JPH0459632B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field 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.

PRIOR TECHNOLOGY Various developing methods using one-component magnetic toner are known, but if the magnetic toner used in these methods is roughly classified by its specific resistance value, low-resistance toner with a value of 10 ¹¹ Ωcm or less is used. There are two types of resistance toners: cases where a low resistance toner having a value of 10 ¹¹ to 10 ¹⁵ Ωcm is used and cases where a high resistance toner having a value of 10 11 to 10 15 Ωcm is used.

In the case of a phenomenon method using low-resistivity toner with a value of 10 ¹¹ Ωcm or less, so-called conductive toner, the electric field caused by the electrostatic latent image on the photoreceptor causes the toner to hold a charge due to electrostatic induction or to conduct electricity. The toner that retains the electric charge due to polarization develops the latent image. Then,
The visible image developed on the 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 toner and the copy paper is likely to occur, and only the charge is transferred under the transfer electric field, and the toner itself is not transferred to the copy paper. Therefore, a problem arises in that only low-density, low-quality images are obtained.

Therefore, in order to prevent the charge exchange between the copy paper and the toner, which causes the above-mentioned problems, a method was invented that uses copy paper that is coated with insulation and has a high resistance, and is currently being put into practical use. ing.
However, although this method has achieved its intended purpose, it has drawbacks such as higher costs due to the processing involved, and lack of versatility as it requires special paper for copying machines. .

Furthermore, a method has been invented in which the charge exchange, which is the cause of the above-mentioned problems, is avoided by making the toner highly resistive. In the case of this method, there is no need to perform special processing on the copy paper, and it is low cost and the versatility of the copy paper is expanded, so it is considered to be a very useful method, but the specific resistance value of the toner
When the resistance becomes as high as 10 ¹¹ to 10 ¹⁵ Ωcm, the electric field caused by the latent image charge has the essential drawback that neither electrostatic induction nor electric polarization for toner charging occurs easily, making it difficult for the latent image to appear. are doing.

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, so the magnetic attraction force from the magnetic roll is However, the electrostatic attraction of the latent image is lost, and the image is developed in a shape that is magnetically rearranged by the magnetic field from the magnetic roll (specifically, a shape in which the toner is chained and oriented along the magnetic field). be done. This kind of toner image is
Compared to the latent image on the photoconductor, the image is not attached in a particularly damaged state, but each toner is attached to the photoconductor in an electrostatically unstable state. If the toner is immobile, a good image can be obtained by transferring it as is to copy paper.

However, in general, when commercializing copiers, printers, etc., various measures are introduced to prevent fluctuations due to the environment. 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 one-component developer, each toner retains sufficient charge and adheres to the photoreceptor in an electrostatically stable state, uniformly. Even when exposed to light, no change occurs in the image after copying. However, high-resistance toner does not have sufficient charge, and therefore, when the toner image is uniformly exposed after development, the toner is disturbed on the photoreceptor, resulting in a situation where a sharp image cannot be obtained.

Purpose of the Invention Therefore, the purpose of the present invention is to use an electrophotographic method for obtaining an image by uniformly exposing a toner image after development and then transferring it to a copy paper as a transfer ^sheet . An 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 even when using resistive magnetic toner.

Structure of the Invention In order to achieve the above object, the electrophotographic method according to the present invention is based on removing or discharging the charge on the photoreceptor more slowly than when forming a latent image after development and before transfer. , the one-component magnetic toner has a specific resistance of 10 ¹¹ Ωcm or more, and after developing an electrostatic latent image on the photoreceptor to form a magnetically connected magnetic toner image on the photoreceptor, transfer is performed. 1/ of the maximum illuminance during image exposure prior to
The present invention is characterized in that the surface of the photoconductor having the magnetic toner image is irradiated with light at an illuminance of 2 or less and for an irradiation time such that the irradiation exposure amount is equal to or more than half the exposure amount of the photoconductor.

Each term used in this document is defined as follows.

The total exposure amount means "the minimum amount of exposure necessary to charge the photoreceptor and then irradiate it with light so that the charged potential becomes only the residual potential", and the exposure amount means illuminance x irradiation time. do.

The image exposure amount means "the exposure amount used when forming an electrostatic latent image" and usually corresponds to the total exposure amount.

The term "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 half of the charged potential."

