JPH06317948A - Image forming device - Google Patents

Abstract

PURPOSE:To provide a printer using an electrophotographic process and forming an image with high resolution. CONSTITUTION:As for the printer using the electrophotographic process, it is constituted so that such relation as 0.9<=¦I1/(I3+I2+I4)¦ and 1<=¦I3/I2¦<=4 is attained when the currents of an electrostatic charging time, a developing time, a transferring time and a cleaning time are defined as I1, I2, I3 and I4. Thus, such an effect that the uniform image without density irregularity or defective transfer can be continuously formed is attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image with toner.

[0002]

2. Description of the Related Art A conventional image forming apparatus is disclosed in Japanese Patent Application Laid-Open No. 56-1.
32356, the charging current is controlled, the developing voltage is controlled by the developing current as disclosed in JP-A-4-34573, and the transfer voltage is controlled by the transfer current as disclosed in JP-A-2-123385. By doing so, optimization of charging, development, and transfer has been achieved.

[0003]

However, although the above-mentioned conventional image forming apparatus has been optimized for charging, developing and transferring, different processes such as charging and developing, developing and transferring are performed. The optimization between
There is a problem that it is not possible to form a high quality image.

The present invention has been made in view of the above-mentioned prior art, and provides an image forming apparatus capable of obtaining a high-resolution image free from background fog, charging memory, and transfer failure by optimizing each process. The purpose is to do.

[0005]

The image forming apparatus of the present invention is a toner in which an electrostatic latent image formed on a surface of a photosensitive layer on a conductive supporting portion by a charging device and an exposing device is charged by a developing device. Image is transferred to a recording medium by applying a voltage of the opposite polarity to that of the toner by a transfer device, and the toner remaining after transfer on the photosensitive layer is removed by a cleaning device. ,
Currents during development, transfer, and cleaning are I ₁ , I ₂ , and I, respectively.
_{When 3} and I ₄ are satisfied, the relationship of 0.9 ≦ | I ₁ / (I ₃ + I ₂ + I ₄ ) | is satisfied.

The image forming apparatus of the present invention is characterized by satisfying the relationship of 1 ≦ | I ₃ / I ₂ | ≦ 4.

The image forming apparatus of the present invention is used for developing an image portion,
When the transfer current is I _2B , I _3B , the development of the non-image area is I _2W , and the transfer current is I _3W , 1 ≦ (I _2W + I _3W + I ₄ ) / (I _2B + I _3B + I ₄ ) ≦ 6 It is characterized by satisfying the relationship of.

The image forming apparatus of the present invention is characterized in that the relationship of 1 ≦ | I _3B / I _2B | ≦ 4 is satisfied.

[0009]

According to the above construction of the present invention, the image formation is carried out by setting the charging potential, the developing potential and the transfer potential satisfying the relation of 0.9≤ | I ₁ / (I ₃ + I ₂ + I ₄ ) | As a result, when the same photosensitive layer is repeatedly used for image formation, the image formation can be performed without generating a charging memory in which the previous image appears as a memory in the subsequent images.

The charging memory means, for example, in a printer in which an electrostatic latent image is formed on a negatively charged photosensitive layer by exposure, visualized by negatively charged toner, and transferred to paper by a positive transfer voltage. This is a phenomenon in which, by being positively charged, the charging potential of the portion that is positively charged at the next charging time becomes small, and light and shade appears in the next image. This phenomenon is particularly remarkable in contact charging, which has been widely used recently.

