JPH1078689A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To excellently prevent transfer dust without providing an additional mechanism by satisfying a specified condition among the moving distance, the surface moving speed, the volume resistivity and the dielectric constant of an intermediate transfer body and the dielectric constant of vacuum. SOLUTION: An intermediate transfer belt 19 is brought into press-contact with a photoreceptor 9 between a transfer bias roller 20a and a ground roller 20b. Then, a toner image on the photoreceptor 9 is successively superposed and transferred to the belt 19 by the roller 20a, the roller 20b grounded to be at potential zero, and a transfer bias power source 40 for impressing specified transfer bias voltage on the roller 20a. When it is assumed that the moving distance of the surface of the intermediate transfer body 19 between a ground electrode and a ground opposed part is L1 , the surface moving speed, the volume resistivity and the dielectric constant of the transfer body 19 are VL, ρV, and E3 , and the dielectric constant of the vacuum is EεO, the condition expressed by L1 /VL</ρv .ε3 ε0 is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as a copying machine, a facsimile, a printer, a printing machine, and the like. More specifically, the present invention relates to a method for transferring a toner image formed on an image bearing member onto an intermediate transfer member. The present invention also relates to an image forming apparatus for transferring a superimposed toner image on an intermediate transfer member onto a transfer material.

[0002]

2. Description of the Related Art In recent years, an electrophotographic image forming apparatus capable of copying and printing a full-color image has been put to practical use. As a method of transferring a full-color image onto a transfer material in this type of image forming apparatus, (A) Transfer drum method: Each image of yellow (Y), magenta (M), cyan (C), and black (BK) formed for each color on an image carrier such as a photoconductor is transferred onto a transfer drum. (B) an intermediate transfer body double transfer method (also simply referred to as an intermediate transfer method): Y formed on an image carrier such as a photoreceptor for each color; M, C, and BK images are sequentially superimposed and transferred on an intermediate transfer body, and a full-color toner image on the intermediate transfer body is collectively transferred and transferred to a transfer material. Paper that can be transferred to thick paper etc. Points with Lee property, and the transfer drum system in terms that can be entirely copied without inability image formed on the clamp holding portion of the tip as an intermediate transfer type (b) above are advantageous.

[0003]

Conventionally, in the above-described image forming apparatus of the intermediate transfer system, a phenomenon of toner dust (hereinafter referred to as "transfer dust") occurs when a toner image is transferred from an image carrier to an intermediate transfer member. It is known that may occur. Here, the transfer dust refers to the toner image (visible image) formed on the image carrier when the toner image is transferred from the image carrier to the intermediate transfer member (primary transfer). It is a phenomenon that the image is not transferred to the position but is diffused and transferred to the surrounding area, resulting in blurred image.
In particular, the sharpness of an image in a thin line portion is impaired.

As a technique for preventing the transfer dust, a technique of non-electrostatically transferring a high-resistance toner to an intermediate transfer medium and then pressing and fixing the toner with a heating roller via a recording sheet (for example, Japanese Patent Application Laid-Open No. JP-A-63-34570), a technique in which a conductive toner is non-electrostatically transferred to an intermediate transfer medium, and then pressed and transferred and fixed by a heating roller with a recording sheet interposed (see JP-A-63-34571). A technology for removing charge from a toner image transferred by a paper peeling charger every time a toner image is transferred to an intermediate transfer medium (Japanese Patent Laid-Open No. 1-282)
No. 571), a technique in which the transfer potential in the final transfer stage is made higher than the immediately preceding transfer potential, and a predetermined voltage is applied to the intermediate transfer medium during each transfer stage (Japanese Patent Laid-Open No. 2-18).
Japanese Patent Application Laid-Open No. 4-147170), and a technique for providing a means for removing charges on the intermediate transfer member before the means for transferring a visible image from the intermediate transfer member to a sheet (see Japanese Patent Application Laid-Open No. 4-147170). . However, among these technologies, Japanese Patent Application Laid-Open Nos. 63-34570 and 63-34
In the technique disclosed in Japanese Patent No. 571, a recording sheet capable of being pressed and transferred and fixed by a heating roller is required, and the paper-free property which is the advantage of the intermediate transfer method (b) cannot be utilized. Further, in the techniques disclosed in JP-A-1-282571, JP-A-2-183276, and JP-A-4-147170, it is necessary to provide a means for static elimination and voltage application and a control means for controlling these means. There are problems that the control mechanism becomes complicated and that it also hinders downsizing of the device.

The inventors of the present invention have conducted intensive studies to solve the above-mentioned problem of the generation of transfer dust, and as a result, the intermediate transfer belt as an intermediate transfer member is brought into contact with a photosensitive member as an image bearing member. (Hereinafter, referred to as the entrance of the contact opposing portion) before the toner reaches the photosensitive member, and is found to be one of the causes of the transfer dust. This is because a strong electric field is applied to the toner at the entrance of the contact opposing portion because the potential of the upper surface of the belt is high.

In order to prevent the movement of the toner at the entrance of the contact opposing portion, it is necessary to lower the potential of the upper surface of the belt at the entrance of the contact opposing portion so that the toner does not transfer. As described above, in order to lower the belt upper surface potential at the entrance of the contact opposing portion, voltage applying means for applying a bias to the intermediate transfer belt on the entrance side and the exit side of the contact opposing portion of the intermediate transfer belt. It is effective to provide a bias roller as described above, ground the bias roller on the entrance side of the contact-facing portion, and apply a transfer bias to the bias roller on the exit side of the contact-facing portion.
Table 1 shows that bias rollers are provided on the entrance and exit sides of the contact facing portion of the intermediate transfer belt, and combinations of voltages applied to the bias rollers and the combinations on the intermediate transfer belt when each combination is employed. The result of observing the image is shown. In this experiment, an intermediate transfer belt having a volume resistivity ρ _v = 1 × 10 ¹¹ Ωcm made of a carbon-dispersed fluororesin was used. Further, the transfer bias Vp
Was set to 1600 V, and observation was performed with a magenta single color image.