The maximum illuminance at the time of image exposure means "the maximum illuminance on the photoreceptor surface when image exposure is performed", and usually applies to the background part of a positive original, and the character part of a negative original. Irradiation of the photoreceptor surface corresponding to the white portion has the maximum illuminance.

EXAMPLES The electrophotographic method of the present invention will be explained in detail below with reference to the drawings. FIG. 1 schematically shows a general copying apparatus, in which a photosensitive drum 1 is charged by a charging corotron 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 using a lamp 5 to erase the charge of the latent image, and then transferred to a transfer sheet 7 by a next transfer corotron 6. Ru. Here, the transfer sheet is plain paper.

Figure 4 is a logarithmic graph with irradiation time on the horizontal axis and illuminance on the vertical axis. It is assumed that the "image exposure amount" in the above-mentioned copying machine is "1" for both illumination intensity and irradiation time. The value is displayed. In the graph of FIG. 4, the area indicated by diagonal lines A indicates the commonly used irradiation time-illuminance characteristics of the pre-transfer exposure lamp 5 shown in FIG. It is higher than the total exposure amount and the irradiation time is also 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 satisfactorily.

However, as mentioned above, toner images developed with high-resistance magnetic toner using a magnetic roll have a small amount of electric charge, and as shown in Figure 2, the toner image is not magnetically connected due to the magnetic field from the magnetic roll. (hereinafter referred to as a chain of toner T). Therefore, if the image is transferred as it is, a good image will be obtained, but when the latent image charge is instantaneously erased by irradiation with the lamp 5, a large displacement current flows momentarily on the photoreceptor, and electromagnetic energy due to this current is generated. The chain of toner T was scattered around the image area, and a sharp image could not be obtained.

Therefore, the present inventors placed a pre-exposure device 8 as shown in Fig. 3 in place of the lamp 5, and measured how the image on the photoreceptor changes depending on the relationship between illuminance and irradiation time. 9 is one in which the illuminance can be changed by changing the type of ND filter. Further, a plurality of tungsten lamps 10 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.

FIG. 4 shows the results of experiments conducted using such an apparatus while varying the illuminance and irradiation time. total exposure,
The relationship between the image exposure amount and the half-decreased exposure amount is shown in this graph, and it has been found that no change (scattering) of the toner image occurs in the diagonally shaded area B. Such a toner image is then transferred to the transfer sheet. It was also confirmed that good images could be maintained even when

These conditions apply to the range of area B in the graph of FIG.
That is, irradiation is performed at an illuminance that is 1/2 or less of the maximum illuminance during image exposure and for an irradiation time such that the irradiation exposure amount is equal to or more than half the exposure amount of the photoreceptor. By irradiating the surface of the photoconductor supporting the toner image under these conditions, even high-resistance magnetic toner can be transferred well because the displacement current used to erase the latent image charge 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, the illuminance and irradiation time were controlled using a tungsten lamp and an ND filter.
Any other lamps such as EL lamps, neon lamps, fluorescent lamps, etc. can be used as long as the photoreceptor can emit light at a wavelength that has spectral sensitivity.

Effects of the Invention According to the present invention, a toner image developed using a single-component high-resistivity magnetic toner having a specific resistance of 10 ¹¹ Ωcm or more is transferred to a plain paper transfer sheet without any special treatment with high quality. It can also be transferred at high density. In particular, according to the present invention, in uniform exposure before transfer, which is performed so as not to be affected by changes in the environment such as humidity, the instantaneous displacement current on the photoreceptor due to the uniform exposure is reduced, resulting in the above-mentioned Since scattering of the single-component high-resistivity magnetic toner image is eliminated, sharp images can always be obtained. Therefore, according to the present invention:
High quality, high density, sharp images can always be obtained on ordinary sheets.

[Brief explanation of the drawing]

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

Claims (1)

[Scope of Claims] 1. After uniformly charging a photoreceptor, exposing the photoreceptor imagewise to form an electrostatic latent image on the surface of the photoreceptor, and developing this electrostatic latent image with a one-component magnetic toner, In the electrophotographic method of transferring the magnetic toner image to a transfer sheet, the toner has a specific resistance of 10 ¹¹ Ωcm or more,
After forming a magnetically continuous magnetic toner image on the photoreceptor by developing the electrostatic latent image,
Prior to transfer, the surface of the photoconductor having the magnetic toner image is irradiated with light at an illuminance of 1/2 or less of the maximum illuminance during image exposure and for 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: