JPS638757A - Image forming method - Google Patents

Abstract

PURPOSE:To obtain an image of high contrast by making the timing when an electrically charged photoconductive toner is exposed to light to extinguish the electric charge different from the timing when electric charge having a polarity opposite to that for electric charge is applied to the toner which loses the electric charge. CONSTITUTION:A prescribed electric field is formed between a conductive electrode 12 and a conductive substrate 11 by a voltage applied from a power source 13. The toner which loses the electric charge by exposure on the conductive substrate 11 is charged with a negative electric charge from the substrate 11 to have the negative polarity. The toner having one polarity on the substrate 11 is electrostatically transferred to transfer paper by a prescribed transfer device. In case of transfer of the toner which has the negative polarity by exposure, plus corona discharge is performed from the rear face of the transfer paper, and only the toner having the negative polarity is electrostatically transferred onto the transfer paper, and there is not a fear that the toner having the positive polarity on the substrate 11 is transferred. The timing when the electric charge of the toner which is not exposed is attenuated is delayed, and this toner at the time of transfer keeps a high extent of electric charge, and the potential difference between this toner and the exposed toner is increased to obtain an image of high contrast.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image forming method using a photoconductive toner.

(Conventional technology) Photoconductive toner absorbs light and increases its conductivity.

It has the characteristic that the polarity is reversed as a result of transferring charge between the electrode and the electrode. An image forming method using such toner is shown in FIG.

First, a cylindrical conductive substrate 31 made of aluminum or the like.
For example, positively charged toner is uniformly deposited thereon. Next, a transparent electrode 32 such as Nesa glass is placed opposite the conductive substrate 31, and an electric field is generated between the conductive substrate 31 and the transparent electrode 32. In this situation,
The original image is exposed to a single layer of toner from above the transparent electrode 32.

The exposed toner other than the original image becomes conductive, its positive charge disappears through the conductive substrate 31, and further becomes negative polarity due to the electric field between the conductive substrate 31 and the transparent electrode 32. Toner that is not exposed maintains positive polarity. In this way, a positive toner image corresponding to the original image is formed on the conductive substrate 31. A predetermined copy image is obtained by transferring this positive polarity toner image onto a transfer paper.

In conventional imaging methods using photoconductive toner, a document image is exposed to the photoconductive toner while the toner is positioned within an electric field. Therefore, the polarity of the exposed toner is reversed and becomes the opposite polarity of the unexposed toner, and during transfer, only toner of one of the polarities is reliably transferred. Therefore, the obtained copy image has a clear contrast.

However, when the entire charged toner is placed in an electric field so that the exposed toner has a polarity opposite to the polarity at the time of charging at the same time as the toner is exposed, the surface potential of the unexposed toner is also attenuated at the same time. Between this exposure and transfer, the surface potential of the unexposed toner is severely attenuated, and the contrast of the resulting image is reduced. When the charged toner is placed in an electric field and exposed to light, a transparent electrode or an electrode having a slit must be brought into contact with or close to the substrate, which may disturb the toner layer.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned conventional problems, and its purpose is to provide an image forming method that can obtain a high-contrast copy image.

(Means for Solving the Problems) The present invention exposes a charged photoconductive toner to light to eliminate its charge, and the toner is placed in an electric field to eliminate its charge. This is an image forming method in which an image is obtained by applying a charge of opposite polarity and then electrostatically transferring toner of one polarity to transfer paper, and the timing of exposing the charged photoconductive toner to light and the disappearance of the charge are determined The above-mentioned object is achieved by changing the timing at which a charge having a polarity opposite to the toner polarity at the time of charging is applied to the charged toner.

(Example) The present invention will be described below with reference to Examples.

The method of the present invention includes one method, for example, as shown in FIG.

A cylindrical conductive substrate 11 rotatable in the direction of arrow A is used. For example, the conductive substrate 11 may be one.

An aluminum substrate is used. For example, positively charged photoconductive toner 1 is deposited on the surface of the conductive substrate 11.
4 is uniformly deposited. The photoconductive toner 14 deposited on the conductive substrate 11 is exposed, for example, to the top of the substrate 11 so that the original image is exposed. The exposed photoconductive toner 14 becomes conductive and loses positive charge through the substrate 11.

On the downstream side of the conductive substrate 11 from this exposure position in the rotational direction, a conductive electrode 12 is disposed facing the surface of the conductive substrate 11 . The conductive electrode 12 has a gap of about 100 to 500 μm from the surface of the substrate 11. between the conductive electrode 12 and the conductive group vi11.