[0007]

[Table 1]

From the observation results in Table 1, it can be seen that the configuration in which the bias roller at the entrance of the contact facing portion is grounded and the transfer bias is applied to the bias roller at the exit of the contact facing portion reduces transfer dust. It can be said that bias conditions which are relatively suitable for good image transfer are given, but still, it is not sufficient to prevent dust. This is because, since the intermediate transfer belt has a medium resistance, electric charges move in the intermediate transfer belt, thereby increasing the potential on the upper surface of the belt. It is considered that a strong electric field is formed between the photoconductor and the toner, and the toner on the photoconductor moves onto the belt.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of favorably preventing transfer dust without providing any additional mechanism. is there.

[0010]

In order to achieve the above object, according to the present invention, there is provided a toner image forming means for forming a toner image on an image carrier, and a transfer surface in contact with the image carrier. A transferable intermediate transfer member, an intermediate transfer means for sequentially transferring the toner image on the image carrier to the intermediate transfer member by superimposing, and a transfer for transferring the superimposed toner image on the intermediate transfer member to a transfer material And an image forming apparatus provided with a material transfer unit, wherein at least a part of the intermediate transfer member is in contact with the intermediate transfer member on the upstream side in the direction of movement of the surface of the intermediate transfer member from a contact facing portion between the intermediate transfer member and the image carrier. part provided ground electrode for applying a ground potential, the moving distance of the intermediate transfer member surface as L _1, the surface moving speed, the volume resistivity of the intermediate transfer member between the ground electrode and the contact facing portion And the relative permittivity V _L , ρ _v and ε ₃
And when the vacuum dielectric constant is ε ₀ , L ₁ / V _L <ρ _v ·
It is characterized by satisfying a condition represented by ε ₃ · ε ₀ .

In this image forming apparatus, the ground electrode which is in contact with at least a part of the intermediate transfer body on the upstream side in the direction of movement of the surface of the intermediate transfer body from the contact opposing portion between the intermediate transfer body and the image carrier, and applies a ground potential to said portion, the moving distance of the intermediate transfer member surface as L _1, the surface moving speed of the intermediate transfer member, the volume resistivity and the ratio between the ground electrode and the contact facing portion Dielectric constants V _L , ρ _v and ε
₃ , and when the dielectric constant of vacuum is ε ₀ , L ₁ / V _L <ρ
_The condition represented by _v · ε ₃ · ε ₀ is satisfied. Thereby, while the intermediate transfer body moves from the position of the ground electrode to the position of the contact opposing portion, electric charges move inside the intermediate transfer body, and the potential of the surface of the intermediate transfer body on the image carrier side is reduced. Never rise.

According to a second aspect of the present invention, there is provided a toner image forming means for forming a toner image on an image carrier, an intermediate transfer member having a transfer surface in contact with the image carrier and endlessly moving; An image forming apparatus comprising: an intermediate transfer means for sequentially transferring the toner images on the image carrier in a superimposed manner; and a transfer material transferring means for transferring the superimposed toner image on the intermediate transfer body to a transfer material. the moving distance of the intermediate transfer member surface between the transfer of the toner image transfer portion and the intermediate transfer body and the contact facing portion between the image bearing member to the transfer material and L _2, the surface of the intermediate transfer member When the moving speed, the volume resistivity and the relative permittivity are V _L , ρ _v and ε ₃ and the permittivity of vacuum is ε ₀ ,
It is characterized by satisfying a condition represented by L ₂ / V _L > ρ _v · ε ₃ · ε ₀ .

In this image forming apparatus, the surface of the intermediate transfer member is moved between a portion where the toner image is transferred from the intermediate transfer member to the transfer material and a contact-facing portion between the intermediate transfer member and the image carrier. The distance is L ₂ , the surface movement speed of the intermediate transfer body, the volume resistivity and the relative permittivity are V _L , ρ _v and ε ₃ ,
When the vacuum dielectric constant is ε ₀ , L ₂ / V _L > ρ _v · ε ₃ ·
The condition represented by ε ₀ is satisfied. Thereby, the electric charge transferred to the surface of the intermediate transfer member in the toner image transfer portion while the intermediate transfer member moves from the toner image transfer portion to the contact opposing portion is attenuated to 1 / e.

According to a third aspect of the present invention, there is provided a toner image forming means for forming a toner image on an image carrier, an intermediate transfer member having a transfer surface in contact with and opposing the image carrier, and an intermediate transfer member. Intermediate transfer means for sequentially superimposing and transferring the toner images on the image carrier, transfer material transfer means for transferring the superimposed toner image on the intermediate transfer body to a transfer material, and cleaning for cleaning the intermediate transfer body Moving the surface of the intermediate transfer member between a portion where the toner image is transferred from the intermediate transfer member to the transfer material and a contact facing portion between the intermediate transfer member and the image carrier. the distance, the moving distance of the intermediate transfer member surface between the contact portion facing the cleaning unit and the intermediate transfer member and the image bearing member by said cleaning means, the shorter distance ones of the L _3, Surface movement speed of the intermediate transfer member, When the product resistivity and the dielectric constant and V _L, ρ _v and epsilon _3, the dielectric constant of vacuum was set to _{ε 0, L 3 / V L} >
It is characterized by satisfying a condition represented by ρ _v · ε ₃ · ε ₀ .

In this image forming apparatus, the surface of the intermediate transfer member is moved between a portion where the toner image is transferred from the intermediate transfer member to the transfer material and a contact-facing portion between the intermediate transfer member and the image carrier. the distance, the moving distance of the intermediate transfer member surface between the contact portion facing the cleaning unit and the intermediate transfer member and the image bearing member by said cleaning means, the shorter distance ones of the L _3, Assuming that the surface movement speed, volume resistivity and relative permittivity of the intermediate transfer member are V _L , ρ _v and ε ₃ , and the vacuum permittivity is ε ₀ , L ₃ / V _L > ρ _v · ε ₃ · The condition represented by ε ₀ is satisfied. Accordingly, while the intermediate transfer member moves from the toner image transfer portion or the cleaning portion closer to the contact opposing portion to the contact opposing portion, the intermediate transfer member contacts the intermediate transfer member surface at the cleaning portion or the cleaning portion. The generated charge attenuates to 1 / e.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a full-color copying machine (hereinafter, referred to as a "color copying machine") as an image forming apparatus will be described. The intermediate transfer member may be configured as an intermediate transfer drum in addition to the intermediate transfer belt. However, in the following description, an example in which the intermediate transfer belt is configured as an intermediate transfer belt will be described.

