JPS62209561A - Image forming device - Google Patents

Abstract

PURPOSE:To limit a primary electrostatically charged area to an image forming area and to prevent toner from being attached to a nonimage area by using a corona discharger capable of adjusting the width of a corona discharge passing aperture in the transverse direction of a photosensitive body for a primary electrostatic charger. CONSTITUTION:In terms of the electrification by the primary electrostatic charger 5, an aperture with regulating plate 51 is advanced or retreated in the direction of an arrow, whereby the corona discharge passing width (w) in the transverse direction of the photosensitive body 4 is preset to the width of a projected original or that of a transfer material on the photosenstive body 4. Next a discharge voltage is impressed while the surface of the photosensitve body 4 moved toward and discharge wire 52 by the length of the projected original or that of the transfer material, thereby executing the electrostatic charge. The aperture width regulating plate 51 is formed with an insulating material that is free of the influence of the electrostatic charge, and the photo sensitive body under said plate is not electrostatically charged. A stepping motor, etc., causes the aperture width regulating plate 51 to go forth and back.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is a method of forming a primary latent image by performing primary charging, image exposure, and secondary charging on a photoreceptor having an insulating surface layer and a distribution layer of color separation functional elements. After that, an apparatus for forming a color image on the insulating surface layer by repeatedly uniformly exposing a specific light to extract a color-separated electrostatic image from the latent image and developing the electrostatic image with a specific color toner. In particular, the present invention relates to an improvement in which toner is prevented from adhering to outside the image forming area, that is, to a non-image area of a photoreceptor.

[Foreground of invention]

The present inventors previously published Japanese Patent Application No. 59-185440 and No. 59-1870 in order to complete various inventions regarding an image forming apparatus using a photoreceptor having a color separation function as described above.
No. 44, No. 6G-229524).

Even in an image forming apparatus using a photoreceptor having such a color separation function, as in an image forming apparatus using a photoreceptor that does not have a color separation function, toner adheres particularly to the non-image area of the photoreceptor. For example, if image exposure is performed using a scanning exposure device that scans the document with an optical system or a scanning exposure device that moves the document table back and forth, the image exposure lamp will turn off and move back. When copying is performed outside the frame of the original document placement area or without placing the platen cover, the surface of the photoreceptor corresponding to areas other than the original area has a black image potential, and the toner that adheres there increases the burden on the cleaning device. This wastes toner and contaminates the device and transfer material. In other words, the surface of the photoconductor that corresponds to areas other than the document section when copying is performed without using a platen cover, and the surface of the photoconductor that corresponds to areas other than the document section frame when reduced copying is performed even with the platen cover. becomes black image potential,
Given the problem mentioned above. Further, the same applies when the size of the transfer material is smaller than the original size in full-size copying. In general,
The above-mentioned problem occurs because the surface of the photoreceptor other than the surface corresponding to the transfer material has a potential to which toner adheres and development is performed.

Therefore, means for preventing toner from adhering to the surface of the photoreceptor, that is, the non-image area, as described above, is particularly employed.

As a means to prevent toner from adhering to non-image areas, in an image forming apparatus using a photoreceptor that does not have a color separation function, it is recommended to In the Carlson method, a method is mainly adopted in which a non-image area exposure device is provided in between to expose the non-image area to remove static electricity. This method is a method in which a photoreceptor that grows a transparent insulating layer on a photoconductive layer is subjected to primary charging, image exposure, and secondary charging, and then uniform π light is applied to form an electrostatic image. For example, in the NP method, even if the charged photoconductor surface is exposed to light, the static electricity cannot be removed like in the Carlson method because of the transparent insulating layer, so it is not adopted.
In the NP method, a method using a uniform exposure device that irradiates white light while limiting the above-mentioned uniform exposure range to an image forming area has been considered.

Non-image area exposure devices and uniform exposure devices used in the above methods include those that consist of an array of light-emitting elements such as light emitting diodes and electroluminescent lamps, those that consist of an array of xenon lamps, and those that consist of a cold cathode. In addition to the discharge tube, lens, and shirt, a method of changing the developing bias applied to the developing electrode of the developing device to the developing condition only when passing through the image forming area is used in both of the above image forming apparatuses.

