JP2000221804A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the irregularity of a transfer electric field acting on an intermediate transfer body by making the electric field dependency of the resistant value of the intermediate transfer body on a primary transfer process large. SOLUTION: This device is provided with the intermediate transfer body B rotating and moving through a primary transfer area Q3 set along the surface of an image carrier PR and also passing through a secondary transfer area Q4 set along the moving path. This device is provided with a primary transferring device T1 transferring a toner image Tn on the image carrier PR to the body B on the area Q3. This device is provided with a secondary transfer device T2 transferring the toner image Tn on the body B to a recording sheet S. Besides, in the body B, the volume resistivity R1 (logΩcm) of the body B in the condition of an electric field with electric field intensity E1 (V/mm) in the same direction as that of a primary transfer electric field perpendicular to the surface of the body B and the volume resistivity R2 (logΩcm) of the body B in the condition of the electric field with the electric field intensity E2 (V/mm) having the same absolute value as that of the intensity E1 and in an opposite direction satisfy R1<R2.

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 such as an electrophotographic copying machine or a laser printer, and more particularly, to an image forming apparatus formed on a latent image carrier such as a photosensitive drum via an intermediate transfer member. The present invention relates to an image forming apparatus that transfers an unfixed toner image to a recording medium such as paper.

[0002]

2. Description of the Related Art Conventionally, as this type of image forming apparatus,
The following techniques are known. (J01) Technology shown in FIG. 6 or FIG. 7 FIGS. 6 and 7 illustrate a conventional image forming apparatus that transfers an unfixed toner image formed on an image carrier to a recording sheet via an intermediate transfer member. FIG. An image forming apparatus using the intermediate transfer member described in FIGS. 6 and 7 is disclosed in Japanese Patent Publication No. 49-209.
JP, JP-A-62-206567, JP-A-3-206567
No. 192,282. 6 and 7, the image forming apparatus U includes an automatic document feeder U placed on a main body UA and a platen glass PG on the upper surface of the main body UA.
B. The image forming apparatus main body UA includes a UI for inputting an operation command signal such as a copy start signal by a user.
(User interface). Light reflected from a document (not shown) on the upper surface of the platen glass PG is R (red) by a CCD (solid-state image sensor) via an exposure optical system A,
The signals are converted into G (green) and B (blue) electric signals. IPS
(Image processing system) converts the RGB electric signals into Y (yellow), M (magenta), C (cyan), and K (black) image data, temporarily stores the image data, and stores the image data in a predetermined manner. At the timing of (1).

The surface of an image carrier (photosensitive drum) PR that rotates in the direction of the arrow Ya is uniformly charged by a charger CR, and a latent image writing position Q1, a development region Q2, and a primary transfer region Q3. Sequentially. An ROS (latent image writing device) driven by the laser driving circuit DL uses an image carrier PR at the latent image writing position Q1 by the laser beam L.
The surface is exposed and scanned to form an electrostatic latent image on the surface. When a full-color image is formed, electrostatic latent images corresponding to four color images of Y (yellow), M (magenta), C (cyan), and K (black) are sequentially formed.
Only the electrostatic latent image corresponding to the (black) image is formed.

The rotary type developing device G has a rotating shaft G
Y that sequentially rotates and moves to the development area Q2 with the rotation of a
(Yellow), M (magenta), C (cyan), K
It has four color (black) developing units GY, GM, GC, and GK, and develops the electrostatic latent image on the surface of the image carrier PR passing through the developing area Q2 into a toner image Tn of a predetermined color. I do. The toner image Tn developed on the surface of the image carrier PR is primarily transferred to the intermediate transfer belt B in the primary transfer area Q3 by a primary transfer device T1 constituted by a transfer roll. The primary transfer unit T1 is configured by a corotron in FIG. 6, and is configured by a transfer roll in FIG. In the case of a full-color image, the toner images of each color sequentially formed on the surface of the image carrier PR are sequentially primary-transferred onto the surface of the intermediate transfer belt B sequentially. After the primary transfer, the image carrier P
The residual toner on the R surface is cleaned by the image carrier cleaner CL1.

The intermediate transfer belt B, which rotates in the direction of the arrow Ya, is rotatably supported by a belt driving roll Rd, a tension roll Rt, a walking roll Rw, an idler roll (free roll) Rf, and a backup roll T2a. The bias roll T2b is disposed so as to be able to separate and press (contact) with the backup roll T2a with the intermediate transfer belt B interposed therebetween, and the bias roll T2b depends on the area (nip) where the bias roll T2b presses against the intermediate transfer belt B. A secondary transfer area Q4 is formed. The backup roll T2a and the bias roll T2b constitute a secondary transfer unit T2.

[0006] The recording sheet S stored in the paper feed tray TR1 is conveyed to the secondary transfer area Q4 at a predetermined timing. The power supply circuit E controlled by the controller C
A secondary transfer voltage is applied to the next transfer unit T2 at a predetermined timing. The secondary transfer device T2 electrostatically secondary-transfers the toner image on the intermediate transfer belt B to the recording sheet S. In addition,
In the case of a full-color image, the toner image primarily transferred and superimposed on the surface of the intermediate transfer belt B is secondarily transferred to the recording sheet S at a time. The residual toner is removed from the intermediate transfer belt B after the secondary transfer by the belt cleaner CL2. The bias roll T2b is a bias roll cleaner CL3.
As a result, the toner adhered to the surface is collected.

The bias roll T2b and the belt cleaner CL2 are arranged so as to be able to be separated from and separated from the intermediate transfer belt B (to be separated and contacted). When a color image is formed, the final color is not fixed. Until the toner image is primarily transferred to the intermediate transfer belt B, the toner image is separated from the intermediate transfer belt B. The bias roll cleaner CL3
Performs a separation / contact movement (movement in a separating direction and an approaching direction) with respect to the backup roll T2a together with the bias roll T2b. The toner image secondarily transferred to the recording sheet S is heated and fixed by the fixing device F when passing through the fixing area Q6. The recording sheet S on which the toner image has been fixed is discharged to the recording sheet discharge tray TR2.

[0008]

The belt material used in the image forming apparatus employing the intermediate transfer member is as follows.
PC (polycarbonate resin) (JP-A-6-95521)
JP), PVDF (polyvinylidene fluoride) (JP-A-5-200904 and JP-A-6-228335),
PAT (polyalkylene phthalate) (JP-A-6-14)
No. 9081), PC (polycarbonate) / PAT
(Polyalkylene terephthalate) blend material (JP-A-6-149083), ETFE (ethylene tetrafluoroethylene copolymer) / PC, ETFE / P
AT, PC / PAT blend materials (Japanese Unexamined Patent Publication No. 6-149)
No. 079) has been proposed to use a conductive endless belt made of a thermoplastic resin. However, it has been clarified that the following problems occur when an image forming apparatus is configured based on an intermediate transfer member formed of these materials.

(Problem 1 in Primary Transfer Step) First, an unfixed toner image is transferred from a latent image carrier onto an intermediate transfer body.
In the next transfer step, since the electric field dependence of the volume resistivity in the electric field direction of the intermediate transfer member determined by the primary transfer electric field is small, the portion having a high resistance value due to the variation in the internal resistance of the intermediate transfer member is the primary transfer electric field. Even at the bottom, it remains high without lowering, and the transfer electric field tends to be uneven. For this reason, transfer failure occurs in the process of the primary transfer of the unfixed toner image from the latent image carrier to the intermediate transfer body. Further, when the volume resistivity of the intermediate transfer member is large, the intermediate transfer member after the primary transfer retains the transfer charge, and the charge discharge during the image forming cycle greatly disturbs the image, thereby deteriorating the image quality.

The material forming the intermediate transfer member disclosed in the above-mentioned prior art is subjected to an electric field having an electric field intensity E1 (E1 (V / mm) = 1111 to 5555) perpendicular to the surface of the intermediate transfer member. As a result of measuring the volume resistivity R1 in the direction perpendicular to the surface and the volume resistivity R2 in the electric field of E2 in the opposite direction perpendicular to the surface, the absolute value of which is equal to the value of E1, the values R1 and R2 show the same value, Both rates are from 10.50 (log Ωcm)
It was 15.50 (logΩcm).