FIG. 1 is an enlarged view around a photoreceptor and an intermediate transfer belt of a color copying apparatus according to this embodiment, and FIG. 2 is a schematic configuration diagram of the entire color copying apparatus. A color image reading device (hereinafter, referred to as a “color scanner”) 1 irradiates an image of a document 3 with an illumination lamp 4 and reflects the reflected light through a mirror group such as mirrors 5 a, 5 b, 5 c and a lens 6. An image is formed on the sensor 7. The color image information of the document 3 formed on the color sensor 7 is, for example, blue (hereinafter, referred to as “B”), green (hereinafter, referred to as “G”), and red (Red, hereinafter referred to as “R”). ) Is read for each color separation light and converted into an electrical image signal. In this embodiment, the color sensor 7 is composed of B, G, and R color separation means and a photoelectric conversion element such as a CCD.
Performs color simultaneous reading.

Based on the intensity levels of the B, G, and R color separation image signals obtained by the color scanner 1 in this manner, a color conversion process is performed by an image processing unit (not shown), and black (Black, Black, Hereinafter, referred to as “Bk”), cyan (C
yan, hereinafter referred to as "C". ), Magenta (Magenta, hereinafter referred to as “M”), yellow (Yellow, hereinafter “Y”)
That. ) Is obtained.

These color image data are visualized in Bk, C, M, and Y colors in a color image recording device (hereinafter, referred to as a “color printer”) 2.
By superimposing these visualized toner images, a four-color full-color image is obtained.

A writing optical unit 8 of the color printer 2 converts the color image data from the color scanner 1 into an optical signal, performs optical writing corresponding to the original image, and a drum-shaped photosensitive member 9 as an image carrier. To form an electrostatic latent image.

The writing optical unit 8 is composed of a laser light source 8a, a light emission driving device (not shown), a polygon mirror 8b and a rotation driving motor 8c, an f-θ lens 8d, a reflection mirror 8e, and the like. .

The photoreceptor 9 rotates counterclockwise as indicated by the arrow, and around the photoreceptor, a photoreceptor cleaning unit (including a pre-cleaning static eliminator) 10, a static elimination lamp 11, a charger 12, a potential sensor 13, Bk Developing device 14, C developing device 1
5, an M developing unit 16, a Y developing unit 17, an optical sensor 18 for detecting a development density pattern, an intermediate transfer belt 19 as an intermediate transfer body, and the like are arranged. The toner image forming means for forming a toner image on the photoreceptor 9 includes the optical unit 8, the charging unit 12, the developing units 14 to 17, and the like.

Each of the developing units rotates developing sleeves 14a and 15a which rotate by contacting the surface of a photoreceptor 9 with an ear of a developer containing a toner and a carrier charged to a predetermined polarity in order to develop an electrostatic latent image. , 16a, 17a, and developing paddles 14b, 15b rotating to pump and agitate the developer.
16b, 17b and developer toner concentration sensor 14
c, 15c, 16c, 17c and the like. In this embodiment, a negatively charged toner is used.

In the standby state of the color copying apparatus, the developing sleeves 14a to 17a are provided for all of the four developing units.
The upper developer is in a cutting state (development is not activated).

Hereinafter, the outline of the copying operation will be described with an example in which the order of the developing operation (color image forming order) is Bk, C, M, and Y. However, the image forming order is not limited to this. When the copy operation is started, reading of Bk image data is started by the color scanner 1 at a predetermined timing. At the same time, the photoconductor 9 is driven to rotate counterclockwise by a photoconductor driving mechanism (not shown), and the photoconductor 9 is uniformly charged to a negative polarity by the charger 12.

Then, based on the Bk image data read by the color scanner 1, optical writing is performed by the laser light from the optical unit 8, and the uniformly charged photoconductor 9 is formed.
Is partially lowered in accordance with the Bk image data, whereby an electrostatic latent image is formed on the photoconductor 9. Hereinafter, the electrostatic latent image based on the Bk image data is referred to as “Bk latent image”. Each of the electrostatic latent images formed based on the image data of C, M, and Y is also referred to as “C
Latent image "," M latent image ", and" Y latent image ". (Hereinafter, margin)

Before the front end of the latent image reaches the developing position of the Bk developing device 14 so that development can be performed from the front end of the Bk latent image, the developing sleeve 14a is started to rotate and the developer is spiked. The Bk latent image is developed with a negatively charged Bk toner. Thereafter, the developing operation of the Bk latent image area is continued, but when the trailing edge of the latent image passes the Bk developing position, the B
The developer on the k-development sleeve 14a is cut off to set the development inoperative state. This is completed at least before the leading end of the C latent image based on the next C image data arrives. The ear cutting is performed by switching the rotation direction of the developing sleeve 14a to a direction opposite to that during the developing operation.

The Bk toner image formed on the photoreceptor 9 is transferred onto the surface of an intermediate transfer belt 19 which is driven at the same speed as the photoreceptor (hereinafter, transfer of the toner image from the photoreceptor to the intermediate transfer belt is referred to as "belt transfer"). "). This belt transfer is performed by applying a predetermined bias voltage to a transfer bias roller 20a, which will be described later, in a contact state between the photoconductor 9 and the intermediate transfer belt 19.

Bk, C, M, and Y toner images are sequentially formed on the photosensitive member 9, and the intermediate transfer belt 1 is formed in the order in which the toner images are formed.
A belt transfer image of four-color superposition is formed by sequentially aligning the same with the same transfer surface of No. 9. After the full-color toner image is thus formed, the full-color toner image is collectively transferred to transfer paper 24 as a transfer material. The transfer from the intermediate transfer belt 19 to the transfer paper 24 is called "paper transfer".

By the way, in the photoreceptor 9, the process proceeds to the process C after the process Bk. At a predetermined timing, the reading of the C image data by the color scanner 1 starts, and the formation of the C latent image is performed by writing the laser light with the image data. Do.

The C developing device 15 starts rotating the developing sleeve 15a with respect to the developing position after the rear end of the preceding Bk latent image has passed and before the leading end of the C latent image has arrived. The latent image is developed with C toner.

Thereafter, the development of the C latent image area is continued, but when the trailing end of the latent image has passed, the developer on the C developing sleeve 15a is cut off in the same manner as in the case of the Bk developing unit described above. Make the development inoperative state. This is also completed before the leading end of the next M latent image arrives. In each of the steps M and Y, the operations of reading the image data, forming the latent image, and developing are the same as those in the steps Bk and C described above.
Description is omitted.

