JPH0510673B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a transfer type electrophotographic apparatus, and particularly to an electrophotographic apparatus in which a developer is attached to a bright area potential area. In a transfer type electrophotographic apparatus, in order to improve the transfer efficiency of a visible image, the photoreceptor is uniformly exposed to light after development and before transfer to attenuate the potential on the photoreceptor. Further, there is a device that applies alternating current corona discharge or the like to the transfer material to remove static electricity and electrostatically separate the transfer material from the photoreceptor after transfer. In this case, the strength of the separation static electricity removal is kept constant, but if the static electricity removal effect is too low, the separation performance is poor, and if it is too strong, re-transfer occurs and the image quality deteriorates. The rate of static elimination strength becomes narrower. Furthermore, the optimum image for separation and charge removal differs depending on the area ratio of the dark area and the bright area, and depending on this area ratio, problems such as poor separation and retransfer occur. However, if pre-transfer exposure is performed between the transfer step and the development step to reduce the difference in surface potential between the bright and dark areas, the separation latitude can be widened. However, in the above-mentioned apparatus, when the dark potential area, which is a high potential area, is a non-information area, and toner is to be attached to the bright potential area, which is a low potential area, by reversal development, it is necessary to perform pre-transfer exposure. When doing so, there are the following problems. To explain this problem with Figure 1, Figure 1 shows the surface potential of the photoreceptor. photoreceptor area). V _L is the surface potential of the bright part (bright part potential) of the electrostatic latent image formed by exposing the above optical information, and V _D
is the surface potential of the dark part (dark part potential) of the same latent image. In FIG. 1, latent images of V _D =+750 ^V and V _L =+250 ^V are formed. The latent image is formed by exposure to optical information, and then the toner T charged to a positive polarity is applied to the bright area, which is a lower potential area than the dark area, by a developing device, and the latent image is developed. Next, in the pre-transfer exposure section, the surface of the photoreceptor is uniformly exposed. However, in bright areas, toner T adheres to the surface, making it difficult for light to reach the surface of the photoreceptor, so the surface potential is less likely to decrease than in dark areas. Therefore, the order of height of the surface potential of the dark area (V _D ′) and the surface potential of the light area (V _L ′) after the pre-transfer exposure is reversed, and the surface potential of the dark area (V D ′) becomes the surface potential of the bright area (V _D ′). V _L ′).
This is shown by the dotted line in FIG. In this situation, the positively charged toner in the bright area has a lower surface potential than the dark area, so the toner tends to scatter to the dark area, causing image disturbance on the photoreceptor before being transferred to the transfer material. However, the image on the transfer material also has the drawback of blurring and blurring. This development is particularly remarkable when reversal development is performed using a one-component developer in which the amount of charge imparted to the toner is mainly obtained by triboelectric charging or contact charging with an electrode. This is presumed to be because the toner has a very low charge amount, about 1/4 to 1/10, compared to conventional two-component developing systems, and thus the adhesion between the toner and the photoreceptor surface is weak. The above development is a problem unique to reversal development and does not occur during regular development. That is, during regular development, toner is attached to the dark area, which is a high potential area, and no toner is attached to the surface of the bright area. Therefore, in the next pre-transfer exposure area, no matter how strong the light is irradiated, the surface potential of the dark area to which toner is attached will not become lower than the surface potential of the bright area. The main object of the present invention is to solve the above-mentioned disadvantages. Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is an explanatory diagram of an embodiment in which the present invention is applied to a laser beam printer. In the figure, a video signal 3 based on the information to be printed from an information source 2 causes an intermittent laser beam 4 to be generated from a laser generator 1 . The intensity of this generated laser beam 4 is controlled by a signal 3. The laser beam 4 is reflected by a rotating polygonal reflecting mirror 5, focused by a θ lens 6, reflected by an optical path direction changing mirror 7, and then directed to a photoreceptor drum 8.
The photosensitive surface 9 is scanned in a direction substantially perpendicular to the direction of rotation of the drum 8. The photosensitive surface 9 is formed by providing a surface photoconductive layer on a conductive layer (for example, an aluminum substrate is provided with a selenium vapor-deposited layer, amorphous silicon, or an OPC layer, etc.), and is used in the so-called Carlson electrophotographic process. Process etc. can be used. First, the photosensitive surface 9 of the photosensitive drum 8 rotating in the direction of the arrow is uniformly charged to, for example, positive polarity by a charger 10 at a charging position. In this state, when the laser beam 4, which is controlled on and off by the video signal 3, is irradiated at the optical information exposure position, a static elimination operation is performed and an electrostatic latent image is formed. The photosensitive surface area (bright area) exposed to the laser beam 15 has a low potential, and the photosensitive surface area (dark area) not exposed to the laser beam 4 remains at a high potential. The latent image is developed and visualized by a developing device 10. The developing device 10 is a developing device that performs so-called reversal development, in which developer is applied to the bright areas and not to the dark areas. To explain the embodiment in detail, a conductive sleeve 11 serving as a developer carrying means that rotates in the direction of the arrow carries positively charged insulating toner T on its circumferential surface and transfers it to the photosensitive surface 9 at the development position. Supply toner T. As described above, the positively charged toner T adheres to the bright potential area that has been lowered in potential by exposure to the laser beam.
Therefore, it is preferable to apply a voltage between the bright area potential and the dark area potential to the sleeve 11 as a bias voltage. When a one-component developer (for example, an insulating magnetic or non-magnetic toner) is used as the developer, this developer has a small amount of charge, so the present invention provides a remarkable effect as described above. The present invention is also applicable to those using a two-component developer (a mixture of toner and carrier). After development, the photosensitive surface 9 carrying the visible image is uniformly exposed to light by a lamp 13 serving as a pre-transfer illumination means at a pre-transfer exposure position. As a result, the surface potential of the photosensitive surface 9 decreases both in bright areas where toner is attached and in dark areas where toner is not attached. (Details will be described later) The photosensitive surface 9 exposed before transfer reaches the transfer position, and the transfer charger 15 charges the transfer paper 14, which is in close contact with the photosensitive surface 9, with a polarity opposite to that of the toner. A toner image (visual image) is transferred by applying corona discharge. After the transfer, the transfer paper 14 is subjected to an AC corona discharge or a DC corona discharge with a polarity opposite to that of the transfer corona discharge to eliminate static electricity by a separation static eliminator 16 at the separation position, and is electrostatically separated from the photosensitive surface 9. After separation, the transfer paper 14 is sent to a fixing device (not shown) and the toner image is fixed thereon, while the photosensitive surface 9 is cleaned of residual toner by a cleaning device 17. After this cleaning, the charger 10
Before charging, the photosensitive surface 9 is exposed to light with a lamp 19 and/or has its surface charge removed, such as by being subjected to an AC corona discharge in a corona discharger 18, and is then subjected to the action of a charger 10. This is desirable. Now, the pre-transfer exposure with the lamp 13 reduces the surface potential difference between the dark area and the bright area of the photosensitive surface 9, but in the present invention, as shown in FIG.
The surface potential (V _D ′) of the dark region after exposure by the lamp 13 is not lowered than the surface potential (V _L ′) of the bright region exposed by the lamp 13 (exposed through the toner layer on the surface). That is, |V _D ′|
The exposure amount of the photosensitive surface by the lamp 13 is set so that ≧|V _L ′|. This prevents the toner image from scattering, and also widens the latitude of the separation static eliminator in the device that performs electrostatic separation as described above. Table 1 shows an example of an experiment in an apparatus in which a photoreceptor having a selenium vapor deposited layer applied to an aluminum substrate was used as a photoreceptor, and an insulating magnetic toner was used as a one-component developer. In terms of image disturbance, 〇 indicates no disturbance, △ indicates slight disturbance, × indicates significant disturbance, and in terms of separation latitude, 〇 indicates wide case, and × indicates narrow case.