(Problem 2 of primary transfer step) Under the transfer electric field formed in the primary transfer step, the resistance value of the primary transfer device (bias roll, bias film, etc.) is smaller than the resistance value of the intermediate transfer body. Therefore, the current flowing into the non-image area of the latent image carrier increases, and an appropriate transfer electric field is not applied to the unfixed toner image between the primary transfer device and the latent image carrier. As in the case of the problem 1), image transfer failure occurs during the process of transferring the unfixed toner image from the latent image carrier to the intermediate transfer member. (This is because if the resistance of the primary transfer device is low, the current flowing outside the image area (non-image area) of the latent image carrier increases in the case of constant voltage transfer, and the electric field to the image area in the case of constant current. To ensure
This is because it is necessary to increase the total current (the total current flowing to the image portion and the non-image portion). In particular, this problem becomes conspicuous in the multiple transfer step in which the image is further transferred onto the toner image on the intermediate transfer member.

If the resistance value of the primary transfer device (bias roll, bias film, etc.) is simply increased to solve this problem, uneven transfer due to the variation in the resistance value of the transfer device may occur, or the resistance increase and charging may occur. Abnormal discharge occurs, and the image quality is greatly affected. Therefore, an increase in the resistance value of only the transfer device side causes a secondary obstacle. As a result of measuring the resistance value of the intermediate transfer body and the resistance value of the primary transfer roll using the electric field during the primary transfer step, the material forming the intermediate transfer body disclosed in the above-mentioned prior art was 7. 98 log Ω and 7.8
It was 3 logΩ.

(Problem 3 in the primary transfer step) As a third problem, there is provided means for erasing the electric charge accumulated in the intermediate transfer body after the secondary transfer of the unfixed toner image from the intermediate transfer body. The charge removal performance required in the charge removal step of the intermediate transfer member is to be able to instantaneously remove the charge accumulated in the intermediate transfer member with a low electric field. In the image forming apparatus using the above-described conventional intermediate transfer body, the intermediate transfer body has residual charges even after static elimination, and an unfixed toner image is transferred in a state where the charges are held in the next primary transfer step. A transfer failure of the unfixed toner image occurs due to a substantial decrease in the transfer electric field. When a high voltage is applied to the static eliminator to solve this problem, a secondary failure such as a malfunction of the control unit of the image forming apparatus is caused by a leak of the belt static eliminator roll or a noise signal generated by the leak. . One of the reasons that this can happen is
The point is that the internal charge is hardly removed because the electric field dependence of the intermediate transfer member at the time of static elimination is small.

As described above, the trouble caused by the problem occurring in the primary transfer process mainly causes the deterioration of the image quality. The derived trouble is that the residual toner increases due to the decrease in the transfer efficiency and the image forming apparatus accompanying it. There is contamination inside, short life of the cleaning device, and deterioration of the intermediate transfer member. Next, a problem that occurs in the secondary transfer step in which an unfixed toner image is transferred from the intermediate transfer member to a recording medium such as paper will be described.

(Problem 1 in Secondary Transfer Step) A voltage is applied to a bias roll of a secondary transfer device to form a secondary transfer electric field, and an unfixed toner image on an intermediate transfer body is transferred onto a recording medium. In the process, since a multi-color toner image has already been formed on the intermediate transfer member, the transfer of the toner image to the recording medium is more dependent on the electric field due to the higher electric field than in the primary transfer step, so that the apparent apparent resistance is reduced. A decrease is triggered. A high voltage is applied to the intermediate transfer body due to the influence of the secondary transfer voltage, and the direction of the electric field in the secondary transfer step (for example, when the direction of the primary transfer electric field is from the back surface to the front surface of the intermediate transfer body, If the electric field direction in the secondary transfer step is large in the electric field direction (direction from the front surface to the back surface), the surface property (unevenness) of the recording medium between the bias roll and the intermediate transfer body in the secondary transfer area Q4. Discharge is induced by the generation of a minute gap.

Further, since a voltage is also applied to the recording medium and the recording medium itself is charged by charge accumulation, when the recording medium is peeled off from the intermediate transfer member after the secondary transfer step, a peeling discharge occurs between the intermediate transfer body and the recording medium. appear. The discharge energy due to the creeping discharge and the partial discharge generated in the secondary transfer process causes a decrease in the insulation in the creeping direction and the thickness direction due to chemical destruction of the polymer constituting the surface and the inside of the intermediate transfer member, thereby reducing the surface resistance. A significant decrease in When the surface resistance is reduced, the electric field formed in the primary transfer process extends to outside the transfer nip region formed by the latent image carrier and the intermediate transfer member, and discharge is caused in a minute gap portion in front of the transfer region. Induced, the effective transfer field is reduced. For this reason, transfer failure occurs, resulting in a partial decrease in density and deterioration in graininess, and deterioration in image quality such as discharge marks on a transferred image. In particular, this phenomenon appears remarkably around an image having a large amount of toner per unit area such as a multi-color image, which becomes a fatal image quality defect for a color image forming apparatus.

Further, an excessive current flows in a portion where the resistance in the volume direction (resistance between the front and back surfaces) of the intermediate transfer member is significantly reduced, and the charging potential of the latent image carrier changes, so that the developing amount in the developing process is increased. , And large density unevenness occurs particularly in low-density images. This is caused by partially changing the potential of the latent image carrier when the resistance of the intermediate transfer member is partially reduced. In addition, since there is a partial resistance difference, a leakage current increases and unevenness in the transfer electric field (electric field unevenness caused by an internal leak (leakage current) due to a resistance difference of the intermediate transfer body itself) occurs. Will happen. For the material forming the intermediate transfer member disclosed in the above-mentioned prior art, 1
The difference R3-R4 (R5-R6) between the resistivity R3 (R5) when applying 100 V in the electric field forming direction of the secondary transfer and the secondary transfer and the resistivity R4 (R6) when applying 500 V is 3. 51 to 4.26.

(Problem 2 of Secondary Transfer Process) In the electric field formed during the secondary transfer process, the resistance value of the bias roll is smaller than the resistance value of the intermediate transfer member, and is larger than the resistance value of the intermediate transfer member. Because of the difference, it is difficult to form an appropriate transfer electric field between the bias roll and the intermediate transfer member, and image transfer failure occurs. When only the resistance of the bias roll is easily adjusted to solve this problem, the resistance value R9 (logΩ) of the intermediate transfer body during the execution of the secondary transfer operation
And the resistance value R10 (logΩ) of the bias roll may not satisfy the following expression (5). R10 <R9 <2R10 ……………………………… (5).

For example, if the resistance value R10 (logΩ) of the bias roll during the execution of the secondary transfer operation becomes higher than the resistance value R9 (logΩ) of the intermediate transfer member, the secondary transfer voltage is increased. Discharge is likely to occur due to the charging of the paper after the next transfer, causing electrical deterioration of the intermediate transfer member. As a result of measuring the resistance value of the intermediate transfer member and the resistance value of the bias roll in the electric field during the secondary transfer step, the material forming the intermediate transfer member disclosed in the above-described prior art was 6.70 ( log Ω), 7.10
(LogΩ). This value does not satisfy Expression (5) because the resistance value of the intermediate transfer member is smaller than the resistance value of the bias roll.

The present invention has been made in view of the above-mentioned problems, and has the following (O)
01) to (O03) The contents to be described are the subject. (O01) To increase the electric field dependency of the resistance value of the intermediate transfer member in the primary transfer step to reduce the transfer electric field unevenness acting on the intermediate transfer member. (O02) The electric field dependence of the resistance value of the intermediate transfer member in the secondary transfer step is reduced, the apparent resistance of the intermediate transfer member in the secondary transfer step (resistance when a secondary transfer voltage is applied) is high, and the recording medium ( To mitigate gap discharge (discharge expressed as a function of voltage, distance and pressure according to Paschen's law) generated between a recording sheet) or a secondary transfer bias roll and an intermediate transfer member. (O03) To increase the electric field dependence of the resistance value of the intermediate transfer member in the charge removal step to facilitate the charge removal of the intermediate transfer member.