From the above, in an image forming apparatus using a photoreceptor having color resolution i, the same method as the NP method can be adopted where the photoreceptor has an insulating surface layer, but the same white light etc. Using a uniform exposure device cannot be used because the electrostatic images of all color separations are extracted at once from the -order latent image, and the method of changing the developing bias is Therefore, it is not possible to prevent toner from adhering to the non-image area that occurs alongside the image forming area.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned background circumstances, and includes a color separation function that limits the secondary charging area to the image forming area and prevents toner from adhering to the non-image area. An image forming apparatus using a photoreceptor is provided.

[Structure of the invention]

In the present invention, a photoreceptor having an insulating surface layer and a distribution layer of color separation functional elements is subjected to primary charging, image exposure, and secondary charging to form a primary latent image, and then electrostatic charge for color separation is generated from the secondary latent image. In the apparatus for forming a color image on the surface layer of the back side of the wA stitching by repeatedly performing uniform exposure with a specific light for drawing out an image and developing the electrostatic image with a specific color toner, at least the charging for the primary charging is performed. The image forming apparatus is characterized in that a corona discharger is used as a container to adjust the width of a corona discharge passage opening in the width direction of the photoreceptor, and this configuration achieves the above object.

〔Example〕

The invention will now be explained with reference to illustrated examples.

1 to 4 are schematic partial cross-sectional views showing examples of the layer structure of a photoreceptor used in the image forming apparatus of the present invention, and FIGS. 5 and 6 are filters of color separation filter layers of the photoreceptor, respectively. FIG. 7 is a partial plan view showing an example of the distribution shape, FIG. 7 is a schematic side view of the configuration of an example of the image forming apparatus of the present invention, and FIGS. 8 and 9 are a partial side view and partial view showing an example of a primary charger. 10 is a signal output chart of the control device, FIG. 11 is an operation timing graph of the primary charger and secondary charger, and FIG. 12 is a graph of changes in photoreceptor surface potential during a color image process.

In FIGS. 1 to 4, ▪ is a conductive member formed into an appropriate shape structure as required, such as a cylindrical shape or an endless belt shape, and 2 is a photoconductive layer made of an inorganic photoconductor or an organic photoconductor. ,
3 consists of a distribution of minute color separation filters for red (R), green (G), blue (B), etc. formed from various polymers, resins, etc. and colorants such as dyes and pigments, that is, color separation functional elements. This is an insulating layer including layer 3a. The insulation N3 of the photoreceptor 4 in FIG. The insulating layer 3 of the photoreceptor 4 shown in FIG. 2 has a transparent insulating layer under the insulating layer 3 shown in FIG. 1, and the insulating layer 3 of the photoreceptor 4 shown in FIG. The insulating layer 3 of the photoreceptor 4 in FIG. 4, which further has a transparent insulating layer thereon, is the same as the insulating layer 3 in FIG.
It is like having a transparent insulating layer on top of it.

R and G in the color separation layer 3a of these insulating layers 3.

The distribution shape of the B filter etc. is not particularly limited, but the fifth
A mosaic distribution as shown in the figure and FIG. 6 is used because it is suitable for reproducing delicate multicolor images.

Regarding the individual sizes of the R, G, B filters, etc., a length range of 10 to 200 μm, as shown by l in the figure, is used from the viewpoint of ease of forming a distribution pattern, image resolution, and color reproducibility. .

The image forming apparatus shown in FIG. 7 has a primary charge as shown in FIG. 8 and FIG. Vessel 5
, an image exposure device 6 including a secondary charger 61, and uniform exposure devices 7B, 7G, and 7R for specific light.

7K, -component 4L, < is by forming a layer of two-component developer on the developing sleeve to a thickness that does not contact the surface of the photoreceptor 4, and using an alternating current bias as the developing bias, toner is removed from the developer layer. A developing device 8Y performs non-contact development in which the particles are caused to fly and adhere to the photoreceptor 4.

8M, 8C, 8K, recharging device for smoothing the surface potential of the photoreceptor 4 after development 9Y, 9M, 9C1 Exposure lamp and corona for white light or infrared light that can pass through even a single layer of toner Transfer pre-processing device 10 using a discharge device, transfer device 1
1. A separator 12, a pre-cleaning static eliminator 13, and a cleaning device 14 are provided, and a color image or a monochrome image is formed on the photoreceptor 4 through the steps described below.