A predetermined electric field is formed by the voltage applied by the power source 13. The toner whose charge has disappeared due to exposure on the conductive substrate 11 is injected with negative charge from the substrate 11.

It becomes negative polarity. Toner of one polarity on the substrate 11.

The image is electrostatically transferred onto a transfer paper by a predetermined transfer device. At this time, for example, when toner that has been exposed to negative polarity is to be transferred, positive corona discharge is performed from the back side of the transfer paper. As a result, only the toner of negative polarity is electrostatically transferred onto the transfer paper, and there is no possibility that the toner of positive polarity on the substrate 1 is transferred. This is because after the toner is exposed to light, the toner is placed within an electric field.

The timing at which the charge of the unexposed toner is attenuated is delayed, and the toner maintains a high charge amount during transfer, resulting in a large potential difference with the exposed toner.

Therefore, the resulting image has high contrast.

Furthermore, the timing of applying charges of opposite polarity is as follows.

It is desirable to carry out this process before the exposure of the photoconductive toner is completely completed.

FIGS. 2 to 4 each show other embodiments of the method of the present invention. In these embodiments, an electric field is formed using a transparent electrode to impart a charge having a polarity opposite to the polarity at the time of charging to the exposed toner. Then, the original image is exposed through this transparent electrode.

In the embodiment shown in FIG. 2, the upstream portion of the transparent electrode 15a in the rotational direction of the conductive substrate 11 has higher translucency than the downstream portion thereof. Simply, the downstream portion of the transparent electrode 15a may be shielded from light. The transparent electrode 15a is connected to the substrate 1
1 and are disposed facing each other with a gap of about 100 to 500 μm. An electric field is formed between the transparent electrode 15a and the substrate 11 by the voltage applied by the power source 13.

The positively charged photoconductive toner on the conductive substrate 11 is exposed to light at the upstream portion of the transparent electrode 15a in the rotational direction of the substrate 11 to lose its charge, and is negatively charged at the downstream portion thereof. be done.

゛ In the embodiment shown in FIG. 3, a transparent electrode 15b having uniform translucency is tilted so that the downstream end in the rotational direction of the conductive substrate 11 approaches the substrate 11. .

A voltage is applied to the transparent electrode 15b by the power source 13,
An electric field is formed between the substrate II and the substrate II.

Because of the inclination as described above, the electric field strength at the downstream portion of the substrate 11 in the rotational direction is increased. Therefore, the positive polarity toner on the substrate 11 is exposed to light at the upstream portion of the transparent electrode 15b, and after its positive polarity charge is eliminated, it is made negative polarity in the high intensity electric field portion.

In the embodiment shown in FIG. 4, the transparent electrode 15b shown in FIG.
Similarly, a transparent electrode 15c having uniform light transmittance is arranged facing the substrate 11 without being inclined with respect to the substrate 11, and on the surface of the transparent electrode 15c facing the substrate 11,
Dielectric material 16 that is thicker on the upstream side in the rotational direction of substrate 11
has been set up. The dielectric 16 is.

As the thickness increases, the dielectric constant increases, and therefore, the electric field between the transparent electrode 15c and the substrate 11 has a higher intensity on the downstream side in the rotational direction of the substrate 11 than on the upstream side. The positive polarity toner on the substrate 11 is exposed to light at the upstream side of the transparent electrode 15c, and after its charge is eliminated, it is made negative in the high intensity electric field.

Step 11''1 A copy image was obtained as shown in FIG. Transparent electrode 15
a has a light transmittance of 95 on the upstream side in the rotational direction of the substrate 11.
%, and gradually decreases toward the downstream portion, reaching 0% at the downstream portion. The center of the transparent electrode 15b is 500 μm apart from the top of the substrate 11, and the base Fi
11 in the tangential direction. As the base 11, an aluminum substrate was used. A voltage of 2 kV was applied to the transparent electrode 15a, and at the same time, image exposure was performed on the surface of the substrate 11 at 3001 ux. In this case, as shown in FIG. 5, there is a time difference T (=T2 T+) between the time T when the exposure intensity is maximum and the time T2 when the electric field intensity is maximum.
is 50m5ec, the time difference between the exposure end time (T4) and the voltage application start time (T□) (=T4-T:l)
was 100m5ec.

