JPH03192278A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent toner from scattering when secondary transfer is performed and to improve the quality of an image by arranging a means for impressing a voltage having a polarity reverse so that of the toner on the back side of a transfer bolt where the transfer belt and a transfer sheet start to come into contact with each other on the upstream side from a secondary transfer position in a transfer belt moving direction. CONSTITUTION:The transfer belt 5 is constituted of a semiconductor belt provided with a volume resistivity nearly equal to that of the transfer sheet S, and the means 11 for impressing the voltage having the polarity reverse to that of the toner T is arranged on the back side of the transfer belt 5 where the transfer belt 5 and the transfer sheet S start to come into contact with each other on the upstream side from the secondary transfer position in the transfer belt 5 moving direction. Then, the toner T is electrostatically attracted on the transfer belt 5, so that the toner T can be prevented from being transferred on the transfer sheet S by means of mechanical contact, and also, the transfer sheet S can be moved to the secondary transfer position in a state that the transfer sheet S is electrostatically attracted on the transfer belt 5 and the transfer sheet S and the transfer belt 5 are made to come into tight contact with each other. Thus, the toner can be prevented from scattering when the secondary transfer is performed, and the quality of the image can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image forming apparatus, and particularly to an image forming apparatus using a transfer belt.

(Prior Art) Image forming apparatuses have heretofore been known in which a toner image formed on a photoconductor is primarily transferred onto a transfer belt, and the toner image on the transfer belt is secondarily transferred onto transfer paper. ing. As the transfer belt, a dielectric type is used, in which a thin dielectric layer having a high volume resistance is formed on the surface of a conductive layer having a low volume resistance as much as possible.

(Problems to be Solved by the Invention) By the way, in an image forming apparatus using a transfer belt as described above, toner scattering occurs during secondary transfer from the transfer belt to transfer paper, resulting in poor image quality. The problem was that there was no.

The cause of this scattering is that, as shown in Figure 3, when the transfer belt (V) and the transfer paper S do not come into close contact with each other and there is a gap δ between them, the toner T on the transfer belt (V) moves toward the transfer paper S. This is thought to be caused by irregular transcription as shown by the arrows.

Therefore, measures such as installing a pressure roller that presses the transfer paper S against the transfer bell (V) or increasing the positional accuracy of the pre-transfer guide plate can be considered, but the pressure roller has the problem of dirt.
There is a problem in that the effect of improving the positional accuracy of the pre-transfer guide plate is uncertain.

In view of the above-mentioned conventional problems, an object of the present invention is to provide an image forming apparatus that can reliably prevent toner from scattering during secondary transfer from a transfer belt to a transfer paper, and can obtain high-quality images. .

(Means for Solving the Problems) In order to achieve the above object, the image forming apparatus of the present invention primarily transfers a toner image formed on a photoreceptor onto a transfer belt, and transfers the toner image on the transfer belt. In an image forming apparatus that performs secondary transfer onto transfer paper, the transfer belt is composed of a semiconductor belt having a volume resistance such as between the transfer paper and the path, and the transfer belt is formed on the upper side in the direction of movement of the transfer belt than the secondary transfer position. The present invention is characterized in that means for applying a voltage having a polarity opposite to that of the toner is provided on the back side of the transfer belt at the position where the transfer belt and the transfer paper start contact.

(Function) According to the above structure of the present invention, since the transfer belt is made of a semiconductor belt, unlike a dielectric belt, an electric field can be applied from the back side to the front side, and this characteristic can be utilized. By applying a voltage of opposite polarity to the toner from the back side of the transfer belt at the position where the transfer belt and the transfer paper start contact, the toner is electrostatically attracted to the transfer belt and transferred to the transfer paper through mechanical contact. In addition to preventing the toner from being transferred, the transfer paper can be electrostatically attracted to the transfer belt and moved to the secondary transfer position in close contact with each other, thereby preventing the toner from flying away at the secondary transfer position. The toner image can be transferred to the transfer paper without any generation.

(Example) An example of the present invention will be described below with reference to FIGS. 1 and 2.

In FIG. 1, reference numeral 1 denotes a photosensitive drum, around which a charger 2, an exposure section 3 using an optical system (not shown), a developing section 4, a transfer belt 5, a drum cleaner 6, and an eraser 7 are arranged in the rotational direction. has been done. The developing section 4 includes:
A yellow developer 4Y, a magenta developer 4M, a cyan developer 4C, and a black developer 4B are installed. Further, each developing device is equipped with a developing sleeve, a grain cutting shutter, a toner concentration detector, a toner replenishing device, and the like.

The transfer belt 5 is made of a flexible semiconductor with good environmental resistance, for example, a volume resistivity of 1 x 1010 to 1 x 10'3 Ω-
1x1 on the surface of a polyurethane rubber belt of about CIIl
It is composed of an endless belt with a thickness of about 600 μm and a surface coat layer of 10 to 30 μm thick formed by applying a fluorine-based paint of about 0.9 to 1×10 12 Ω-cm.

On the inner periphery of the transfer belt 5, there is a 1 which transfers the toner image from the photoreceptor drum 1 to the transfer belt 5 along the moving direction of the transfer belt 5.
Next transfer charger 8, drive roller 9, tension roller lO1, bias roller 11 connected to an application power supply 12 so as to apply a voltage of opposite polarity to the toner from the back side of the transfer belt 5, and a pair of rollers 13 with at least one side grounded. The conductive belt 14 is wound around the conductive belt 14, the backup roller 16 supports the transfer belt 5 at a cleaning position for scraping off the toner remaining on the surface of the transfer belt 5, and the rollers are disposed on both sides of the primary transfer charger 8 and at other appropriate positions. A guide roller 17 is provided. A secondary transfer charger 18 and a separation charger 19 are arranged on the outer periphery of the transfer belt 5, facing the conductive belt 13, and a belt cleaner 15 is arranged facing the backup roller 16 at the cleaning position. There is.