In FIG. 1, the intermediate transfer belt 19 is wound around a drive roller 21, a transfer bias roller 20a, a ground roller 20b, and a group of driven rollers. The intermediate transfer belt 19 is provided with a transfer bias roller 20a.
And the ground roller 20b, the roller 20a and 20b are arranged so that an appropriate nip pressure is applied at the pressure contact portion. A drive motor (not shown) is connected to the drive roller 21, and the rotation of the intermediate transfer belt 19 is controlled via the drive motor.

Further, a predetermined transfer bias voltage (positive voltage in the present embodiment) is applied to the transfer bias roller 20a, the earth roller 20b which is grounded to be at zero potential, and the transfer bias roller 20a. The transfer bias power supply 40 and the like constitute an intermediate transfer means for transferring the toner images on the photoconductor 9 to the intermediate transfer belt 19 in a superimposed manner.

The belt cleaning unit 22 includes a brush roller 22a, a rubber blade 22b, a mechanism 22c for contacting and separating from the belt, and the like.
After the image is transferred to the belt, the second, third and fourth colors are separated from the belt surface by the contact / separation mechanism 22c during the belt transfer.

A paper transfer unit 23 as a transfer material transfer means for transferring the superimposed toner image on the intermediate transfer belt 19 to the transfer paper 24 includes a paper transfer bias roller 23a, a roller cleaning blade 23b, and a mechanism 2 for contacting and separating from the belt.
3c and the like. Paper transfer bias roller 23
a is usually separated from the transfer surface of the intermediate transfer belt 19, but when transferring the four-color superimposed images formed on the transfer surface onto the transfer paper 24 at a time, the contact and separation mechanism 23c is timed. , And a predetermined bias voltage is applied to the roller 23a to perform transfer to the transfer paper 24.

As shown in FIG. 2, transfer paper 24 is fed by paper feed roller 25 and registration roller 26 at the timing when the leading end of the four-color superimposed image on intermediate transfer belt 19 reaches the paper transfer position. Paper is fed between the driving roller 21 and the paper transfer bias roller 23a, and the paper is transferred. The transfer paper 24 after the transfer is conveyed by a conveyance belt 27 and sent to a fixing device 28, where the toner image is fixed, and then discharged onto a tray 29.

Here, the drive control of the intermediate transfer belt 19 will be described. As a method of driving the intermediate transfer belt 19, the following three methods can be considered as an operation method after the belt transfer of the Bk toner image of the first color is completed to the end, and one of these methods or one of the copy speeds is considered. The intermediate transfer belt 19 is driven by efficiently combining a plurality of these methods according to the copy size from the surface.

(1) Constant-speed forward movement method Even after the belt transfer of the Bk toner image, the forward movement is continued at a constant speed. Then, when the front end position of the Bk image on the surface of the intermediate transfer belt 19 reaches the belt transfer position of the contact portion with the photoconductor 9 again, the front end portion of the next C toner image on the photoconductor 9 side is exactly at that position. The images are formed at appropriate timings. As a result, the C image is belt-transferred on the intermediate transfer belt 19 while being accurately aligned with the Bk image. Thereafter, the process proceeds to the M and Y image processes by the same operation, and a belt transfer image of four-color superposition is obtained. Following the belt transfer process for the fourth color Y toner image,
While moving forward, the four-color superimposed toner image on the surface of the intermediate transfer belt 19 is collectively transferred to the transfer paper 24 as described above.

(2) Skip Forward System When the belt transfer of the Bk toner image is completed, the photosensitive member 9
The intermediate transfer belt 19 is separated from the surface, skipped at a high speed in the forward movement direction, and moved by a predetermined amount, and then returned to the original forward movement speed. Thereafter, the intermediate transfer belt 19 is brought into contact with the photoconductor 9 again. When the front end position of the Bk image on the surface of the intermediate transfer belt 19 reaches the belt transfer position again, the photosensitive member 9 forms an image at a timing such that the front end of the next C toner image is exactly at that position. Have been. As a result, the C image is transferred to the Bk image while being accurately aligned with and superimposed on the Bk image. Thereafter, the process proceeds to the M and Y image processes by the same operation, and a belt transfer image of four-color superposition is obtained. Subsequent to the fourth color Y toner image belt transfer step, the four-color superimposed toner image on the surface of the intermediate transfer belt 19 is collectively transferred onto the transfer paper 24 at the same forward movement speed.

(3) Reciprocating (Quick Return) Method When the belt transfer of the Bk toner image is completed, the photosensitive member 9
The intermediate transfer belt 19 is separated from the surface, and the forward movement is stopped. By this return operation, the front end position of the Bk image on the surface of the intermediate transfer belt 19 passes through a position corresponding to the belt transfer in the reverse direction, and after moving a predetermined distance, stops and enters a standby state. Next, when the leading end of the C toner image on the photoconductor 9 reaches a predetermined position before the belt transfer position, the intermediate transfer belt 19 is started again in the forward movement direction. Further, the intermediate transfer belt 19 is brought into contact with the surface of the photoconductor 9 again. Also in this case, the C image is transferred to the intermediate transfer belt 19 under the condition that the C image accurately overlaps the Bk image on the intermediate transfer belt 19. Thereafter, the process proceeds to the Y and M image processes by the same operation, and a belt transfer image of four-color superposition is obtained. Following the belt transfer process for the fourth color Y toner image,
The toner image moves forward at the same speed without returning, and the four-color superimposed toner image on the surface of the intermediate transfer belt 19 is collectively transferred to the transfer paper 24.

The transfer paper 24 on which the four-color superimposed toner image is collectively transferred from the surface of the intermediate transfer belt 19 by any one of the above methods is transferred to the fixing device 2 by the transport belt 27 of the paper transport unit.
The toner image is melted and fixed by a fixing roller 28a and a pressure roller 28b controlled to a predetermined temperature, and is conveyed to a copy tray 29 to obtain a full-color copy.

On the other hand, the photoreceptor 9 after the belt transfer is a photoreceptor cleaning unit 1 comprising a pre-cleaning neutralizer 10a, a brush roller 10b, a rubber blade 10c and the like.
At 0, the surface is cleaned, and the charge is uniformly removed by the charge removing lamp 11.

The surface of the intermediate transfer belt 19 after the transfer of the toner image onto the transfer paper 24 is cleaned. This cleaning is performed by pressing the cleaning unit 22 again by the contact / separation mechanism 22c.

