JPH0143309B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for preventing fog toner attached to bright image areas of an electrophotographic photoreceptor from being transferred to a transfer material. The present invention relates to an electrophotographic apparatus having a pre-transfer corona discharger. More specifically, only the polarity of the toner adhering to the bright area of the image is changed without changing the polarity of the toner adhering to the dark area of the image, thereby preventing this fog toner from being transferred onto the transfer material. The present invention relates to an electrophotographic apparatus characterized by the following.

As a conventional example, US Pat. No. 3,444,369 discloses a method and means for preventing fog toner transfer by applying extremely weak corona discharge having a polarity opposite to that of the developed toner onto a developed photoreceptor before transfer. The contents can be summarized as follows.

For example, a selenium photoreceptor is used as a photoreceptor, and a dark area latent image potential +
800V, bright area latent image potential +200V is formed. When uniform corona discharge is performed using a corotron on a photoreceptor on which a latent image is formed in this manner, a difference occurs in the amount of charge increase due to corona discharge between dark areas and bright areas. When the polarity of the corotron is set, the amount of charge given by the corotron in the dark part of the photoreceptor leaks to the photoreceptor substrate through the photoreceptor layer as an amount of charge greater than that allowed by the photoreceptor, and the potential of the photoreceptor surface becomes +800V.
is maintained. On the other hand, in the bright portion of the photoreceptor, the surface potential gradually increases due to the charge from the corotron.

Comparing the amount of charge applied to the surface of the photoreceptor per unit time, the electric field due to the surface potential of 800 V in the dark area of the photoreceptor suppresses corotron corona discharge more strongly than the electric field due to the surface potential of 200 V in the bright area of the photoreceptor. , the amount of charge applied to the dark areas of the photoreceptor is small, and the amount of charge applied to the bright areas of the photoreceptor is large. When toner adheres to the surface of the photoreceptor, the polarity of the toner adhered to the bright portion changes more easily. Therefore, the toner in the bright areas easily changes polarity, and then when a polar transfer corona is applied to the back of the transfer material, the toner in the dark areas is transferred to the transfer material, but the toner in the bright areas is not transferred. , it was possible to obtain a copy image without fog.

By the way, when the anti-fogging means described in U.S. Pat. It has the disadvantage that the ability to prevent transfer is reduced.

FIG. 1 is an explanatory diagram showing the reason. 1 indicates a selenium photoreceptor. D indicates a dark part of the image, and the photoreceptor surface potential is +800V. 2 is the toner attached to the dark part of the image, and the surface potential of the photoreceptor after the toner is attached is +700V. L indicates the bright part of the image, and the photoreceptor surface potential is +200V. 2 is toner attached to the bright portion of the image, and 3 is uncharged toner, which is attached electrostatically or mechanically. Even after the toner is attached, the surface potential of the photoreceptor hardly changes. A corotron is provided on the photoreceptor, and 4 indicates a discharge wire of the corotron. The distance between the photoreceptor 1 and the corona wire 4 is 13 mm.

For example, when a voltage of +6KV is applied to the corotron, the voltage between the toner surface and the corona wire is E _D = E _O − E _P + E _T /13 = 6000 − 800 + (800 − 700) / 13 ≒ 408 V / mm In the bright area, an electric field of E _L = 6000−200/13≒446V/mm is generated. Note that E _O represents the electric field due to the corotron, E _P represents the electric field due to the photoreceptor, and E _T represents the electric field due to the toner.

Corona ions emitted from the corotron move through the electric field and charge the attached toner. As is easily known, the electric field in the bright area and the electric field in the dark area are approximately equal. Therefore, with this conventional method, it is extremely difficult to change the polarity of only the toner adhered to the bright areas and not change the polarity of the toner adhered to the dark areas at all. In other words, part of the toner adhering to the dark area undergoes polarity conversion, and when the toner is then subjected to transfer corona, the polarity-converted toner is not transferred, resulting in uneven images.