I ₁ is a current when a charge is applied to the photosensitive layer from a charger to charge the photosensitive layer. In the case of an organic photoreceptor, which is commonly used, a current flows in a direction in which a negative charge is applied to a photosensitive layer in order to make it negatively charged.
I ₂ is a current when the charged toner is moved from the developing device to the photosensitive layer in the developing process for visualizing the electrostatic latent image formed on the photosensitive layer. In the case of reversal development in which an electrostatic latent image is formed by exposing the image portion of the negatively charged photosensitive layer and visualized with negatively charged toner, the developing device is removed from the photosensitive member according to the amount of charged toner that moves to the photosensitive member. Current flows in the direction of. I ₃ is a current when the toner on the photoconductor is moved to a transfer medium such as paper. When the negatively charged toner is transferred to the paper, a current flows from the transfer device to the photoconductor in accordance with the amount of toner. When the toner is present on the photoconductor (image area), a current flows to move the toner to the paper, but when the toner is not present on the photoconductor (non-image area), the photoconductor is positively charged. . I ₄ is a current when the toner remaining on the photoconductor after the transfer is removed by the cleaning device. In the case of a commonly used method of pressing a rubber blade, a current flows from the photoconductor to the cleaning device by removing the toner from the photoconductor and rubbing the photoconductor with the blade to charge the photoconductor. FIG. 2 is a schematic diagram of the current in each step in a printer that forms an electrostatic latent image on a generally negatively charged photosensitive layer by exposure, visualizes it with negatively charged toner, and transfers it to paper with a positive transfer voltage.
Shown in. However, FIG. 2 is a diagram showing the direction of the current, and is not limited to the case where each step is actually directly grounded. The direction of the current in each step can be known from the surface potential of the photoconductor before and after each step as well as the method of directly measuring the current. For example, if the surface potential of the photoconductor changes from 0 V to −100 V before and after a certain process, a current flows from the photoconductor toward this process.

FIG. 3 shows the relationship between the stability of the charging potential during repeated image formation and the ratio of the charging current to the current flowing in the developing, transferring and cleaning steps. As a measure showing the stability of the charging potential, the ratio of the number of times of repeated charging n-1 times and the charging potential of n times was used as V ₀ n-1 and V ₀ n, respectively. The charging potential is stable when the ratio of the charging current to the current flowing in the developing, transferring and cleaning steps is 0.9 or more. Therefore, by setting the potential of each process so that the ratio of the charging current and the current flowing in the developing, transferring, and cleaning processes is 0.9 or more, the previous image is repeatedly used when the image is formed using the photoconductor repeatedly. Due to the potential remaining during formation, a memory such as light and shade does not occur in the next image formation, and there is no variation in density between print individuals when a plurality of sheets are printed.

According to the above configuration of the present invention, 1 ≦
By setting the developing potential and the transfer potential that satisfy the relationship of | I ₃ / I ₂ | ≦ 4 and performing image formation, a uniform image without transfer omission can be formed. The relationship between | I ₃ / I ₂ | and transfer efficiency is shown in FIG. | I ₃ / I ₂ | is 1 or more and 4 or less, and the transfer efficiency is 90% or more. Good transfer can be performed by setting transfer conditions so that a transfer current having a polarity opposite to that of the developing current and having a magnitude greater than or equal to the developing current can flow. However, if | I ₃ / I ₂ | exceeds 4, a current more than the current required to move the toner from the photoconductor to the paper is injected into the photoconductor, and the photoconductor is charged, which causes the next image formation. Memory such as light and shade is generated.

According to the above construction of the present invention, the developing potential and the transfer potential satisfying the relation of _1≤ (I _2W + I _3W + I ₄ ) / (I _2B + I _3B + I ₄ ) ≤6 are set and the image is formed. By forming the image, when the image formation is repeatedly performed using the same photosensitive layer, the image formation can be performed without generating a charging memory in which the previous image appears as a memory in the subsequent images.

I _2W is a current that flows when the toner moves to the non-image portion, and usually hardly flows. I _2B is a current flowing when the toner moves to the image portion. I _3W
Is a transfer current flowing in the non-image portion, and may cause the photoreceptor to be reversely charged. I _3B is a current flowing when the toner in the image area moves to the transfer medium. At the time of repeatedly forming images, the charging stability of the portion where the charging potential of the portion which was the non-image portion last time was V _0W and the charging potential of the portion which was the image portion last time was V _0B
0W / V _0B ) and (I _2W + I _3W + I ₄ ) / (I _2B + I _3B +
The relationship of I ₄ ) is shown in FIG. (I _2W + I _3W + I ₄ ) / (I
_It can be seen that the charging potential is stable regardless of the previous image when _2B + I _3B + I ₄ ) is between 1 and 6. Therefore, by setting the potential of each process so that it becomes (I _2W + I _3W + I ₄ ) / (I _2B + I _3B + I ₄ ), when the image is repeatedly formed using the photoconductor, Due to the remaining potential of No. 2, a memory such as light and shade does not occur in the next image formation, and density unevenness does not occur between individual prints when printing a plurality of sheets.

