JPH11161061A - Secondary transfer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary transfer device by which an intermediate transfer body is not damage and deflective transfer is not caused even when secondary transfer is performed to paper sheet of smaller size than the paper sheet of maximum standard size. SOLUTION: A backup roll 14b is constituted by coating an insulating roll 14b1 molded of the foaming rubber of EPDM with a semiconductive thin layer tube 14b2 in which carbon black is dispersed, and adjusted so that its surface resistivity may be 10<7> to 10<11> Ω/square. Since a contact roll 14c is arranged at a position where the fluctuation width of total transfer current at the time of rotating the roll 14b is within 17 to 24 μA, the faulty transfer is prevented even when the surface resistivity of the roll 14b is uneven. By arranging the roll 14c at a position where the peripheral distances of the rolls 14b and 14a from a contact B between them are equal, a more excellent result is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary transfer device for an image forming apparatus such as an electrophotographic copying machine and a laser printer, and more particularly, to a toner image formed on a photosensitive drum.
The present invention relates to a secondary transfer device that transfers an image to a recording medium such as a sheet via an intermediate transfer member.

[0002]

2. Description of the Related Art An image forming apparatus using an intermediate transfer member of this kind is disclosed in, for example, Japanese Patent Application Laid-Open Nos.
It is known as described in U.S. Pat. This image forming apparatus has, for example, a configuration as shown in FIG. The configuration and operation will be briefly described. A latent image formed on the photoreceptor 51 rotated clockwise is visualized by developing units 52Y, 52M, 52C and 52K, and formed by the visualization. The plurality of color toner images are primarily transferred to a belt-shaped intermediate transfer body 53 by a primary transfer device. The primary transfer device is, for example, a corona charger 54.
A voltage having a polarity opposite to that of the toner image is applied to the back side of the intermediate transfer body 53, and the toner image is primarily transferred from the photoconductor 51 to the intermediate transfer body 53. The intermediate transfer member 53 is stretched between four rollers, and is driven by a driving roller 55 to rotate counterclockwise. The toner image formed on the intermediate transfer member 53 is rotated by the secondary transfer device 5
6 is carried.

The secondary transfer device 56 includes a secondary transfer roll 56a to which a predetermined voltage is applied from a high-voltage power supply 57, and a backup roll 56b which is disposed opposite to the opposite side of the intermediate transfer body 53 and is grounded. It is composed of With this configuration, the secondary transfer device 56 generates a transfer electric field of a predetermined size, and the toner image on the intermediate transfer body 53 is transferred onto the sheet p conveyed while being sandwiched between the secondary transfer roll 56a and the backup roll 56b. It is made to be electrostatically attracted. The control means 59 controls the output voltage of the high-voltage power supply 57 according to the transfer current detected by the ammeter 58.

[0004]

However, the sheet p having a size smaller than the maximum size that can be printed by the image forming apparatus is transferred to the intermediate transfer body 53 and the secondary transfer roll 56a.
In this case, a part of the secondary transfer roll 56a that does not contact the sheet p directly contacts the semiconductive intermediate transfer body 53. For this reason, a current flows between the secondary transfer roll 56a and the backup roll 56b, and it is not possible to form a sufficient transfer electric field for transferring the toner image onto the paper p, thereby causing a transfer failure or There is a problem that the intermediate transfer body 53 is easily damaged because an excessively large current flows suddenly.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned problems of the prior art, and to damage the intermediate transfer member even if the secondary transfer is performed on paper smaller than the maximum standard size paper.
An object of the present invention is to provide a secondary transfer device which does not cause transfer failure.

[0006]

In order to achieve the above object, the present invention provides an intermediate transfer member, a backup roll having a semiconductive surface for supporting the intermediate transfer member from the back surface, and an intermediate transfer member. A secondary transfer roll disposed opposite to the backup roll with the body interposed therebetween, and means for measuring a current flowing through the backup roll, the intermediate transfer body and the secondary transfer roll, and the primary transfer roll held by the intermediate transfer body. In a secondary transfer device for secondary transfer of a transfer toner image to a recording medium, a contact roll that is in electrical contact with the backup roll, and at the time of secondary transfer, a voltage is applied to one of the contact roll and the secondary transfer roll. Means for applying a voltage, wherein the contact roll does not cause uneven transfer due to the fluctuation width of the secondary transfer total current when the backup roll is rotated. There is a first feature in that arranged at a position to be within the expected current range. A second feature is that the predetermined current range of the secondary transfer total current is 17 to 24 μA.

