JPH0516590B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a multicolor image forming apparatus that forms a plurality of toner images on an image forming body by superimposing them.

[Conventional technology]

2. Description of the Related Art Conventional multicolor image forming apparatuses include those in which toner images of each color formed on an image forming body are sequentially transferred onto recording paper, and the toner images of each color are superimposed on the recording paper. However, such multicolor image forming apparatuses have problems such as the need for a transfer drum, which increases the size of the apparatus, and the transfer misalignment of each color toner image, making it impossible to obtain a clear multicolor image. For example, patent application 183152, patent application 183152,
58-184381, patent application 187000, patent application 1982-
187001, a multicolor image forming apparatus is proposed in which toner images of each color are superimposed on an image forming member. FIG. 6 is a diagram illustrating the configuration of such an image forming apparatus. In FIG. 6, 1 is a drum-shaped image forming body that includes a conductive substrate, a selenium vapor deposited layer provided thereon, a resin dispersion layer of cadmium sulfide or zinc oxide, polyvinyl carbazole, anthracene, polycyclic quinone dye, or bisazo dye. It consists of a photosensitive layer made of an organic semiconductor such as. The image forming body 1 is rotated in the direction of the arrow and uniformly charged with a positive charge by a charger 2, and then subjected to image exposure via a laser device (image exposure device) 3 using a type of image information from the original document. is applied to form an electrostatic image. This electrostatic image is developed by the developing device 4A to form a corresponding toner image. The image forming body 1 carrying this toner image includes developing devices 4B to 4D, a transfer device 7 consisting of a pre-transfer charger 5, a pre-transfer exposure lamp 6, a transfer electrode 7a and a separation electrode 7b, a pre-cleaning static eliminator 9, and a cleaning device. 10, etc., and is rotated to the charger 2 again.

After being uniformly charged by the charger 2, image exposure is performed based on another type of image information to form an electrostatic image, and the developing device 4B develops the corresponding toner image. formed by overlapping.

Similar steps are repeated, and the toner images are developed by the developing device 4C and the developing device 4D, and a multicolor toner image is formed by overlapping these toner images.

This multicolor toner image is made easier to be transferred by the operation of the pre-transfer charger 5 and the pre-transfer exposure lamp 6, which were stopped, and then transferred to the recording paper P by the action of the transfer device 7, and then transferred by the fixing device 8. It is fixed by applying pressure or heating. After the transfer is completed, the image forming body 1 is equipped with a static eliminator 9 consisting of a static eliminator lamp 9a and a corona discharger 9b.
The remaining toner is removed by the cleaning blade 11 of the cleaning device 10, which was released during toner image formation, and is prepared for the next image formation. It is preferable that the developing devices 4A to 4D, etc. installed in this multicolor image forming apparatus are developing devices using a non-contact developing method, and in particular, the later developing devices 4B to 4D should not damage the toner images. A developing device using a non-contact developing method is desirable because it is extremely easy to turn on and off development. When the development is off, the AC bias component during development (on) is cut off and only the DC bias component is left, is it in a floating state, is it grounded, or is a DC bias with the opposite polarity to the toner applied? Alternatively, the developing device is separated from the image forming body. Moreover, these treatments can also be used in combination.

Improvements have been made in such image forming devices, such as the device being made more compact, the misalignment of toner images being reduced, and developing properties being excellent, resulting in clearer multi-color images being obtained. .

[Problem that the invention seeks to solve]

However, in the image forming apparatus, the cleaning device 10 is disposed close to the top of the transfer device 7 for the recording paper P and the feeding system for the recording paper P;
Since it is also adjacent to the charger 2, it is likely to become a source of contamination to these devices and equipment. Therefore, there are problems in that the measures for collecting the toner and preventing scattering of the toner in the cleaning device become complicated and troublesome.

Furthermore, since the first copy is slow in a copying operation, there are disadvantages in that it makes the copying worker feel impatient and that it takes an extremely long time to make a monochrome copy, for example, one black and white copy. This is because the image forming apparatus is configured to develop a multicolor image, so the diameter of the image forming body drum 1 is large, and the distance between the electrostatic image forming means (charging and image exposure means) and the transfer device 7 is large. This is because the distance is long.

[Means for solving problems]

The present invention has been proposed based on the above-mentioned circumstances, and an object of the present invention is to form a plurality of toner images in a superimposed manner on an image forming body.
It is an object of the present invention to provide an image forming apparatus in which a first copy can be recorded at high speed even though the image forming body is enlarged, and toner contamination caused by a cleaning device or the like is reduced.