Reference numeral 20 denotes a paper feed cassette, 21 and 22 a paper feed roller and a separating plate that take out the transfer paper S one by one from the paper feed cassette 20 and supply it to the secondary transfer position between the transfer belt 5 and the secondary transfer charger 17; 23 is a registration roller that sends out the transfer paper S to the secondary transfer position in a timely manner, 24 is a transfer paper conveyance belt that conveys the transfer paper S after the secondary transfer toward the fixing section 25, and 25a has a built-in heater. The fixing roller 25b is a pressure roller that presses the transfer paper S against the fixing roller.

Next, the operation will be explained.

First, an overview of the process of forming a monochrome image will be explained. The photosensitive drum 1 is charged by a charging charger 2 and exposed by an exposure section 3 using an optical system (not shown) to form an electrostatic latent image. This latent image is developed with toner in the developing section 4. The developing devices used at this time are yellow developing device 4Y,
Any one of the magenta developer 4M, the cyan developer 4C, and the black developer 4B is selected. The toner image on the photosensitive drum 1 is transferred onto the transfer belt 5 by a primary transfer charger 8. Thereafter, the photosensitive drum 1 is cleaned by a drum cleaner 6, residual potential is removed by an eraser 7, and the same process is repeated again.

The toner image transferred to the transfer belt 5 is transferred to the transfer paper S which is sent in synchronization with the toner image by the secondary transfer charger 18.
The image is transferred to the fixing unit 25, fixed by the fixing unit 25, and then discharged. The transfer belt 5 after the secondary transfer is cleaned by the belt cleaner 15, and the same process is repeated again.

Next, an overview of the process of forming a full-color image will be explained. Through the same process as for monochrome images,
A yellow toner image is formed on the photosensitive drum 1 and transferred onto the transfer belt 5.

Then, while being supported on the transfer belt 5, it goes around once again and returns to the primary transfer position. At this time, paper is not fed and 2
The next transfer charger 18 and the separation charger 19 are not operated, and the belt cleaner 15 is also retracted from the transfer belt 5.

A magenta toner image is formed on the photosensitive drum 1 in synchronization with the yellow toner image on the transfer belt 5, and is transferred onto the transfer belt 5 in an overlapping manner.

Similarly, a cyan toner image and a black toner image are transferred onto the transfer belt 5 in an overlapping manner, and a full-color toner image is formed on the transfer belt 5, which is transferred onto the transfer@S by the secondary transfer charger 18 and fixed. and discharged. Further, residual toner that has not been transferred to the transfer paper S is cleaned by a belt cleaner I5.

In the case of two colors or three colors, an image is formed by the same operation.

In the image forming process as described above, the transfer belt 5
At the time of secondary transfer in which the toner image is transferred from the toner image to the transfer paper S, as shown in part A of FIG. Since a voltage of opposite polarity to the toner T is applied to the back side of the belt 5 by the bias roller 11, the transfer belt 5
The upper toner T is electrostatically attracted, the toner image is not transferred by mechanical contact with the transfer paper S, and the transfer paper S is electrostatically attracted to the transfer belt 5 and moved to the secondary transfer position. The transfer belt 5 and the transfer paper S are moved at part B in FIG.
By performing the transfer in the secondary transfer charger 1 day while the toner T is in close contact with the toner T, the toner T is transferred without scattering, and a high-quality image is formed on the transfer paper S.

Furthermore, since a grounded conductive belt 14 is disposed on the back side of the transfer belt 5 at the secondary transfer position, this conductive belt 14 is connected to the transfer charger 18 and the separation charger 19.
functions as a counter electrode, ensuring high transfer efficiency.

(Effects of the Invention) According to the image forming apparatus of the present invention, as is clear from the above description, a voltage of polarity opposite to that of the toner is applied from the back side of the transfer belt at the position where the transfer belt and the transfer paper start contact. By doing this, the toner is not electrostatically attracted to the transfer belt and transferred to the transfer paper through mechanical contact, and the transfer paper is electrostatically attracted to the transfer belt and remains in close contact with the transfer belt until it reaches the secondary transfer position. Because the toner moves, toner scattering does not occur during secondary transfer, and a high-quality image can be obtained.

[Brief explanation of drawings]

1 and 2 show an embodiment of the image forming apparatus of the present invention, FIG. 1 is an overall schematic configuration diagram omitting the optical system, and FIG.
The figure is an enlarged view of the main part, and FIG. 3 is an explanatory diagram of the toner scattering phenomenon during secondary transfer. 1--...---------------------------]-
・Transfer belt 8・・・・・・・・・・・・・・・・・・・・・
...Primary transfer charger 11...
−・・・・・・・・・・・・Bias roller 1

Claims (1)

[Claims] (1) In an image forming apparatus that primarily transfers a toner image formed on a photoreceptor onto a transfer belt, and secondarily transfers the toner image on the transfer belt onto transfer paper, the transfer belt is used as the transfer paper. It is composed of a semiconductor belt having approximately the same volume resistance, and has a polarity opposite to that of the toner on the back side of the transfer belt at the position where the transfer belt and the transfer paper start contact on the upper side in the direction of movement of the transfer belt than the secondary transfer position. 1. An image forming apparatus characterized in that an image forming apparatus is provided with means for applying a voltage of .