After the voltage was applied, the toner on the substrate 11 was transferred onto a transfer paper using an ordinary transfer device to obtain a copy image. The contrast ratio (the ratio of the exposed area density to the unexposed area density expressed as a percentage) of the copied image is:

It was about 16.6.

A copy image was obtained as shown in FIG. Transparent electrode 15
For c, uniform Nesa glass with a light transmittance of 95% was used, and the substrate 11 was tilted at an interval of 28% on the upstream side in the rotational direction and 0.5 cm on the downstream side. in this case,
The time difference T between the time T1 when the exposure intensity is maximum and the time T2 when the electric field strength is maximum is 150 m5 ec, and the time difference t between the exposure end time T4 and the voltage application start time T is 1.
It was 00m5ec. Copy images were obtained under the same conditions as in Experimental Example 1. The contrast ratio of the obtained copied image was 27.3.

As shown in Figure 6, a transparent electrode made of uniform Nesa glass with a light transmittance of 95% was placed 500 μm from the top of the substrate.
They were placed at a distance and a voltage was applied at the same time as one image was exposed. There is no difference between the time T1 when the exposure intensity is maximum and the time T2 when the electric field strength is maximum (T=O), and the time difference between the exposure end time T4 and the voltage application start time T is 10
It was 0m5ec. Other conditions were the same as in Experimental Example 1. The contrast ratio of the obtained copied image was 4.8.

Transparent electrodes were provided in the same manner as in Comparative Example 1, and a voltage was applied (1=0) when exposure was completed. Other conditions were the same as in Comparative Example 1. The contrast ratio of the obtained copied image was 1 or less.

Table 1 shows Experimental Examples 1 and 2, Comparative Example 1, and Comparative Example 2.
Shown below.

Table 1 (Effects of the Invention) In the image forming method of the present invention, as described above, the timing at which the charged photoconductive toner is exposed to light to eliminate its charge and the polarity when charging the toner that has lost its charge are determined. Since the timing of applying charges of opposite polarity is different and the latter timing is delayed than the former timing, it is possible to suppress the attenuation of the surface potential of the unexposed toner, and therefore, a high-contrast image can be obtained. can get.

4. Figure 1 is a schematic diagram showing an example of the image forming method of the present invention, and Figures 2 to 4 are schematic diagrams showing another embodiment of the method of the present invention, respectively. FIG. 5 is a graph for explaining the method of the present invention, and FIG. 6 is a schematic diagram showing an example of a conventional image forming method.

11... Conductive substrate, 12... Conductive electrode, 13.
··power supply.

14... Photoconductive toner, 15a, 15b, 15c.
...Transparent electrode.

that's all

Claims (1)

[Scope of Claims] 1. Charged photoconductive toner is exposed to light to eliminate its charge, and the toner is placed in an electric field to eliminate its charge, and a charge with a polarity opposite to the toner polarity at the time of charging is imparted to the toner. This is an image forming method in which the toner of one polarity is then electrostatically transferred to a transfer paper to form an image. An image forming method that differs in the timing of applying charges of opposite polarity to the toner polarity. 2. The image forming method according to claim 1, wherein the timing of applying the charges of opposite polarity is started at a time point when exposure of the photoconductive toner is not completely completed. 3. The image forming method according to claim 1, wherein the photoconductive toner is deposited on a movable conductive substrate, and the toner is exposed to light as the substrate moves. 4. The electric field is formed by a conductive electrode disposed opposite to the substrate, and the conductive electrode is located downstream of the exposure position of the substrate in the direction of movement thereof. The image forming method described. 5. According to claim 3, the electric field is formed by a transparent electrode disposed opposite to the substrate, and the photoconductive toner on the substrate is exposed through the transparent electrode. image forming method. 6. The image forming method according to claim 5, wherein the transparency of the transparent electrode is higher in an upstream portion of the substrate than in a downstream portion in the moving direction of the substrate. 7. The image forming method according to claim 5, wherein the electric field strength of the transparent electrode is greater in a downstream portion in the moving direction of the substrate than in an upstream portion. 8. The image forming method according to claim 7, wherein the transparent electrode is inclined such that the downstream end in the moving direction of the substrate approaches the substrate. 9. The image forming method according to claim 7, wherein a dielectric material that increases the dielectric constant of an upstream portion of the substrate in the moving direction is provided on a surface of the transparent electrode facing the substrate.