In the case of the repeat copy, the operation of the color scanner 1 and the image formation on the photosensitive member 9 are performed on the first sheet Y (4
Subsequent to the (color) image process, the process proceeds to a second Bk (first color) image process at a predetermined timing.

In the intermediate transfer belt 19, following the batch transfer process of the first four-color superimposed image onto the transfer paper 24, the surface of the intermediate transfer belt 19 is cleaned by the cleaning unit 22 so that the second Bk The toner image is transferred to the belt. After that, the operation is the same as that of the first sheet.

In FIG. 2, transfer paper cassettes 30, 3
Transfer rollers 1, 32, and 33 store transfer papers of various sizes, and the registration rollers 2 are set at appropriate timing from a storage cassette of the size paper specified on an operation panel (not shown).
Paper is fed and transported in six directions. Reference numeral 34 denotes a paper feed tray for manually feeding OHP paper for an overhead projector or transfer paper such as thick paper.

The copy mode for obtaining four full colors has been described above. However, in the case of the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. Will be.

In the case of the single-color copying mode, only the developing unit of the color is set in the developing operation (springing) until the predetermined number of sheets is completed, and the intermediate transfer belt 19 is set.
Is driven at a constant speed in the forward direction while being in contact with the surface of the photoreceptor 9, and the copying operation is performed with the belt cleaner 22 still in contact with the belt 19.

In the present embodiment, when a toner image is transferred from the photosensitive member 9 onto the intermediate transfer belt 19, a contact facing portion where the photosensitive member 9 contacts the intermediate transfer belt 19 (hereinafter referred to as a transfer nip portion). (Hereinafter referred to as “pre-transfer”), the potential on the upper surface of the belt at the entrance of the transfer nip before the toner reaches the intermediate transfer belt due to the potential rise on the upper surface of the belt. ing.
Here, conditions under which pre-transfer does not occur will be described. The rise in the potential on the upper surface of the belt is caused by the movement of charges inside the belt. Here, the time required for the intermediate transfer belt 19 to reach the transfer nip portion from the ground roller 20b is longer than the time required for the potential on the upper surface of the belt to reach a steady state due to the movement of the charge (hereinafter referred to as a time constant). If it is shorter, the potential on the upper surface of the belt does not increase, and pre-transfer does not occur. It is generally known that the time constant τ of a resistor is represented by τ = (dielectric constant of resistor) × (volume resistivity of resistor). This is a time constant in the case of a circuit in which the resistance component and the capacitance component of the resistor are simply connected in parallel, and applies to the time constant of the intermediate transfer belt 19 in the circumferential direction. However, in the belt thickness direction, the resistance component and the capacitance component of the intermediate transfer belt 19 are connected in series with the capacity of the photoconductor 9 and the capacity of the gap between the photoconductor 9 and the intermediate transfer belt 19. Therefore, the time constant in the belt thickness direction may not apply to the above equation due to the influence of the capacity. Therefore, the time constant of the intermediate transfer belt 19 in the thickness direction is obtained by using a model shown in FIG.

In the model shown in FIG. 3, the photosensitive member 9, the intermediate transfer belt 19, and the gap between the photosensitive member 9 and the intermediate transfer belt 19 are approximated by a capacitor and a resistor, respectively. That is, the photoreceptor 9 by the capacitor C _1, the gap between the drum 9 and belt 19 by the capacitor C _2, to approximate the belt in parallel elements of the capacitor C ₃ and resistor R _3. Here, the potential V _{0 applied to the} lower surface of the belt is
0b corresponds to the potential of the lower surface of the intermediate transfer belt 19 when the intermediate transfer belt 19 moves to the transfer nip portion. Therefore, a change in potential with time should be considered. However, it is considered that the time constant when the potential is fixed is shorter than the time constant when the change in potential with time is considered.
Therefore, if the time required for the intermediate transfer belt 19 to reach the transfer nip from the ground roller 20b is shorter than the time constant when the potential is kept constant, the upper surface of the belt at the entrance of the transfer nip is formed. Does not rise. Therefore, here it is obtained a time constant in the case of a constant above V _0.

In the model shown in FIG. 3, the voltage applied to the photoconductor is V ₁ , the voltage applied to the gap is V ₂ , the voltage applied to the intermediate transfer belt is V _3, and these voltages are stored in capacitors C ₁ , C ₂ , and C _3. Assuming that the applied charges are q ₁ , q ₂ , and q ₃ respectively, and the displacement current flowing through the resistor R ₃ is I ₃ ,

[Equation 1] q ₁ = C ₁ V ₁

[Equation 2] q ₂ = C ₂ V ₂

[Equation 3] q ₃ = C ₃ V ₃

## EQU4 ## I ₃ = V ₃ / R ₃

V ₁ + V ₂ + V ₃ = V ₀

[6] the q ₁ = q _2. When the change in V ₃ due to the current flowing through R ₃ is obtained by solving the above equations (1) to (6),

(Equation 7) Where a is

(Equation 8) Becomes From the above equations (7) and (8), the time until V ₃ attenuates to 1 / e, that is, the time until the potential difference between the upper surface of the belt and the lower surface potential becomes 1 / e of the potential difference in the initial state. Corresponds to the time constant τ of the belt, and τ = 1 / a. Here, in the transfer nip inlet side of the belt and the photosensitive member is not yet in contact, since the gap between the drum 9 and belt 19 is considered sufficiently large, C ₂
≒ 0. Therefore, the belt time constant τ
Is

## EQU9 ## It can be approximated as τ ≒ C ₃ R ₃ . C ₃ and R ₃ per unit area
Represents the thickness of the intermediate transfer belt as d3, the volume resistivity as ρ _v ,
When the relative permittivity is ε ₃ and the permittivity of vacuum is ε ₀ ,

## EQU10 ## C ₃ = ε ₃ ε ₀ / d3

Since R ₃ = ρ _v d3, the time constant τ is

Τ = ε ₃ ε ₀ ρ _v Therefore, on the entrance side of the transfer nip where the gap between the photoreceptor and the intermediate transfer belt is sufficiently large, the time constant in the belt thickness direction is τ =
It can be seen that it is expressed by (dielectric constant of intermediate transfer belt) × (volume resistivity of intermediate transfer belt).

