JPH01191176A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent deterioration in image quality by providing a means AC- discharging to a photosensitive body and a means uniformly projecting light of wavelength transmitting toner on the photosensitive body almost at the same time as discharging, after a developing step and before a transfer step. CONSTITUTION:A discharger/exposer 10 is provided between a developing unit 4 and a transfer electrode 5. The light source 14 of the discharger/exposer 10 uniformly projects light on the photoconductive layer surface of the photosensitive drum 1, and simultaneously an electrode 12 discharges AC coronas (positive, negative corona ions) eccentrically electrified to polarity opposite from an image part potential. Thus, negative charges on the photosensitive body in a positive toner adhering part disappear to lower the potential. In case of electric charges in a part below the toner, it can also be exposed when wavelength transmitting the toner is employed as that of light from the light source 14. Thus, toner scattering is reduced to prevent deterioration in image quality.

Description

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

[Background of the invention]

There are two types of development methods for electrostatic image forming apparatuses: reversal development and regular development. In reversal development, a dry toner with the same polarity as the latent image is formed by reducing the electric charge on the surface of a photoconductive photoreceptor using high DC voltage using image exposure light, and then applies a dry toner with the same polarity to the exposed area. This is a development method in which toner is attached to form a toner image, and is used when reproducing a negative image as a positive image, recording character information displayed on a cathode ray tube, or in printers that use a laser beam as the exposure light. be done.

On the other hand, regular development is a development method in which dry toner having a charge opposite to that of the latent image is attached to the latent image to form a toner image in the non-exposed area.

[Problem to be solved by the invention]

However, in this regular development method, when the photoreceptor potential is high, a large transfer current flows, the adhesive force between the paper and the photoreceptor is strong, and the electrostatic separation conditions become unstable. This is particularly noticeable when the leading edge of the image is the toner-attached portion.

Therefore, as a countermeasure against this, it has been considered to uniformly irradiate the photoreceptor with light after development and before transfer to lower the potential. The potential on the surface of the photoreceptor does not drop sufficiently, causing toner scattering.

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 improve electrostatic separation performance and prevent deterioration of image quality when a regular development method is employed.

[Means to solve the problem]

For this purpose, the present invention provides an image forming apparatus that electrostatically transfers a dry toner image obtained by regularly developing an electrostatic image formed on a photoreceptor onto a transfer material, and then performs electrostatic separation on the photoreceptor. After the development step and before the transfer step, the toner is provided with means for discharging alternating current and means for uniformly irradiating the photoreceptor with light having a wavelength component that transmits the toner substantially simultaneously with the discharge.

〔Example〕

Examples of the present invention will be described below. FIG. 1 is a diagram showing an image forming apparatus according to one embodiment.

2 is a photosensitive drum which 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 charging the surface of the photoreceptor drum 1 with a high voltage charge; 3 is an image light scanning system that scans and exposes the surface of the photoreceptor 1 with image light corresponding to the image to be recorded; 4 is a toner 5 is a transfer pole, 6 is a separation pole, 7 is a cleaning device, 8 is a developing device having a
9 is a heat fixing roller, and 9 is a paper feeding section.

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

FIG. 2 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 the charging electrode 2, and is exposed to light from the image light 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. Next, toner having a positive charge is attached to the remaining charge portion of the photoreceptor surface by the developing device 4 to form a toner image.

After being subjected to the action (described later) of the discharge/exposure device 10, the toner image is 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, 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 photosensitive drum 1 is charged to, for example, -700V (Fig. 3(a)
)), and the charge in the background area of the image is removed by exposure, but in the unexposed area, positive toner is attached by development (Figure 3(b)), and the potential of the toner layer is +100~3.
00V, and a potential contrast is generated between the image background part and the image background part.

Therefore, by the light source 14 of the discharge/exposure device 10 described above,
Light is uniformly irradiated onto the photoconductive layer surface of the photosensitive drum 1, and an alternating current corona (positive corona ions, negative corona ions) polarized to the opposite polarity to the image area potential is discharged by the electrode 12. As a result, the negative charges existing on the photoreceptor in the positive toner adhesion area can be eliminated, and the potential can be lowered.