According to the above configuration of the present invention, 1 ≦
By setting a developing potential and a transfer potential that satisfy the relationship of | I _3B / I _2B | ≦ 4 and performing image formation, a uniform image without transfer defects can be formed. FIG. 6 shows the relationship between | I _3B / I _2B | and transfer efficiency. | I _3B / I _2B | is 1 or more and 4 or less, and the transfer efficiency is 90% or more. Good transfer can be performed by setting transfer conditions so that a transfer current having a polarity opposite to that of the developing current and having a magnitude greater than or equal to the developing current can flow. However, when | I _3B / I _2B | exceeds 4, a current more than the current required to move the toner from the photoconductor to the paper is injected into the photoconductor, and the photoconductor is charged, which causes the next image formation. Memory such as light and shade is generated.

[0017]

【Example】

(Embodiment 1) FIG. 1 is a schematic sectional view of an image forming apparatus according to an embodiment of the present invention. In this embodiment, the latent image carrier 1 is composed of a conductive support 2 and a photoconductive photosensitive layer 3 formed on the conductive support 2. The photosensitive layer 3 is charged by a corona charger, a charging roller, a charging film or the like. After being charged by using the container 4, a light source 5 such as a laser or an LED selectively irradiates the photosensitive layer 3 with light according to an image through an imaging optical system 6 to obtain a potential contrast. An electrostatic latent image is formed on the photosensitive layer 3.

On the other hand, the developing device 21 conveys and develops the toner 8, and the toner carrier 9 which conveys the toner 8 has a conductive elastic layer 11 on the outer periphery of the shaft 10.
Are arranged concentrically, and the supply member 17 for supplying the toner 8 to the toner carrier 9 is such that the foam 19 is concentrically arranged on the outer circumference of the shaft 18. Is a plate made of a non-magnetic or magnetic metal or resin, which is pressed against the toner carrier 9 and rotates to press the toner against the toner carrier 9 to charge it by rubbing the toner to directly hold the toner on the toner carrier. The toner carrier 9 is rotated to convey the thin-layer toner 8 while being regulated to an appropriate amount by the regulation member 22. The seal member 20 is for preventing the toner from leaking from the developing device 21.

The toner carrier 9 made of a specific elastic body is pressed against the surface of the photosensitive layer 3 of the latent image carrier 1 with a predetermined pressure, and the toner 8 on the toner carrier 9 is conveyed to the pressure contact portion. Then, the toner 8 charged according to the potential contrast of the latent image carrier 1 and the developing electric field by the developing bias applying means 14 adheres to the photosensitive layer 3, whereby the electrostatic latent image is visualized. Further, a transfer device 15 such as a corona transfer device or a transfer roller is used to transfer the toner image onto the recording paper 16 and the transfer toner is fixed onto the recording paper by heat or pressure to form a desired image on the recording paper. You can The toner 8 remaining on the latent image carrier 1 after the transfer is removed from the latent image carrier 1 by the cleaning device 23 such as a cleaning blade, and the latent image carrier 1 is used for the next electrostatic latent image formation.

The elastic layer 11 and the supply member 17 are made of soft foam material such as polyurethane foam, polystyrene foam, polyethylene foam, elastomer foam, rubber foam, natural rubber, silicone rubber, urethane rubber, butadiene rubber, chloroprene rubber. A rubber such as a neoprene rubber or NBR, or an elastomer containing a styrene resin, a vinyl chloride resin, a polyurethane resin, a polyethylene resin, a methacrylic resin, or the like can be used. Further, as the regulating member 22, a thin leaf spring made of a metal such as stainless steel or phosphor bronze and having a thickness of about several hundred μm, or a thin resin such as rubber or elastomer can be used.

Image formation is carried out continuously with the above-mentioned structure, and currents of charging, development, transfer, cleaning and unevenness of image density at that time are shown in Table 1. Each current was measured by disposing an ammeter in each step. For example, in the case of development, an ammeter is arranged between the toner carrier 9 and the developing bias applying means 14 to measure. Regarding cleaning, the surface potential of the photosensitive layer before and after the cleaning device 23 was measured and the cleaning current was calculated. Each current is indicated by the maximum value because it changes depending on the type of image and history. │I ₁ / (I ₂ + I ₃ +
When I ₄ ) | <0.9, uneven image density occurred. On the other hand, by setting 0.9 ≦ | I ₁ / (I ₂ + I ₃ + I ₄ ) |, it was possible to form a uniform image without density unevenness.