[0021]

Next, a description will be given of the present invention which has solved the above-mentioned problems. In the description of the present invention, reference numerals in parentheses added after constituent elements of the present invention denote constituent elements of the present invention. Reference numerals of corresponding components of the embodiment described later. The reason why the present invention is described in association with the reference numerals of the components of the embodiments described later is to facilitate understanding of the present invention, and not to limit the scope of the present invention to the embodiments.

(1st invention) In order to solve the aforementioned problem,
The image forming apparatus of the first invention has the following requirements (A01) to (A01).
08), (A01) a latent image writing position (Q1; Q1y to Q1) set along a rotating surface.
k) on which an electrostatic latent image is formed (PR; P
Ry to PRk), (A02) the image carrier (PR; PRy to
PRk) Development area set along the surface (Q2; Q2y ~
Q2k) a developing device (G; Gy to Gk) for developing the electrostatic latent image into a toner image (Tn); (A03) a primary device set along the surface of the image carrier (PR; PRy to PRk) A secondary transfer area (Q4) that rotates through the transfer area (Q3; Q3y to Q3k) and is set along the movement path
(B), (A04) the image carrier (PR) in the primary transfer area (Q3; Q3y to Q3k).
PRy to PRk) primary transfer units (T1; T1y to T1k) for transferring the toner image (Tn) on the surface to the intermediate transfer body (B);
(A05) a recording sheet transport device (SH) for transporting and passing the recording sheet (S) to a secondary transfer area (Q4) set in the movement path of the intermediate transfer body (B); (A06) the secondary transfer In a region (Q4), a toner image (Tn) on the intermediate transfer member (B) is applied to the recording sheet by applying a secondary transfer voltage between the intermediate transfer member (B) and the recording sheet (S). Secondary transfer unit (T2) for transferring to (S), (A0
7) The toner image (T) transferred onto the recording sheet (S)
n) fixing device (F), (A08) the intermediate transfer member (A08) under an electric field of electric field intensity E1 (V / mm) in the same direction as the primary transfer electric field perpendicular to the surface of the intermediate transfer member (B) B), the volume resistivity R2 (log Ωcm) of the intermediate transfer body (B) under an electric field having an electric field strength E2 (V / mm) having the same absolute value as E1 and an opposite electric field intensity E2 (logΩcm). The intermediate transfer member (B) that satisfies the following formula (1): R1 <R2 ……………………………… (1).

(Operation of the First Invention)
In the image forming apparatus of the present invention, the image carrier (PR; PRy to Py)
The latent image writing position (Q1; Q1y)
To Q1k), an electrostatic latent image is formed. The developing device (G; Gy to Gk) is provided with the image carrier (PR; PRy to Pk).
Rk) Development area (Q2; Q2y to Q) set along the surface
In 2k), the electrostatic latent image is developed into a toner image (Tn). The intermediate transfer member (B), which rotates through a primary transfer area (Q3; Q3y to Q3k) set along the surface of the image carrier (PR; PRy to PRk), is set along a movement path. Pass through the secondary transfer area (Q4). The primary transfer unit (T1; T1y to T1k) is connected to the primary transfer area (Q3; Q3y).
To Q3k), the image carrier (PR; PRy to PRk)
The toner image (Tn) on the surface is transferred to the intermediate transfer body (B). The recording sheet transport device (SH) transports and passes the recording sheet (S) to a secondary transfer area (Q4) set in the movement path of the intermediate transfer body (B). Secondary transfer unit (T
2) The toner on the intermediate transfer member (B) is applied by applying a secondary transfer voltage between the intermediate transfer member (B) and the recording sheet (S) in the secondary transfer region (Q4). The image (Tn) is transferred to the recording sheet (S). The fixing device (F) fixes the toner image (Tn) transferred onto the recording sheet (S).

The volume resistivity R1 (logΩc) of the intermediate transfer member (B) under an electric field having an electric field intensity E1 (V / mm) in the same direction as the primary transfer electric field perpendicular to the surface of the intermediate transfer member (B)
m) and the electric field intensity E2 having the same absolute value as E1 and the opposite direction.
The volume resistivity R2 (log Ωcm) of the intermediate transfer member (B) under an electric field of (V / mm) satisfies the following expression (1). R1 <R2 .................................................................. (1).

In this case, since the electric field dependence is large in the primary transfer electric field forming direction (the resistance value is largely reduced), the unfixed toner image (Tn) on the surface of the image carrier (PR; PRy to PRk)
Of the intermediate transfer member (B) in the primary transfer step of transferring the intermediate transfer member to the intermediate transfer member (B) (the resistance value when a primary transfer voltage is applied) is reduced. An uneven transfer is hardly generated in the electric field acting on (B), and an appropriate transfer electric field can be formed. In such a case, the image quality is prevented from deteriorating, the degree of insulation of the intermediate transfer body is increased, and electric stress (discharge, etc.)
Therefore, it is possible to provide a highly reliable image forming apparatus which has a long service life and a high maintenance efficiency.

[0026]

(First Embodiment of the First Invention) First
Embodiment 1 of the image forming apparatus of the invention is characterized in that the first invention has the following requirement (A09):
(A09) A voltage 100 that generates an electric field in the same direction as the primary transfer electric field in the primary transfer area (Q3; Q3y to Q3k).
(V) Volume resistivity R3 of the intermediate transfer member (B) at the time of application
(Log Ωcm) and the volume resistivity R4 (log Ωcm) of the intermediate transfer member (B) at the time of applying 500 (V),
The volume resistivity R5 (log) of the intermediate transfer member (B) when a voltage of 100 (V) that generates an electric field in the direction opposite to the next transfer electric field is applied.
Ωcm) and the volume resistivity R6 (log Ωcm) of the intermediate transfer member (B) at the time of applying 500 (V) satisfying the following formulas (2) and (3): R3−R4> 2.0 …………………………… (2) R5-R6 <1.0 …………………………………… ............ (3).

(Operation of the First Embodiment of the First Invention) In the first embodiment of the image forming apparatus of the first invention having the above-described configuration, the first transfer area (Q3; Q3y to Q3k) is
The volume resistivity R3 (log) of the intermediate transfer member (B) when a voltage of 100 (V) that generates an electric field in the same direction as the next transfer electric field is applied.
Ωcm) and 500 (V), and a volume resistivity R4 (log Ωcm) of the intermediate transfer member (B), and the intermediate transfer member (B) when a voltage of 100 V that generates an electric field in a direction opposite to the primary transfer electric field is applied. ) Volume resistivity R5 (logΩc
m) and the intermediate transfer member (B) when 500 (V) is applied
And the volume resistivity R6 (log Ωcm) of the following equation (2),
(3) is satisfied. R3−R4> 2.0 …………………………… (2) R5−R6 <1.0 …………………………. ………………… (3).

In this case, since the intermediate transfer member (B) has a large electric field dependence in the primary transfer electric field forming direction, the apparent resistance value of the intermediate transfer member (B) decreases in the primary transfer step, and The unevenness in the electric field acting on (B) can be reduced. In that case, the image quality is prevented from deteriorating and the intermediate transfer body (B)
Since the degree of insulation of the intermediate transfer member (B) can be increased and the life of the intermediate transfer member (B) can be increased, the maintenance efficiency is high, and the reliability is high. An image forming apparatus can be provided. Further, in the secondary transfer area (Q4), the electric field dependency in the direction of forming the secondary transfer electric field is small, so that the apparent resistance of the intermediate transfer body (B) is high in the secondary transfer step, and between the recording medium and the secondary transfer area. The gap discharge generated between the bias rolls in the transfer area (Q4) is reduced. Further, ionization destruction of the material caused by charge transfer inside the intermediate transfer member (B) due to the influence of the secondary transfer electric field and the peeling discharge (electronic carriers increase when a high voltage is applied to a solid and the avalanche phenomenon occurs) (Destruction caused by (impact ionization))
Can be reduced.