When the copy switch is turned on, the photoreceptor 4 rotates in the direction of the arrow, and the negative charger 5 performs corona discharge to uniformly charge the image forming area of the photoreceptor 4.

- The charging by the charger 5 is performed using detection information of a known document size detection device, magnification ratio detection device, or transfer material size detection device (not shown), or designation information of a magnification ratio or transfer material size specifying means for the document size. etc., the aperture width regulating plate 51 is moved back and forth in the direction of the arrow in FIG. 9 to preset the corona discharge passage width W in the width direction of the photoreceptor 4 to the width of the projection document or transfer material on the photoreceptor 4, Then the discharge wire 52
This is performed by applying a discharge voltage for a period of time during which the surface of the photoreceptor 4 moves by the length of the projection original or the length of the transfer material. The aperture width regulating plate 51 is made of an insulating material that is not affected by charging, and the photoreceptor under the regulating plate is not charged.The aperture regulating plate 51 is moved forward and backward by a stamping motor or the like. This is a roller that also serves as a guide to ensure smooth operation. This roller is also made of an insulating material that is not affected by static electricity. Under copying conditions where the transfer material width and length are shorter than the projection document width and length, the corona discharge passage width W and the discharge voltage application time are set to the transfer material width and length.

If the document is thick, the edge of the document may be considered a black image due to lifting from the document table, and the edge of the resulting image may become black.
It is preferable to narrow it by ~5 dragons.

To explain the above-mentioned charged area control with reference to FIG. 10, the method of controlling the charged area from detection information is to combine the image exposure size determined from the detected document size and magnification ratio with the detected size of the transfer material. They are compared in the central processing unit CPU, and the smaller size is transferred as a signal to the stamping motor and an ON/OFF signal for the charger power source. Furthermore, the method of controlling the charging area using the specified LFF information depends on the content of the specified information. Detection information is used for all but the specified information among the three pieces of information: document size, magnification ratio, and transfer material size. The specified information has priority for the charged area. If only the magnification ratio is specified, the image exposure size obtained from the detected document size becomes the charged area. If all three pieces of information are input, the process will be the same as that using detected information. The charged area based on the above detection information and designation information does not become larger than the size of the transfer material.

If the photoreceptor 4 uses an n-type semiconductor such as cadmium sulfide for the photoconductor 2, the corona discharge of the negative charger 5 is a positive discharge, and if a p-type semiconductor such as selenium is used for the photoconductor FJ2. If used, it is a negative discharge.

As described above, primary charging is performed only on the image forming area of the photoreceptor 4, and not on the non-image area. An image exposure device 6 may be provided on the surface of the photoreceptor 4 that has been electrically charged, or an original document may be scanned and exposed by passing over a platen. In the illustrated example, the reflected light from the document tray enters as the image exposure I, but it is also possible to make the light passing through the document tray enter as the image exposure I.

The secondary charger 61 performs alternating current or direct current corona discharge of substantially opposite polarity to the corona discharge of the primary charger 5 on the surface of the photoreceptor 4 on which the image exposure (1) is incident.

A primary latent image consisting of a charge density that does not function as an electrostatic image to be developed with toner is formed on the image forming area of the photoreceptor 4 by 0 or more, which will be explained below using an example using a corona discharge of opposite polarity.

FIG. 11 shows an example in which the secondary charger 61 starts discharging when the copy switch is turned on and continues for m, and the negative charger 5 starts discharging after a delay. However, the secondary charger 61
Also, using a Rona discharger as shown in Figure 8.9,
Only the image forming area may be secondarily charged. In this case, it is preferable that the aperture width regulating plate 5 does not block the image exposure r. - The secondary charging area may be approximately the same as the incident area of imagewise exposure (1). However, the secondary charging area must include the primary charging area. Otherwise, the primary charger 5, where neither secondary charging nor image exposure was performed, will have a black image potential, and the toner adhering there will be transferred to the cleaning device 1.
This causes problems such as increasing the burden on the printer and causing toner stains.

On the other hand, even if image exposure or secondary charging is performed beyond the -order charging area, that area will not reach a potential to which toner will adhere.

