JPH01191170A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent deterioration in image quality by providing a means AC discharging a photosensitive body after a developing step and before a transfer step. CONSTITUTION:A discharger/exposer 10 is provided between the developing units 4A-4D of an image forming device and a transfer electrode 5. When the electrification electrode 12 of the discharge/exposer 10 discharges AC coronas eccentrically electrified to polarity identical to a background potential (negative), the uniformly of the surface potential of the photosensitive body is improved by positive and negative corona ions, and almost negative ions 41 in the background disappear to lower the potential. In a negative corona attaching part, opposite charges (positive) on the base side of the photosensitive body move toward a photosensitive body layer, and toner scattering can be prevented. The toner, which is re-electrified and highly charged in an overlapping process, is destaticized, whereby transfer conditions can be made uniform. Thus, deterioration in image quality can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus that employs a reversal development method.

[Background of the invention]

There are two types of development methods for electrostatic image forming apparatuses: regular development and reversal development. In regular development, a dry toner with a polarity opposite to that of the latent image formed by lowering the electric charge on the photoconductive photoreceptor surface using image exposure light using high DC voltage is applied to the unexposed area. This is a development method in which a toner image is formed by attaching the toner to the surface of the toner. On the other hand, reversal development
This is a development method in which dry toner having the same polarity as the latent image is attached to the exposed area to form a toner image.

This reversal development method is used when reproducing a negative image as a positive image, recording character information displayed on a cathode ray tube, or in a printer using a laser beam, ELD, etc. as exposure light.

[Problem to be solved by the invention]

However, in this reversal development method, even after the toner image is formed, a charge remains on the image background part (the part where toner does not adhere) on the photoreceptor surface, so this residual charge causes problems when transferring the toner image to the transfer material (paper). There is a problem in that the transfer current increases, and therefore the adhesion between the transfer material and the photoreceptor becomes strong, and subsequent electrostatic separation becomes unstable.

Therefore, Japanese Unexamined Patent Publication No. 53-1223146, Japanese Unexamined Patent Publication No. 5
In Japanese Patent No. 5-17111, uniform light irradiation is performed on the photoreceptor after development and before transfer to release residual charges in the image background area and improve separation performance.

However, with this method, the potential of the photoreceptor surface of the portion of the photoreceptor surface where the toner adheres to the photoreceptor surface is not sufficiently lowered, and the toner potential becomes higher than that of the other surface. Therefore, the toner tends to scatter laterally. In particular, in a device that forms a color image on a transfer material in a single transfer process by depositing toner of multiple colors in multiple cycles, the toner deposited in the previous cycle is charged again. The scattering phenomenon becomes noticeable.

When this scattering occurs, the toner not only contaminates the inside of the machine, but also causes blurring in the image after transfer, blurring of details and thin lines in the image, and noise in the halftone dots. Image quality deteriorates.

The present invention has been made in view of the above points, and its purpose is to improve electrostatic separation performance and prevent deterioration of image quality when adopting a reversal development method, and also to prevent toner image overlapping. The purpose is to make it possible to realize this even with a combination method.

[Means to solve the problem]

For this purpose, the present invention provides an image forming apparatus that performs reversal development of an electrostatic image formed on a photoreceptor, electrostatically transfers the obtained dry toner image onto a transfer material, and then performs electrostatic separation. A means for discharging was provided after the development process and before the transfer process.

〔Example〕

Examples of the present invention will be described below. FIG. 1 is a diagram showing a multicolor image forming apparatus according to one embodiment. A photosensitive drum 1 rotates in the direction of arrow a, and has a photoconductive layer of organic semiconductor, selenium, silicon, etc. formed on the surface of a grounded conductive metal base. 2 is a charging electrode for applying electric charge to the surface of the photosensitive drum 1; 3 is a laser scanning system as a writing means; 4A to 4D are developing devices having yellow, magenta, cyan, and black toners; 5 is a transfer device; pole, 6 is a separation pole, 7 is a cleaning device, 8
9 is a heat fixing roller, and 9 is a paper feeding section.

As shown in FIG. 2, the laser scanning system 3 described above includes a laser light source/modulator 31 that modulates the laser light from a semiconductor laser diode on/off according to written data, and a laser light source/modulator 31 that modulates the laser light from a semiconductor laser diode on and off according to written data, and a laser light source/modulator 31 that modulates the laser light from a semiconductor laser diode on and off according to written data, and a photoreceptor drum that transmits the modulated laser light. It is equipped with a rotating polygon mirror 32 that scans and deflects the laser beam in the axial direction on the surface of the laser beam 1, and an f-θ lens 33 that adjusts the focus of the scanned laser beam depending on the location.

In this embodiment, a discharge/exposure device 10 is provided between the developing units 4A to 4D and the transfer pole 5 of the image forming apparatus basically configured as described above.

FIG. 3 is a diagram showing the discharge/exposure device 10 in detail.
An AC discharge electrode 12 made of a wire stretched inside the case 11, a negative bias grid 13 stretched on the photosensitive drum 1 side of the discharge electrode 12, and an opening 1 on the upper surface of the case 11.
A rod-shaped light source 1 that uniformly illuminates the surface of the photoreceptor drum 1 from 1a.
It becomes 4.

