JPS625264A - Image forming method using photoconductive toner - Google Patents

Abstract

PURPOSE:To obtain a sharp copied image by subjecting a photoconductive toner to frictional electrostatic charging prior to the formation of a toner layer then to main electrostatic charging to the polarity opposite from the polarity of the frictional electrostatic charge. CONSTITUTION:The frictional electrostatic charge is preliminarily applied to the photoconductive toner to the specified polarity and thereafter the toner layer is formed on a substrate by using such toner. The image is exposed by subjecting the toner layer to the main electrostatic charge of the polarity reverse from the polarity of the frictional charge. The photosensitivity of the toner is improved by the combination of the frictional electrostatic charge and the main electrostatic charge in the above-mentioned manner. The electrostatic latent images formed in the exposed part and non-exposed part have the charges of the polarities reverse from each other and can be electrically and thoroughly discriminated. As a result, the sharp image having excellent contrast is obtd. The negative or positive image is easily obtd. by changing the electric polarities in the stage of transfer.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to an image forming method using a photoconductive toner,
More specifically, before forming photoconductive toner particles as a toner layer on a substrate, a triboelectric charge is applied in advance, and a main charge with a polarity opposite to that of the charge is performed, thereby producing a copied image with excellent contrast. The present invention relates to an image forming method capable of forming an image.

(Prior Art) In recent years, the use of photoconductive toner has attracted attention as a method of forming copied images without using a photosensitive drum or the like. This photoconductive toner is a toner made by classifying or dissolving a photoconductive pigment and/or a charge transport substance in a binder resin and pulverizing or atomizing it into particles. It has electrical conductivity.

Typical image formation using this photoconductive toner
The method is as follows. That is, (i) charged photoconductive toner is uniformly adhered and held on a conductive substrate to form a toner layer.

(ii) At this time, if necessary, corona charging with the same polarity is performed to improve the amount of charge on the toner.

(iii) Perform image exposure.

(iv)) Copy sheets or the like are stacked in a single layer, and corona discharge is applied from the back side of the copy sheets to transfer the toner image.

(V) Fixing the transferred toner image.

This is a method that sequentially performs these steps.

However, in this method, due to the fact that the photosensitivity of photoconductive toner is generally low, the difference in charge between exposed and non-exposed areas in the latent image formed after exposure is small, and as a result, it is difficult to copy. The drawback is that only images with low contrast can be obtained.

In addition, although originally it is possible to easily select and obtain a positive or negative image for an exposed image by controlling the polarity during transfer, as mentioned above, the difference between the exposed and non-exposed areas is The disadvantage is that this advantage cannot be utilized because the difference in the amount of charge is low.

(Object of the Invention) Therefore, an object of the present invention is to provide an image forming method that uses a photoconductive toner to obtain a clear copy image with contrast.

Another object of the present invention is to provide an image forming method capable of increasing the photosensitivity of a photoconductive toner.

Still another object of the present invention is to provide an image forming method that can easily create a clear negative or positive image from an exposed image using a photoconductive toner.

(Summary of the Invention) According to the present invention, after a toner layer is formed by uniformly holding a photoconductive toner on a substrate, the toner layer is uniformly charged (main charging), and then imagewise exposure is performed. forming an electrostatic latent image on a toner layer, electrically transferring the toner layer onto a recording medium in accordance with the latent image, and then fixing the transferred image; An image forming method is provided, which includes: triboelectrically charging a photoconductive toner prior to forming a toner layer, and performing main charging with a polarity opposite to the tribocharging polarity.

(Practice of the invention by Mr. A) The principle and embodiments of the method of the present invention are shown below.

In the image forming method of the present invention, a triboelectric charge is applied in advance to a negative polarity, and then a toner layer formed on a substrate using this toner is mainly charged with a polarity opposite to that of the triboelectric charge, and image exposure is performed. It has the greatest feature in this respect.