Second Embodiment of the First Invention The second embodiment of the image forming apparatus according to the first invention is the same as the first invention or the first invention.
In the first embodiment of the invention, the following requirements (A010),
(A010) The above-mentioned 1 comprising a primary transfer roll (T1; T1y to T1k), characterized by comprising (A011).
The secondary transfer unit (T1; T1y to T1k), (A011) sets the resistance value of the intermediate transfer body (B) to R7 (log) during the primary transfer operation in the primary transfer area (Q3; Q3y to Q3k).
Ω), when the resistance value of the primary transfer roll (T1; T1y to T1k) is R8 (logΩ), the intermediate transfer member (B) that satisfies the following expression (4): R7 <R8... …………………………… (4).

(Operation of the Second Embodiment of the First Invention) In the second embodiment of the image forming apparatus of the first invention having the above configuration, the primary transfer unit (T1; T1y to T1k) performs primary transfer. It is composed of a roll (T1; T1y to T1k). The intermediate transfer member (B) includes the primary transfer region (Q3; Q3y to Q3).
During the execution of the primary transfer operation in k), the resistance value R7 (logΩ) of the intermediate transfer body (B) and the primary transfer roll (T1; T1y to T1) for transferring to the intermediate transfer body (B)
At the time of the resistance value R8 (logΩ) of k), the following expression (4) is satisfied. R7 <R8 ………………………………… (4). Resistance R8 of the primary transfer roll (T1; T1y to T1k)
(LogΩ) is the resistance R7 (log) of the intermediate transfer member (B).
Ω), the flow of the transfer current into the non-image area on the image carrier is small, and an appropriate electric field with small transfer electric field unevenness is formed.

(Third Embodiment of the First Invention) The third embodiment of the image forming apparatus of the first invention is characterized in that the first invention has the following requirements (A012) and (A013). (A012) the secondary transfer device (T2) constituted by a bias roll (T2b); (A013) the intermediate transfer member (B) during a secondary transfer operation in the secondary transfer region (Q4). When the resistance value is R9 (logΩ) and the resistance value of the bias roll (T2b) is R10 (logΩ),
The intermediate transfer member (B) that satisfies the following expression (5): R10 <R9 <2R10 (5).

(Operation of the Third Embodiment of the First Invention) In the third embodiment of the image forming apparatus of the first invention having the above-described configuration, the secondary transfer unit (T2) includes a bias roll (T2).
b). The intermediate transfer member (B) has a resistance value R9 (logΩ) of the intermediate transfer member (B) during a secondary transfer operation in the secondary transfer region (Q4).
When the resistance value R10 (logΩ) of the bias roll (T2b) transferred to the intermediate transfer member (B), the following expression (5) is satisfied. R10 <R9 <2R10 ……………………………… (5). In the secondary transfer area (Q4), the resistance value R9 (logΩ) of the intermediate transfer member (B) and the resistance value R10 (logΩ) of the bias roll (T2b) transferred to the intermediate transfer member (B) are determined. Since the difference is small, it is possible to suppress a discharge (discharge in a direction of a smaller potential) generated between the transfer sheet and the transfer sheet (S) in the secondary transfer step, and to form an appropriate electric field.

(Fourth Embodiment of the First Invention) The fourth embodiment of the image forming apparatus of the first invention is characterized in that the first invention has the following requirements (A014) and (A015). (A014) The static elimination area (Q) set on the downstream side of the secondary transfer area (Q4) in the movement path of the intermediate transfer body (B).
And a static eliminator (Rd + JR) disposed in the neutralization area (Q5) and neutralizing the charge on the intermediate transfer body (B) passing through the neutralization area (Q5).
B), (A015) A neutralizing electric field having the same direction as the direction of the primary transfer electric field applied between the front and back surfaces of the intermediate transfer member (B) during the primary transfer operation is applied between the front and back surfaces of the intermediate transfer member. Power supply for driving the static eliminator (Rd + JRB) as described above.

(Operation of Embodiment 4 of First Invention) In Embodiment 4 of the image forming apparatus according to the first invention having the above-described configuration, the image forming apparatus passes through the charge elimination area (Q5) and the intermediate transfer body (B). A static eliminator (Rd + JRB) for eliminating the charged charges is disposed in a static elimination area (Q5) set downstream of the secondary transfer area (Q4) in the movement path of the intermediate transfer body (B). The power supply for static elimination is used for the intermediate transfer member (B) during the primary transfer operation.
The neutralization device (Rd + JRB) is driven such that a neutralization electric field having the same direction as the primary transfer electric field applied between the front and back surfaces is applied between the front and back surfaces of the intermediate transfer member. Since the intermediate transfer member (B) has a large electric field dependency with respect to the electric field direction of the primary transfer electric field, the intermediate transfer member (B) is used during the primary transfer operation.
It is difficult to hold charges inside. For this reason, the electric charge held in the intermediate transfer body (B) at the time of the secondary transfer is changed to the charge removal area (Q
5) At the time of passage, the intermediate transfer body (B) is neutralized by a neutralization electric field applied in a direction in which the electric field dependence is large. For this reason, the electric field can be instantaneously removed by the low static electric field.

(Fifth Embodiment of the First Invention) The fifth embodiment of the image forming apparatus of the first invention is characterized in that the first invention has the following requirements (A016) and (A017). , (A016) being disposed with the intermediate transfer member (B) interposed therebetween,
The static eliminator (Rd + JR) having a belt static elimination roll (Rd) to which a static elimination voltage is applied and a ground member (JRB).
B), (A017) When the resistance value R11 (logΩ) of the intermediate transfer member (B) in the electric field for static elimination and the resistance value R12 (logΩ) of the belt static elimination roll (Rd) to which the static elimination voltage is applied, The intermediate transfer member (B) that satisfies the formula (6), R11 <R12.........

The ground member of the static eliminator (Rd + JRB) is a brush, a roll, a rotating belt (rotating film).
And so on. When a roll is used as the grounding member, the static eliminator includes one of a belt supporting roll (a belt driving roll and the like) rotatably supporting the intermediate transfer member (B) and a roll disposed to face the belt supporting roll. And can be configured by In that case, the static eliminator is constituted by a pair of rolls arranged so as to sandwich the intermediate transfer member (B). For example, when the static eliminator (Rd + JRB) is composed of a belt driving roll (Rd) and a belt neutralizing roll (JRB) arranged opposite thereto, one of the rolls is used as a belt neutralizing roll for applying a static elimination voltage. , The other can be used as a ground member.

The resistance value of the belt static elimination roll according to the fifth embodiment of the present invention means a roll to which a static elimination voltage is applied (a roll different from the grounded side). Therefore, the static eliminator (Rd + JRB) is composed of the drive roll (Rd) and the belt static elimination roll (JRB), and when the static elimination voltage is applied to the drive roll (Rd), the drive roll (Rd) is connected to the “static elimination voltage”. Is applied to the belt.

(Effect of Embodiment 5 of the First Invention) In Embodiment 5 of the image forming apparatus of the first invention having the above configuration, the static eliminator (Rd + JRB) has a belt static elimination roll (Rd). The intermediate transfer member (B) has a resistance value R11 (log) of the intermediate transfer member (B) within the neutralization electric field.
Ω), a belt static elimination roll (R
In the case of the resistance value R12 (logΩ) of d), the following expression (6) is satisfied. R11 <R12 ………………………………… (6). The resistance value R11 (l) of the intermediate transfer member (B) in the electric field for static elimination.
ogΩ) is the resistance value R12 of the belt static elimination roll (Rd).
(Log Ω), the difference in the density of the inflow charge at the time of static elimination becomes small with respect to the unevenness of the residual electric charge, and it becomes difficult to apply a high voltage to the belt static elimination roll (Rd). Can be increased.

[0039]

Next, specific examples (examples) of embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following examples. (Embodiment 1) FIG. 1 is an overall explanatory view of Embodiment 1 of the image forming apparatus of the present invention. FIG. 2 is an enlarged view of a main part of FIG. In FIG. 1, the image forming apparatus U has a main body UA and an automatic document feeder UB placed on a platen glass PG on the upper surface of the main body UA. The image forming apparatus main body U
A has a UI (user interface) for a user to input an operation command signal such as a copy start signal.

