JPH01191174A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent deterioration in image quality by providing a means discharging to a photosensitive body with electric charges of polarity opposite from the background potential of said body, and a means uniformly projecting light possessing 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 developing units 4A-4D and a transfer electrode 5. When the electrification electrode 12 of the discharger/exposer 10 discharges coronas of polarity opposite from the background potential (negative), the potential drops. The toner, which is re- electrified and charged at a high level, is also destaticized to ease transfer conditions. In case of electric charges below a toner overlapping area, the photosensitive body beneath a toner adhering part is also exposed when wavelength transmitting the toner is employed as that of light from a 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 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 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, 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.Especially, in a device that forms a color image by depositing toner of multiple colors in multiple cycles and overlapping them, the toner deposited from the previous cycle Since it 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 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. The object of the present invention is to prevent this problem and to make it possible to realize this even if the toner image superimposition method is used.

[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 performs electrostatic separation. means for discharging a charge having a polarity opposite to the background potential of the photoreceptor; and means for uniformly irradiating the photoreceptor with light having a wavelength component that transmits the toner substantially simultaneously with the discharge. It was configured after the 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 charging the surface of the photosensitive drum 1; 3 is a laser scanning system as a writing means; 4A to 4D are developing devices containing yellow, magenta, cyan, and blank toner; 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. Next, yellow toner having a negative charge is attached to the portion where the potential has decreased by the developing device 4A, thereby forming 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 4C24D in the same manner. After receiving the action of the discharge/exposure device 10, those toner images are transferred to the transfer paper 20 by the transfer pole 5, and this transfer paper 20 is transferred to the separation pole 6.
The toner image is separated from the photosensitive drum 1 and reaches the fixing roller 8, where 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, if a corona discharge with a polarity opposite to the background potential (negative potential) is performed using the charged electrode 12 of the discharge/exposure device 10 described above,
As shown in FIG. 4(b), the potential decreases. The charge is also removed from the toner which has been recharged by the superimposition process and has a high charge amount, so that the transfer conditions can be relaxed. Since this corona discharge characteristic has a polarity opposite to that of the toner charge, it is controlled so that toner with a reverse polarity is not produced. Further, by controlling the charging ability using the grid 13, it is possible to prevent the charge amount of the toner from decreasing.

If exposure by the light source 14 is performed simultaneously, the potential of the toner adhering area can be sufficiently lowered.

In the case of monochrome development, a good amount of light is about 1 to 5 times the half-decreased exposure light IT E I/Z of the photoreceptor drum, but for multicolor development, it is necessary to use an overlapping process to recharge In the state obtained in the process, it is preferable to set it to about 1 to 20 times El/□. In all of the above, the upper limit of the amount of light is determined by the optical memory of the photoreceptor drum, etc. (see Figure 4).
C)).

The potential of the photoconductor that has been neutralized as described above 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 (-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. Experiments have revealed that scattering can be reduced by keeping the difference between the background potential and the toner layer potential within a range of not exceeding 300V.

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

Regarding the above-mentioned 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 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.

By the way, regarding the electric charge at the bottom of the area where the toner is superimposed, if the wavelength of the light from the light source 14 is set to a wavelength component that transmits the toner, the photoconductor on the lower surface to which the toner is adhered will also be exposed, so the charge there will be reduced. The electric charge is reduced in the same way as the electric charge on the non-adhered area, eliminating potential contrast and further reducing toner scattering. Also, since opposing charges can easily come under the toner layer, scattering is reduced. Light transparency can be imparted to yellow, magenta, diene, and blank toners. In particular, black toner can be made by blending dyes and pigments of yellow, magenta, cyan, or complementary colors that are transparent to infrared light. In this case, the black toner and each color toner are 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. 5, the combination shown in FIG. A light source in which GaAj2AS infrared LEDs having the spectral characteristics shown in FIG. FIG. 5 shows the spectral transmittance when each toner was coated on a transparent film to a thickness of 5 μm.

〔Effect of the invention〕

As described above, the present invention is equipped with a means for discharging corona having a polarity opposite to the background potential of the photoreceptor, thereby stabilizing the recharging potential and improving electrostatic separation by eliminating charges on the photoreceptor surface. In addition to this, it is possible to prevent potential contrast between the toner-attached area and the background area, thereby preventing the toner from collapsing and preventing image quality deterioration such as bleeding. Furthermore, this is suitable when the toner image stacking method has a recharging part, and is good against fluctuations in the charge amount of 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.
4(a) to 4(L) are diagrams illustrating the operation of the charging/exposure device, FIG. 5 is a spectral characteristic diagram of toner, and FIG. 6 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 Figure 3 Figure 4

Claims (2)

[Claims] (1) In 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 performs electrostatic separation, the photoreceptor is After the development process, a means for discharging a charge having a polarity opposite to the background potential of the body, and a means for uniformly irradiating the photoreceptor with light having a wavelength component that transmits the toner substantially simultaneously with the discharge. An image forming apparatus characterized in that it is provided 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.