[0022]

[Table 1]

(Embodiment 2) An image is formed by using the image forming apparatus as shown in FIG. 1, and development and transfer current at that time are shown in FIG. 1> | I ₃ / I ₂ |, or | I ₃
When / I ₂ |> 4, a transfer failure occurred and a uniform image could not be formed. On the other hand, when 1 ≦ | I ₃ / I ₂ | ≦ 4, it was possible to form a uniform image without transfer defects.

(Embodiment 3) An organic photoconductor (OPC) is used as a latent image carrier 1 as shown in FIG. 7, and a thickness of 4 is used as a charger.
0 μm, volume resistance 8 × 10 ⁷ Ωcm, nylon film charger 41, toner carrier 9 single layer, volume resistance 3 × 10 ⁷ Ωcm, urethane rubber roller, transfer device 15 volume resistance 2 × 10 ⁷ Ωcm, urethane sponge roller, urethane rubber blade as cleaning device 23, polyester toner having a volume average particle diameter of 9 μm as toner, and A4 size transfer paper is vertically fed (width 21 cm) at a feed speed of 3 cm / s. Image formation was performed. By applying -1100 V to the film charger 41, a charging potential of -600 V was obtained, and a developing bias of -250 V and a transfer bias of +800 V were applied. At this time, I ₁ = −6 μA, I ₂ = −1 μA, I ₃ =
+4 μA, I ₄ = -1 μA, | I ₁ / (I ₂ + I ₃ + I ₄ )
| = 3 and | I ₃ / I ₂ | = 4. 100 under this condition
When images were continuously formed on 0 sheets, good printing without unevenness in density and transfer omission could be obtained.

Comparative Example 1 As shown in FIG. 1, an organic photosensitive member (OPC) is used as the latent image carrier 1, a volume resistance of 2 × 10 ⁷ Ωcm is used as the charger 4, a urethane sponge roller, and a toner carrier 9. As a single layer, volume resistance 3 × 10 ⁷ Ω
cm, urethane rubber roller, volume resistance 2 × 10 ⁷ Ωcm as transfer device 15, urethane sponge roller, urethane rubber blade as cleaning device 23, polyester toner with volume average particle size 9 μm as toner, A4 size Feed the transfer paper vertically (width 21c
m), image formation was performed at a feed rate of 3 cm / s. By applying -1150 V to the charger 4, a charging potential of -600 V was obtained, and -250 V was applied as the developing bias and +1200 V was applied as the transfer bias. At this time I ₁
= -6 μA, I ₂ = -1 μA, I ₃ = + 10 μA, I ₄ =
−1 μA, | I ₁ / (I ₂ + I ₃ + I ₄ ) | = 0.75, |
I ₃ / I ₂ | = 10. When images were continuously formed under these conditions, uneven density and transfer omission occurred, and good printing could not be obtained.

(Embodiment 4) As shown in FIG. 8, an organic photoconductor (OPC) is used as a latent image carrier 1, a volume resistance of 2 × 10 ⁸ Ωcm is used as a charger 4, a sponge roller made of urethane, and a toner carrier 9 Volume resistance 4 × 10 ⁴ Ωcm,
NBR nylon coated multi-layer rubber roller, transfer device 15 volume resistance 2 × 10 ⁷ Ωcm, urethane sponge roller, cleaning device 23 urethane rubber blade, toner average volume particle size 9 μm
The A4 size transfer paper was longitudinally fed (width 21 cm) using the styrene-acrylic toner of No. 1 to form an image at a feeding speed of 1.5 cm / s. By applying -1200V to the charger, a charging potential of -650V was obtained, and a developing bias of -230V and a transfer bias of + 800V were applied. At this time, I ₁ = −3.3 μA, I ₂ = −0.5 μ
A, I ₃ = + ₂ μA, I ₄ = −0.5 μA, | I ₁ / (I ₂
+ I ₃ + I ₄ ) | = 3.3 and | I ₃ / I ₂ | = 4.
When 1000 sheets of images were continuously formed under these conditions, good printing without unevenness in density and transfer omission could be obtained.