According to the feature of the present invention, even if the secondary transfer is performed on a sheet of a smaller size than the sheet of the maximum standard size,
No damage to the intermediate transfer member or poor transfer is prevented.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing an example of an image forming apparatus to which the secondary transfer device of the present invention is applied.

As shown in the figure, the image forming apparatus includes a photosensitive member 1 which rotates in the direction of arrow A. An electrostatic latent image corresponding to image information is formed on the photoconductor 1 by a known electrophotographic process such as a charging device 3 and an exposure device 4. Around the photoreceptor 1, developing units 2K, 2Y, 2M and 2C corresponding to respective colors of black (BK), yellow (Y), magenta (M) and cyan (C) are rotatably arranged. This rotation is performed in synchronization with the electrostatic latent images corresponding to each color written on the photoconductor 1. Therefore, for example, yellow image information is developed by the yellow developing device 2Y,
A yellow toner image is formed on the photoconductor 1. A density measuring device 5 for measuring a development density is arranged around the photoreceptor 1.

A belt-like intermediate transfer member 1 is provided downstream of the developing position of the photosensitive member 1 so as to contact the surface of the photosensitive member 1.
1 is stretched over four rolls, and is configured to rotate in the direction of arrow B. A driving roll 12 drives the intermediate transfer body 11 in the direction of arrow B. At a position where the intermediate transfer member 11 comes into contact with the surface of the photoreceptor 1, a primary transfer means 13 including a corona discharger or a transfer roll is disposed. The primary transfer means 13 applies a voltage having a polarity opposite to the charging polarity of the toner image formed on the surface of the photoconductor 1 to the intermediate transfer body, and electrostatically attracts the toner image from the photoconductor 1 to the intermediate transfer body 11. Primary transfer.

On the other hand, the transfer roll 14 is located at the secondary transfer position.
a, backup roll 14b, contact roll 14
c is provided. After the primary transfer is completed, the transfer roll 14a contacts the intermediate transfer body 11 by a driving device (not shown), and transfers the sheet p as the recording medium carried out of the sheet supply tray at a predetermined timing to the intermediate transfer body 11. The toner image formed on the intermediate transfer body 11 is secondarily transferred and transported to a fixing device. Ammeter 1
5 when the voltage from the power supply 16 is applied to the secondary transfer means 14 via the contact roll 14c,
The current flowing through 4 is measured.

A detection sensor 1 is provided around the intermediate transfer body 11.
7, an intermediate transfer member cleaner 18 and the like are provided. The detection sensor 17 is a reflection type sensor that detects an image writing signal transmission marker 19 such as a tape disposed on the intermediate transfer body 11 and outputs an image writing signal. The intermediate transfer member cleaner 18 functions to remove residual toner not transferred by the secondary transfer unit 14.

[0013] In order to solve the problem described in the above-mentioned "Problem to be Solved by the Invention", which occurs when the secondary transfer is performed on paper smaller in size than the maximum standard size, As shown in FIG. 2, the backup roll 14b is used as an insulating roll 1 formed of foamed rubber of EPDM (ethylene propylene diene monomer).
4b1 and this is covered with a semiconductive thin tube 14b2 in which carbon black is dispersed,
The surface resistivity is adjusted so as to be 10 ⁷ to 10 ¹¹ Ω / □. FIG. 2 is an enlarged view of the secondary transfer means 14 which is a main part of the present invention.

Thus, even if the transfer roll 14a comes into direct contact with the intermediate transfer body 11, the backup roll 14b
Prevents excessive current from flowing from the backup roll 14b to the transfer roll 14a. Therefore, a stable transfer electric field can be formed even with a small-sized paper p, and damage to the intermediate transfer body 11 can be prevented. Further, a material having low resistance can be selected as the material of the intermediate transfer body 11.

