JPH05307314A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the density of a first image from being lowered by providing a preliminary electrostatic charge means which previously preliminarily electrostatically charges an image forming area on a latent image carrier so that triboelectrified charge on the surface of the latent image carrier is negated. CONSTITUTION:The preliminary electrifying means (an electrostatic charger 4 or a transfer charger 8 used also as electrostatic charge means) by which the image forming area on a photosensitive body 1 is previously preliminarily electrified so as to negate the triboelectrified change on the surface of the body 1 generated by allowing a cleaning member to rub on the surface of the body 1 when the first image is formed after the standby of a device is provided. By previously imparting electric charge whose polarity is positive to the surface of the body 1 before the image forming area of the body 1 used for forming the first image arrives at the part of the roller 9 or the blade 10 of a cleaning device 2, the triboelectric charge whose polarity is negative is prevented from being left. Therefore, the surface of the body 1 can be eloectrostatically charged by the surface potential at the time of forming and subsequent images and the density of the image can be prevented from being lowered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus provided with a cleaning member for rubbing the surface of a latent image carrier.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a printer which uses a latent image carrier such as a photoconductor, the latent image carrier is charged and exposed to a predetermined surface. An electrostatic latent image is formed, and the electrostatic latent image is visualized as a toner image by a wet developing device or a dry developing device, and the toner image is transferred to a predetermined recording medium.

The conventional problems will be described below by taking an image forming apparatus using a drum-shaped photosensitive member as a latent image carrier as an example.

If, for example, a selenium photoconductor is used as the photoconductor, it has a positive charging characteristic, and therefore, the developing toner is usually one having a negative charging characteristic. The electrostatic latent image on the photoconductor is visualized as a toner image by using such toner, but at the time of transfer, a corona having a positive polarity is formed from the back surface of a recording medium such as transfer paper made of plain paper. The discharge is performed to apply a positive charge to the recording medium, and the toner of the toner image is electrostatically attracted toward the recording medium.

After such transfer, since the toner that has not contributed to the transfer remains on the surface of the photosensitive member, it is removed by a cleaning device. For example,
In a cleaning device that uses a cleaning blade as a cleaning member, this blade scrapes off and removes residual toner. After that, the entire surface of the photoconductor is exposed with a charge eliminating lamp or the like to erase the residual charges on the surface, and the next image formation is prepared.

In such an image forming apparatus, when a cleaning member such as a cleaning blade is used as a cleaning member, the surface of the photosensitive member is triboelectrically charged to a predetermined polarity. I will end up. For example, when a cleaning blade made of rubber or the like is used, the surface of the photoreceptor is negatively charged by friction.

After the cleaning step, the charge of the original positive polarity is erased by a static elimination lamp or the like, but the triboelectric charge of the negative polarity is not erased by it. When the next charging step is started while such negative charges remain, the surface of the photoconductor becomes difficult to be charged to a predetermined potential, which causes a decrease in image density.

By the way, in this type of image forming apparatus, a transfer charger for carrying out corona discharge is used for transfer. However, when corona discharge is carried out by such a transfer charger, the photosensitive member itself is also charged. .. This polarity is positive. When such positive charges or positive charges remaining after the charging process pass through the cleaning blade portion while remaining on the photoreceptor, the negative triboelectric charges generated at this point are generated. The charge is canceled by the positive charge, and there is no negative charge. Then, after that, the positive charge is removed by the charge eliminating lamp, and the surface of the photoconductor is charged in a state where the surface potential is almost zero or a slight positive charge remains.

As described above, before cleaning,
If the surface of the photoconductor is positively charged, the triboelectric charge will be canceled by it, and the surface potential at the time of the next charging will not drop, but after waiting for the device,
When the first image formation is performed, when the image forming area on the surface of the photoconductor passes through the cleaning device, such surface is in a state where no such electric charge is carried. The surface portion of the photoconductor that is not charged by the charging means or the transfer charger passes through the cleaning device.

For example, in a wet developing type image forming apparatus, a developing solution is supplied to a developing apparatus and a cleaning apparatus is also supplied with the developing solution. When the image forming apparatus starts the image formation after the standby, it rotates the photoconductor and simultaneously operates the pump to supply the developing solution to the developing apparatus and the cleaning apparatus. Then, in the cleaning device section, while the developing solution is flowing, the cleaning blade scrapes off the toner adhering to the photoconductor to clean the surface thereof.

The charging process and the transfer process are started when the developing solution is sufficiently supplied to the developing device. If the cleaning process is performed before this,
As described above, the surface of the photoconductor is charged with the triboelectric charge, and the charging process is started in this state. That is, since the selenium photoconductor has a positive charging characteristic, the negative charge cannot be completely erased by the charge eliminating lamp, and the negative charge remains for the first charging for image formation. Will be faced with.