The above purpose is to form an electrostatic image on the image forming body by arranging a charger, an image exposure device, a plurality of developing devices, a transfer device, and a cleaning device in opposition to the moving path of the image forming body. In an image forming apparatus that repeats the process of developing an electrostatic image with color toner to form a plurality of toner images in a superimposed manner on an image forming body, and then transfers the toner images to a recording material, rotation of the image forming body is performed. one developing device of a specific color is disposed between the image exposure device and the transfer device with respect to the direction, a plurality of developing devices of other colors are disposed between the transfer device and the charger, and the An image characterized in that each time a specific color of a latent image formed on the image forming body is developed, the image forming body is rotated to form toner images superimposed, and then transferred to a transfer material by the transfer device. This is accomplished by a forming device.

Specifically, at least an electrostatic image forming means, a specific developing device, a transfer section, and a developing device other than the specific developing device are arranged in this order in the moving direction of the image forming body.

[Effect]

The configuration of the present invention will be specifically explained below with reference to FIGS. 1 and 2. FIG. 1 is a sectional view of a main part of a typical image forming apparatus of the present invention, and FIG. 2 is a modification thereof, and the same parts as in FIG. 6 are given the same reference numerals.

The image forming apparatus shown in FIG. 1 is characterized by a developing device 4A containing a specific toner, a charging device 2 serving as an electrostatic image forming means, a feeding system for recording paper P including an image exposure device 3, and a transfer device 7. The point is that the first print using the specific toner is achieved in the shortest path.

Furthermore, most of the cleaning device 10 and developing device, which are the sources of toner scattering, are located below the image forming device, which reduces toner contamination of the electrostatic image forming means, transfer device 7, and recording paper P feeding system. It is at the point where it is done.

Note that the specific toner is, for example, yellow.
(Y), magenta (M), cyan (C), black (BK), etc., but BK toner is often used most frequently in printing work.

(a) The process of forming black and white prints using BK toner using the image forming apparatus shown in FIG. 1 will be described below. For example, the image forming body 1 having a selenium photosensitive layer is rotated in the direction of the arrow while being uniformly positively charged by the charger 2, and then BK from the original is applied.
Based on the image information, image exposure is performed via the laser device 3 to form an electrostatic image. This electrostatic image is BK
The toner is developed by the developing device 4A containing the toner, and a BK toner image is formed. This BK toner image is produced by a pre-transfer charger 5 and a pre-transfer exposure lamp 6.
After being facilitated to be transferred by the action of the image forming member 1, the image is transferred to the recording paper P fed in synchronization with the image forming body 1 by the action of the transfer electrode 7a. After the transferred recording paper P is separated by the action of the separation electrode 7b, it is carried into the fixing device 8 and fixed by heating or pressure. In this way, the first black-and-white print is formed in the shortest path and can meet the operator's request.

The surface of the image forming body 1 after transfer is covered with a static elimination lamp 9.
After being neutralized by the actions of the static eliminating electrode 9b and the static eliminating electrode 9b, it is cleaned by the blade 11 of the cleaning device 10, and after passing through the developing devices 4B, 4C, and 4D whose developing action has been released, it is prepared for the next image formation. .

(b) Next, a process of forming a monochrome print using any one of the developing device 4B containing Y toner, the developing device 4C containing M toner, and the developing device 4D containing C toner will be described. First, after a uniform positive charge is applied to the surface of the image forming body 1 by the charger 2, an electrostatic image is formed by image exposure from the laser device 3 modulated by, for example, a Y image signal, and the image forming body 1 is inactivated. developing device 4
A, the pre-transfer static elimination electrode 5, the exposure lamp 6, and the transfer device 7 are passed through, and the Y toner is developed by the developing device 4B containing the Y toner, thereby forming a Y toner image. This Y toner image passes through the developing device 4C, the static eliminator 9, the cleaning device 10, the developing device 4D, the charger 2, the image exposure device 3, and the developing device 4A, which are inactive, and then before transfer, which is activated. After being facilitated to be transferred by the action of the charger 5 and the exposure lamp 6, the image is transferred to the recording paper P by the transfer device 7, and after being separated, it is fixed by the fixing device 8.

After the transfer, the surface of the image forming body 1 is neutralized by the static eliminating device 9 and then cleaned by the blade 11 of the cleaning device 10, passing through the inactive developing devices 4B, 4C, and 4D, and is then transferred to the next stage. image formation.