[0053] Here, when the time belt 19 passes from the ground roller 20b to the transfer nip portion is T _1, T ₁ if the <tau belt upper surface potential hardly rises, becomes pre-transfer hardly occur . The above T ₁ is L ₁ a distance from the ground roller 20b to the transfer nip portion, when the moving speed of the intermediate transfer belt 19, V _L, so is represented as _{T 1 = L 1 / V L} , pre-transfer does not occur condition is

The [number 13] _{L 1 / V L <ε 0} ε 3 ρ v. Therefore, the volume resistivity, relative dielectric constant, belt moving speed, and
By setting the distance from the ground roller 20b to the transfer nip, pre-transfer can be prevented and transfer dust can be reduced.

FIGS. 4 and 5 show the results obtained by simulation of the potential distribution on the upper surface of the intermediate transfer belt 19.
Shown in FIG. 4 shows the volume resistivity of the belt ρ _v = 1 × 10 ¹¹
In the case of Ωcm, FIG. 5 shows the volume resistivity of the belt ρ _v = 1 × 10
The result is for ¹⁰ Ωcm. Here, the latent image potential of the photoreceptor is -600 V, the transfer bias Vp is 1600 V, the linear velocity V _{L of} the belt is 200 mm / s, the width of the transfer nip between the photoreceptor and the intermediate transfer belt is 10 mm, and the transfer from the ground roller 20b is performed. The distance L ₁ = 10 mm from the entrance end of the nip (hereinafter referred to as the left end of the transfer nip), and the distance from the exit side end of the transfer nip (hereinafter referred to as the right end of the transfer nip) to the transfer bias roller 20a is 10 mm. , Photoconductor 9 radius is 6
It was calculated at 0 mm. The relative dielectric constant of the belt was set to ε ₃ = 8.

According to equation 13, ρ _v > L ₁ / (V _L ε
₀ ε ₃ ) = 10 mm / (200 mm · 8.85 × 10 ^−12.
8) ≒ 7 × 10 ¹⁰ Ωcm, and volume resistivity ρ _v is 7 × 1
If the belt is larger than 0 ¹⁰ Ωcm, the potential of the upper surface of the intermediate transfer belt hardly increases at the entrance side of the transfer nip, and pre-transfer does not occur. As can be seen from the results shown in FIG. 4, when the belt resistance is high, the potential on the upper surface of the belt at the left end of the transfer nip is low and rises from the middle of the transfer nip. On the other hand, as can be seen from the results of FIG. 5, when the belt resistance is low, the belt upper surface potential between the ground roller 20b and the transfer bias roller 20a is linear, and the belt upper surface is close to 500 V even at the left end of the transfer nip portion. Has potential. Therefore, the belt resistance is 7 ×
If it is smaller than 10 ¹⁰ Ωcm, a strong electric field is applied to the toner on the photoconductor at the entrance side of the transfer nip, and the toner is expected to move on the intermediate transfer belt and pre-transfer occurs. .

From the above discussion, it is understood that the higher the resistance of the intermediate transfer belt is, the less pre-transfer occurs and the more suitable it is. However, when the belt resistance increases, the transfer of the toner image on the intermediate transfer belt to the transfer paper (hereinafter referred to as “2.
The electric charge that has moved onto the intermediate transfer belt 19 at the time of the next transfer, or the triboelectric charge generated on the intermediate transfer belt 19 during cleaning of the intermediate transfer belt by the cleaning unit 22 moves from above the intermediate transfer belt into the belt. Before the surface charge on the intermediate transfer belt is sufficiently attenuated, the toner on the photoreceptor is transferred onto the intermediate transfer belt again (hereinafter, referred to as primary transfer). The image may be disturbed due to the effect of the residual charges remaining on the belt. Therefore, even if the volume resistivity of the intermediate transfer belt is too high, a good image cannot be obtained.

Here, in order to prevent the image from being disturbed due to the residual charge, the time required for the charge applied to the intermediate transfer belt during the secondary transfer or cleaning to perform the primary transfer on the intermediate transfer belt. The intermediate transfer belt may be configured so that the electric charge applied to the intermediate transfer belt is attenuated. The time required for the charge imparted on the intermediate transfer belt by the secondary transfer or cleaning to move in the belt and attenuate to 1 / e by the time of the primary transfer and to reach a steady state is determined by the time constant of the intermediate transfer belt. Is equivalent to As described above, the time constants in the circumferential direction and the thickness direction of the intermediate transfer belt are both (dielectric constant of the intermediate transfer belt) ×
(Volume resistivity of the intermediate transfer belt). Of the distance to the transfer nip portion for performing primary transfer from the cleaning unit by the secondary transfer unit or the cleaning unit 22, the shorter, the distance from the cleaning unit to the transfer nip portion and the L ₃ in the example of FIG. 1, for example Assuming that the belt moving speed is V _L , the charge on the belt only needs to be attenuated within the time of T ₃ = L ₃ / V _L.

The condition L ₃ / V _L > ε ₀ ε ₃ ρ _v is derived. Therefore, if the volume resistivity, the relative dielectric constant, the belt moving speed, and the distance from the ground roller 20b to the transfer nip portion of the intermediate transfer belt are set so as to satisfy Expression 14, at the time of secondary transfer or cleaning Since the charge generated on the intermediate transfer belt attenuates to 1 / e by the time of the primary transfer, transfer failure, transfer unevenness, transfer dust, and the like due to residual charge can be prevented. (Hereinafter, margin)

FIG. 6 shows that 200 μC
² shows the results of a simulation calculation of how the charge moves inside the belt with time and the surface charge attenuates when a surface charge of / m ² is applied. In FIG. 6, when a belt having a volume resistivity of 5 × 10 ¹² Ωcm (hereinafter referred to as belt 1) is used as a characteristic line a1, a characteristic line a2 is used for a belt having a volume resistivity of 1 × 10 ¹¹ Ωcm (hereinafter referred to as belt 1). , Belt 2). Here, 200 meters distance L ₃ from the cleaning unit to the transfer unit
m, and the belt moving speed is V _L = 200 mm / s, the time required for the intermediate transfer belt to reach from the cleaning section to the primary transfer section is L ₃ / V _L = 200/200 = 1 sec. In FIG. 6, when the surface charge after 1 second has passed after passing through the cleaning unit is compared between the belt 1 and the belt 2,
It can be seen that while nearly half of the charge remains on the belt surface in belt 1, almost all of the charge has disappeared in belt 2. Therefore, in the case of the belt 2, it is expected that transfer failure, transfer unevenness, transfer dust, and the like due to residual charges do not occur, and image formation is performed favorably.

