JPH0750369B2 - Image recorder - Google Patents

Description

The present invention relates to an image recording apparatus using a reversal development method, and relates to an apparatus for preventing stains on the edge of an image.

The reversal development method of the conventional electronic copying apparatus is an image recording device in which a laser beam of a laser beam printer is used to write on a photoconductor or an OFT / L.
It is often used in recording devices that use light-emitting elements such as ED and plasma. In the reversal development, the polarities of the primary charger and the transfer electric device are opposite to each other. For example, in a device using an organic semiconductor (OPC), the polarity of the primary charger is negative and the polarity of the transfer charger is positive.

In this type of device, the positional relationship among the photosensitive member, the primary charging area, the image area, the developer supplying area, the transfer charging area, the separating member area, and the pre-exposure area in the direction perpendicular to the photosensitive member moving direction is shown in FIG. As shown. In the image recording apparatus having the separation member as shown in the figure, the width of the transfer charger is substantially regulated by the separation member, and the width of the transfer charger becomes shorter than the width of the primary charging area.

The pre-exposure then illuminates the entire primary charging area and is used to erase the image memory. Therefore, as shown in FIG. 1, the portion A, that is, the portion which is not subjected to the transfer charging but is subjected to the primary charging and is subjected to the pre-exposure is lower in durability than the portion B to which the primary charging, the transfer charging and the pre-exposure are applied. The dark area potential V _{D of the} image tends to decrease further. This situation is shown in FIG. 2, where the horizontal axis represents the number of continuous copies and the vertical axis represents the potential, and the curve B is the portion corresponding to B in FIG.
_Shows the potential change of V _{D in} the portion corresponding to A in FIG. If the charging of the same polarity as the charging polarity of the photosensitive member and the charging and discharging of the photosensitive member are repeatedly performed as the characteristics of the photosensitive member, the sensitivity characteristic of the photosensitive member gradually deteriorates. On the other hand, if the process of repeating the process of applying a charge having the same charge polarity as that of the photoconductor, then applying a charge having a polarity opposite to the charge polarity of the photoconductor, and then exposing and removing the charge, the sensitivity characteristic of the photoconductor is changed. Degradation does not progress much. This is because after the photosensitive member is charged with the charging polarity, the charging polarity of the photosensitive member is opposite to the charging polarity of the photosensitive member. Therefore, the deterioration of the sensitivity characteristic of the photoconductor due to the durability is relatively large because the transfer charge, which is the opposite polarity to the charge polarity of the photoconductor, is not applied in the portion A, and only the primary charge having the charge polarity of the photoconductor is applied. In the portion B, the primary charging having the charging polarity of the photoconductor and the primary charging that alleviates the charge and the transfer charge, which is the opposite polarity to the charging polarity of the photoconductor, are applied, and thus become relatively small. Therefore, as shown in FIG. 2, in the portion A, the decrease in V _D due to the durability is larger than in the portion B. V _{D for} reversal development
The lower the value, the more easily it becomes fogging. Particularly, in the separation belt system, the edge of the image area is adjacent to the edge of the separation member, and the toner on the developing sleeve adheres to this portion where the V _D potential is lowered and stains the image edge. This is because the toner attached to the portion A of the photoconductor stains the separation member or directly stains the transfer material.

It is an object of the present invention to prevent the local decrease in dark area potential due to the durability as described above. According to the present invention, a charging unit that charges the electrophotographic photosensitive member to form an electrostatic latent image on the electrophotographic photosensitive member, and a developing process that develops the electrostatic latent image with a toner having the same polarity as the charging polarity of the charging unit Means, a transfer means to which a voltage having a polarity opposite to the charging polarity of the charging means is applied to transfer the toner image formed on the photoconductor to a transfer material, and the charging means after transfer by the transfer means. Pre-exposure means for uniformly exposing the photoreceptor before charging,
In the image recording apparatus having: the first area of the photoconductor that is charged by the charging means and is not charged by the transfer means, the second area of the photoconductor that is charged by the charging means and the transfer means. The amount of light by the pre-exposure means is smaller than that in the area (1).