For example, if +4KV is applied to the corotron,
An electric field is generated between the toner surface and the corona wire of E _D = 4000-800 + (800-700)/13254V/mm in the dark area and E _L = 4000-200/13292V/mm in the bright area.

Since the electric field in the dark direction is less than the corona discharge starting electric field, there is little corona current generated in this direction. Therefore, it is very unlikely that the corona generated by the corotron will adhere to the dark area and change the toner polarity. On the other hand, corona is applied to the toner adhering to the bright areas, making it possible to prevent fogging.

However, since the electric field strength of E _L is small, the moving speed of the corona from the discharge electrode to the photoreceptor is slow, and there is a drawback that it takes too much time to provide sufficient corona to prevent fogging. Also, since the corotron is used near the corona starting voltage,
When the temperature and humidity change, corona generation is suppressed too much, resulting in insufficient fog prevention.

The present invention provides an electrophotographic apparatus having a pre-transfer corona discharger for preventing the above-mentioned drawbacks and obtaining copy images free of transfer unevenness and fog.

The present invention includes a photoreceptor, a developing means for developing electrostatic latent lines formed on the photoreceptor, and a transfer means for transferring a developed image formed on the photoreceptor by the developing means to a transfer material. An electrophotographic apparatus comprising: a corona discharge electrode provided between the developing means and the transfer means, to which positive and _negative voltages are applied alternately; This electrophotographic apparatus is characterized in that it has a pre-transfer corona discharger equipped with a control grid to which a voltage between the electric potential V _L of the bright part of the body and a control grid is applied.

This has the advantage that a copy image without fog or uneven transfer can be obtained.

Embodiments of the present invention will be described below based on the drawings.

FIG. 2 is a configuration explanatory diagram showing an embodiment of the present invention. Components in the figure that are the same as those in FIG. 1 are given the same reference numbers. 1 is a photoreceptor, and its surface has a dark area surface potential V _D +800V and a light area surface potential V _L +200V.
A latent image is formed. The surface potentials after development are +700V and +200V, respectively. 5 is a discharger shield, and 4 is a discharge electrode, to which an AC high voltage of about 6 KV is applied by a power source 8. The opening of the discharger on the photoreceptor side is equipped with a control grid of φ60μ.
Tungsten wires of 100 μm in diameter are provided at intervals of 0.5 to 2 mm and approximately 1 mm apart from the surface of the photoreceptor, and these wires are connected to a bias power source 7.

As the bias voltage, a voltage between the bright area potential and the dark area potential of the photoreceptor after development is selected. This is because a promoting electric field and a suppressing electric field for corona ions are formed between the surface potential of the photoreceptor and the control lattice, and as a result, the dark area toner is charged more negatively, improving transferability, and the image becomes brighter. Fog prevention is achieved by converting only the toner adhering to the area to the opposite polarity. Moreover, since a voltage higher than the corona starting voltage can be applied to the discharge electrode, the conventional drawback that the anti-fogging effect is reduced due to environmental changes such as temperature and humidity can be avoided.

Figure 3 shows the bright area during positive corona discharge. A bias of approximately +400V is applied to the control grid. After the positive corona ions generated at the discharge electrode 4 reach the vicinity of the control grid 6, the promoting electric field E=200V/
It reaches the surface of the photoreceptor along mm and converts the fog toners 2 and 3 in the bright areas of the image into positive polarity. This charging continues until the photoreceptor surface potential reaches +400V, and the fog toner is sufficiently converted to positive polarity.

Figure 4 shows the bright area during negative corona discharge. Negative corona ions generated at the discharge electrode 4 reach the vicinity of the control grid 6, but the control grid 6 and the photoreceptor 1
Because of the suppressing electric field E=200V/mm formed between the photoreceptor and the photoconductor, the photoreceptor cannot reach the photoreceptor and is collected by the control grid. Therefore, the toner adhering to the bright areas of the image is not negatively charged.

