JPH01191169A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent deterioration in image quality such as blurring by providing a means discharging a photosensitive body with electric charges of polarity identical to the potential of the image background of the photosensitive body, and a means uniformly projecting light on the photosensitive body almost at the same time as discharging. CONSTITUTION:The potential of the photosensitive body destaticized by exposure is set at 0--400V in areas with and without a toner layer. When the potential of the background is sharply set at 0V, toner is easy to scatter because potential contrast occurs owing to a toner layer potential (-100V--300V). This contrast can be prevented by setting the toner layer potential almost at the background potential. Namely, when an electrification electrode 12 electrifies with negative charges whose polarity identical to charges electrified by the electrode 12, opposite charges (positive) on the base side of the photosensitive drum 1 move toward a photoelectric layer part, and attract toner (electrified negative) attaching to that part toward the surface of the photosensitive body 1, thereby preventing the toner from scattering. 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 toner. On the other hand, reversal development
This is a development method in which dry toner having the same charge 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, LED, 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 devices that form color images by depositing toner of multiple colors in multiple cycles and superimposing them, the toner deposited in the previous cycle is charged again, so the scattering phenomenon is noticeable. Become.

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 these points, and its purpose is to stabilize the recharging potential and improve electrostatic separation performance, as well as to prevent deterioration of image quality when adopting a reversal development method. However, it is another object of this invention to be able to realize this even when using a toner image superimposition 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 resulting dry toner image onto a transfer material, and then electrostatically separates the image on the photoreceptor. A means for discharging a charge having the same polarity as the potential of the background portion onto the photoreceptor, and a means for uniformly irradiating the photoreceptor with light substantially simultaneously with the discharge are provided after the development step and before the transfer step. It was configured as follows.

〔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 photosensitive layer of organic semiconductor, selenium, silicon, etc. formed on the surface of a grounded conductive metal base. 2 is a charging electrode for charging 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 device 4A-40 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.
A discharge electrode 12 made of a wire stretched inside a case 11, and a grid 1 stretched on the photosensitive drum 1 side of the discharge electrode 12.
3, and a rod-shaped light source 14 that uniformly illuminates the surface of the photoreceptor drum 1 from the opening 11a on the upper surface of the case 11.

Now, the photoreceptor surface of the photoreceptor drum 1 is uniformly charged to, for example, a negative high voltage by a charging electrode 2, and is exposed to laser light from a 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 devices 4G and 4D in the same manner. After being subjected to 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 then transferred to the fixing roller 8.
At this 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 toner images of the respective colors described above are formed and transfer is completed.

The surface of the photosensitive drum 1 after development and before transfer is shown in FIG.
), the background of the image is charged with negative ions (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, by the light source 14 of the discharge/exposure device 10 described above,
When the photoconductive layer surface of the photosensitive drum 1 is uniformly irradiated with light, as shown in FIG.
disappears and its potential decreases.

Note that the amount of exposure from this light source 14 is set to a light amount that sufficiently lowers the potential of the toner adhesion area. In the case of monochrome development, this amount of light is the half-reduced exposure light i of the photoreceptor drum.
A value of about 1 to 5 times of i E l/l is good; It is necessary to sufficiently eliminate the electric potential of the upper surface by light irradiation, and for this reason, it is preferable to set the above-mentioned light amount to about 1 to 20 times the EI7□. 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 whose charge has been removed by exposure in this way is set to about O to -400 V in the areas with and without the toner layer, but when the potential of the background area is completely set to Ov, the toner layer potential (-100 to -300V) 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 other words, when the charging electrode 12 is charged with a negative charge of the same polarity as that of the charging electrode 2, an opposing charge (positive charge) on the base side of the photoreceptor drum 1 is generated as shown in FIG. ) moves to the photoconductive layer portion and attracts the toner (negatively charged) attached thereto to the surface of the photoreceptor 1, thereby preventing the toner from scattering.

In the experiment, the difference between the background potential and the toner layer potential was set to 300V.
It has become clear that scattering can be reduced by keeping the amount within a range that does not exceed .

This step is carried out under scorotron charging conditions, that is, under conditions where the electric potential of the surface of the photoconductive layer of the photosensitive drum 1 is kept approximately constant by bias control of the grid 13.

Regarding the above-described relative positional relationship between charging and exposure, exposure is performed under conditions where the potential of the photoreceptor remains constant regardless of the presence or absence of toner. In other words, the exposed area consists of 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 charging electrode 12 or downstream.If the exposure light source 14 is shifted significantly upstream from the charging electrode 12, a state where the charging control ability is lost will result.
A potential contrast occurs depending on the presence or absence of toner, and scattering occurs.

As described above, in this embodiment, the scorotron performs the action of lowering the potential while preventing the potential contrast that may occur with light irradiation alone. Furthermore, since the corona discharge characteristics of the charged electrode 12 are the same polarity as the charged toner, toner of opposite polarity is not generated. By controlling the charging performance using the grid 13, it is also possible to prevent the charge amount of the toner from increasing. When using a - component developer, since the charge amount is originally as low as 5 μc/g, it is possible to increase the charge amount to 10 to 20 μc/g to improve the transfer efficiency.

〔Effect of the invention〕

As described above, the present invention includes a means for discharging charges having the same polarity as the potential of the image background portion of the photoreceptor, and a means for uniformly irradiating the photoreceptor with light substantially simultaneously with the discharge. This not only makes it possible to stabilize the recharging potential and improve electrostatic separation by eliminating charges on the photoreceptor surface, but also prevents the occurrence of potential contrast between the toned front area and the background area. Therefore, it is possible to prevent toner from being damaged.
Deterioration of image quality such as blurring 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 explanatory views of the exposure device, and are explanatory views of the operation of the charging/exposure device. 10...Charging/exposure device, 11...Case, 12...
- Charged electrode, 13... Grid, 14... Light source. Agent Patent Attorney Tsuneaki Nagao Figure 1 Figure 2

Claims (2)

[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 electrostatically separates the image background portion of the photoreceptor. A means for discharging a charge of the same polarity as the potential onto the photoreceptor, and a means for uniformly irradiating the photoreceptor with light substantially simultaneously with the discharge, are provided after the development step and before the transfer step. Features of the image forming device. (2) The image forming apparatus according to claim 1, wherein the dry toner image is a superimposed toner image of a plurality of colors.