This is not the case in the second and subsequent image formations. However, in the first image formation, the surface potential of the photoconductor after the charging process is lower than in the second and subsequent image formations. Even if the surface of the photoconductor is exposed with the same amount of light, the potential after exposure will be low, and the toner that electrostatically adheres to the photoconductor during the development process will be reduced and the image density will decrease. become.

When forming an image longer than the circumference of the photosensitive member, the photosensitive member is rotated once or more in the first image formation.
This causes a problem that the image density of the first copy sheet becomes high in the middle.

[0014]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which is less likely to reduce the density of the first image obtained on a recording medium.

[0015]

In order to achieve the above object, the present invention provides a charging means for uniformly charging the surface of a latent image carrier and an electrostatic latent image on the surface by exposing the charged surface. After forming the electrostatic latent image, a developing unit that visualizes the electrostatic latent image as a toner image, a transfer unit that transfers the toner image onto a recording medium, and a latent image carrier used for image formation for the next image formation. A cleaning unit that cleans the surface of the latent image carrier after the toner image transfer by rubbing with a cleaning member, and a static eliminator that neutralizes the surface of the latent image carrier for the next image formation. In performing the first image formation after the apparatus is on standby, the latent image carrier is so formed that the triboelectric charges on the surface of the latent image carrier, which are generated by the rubbing of the surface of the latent image carrier by the cleaning member, are canceled. Preliminarily reserve image formation area Is to propose an image forming apparatus and a preliminary charging unit that charges the.

It is effective if the charging means also serves as the preliminary charging means.

Further, it is effective to use the transfer means also as the preliminary charging means.

[0018]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows a schematic structure of an image forming apparatus according to an embodiment of the present invention.

Reference numeral 1 denotes a drum-shaped selenium photosensitive member which is an example of the constitution of the latent image carrier, and this is rotatively driven in the direction of the arrow by a driving means (not shown). A cleaning device 2, a charge removing lamp 3, a charging charger 4, an eraser 5, a wet developing device 7, a transfer charger 8 and the like are provided around the photoconductor 1 in the order of rotation of the photoconductor 1.

When a print button (not shown) is pressed, a start signal is also generated from a control unit (not shown), and the photoreceptor 1 starts to rotate in the arrow direction. At the same time, a pump (not shown) starts to operate, and a developing solution is supplied from a developing solution tank (not shown) to the cleaning device 2 and the wet developing device 7, respectively.

The wet developing device 7 includes a developing roller 12 and a squeeze roller 12A, and the developing solution sent to the wet developing device 7 and the developing roller 12 which starts rotating at the same time as the rotation of the photosensitive member 1, A liquid pool is formed in the gap between the photoconductor 1. It takes a predetermined time until a liquid pool is formed for good development, and it takes, for example, about 4 seconds depending on the model. That is, it takes about 4 seconds after the start signal is generated until the charging process is started.

Now, assuming that the photosensitive member 1 makes one revolution in about 1 second, the photosensitive member 1 makes about 4 revolutions during that time. During such time, the cleaning device 2 cleans the surface of the photoconductor. As a result, the toner attached to the photoconductor 1 can be sufficiently removed while the image forming apparatus is on standby (when not in use).

The cleaning device 2 is provided with a cleaning roller 9 and a cleaning blade 10 which start rotating simultaneously with the rotation of the photosensitive member 1, the former being, for example, a sponge roller, and the latter being made of elastic rubber. While the photoconductor 1 is rotating four times, for example, the cleaning roller 9 and the cleaning blade 10 scrape off the toner remaining on the surface of the photoconductor. Note that the cleaning blade 10 can be brought into and out of contact with the surface of the photoconductor 1 so as to come into contact with the photoconductor at the first rotation of the photoconductor and to be separated from the photoconductor after completing a series of image forming cycles. It has become. The cleaning roller 9 and the cleaning blade 10 constitute an example of a cleaning member, and the photosensitive member 1 may be cleaned by one cleaning member.

As described above, the cleaning device 2 uses the cleaning member such as the cleaning roller 9 and the cleaning blade 10 to clean the surface of the photoconductor after the toner image transfer so that the photoconductor 1 used for image formation can be used for the next image formation. Cleaning means for cleaning by rubbing. In the case of this example, the surface of the photoconductor 1 is triboelectrically charged with negative polarity due to the relative rubbing between the cleaning roller 9 and the cleaning blade 10 and the photoconductor 1.

After the cleaning step, the positive charges remaining on the surface of the photoconductor 1 are removed by the irradiation of the static elimination lamp 3 with light. The static elimination lamp 3 is used for the cleaning device 2
In cooperation with the above, an example of a charge removing unit that puts the surface of the photoconductor 1 into a charge-removing state so that the photoconductor 1 used for image formation is subjected to the next image formation is configured. The triboelectric charge having the negative polarity cannot be removed by the charge removing means.