In the image forming process, if the cleaning device 10 does not disturb the image when the toner image passes through, it is not necessary to release the cleaning device 10, but it is normally desirable to release the cleaning device 10, and furthermore, during electrostatic image formation and development, the cleaning device 10 does not need to be released when the image forming member 1 rotates. In order to avoid unevenness, it is better not to press or release the cleaning device against the image forming body 1. In addition, pre-transfer charging and exposure to increase the transfer efficiency of the toner image include:
The charging device 2 and the image exposure device 3 may be used, or the charging device 5 and the exposure lamp 6 may be used together.

(c) Next, developing devices 4A and Y that accommodate BK toner
A process of forming a full-color print using a developing device 4B containing toner, a developing device 4C containing M toner, and a developing device 4D containing C toner will be described.

First, the charger 2 applies a uniform positive charge to the surface of the image forming body 1, and then the laser device 3
A developing device 4 in which an electrostatic image is formed by image exposure based on a BK image signal and contains BK toner.
A is developed to form a BK toner image. Thereafter, the toner image is transferred to a pre-transfer charger 5, an exposure lamp 6, a transfer device 7, a pre-cleaning static eliminator 9, a cleaning device 10, each developing device 4B,
4C and 4D are deactivated or released, they pass through these devices and are recharged by the charger 2 again. After the recharging, image exposure is performed based on the Y image signal to form an electrostatic image, and this electrostatic image is transferred to the various devices (excluding the developing device 4B) and the developing device 4A.
The toner image is deactivated and passes through without any trouble, and is developed by the developing device 4B containing the Y toner, so that a Y toner image is formed superimposed on the BK toner image.

The same process is repeated, and the M toner image is developed by the developing device 4C containing the M toner and the developing device 4D containing the C toner.
A toner image is formed to be superimposed on the BK toner image and the Y toner image to form a multicolor toner image. This multicolor toner image is made easier to be transferred by the action of the stopped pre-transfer charger 5 and the pre-transfer exposure lamp 6, and then transferred to the recording paper P by the action of the transfer device 7, separated, and then fixed. It is fixed by the device 8. The surface of the image forming body 1 after the transfer is cleaned by the cleaning blade 11, which was released during toner image formation, as in the above items (a) and (b), and is prepared for the next image formation.

In the above process, it is preferable that the cleaning device 10 is released when the toner image passes so as not to disturb the image, and furthermore, during electrostatic image formation and development, the cleaning device 10 is released to avoid uneven rotation of the image forming body 1. It is better not to press or release the image forming member 1 . Further, in order to improve the transfer efficiency of the toner image, pre-transfer charging and exposure are performed using the pre-transfer charger 5 and the exposure lamp 6, but the charger 2 and the image exposure device 3 may also be used.

In addition, the developing device 4A containing the BK toner in the image forming process is released and the Y, M, and C toners are removed.
It is also possible to create a multicolor image with only three colors, and the developing device 4A may be filled with Y toner, the developing device 4B with M toner, the developing device 4C with C toner, and the developing device 4A with Y toner, the developing device 4B with C toner,
BK toner may be stored in D.
In addition, after forming a multicolor image of three colors of Y, M, and C,
BK image formation may also be performed.

(d) Next, the image forming apparatus shown in FIG. 2 shows a modification of the present invention, and the difference from the image forming apparatus shown in FIG. 1 is that the cleaning device 10 and the pre-cleaning static eliminator 9 in FIG. being relocated between the device 4C and the developing device 4D,
The basic idea and effects remain unchanged.

Next, a developing device suitable for the image forming apparatus of the present invention,
The developer, development conditions, etc. will be explained. As the developing method in the image forming apparatus of the present invention, either normal development or reversal development can be performed, and the developing method, conditions, equipment, etc. are not particularly limited, but as described above, the developing method, conditions, equipment, etc. In order not to disturb the toner image that has already been formed,
It is preferable to use a developing method called non-contact development in which the developer layer containing toner does not come into direct contact with the surface of the image forming member.