1 from time t0 in FIG. The primary charging during this period is achieved by using a p-type semiconductor such as Se-Te for the photoconductive layer 2 of the photoreceptor 4, and the surface potential of the photoreceptor 4 is changed by negative corona discharge from the charger 5. Indicates the state of Continued Time t, 1. The dark decay during this period indicates a state in which the potential changes due to charge injection and dissipation of the injected charge until the -order charged surface reaches the position of the secondary charger 61. The curves VL and V in the secondary charging simultaneous image exposure between time [2 and [C] indicate that portions corresponding to the bright and dark areas of the image exposure (2) are incident on the -order charged surface of the photoreceptor 4. Then, the secondary charge with the opposite polarity to the -order charge is added to the potential v
Both L and the dark potential v0 are substantially smoothed, and there is no potential pattern on the surface of the photoreceptor 4 after passing through the secondary charger 61 to which toner adheres even if it is subjected to a developing action. The potential of the surface on which the portion corresponding to the intermediate gradation between the bright and dark areas of exposure (2) is incident is also the bright area potential vL and the dark area potential V.

It has a smoothed potential between 2 and 3, and does not function as an electrostatic image to which toner adheres. Also, the curve v0 is ■. . Ha-
V OL and V oa at 0 time t, which shows the potential change when the areas corresponding to the bright and dark areas of image exposure (2) are incident on the secondary charged area outside the secondary charging area, are as follows: -Because it receives a secondary charge of opposite polarity to the secondary charge,
This is a potential higher than the VL and V11 potentials, at which toner does not adhere.

The uniform exposure device 7B uniformly applies blue light onto the surface of the photoreceptor 4 on which the primary latent image has been formed as described above. Due to this uniform exposure to the blue light, a potential pattern is generated on the surface of the B filter portion of the photoreceptor 4 from the -th layer image. The uniform exposure between times t3 and t4 in FIG. 11 illustrates this. In other words, by uniform exposure to blue light, the dark potential of the B filter portion increases.

changes to the potential at which toner adheres; on the other hand, the bright area potential vL hardly changes from the potential at which toner does not adhere;
The intermediate gradation potential of the B filter portion is the dark potential ■.

The potential is changed to an appropriate potential between the bright area potential VL and the potential to which toner adheres, and a potential pattern, that is, an electrostatic image is formed on the surface of the B filter portion. On the other hand, the potential ■ of the part that received secondary charging outside the -order charging area. L, ■. . is higher than the potential of VL even if both are uniformly exposed. That is, even if the area outside the negative-order charging area is uniformly exposed, the potential does not reach a level where toner adheres.

The electrostatic image formed as described above is developed with a developing bag H8Y containing yellow toner. As a result, the B of the photoreceptor 4
A yellow toner image is formed from the yellow toner adhering to the filter portion.

In this case as well, toner does not adhere outside the primary charging area.During development between time t4 and t2 in FIG. 11, positively charged yellow toner adheres and the dark potential V of the B filter portion decreases. In other words, the bright area potential vL and the potential outside the primary charging area ■. L+vOD shows that there is almost no change since there is no toner adhesion. The recharging device 9Y, which performs corona discharge to adjust the potential of this developing surface to the same potential as that in the secondary charger 61, smoothes the developing surface. With this, the 11th
As seen in the recharging between times t and t in the figure, the dark area potential v9 changes to a potential at which toner does not adhere, which is the same potential as the light area potential vL.

Of course, the intermediate gray level potential changes similarly. The potential V0° of the dark area outside the -order charging area is the same potential as the potential VOL of the bright area of the same area. Vo at this point. .

■. , the potential is ■. , is higher than the VL potential, so it is also a potential at which toner does not adhere. The uniform exposure device 7G uniformly applies green light to the surface of the photoreceptor 4 whose potential has been smoothed. As a result, - from the next layer image to the photoreceptor 4;
A potential pattern is generated on the surface of the G filter portion. 1st
The uniform exposure between time t6 and t7 in Figure 1 illustrates this. Of course, this uniform exposure does not change the potential outside the -order charging area to the potential to which toner adheres.The electrostatic image formed by this uniform exposure is developed by the developing device 8M containing magenta toner. , a magenta toner image consisting of magenta toner adhered to the surface of the G filter portion is formed. The development between time t1 and t in FIG. 11 shows the potential change on the surface of the photoreceptor 4 due to this development, and the potential change in this case is the same as that during development between time t4 and t. . The potential of this developing surface is further smoothed by a recharging device 9M, and then a uniform exposure device 7R is applied to the smoothed surface.
makes red light uniformly incident. As a result, a potential pattern is generated on the surface of the R filter portion of the photoreceptor 4 from the primary latent image. This potential pattern is developed by a developing device 8C containing cyan toner to form an R toner image. As a result, yellow, magenta,
A color image is formed consisting of a composite of cyan toner images.