However, it is difficult to uniformly cover the semiconductive thin tube 14b2 in the circumferential direction of the backup roll 14b, and the circumferential surface resistance changes with the rotation of the backup roll 14b. In addition, when a voltage is applied to the transfer roll 14a, the transfer electric field changes, which causes a new problem that the secondary transfer cannot be performed stably. Therefore, in the present invention, as shown in the figure,
Contact A between the contact roll 14c and the backup roll 14b, the backup roll 14b, and the transfer roll 14a
In the running direction B of the intermediate transfer body 11
The contact roll 14c is disposed so that the upstream side U and the downstream side D of the backup roll 14b are equal.

The intermediate transfer member 11 is made of acrylic,
A resin or various rubbers such as vinyl chloride, polyester and polycarbonate are coated with an antistatic agent such as carbon black to constitute a semiconductive belt having a thickness of about 0.1 mm and a volume resistance of 10 ⁶ to 10. Adjusted to ¹⁴ Ω. The transfer roll 14a of the secondary transfer means 14 is formed by covering a conductive roll 14a1 formed by dispersing carbon black in urethane foam with a semiconductive thin film 14a2. 10μ
The volume resistance is adjusted to 10 ⁷ to 10 ¹¹ Ω in a range of m to 200 μm. The contact roll 14c is made of metal, and the thin layer tube 14 of the backup roll 14b is formed.
b2, and serves to apply the voltage of the power supply 16 to the thin tube 14b2.

In this embodiment, as described above, the contact A between the contact roll 14c and the backup roll 14b is used.
And the peripheral surface distance between the backup roll 14b and the contact point B of the transfer roll 14a is made equal between the upstream side U and the downstream side D of the backup roll 14b. Even when the surface resistance of the layer tube 14b2 is uneven, the fluctuation of the total current flowing through the upstream side and the downstream side can be made extremely small. In other words, the fluctuation of the combined resistance of the backup roll 14b can be reduced.

To clarify the reason, a comparison will be made between a case where the distance between the upstream side U and the downstream side D between the contacts A and B is equal and a case where the distance is not equal.

First, as a precondition, the volume resistance Rp of the sheet p is 6.7 MΩ, the volume resistance Rbelt of the intermediate transfer body 11 is 6.7 MΩ, the volume resistance Rbtr of the secondary transfer roll 14 a is 10 MΩ, and the backup roll 14 b Has a peripheral length of 8.8 cm, a length in the axial direction of 30 cm, a surface resistivity of a low resistance portion thereof is 100 MΩ / □, and a surface resistivity of a normal resistance portion thereof is 1000 MΩ / □. Further, the length of one portion of the low resistance portion is set to the backup roll 14b.
Is 1.1 cm, which is 1/8 of the circumference of.

Therefore, when the distance between the upstream side U and the downstream side D between the contact points A and B of the backup roll 14b is made equal, the variation of the total transfer current passing through the upstream side and the downstream side is obtained as follows. Become.

Now, assuming that only one low resistance portion (surface resistivity 100 MΩ / □) of the backup roll 14b is on the downstream side D, the resistance RD in the downstream D direction, the resistance RU in the upstream U direction, and both of them. Overall resistance Rt1 which is a combined resistance
Are as follows, respectively.

RD = (3.3 cm × 1000 MΩ) ÷ 3
0 cm + (1.1 cm × 100 MΩ) ÷ 30 cm = 11
3.7 MΩ RU = (4.4 cm × 1000 MΩ) ÷ 30 cm = 14
6.7 MΩ Rt1 = (113.7 MΩ × 146.7 MΩ) / (11
(3.7 MΩ + 146.7 MΩ) = 64 MΩ The total resistance R 1 of the secondary transfer means 14 is as follows. R1 = Rt1 + Rp + Rbelt + Rbtr = 87.4MΩ Next, assuming that only one low-resistance portion of the backup roll 14b is located on the upstream side U, the resistance RD in the downstream D direction,
The resistance RU in the upstream U direction and the total resistance Rt2 are as follows.