FIG. 3 shows an example of a developing device suitable for carrying out the above-mentioned non-contact development, in which 22 is a sleeve made of a non-magnetic material such as aluminum or stainless steel;
23 is a magnet body provided inside the sleeve 22 and has a plurality of magnetic poles in the circumferential direction; 24 is the sleeve 22;
A layer thickness regulating blade 25 regulates the thickness of the developer layer formed on the sleeve 22, a scraper blade 25 removes the developed developer layer from the sleeve 22, and 26 stirs the developer in the developer reservoir 27. stirring rotor,
28 is toner hopper, 29 is toner hopper 2
A toner replenishing roller 8 supplies toner to the developer reservoir 27. A toner replenishing roller 30 has a recess on the surface into which the toner enters; A power source for forming an electric field for controlling the movement of toner between the image forming body 1;
The figure shows that the sleeve 22 and the magnet body 23 rotate in the directions of the arrows, but even if the sleeve 22 is fixed, the magnet body 23 is fixed, or the sleeve 22 and the magnet body 23
may rotate in the same direction.
When the magnet body 23 is fixed, the magnetization is usually strengthened 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.
Two magnetic poles of the same polarity or different polarities are placed close to each other.

In such a developing device, the magnetic pole of the magnet body 23 is normally magnetized to a magnetic flux density of 500 to 1500 Gauss,
The developer in the developer reservoir 27 is attracted to the surface of the sleeve 22 by the magnetic force, and the thickness of the adsorbed developer is regulated by the layer thickness regulating blade 24 to form a developer layer, and the developer is developed. The agent layer moves in the same direction or in the opposite direction to the rotation arrow direction of the image forming body 1,
Developing the electrostatic image on the image forming body 1 in a developing area where the surface of the sleeve 22 faces the surface of the image forming body 1;
The remainder is removed from the surface of the sleeve 22 by the scraper blade 25 and returned to the developer reservoir 27.

As the developer used in the method of the present invention, a non-magnetic two-component developer, a non-magnetic one-component developer, and a so-called one-component magnetic developer that uses only a magnetic toner containing a magnetic substance can be used. It is made of a mixture of a non-magnetic toner and a magnetic carrier, which makes it possible to obtain a toner with a clear color without the need to include a black or brown magnetic substance in the toner, and toner charge control can be easily controlled. It is preferable to use a so-called two-component developer. 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 Products containing dispersed fine particles of ferromagnetic or paramagnetic materials such as chromium, manganese oxide, ferrite, manganese-copper alloy, or materials whose surfaces are coated with the above-mentioned resins. consisting of a resistivity of 10 ⁸ Ωcm or more, preferably 10 ¹³ Ωcm
The above insulating carrier is preferred. If this resistivity is low, when a bias voltage is applied to the developing sleeve 22, charges may be injected into the carrier particles, making it easier for the carrier particles to adhere to the surface of the image forming body. The problem arises that no voltage is 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 was measured by placing particles in a container with a cross-sectional area of 0.50 cm ² and tapping them, then applying a load of 1 kg/cm ² on the packed particles, and comparing the electrode that also served as the load and the bottom electrode. This value is obtained by reading the current value when applying a voltage that creates an electric field of 1000 V/cm between the two.

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, and breakdown or discharge will easily occur.
Since this tends to make it impossible to apply a high voltage, it is preferable that the average particle size is 5 μm or more and 50 μm or less, and if necessary, a suitable amount of a flow agent such as hydrophobic silica is added as an additive.

As for the toners, the cyan one has copper phthalocyanine added instead of black carbon black, the magenta one has the same polytungstophosphoric acid added, and the yellow one has the same benzidine derivative added. Additives are used. However, the toner is not limited to such colored toners using pigments, and colored toners using dyes may also be used, and it goes without saying that a charge control agent or the like may be added as necessary. The toner preferably has an average particle size of 1 to 20 μm,
In addition, the average charge amount is 3 to 300μc/g, especially 5 to 300μc/g.
100 μc/g is preferred. When the average particle size of 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. Note that the average particle size is a weight average particle size, and is measured with a Coulter counter (manufactured by Coulter Inc.).

When a developer consisting of a mixture of an insulating carrier and toner as described above is used, the sleeve 2 shown in FIG.
It is now possible to easily set the bias voltage applied to 2 so that the toner sufficiently adheres to the electrostatic image and fog does not occur without fear of leakage. In order to more effectively control the development movement of the toner by applying such a bias voltage, the toner may also contain a magnetic material such as that used in magnetic carriers to the extent that color clarity is not impaired. It's okay.

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 thereto.
It is also possible to use the developing device and developer described in each of the Japanese Patent Application Nos. 58-116553 to 116554, and more preferably, the Japanese Patent Application No. 58
-57446, 58-96900 to 96903, 58-97973
No. 58-23829, No. 58-238296, using the developing device and developer described in each specification.
In non-contact development using a one-component developer or a two-component developer, that is, when there is no potential difference between the surface of the image forming body 1 and the sleeve, the thickness of the developer layer formed on the sleeve in the development area is It is preferable to perform development under conditions set so that the gap is thinner than the gap between the body surface and the sleeve.

