JPS59223464A - Electrophotographic method - Google Patents

Abstract

PURPOSE:To obtain a stable toner image by irradiating the surface of a photosensitive body for an irradiation time making the quantity of exposure half exposure or more of the photosensitive body with the specific intensity of illuminance prior to transfer after development. CONSTITUTION:The relation among full exposure, image exposure and half exposure prevents the dispersion of a toner image in a B area. Said condition is attained by irradiating the surface of the photosensitive body by the illuminance intensity a half or less of the maximum illuminance intensity during the irradiation time making the irradiated exposure the half exposure of the photosensitive body. The reason why fine transfer is attained by irradiating the surface of the photosensitive body supporting the toner image under said conditions even if high resistance magnetic toner is used is that displacement current for erasing the charge of a latent image can be reduced, the electromagnetic energy is also reduced and disturbance of the toner image may be prevented. In said procedure, a fine picture can be obtained always stably from the toner image on the photosensitive body which is formed by high resistance magnetic toner and developed by a magnetic roll.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic method, and more particularly to a transfer type electrophotographic method in which a developed toner image is transferred onto a sheet using a magnetic toner as a developer.

Various conventional development methods using one-component magnetic toner are known, but if the magnetic toner used in these methods is roughly classified by the specific resistance value, low-resistance toner with a value of 10 Ω or less is used. When using / o 11 ~ i o 15Ωα
It can be divided into cases where a high resistance toner with a value of .

In the case of a development method using a low-resistance toner with a value of 10 Ω or less, so-called conductive toner, the electric field generated by the electrostatic latent image on the photoreceptor causes the toner to retain charge due to electrostatic induction. Alternatively, toner that retains a charge due to electrical polarization develops a latent image. Next, the visible image developed with this conductive toner is transferred onto copy paper as a transfer sheet by a transfer method using an electric field such as electrostatic transfer or bias transfer. In this case, if the specific resistance value of the copy paper is low, charge exchange between the conductive l-ler and the copy paper is likely to take place, and only the charge is transferred under the electric field while the toner itself is transferred to the copy paper. This causes the problem that low-density, low-quality images cannot be obtained.

Therefore, in order to prevent the charge exchange between the copy paper and the gutter, which causes the above-mentioned problems, a method was invented in which the copy paper is treated with an insulation coating to make it highly resistant. It is currently being put into practical use.

However, although this method achieved its intended purpose, it also had drawbacks such as high costs due to the processing involved, and a lack of versatility since special paper was used for the copying machine. have.

Furthermore, the Z method has been invented in an attempt to avoid the charge exchange, which is the cause of the above-mentioned problems, by making the toner highly resistive. In the case of this method, there is no need to apply special processing to the copy paper, and the versatility of the copy paper is expanded due to the low nit density, so it is considered to be a very useful method.However, the specific resistance value of the toner is 1 When it is as high as io to 10 Qcm, the electric field surrounding the latent image charge has the essential drawback that neither electrostatic induction nor electric polarization for charging the toner occurs easily, making it difficult to develop the latent image. There is.

When such high-resistance toner is developed using a magnetic roll, for the reason mentioned above, the toner adheres to the photoreceptor without sufficient charge and develops a latent image. The electrostatic attraction of the latent image is overcome by the attraction,
The toner image is developed in a shape that is magnetically rearranged by the magnetic field from the magnetic roll (specifically, the toner is oriented in a chain shape along the continuous magnetic field.Such a toner image is formed on the photoconductor). Rather than the image being deposited in a particularly damaged state compared to the latent image, each toner is deposited on the photoreceptor in an electrostatically unstable state; If it does not move, a good image can be obtained by transferring it to copy paper as is.

However, in general, when commercializing copiers, printers, etc., various measures are introduced to ensure that they are not affected by environmental changes. The most well-known method to improve transfer efficiency, especially at high humidity, is to uniformly expose the photoconductor to light after development and before transfer to erase the latent image charge and weaken the adhesion of toner to the photoconductor. It is also highly effective and has been adopted in many copying machines and the like.

In the development method using a two-component developer and the development method using a conductive-component developer, each toner retains sufficient charge and adheres to the photoreceptor in an electrostatically stable state. No change occurs in the image after copying even if it is exposed to light. However, high-resistance toner does not have sufficient charge, and for this reason, when the toner image is uniformly exposed to one light beam after development, the toner becomes disordered on the photoreceptor, resulting in a situation where a sharp image cannot be obtained. .

OBJECT OF THE INVENTION Therefore, the object of the present invention is to provide an electrophotographic method for obtaining an image by uniformly exposing a developed toner image to copy paper as a transfer sheet, using a highly resistive magnetic toner. Another object of the present invention is to provide an electrophotographic method that makes it possible to obtain a stable toner image that is not affected by the environment.

In the photographic method, after development and prior to transfer, a toner image is formed at an illuminance that gently eliminates or discharges the charge on the photoreceptor compared to the time of image formation, and at an irradiation time such that the exposed bone is at least half the exposure amount of the photoreceptor. It is characterized by irradiating the surface of the photoreceptor with light.

Each term used in this document is defined as follows.

The total exposure amount means ``the minimum exposure amount necessary to charge the photoreceptor and then irradiate it with light to make it have a residual potential'', and the exposure amount is defined as ``illuminance x irradiation time''.