RD = (4.4 cm × 1000 MΩ) ÷ 30 cm = 14
6.7 MΩ RU = (3.3 cm × 1000 MΩ) ÷ 30 cm +
(1.1 cm × 100 MΩ) ÷ 30 cm = 113.7 M
Ω Rt2 = (146.7 MΩ × 113.7 MΩ) / (14
6.7MΩ + 113.7MΩ) = 64MΩ The total resistance R2 of the secondary transfer means 14 is as follows. R2 = Rt2 + Rp + Rbelt + Rbtr = 87.4 MΩ As described above, when the contact roll 14c is disposed at a position (equal position) where the distance between the upstream side U and the downstream side D between the contacts A and B is equal, the backup roll 14b is provided. , The total resistance of the secondary transfer means 14 is equal to R1
= R2. Therefore, when the voltage applied to the contact roll 14c is set to 1748 V, the total secondary transfer current becomes 2
0 μA, and no fluctuation occurs when the backup roll 14b rotates. This means that backup roll 1
The same is true even if there are two or more low resistance portions on 4b.

Next, it is assumed that the contact roll 14c is shifted 1 cm upstream from the above-mentioned equal position and the low-resistance portion of the backup roll 14b is located at three places downstream, and in this case, in the downstream D direction. , The resistance RU in the upstream U direction, and the total resistance Rt1 are as follows.

RD = (2.1 cm × 1000 MΩ) ÷ 3
0 cm + (3.3 cm × 100 MΩ) ÷ 30 cm = 8
1.0 MΩ RU = (3.4 cm × 1000 MΩ) ÷ 30 cm = 11
3.3 MΩ Rt1 = (81.0 MΩ × 123.3 MΩ) / (81.0 MΩ
(MΩ + 133.3 MΩ) = 47.2 MΩ The total resistance R 1 of the secondary transfer means 14 is as follows. R1 = Rt1 + Rp + Rbelt + Rbtr = 70.6 MΩ On the other hand, assuming that the low resistance portion of the backup roll 14b is located at three places upstream, the resistance in the downstream D direction is RD, the resistance in the upstream U direction is RU, and the total resistance Rt2 is become that way.

RD = (5.4 cm × 1000 MΩ) ÷ 3
0 cm = 180 MΩ RU = (3.3 cm × 100 MΩ) ÷ 30 cm + (0.
1 cm × 1000 MΩ) ÷ 30 cm = 14.3 MΩ Rt2 = (180 MΩ × 14.3 MΩ) / (180 MΩ +
14.3 MΩ) = 13.2 MΩ The total resistance R1 of the secondary transfer means 14 is as follows. R1 = Rt1 + Rp + Rbelt + Rbtr = 36.6 MΩ Therefore, when the contact roll 14c is displaced by 1 cm upstream from the equal position, the backup roll 14b rotates, and the low-resistance portion moves upstream and downstream of the contact roll 14c. The fluctuation of the secondary transfer total current when it is present on the side is as follows.

If the standard total secondary transfer current is 20 μA, the standard secondary transfer voltage Vs is as follows. Vs = {(Rt1 + Rt2) / 2 + Rp + Rbelt + Rbtr} × 20 μA = 1073V The standard secondary transfer voltage Vs = 1073V was applied to the contact roll 14c when the contact roll 14c was shifted 1 cm upstream from the above-mentioned even position. Sometimes, the total secondary transfer current I1 when three low resistance portions are present downstream of the contact roll 14c and the total secondary transfer current I2 when three low resistance portions are present upstream are obtained as follows. Become. I1 = 1073V ÷ 70.6 MΩ = 15.19 μA I2 = 1073V ÷ 36.6 MΩ = 29.3 μA Therefore, the secondary transfer total currents I1 and I2 are 15.19.
変 動 29.3 μA.

The same as above is performed for the contact roll 1
4c, the moving distance to the upstream side was changed to 0, 1, 2, and 3 cm, and the number of low resistance portions was changed to 1, 2, 3, and 4 places. FIG. 3 summarizes the fluctuations of I1 and I2.