In the embodiment described above, only the case where the ground potential is applied to the intermediate transfer belt by the ground roller 20b at the entrance of the transfer nip is described.
The ground electrode for applying the ground potential to the intermediate transfer belt does not need to be in the form of a roller, and may be, for example, a conductive brush or a form in which a flat metal plate is adhered to the belt.

In order to satisfy the above equation (13), it is necessary to use an intermediate transfer belt having a relative dielectric constant larger than 3, for example, so that the transfer bias at the time of the primary transfer can be relatively small and a low-voltage power supply can be used. As a result, cost can be reduced. However, if the relative dielectric constant is, for example, 20
If a larger intermediate transfer belt is used, it is necessary to use a low-resistance belt in order to satisfy Equation 14, and the current flowing through the belt increases, resulting in an increase in power consumption and an increase in cost. Therefore, the relative dielectric constant ε of the intermediate transfer belt
₃ is preferably in the range of 3 <ε ₃ <20, and in particular,
It is desirable that the range of 5 <ε ₃ <15 is satisfied.

[0061]

EXAMPLES Next, more specific examples of the present embodiment will be described. As the photoconductor 9, an organic photoconductor having a radius of 60 mm was used. As the intermediate transfer belt 19, two types of seamless belts made of a fluororesin sheet having a relative dielectric constant of ε = 8, a thickness of 150 μm, and a perimeter of 540 mm having different belt resistances were used.

The volume resistivity ρ _v and the surface resistivity ρs of the two types of intermediate transfer belts 19 were measured with a measuring device (trade name: Hiresta, probe: HRS) manufactured by Mitsubishi Yuka. , Belt A) has a volume resistivity ρ _v = 1 × 10 ^{11 to} 5 × 10 ¹¹ Ωcm and a surface resistivity ρs = 1 × 10 ⁹ to 1 × 10 ¹⁰ Ω / □ (applied voltage: 50).
0 V, timer: 10 seconds). The other belt (hereinafter, referred to as belt B) has a volume resistivity ρ _v = 5 × 1
0 ¹⁰ to 1 × 10 ¹¹ Ωcm and surface resistivity ρs = 5 × 10
⁸ to 1 × 10 ⁹ Ω / □ (applied voltage: 500 V, timer:
10 seconds). The width of these measured resistivity values corresponds to the variation in measured values depending on the measurement location.

A metal roller having a diameter of 20 mm is used as the ground roller 20b and the transfer bias roller 20a, and both rollers are equidistant from the center of the transfer nip (15 mm).
mm). Nip width of transfer nip is 10mm
Met. Therefore, the distance L ₁ from the ground roller 20b to the transfer nip inlet end is 10 mm. For belt cleaning, a counter blade method is adopted, and one belt is located upstream from the center of the nip in the belt movement direction.
The blade was arranged at a position of 00 mm. Thereby, the belt is automatically cleaned before the primary transfer.

In the color copying machine constructed as described above, the transfer bias voltage applied to the transfer bias roller 20a is set to +1600 V, and the belt moving speed of the intermediate transfer belt 19 is set to 50 mm / s for each of the two types of intermediate belts. Intermediate transfer belt 1 by changing up to ~ 300mm / s
Immediately after the M one-color toner image (line image in the sub-scanning direction with a line width of 100 μm and a line interval of 100 μm) is formed on the intermediate transfer belt 9, the apparatus is forcibly stopped and the intermediate transfer belt 19 is stopped.
The upper toner image was observed in an observation area of 500 μm × 500 μm.

Table 2 shows the evaluation results of the transfer dust when the belt A was used, and Table 3 shows the evaluation results of the transfer dust when the belt B was used. From Table 2, when the belt A is used, the belt moving speed is 2
According to Table 3, when the belt moving speed is set to about 300 mm / s when the belt B is used at around 00 mm / s and when the belt B is used, the transfer dust rank is 4 or more, the transfer dust is small, and transfer failure occurs. It can be seen that the transfer is performed favorably without any. The speed satisfies the conditions of Equations 13 and 14 above. When the linear speed is lower than the above speed and the condition of the expression 13 is not satisfied, pre-transfer occurs and transfer dust increases. On the other hand, if the linear speed is higher than the above speed and does not satisfy the condition of Expression 14, the charge generated on the surface of the intermediate transfer belt 19 at the time of cleaning does not sufficiently attenuate until the primary transfer is performed. Get up.

It should be noted that the occurrence of dust due to the belt position at the belt moving speed of 100 mm / s in Table 2 is due to the dispersion of the belt resistance value.
The same applies to the cases of 50 mm / s, 250 mm / s and 250 mm / s in Table 3.

The values of the transfer chile rank in Tables 2 and 3 above are the values for the predetermined observation area (500 μm × 500 μm).
m) was obtained from a correspondence table (Table 4) showing a relationship between the number of dust toners per m) and the transfer dust rank. FIG.
(E) is an enlarged view of an evaluation reference image (line image in the sub-scanning direction with a line width of 100 μm and a line interval of 100 μm) for each numerical value of the transfer chile rank. The number of dust toners per predetermined observation area (500 μm × 500 μm) is counted for each transfer chile rank evaluation reference image, and the average value of count values for successive transfer chile ranks (for example, rank 1 and rank 2) is calculated between the transfer chile ranks. The range of the number of dust particles in each transfer dust rank in the correspondence table of Table 3 is set as the boundary value of. Here, an image having a transfer chile rank of 4 or more (FIG. 7)
(A) and (b)) were good images with less transfer dust as a result of observation with the naked eye. Also, FIG.
The white portion in (e) is the toner particles, and the line width and the line interval of the image in FIG. 7A corresponding to the transfer dust rank 5 are 100 μm.

[0068]

[Table 2] (Hereinafter, margin)

[0069]

[Table 3]

[0070]

[Table 4]

As described above, according to the present embodiment, the volume resistivity, the relative permittivity, and the
By setting the belt moving speed and the distance from the ground roller 20b to the transfer nip, the intermediate transfer belt 19 is moved to the transfer nip before the surface potential of the intermediate transfer belt 19 at the entrance of the transfer nip rises. Can be moved to the photosensitive member 9 at the entrance side of the transfer nip.
No strong electric field is applied to the upper toner. Accordingly, it is possible to prevent the toner from moving from the photosensitive member to the intermediate transfer belt before the photosensitive member 9 and the intermediate transfer belt 19 come into contact with each other, and to obtain a high-quality image.

Further, according to the present embodiment, the charge on the surface of the intermediate transfer belt generated at the time of the secondary transfer and the belt cleaning can be transferred to the primary transfer portion without adding any special charge removing means. By attenuating it to less than 1 / e, stable image formation becomes possible.

In the above-described embodiment, the N / P developing method is used in which the photosensitive member 9 is uniformly charged to the negative polarity, and the electrostatic latent image formed on the photosensitive member 9 is developed using the negatively charged toner. However, the present invention can be applied without being limited to these charging polarities and developing methods. For example, a toner that uniformly charges the photosensitive member 9 to a positive polarity and uses a toner charged to a positive polarity is used. And the same effect can be obtained when the P / P developing method is adopted.

[0074]

According to the first aspect of the present invention, while the intermediate transfer member moves from the position of the ground electrode to the position of the contact opposing portion, the electric charge moves inside the intermediate transfer member and the intermediate transfer member moves. Since the potential of the surface of the body on the image carrier side does not rise, a strong electric field is not applied to the toner on the image carrier before reaching the contact facing portion. Thus, without providing any additional mechanism, the occurrence of transfer dust due to the toner on the image carrier moving onto the intermediate transfer body before the image carrier and the intermediate transfer body come into contact with each other and facing each other can be prevented. There is an excellent effect that it can be prevented well and a high-quality image can be obtained.

According to the second aspect of the present invention, the electric charge transferred to the surface of the intermediate transfer member in the toner image transfer portion while the intermediate transfer member moves from the toner image transfer portion to the contact opposing portion is reduced by 1 /. e, the transfer failure due to the residual charge on the surface of the intermediate transfer member can be favorably prevented, and there is an excellent effect that stable image formation becomes possible.

According to the third aspect of the present invention, while the intermediate transfer body moves from the cleaning section to the contact facing section, the charge generated on the surface of the intermediate transfer body in the cleaning section is attenuated to 1 / e. In addition, transfer defects due to residual charges on the surface of the intermediate transfer member can be favorably prevented, and there is an excellent effect that stable image formation is possible.

[Brief description of the drawings]

FIG. 1 is an enlarged view around a photoconductor and an intermediate transfer belt of a color copying apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of the entire color copying apparatus.

FIG. 3 is an explanatory diagram in which a photoconductor, an intermediate transfer belt, and a gap between the two are modeled.

FIG. 4 is an explanatory diagram showing a result obtained by simulation of a potential distribution on an upper surface of an intermediate transfer belt.

FIG. 5 is an explanatory diagram showing a result obtained by simulation of a potential distribution on an upper surface of an intermediate transfer belt.

FIG. 6 is an explanatory diagram showing a result obtained by simulation of a state in which the charge is attenuated when the charge is applied to the surface of the intermediate transfer belt.

7A to 7E are enlarged views of an evaluation reference image corresponding to each numerical value of a transfer chile rank.

[Explanation of symbols]

 Reference Signs List 9 photoconductor 12 charger 14 Bk developing device 15 C developing device 16 M developing device 17 Y developing device 19 intermediate transfer belt 20 a transfer bias roller 20 b entrance roller (counter electrode) 24 transfer paper 40 transfer bias power supply

Claims (3)

[Claims] A toner image forming means for forming a toner image on the image carrier; an intermediate transfer member having a transfer surface movable in contact with and facing the image carrier; An image forming apparatus comprising: an intermediate transfer means for sequentially superimposing and transferring the toner images of the intermediate transfer member; and a transfer material transfer means for transferring the superimposed toner image on the intermediate transfer body to a transfer material. A ground electrode for contacting at least a part of the intermediate transfer body and applying a ground potential to the part at an upstream side of the intermediate transfer body surface moving direction from the contact facing portion with the carrier, and providing the ground electrode with the ground electrode; The moving distance of the surface of the intermediate transfer member between the opposing portions is L _1, and the surface moving speed, volume resistivity, and relative permittivity of the intermediate transfer member are V _L , ρ _v, and ε _3.
An image forming apparatus that satisfies a condition represented by L ₁ / V _L <ρ _v · ε ₃ · ε ₀ when a vacuum dielectric constant is ε ₀ . 2. A toner image forming means for forming a toner image on an image bearing member, an intermediate transfer member having a transfer surface in contact with and facing the image bearing member moving endlessly; An image forming apparatus comprising: an intermediate transfer means for sequentially superimposing and transferring the toner images of the intermediate transfer member; and a transfer material transfer means for transferring the superimposed toner image on the intermediate transfer member to a transfer material. the moving distance of the intermediate transfer member surface between the toner image transfer portion and the intermediate transfer body and the contact facing portion between the image bearing member to the wood and L _2, the surface moving speed of the intermediate transfer member, the volume resistivity the rate and dielectric constant and V _L, ρ _v and epsilon _3, when the dielectric constant of vacuum was set to epsilon _0, that satisfies the condition represented by _{L 2 / V L> ρ v} · ε 3 · ε 0 Characteristic image forming apparatus. 3. A toner image forming means for forming a toner image on an image bearing member, an intermediate transfer member having a transfer surface in contact with and facing the image bearing member moving endlessly; Intermediate transfer means for sequentially superimposing and transferring the toner images, transfer material transferring means for transferring the superposed toner image on the intermediate transfer body to a transfer material, and cleaning means for cleaning the intermediate transfer body. In the image forming apparatus, a moving distance of a surface of the intermediate transfer member between a portion where the toner image is transferred from the intermediate transfer member to the transfer material and a contact-facing portion between the intermediate transfer member and the image carrier; a moving distance of the intermediate transfer member surface between the contact portion facing the cleaning unit and the intermediate transfer member and the image bearing member by means, the shorter distance ones of the L _3, of the intermediate transfer member Surface movement speed, volume resistivity and specific induction The rate and V _L, ρ _v and ε _3,
An image forming apparatus which satisfies a condition represented by L ₃ / V _L > ρ _v · ε ₃ · ε ₀ where a vacuum dielectric constant is ε ₀ .