JPH04138483A - Image forming device - Google Patents

Abstract

PURPOSE:To correct the electrostatically charged quantity of the toner transfered primarily to an intermediate transfer body and to prevent the reduction of the retransfer and transfer efficiencies to the electrostatic latent image carrier of the toner by providing an AC corona discharging means and a DC corona discharging means between a primary transfer means and a secondary transfer means. CONSTITUTION:In an inside of an intermediate transfer belt 5, a primary transfer charger 6 is arranged at a position opposed to a photosensitive drum 1. Also on an upper stream side of the secondary transfer charger 25, an AC charger 16, CD charger 17 are disposed by opposing to the intermediate transfer belt 5. Further, AC voltage is applied on the charge wire of the AC charger 16 and AC corona discharge is applied to a toner image on the intermediate transfer belt 5. Besides, the DC charger 17 applies DC corona discharge with the same polarity as the charge polarity of the toner against a toner image on the intermediate transfer belt 5. Hence the retransfer of the toner from the intermediate transfer body 5 to the electrostatic latent image carrier 1 is prevented, the transfer efficiency is enhanced and the improvement of color balance of the color image and the reduction of the waste toner are contrived.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus using a toner image transfer type electrophotographic method.

After the toner image carried on the photoconductor (electrostatic latent image carrier) is firstly transferred to the intermediate transfer member using the conventional electrophotographic method, the toner image is transferred secondarily from the intermediate transfer member to the transfer material. In image forming apparatuses that perform image transfer, image noise such as density unevenness and white spots occurs during secondary transfer from an intermediate transfer body to a transfer material. This is because the amount of charge on the toner increases during the primary transfer from the photoreceptor to the intermediate transfer member. In order to correct such an increase in the amount of charge of the toner, the present inventors attempted to apply AC corona discharge to the toner image primarily transferred onto the intermediate transfer member, and as a result, the image noise was reduced. It decreased significantly, and the transfer efficiency to the transfer material also increased. Note that Japanese Patent Publication No. 62-36220 discloses a method for eliminating surface charges on the intermediate transfer member immediately after primary transfer.

However, simply applying AC corona discharge to the intermediate transfer member does not allow the toner image on the intermediate transfer member to come into contact with the photoreceptor surface again (to create a full color image, multiple primary transfers are required). (needs to be repeated several times)
, a problem occurred in that part of the toner image was retransferred to the photoreceptor. This is considered to be because part of the toner was reversely polarized due to the application of AC corona discharge.

OBJECTS, STRUCTURE, AND WORK OF THE INVENTION Accordingly, an object of the present invention is to prevent retransfer of toner from an intermediate transfer member to an electrostatic latent image carrier, increase transfer efficiency, improve color balance of color images, and reduce waste toner. It is an object of the present invention to provide an image forming apparatus that can reduce the amount of paper used.

In order to achieve the above object, the image forming apparatus according to the present invention includes an AC corona discharge means between the primary transfer means and the secondary transfer means, and a connection between the AC corona discharge means and the secondary transfer means. A DC corona discharge means was provided in between. The DC corona discharge means applies DC corona discharge having the same polarity as the charged polarity of the toner to the toner image immediately after the AC corona discharge has been applied.

The toner image supported on the electrostatic latent image carrier is transferred (primary transfer) to the intermediate transfer member by corona discharge, which has a polarity opposite to the toner charging polarity discharged from the primary transfer means [Fig.
b) Reference. The primary transferred toner image is first subjected to AC corona discharge by an AC corona discharge means. The amount of charge on the toner image increases slightly during the primary transfer, but the amount of charge returns to the original amount with AC corona discharge and some of the charge (especially on the surface layer) increases.
is charged with opposite polarity [see Figure 4(c)]. This toner image is further applied with DC corona discharge having the same polarity as the charged polarity of the toner by a DC corona discharge means.

As a result, the reverse polarity layer of the toner image is neutralized (see FIG. 4(d)).

