JP2002268498A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To not only prevent toner from scattering at the time of exposure before transfer but also stably separate a transfer material. SOLUTION: When the surface of a photosensitive drum 1 is exposed before transfer by a pre-transfer exposure device 5, exposure is started at most 0.2 seconds before arrival at an exposure area of the front end in the rotation direction of the photosensitive drum 1 of an image forming area on the surface of the photosensitive drum 1 and is terminated at most 0.2 seconds after passage in the exposure area of the rear end in the rotation direction of the photosensitive drum 1 of the image forming area. Thus the uniformity of transfer and separation in the front end part and the rear end part of an image area can be secured, and scattering of a developer image at the time of pre-transfer exposure is prevented to obtain a picture of high quality, and the transfer material is stably separated.

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 such as a copying machine, a printer, a facsimile, etc., which forms an image using an electrophotographic system, and more particularly, to an image carrier having the same polarity as that of an image carrier. The present invention relates to an image forming apparatus that performs reversal development with a developer.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer, a facsimile, etc., which forms an image using an electrophotographic system, an electric charge having the same polarity as an electrostatic latent image formed on the surface of an image carrier is provided. A reversal development system in which a reversal development is performed with a developer to make a visible image is often used.

FIG. 4 is a schematic sectional view showing a conventional electrophotographic image forming apparatus using a reversal developing method. In this image forming apparatus, a photosensitive drum 100 serving as an image carrier is charged to a predetermined positive potential by a primary charger 101, and is exposed to exposure light (laser light, LED light, or the like) E from an exposure device 102 to be exposed to light. An electrostatic latent image is formed on the drum 100. The electrostatic latent image on the photosensitive drum 100 is reversely developed by a developing device 103 with toner (developer) whose exposed portion is charged to a positive polarity, and is visualized as a toner image (developer image). A charge is applied to the toner image formed on the photosensitive drum 100 by a pre-transfer charger (not shown), and then the potential of a non-image portion (white background) is reduced by a pre-transfer exposure device 104.

At a predetermined timing, a transfer material P such as a sheet is conveyed to a transfer site between a transfer charger 105 and a separation charger 106 which are arranged opposite to the photosensitive drum 100,
The toner image on the photosensitive drum 100 is transferred onto the transfer material P by the transfer charger 105 to which an electric field having a polarity opposite to that of the toner is applied. Then, after the transfer material P is electrostatically separated from the photosensitive drum 100 by the charge removing action of the separation charger 106,
The toner image is heated and pressurized and fixed on the transfer material P by a fixing device (not shown), and is discharged to the outside.

On the other hand, the transfer residual toner remaining on the surface of the photosensitive drum 100 is removed by a cleaning device (not shown), and the residual charge is erased by a pre-exposure device (not shown). Prepare.

As described above, in the image forming apparatus using the conventional reversal developing method, the toner is applied to the back surface (the surface that is not in contact with the toner image) of the transfer material P that has been brought into contact with the toner image during transfer. The transfer charge of the opposite polarity is applied, and the toner image is transferred onto the transfer material P. At this time, since the transfer material P is charged to a polarity opposite to that of the photosensitive drum 100, an electrostatic attraction force is generated between the transfer material P and the surface of the photosensitive drum 100, and the transfer material P is separated from the photosensitive drum 100 thereafter. Difficult to do. In particular, since the background portion, that is, the portion where the toner is not attached, is not exposed to the image, the potential of the photosensitive drum 100 is high and the electrostatic attraction force is large.

When transfer separation is performed by the separation charger (corona charger) 106 as described above, the balance between the electrostatic force and the stiffness (rigidity) of the paper (transfer material P) is used. Therefore, it is important to stably transfer the toner image and separate and transport the toner image from the photosensitive drum 100.

Therefore, before the transfer step, the photosensitive drum 10 is exposed by a pre-transfer exposure device 104 as exposure means such as an LED.
The surface 0 is uniformly exposed, the background potential is reduced, and the electrostatic attraction generated during transfer is weakened to facilitate separation.

[0009]

When the surface of the photosensitive drum 100 is subjected to pre-transfer exposure by the pre-transfer exposure device 104 as in the conventional image forming apparatus described above, if the exposure amount is insufficient, the potential of the photosensitive drum 100 is reduced. When the exposure amount is excessive, the background potential (non-exposed portion potential) of the photosensitive drum 100 becomes higher than the toner portion potential (exposed portion potential). As a result, a part of the toner forming the toner image scatters toward the background portion having a lower potential, thereby deteriorating the image quality.

This will be described with reference to FIG. FIG. 5 shows the potential of the photosensitive drum 100 in the image forming process.