The combination of such triboelectric charging, that is, preliminary charging and main charging, increases the photosensitivity of the photoconductive toner, and the electrostatic latent image formed in the exposed and non-exposed areas has charges of opposite polarity and is electrically It becomes possible to make a sufficient distinction. As a result, a clear image with excellent contrast can be obtained, and by changing the electrical polarity during transfer, a negative or positive image can be easily obtained. Although the inventors have not yet elucidated the exact reason for this, they believe that it is due to the following reasons.

That is, in the conventional method, a toner layer is simply formed on a substrate using a charged photoconductive toner, or main charging with the same polarity as the toner charge is performed as necessary for the purpose of increasing the amount of charge of the toner layer. The purpose of the known method is to use + and - photocarriers generated inside the photoconductive toner by imagewise exposure to eliminate the charge on the toner as well as the charge on the substrate induced in response to the charge on the toner. . Accordingly, such conventional methods attempt to obtain an electrostatic latent image consisting of dark areas where charge is maintained and bright areas where charge has disappeared. However, in reality, some of the photocarriers are trapped inside the photoconductive toner, so it is impossible to completely eliminate the initially existing charge. As a result, since residual charges exist in the bright areas, the difference in charge between the dark areas and the bright areas becomes small, resulting in low contrast of the transferred image.

On the other hand, when main charging is performed with the polarity opposite to that of the preliminary charging charge as in the present invention, the polarity of the charge in the bright area is reversed by exposure, resulting in a large potential difference between the dark area and the bright area. be able to.

Now, a negatively charged photoconductive toner will be explained as an example. When a positive corona discharge is applied to the uniformly formed toner layer due to the potential difference with the substrate, positive corona ions adhere to the toner surface and the toner layer is positively charged.

Next, when this toner layer is subjected to image exposure, positive and negative photocarriers are generated inside the photoconductive toner particles in the exposed area, and negative triboelectric charges, positive surface charges, or substrate charges and photocarriers are generated, respectively. combine and eliminate charge.

At this time, as the photocarrier moves, some of the positive charges on the surface move into the photoconductive toner, which has increased conductivity.
The toner in the bright area will have a positive charge. As a result, the internal charge of the toner in the bright area is reversed from negative to positive, and the bright area and
An electrostatic latent image having internal charges of opposite polarity is formed in the dark area.

Next, the principle of easily obtaining a positive or negative copy of an original (image exposure) by using the method of the present invention will be explained.

In the above-mentioned example (an example using a negatively charged photoconductive toner), the electrostatic latent image formed by imagewise exposure has a dark area that retains positive corona ions on the surface and has a negative triboelectric charge inside. It consists of a bright part that has a positive charge inside.

In order to obtain a positive image from this latent image, a transfer medium is superimposed on the toner layer having the latent image, and a positive charge is applied from the back side of the transfer medium. In this case, only the toner in the dark area that has negative charges inside is attracted to the positive charges on the transfer medium and is transferred.

Note that the toner in the dark area has a positive corona ion charge on its surface, but this charge is transferred to the transfer medium side when the transfer media are overlapped, and the toner is transferred along with the transfer charge added from the back side for the purpose of transfer. This will contribute to the transcription of

Further, in order to obtain a negative image, a negative charge may be applied from the back side of the transfer medium. In this case, a negative image is obtained because the toner in the bright areas having a positive charge is transferred together with the positive corona ion charge adhered to the surface of the toner in the dark areas.

Based on this principle, according to the present invention, a positive or negative image can be easily obtained.

As the photoconductive toner used in the method of the present invention, those known per se can be used.

For example, a photoconductive pigment such as phthalocyanine, perylene, azo, or ZnO dispersed in a wAm resin medium such as styrene-acrylic resin or polyester resin can be used. The content of the pigment can be appropriately determined at a ratio of 5 to 50, preferably 10 to 40, per 100 parts by weight of the resin. Further, for the purpose of improving the sensitivity of the photoconductive toner, a hole or electron transporting substance may be added to the toner composition at a ratio of 0.5 to 2 parts by weight of the resin. Typical of these substances are: Label transport substances: polyvinyl carbazole, hydrazone, pyrazoline,
Examples include triphenylamine derivative electron transport substances such as nitrinitrofluorenone and tetranitrofluorenone.