Comparative Example 2 An organic photoconductor (OPC) is used as the latent image carrier 1 as shown in FIG. 7, and a thickness of 4 is used as the charger.
0 μm, volume resistance 8 × 10 ⁷ Ωcm, polypropylene film charger 41, single layer as toner carrier, volume resistance 3 × 10 ⁷ Ωcm, urethane rubber roller, transfer device 15 volume resistance 2 × 10 ⁷ Ωcm , Urethane sponge roller, urethane rubber blade as cleaning device 23, volume average particle diameter 9 μm as toner
An image was formed at a feed rate of 1.5 cm / s by longitudinally feeding a transfer paper of A4 size (width 21 cm) using the polyester toner of No. 1. By applying -110 V to the film charger 41, a charging potential of -600 V is obtained, a developing bias of -300 V and a transfer bias of +1200.
V was applied. At this time, I ₁ = −3 μA, I ₂ = −1 μ
A, I ₃ = + 5 μA, I ₄ = -1 μA, | I ₁ / (I ₂ + I
₃ + I ₄ ) | = 1 and | I ₃ / I ₂ | = 5. When images were continuously formed under these conditions, density unevenness did not occur, but transfer omission occurred and good printing could not be obtained.

(Embodiment 5) Images are continuously formed by using the image forming apparatus as shown in FIG. 1, and currents of development, transfer, cleaning and unevenness of image density are shown in Table 2.
Shown in. 1> (I _2W + I _3W + I ₄ ) / (I _2B + I _3B +
I ₄ ) or (I _2W + I _3W + I ₄ ) / (I _{2 B} + I _3B +
When I ₄ )> 5, uneven image density occurred. On the other hand, 1 ≦
By setting (I _2W + I _3W + I ₄ ) / (I _2B + I _3B + I ₄ ) ≦ 6, a uniform image without density unevenness could be formed.

[0029]

[Table 2]

(Embodiment 6) An image is formed by using the image forming apparatus as shown in FIG. 1, and the state of development and transfer current at that time is shown in FIG. 1> | I _3B / I _2B |, or | I
_{When 3B} / I _2B |> 4, a transfer failure occurred and a uniform image could not be formed. On the other hand, 1 ≦ | I _3B / I _2B | ≦
In No. 4, it was possible to form a uniform image with no transfer omission.

(Embodiment 7) An organic photoconductor (OPC) is used as a latent image carrier 1 as shown in FIG. 7, and a thickness of 5 is used as a charger.
0 μm, volume resistance 5 × 10 ⁷ Ωcm, nylon film charger 41, toner carrier 9 single layer, volume resistance 5 × 10 ⁷ Ωcm, urethane rubber roller, transfer device 15 volume resistance 2 × 10 ⁷ Ωcm, urethane sponge roller, urethane rubber blade as cleaning device 23, polyester toner having a volume average particle diameter of 9 μm as toner, and A4 size transfer paper is vertically fed (width 21 cm) at a feed speed of 3 cm / s. Image formation was performed. By applying -1200V to the film charger 41, a charging potential of -600V was obtained, and a developing bias of -250V and a transfer bias of + 800V were applied. At this time, I _2W = 0 μA, I _2B = -1 μA, I _3W =
+4 μA, I _3B = 2.5 μA, I ₄ = -1 μA, (I _2W
+ I _3W + I ₄ ) / (I _2B + I _3B + I ₄ ) = 6, | I _3B / I
_2B | = 2.5. When 1000 sheets of images were continuously formed under these conditions, good printing without unevenness in density and transfer omission could be obtained.

Comparative Example 3 As shown in FIG. 1, an organic photosensitive member (OPC) is used as the latent image carrier 1, a volume resistance of 7 × 10 ⁷ Ωcm is used as the charger 4, a sponge roller made of silicon, and a toner carrier 9 As a single layer, volume resistance 2 × 10 ⁷ Ω
cm, urethane rubber roller, volume resistance 8 × 10 ⁷ Ωcm as transfer device 15, urethane sponge roller, urethane rubber blade as cleaning device 23, polyester toner with volume average particle size 9 μm as toner, A4 size Feed the transfer paper vertically (width 21c
m), image formation was performed at a feed rate of 3 cm / s. By applying -1150 V to the charger 4, a charging potential of -600 V was obtained, and -250 V was applied as the developing bias and +1200 V was applied as the transfer bias. At this time I _2W
= 0 μA, I _2B = -1.3 μA, I _3W = + 11 μA, I
_3B = ₄ μA, I ₄ = -1 μA, (I _2W + I _3W + I ₄ ) /
(I _2B + I _3B + I ₄ ) = 6.4, | I _3B / I _2B | = 3.
Became 1. When images were continuously formed under these conditions, uneven density occurred and good printing could not be obtained.

Although this embodiment describes reversal development using a negatively charged photoreceptor and toner, the present invention is not limited to this, and a positively charged photoreceptor and negatively charged toner are used. It can also be used for regular development using, a negative development using a negatively charged photoreceptor and positively charged toner, and a reversal development using a positively charged photoreceptor and toner.

Although the ammeter is used to measure the current in this embodiment, it can be known by measuring the surface potential of the photoconductor after passing through each step. That is, (current) = (capacity of photoconductor) × (surface potential of photoconductor) /
It can be calculated from the relationship of (time). For example, the current in the charging process is calculated. If the film thickness of the photoconductor is 20 μm, the nip of the charging roller is 1 mm, the moving speed of the photoconductor is 3 cm / s, and the surface potential before and after charging changes from 0 V to −600 V, it becomes −4.8 μA, which is in agreement with the actual measurement value. did.

[0035]

As described above, when the currents for charging, developing, transferring and cleaning are I ₁ , I ₂ , I ₃ and I ₄ , respectively, 0.9 ≦ | I ₁ / (I ₃ + I By setting the conditions of each process so as to satisfy the relationship of ₂ + I ₄ ) |, it is possible to continuously perform uniform image formation without density unevenness.

By setting the conditions of each process so as to satisfy the relationship of 1 ≦ | I ₃ / I ₂ | ≦ 4, it is possible to form a uniform image without transfer defects. .

Further, the current for developing and transferring the image portion is I _2B ,
When the currents of I _3B , development and transfer of non-image area are I _2W and I _3W , the relation of 1 ≦ (I _2W + I _3W + I ₄ ) / (I _2B + I _3B + I ₄ ) ≦ 6 should be satisfied. By setting the conditions of each step, it is possible to continuously perform uniform image formation without density unevenness.

By setting the conditions of each step so as to satisfy the relationship of 1 ≦ | I _3B / I _2B | ≦ 4, it is possible to form a uniform image without transfer defects. .

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a diagram showing a current flow in each process of the image forming apparatus according to the exemplary embodiment of the present invention.

FIG. 3 is a diagram showing the relationship between the charging potential of the present invention and the current in each step.

FIG. 4 is a diagram showing the relationship between the transfer efficiency and the current in each step according to the present invention.

FIG. 5 is a diagram showing the relationship between the charging stability of the present invention and the current in each step.

FIG. 6 is a diagram showing the relationship between the transfer efficiency and the current in each step according to the present invention.

FIG. 7 is a schematic cross-sectional view of the image forming apparatus according to the exemplary embodiment of the present invention.

FIG. 8 is a schematic cross-sectional view of the image forming apparatus according to the exemplary embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Latent image carrier 2 Conductive support 3 Photosensitive layer 4 Charger 5 Light source 6 Imaging optical system 8 Toner 9 Toner carrier 10 Shaft I 11 Elastic layer 12 Surface coat layer 14 Development bias applying means 15 Transfer device 16 Recording Paper 17 Supplying member 18 Shaft II 19 Foam 21 Developing device 22 Controlling member 23 Cleaning device 41 Film charger

Claims (4)

[Claims] 1. An electrostatic latent image formed on the surface of a photosensitive layer on a conductive support by a charging device and an exposing device is visualized by a toner charged by a developing device, and the obtained toner image is transferred by a transfer device. In the image forming apparatus in which the toner having the polarity opposite to that of the toner is transferred to the recording medium by the toner, and the toner remaining after the transfer on the photosensitive layer is removed by the cleaning device, the currents at the time of charging, developing, transferring and cleaning are respectively I
An image forming apparatus characterized by satisfying a relationship of 0.9 ≦ | I ₁ / (I ₃ + I ₂ + I ₄ ) |, where ₁ , I ₂ , I ₃ and I ₄ are satisfied. 2. The image forming apparatus according to claim 1, wherein the relationship of 1 ≦ | I ₃ / I ₂ | ≦ 4 is satisfied. 3. A current for developing and transferring an image area is set to I _2B ,
When the currents for developing and transferring I _3B and non-image area are I _2W and I _3W, it is necessary to satisfy the relationship of 1 ≦ (I _2W + I _3W + I ₄ ) / (I _2B + I _3B + I ₄ ) ≦ 6. A characteristic image forming apparatus. 4. The image forming apparatus according to claim 3, wherein the relationship of 1 ≦ | I _3B / I _2B | ≦ 4 is satisfied.