In color copy mode, the above steps are repeated multiple times, and the final colored toner image is transferred from the intermediate transfer member by corona discharge, which has a polarity opposite to that of the toner charged from the secondary transfer charger. Transfer to material (secondary transfer)
be done.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an image forming apparatus according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a full-color copying machine which is an embodiment of the present invention.A photosensitive drum 1, which can be rotated in the direction of arrow a, is surrounded by a charger 2, developing devices 4Y, 4M, and 4C.
, 4B, an intermediate transfer belt 5, a residual toner cleaning device 7, and a residual charge elimination lamp 8 are arranged.

A light image from a document placed on a document table glass (not shown) is irradiated onto the photosensitive drum 1 from the direction of the arrow by an optical system (not shown).

The developer 4Y contains yellow toner, the developer 4M contains magenta toner, the developer 4C contains cyan toner, and the developer 4B contains black toner, each of which can be selectively driven.

The intermediate transfer belt 5 includes rollers 10.11.12.13.
14 in an endless manner, and rotates in the direction of arrow C at the same speed as the photosensitive drum 1 based on the rotation of the drive roller 11. This intermediate transfer belt 5 has a volume resistance of lXl0IO
-Polyurethane rubber or EP of about lx1013Ωcm
DM (a terpolymer obtained by ternary polymerization of ethylene, propylene, and diene components) is shaped into a belt with a thickness of about 600 μm, and a fluorine-based water-based paint with a volume resistance of about 1×10 9 to 1×10 12 Ωeln is applied to the surface to a thickness of about 10 to 30 μm. The product that has been coated with smoothness and toner releasability has been used.

The roller 10 functions as a counter electrode for secondary transfer, which will be described below. A primary transfer charger 6 is installed inside the intermediate transfer belt 5 at a position facing the photosensitive drum 1 . Further, around the intermediate transfer belt 5, a secondary transfer charger 25 and an AC separation charger 26 are provided.
is installed facing the electrode roller 10, and a residual toner cleaning device 15 is installed facing the backup roller 13.

Furthermore, in this embodiment, the secondary transfer charger 25
An AC charger 16 and a DCC charger 1 are installed on the upstream side of the transfer belt 5, facing the intermediate transfer belt 5. In this embodiment, the AC charger 16 applies an AC voltage of 5 kV to its charge wire, and applies AC corona discharge to the toner image on the intermediate transfer belt 5. DC charger 1
Reference numeral 7 is for applying a DC corona discharge having the same polarity as the charge polarity of the toner to the toner image on the intermediate transfer belt 5, and in this embodiment, a DC voltage of 5 kV is applied to the charge wire.

On the other hand, the transfer paper S is fully accommodated in an automatic paper feed cassette 20 that can be attached to and detached from the copying machine, and as the paper feed roller 21 rotates in the direction of the arrow d, the paper S is separated by the action of the separating plate 22 that presses against the paper feed roller 21. The sheets are separated one by one and fed to the secondary transfer section. The transfer paper conveyance path includes various guide plates and timing roller pairs 23.
, a conveyor belt 27, and a fixing device 28.

In the above configuration, in monochrome copy mode,
A negative charge is uniformly applied to the surface of the photoreceptor drum 1 by charges 2 to 2, and an electrostatic latent image is formed by irradiating the original image from an optical system (not shown). This electrostatic latent image is transferred to developing devices 4Y and 4M.

The toner image is developed with toner positively charged by a preselected one of 4C and 4B, and the toner image is transferred onto the intermediate transfer belt 5 by an electric field formed by negative charges emitted from the primary transfer charger 6. The first transfer is made to The toner image primarily transferred onto the intermediate transfer belt 5 is first transferred to the AC
AC corona discharge is applied in the charger 16, and then,
In the DC charger 17, D is charged with the same polarity as the charging polarity of the toner.
C corona discharge is applied. Note that changes in the charged state of the toner due to such corona discharge will be described in detail later. Thereafter, the toner image is secondarily transferred onto the transfer paper S by an electric field formed by negative charges emitted from the second transfer charger 25. Transfer paper S after secondary transfer is A
The charge is removed by the AC electric field formed by the C separation charger 26, and the belt is peeled off from the intermediate transfer belt 5 and transferred to the fixing device 28.
After the toner is heated and fixed, it is discharged to a tray (not shown).