An IIT as a document reading device disposed below the transparent platen glass PG on the upper surface of the copying machine main body UA
Has an exposure system registration sensor (platen registration sensor) Sp and an exposure optical system A arranged at a platen registration position (OPT position). Reflected light from a document Gi conveyed to the platen glass PG by the automatic document feeder UB or a document (not shown) manually placed on the platen glass PG is transmitted via the exposure optical system A to a CCD (CCD). It is converted into an electric signal by a solid-state imaging device.

The IPS (Image Processing System) converts the R, G, B electric signals input from the CCD into Y (yellow), M (magenta), C (cyan),
The image data is converted into K (black) image data, temporarily stored, and output to the laser drive circuit DL as latent image formation image data at a predetermined timing. The laser drive circuit DL outputs a laser drive signal to a ROS (latent image forming apparatus) according to the input image data.

Image carrier P composed of a photosensitive drum
R rotates in the direction of the arrow Ya, and its surface is neutralized by a photoconductor neutralizing roll JRP, and then uniformly charged by a charger CR, and then the ROS (latent image) is written at a latent image writing position Q1. The latent image is exposed and scanned by the laser beam L of the forming apparatus) to form an electrostatic latent image. When a full-color image is formed, electrostatic latent images corresponding to four color images of Y (yellow), M (magenta), C (cyan), and K (black) are sequentially formed. Only the electrostatic latent image corresponding to the (black) image is formed.

The surface of the image carrier PR on which the electrostatic latent image is formed rotates and sequentially passes through the development area Q2 and the primary transfer area Q3. The rotary developing device G is a developing device for four colors of Y (yellow), M (magenta), C (cyan), and K (black) that sequentially rotates and moves to the developing area Q2 with the rotation of the rotation axis Ga. GY, GM, GC, and GK. Each of the developing units GY, GM, GC, and GK has a developing roll GR for transporting a developer to the developing area Q2, and forms an electrostatic latent image on the image carrier PR passing through the developing area Q2. Develop into a toner image.

Below the image carrier PR, a slide frame F1 is provided by a pair of left and right slide rails SR, SR.
(Indicated by a two-dot chain line) is supported so as to be slidable back and forth (in a direction perpendicular to the paper surface). Slide frame F1
Supports a belt frame F2 of the belt module BM so as to be rotatable around a hinge axis F2a. The belt module BM includes the intermediate transfer belt B and a plurality of belt support rolls (R) including a belt drive roll Rd, a tension roll Rt, a walking roll Rw, an idler roll (free roll) Rf, and a backup roll T2a.
d, Rt, Rw, Rf, T2a), the primary transfer roll T1,
And a belt frame F2 for supporting them. The intermediate transfer belt B is connected to the belt support roll (R
d, Rt, Rw, Rf, T2a). The primary transfer roll T1 is supplied with a primary transfer voltage having a polarity opposite to the toner charging polarity from a primary transfer power supply Ea of a power supply circuit E (see FIG. 2).
Is controlled by the controller C.

A belt position sensor SB for detecting a mark MK (see FIG. 2) for detecting the position of the intermediate transfer belt B is provided. The timing of writing the latent image on the image carrier PR is controlled by a very accurate position detection signal of the intermediate transfer belt B output from the belt position sensor SB. When forming a full-color image, a first-color electrostatic latent image is formed at the latent-image writing position Q1, and a first-color toner image Tn is formed at the developing region Q2. This toner image Tn is firstly electrostatically transferred onto the intermediate transfer belt B by the primary transfer roll T1 when passing through the primary transfer area Q3. Thereafter, similarly, the second color, the third color, and the fourth color toner images Tn are sequentially superimposed on the intermediate transfer belt B carrying the first color toner image Tn, and primary-transferred. Is formed on the intermediate transfer belt B. When a monochromatic monocolor image is formed, only one developing unit is used, and the monochromatic toner image is primarily transferred onto the intermediate transfer belt B. After the primary transfer, the surface of the image carrier PR is cleaned of residual toner by the image carrier cleaner CL1, and is discharged by the photoconductor discharging roller JRP.

Below the backup roll T2a,
A secondary transfer slide frame Fs slidable back and forth (in a direction perpendicular to the paper surface) by a pair of left and right slide rails SR is detachably supported on the image forming apparatus main body. A secondary transfer lifting frame Ft of the secondary transfer unit Ut is supported on the secondary transfer slide frame Fs so as to be rotatable up and down around a hinge axis Fta. The secondary transfer unit Ut includes a bias roll T2b, a bias roll cleaner CL3, and a roll support lever LV.
, Sheet guide SG2 after transfer, and sheet conveying belt B
H and the secondary transfer lifting frame Ft supporting them.
And

The roll support lever LV is a lever rotatable around an axis LVa that supports the bias roll T2b and the bias roll cleaner CL3. 2 above
When the next transfer unit Ut is moved to the use position, the roll support lever LV is rotated by a motor (not shown) to move the bias roll T2b to the secondary transfer position and the intermediate transfer position where the bias roll T2b comes into contact with the intermediate transfer belt B. Move between standby positions away from the belt. The post-transfer sheet guide SG2 includes a secondary transfer area Q which is a contact area between the bias roll T2b and the intermediate transfer belt B.
The recording sheet that has passed through 4 is transferred to the sheet transport belt B on the downstream side.
Guide to H.

A backup roll T2a, which is a support roll of the intermediate transfer belt B and forms an opposite electrode of the bias roll T2b, is grounded, and its surface is covered with a semiconductive or insulating thin film. The resistivity is adjusted to 10 ⁸ Ω · cm or more. The bias roll T2b is formed by winding a semiconductive elastic body around a conductive metal roll, and a secondary transfer voltage (for example, a constant DC voltage of 3 kV) having a polarity opposite to the charging polarity of the toner is applied to the power supply circuit E. The power is supplied from a next transfer power supply Eb (see FIG. 2), and the power supply circuit E is controlled by a controller C. The backup roll T2a and the bias roll T2b constitute a secondary transfer unit T2.

The recording sheets S stored in the paper feed tray TR1 are taken out by a pickup roll Rp at a predetermined timing, separated one by one by a separation roll Rs, and conveyed to a registration roll Rr. The recording sheet S conveyed to the registration roll Rr is transferred to the pre-transfer sheet guide SG in synchronization with the movement of the primary-transferred multi-toner image or single-color toner image to the secondary transfer area Q4.
It is transported from 1 to the secondary transfer area Q4. In the secondary transfer area Q4, the secondary transfer unit T2 electrostatically secondary-transfers the toner image on the intermediate transfer belt B onto the recording sheet S. 2
After the next transfer, the residual toner is removed from the intermediate transfer belt B by the belt cleaner CL2. The toner adhered to the surface of the bias roll T2b is collected by a bias roll cleaner CL3.

The bias roll T2b and the belt cleaner CL2 are disposed so as to be able to be separated (separated and contacted) from the intermediate transfer belt B. When a color image is formed, the unfixed toner of the final color is formed. The image is separated from the intermediate transfer belt B until the image is primarily transferred to the intermediate transfer belt B. The bias roll cleaner CL3 is
The separation / contact movement is performed together with the bias roll T2b. The recording sheet S on which the toner image has been secondarily transferred is conveyed to a fixing area Q6 by a post-transfer sheet guide SG2 and a sheet conveying belt BH, and includes a heating roll Fh and a pressure roll Fp when passing through the fixing area Q6. The fixing is performed by a fixing device F having a pair of fixing rolls. The recording sheet S on which the toner image has been fixed is discharged to the recording sheet discharge tray TR2. The codes Rp, Rs, Rr, SG1,
The sheet conveying device SH is constituted by elements indicated by SG2 and BH.
Is configured.

