JPH10207260A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the toner restraint of a paper in an image forming device constituted so that a transfer roll is used also as the carrying roll of the paper. SOLUTION: The image forming device is provided with a first photoreceptor 50a, the first transfer roll 60a, a second photoreceptor 50b and the second transfer roll 60b along the carrying path of the paper 10. Then, the toner image of a first color is transferred on the paper 10 by the first photoreceptor 50a and the first roll 60a and the paper 10 is carried toward the second photoreceptor 50b by a chute 7O. An electrode member 100 made of a non- insulating material is disposed on the chute 70 and potential is impressed on the back surface of the paper 10 by a power source 120. Thus, since the restraint of toner on the paper 10 whose dielectric constant is low is enhanced by the potential, the toner is prevented from being returned to the photoreceptor side.

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 having a plurality of image forming units disposed along a recording paper transport path.

[0002]

2. Description of the Related Art An apparatus for transferring a recording sheet between the photosensitive drum and a toner image on the photosensitive drum and transferring the toner image onto the recording sheet is provided with a photosensitive drum and a transfer roll facing the photosensitive drum. Are known. In this type of apparatus, the transfer roller has two functions of conveying the recording paper and transferring the toner image. This type of apparatus is disclosed in, for example,
No. 165,376.

[0003]

However, when multiple transfer of a multicolor toner image is performed using only a transfer roll, the dielectric constant of the paper itself is low, so that the toner of the paper between the transfer units is low. The so-called retransfer occurs in which the binding force is reduced and the toner on the paper returns to the photoconductor side, which causes problems such as a decrease in transfer efficiency and a decrease in image density. The present invention provides an image forming apparatus that solves the above-described problem.

[0004]

An image forming apparatus according to the present invention is provided with a plurality of image forming units disposed along a recording paper transport path and a photoconductor of each image forming unit. A transfer roll that also serves as a transfer roll for the recording paper, and is provided at a position in contact with the back side of the recording paper in the recording paper transport path between the image forming units and has a width at least equal to or greater than the width of the recording paper. It comprises an insulative electrode member and means for applying a voltage to the electrode member.

[0005] The disposition position of the non-insulating electrode member is as follows:
A means for applying a voltage to the electrode member, which is in the vicinity of a transfer electric field effective area formed by the photoconductor and the transfer roll, is a conductive member that contacts the transfer roll and transmits a voltage applied to the transfer roll to the electrode member. It is something that is. Further, the plurality of non-insulating electrode members may have a volume resistivity that increases toward the downstream side of the recording paper, and may include a unit in which the same voltage is applied to all the electrode members. The non-insulating electrode member has the same volume resistivity, and the means for applying a voltage to the electrode member may be a means for applying a higher voltage toward the downstream side of the recording paper.

[0006]

FIG. 1 is an explanatory view showing an outline of an image forming apparatus to which the present invention is applied. The image forming apparatus indicated by reference numeral 1 is provided with a paper tray 5, takes out the paper 10 from the tray 5 by a feed roll 6, and transports the rolls 20 and 2.
The paper is sent out to the transfer device side by 2.

The image forming unit 40 has four process units 40a, 40b, 40c, and 40d. Each unit for forming a yellow, magenta, cyan, and black toner image is an optical system including a rotary polygon mirror. 42a,
42b, 42c, 42d, and four photoconductors 50a,
The electrostatic latent images are written on 50b, 50c, and 50d. The first latent image on the first photoconductor 50a is developed by the developing unit 52a, and the recording paper 1 is moved by the first transfer roll 60a.
0. The toner image on the second photoconductor 50b is stacked on the first toner image by the second transfer roll 60b, and the toner images of each color are overlapped by the third transfer roll 60c and the fourth transfer roll 60d. Can be A chute 70 is provided between the transfer rolls. The recording paper that has passed through the transfer device is sent to the fixing device 80, where a full-color image is formed.

FIG. 2 is a perspective view showing a first embodiment of the present invention, and FIG. 3 is a sectional view. The toner image is transferred to the paper 10 sent along the arrow by the unit of the photoconductor 50 a and the transfer roll 60 a located on the upstream side, and guided by the chute 70 to the next photoconductor 50 b and the transfer roll 6.
The toner image is conveyed to the unit No. 0b, and the next color toner image is multiplex-transferred. Since the sheet 10 has a low dielectric constant, the toner binding force on the sheet is reduced during the conveyance, causing a problem that the toner on the sheet returns to the photoconductor side.

In this embodiment, a non-insulating electrode member 100 is provided on a chute 70. The non-insulating electrode member 100 is a plate-shaped member made of a material such as PVDF, nylon, or polycarbonate, and has a width corresponding to at least the width of a sheet. Among these materials, in particular, the volume resistivity is 10 5 to 10 13
It is desirable to have an electric resistivity of the power of Ωcm. The line 11 is connected to the non-insulating electrode member 100.
0, for example, a voltage of about 1000 V DC is applied by the power supply 120. When the paper 10 passes over the electrode member 100 to which the voltage is applied, the binding force of the toner on the paper is given to prevent the toner on the paper from returning to the photoconductor side.