Figure 5 shows the state of negative corona discharge in the dark area. A bias of approximately +400V is applied to the control grid. After the negative corona ions generated at the discharge electrode 4 reach the vicinity of the control grid 6, they reach the surface of the photoconductor along the promoting electric field of 300 V/mm formed between the control grid 6 and the photoconductor 1, causing dark areas of the image. toner to a more negative polarity. As a result, the dark area toner is sufficiently negatively charged, and the transfer efficiency can be improved.

Figure 6 shows the state of positive corona discharge in the dark area. The positive corona ions generated at the discharge electrode 4 reach the vicinity of the control grid 6, but the control grid 6 and the photoreceptor 1
Because of the suppressing electric field of 300 V/mm formed between the photoreceptor and the photoconductor, the photoreceptor cannot reach the photoreceptor and is collected by the control grid. Therefore, the toner attached to the dark areas of the image is not converted to positive polarity.

As described above, the toner polarity in the dark areas of the image is charged to a stronger negative polarity, and at the same time, it is possible to convert the toner polarity in the bright areas of the image to the opposite polarity.
It becomes possible to obtain a copy image without fog or uneven transfer.

Incidentally, a configuration in which uniform light irradiation is applied substantially simultaneously with the discharge of the pre-transfer corona discharger configured in FIG. 2 is also possible. The amount of uniform light is sufficient to make the toner-free portion of the photoreceptor, that is, the photosensitive layer portion in the bright area of the image, conductive, and the amount of light is set to be 1/2 or equivalent to the image exposure amount. Since no corona charge is accumulated on the conductive surface of the photoconductor, the potential of the photoconductor surface is maintained at 200V, and the potential of the photoconductor surface increases to increase the voltage between the photoconductor surface and the control grid. Since the promoting electric field continues to remain sufficiently large without weakening, the toner is given a charge of sufficient opposite polarity to prevent fogging. In the dark areas of the image, the uniform light amount is 1/10 to 1/2 because it is blocked by the toner layer.
10, so the effect on the charge on the surface of the photoreceptor is small.

In the explanation of the embodiments of the present invention, an example was shown in which a two-layer photoreceptor based on the Carlson method was used as the photoreceptor, but the photoreceptor used in the electrophotographic method described in Japanese Patent Publication No. 42-23910 etc. The present invention is also applicable to such a three-layer photoreceptor having an insulating layer on its surface.

As described above, in the present invention, a pre-transfer corona discharger is provided between the developing means and the transfer means. Since the control grid is equipped with a control grid that applies a voltage between the potential V _D of the photoconductor and the potential V _L of the bright area of the photoreceptor after development, the toner in the dark area is more strongly charged, and the toner in the bright area is charged with the opposite polarity. As a result, the transferability of the dark toner image is improved, a fog-free copy image can be obtained, and pre-transfer corona discharge can be performed without being affected by environmental changes.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the reason for the drawbacks of the conventional device.
FIG. 2 is a configuration explanatory diagram showing an embodiment of the present invention, and FIG.
6 to 6 are explanatory diagrams showing the operation of the apparatus of the present invention. In the figure, 1... photoreceptor, 2... toner attached to the bright area of the image, 3... uncharged toner, 4... discharge wire, 5... discharger shield, 6... control grid, 7... bias Power supply, 8...represents an AC high voltage power supply.

Claims (1)

[Claims] 1 Electrophotography comprising a photoreceptor, a developing means for developing an electrostatic latent image formed on the photoreceptor, and a transfer means for transferring the developed image formed on the photoreceptor by the developing means to a transfer material The apparatus comprises a corona discharge electrode provided between the developing means and the transfer means, to which positive and negative voltages are applied alternately, and a potential V _D of the dark part of the photoreceptor after development and a brightness of the photoreceptor after development. An electrophotographic apparatus characterized in that it has a pre-transfer corona discharger comprising: a control grid to which a voltage is applied between the electric potential V _L of the part and the electric potential V L of the part;