(Electric neutralizer (Rd + JRB)) A belt neutralizing roll JRB is disposed at a position opposite to the conductive driving roll Rd with the intermediate transfer belt B interposed therebetween, and between the belt neutralizing roll JRB and the driving roll Rd. The drive roll Rd is used as a belt charge elimination roll (Rd) to which a charge elimination voltage is applied.
The belt static elimination roll JRB is formed of a grounded (earthed) conductive metal roll, and is used as an earth member. The drive roll is formed by winding a semiconductive elastic body around a conductive metal roll. For example, the volume resistivity of the drive roll is adjusted to 10 ⁶ Ω · cm. A layer whose surface is coated with PTFE (polyfluoroethylene) is used. The static elimination voltage applied to the drive roll Rd is a power supply circuit E
(See FIG. 2), and the charge is removed by the belt charge roll JRB at the opposing position. The power supply circuit E is controlled by a controller C.

As can be seen from FIG. 2, the primary transfer power source Ea
The direction of the electric field applied to the intermediate transfer belt B by the charge elimination power supply Ec is a direction from the back surface to the front surface of the intermediate transfer belt B. As will be described later, the intermediate transfer belt B has a high electric field dependency under an electric field from the back surface to the front surface of the intermediate transfer belt B. Therefore, the resistance value of the intermediate transfer belt B under the electric discharge electric field applied to the intermediate transfer belt B by the electric discharge power source Ec is high. descend. For this reason, it is possible to perform the charge elimination of the intermediate transfer belt B by a low charge elimination electric field.

(Intermediate Transfer Belt B) In a thermosetting seamless belt in which carbon black is dispersed as a conductive material, carbon black is mixed with U Varnish-S, a polyimide varnish for heat-resistant coatings of Ube Industries, Ltd. using a mixer. This stock solution is poured into a cylindrical mold and centrifugally molded while heating. At that time, the number of rotations of the cylindrical mold is usually increased at an initial stage by rotating the carbon at a speed of at least twice the number of rotations required for uniform dispersion inside the resin, for example, at a speed of about 6000 rpm,
After that, it is fixed to the normal rotation speed. By this step, the carbon particles are formed in a state of being ubiquitous in the surface direction due to the centrifugal force. The semi-cured seamless belt is removed from the cylindrical mold, covered with an iron core, and re-heated to be fully cured (imidization reaction).
¹⁰ (Ω / □), volume resistivity 10 ⁹ (Ωcm) thickness 90
A μm seamless belt (intermediate transfer belt) is obtained. The intermediate transfer belt is characterized in that there is a great difference in the electric field dependence in the creeping direction on the surface on the side where many carbon particles are ubiquitous and on the back side.

Here, carbon black as a conductive agent for imparting conductivity to the polyimide resin is several wt% (wtt).
% =% By weight) to several tens wt%, for example, about 35 wt% to obtain a desired resistance value. The basic constituent factors (structure) of carbon black include particle diameter, structure, and physicochemical properties of the surface. The particle diameter of the carbon black is generally composed of what is called primary particles of about several tens of nanometers (nanometers), and the primary particles are further fused to form a secondary aggregate. Secondary aggregates vary depending on the type of carbon black, various dispersion conditions, and the like, and are generally fine particles having an average particle diameter of several μm or less and dispersed in the resin. Surface and internal conductivity when an electric field is formed in the resin in which carbon black is dispersed can be obtained by moving the carrier in the contact portion between the secondary aggregates and the minute gap thereof. . Therefore, the size of the specific surface area of the secondary aggregate, the number of the aggregate itself, the wettability with the resin, and the like have a great effect on the conductivity.

Further, the polyimide belt was used as a base material, and a conductive agent was dispersed in a water emulsion paint (Emuralon 345, JYL-601) containing urethane rubber and TFE (tetrafluoroethylene) resin on the surface thereof. Emuralon 345 ESD, J, manufactured by Acheson Co., Ltd.
Water emulsion paint containing YL-601 ESD, fluoro rubber and FEP (Daily latex GLS-2
13) Daikin Latex NF-915 manufactured by Daikin Industries Co., Ltd. in which a conductive agent is dispersed is coated by spray coating, and then heated at, for example, 250 ° C. for 20 minutes, and is made of a 50 μm-thick fluororubber and a fluororesin. Obtain a coat layer. The surface resistivity on the coat layer side is 10 ¹³ log Ω / □, and the volume resistivity is 10 ¹⁰ log Ωcm.

(Operation of the First Embodiment) The Intermediate Transfer Belt B
When an electric field is applied from the base layer side, the amount of free charges on the surface of the base layer on the side where the number of carbon particles is large and unevenly distributed is larger than that on the inner side surface of the base layer, so that the free layer is induced in the coat layer. High charge. On the other hand, when an electric field is applied from the coat layer side, the amount of free charge on the coat layer side is small and the amount induced on the base layer side is also small. The phenomenon is that the base layer has a large gradient in the resistance (the resistance of the base layer changes in the thickness direction), causing a non-uniform state in the dielectric constant inside the dielectric material. Occurs.

In the case of a seamless belt having a two-layer structure having a surface resistivity of 10 ¹³ (Ω / □) and a volume resistivity of 10 ¹⁰ (Ωcm), for example, the electric field intensity E 1 in the surface direction (primary transfer electric field direction) = 11111. The volume resistivity R1 (log Ω) and R2 (log Ω) under the electric field intensity E2 of 111 (V / mm) and the electric field intensity E2 of 1111.1 (V / mm) in the direction opposite to the above E1 were respectively as follows. . R1 = 10.00 (logΩ / cm), R2 = 10.60 (logΩ / cm) Therefore, the following expression (1) is satisfied. R1 <R2 .................................................................. (1).

In this case, the electric field dependence is large in the direction of electric field formation in the primary transfer step, and during the primary transfer step in which the unfixed toner image is primarily transferred from the image carrier PR to the intermediate transfer belt B, the intermediate transfer belt The apparent resistance of B is reduced, and unevenness in the electric field during the primary transfer hardly occurs. In addition, the charge generated in the primary transfer step is hardly retained inside the intermediate transfer member, and the primary transfer electric field can be stabilized. For this reason, it is possible to form an appropriate primary transfer electric field. Therefore, a high-grain image quality can be obtained without deteriorating the transfer image quality of the unfixed toner image from the image carrier PR to the intermediate transfer member. Further, since the transfer efficiency of the unfixed toner image can be increased, the residual toner on the image carrier PR decreases. Therefore, it is possible to extend the life of the image carrier cleaner CL1 and to prevent contamination inside the image forming apparatus. Therefore, it is possible to provide an image forming apparatus having high maintenance easiness, high image quality and high reliability.

The volume resistivity R3 (logΩ) of the intermediate transfer belt B when a voltage of 100 (V) that generates an electric field in the same direction as the primary transfer electric field in the primary transfer area Q3 is applied.
cm) and 500 (V), and the volume resistivity R4 (log Ωcm) of the intermediate transfer belt B, and the voltage of the intermediate transfer belt B when a voltage of 100 (V) that generates an electric field in a direction opposite to the primary transfer electric field is applied. The volume resistivity R5 (logΩcm) and the volume resistivity R6 (logΩcm) of the intermediate transfer belt B when 500 (V) was applied were as follows. R3 (logΩcm) = 10000 (logΩcm), R4 (logΩcm) = 7.87 (logΩcm), R5 (logΩcm) = 10.60 (logΩcm), R6 (logΩcm) = 9.65 (logΩcm) The following expressions (2) and (3) are satisfied. R3−R4> 2.0 …………………………………… (2). R5−R6 <1.0 ………………………………… (3).

In this case, since the electric field dependence is large in the electric field forming direction in the primary transfer step, the same operation and effect as in the case where the above expression (1) is satisfied can be obtained. Further, since the electric field dependency in the electric field forming direction in the secondary transfer step is small, the apparent resistance of the intermediate transfer belt B (resistance when a secondary transfer voltage is applied) is high in the secondary transfer step, and the recording medium (recording sheet) or Gap discharge generated between the secondary transfer bias roll T2b and the intermediate transfer belt B is reduced. Further, it is possible to reduce the ionization destruction of the material caused by the charge transfer inside the intermediate transfer belt B under the influence of the transfer electric field and the peeling discharge. For this reason, the occurrence of transfer failure induced by a partial decrease in the resistance of the intermediate transfer belt B is eliminated, and it is possible to prevent the image quality from deteriorating over time.