Recharging during time t, entanglement, time t in FIG.

From tl. uniform exposure between and times t1° to t,
The development between is performed by recharging with a recharging device 9M, and
It shows how the surface potential of the photoreceptor 4 changes due to uniform exposure by the uniform exposure device 7R and development by the development device 8C, and the changes in each are due to the previously performed recharging, uniform exposure, and development. It is similar to In other words, toner does not adhere to areas outside the negative-order charging area.

Although an example has been described above in which the polarity of the secondary charging is opposite to that of the primary charging, similar results can be obtained by AC corona discharge.

In the image forming apparatus shown in FIG. 7, when forming a color image with high image density, the surface potential of the photoreceptor 4 on which the cyan toner image is formed is further smoothed by a recharger 9C; White light or B, G is applied to the surface by -1 exposure device 7K.

Infrared light that passes through all of the R filters and makes the photoconductive layer 2 conductive is uniformly incident, thereby converting the next layer image into B,
A potential pattern that supplements the black portion of the original image is formed on the surface of the G and R filter portions, and the potential pattern is developed by a developing device 8 containing black toner. This causes yellow to appear on the photoreceptor 4.

A high density visible color image is formed consisting of a composite of 7 zenta, cyan, and black toner images. Also in this case, the black toner does not adhere outside the primary charging area.

Note that when the original image is a monochrome image, a toner image representing a monochrome image made of toner of one color or a plurality of colors is formed on the photoreceptor 4 through the above steps.

The toner image formed on the photoconductor 4 as described above is easily transferred by the transfer pre-processing device 10, and
The image is transferred by the transfer device 11 onto the transfer material P fed by. The transfer material P to which the toner image has been transferred is transferred to a separator 1.
2, and the fixing device is separated from the photoreceptor 4 by the conveyance means 16! 17, the toner image is fixed by the fixing device 17, and the toner image is discharged outside the machine. On the other hand, the surface of the photoconductor 4 to which the toner image has been transferred is charged by the pre-cleaning static eliminator 13, and the cleaning device 14 removes any residual static electricity.
Even if there are fewer or more sets of developing devices, etc., colors other than yellow, magenta, and cyan, such as blue, green,
It may be one that forms a color image using red toner. Further, in order to form monochrome images other than black with the same image density and resolution as in a monochrome copying machine, for example, a uniform exposure device similar to the -1 exposure device 7 is installed in the uniform exposure devices 7B and 7G. , 7R, and when forming a monochrome image, -1 exposure device 7
When uniform exposure is performed using the uniform exposure device instead of B, IG, and 7H, a potential pattern is generated in the R, G, and B filter portions, so it is possible to obtain a monochrome image similar to that in a monochrome copying machine. . In this case, without smoothing the surface potential developed by uniform exposure, the same potential pattern is further developed using another developing device, for example, yellow toner and magenta toner are placed on the same latent image. A red image can also be formed by overlapping development.

The present invention further provides image formation in which, after secondary charging, secondary charging and image exposure, charging for smoothing, whole surface exposure with specific light, and development are repeated, as described in Japanese Patent Application No. 60-229524. It can also be applied to devices.

In addition, a configuration in which the photoreceptor is provided with a filter on the side opposite to the side receiving corona discharge from a charger or the like and receives image exposure and uniform exposure from the filter side (Japanese Patent Application No. 59-199547) and other configurations (Patent Application Showa 59-198166.

1998167 and 201084).

In addition, the leading layer of the photoreceptor is not a single layer, but has a functionally separated structure consisting of a charge generation layer and a charge transfer layer (Japanese Patent Application No. 60-2
No. 29524, No. 60-245178),
Photoreceptor has color separation function and light guide 11! Layers (Japanese Patent Application No. 59-201085, Patent Application No. 60-245177)
But that's fine.

Finally, more specific examples of the present invention will be shown.