[Table] The pre-transfer exposure amount, |V _D ′|≧|V _L ′|, is determined depending on the material of the photoreceptor, etc. In addition, the exposure amount is set so that |V _D ′|≧|V _L ′| as described above, especially 50V≦|
It is more preferable to set the pre-transfer exposure amount so that the relationship V _D ′|−|V _L ′|≦150V holds. In the above embodiment, the charging polarity of the charger 10 was set to be positive, but it may be set to be negative. In that case, development is performed with negatively charged toner. In this case V _D , V _L
has negative polarity, and V′ _D and V′ _L also have negative polarity, but V′ _D is not lower than V′ _L because |V′ _D |
Suppose that ≧ |V′ _L |. Further, in the embodiment described above, the corona discharger 15 was used as the transfer means, but the transfer paper 1
A roller-like roller for holding and conveying the toner may also be used. In this case, it is preferable to make the transfer roller conductive and apply a bias voltage having a polarity opposite to the charged polarity of the toner in order to improve the transfer efficiency. Further, in the above embodiment, an electrostatic separating means was used to separate the transfer paper 14 from the photosensitive surface, but the photosensitive surface 9
and a part of the transfer paper 14, the transfer paper 1
A mechanical separating means such as a claw or a belt may be used to mechanically separate the photosensitive surface 4 from the photosensitive surface 9, or an electrostatic separating means and a mechanical separating means may be used together. Further, although the embodiment described above is a laser beam printer, the present invention can also be applied to an electrophotographic apparatus that converts a negative original such as a microfilm into a positive copy image. In any case, as explained above,
According to the present invention, in an electrophotographic apparatus that performs reversal development in which a developer is attached to a bright area that is a low potential area, and then performs pre-transfer exposure to reduce the difference between the potential of a dark area and a bright area, By performing pre-transfer exposure at an exposure amount that does not lower the dark area potential (V _D ') after pre-exposure than the bright area potential after pre-transfer exposure, it has become possible to obtain images without disturbance.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the relationship between the potential of a dark area and the potential of a bright area in a conventional example, FIG. 2 is an explanatory diagram of an embodiment of the present invention, and FIG. 3 is an explanatory diagram of an embodiment of the present invention. FIG. 3 is an explanatory diagram showing the relationship between the potential of a dark part and the potential of a bright part. 1 is a laser light source, 9 is an electrophotographic photosensitive surface, 10 is a developing device, 13 is a pre-transfer illumination lamp, 15 is a transfer charger, and 16 is a separation static eliminator.

Claims (1)

[Scope of Claims] 1. A latent image forming means for forming an electrostatic latent image having a dark area and a bright area on a photoconductor, a developing means for developing by applying a developer to the bright area; an electrophotographic apparatus comprising: a transfer charging means for transferring a developed image formed on a photoreceptor to a transfer material; An electrophotographic apparatus characterized in that the exposure amount is set so that the potential after exposure is higher in the dark area than in the bright area.