During the execution of the primary transfer operation in the primary transfer area Q3, the resistance value R7 (l
ogΩ), the resistance value R8 (logΩ) of the primary transfer roll T1 to be transferred to the intermediate transfer belt B was as follows. R7 (logΩ) = 7.13 (logΩ) R8 (logΩ) = 7.83 (logΩ) Therefore, the following expression (4) is satisfied. R7 <R8 ………………………………… (4).

In this case, since the resistance value of the primary transfer roll T1 during the primary transfer step is higher than the resistance value of the intermediate transfer belt B, the current flowing into the non-image area of the image carrier PR is relatively small. . Therefore, an appropriate transfer electric field can be applied to the unfixed toner image between the primary transfer roll (primary transfer device) and the image carrier PR. Therefore, the transferability of the unfixed toner image from the image carrier PR to the intermediate transfer belt B is improved, and it is possible to provide image quality without image unevenness. In particular, since the transfer efficiency in the multiple transfer step of transferring the toner image on the intermediate transfer belt B can be improved, low electric field transfer can be performed, and the amount of generated ozone can be reduced.

During the execution of the secondary transfer operation in the secondary transfer area Q4, the resistance value R9 (lo
gΩ), and the resistance value R10 (logΩ) of the bias roll T2b transferred to the intermediate transfer belt B was as follows. R9 (logΩ) = 9.50 (logΩ) R10 (logΩ) = 7.68 (logΩ) Therefore, the following expression (5) is satisfied. R10 <R9 <2R10 ……………………………… (5).

In this case, the resistance value R 9 (logΩ) of the intermediate transfer member B and the resistance value R 10 of the bias roll T 2 b transferred to the intermediate transfer member B in the secondary transfer step
(LogΩ), a discharge generated between the transfer sheet S and the transfer sheet S in the secondary transfer step can be suppressed, and an appropriate electric field can be formed. For this reason,
It is possible to prevent image quality deterioration, prevent a decrease in the degree of insulation of the intermediate transfer belt B, and prevent a chemical change of a material caused by an electric stress. Therefore, it is possible to provide an image forming apparatus that has a long service life and high maintenance easiness and high reliability.

The resistance value R11 (logΩ) of the intermediate transfer member B and the resistance value R12 (log) of the driving roll (belt discharging roll to which the discharging voltage is applied) Rd in the discharging electric field.
Ω) were the following values. R11 (logΩ) = 7.50 (logΩ) R12 (logΩ) = 7.90 (logΩ) Therefore, the following expression (6) is satisfied. R11 <R12 ………………………………… (6).

Since the resistance value R11 (log Ω) of the intermediate transfer member B in the electric field for static elimination is lower than the resistance value R12 (log Ω) of the charge elimination roller JRB for the belt, the inflow charge density at the time of charge elimination against the unevenness of the residual charge. , The high voltage is less likely to be applied to the belt static elimination roll JRB, thereby preventing the occurrence of leak and improving the static elimination performance. Further, since the resistance value of the belt static elimination roll JRB is higher than the resistance value of the intermediate transfer belt B, the residual charge of the intermediate transfer belt B can be removed with a low static elimination voltage. Therefore, power saving of the static elimination power supply can be achieved.

In addition, the power supply for static elimination supplies a neutralization electric field having the same direction as the direction of the primary transfer electric field applied between the front and back surfaces of the intermediate transfer belt B during the primary transfer operation. To be applied to the static eliminator (Rd + JR
B) drive. Since the intermediate transfer belt B has a large electric field dependency with respect to the direction of the electric field of the primary transfer electric field, it is difficult for electric charges to be held inside the intermediate transfer belt B during the primary transfer operation. Therefore, the charges held on the intermediate transfer belt B at the time of the secondary transfer are neutralized by the neutralization electric field applied in the direction in which the electric field dependence of the intermediate transfer belt B increases when passing through the neutralization area Q5. For this reason, the electric field can be instantaneously removed by the low static electric field.

The measurement of the surface resistivity, the volume resistivity of the intermediate transfer belt B, and the volume resistivity of the driving roll (a belt static elimination roll to which a static elimination voltage is applied) Rd was performed by using a Hiresta IP manufactured by Mitsubishi Yuka. Using an HR probe, a voltage of 100 to 1000 V was applied, and the value was obtained from a current value after 30 seconds.

(Embodiment 2) FIG. 3 is an explanatory view of Embodiment 2 of the image forming apparatus of the present invention. In the description of the first embodiment, components corresponding to the components of the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. The second embodiment differs from the first embodiment in the following points.
In other respects, the configuration is the same as that of the first embodiment. FIG.
In the first embodiment, the intermediate transfer belt B shown in FIG.
, An intermediate transfer drum B is provided. The intermediate transfer drum B is connected to a pair of disc-shaped hubs (not shown) provided at both ends in the axial direction, and a part of the outer periphery thereof by a tie bar (not shown) extending in the axial direction. A belt-like intermediate transfer member is cylindrically supported on the outer surfaces of the hub and tie bar (not shown). As the intermediate transfer member B, the same one as the intermediate transfer belt B of the first embodiment is used.

A primary transfer area Q3, a secondary transfer area Q4, and a charge elimination area Q5 are set along the movement path on the surface of the cylindrical intermediate transfer body B. In the charge removal area Q5, a belt charge removal roll JRB is movably disposed between a charge removal position in contact with the surface of the intermediate transfer drum B and a separation position separated from the surface of the intermediate transfer drum B. When the intermediate transfer drum B as in the second embodiment is used, the same operation as in the first embodiment can be obtained.

(Embodiment 3) FIG. 4 is an overall explanatory view of Embodiment 3 of the image forming apparatus of the present invention. FIG. 5 is an enlarged view of a main part of FIG. In the description of the third embodiment, components corresponding to the components of the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. Example 3
Is different from the first embodiment in the following points, but is configured similarly to the first embodiment in other points. In FIG. 4, the image forming apparatus according to the third embodiment of the present invention is a tandem digital color copying machine U, and the laser drive signal output devices DL are laser drive signal output devices DLy, DLy, Y, M, C, and K for each color.
It is composed of DLm, DLc and DLk. The laser drive signal output devices DLy, DLm, DLc, DLk for each color are
At a predetermined timing, a laser drive signal corresponding to the input image data is supplied to each of the latent image writing devices ROSy, ROSm,
Output to ROSc and ROSk.

The image carriers PRy, PRm, PRc, PRk are uniformly charged by the respective chargers CRy, CRm, CRc, CRk, and then image writing areas Q1y, Q1m, Q1c, Q
1k, the latent image writing devices ROSy, ROSm, RO
Laser beams Ly, Lm, Lc, output from Sc and ROSk
Lk forms an electrostatic latent image on the surface. The electrostatic latent images on the surfaces of the image carriers PRy, PRm, PRc, PRk are developed in the developing regions G2y, Q2m, Q2c, Q2k by the developing devices Gy,
The toner image is developed by Dm, Dc, and Dk. The developed toner images are transferred to primary transfer areas Q3y, Q3m, Q3c, Q
At 3k, primary transfer is performed on the intermediate transfer belt B by the primary transfer units T1y, T1m, T1c, and T1k. Image carrier PRy, PRm, P
After transferring the toner image to the intermediate transfer belt B, Rc and PRk remove the residual toner on the surface thereof from the image carrier cleaners CLy and CLy.
It is removed by CLm, CLc and CLk.

As the intermediate transfer belt B of the third embodiment shown in FIG. 4, a belt similar to the intermediate transfer belt B of the first embodiment is used. When the intermediate transfer belt B of the first embodiment is used as the intermediate transfer belt B of the tandem-type image forming apparatus of the third embodiment, the same operation as that of the first embodiment is obtained.