On the other hand, in full-color copy mode, the original image is separated into yellow, magenta, cyan, and black images by the optical system, and each image is formed as an electrostatic latent image on the surface of the photoreceptor drum 1. , developing devices 4Y, 4M, 4C, having corresponding color toners,
4B, the images are sequentially primary transferred onto the intermediate transfer belt 5, and the images are superimposed. At this time, the toner image primarily transferred onto the intermediate transfer belt 5 is
16 and DC charger 17, AC corona discharge and DC corona discharge are applied to adjust the amount of charge on the toner. Note that changes in the charged state of the toner due to such corona discharge will be described in detail later.

While color toner is being superimposed on the intermediate transfer belt 5, the transfer paper S is not fed, and the secondary transfer charger 25 and the separate Chill-G! ! 26 also remains off. Further, the cleaning device 15 also stops its toner scraping action. When the four types of toner images are superimposed on the intermediate transfer belt 5, the transfer paper S is fed, the secondary transfer charger 25 and the separation charger 26 are turned on, and the full color toner images are secondarily transferred onto the transfer paper S. Ru.

Next, changes in the charged state of toner based on the application of corona discharge from the AC charger 16 and the DCC charger 1 will be explained.

Here, for comparison, a case in which nothing is applied to the primary transferred toner and a case in which only an AC corona discharge is applied will be explained.
The case where C corona discharge is applied will be explained.

First, with reference to FIG. 2, a case will be described in which nothing is applied to the primarily transferred toner.

The toner Ta deposited on the photosensitive drum 1 is first transferred onto the intermediate transfer belt 5 by negative DC corona discharge from the primary transfer charger 6 .

At this time, the amount of charge of the toner Ta increases slightly [see FIGS. 2(b) and 2(c)]. Some of the toner Ia' remains on the photosensitive drum 1, and this residual toner Ta' can be removed by the cleaning device 7. Next, when the second color toner Ib is primarily transferred onto the intermediate transfer belt 5, the amount of charge of the toner Ia already transferred onto the intermediate transfer belt 5 further increases [FIG. 2(e), (f)]. Here, when the secondary transfer to the transfer paper S is performed, the toner Ia,
Tb is transferred onto the transfer paper S [see Figure 2 (g>).

The amount of transferred toner Ia, Ib is approximately inversely proportional to the amount of charge,
Overall, the transfer efficiency is poor, and toners Ia'' and Tb'' remain on the intermediate transfer belt 5. Moreover, a difference occurs in the amount of transfer, and color shift occurs due to this difference. At the same time, white spots occur in the toner Ta portion.

FIG. 3 explains the case where only AC corona discharge is applied to the primary transferred toner.

Here, AC corona discharge is applied to the toner Ia primarily transferred onto the intermediate transfer belt 5 by the ACC charger 1. Then, the surface layer of the toner Ta is charged to the opposite polarity [see FIG. 3(c)]. Next, the second color toner T
When toner b is primarily transferred onto the intermediate transfer belt 5, the surface layer (reverse polarity layer) of the toner Ta that has already been primarily transferred is retransferred onto the photoreceptor drum 1, and the toner Ta is transferred onto the intermediate transfer belt 5.
The amount of toner Ta on the top decreases. However, the amount of charge on the toner Ta returns to the same amount as during the original primary transfer. Furthermore, for the toner 1a + Ib, the AC charger 16
A corona discharge is applied, and each surface layer is partially charged to the opposite polarity [see FIG. 3(f)]. Here, when the secondary transfer is performed by DC corona discharge from the secondary transfer charger 25, the toners Ia and Tb are transferred to the transfer paper S with good transfer efficiency, and image noise such as white spots is also reduced. See Figure 3 (g)]. However, the problem that the surface layer of toner Ta is retransferred to the photoreceptor drum 1 [see FIG. 3(e)] causes a difference in the amount of transfer, resulting in color misregistration, which has not been completely resolved.