Next, the charging step is finally started. From this charging step, the image forming cycle is substantially started and the image formation is started. Charger 4
Is a constitutional example of a charging means for uniformly charging the surface of the photoconductor ₁ and is connected to a direct current high voltage power source E ₁ to perform positive corona discharge. Due to this corona discharge, the surface of the photoconductor 1 is uniformly charged with positive polarity.

Next, at the exposure section 6, image exposure is performed on the charged surface of the photoconductor to form a predetermined electrostatic latent image on the surface of the photoconductor 1. After that, the electrostatic latent image is transferred to the developing roller 1 provided in the wet developing device 7.
2 is visualized as a toner image by the toner T in the developer interposed between the photosensitive member 1 and the photosensitive member 1. As described above, the wet developing device 7 constitutes an example of a developing unit that visualizes the electrostatic latent image as a toner image.

In this way, the toner image formed on the photoconductor 1 is transferred onto the recording medium 13 such as transfer paper. The transfer charger 8 constitutes a transfer means for transferring the toner image on the photoconductor to a recording medium.
A direct current high voltage power source E ₂ is connected to the transfer charger 8.

When a corona discharge having a positive polarity is performed from the back surface of the recording medium 13 that is in close contact with the photoconductor 1 by such a transfer charger 8, the recording medium 13 is positively charged,
As a result, the toner (toner charged negatively) of the toner image on the photoconductor 1 is electrostatically attracted to the recording medium, and the toner image is transferred onto the recording medium 13. At this time, at the same time, the photoconductor 1 is also charged to the positive polarity.

The recording medium 13 onto which the toner image is transferred passes between the turn belt 14 and the separator roller 15 and is sent to a predetermined fixing device section. On the other hand, the toner that has not contributed to the transfer on the photoconductor 1 is cleaned by the cleaning device 2.
Removed by.

The surface of the photoconductor 1 is uniformly charged by the charging charger 4, but the positive charge due to this charging and the positive charge due to the transfer charging are removed by the charge eliminating lamp 3. Hereinafter, such charges will be referred to as “removed positive charges”.

As described above, the friction between the cleaning blade 10 and the cleaning roller 9 and the photoconductor 1 causes the surface of the photoconductor to be negatively charged. When the surface is neutralized by the static elimination lamp 3 and is uniformly charged by the charging charger 4, the surface potential becomes low, which causes a decrease in image density.

On the other hand, in the second and subsequent image formation, the charging charger 4 and the transfer charger 8 are already in operation, and the tip of the area on the surface of the photosensitive member where the image should be formed is cleaned. Before the roller 9 or the cleaning blade 10 is rushed into the site, the surface of the roller 9 has a positive charge to be removed, so that the negative charge is canceled by this charge.
Therefore, in this case, although not a problem, the triboelectric charge is not canceled in the first image formation.

Therefore, the image forming area on the photosensitive member, which is used for the first image formation, is the portion of the cleaning device 2 (the portion of the cleaning roller 9 or the cleaning blade 10).
If a positive charge is applied to the surface of the photoconductor 1 before the above, it is possible to prevent the negative triboelectric charge from remaining. By this, 2
The surface of the photoconductor can be charged with the same potential as the surface potential during the subsequent image formation, and the reduction in image density can be prevented.

A feature of the image forming apparatus of the present invention is that in each of the above-mentioned constitutions, the preliminary charging means, that is, the first image formation after the apparatus waits, is rubbed against the surface of the photosensitive member by the cleaning member. This is because a means for preliminarily charging the image forming area on the photoconductor is added so that the triboelectric charge generated by the above is canceled.

As such a pre-charging means, a dedicated corona discharger arranged opposite to the photoconductor 1 may be used. For example, it may be charged by a charging means such as the charging charger 4. If they are also used, a dedicated corona discharger becomes unnecessary and the structure of the image forming apparatus can be simplified.

In FIG. 2, the charging charger 4 is attached to the pre-charging means.
With a diameter of 80 mm and a surface linear velocity of 266 mm / s
FIG. 7 shows a time schedule when performing lateral feed image formation of the size of row A number 4 using the ec photoconductor. Here, the lateral feed is a feed in which the long side of the long and short sides of the recording medium in the fourth row of column A coincides with the generatrix direction of the photoconductor 1. In this case, the short side length of the recording medium is shorter than the peripheral length of the photoconductor 1.

In this figure, when a start signal is generated, the pump starts operating at the same time as the photoconductor starts rotating, and the developing solution is supplied to the wet developing device 7. Then, after the developing solution is sufficiently supplied, that is, about 4 seconds after the start signal is generated (after the photosensitive member has rotated about 4 times), the charging is started. Before the charging is started, the charging charger 4 is operated to precharge the surface of the photoconductor to the positive polarity. The cleaning operation of the photoconductor by the cleaning device is started, for example, 2 seconds after the start signal is generated.

