to overlap, the DC bias for each development is set lower in sequence. By doing so, it is possible to prevent the occurrence of overlapping, and thereby a color image with excellent clarity can be obtained.

In the example of FIG. 6, it is not possible to actively form an electrostatic image at the position where the electrostatic image was formed earlier than 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 of FIG. 6, the steps from the initial stage to the first development are the same as those shown in FIG. Or, omitting the static elimination, in the second rotation, the charger 2 performs a second charge, performs a second image exposure on the charged surface, performs a second development, 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 1 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 toner of a later 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 10 or the static elimination lamp of the static eliminator 12 is used. First, the surface of the image forming body l 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 body l 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 a second charge is applied to uniformly charge the surface of the image forming body l, and then an inter-stack exposure is performed, the charged state of the surface of the image forming body l will be the same as that of the uniform exposure 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, so that the laser beam Even when using the electrostatic image forming method or the developing method shown in the examples of FIGS. 5 to 7, in which an image exposure device such as a scanner is advantageously used, it is possible to record a color image with high development density and excellent clarity. can.

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 foreground potential of -50
An electrostatic image was formed in which the potential of the non-exposed area DA was 1500V with respect to V. This electrostatic image was first developed using a developing device 5 as shown in FIG.

The developing device 5 contains 50 wt% magnetite dispersed in the resin, with an average particle size of 20 μm1 and a magnetization of 30 em71/g.
A carrier with a resistivity of 10 Ωcm or more, a styrene acrylic resin, 10 parts by weight of a benzene derivative as a yellow pigment, and other charge control agents, with an average particle size of 10 μm.
A developer consisting of 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 loOrpm, 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 11000 rpm, 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 rpm.
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 kHz and 100 OV 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 applying a direct current to the developing sleeve 31 with the same polarity as the charge on the image forming body 1 and the opposite polarity to the charge on the toner. This is 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, color toners based on other pigments or dyes can be used, 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 performed using the developing unit 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 SlooV 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 development after the second development, the DC bias component and AC component of the voltage applied to the developing sleeve 31 are adjusted appropriately according to the change in the surface potential of the image-forming body 1, the development characteristics, and the color reproducibility. The amplitude, 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.

When the fourth development is performed and a four-color image is formed on the image forming body 1, the image is easily transferred by the pre-transfer electric device 9 and the pre-transfer exposure lamp IO, and then transferred to the recording body by the transfer device 11. The image is transferred to the printer and fixed by the fixing device 12.

The image forming body 1 on which the color image has been transferred is neutralized by the static eliminator 13, and 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. Once it 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 was charged to +500 V by a charger 2 using a scorotron corona discharger, and a laser beam scanner using a He-Ne laser as shown in FIG. A first image exposure was made at density. As a result, the image forming body 1 has a foreground potential of +500
An electrostatic image was formed in which the potential of the exposed portion r+H was +50V with respect to V. This electrostatic image is transferred to a developing device 5 as shown in FIG.
The first development was carried out.

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 is applied with a superimposed voltage of +400 V DC voltage and 1.5 kHz 100 OV AC voltage. The procedure was the same as in Example 1 except that the voltage was applied. In addition, the conditions for the other developing devices 6 to 8 were the same as in the embodiment except for the bias voltage. However, in this case, the bias voltage that keeps the developing devices that do not participate in development in a non-developing state is The polarity is opposite to that of the charging, and the polarity of the charging of the image forming body 1 is also opposite.

A pre-transfer charger 9, a pre-transfer exposure lamp 10. Static eliminator 13. Without operating the cleaning device I4 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 1 hour 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 body L, the rest is transferred and fixed to the recording medium P, and the image forming body is destaticized 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.

Embodiment 3 (Example shown in FIG. 6) Using the same device as in Embodiment 2, the voltage applied to the developing sleeve 31 of the developing device was set to +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, the static electricity was removed by the transfer exposure lamp lO, and then the surface potential of the image forming body l 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 that brings the surface potential of the image forming body 1 to +600 V, and by an exposure lamp 3 that lowers 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 1-toner color mixing even in areas where the color toners adhered closely 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 generated, or 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 configuration diagram showing an example of a recording device for implementing the method of the present invention, FIG. 2 is a schematic configuration diagram 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. L... Image forming body, 3... Exposure lamp, 5-8... Developing device, 11... Transfer device, 13... Static eliminator, P... Recording body, 22... Acousto-optic Modulator, 24... f-theta lens for imaging, 25.26... Mirror 31... developing sleeve, 33... layer thickness regulation blade, 34... scraper play 35... stirring rotor, 36... Developer reservoir, 37... Toner hopper 38... Toner supply roller, 39... Power source, 40... Protective resistor, 2... Charger, 4... Image exposure, 10 ... Pre-transfer exposure lamp, 12... Fixing device, 14... Cleaning device, 21... Laser 23... Mirror scanner, 27... Lens, 32... Magnet,

Claims (1)

[Claims] (1) In an image forming apparatus that forms a composite toner image on a photoreceptor by repeating charging, exposure, and development on the photoreceptor, and transfers the composite toner image to a transfer material, the charging is performed on the photoreceptor. An image forming apparatus characterized in that a scorotron charger is used as a charging means.