Based on the above calculation results, an experiment of secondary transfer was performed using an actual apparatus. As a result, the case where the distance of movement of the contact roll 14c to the upstream side was 1 cm and the number of low resistance portions was up to two was acceptable. Although it was within the range of possible transfer unevenness (OK), it was out of the allowable range (N
G). In addition, the moving distance of the contact roll 14c to the upstream side was 2 cm, and was within the allowable range of transfer unevenness when the low resistance portion was one place, but was within the allowable range when the low resistance part was more than two places. Went outside. Further, when the moving distance of the contact roll 14c to the upstream side was 3 cm or more, the transfer unevenness was out of the allowable range even in one low resistance portion.

From the above, the backup roll 14
The total secondary transfer current when b rotates once is 17 to 24 μA
It has been clarified that transfer unevenness can be tolerated within the range of the variation.

In the above description, as shown in FIG. 2, a voltage was applied from the power supply 16 to the contact roll 14c, and the secondary transfer device 14 was used in which the transfer roll 14a was grounded. The present invention is not limited to this, and the same effect can be obtained even when the present invention is used in a secondary transfer device configured to ground the contact roll 14c and apply a power supply voltage to the transfer roll 14a.

[0032]

As is apparent from the above description, according to the present invention, even if the secondary transfer of a sheet smaller in size than the sheet of the maximum standard size, an excessive amount of paper is caused between the secondary transfer roll and the backup roll. Even if a large current does not flow and the surface resistance of the backup roll in the circumferential direction is uneven, the total transfer current can be kept within an allowable value. For this reason, there is an effect that defects such as damaging the intermediate transfer member and causing transfer failure can be eliminated or reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a schematic configuration of an image forming apparatus to which the present invention is applied.

FIG. 2 is an enlarged explanatory view of a secondary transfer unit.

[FIG. 3] A contact roll is shifted by 0 to 3 cm to the upstream side, and a low resistivity portion is set to 1 to 3 on a backup roll.
FIG. 7 is a diagram illustrating a change in the total transfer current when the rotation is provided at some locations.

FIG. 4 is a schematic configuration diagram of an image forming apparatus having a conventional secondary transfer device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoreceptor, 2K, 2Y, 2M, 2C ... Developing device, 3 ... Charging device, 4 ... Exposure device, 5 ... Density measuring device, 11 ... Intermediate transfer body, 12 ... Drive roll, 13 ... Primary transfer means, 14
.. Secondary transfer member, 14a transfer roll, 14b backup roll, 14c contact roll, 15 ammeter, 16 power supply, 17 detection sensor, 19 image writing signal transmission marker.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tsuyoshi Dobata 3-7-1, Fuuchi, Iwatsuki-shi, Saitama Prefecture Fuji Xerox Co., Ltd. (72) Masao Kimura 3-7-1, Fuuchi, Iwatsuki-shi, Saitama Prefecture Fuji Xerox Co., Ltd.

Claims (4)

[Claims] 1. An intermediate transfer member, a backup roll having a semiconductive surface for supporting the intermediate transfer member from the back surface thereof, and a secondary transfer roll disposed opposite to the backup roll with the intermediate transfer member interposed therebetween. And a means for measuring a current flowing through the backup roll, the intermediate transfer body and the secondary transfer roll, and a secondary transfer device for secondary-transferring the primary transfer toner image held on the intermediate transfer body onto a recording medium. A contact roll that is in electrical contact with the backup roll; and means for applying a voltage to one of the contact roll and the secondary transfer roll at the time of secondary transfer. Is located at a position where the fluctuation range of the secondary transfer total current when rotating is within the expected current range where transfer unevenness does not occur. Secondary transfer device. 2. The secondary transfer device according to claim 1, wherein the predetermined current range of the total secondary transfer current is 17 to 24 μA.
A secondary transfer device, characterized in that: 3. The secondary transfer device according to claim 1, wherein the contact roll has a peripheral surface distance on one side and a peripheral surface distance on the other side up to a contact point between the backup roll and the secondary transfer roll. Are disposed at substantially equal positions. 4. The secondary transfer device according to claim 1, wherein the backup roll is covered with a semiconductive thin tube.