〔Example〕

EXAMPLES The present invention will be specifically explained below with reference to Examples, but the embodiments of the present invention are not limited thereto.

(Example 1) A black-and-white copy image was formed using the image forming apparatus shown in FIG. 1 according to the image forming process described in (a) above. The image forming body 1 incorporated in the apparatus is made of an amorphous silicon layer formed on the surface of an aluminum drum, and has a diameter of 120 mm and a diameter of 120 mm/120 mm in the direction of the arrow.
It was rotated at a speed of sec. First, a scorotron charger 2 applies a uniform charge of +600V to the surface of the image forming body 1, and a semiconductor laser beam scanner 3 (image exposure device) applies a uniform charge of 16 spots/mm to this.
BK image information is written at a density of
An electrostatic image was formed. This electrostatic image is applied to bias power supply 30 in Figure 4 with +400V DC bias and 1.5KHz.
Developing device 4 to which 1000V AC bias was applied
A BK toner image was formed by non-contact reversal development. The developing device 4A includes a carrier made of magnetite and resin, containing 75 wt% magnetite dispersed therein, having an average particle diameter of 30 μm, magnetization of 30 emu/g, and resistivity of 10 ¹⁴ Ωcm or more, and a carrier made of styrene-acrylic resin with 10 wt of carbon black. % and a non-magnetic toner with an average particle diameter of 10 μm and an average charge amount of 20 μc/g, including a charge control agent, and the ratio of the toner was 20 wt %.

The outer diameter of the sleeve 22 of the developing device is 30 mm.
mm, the rotation speed in the direction of the arrow is 100 rpm, magnet body 2
The magnetic flux density of the N and S magnetic poles of No. 3 is 1000 Gauss, the rotation speed in the direction of the arrow is 1000 rpm, the thickness of the developer layer in the developing area is 0.6 mm, and the gap between the sleeve 22 and the image forming body 1 is 0.8.
mm.

The BK toner image thus obtained is immediately transferred to the recording paper P in the shortest path as described above, and is heat-fixed to obtain a desired black and white printed image.

(Example 2) In this example, a full-color image was formed using the image forming apparatus shown in FIG. 1 according to the image forming process (c) above. FIG. 5 is a plan view showing the reference image formed on the image forming body and the image forming position;
The drum-shaped image forming body shown in FIG. 1 is laid out flat. FIG. 6 is a timing chart of the image forming process. The image forming body incorporated in the image forming apparatus is the same as that in Example 1, and four color toner images of BK, Y, M, and C are formed by superimposing them. First, during the first rotation, the image forming body 1 is uniformly charged with +600V by the corona charger 2.
Vb is given, and BK information b1 and b is added to this by a semiconductor laser beam scanner (image exposure device) 3.
BK reference latent image Eb1 and BK image latent image Eb, which are color image information written in 2 and read by the image reading device in synchronization with the rotation of the image forming body.
2 was formed. These latent images are reversely developed with positive BK toner by the developing device 4A to form a BK reference toner image Db1 and a BK image toner image Db2.

The structure of the developing device 4A, the developer contained therein, and the developing conditions were the same as in Example 1. It should be noted that during each rotation of the image forming body 1, the developing device other than the developing device used for developing is inactive, but for this purpose, the sleeve 22 shown in FIG. This is achieved by applying only a DC component or actively applying a DC bias voltage of opposite polarity to the charging of the image forming member 1 to the developing sleeve 22.Among these methods, applying a DC bias voltage is the preferred method. preferable.

After the second rotation of the image forming body 1, uniform positive charges Vy, Vm, and Vc are sequentially applied in the same manner except that the formation position of the latent image differs as shown in FIGS. 4 and 5, and the laser By beam writing, latent image
Ey1, Em1, Ec1 and image latent image Ey2, Em2,
Ec2 is formed. These latent images are sequentially developed by developing devices 4B, 4C, and 4D to form superimposed multicolor toner images.

That is, while the pre-transfer exposure lamp 6 is applied to the surface of the image forming body 1 that has been subjected to the first development, the second rotation is also performed without applying the static eliminator 9 or the cleaning device 10. + with charger 2
After performing a second charge to 600V, a second image exposure is performed again using the same laser beam scanner at the same spot density so that the spot positions do not overlap, and then a second development of magenta toner is performed using the developing device 4B. I went to Similarly, the third development of the cyan toner by the developing device 4C and the fourth development of the black toner by the developing device 4D were repeated.