FIGS. 4A and 4B show examples of the positions where the non-insulating electrode members 100 are disposed. Between the photosensitive member 50 and the transfer roller 60, the transfer electric field effective area L ₁ is a nip for transferring the toner T on the photosensitive member 50 on the sheet 10 is formed. In the (A) in the figure, in which the non-insulated electrode member 100a is disposed near the upstream side than the transfer field effective area L _1. FIG. 6B shows the transfer electric field effective area L
₁ , a non-insulating electrode member 100b is disposed near the downstream side. In any configuration, the binding force of the transfer toner on the sheet 10 is improved.

FIG. 5 shows a sectional view of another embodiment of the present invention. In this apparatus, a non-insulating electrode member 200 is disposed on a chute 70 downstream of the photoconductor 50a and the transfer roll 60a. Then, a structure is employed in which one end 210 of the electrode member 200 is brought into contact with the transfer roll 60a. A transfer voltage of, for example, about 700 V is applied to the transfer roll 60a, and a current of about 2 μA flows. Then, the electrode member 200 receives this voltage from the transfer roll 60a and increases the toner binding force of the paper 10.

FIG. 6 shows still another embodiment of the present invention. In this apparatus, three electrode members 300a and 300 are mounted on a chute 70 connecting the four image forming units.
b, 300c are provided. The three electrode members are connected in parallel to a power supply 320 via a line 310.
For example, the power supply 320 is an 800 V DC power supply. The first electrode member 300a is made of a material having a volume resistivity of, for example, 10 8 Ωcm. Second electrode member 3
00b is made of, for example, a material having a resistivity of 10 8.5 Ωcm. Then, the third electrode member 300c
Is made of a material having a resistivity of, for example, 10 9 Ωcm. With this configuration, as the sheet is transported downstream, the potential of the sheet increases, and the toner binding force is increased.

FIG. 7 shows still another embodiment of the present invention. In this apparatus, three non-insulating electrode members 400 are mounted on the chute 70 disposed between the four image forming units.
a, 400b, 400c. Each electrode member is
For example, they are made of the same material having a volume resistivity of 10 10 Ωcm. Each electrode is connected to a separate power supply. The first electrode 400a arranged at the most upstream is
A first power supply 412 is connected via a line 410.
The first power supply 412 applies a voltage of, for example, 800 V to the first electrode 400a.

The second electrode 400b is connected to the second electrode 422 via a line 420. Second power supply 422
Applies, for example, a voltage of 900 V to the second electrode 400b. Third electrode 400c is connected to third power supply 432 via line 430. The third power supply 432 applies, for example, a voltage of 1000 V to the third electrode 400c. With this configuration, as the sheet is transported downstream, a higher potential is applied to the sheet, and the binding force of the toner is increased.

[0015]

As described above, the present invention relates to an image forming apparatus for transferring a toner image to a recording sheet and transporting the sheet by using a plurality of photosensitive members and transfer rolls disposed opposite to the photosensitive members. In this case, a potential is applied to the sheet between the transfer rolls from the back side to enhance the toner binding force. Therefore, the return phenomenon of the toner on the paper is prevented, and the effect of improving the image quality can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a perspective view showing an embodiment of the present invention.

FIG. 3 is a sectional view showing an embodiment of the present invention.

FIG. 4 is an enlarged view of a main part of the present invention.

FIG. 5 is a sectional view showing another embodiment of the present invention.

FIG. 6 is a sectional view showing still another embodiment of the present invention.

FIG. 7 is a sectional view showing still another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Image forming apparatus, 5 Paper tray, 10 Recording paper, 40a-40d image forming unit, 50a-5
0d photoreceptor, 60a-60d transfer roll, 10
0 Non-insulating electrode member, 120 power supply.

Claims (5)

[Claims] An image forming apparatus includes: a plurality of image forming units disposed along a recording paper conveyance path; and a transfer roll serving also as a recording paper conveyance roll disposed to face a photosensitive member of each image forming unit. An image forming apparatus, wherein a non-insulating electrode member having a width dimension at least equal to or greater than the width dimension of the recording paper, which is disposed at a position in contact with the recording paper back surface of the recording paper transport path between the image forming units, Means for applying a voltage to the electrode member. 2. The image forming apparatus according to claim 1, wherein the disposition position of the non-insulating electrode member is near a transfer electric field effective area formed by the photoconductor and the transfer roll. 3. The image forming apparatus according to claim 1, wherein the means for applying a voltage to the electrode member is a conductive member that contacts the transfer roll and transmits a voltage applied to the transfer roll to the electrode member. 4. The image according to claim 1, wherein the plurality of non-insulating electrode members have a volume resistivity that increases toward the downstream side of the recording paper, and the same voltage is applied to all the electrode members. Forming equipment. 5. The non-insulating electrode member has the same volume resistivity, and the means for applying a voltage to the electrode member applies a higher voltage toward the downstream side of the recording paper.
The image forming apparatus as described in the above.