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a sectional view of an embodiment for explaining the image recording method of the present invention, in which L is a laser beam which is blink-modulated in response to a recorded image information signal from a computer, a word processor, a facsimile transmitter or the like. Reference numeral 1 is an electrophotographic photosensitive drum, which is sensitive to a laser oscillation wavelength of 770 to 800 nm,
For example, a metal phthalocyanine-based organic photoconductor, a selenium-based photoconductor, amorphous silicon, or the like may be used. The photosensitive drum 1 is uniformly charged by the primary charger 2 and rotated in the direction of the arrow, scanned by the laser beam L, an electrostatic latent image is formed, and the developer 3 visualizes it with toner. The toner is charged to have the same polarity as the charging polarity of the primary charger 2, and adheres to the photoconductor portion exposed by the laser beam, that is, the bright portion potential portion. That is, the latent image is reversely developed.
The visible image is transferred onto the transfer material by the transfer charger 4 having a polarity opposite to that of the primary charging. The end of the transfer material is engaged with the separation belt 7 arranged at the end of the drum 1 and thereby separated from the drum 1. After that, the transfer material is sent to the fixing device. On the other hand, the toner remaining on the surface of the drum 1 is removed by the cleaning device 5 and then uniformly exposed by the pre-exposure light source 6. The pre-exposure removes the charge from the drum 1 and prevents the ghost phenomenon from occurring. As the light source 6, a halogen lamp, an incandescent bulb, an LED or the like can be used. In order to uniformly guide the light of the light source 6 to the drum 1, an optical fiber, a cylindrical lens or the like may be used.

In this embodiment, as indicated by a broken line C in FIG. 1, the amount of pre-exposure light at the end A of the photosensitive member, that is, the portion A that receives only the primary charging without being subjected to the transfer charging having the polarity opposite to that of the primary is The part B is reduced. Generally, the pre-exposure aims at erasing the image memory and making the potential uniform, but since the portion A is a portion where an image is not formed, it is not necessary to consider the above, and only the potential is applied. You can think about it. By reducing the amount of light for pre-exposure in the portion A in this manner, the fall of the drum potential can be prevented, and fog in this portion can be eliminated. In this case, it is preferable that the pre-exposure light amount of the portion A is about 40 to 80% of the average light amount of the portion B.

As a means for reducing the amount of light, a slit may be provided near the photoconductor. For example, as shown in FIG. 3, a part 2b of the shield case 2a of the primary charger may be bent so as to protrude to a portion to which the pre-exposure is irradiated. Alternatively, a photosensitive filter may be provided corresponding to the portion A, or the emission intensity of the pre-exposure light source for illuminating the portion A may be set lower than the emission intensity of the pre-exposure light source for illuminating the portion B.

Although the image recording apparatus having the separation belt is shown in the above-mentioned embodiment, it is not a belt-shaped or claw-shaped one or does not have such a separation member so that the width of the primary charging and the transfer charging are largely different from each other. The above embodiment can be applied to various device configurations.

As described above, the pre-exposure has an effect of making the erase potential of the image memory uniform and the like, but on the other hand, by repeating the charging having the charging polarity of the exposed body and the pre-exposure, the fall of the dark part potential is promoted. It also has the effect of Therefore, the dark part potential (V _D ) tends to gradually fall in the repeating process of primary charging → pre-exposure → primary charging without being subjected to transfer charging having a polarity opposite to that of primary charging as in the image end portion. Therefore, reducing the pre-exposure amount in such a part significantly improves the fall of the dark part potential, and prevents that part from being fogged by the reversal developing agent and contaminating the image end part. It has an effect that can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a positional relationship among a primary charging area, an image area, a developer supplying area, a separating member area, a transfer charging area, and a pre-exposure area.
FIG. 3 is a graph showing changes in dark area potential in that embodiment, and FIG. 3 is a view showing a main part of an image recording apparatus to which the present invention is applied. L is a laser beam, 1 is a photosensitive drum, 2 is a primary charger, 3 is a developing device, 4 is a transfer charger, 5 is a cleaning device, 6 is a pre-exposure light source, 7 is a separation belt, and 2a is pre-exposure irradiation. Slit regulation member.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Jun Asai 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Hiroshi Sasame 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Within the corporation (56) Reference JP 55-95974 (JP, A) JP 56-54458 (JP, A) JP 58-43483 (JP, A) JP 59-218469 (JP, A) JP 57-128369 (JP, A) JP 56-140370 (JP, A) JP 50-99743 (JP, A) JP 53-6032 (JP, A) Actual development Sho 59 -35963 (JP, U) JP-B 63-3314 (JP, B2) JP-B 56-18953 (JP, B2)

Claims (1)

[Claims] 1. A charging unit for charging the photosensitive member to form an electrostatic latent image on the electrophotographic photosensitive member, and a developing process for developing the electrostatic latent image with a toner having the same polarity as the charging polarity of the charging unit. Means, a transfer means to which a voltage having a polarity opposite to the charging polarity of the charging means is applied to transfer the toner image formed on the photoconductor to a transfer material, and the charging means after transfer by the transfer means. In an image recording apparatus having a pre-exposure unit that uniformly exposes the photosensitive member before charging, the first region of the photosensitive member that is charged by the charging unit and is not charged by the transfer unit, An image recording apparatus characterized in that the amount of light by the pre-exposure unit is smaller than that in the second region of the photoconductor that is charged by the charging unit and the transfer unit.