Example 1゜A filter with a pattern as shown in Fig. 5 was printed on a ceramic polyethylene terephthalate thin film with a thickness of 25 μm.
60 μm thick insulating layer-forming film sensitized with Te
A photoreceptor 4 having a color separation function, which was formed by adhering it to a 5eTe photoconductor layer, was used in an image forming apparatus capable of variable magnification copying as shown in FIG. Using this image forming apparatus, images were formed on an A4 manuscript size, an 85 recording paper size, and a reduction rate of 86% by the process described with reference to FIG.

First, while the photoreceptor 4 is uniformly negatively charged by the charger 5 and subjected to zero-order image exposure I, the photoreceptor 4 is charged by the charger 61 with a reverse polarity so that the surface potential becomes approximately 0. The corona discharge passage width in this charger 61 is preferably wider than that in the charger 5.

In order to form a perfect image in the image forming apparatus of the present invention, (i) corona discharge passage width in charger 5 ≦ corona discharge passage width in charger 61 (11) corona discharge passage width in charger 5 ≧ image exposure width; It is preferable to do so.

The size of the A4 version is 210 x 297 Dragon, and the size of the 85 version is 182 x 257 Ill.

Then, the A4 size original is reduced to 85 size by an optical system and subjected to image exposure. To be exact, it is A4 size 86
The % reduction is 181 x 256 ms, and the transfer material size in this case is 182 x 257 m. Therefore, a charging area of 181 x 256 m, which is a small size when comparing both sizes, is sufficient.

The 181 field in the fil area is controlled by turning on and off the power supply that supplies power to the charger, and the 256 field is controlled by 181 x 256 obtained from the document size information and reduction rate.
A size signal of m is sent to the stamping motor that operates the aperture width regulating plate 51 to operate and control the motor.

These controls are performed by the control device shown in FIG.

Note that in order to remove the black border at the edge that occurs when copying a thick original, it is possible to make the charging area somewhat narrower.

The control device starts image formation after transmitting the size signal of the charged area to the power source and the stenting motor. As a result, it was possible to obtain a copying transfer material with high image quality and no black borders.

〔Effect of the invention〕

According to the image forming apparatus of the present invention, a color image can be formed on a photoreceptor without color shift, and toner does not adhere to a non-image area, reducing the burden on a cleaning device and reducing toner consumption.
An excellent effect is obtained in that the occurrence of toner contamination is reduced.

[Brief explanation of drawings]

1 to 4 are schematic partial cross-sectional views showing examples of the layer structure of a photoreceptor used in the image forming apparatus of the present invention, and FIGS. 5 and 6 are filters of color separation filter layers of the photoreceptor, respectively. FIG. 7 is a schematic side view of the configuration of an example of the image forming apparatus of the present invention, and FIGS. 8 and 9 are a partial side view and a partial front view of an example of a primary charger. -1 FIG. 10 is a signal input/output chart of the control device, FIG. 11 is an operation timing graph of the primary charger and secondary charger, and FIG. 12 is a graph of changes in photoreceptor surface potential during the color image forming process. DESCRIPTION OF SYMBOLS 1... Conductive member, 2... Photoconductive layer, 3...
...Insulating layer, 3a...Color separation layer, 4...
・Photoreceptor, 5...-Fukiyose electric device, 51...
・Aperture width regulating plate, 6... Image exposure device, 61...
Secondary charger, 7B, 7G, 7R, 7K...-1 Exposure device, 8Y, 8
M, 8C, 8K...Developing device, 9Y, 9M, 9C...
・Recharger, 10...Transfer pre-processing device, 11...Transfer device, 12
... Separator, 13... Pre-cleaning static eliminator, 14... Cleaning device. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 6 Figure 9 Section 10

Claims (2)

[Claims] (1) After forming a primary latent image by performing primary charging, image exposure, and secondary charging on a photoreceptor having an insulating surface layer and a distribution layer of color separation functional elements, a color separation electrostatic image is generated from the primary latent image. In an apparatus for forming a color image on the insulating surface layer by repeatedly exposing the electrostatic image to specific light to be extracted and developing the electrostatic image with a specific color toner, at least the charger for primary charging is provided with the photoreceptor. An image forming apparatus characterized by using a corona discharger that can adjust the width of a corona discharge passage opening in the width direction. (2) The image forming apparatus according to claim 1, wherein the corona discharge passage opening width of the charger is adjusted according to the size of the transfer material.