FIG. 4 shows an embodiment of the present invention, in which a DC corona discharge is applied to the primary transferred toner in addition to an AC corona discharge.

In addition to AC corona discharge by ACC chiller 16, D
D with the same polarity as the charging polarity of the toner by the C charger 17
When C corona discharge is applied, the charges of opposite polarity on the surface layer of the toner Ia disappear [see FIG. 4(d)]. Thereafter, when the second color toner Tb is primarily transferred onto the intermediate transfer belt 5, the toner Ia is not retransferred onto the photosensitive drum 1 [see FIG. 4 (f>)]. Toner Ta+
AC corona discharge and DC corona discharge are applied to Ib, and the amount of charge of toner Ta and Ib is adjusted [4th
(see FIGS. 4(g) and 4(h)), the amount of charge on the toners Ta and Tb after application of the DC corona discharge is equal, and is approximately equal to the amount of charge on the photoreceptor drum 1 shown in FIG. 4(a). Here, when the secondary transfer is performed, the toners Ta and Tb are transferred to the transfer paper S with good transfer efficiency, and there is no difference in the transfer amount between the toners Ia and Ib [see Fig. 4 (i)]. There will be no color shift. Of course, the toner Ta that has already been primarily transferred onto the intermediate transfer belt 5 is not partially retransferred to the photoreceptor drum 1 during color overlapping in the primary transfer. Therefore, as a whole, the photoreceptor drum 1 and the intermediate transfer belt 5
There is less toner remaining in the toner, and the amount of waste toner is also reduced.

Note that although FIGS. 2, 3, and 4 are explained as cases in which a two-color toner image is reproduced, in the full-color copy mode, one image is reproduced four times when one image is formed.
Next transfer is performed.

Note that the image forming apparatus according to the present invention is not limited to the above-mentioned embodiments, and can be variously modified within the scope of the gist.

In particular, the transfer material may be not only plain paper but also special paper such as an OHP sheet.

Furthermore, the image exposure method may be a digital method using a laser beam instead of an analog method using visible light.

As is clear from the above description, according to the present invention, since the AC corona discharge means and the DC corona discharge means are provided between the primary transfer means and the secondary transfer means, the Effectively corrects the charge amount of the toner that has been primarily transferred to the electrostatic latent image carrier, prevents the toner from being retransferred to the electrostatic latent image carrier, and prevents a decrease in transfer efficiency, resulting in colors with good color balance. You can get the image. Further, the amount of waste toner is reduced, which is economical and reduces the burden on the cleaning device.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of an image forming apparatus according to the present invention. FIGS. 2, 3, and 4 are explanatory diagrams showing changes in toner charge amount in the transfer process. FIGS. 2 and 3 show a comparative example, and FIG. 4 shows an example of the present invention.

Claims (1)

[Scope of Claims] 1. In an image forming apparatus that primarily transfers a toner image carried on an electrostatic latent image carrier to an intermediate transfer member, and then secondarily transfers the toner image from the intermediate transfer member to a transfer material, AC corona discharge means installed between the primary transfer means and the secondary transfer means and applying an AC corona discharge to the toner image transferred onto the intermediate transfer body; and the AC corona discharge means and the secondary transfer means. is installed between the intermediate transfer member and the toner image transferred onto the intermediate transfer member, and a DC voltage having the same polarity as the charging polarity of the toner is applied to the toner image transferred onto the intermediate transfer member.
An image forming apparatus comprising: DC corona discharge means for applying corona discharge.