The image exposure amount is the amount of exposure used when forming an electrostatic latent image.
, which usually corresponds to the total exposure amount.

The half-reduced exposure amount means ``the amount of exposure required to charge the photoreceptor and then irradiate it with light to reduce the potential to the half of the charged potential.''

The maximum illuminance during image exposure means the maximum illuminance on the photoreceptor surface when image exposure is performed, and usually applies to the white parts of the document, such as the background area in the case of a tenon original and the character area in the case of a negative original. The irradiation of the photoreceptor surface corresponds to the maximum illuminance.

EXAMPLES Below, the electrophotographic method of the present invention will be explained in detail with reference to the drawings. FIG. 1 schematically shows a general copying apparatus, in which a photosensitive drum 1 is charged by a charging corotorene 2 and imagewise exposed at a position 3 to form an electrostatic latent image on the drum. This latent image is developed in a developing device 4 using high-resistance magnetic toner, and then subjected to pre-transfer exposure in a land 5 to erase the electric charge of the latent image, and then transferred to a transfer sheet 7 by a next transfer corotron 6. It was transferred to '7y. Here, the transfer sheet is plain paper.

The figure is a logarithmic graph with irradiation time on the horizontal axis and illuminance on the vertical axis, and assuming that the "image exposure amount" in the above-mentioned copying device is "/" for both illuminance and irradiation time, relative values are shown. This is what is displayed. In the graph of FIG. 9, the area indicated by diagonal lines A indicates the generally used irradiation time-illuminance characteristics of pre-transfer exposure rung 5 shown in FIG. 1, and as shown in this area A, the illuminance of run f5 is It is higher than the total exposure amount and the irradiation time is also much longer. Therefore, the charge representing the latent image on the photoreceptor is immediately erased, and if the toner has sufficient charge, the toner can be transferred to the transfer sheet 7 successfully.

However, toner images developed with high-resistance magnetic toner using a magnetic roll have a small amount of electric charge as mentioned above, and as shown in Figure 2, the toner image is not magnetically developed by the magnetic field from the magnetic roll. The toner T is developed in a continuous state (hereinafter referred to as a chain of toner T).

Therefore, although a good image can be obtained if the image is transferred as is, when the latent image charge is instantaneously erased by the irradiation by rung 5, a momentary but large displacement current flows on the photoreceptor, and the electromagnetic energy generated by this current causes the above-mentioned The chain of toner T was scattered around the image area, and a sharp image could not be obtained.

Therefore, the present inventors placed the lamp 5 in place of the pre-exposure device 87 as shown in FIG. 9 is
By changing the type of ND filter, the illuminance can be changed. Further, a plurality of tungsten lamps 1O are arranged along the surface of the photoreceptor, and each can be turned on/off independently. Therefore, this allows the irradiation time to be changed.

Figure 1 shows the results of experiments conducted using such an apparatus while varying the illuminance and irradiation time. This graph shows the relationship between the total exposure amount, the image exposure amount, and the half-decreased amount of light, and it was found that the toner image changes (scattering) and is weak in the area B indicated by the diagonal line. It was also confirmed that a good image could be maintained even after being transferred to a transfer sheet.

These conditions apply to the range of region B in the graph of FIG.
ITr at the time of irradiation when the light amount is more than half the exposure amount of the photoreceptor
i. The reason why even high-resistance magnetic toner can be transferred well by irradiating the surface of the photoconductor supporting the toner image processing under these conditions is because the displacement current used to erase the charge of the latent image can be reduced. This is thought to be because the electromagnetic energy is also small, so that no disturbance of the toner image occurs.

In this example, a tungsten lamp and an ND filter were used to control the illumination intensity and irradiation time, but any other lamp such as an EL clamp neon lamp or a fluorescent lamp could be used, and the wavelengths for which the photoreceptor has spectral sensitivity may be used. Any object can be used as long as it can emit light.

Effects of the Invention According to the present invention, in an electrophotographic method in which a toner image on a photoconductor developed with a magnetic roll is uniformly exposed to light using a high-resistance magnetic toner, and then transferred to a transfer sheet. , it is possible to always obtain a stable and good image φ even with changes in the environment and transfer sheets under various conditions.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a general copying machine; Fig. 1 is a diagram showing a toner chain in a latent image on the surface of a photoreceptor; Fig. 3 is an explanation showing a configuration for confirming or implementing the method according to the present invention. Figures 1 and 2 are logarithmic graphs showing the relationship between dust and irradiation time in the pre-transfer exposure field. 1......Photoreceptor, 4......
Developing device, 5... Pre-transfer exposure lamp,
7...Transfer sheet, 8...
...Pre-transfer exposure device, 9...ND filter, 10...Tungsten lamp. Bud I Figure 3 Figure 4 Bud

Claims (1)

[Claims] The photoreceptor is uniformly charged, the photoreceptor is imagewise exposed to form an electrostatic latent image on the surface of the photoreceptor, this electrostatic latent image is developed with magnetic toner, and then the magnetic toner image is transferred to a transfer sheet. In the electrophotographic method for transferring, after development and prior to transfer, a photoconductor having a toner image at an illuminance below the maximum illuminance at the time of image exposure and an irradiation time such that the irradiation exposure amount is equal to or more than half the exposure amount of the photoconductor. An electrophotographic method characterized by irradiating a surface with light.