In addition, in the development using each of the above-mentioned developing devices,
The voltage of the DC bias component applied to the sleeve 22, the amplitude, frequency, application time, etc. of the AC bias component may be appropriately changed in accordance with changes in the surface potential of the image forming body 1, development characteristics, color reproducibility, etc., or The density of each color toner image is adjusted. Similar to the developing device 4A, the non-contact developing devices shown in FIG. 3 are used in the developing devices 4B to 4D, and the coloring agent of the toner in the developer contained in them is a benzidine derivative as a yellow pigment in the developing device 4B, and a benzidine derivative as a yellow pigment. The same development was performed except that polytungstophosphoric acid was used as the magenta pigment in the apparatus 4C, and copper phthalocyanine was used as the cyan pigment in the developing apparatus 4D.

Furthermore, other pigments and dyes can be used as colorants.

After the fourth development is performed and a four-color image is formed on the image forming body 1, it is made easier to be transferred by the pre-transfer charger 5 and the pre-transfer exposure lamp 6,
The image is transferred onto the recording medium P by the transfer device 7 and fixed by the fixing device 8 . The image forming body 1 to which the color image has been transferred is charged by a static eliminator 9, and the cleaning device 1
One cycle of color image recording is completely completed when the surface on which the color image has been formed passes through the cleaning device 10 after residual toner is removed from the surface by contact with the blade or fur brush. In this embodiment, a multicolor toner image in which toner images of each color are superimposed is formed based on the reference latent image and feedback information from the reference toner image, so that a multicolor image with excellent reproducibility is formed. The cleaning device 10 and the developing devices 4B to 4D, which are sources of scattering, are arranged together below the image forming device, and the transfer device 7, charger 2, image exposure device 3, etc. that receive toner stains are also arranged together. Since the image forming apparatus is located above the image forming apparatus, toner contamination of these devices is reduced and toner contamination of the entire area of the image forming apparatus is eliminated, resulting in a clear multicolor image.

〔Effect of the invention〕

As explained above, according to the image forming apparatus of the present invention, the apparatus is compact, there is no transfer misalignment of toner images of each color, the developability and color reproducibility are excellent, toner contamination is reduced, and the image is clear and high quality. In addition to being able to obtain a high-quality multicolor image, there are also effects such as being able to obtain a copy at the start in the shortest path.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of the image forming apparatus of the present invention, FIG. 2 is a sectional view showing another example of the image forming apparatus of the invention, and FIG. 3 is a sectional view showing the image forming apparatus of FIGS. 1 and 2. FIG. 3 is a cross-sectional view of a developing device incorporated into the apparatus.
FIG. 4 is a plan view showing the reference image formed on the image forming body and the image forming position, FIG. 5 is a timing chart of the image forming process, and FIG. 6 is a sectional view of a conventional image forming apparatus. 1... Image forming body, 2... Charger, 3... Laser beam scanner (image exposure device), 4A, 4B,
4C, 4D...Developing device, 5...Pre-transfer charger,
6... Pre-transfer exposure lamp, 7... Transfer device, 7a
... Transfer electrode, 7b ... Separation electrode, 8 ... Fixing device, 9 ... Static eliminator before cleaning, 9a ... Static eliminator lamp, 9b ... Static eliminator electrode, 10 ... Cleaning device, 11 ... Cleaning brush blade), P...recording paper, 22...sleeve,
23...Magnet, 28...Toner replenishment hopper,
29...Toner supply roller, 30...Bias power supply.

Claims (1)

[Claims] 1. A charger, an image exposure device, a plurality of developing devices, a transfer device, and a cleaning device are arranged opposite to the moving path of the image forming body to form an electrostatic image on the image forming body, and the electrostatic image is In an image forming apparatus that repeatedly forms a plurality of toner images on an image forming body by repeating the process of developing with color toner, and then transfers the toner images to a recording material, One developing device of a specific color is disposed between the image exposure device and the transfer device, and a plurality of developing devices of other colors are disposed between the transfer device and the charger, and the developing device is disposed on the image forming body. An image forming apparatus characterized in that each time a specific color of a latent image formed on a latent image is developed, the image forming body is rotated to form toner images superimposed, and then the toner images are transferred onto a transfer material by the transfer device.