Among the photoconductive toners obtained from these configurations,
Since the method of the present invention mainly performs charging with a polarity opposite to that of the triboelectric charge, a material having a high ability to retain these two charges is particularly preferred in the method of the present invention.

Examples of suitable photoconductive toners include phthalocyanine-rich styrene-acrylic, phthalocyanine-polyester, and the like.

In the method of the present invention, several methods can be applied to form the toner layer on the substrate. For example, a two-component system is prepared by mixing a photoconductive toner with a carrier, and this is carried out by forming a two-component magnetic brush, which is known per se, on a conductive sleeve. One method is to hold it alone on a fur brush.

In this case, the toner layer can be easily formed by applying a bias voltage between the conductive base made of a metal material such as AI and the sleeve or fur brush.

In addition, instead of applying a bias voltage between the sleeve, etc. and the substrate in order to create a potential difference between them, an insulating layer is provided on the surface of the substrate, and the surface of the insulating layer is treated with appropriate means such as corona discharge. It is also possible to adopt a method of charging using a battery.

As the recording medium used in the method of the present invention, in addition to paper and a transparent resin film for OHP, cloth, an insulated metal plate or metal foil, etc. can be used.

As the transfer method, in addition to using corona discharge, methods known per se can be employed, such as applying a transfer voltage between the substrate and the electrode using a counter electrode.

The photoconductive toner transferred onto the recording medium is fixed to the medium by heat or pressure.

The present invention will be explained below based on a specific example using a photoconductive toner using a phthalocyanine pigment as a photoconductive material.

1 part by weight of copper phthalocyanine to 3 parts of styrene-acrylic resin
A spherical toner having a particle size of 5 to 15 μm, which is dispersed in a toluene solution containing parts by weight and obtained by a spray drying method, is used as the photoconductive toner.

This photoconductive toner is mixed with a carrier at a weight ratio of 1:10, and mixed and stirred so that a negative triboelectric charge is imparted to the toner. Using this two-component developer, a photoconductive toner is applied onto a substrate by a magnetic brush method using a development device for a two-component developer known per se to form a toner layer. When forming the toner layer, a layer of 1,300 mm on the sleeve side is placed between the conductive sleeve and the grounded AI conductive base as the base.
A bias voltage was applied so that the potential was set to v. Under these conditions, about 10 or less toner layers were formed.

Next, the toner layer was positively charged by a corona charger to which a voltage of +6 KV was applied. At this time, the toner layer is approximately +
It had a surface potential of 300V.

After imagewise exposing this toner layer using a well-known method, transfer paper is placed on top of the toner layer, and a voltage of 16 KV is applied from the back side of the paper.
When a voltage of 100% was applied, a copy image faithful to the original image was obtained.

In addition, when a voltage of +6 KV□ was applied to the electrostatic latent image of the toner layer formed in the same manner from the back side of the paper, completely contrary to the above, a copy image faithful to the original image was obtained.

For reference, the data of the copied image obtained when positive corona charging was omitted (comparative example) is shown in Table 1 together with the data of the above experimental example.

Table 1 and above According to the invention, a clear negative or positive copy image with excellent contrast can be obtained using a photoconductive toner.

Claims (3)

[Claims] (1) After uniformly holding photoconductive toner on a substrate to form a toner layer, the toner layer is uniformly charged (main charging)
and then imagewise exposure to form an electrostatic latent image on the toner layer, electrically transfer the toner layer onto a recording medium according to the latent image, and then fix the transferred image. In an image forming method using conductive toner,
1. An image forming method comprising triboelectrically charging a photoconductive toner prior to forming a toner layer, and performing main charging with a polarity opposite to the tribocharging polarity. (2) The image forming method according to claim 1, wherein the toner layer formation is performed while applying a bias voltage to the conductive substrate. (3) The image forming method according to claim 1, wherein the toner layer is formed by charging the surface of an insulating layer provided on the substrate and adsorbing the toner.