(Modifications) Although the embodiments of the present invention have been described in detail, the present invention is not limited to the above-described embodiments, but falls within the scope of the present invention described in the appended claims. Thus, various changes can be made. Modified embodiments of the present invention will be exemplified below. (H01) Although the method of manufacturing the intermediate transfer belts of Examples 1 and 2 is based on centrifugal molding, in the present invention, the molding method is not limited to the centrifugal molding, and the casting method of molding on a metal sheet is used. Either may be used. (H02) In addition to the above-described carbon black, the conductive agent mixed in the intermediate transfer member is a composite metal oxide such as copper, iron, manganese, nickel, zinc, cobalt, barium, aluminum, tin, lithium, magnesium, silicon, Solid solutions of metal oxides obtained by firing at least three types selected from oxides, hydroxides, carbonates, metal compounds, etc. containing different metal elements such as phosphorus, tin oxide and antimony monoxide composite oxides Etc. can be used. (H03) In the first embodiment, the belt driving roll Rd
Can be used as a ground member, and the belt discharging roller JRB can be used as a belt discharging roller for applying a discharging voltage. In this case, the drive roll Rd is grounded (grounded) as a metal roll, the belt static elimination roll JRB is formed with a semiconductive layer for resistance adjustment on the surface of the metal roll, and a negative bias voltage for negative elimination is applied. . At this time, the electric field in the same direction as the electric field at the time of the primary transfer is applied to the intermediate transfer belt B, so that the intermediate transfer belt B can be neutralized. (H04) As a ground member of the static eliminator, a static elimination brush can be used instead of a roll.

[0075]

The above-described image forming apparatus of the present invention has the following effects. (E01) The electric field dependency of the resistance value of the intermediate transfer member in the primary transfer step can be increased to reduce the transfer electric field unevenness acting on the intermediate transfer member. (E02) The electric field dependency of the resistance value of the intermediate transfer member in the secondary transfer step is reduced, and the apparent resistance (resistance when a secondary transfer voltage is applied) of the intermediate transfer belt B in the secondary transfer step is high.
The gap discharge generated between the recording medium (recording sheet) or the secondary transfer bias roll and the intermediate transfer member can be reduced. (E03) It is possible to increase the electric field dependency of the resistance value of the intermediate transfer member in the charge removal step, thereby facilitating the charge removal of the intermediate transfer member. (E04) Intermediate transfer belt B due to transfer electric field and peeling discharge
It is possible to reduce the ionization destruction of the material caused by internal charge transfer. For this reason, the occurrence of transfer failure induced by a partial decrease in the resistance of the intermediate transfer belt B is eliminated, and it is possible to prevent the image quality from deteriorating over time. (E05) The transferability of the toner image is improved, the scattering of the toner and the generation of the untransferred toner on the recording medium are prevented, the contamination inside the image forming apparatus is prevented, the life of the cleaning member is prolonged, and the maintenance is easy. A highly reliable image forming apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is an overall explanatory diagram of Embodiment 1 of an image forming apparatus of the present invention.

FIG. 2 is an enlarged view of a main part of FIG. 1;

FIG. 3 is an explanatory view of Embodiment 2 of the image forming apparatus of the present invention.

FIG. 4 is an overall explanatory diagram of Embodiment 3 of the image forming apparatus of the present invention.

FIG. 5 is an enlarged view of a main part of FIG. 4;

6 is an explanatory diagram of a conventional image forming apparatus that transfers an unfixed toner image formed on an image carrier to a recording sheet via an intermediate transfer member. The primary transfer device T1 is
It consists of a corotron.

FIG. 7 is an explanatory diagram of a conventional image forming apparatus that transfers an unfixed toner image formed on an image carrier to a recording sheet via an intermediate transfer member. The primary transfer device T1
Is constituted by a transfer roll.

[Explanation of symbols]

B: intermediate transfer member (intermediate transfer belt), G: GY to GK: developing device, F: fixing device, JRB: belt neutralizing roll, P
R: PRy to PRk: image carrier, (Rd + JRB): static eliminator, S: recording sheet, SH: recording sheet transporter, T
1; T1y to T1k ... primary transfer device, T2 ... secondary transfer device, T2b ...
Bias roll, Tn: toner image, Q1; Q1y to Q1k: latent image writing position, Q2; Q2y to Q2k: development area, Q3: Q3y to
Q3k: primary transfer area; Q4: secondary transfer area; Q5: static elimination area.

Claims (6)

[Claims] 1. An image forming apparatus having the following requirements (A01) to (A08): (A01) an electrostatic latent image at a latent image writing position set along a surface that rotates and moves; (A02) A developing device for developing the electrostatic latent image into a toner image in a development area set along the surface of the image carrier, (A03) Along the surface of the image carrier An intermediate transfer member that rotates through the set primary transfer area and passes through the set secondary transfer area along the movement path; (A04) the toner image on the surface of the image carrier in the primary transfer area (A05) a recording sheet transport device for transporting and passing a recording sheet to a secondary transfer area set in a movement path of the intermediate transfer member; (A06) the secondary transfer device In the transfer area, the intermediate transfer body and the recording sheet (A07) a secondary transfer device for transferring the toner image on the intermediate transfer member to the recording sheet by applying a secondary transfer voltage therebetween, and (A07) fixing for fixing the toner image transferred on the recording sheet Equipment, (A08)
The volume resistivity R1 (log Ωcm) of the intermediate transfer member under an electric field of an electric field intensity E1 (V / mm) in the same direction as the primary transfer electric field perpendicular to the surface of the intermediate transfer member is equal to the absolute value of E1 and is in the opposite direction. The intermediate transfer member having a volume resistivity R2 (log Ωcm) of the intermediate transfer member under an electric field of electric field strength E2 (V / mm) satisfying the following formula (1): R1 <R2 ………………………… (1). 2. The image forming apparatus according to claim 1, wherein the following requirement (A09) is satisfied: (A09) A voltage 100 that generates an electric field in the same direction as the primary transfer electric field in the primary transfer area. (V) Volume resistivity R of the intermediate transfer member at the time of application
3 (logΩcm) and the volume resistivity R4 (logΩcm) of the intermediate transfer member when 500 (V) is applied,
The volume resistivity R5 (logΩc) of the intermediate transfer member when a voltage of 100 (V) that generates an electric field in the direction opposite to the next transfer electric field is applied.
m) and the intermediate transfer member (B) satisfying the following formulas (2) and (3) when the volume resistivity R6 (log Ωcm) of the intermediate transfer member when 500 (V) is applied: R3−R4> 2.0 ………………………… (2) R5-R6 <1.0 ………………………………………… ............ (3). 3. The image forming apparatus according to claim 1, further comprising the following requirements (A010) and (A011): (A010) The image forming apparatus according to claim 1, wherein the image forming apparatus includes a primary transfer roll (A010).
(A011) The resistance value of the intermediate transfer body during the primary transfer operation in the primary transfer area is set to R7 (lo).
gΩ) and the resistance value of the primary transfer roll is R8 (log
Ω), the intermediate transfer member that satisfies the following expression (4): R7 <R8 ………………………………… (4) . 4. The image forming apparatus according to claim 1, further comprising the following requirements (A012) and (A013).
2) The secondary transfer device having a bias roll, (A013)
When the resistance value of the intermediate transfer member is R9 (logΩ) and the resistance value of the bias roll is R10 (logΩ) during the execution of the secondary transfer operation in the secondary transfer region, the following expression (5) is satisfied. Intermediate transfer member, R10 <R9 <2R10 …………………………… (5). 5. The image forming apparatus according to claim 1, further comprising the following requirements (A014) and (A015).
4) a static eliminator that is disposed in a static elimination area set on the downstream side of the secondary transfer area in the movement path of the intermediate transfer body and that eliminates a charge of the intermediate transfer body that passes through the static elimination area;
015) The neutralization device is driven such that a neutralization electric field having the same direction as the primary transfer electric field applied between the front and back surfaces of the intermediate transfer body during the primary transfer operation is applied between the front and back surfaces of the intermediate transfer body. To remove static electricity. 6. The image forming apparatus according to claim 5, wherein the following requirements (A016) and (A017) are provided.
6) The static eliminator having a belt static eliminator roll and a ground member to which a static elimination voltage is applied, interposed between the intermediate transfer members, and (A017) a resistance value R11 (logΩ) of the intermediate transfer member in the static elimination electric field; When the resistance value of the belt static elimination roll to which the static elimination voltage is applied is R12, the intermediate transfer member that satisfies the following formula (6): R11 <R12 …………………………………. …………… (6).