Now, the photoreceptor surface of the photoreceptor drum 1 is uniformly charged to, for example, a negative high voltage by the charging electrode 2, and is exposed to laser light from the laser/scanning system 3. Then, the potential of the exposed portion is significantly reduced by the action of the photoconductive layer, thereby forming an electrostatic latent image. In the part where this potential has decreased,
Next, yellow toner having a negative charge is attached by the developing device 4A to form a yellow toner image. After being subjected to the action of the discharge/exposure device 10 (described later), it is charged again by the charging electrode 2, and a magenta toner image is formed by the developing device 4B through the same process. Thereafter, cyan and black toner images are successively formed by the developing device 4C14D in the same manner. After receiving the action of the discharge/exposure device 10, those toner images are transferred to a transfer paper 20 by the transfer pole 5, and this transfer paper 20 is separated from the photoreceptor drum 1 by the separation pole 6 and transferred to the fixing roller 8. At that point, the toner image is fixed and discharged. Further, the photosensitive drum 1 to which the toner image has been transferred is cleaned by a cleaning device 7. The cleaning device 7 is separated from the photoreceptor drum 1 during the image forming process so that this cleaning is performed after all of the above-described toner images of each color are formed and transfer is completed.

The surface of the photosensitive drum 1 after development and before transfer is shown in FIG.
), the image background area is charged with negative ions 41 (for example, a potential of -700V), and the negatively charged toner 42 is charged.
is attached. On the lower surface of this toner 42, negative ions 43 whose potential is lower than that of the negative ions 41 due to exposure by the laser scanning system 3 (-potential is -100 to -300 V) remain.

Therefore, when AC corona discharge polarized to the same polarity as the background potential (negative potential) is performed using the charged electrode 12 of the discharge/exposure device 10 described above, positive corona ions and negative corona ions cause
The uniformity of the surface potential of the photoreceptor is improved, and as shown in FIG. 4(b), most of the negative ions 41 in the background disappear and the potential is lowered.

In addition, in the negative toner adhesion area, the opposing charges (positive charges) on the photoconductor base side move to the photoconductor layer side, and the toner is prevented from scattering (Fig. 4 (C1), due to the overlapping process. Charge removal is also performed on toner that has been recharged and has a high charge amount, so that transfer conditions can be made uniform.

The above steps are preferably carried out under scorotron charging conditions. The strotron has the effect of keeping the surface potential constant using a grid bias.

Note that if the exposure using the light source 14 is performed at the same time, the potential of the toner adhering area can be sufficiently lowered. In the case of monochrome development, this light amount is preferably about 1 to 5 times the half-decreased exposure light amount El/□ of the photoreceptor drum, but for multicolor development, a recharging process is required using an overlapping process. In the obtained state, it is preferable to set it to about 1 to 20 times E,/2. In all of the above, the upper limit of the amount of light is determined by the optical memory of the photoreceptor drum or the like.

The potential of the photoreceptor that has been neutralized as described above is set to about θ~-400V in the region with or without the toner layer, but if the potential of the background part is completely set to Ov, the toner layer potential (-10
0 to -300 V), which causes a potential contrast, which tends to cause toner scattering.

This can be prevented by making the toner layer potential approximately the same as the background potential. In experiments, it has been found that scattering can be reduced by keeping the difference between the background potential and the toner layer potential within a range of not exceeding 300 V.

Regarding the relative positional relationship between charging and exposure described above, exposure is performed under conditions where the photoreceptor potential is constant regardless of the presence or absence of toner, that is, the exposure area is between the charged electrode 12 and the grid 1
It is better to be in a region where the charge control ability according to No. 3 is sufficiently effective. If the potential remains, the charge may be removed by exposure again.

From the above, it is preferable that the exposure center be near the center of the charged electrode 12 or downstream. If the exposure light source 14 is moved far upstream from the charging electrode 12, there will be no charging control ability.
A potential contrast occurs depending on the presence or absence of toner, and scattering occurs.

Although light irradiation is not always necessary, if it is not used, the photoreceptor potential should be -100 to -400V.
is preferable; Ov removes too much charge from the toner layer, resulting in a decrease in the amount of charge.

In addition to the configuration shown in FIG. 3, the configuration for the AC co-current discharge may be a configuration in which DC is cut off using a capacitor C as shown in FIG.

The light source is omitted here. The back plate may be grounded without applying a bias voltage.

〔Effect of the invention〕

As described above, since the present invention is equipped with a means for discharging AC corona, it is possible not only to improve electrostatic separation by removing the charge on the photoreceptor surface, but also to stabilize the recharging potential and to prevent the toner from adhering to the surface. Since potential contrast with the background area is also prevented from occurring, toner scattering can be prevented, and image quality deterioration such as bleeding can be prevented.

Furthermore, this can be applied even when the toner image stacking method has a recharging part, and it is good against fluctuations in the amount of charge on the toner, and can also cope with environmental fluctuations and developer deterioration. can.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a multicolor image forming apparatus according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of a laser scanning system, and FIG.
FIGS. 4(a) to 4(C) are diagrams for explaining the operation of the charging/exposure device, and FIG. 5 is a diagram for explaining another example of the charging device. 10...Charging/exposure device, 11...Case, 12...
- Charged electrode, 13... Grid, 14... Light source. Agent Patent Attorney Tsuneaki NagaoFigure 1Figure 2Figure 3Figure 4

Claims (3)

[Claims] (1) In an image forming apparatus that performs reversal development of an electrostatic image formed on a photoreceptor, electrostatically transfers the obtained dry toner image onto a transfer material, and then performs electrostatic separation, AC discharge is applied to the photoreceptor. An image forming apparatus characterized in that a means is provided after a developing process and before a transfer process. (2) The image forming apparatus according to claim 1, wherein the dry toner image is a superimposed toner image of a plurality of colors. (3) The image forming apparatus according to claim 1, wherein uniform irradiation light is applied to the photoreceptor substantially simultaneously with the discharge by the discharge means.