In particular, corona discharge can be adjusted to suit transfer conditions by neutralizing toner having a high charge amount or a low charge amount. --like irradiation light is effective in bringing the toner-attached portion of the photoreceptor to approximately Qv. Preferably, this step is carried out under scorotron charging conditions. The scorotron has the effect of keeping the surface potential of the photoreceptor almost constant using a grid bias. Therefore, charging of the toner layer portion whose potential is below a certain level is suppressed. Furthermore, this scorotron lowers the potential while preventing the potential contrast that can occur with light irradiation alone. Further, since the polarity of the corona discharge by the electrode 12 is substantially the same as that of the toner, toner of opposite polarity is not generated. Further, by controlling the charging ability using the grid 7 grid 13, it is possible to prevent the charge amount of the toner from decreasing. In the case of 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.

The amount of exposure from the light source 14 is set to a level that sufficiently lowers the potential of the toner adhesion area.

In normal forward development, the photoreceptor is neutralized, so
This amount of light is 1 of the half-reduced exposure light amount E1/+1 of the photoreceptor drum.
~5 times is good. The upper limit of this amount of light is determined by the optical memory of the photoreceptor drum or the like.

The potential of the photoreceptor whose charge is removed by exposure in this way is set to about θ~-400V in the areas with and without the toner layer, but when the potential of the background area is completely set to Ov, the potential contrast changes due to the toner layer potential. Because of this, toner scattering tends to occur.

This can be prevented by making the toner layer potential approximately the same as the background potential. Experiments have revealed that failure can be reduced by keeping the difference between the background potential and the toner layer potential within a range of not exceeding 300V.

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 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.
Depending on the presence or absence of toner, potential contrast occurs and failure occurs.

By the way, as for the charge on the lower part of the toner, if the wavelength of the light from the light source 14 is set to a wavelength component that transmits the toner, that part will also be exposed, so the charge there will decrease in the same way as the charge on the non-adherent part. , it is possible to eliminate potential contrast and further reduce toner scattering. Light transparency can be imparted to each of black, yellow, magenta, and cyan toners used as desired. In particular, black toners can be made by blending dyes and pigments of yellow, magenta, cyan, or complementary colors that are transparent to infrared light. In this case, each toner is transparent to infrared light, and the photoreceptor is effectively neutralized.

As a combination of toner and light source used here, for example, for magenta, cyan, and yellow toners having the spectral transmittance characteristics (good infrared light transmittance) shown in FIG. A light source in which GaAj2As infrared LEDs having the spectral characteristics shown in the figure are arranged in a rod shape, or a light source in which a white light source and an infrared transmission filter are combined is suitable. Fourth
The figure shows the spectral transmittance when each toner is coated on a transparent film in a thickness of 5 μm.

Note that the AC power can be applied to the charging electrode 12 by cutting off the DC power (without applying a DC bias) using an AC power source via a capacitor.

〔Effect of the invention〕

As described above, the present invention includes means for discharging alternating current onto a photoreceptor during forward development, and substantially simultaneously with the discharge, uniformly irradiating the photoreceptor with light having a wavelength component that is transparent to the toner. Since the present invention is equipped with means, it is possible not only to improve electrostatic separation by eliminating the charge on the photoreceptor surface, but also to prevent the generation of potential contrast between the toner-attached area and the background area, thereby preventing toner scattering. This makes it possible to prevent image quality deterioration such as blurring.

[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 charging/exposure device, and FIG. 3 (al,
(b) is an explanatory diagram of the effects of charging and exposure, FIG. 4 is a spectral characteristic diagram of toner, and FIG. 5 is a spectral characteristic diagram of a light source. 10...Charging/exposure device, 11...Case, 12...
- Charged electrode, 13... Grid, 14... Light source. Agent Patent Attorney Tsuneaki Nagao Figure 1 Figure 2 Cause Figure 3

Claims (1)

[Claims] (1) In an image forming apparatus that performs regular development of an electrostatic image formed on a photoreceptor, electrostatically transfers a dry toner image onto a transfer material, and then performs electrostatic separation, an alternating current is applied to the photoreceptor. An image characterized by comprising a means for discharging, and a means for uniformly irradiating the photoreceptor with light having a wavelength component that transmits the toner substantially simultaneously with the discharge, after the development step and before the transfer step. Forming device.