Here, regarding the pre-charging and the charging operation timing, the region (image forming region) to be used for the first image formation on the photoconductor is pre-charged by the charging charger 4, and this region is The timing may be such that the actual charging starts after passing through the part of the cleaning device. In order to do so, for example, it takes 0.94 seconds for one rotation of the photosensitive member. As such, pre-charging may be performed within 3 seconds after the start signal is generated and up to 4 seconds (while the photosensitive body makes one rotation before charging is started). The point is that at least one revolution of the surface of the photosensitive member before the actual charging is precharged. As a matter of course, the precharged photoconductor portion is also subjected to the static elimination action by the static elimination lamp 3.

As described above, the charging charger 4 may be used also as the pre-charging means, but in addition to this, the transfer charger 8 may also be used as it. Figure 3
Shows an example of the time schedule in this case.

As shown in FIG. 1, the transfer charger 8 is
It is located about 170 ° upstream of the charger 4 with respect to the rotation direction of the photoconductor 1. Now, assuming that the time required for the photoconductor 1 to rotate by 170 ° is t, the time t before the charging of the region on the photoconductor used for the first image formation is started. The precharge by the transfer charger 8 may be started, and after the start, the precharge may be continued for one rotation of the photoconductor. That is, after the start signal is generated,
After 3.5 seconds, until 4.5 seconds,
It suffices to carry out preliminary charging. As described above, also in this case, at least one rotation of the photoconductor 1 is precharged, and the static elimination lamp 3 also performs static elimination on this portion.

In any case, in carrying out the first image formation, the positive charging is applied to the surface of the photosensitive member by the pre-charging means before the cleaning step. Thus, even if the surface of the photoconductor is triboelectrically charged with negative polarity, the triboelectric charge of negative polarity is canceled by the positive charge.

As a result, the negative charge disappears on the surface of the photoconductor, and the positive charge is also removed by the charge eliminating lamp 3, so that the surface of the photoconductor is at a substantially zero potential or slightly. It is uniformly charged by the charging charger 4 while having a positive charge.

In other words, the charging potential of the first image-formed area becomes the same as that of the second and subsequent image-formed areas, so that the image of the required density can be obtained at the first time. It will be. In the image forming apparatus of this example, when using a recording medium longer than the circumference of the photoconductor,
It is possible to prevent the image density from increasing.

A technique in which an AC corona charger is used in order to reduce the potential on the surface of the photosensitive member to zero before charging is disclosed in, for example, JP-A-59-113475.

As the charging means and the transfer means, in addition to the charger, it is also possible to use a charging roller or a transfer roller that comes into contact with the photosensitive member.

[0048]

According to the image forming apparatus of the first aspect, the latent image carrier is formed such that the charged potential of the area on the latent image carrier, which is imaged for the first time, is imaged for the second time and thereafter. Since it can be made almost equal to the charged potential of the area on the body, from the first time,
It is possible to obtain an image of good quality without density reduction.

According to the image forming apparatus of the second and third aspects, the dedicated pre-charging means is not required, and the structure of this type of image forming apparatus can be further simplified.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a time schedule when a charging charger is used as a preliminary charging unit.

FIG. 3 is a diagram showing an example of a time schedule when a transfer charger is used as a preliminary charging unit.

[Explanation of symbols]

 1 Photoreceptor as a latent image carrier 2 Cleaning device as a cleaning unit 3 Discharge lamp as a charge eliminating unit 4 Electric charge charger as a charging unit 7 Wet developing device as a developing unit 8 Transfer charger as a transferring unit

Claims (3)

[Claims] 1. A charging unit for uniformly charging the surface of a latent image carrier, and an electrostatic latent image is formed on the charged surface by exposing the charged surface, and the electrostatic latent image is used as a toner image. Developing means for making the image visible, transfer means for transferring the toner image onto a recording medium, and the surface of the latent image carrier after the toner image is transferred so that the latent image carrier for image formation is used for the next image formation. In the same manner as the cleaning means for cleaning by cleaning the cleaning member with a cleaning member, the charge removing means for removing the charge on the surface of the latent image bearing body for the next image formation, and the first image formation after waiting for the apparatus. Pre-charging means for pre-charging the image forming area on the latent image carrier so that the triboelectric charges on the surface of the latent image carrier, which are caused by the rubbing of the surface of the latent image carrier by the cleaning member, are canceled. Is equipped with Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the charging means also serves as the preliminary charging means. 3. The image forming apparatus according to claim 1, wherein the transfer means also serves as the preliminary charging means.