First, after uniformly charging the photosensitive drum 100 to the potential Vd1, exposure E is performed on a portion where a toner image is to be formed to lower the potential to the potential Vs to form an electrostatic latent image (FIG. 5 (a) )). Next, reversal development is performed using toner charged to the same polarity as the photosensitive drum 100, and toner particles T are attached to a potential Vs portion (exposure portion potential) to form a toner image (FIG. 5B). . This toner image has the potential Vt due to the charge held by the toner. Next, when the pre-transfer exposure P is performed on the photosensitive drum 100 carrying the toner image, the background portion potential (non-exposed portion potential) decreases to Vd2 (FIG. 5C).

On the other hand, the potential of the toner image portion on the surface of the photosensitive drum 100 does not decrease because the toner particles T block the pre-transfer exposure P, and the residual charge of the toner remains after the pre-transfer exposure. The potential Vt of the toner image portion becomes higher than the background portion potential Vd2 (FIG. 5C). For this reason,
A potential difference is generated at the boundary between the background portion and the toner image portion on the surface of the photosensitive drum 100, and the toner image is scattered d by receiving an electric attraction based on the potential difference.

For this reason, for example, Japanese Patent Application Laid-Open No. 1-1191168 / 1991.
As disclosed in Japanese Patent Application Laid-Open Publication No. H11-260, the light amount of the pre-transfer exposure is set to a predetermined light amount such that the background portion potential does not become lower than the toner image portion potential. However, the light quantity of the light emitting element of the exposure means such as an LED for performing the pre-transfer exposure changes with time, and the light quantity decreases by about 15% in 30 seconds to 1 minute from the start of light emission. It is known that the accumulated light emission time is reduced by about 20% at 3000 hours compared to the initial time.

Japanese Patent Application Laid-Open No. 10-340014 discloses that only a non-image portion where no toner image is present on the photosensitive drum is exposed, but the image portion and the non-image portion are separated (rotation of the photosensitive drum). Considerably complicated and detailed control such as two-dimensional division in the direction and the longitudinal direction) and switching of the light amount.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus which can prevent a developer image from scattering at the time of exposure before transfer and can stably separate a transfer material.

[0016]

According to a first aspect of the present invention, there is provided an image carrier, comprising: a movable image carrier; a charging unit configured to charge the image carrier by applying a charging voltage;
An exposing means for exposing the charged image carrier to an image to form an electrostatic latent image according to image information; and an electrostatic latent image formed by a developer charged to the same polarity as the charged polarity of the image carrier. Developing means for forming a developer image by reversing development of the developing means, and a transfer means for transferring the developer image to a transfer material, the developing means of the developing means along the moving direction of the image carrier A pre-transfer exposure unit provided on the downstream side and upstream of the transfer unit, and exposing a surface of the image carrier on which a developer image is formed by the developing unit to reduce the surface potential; At the time of exposing before transfer to the surface of the image carrier by the pre-exposure means, at most 0.2 seconds before the leading end of the image forming area on the surface of the image carrier in the moving direction of the image carrier reaches the exposure area. The exposure is turned on, and the image bearing of the image forming area is performed. Moving direction rear end is characterized in turning off the exposure even after 0.2 seconds long from finished passing through the exposure region.

According to a second aspect of the present invention, there is provided a movable image carrier, charging means for charging the image carrier by applying a charging voltage, and image exposure by exposing the charged image carrier to an image. Exposure means for forming an electrostatic latent image according to information, and developing means for forming a developer image by reversal developing the electrostatic latent image with a developer charged to the same polarity as the charging polarity of the image carrier And an image forming apparatus including a transfer unit that transfers the developer image to a transfer material, wherein the transfer unit is provided downstream of the developing unit and upstream of the transfer unit along a moving direction of the image carrier. A pre-transfer exposure unit configured to expose a surface of the image carrier on which the developer image is formed by the developing unit to reduce a surface potential of the image carrier; At the time of exposure, an image forming area on the surface of the image carrier The exposure is turned on at least 0.2 seconds before the leading end of the image carrier in the moving direction reaches the exposure area, and the rear end of the image forming area in the moving direction of the image carrier passes through the exposure area. And at the same time, turn off the exposure.

According to a third aspect of the present invention, there is provided a movable image carrier, charging means for charging the image carrier by applying a charging voltage, and image exposure by exposing the charged image carrier to an image. Exposure means for forming an electrostatic latent image according to information, and developing means for forming a developer image by reversal developing the electrostatic latent image with a developer charged to the same polarity as the charging polarity of the image carrier And an image forming apparatus including a transfer unit that transfers the developer image onto a transfer material, wherein the transfer unit is provided downstream of the developing unit and upstream of the transfer unit along the moving direction of the image carrier. A pre-transfer exposure unit that exposes the surface of the image bearing member on which the developer image is formed by the developing unit to reduce the surface potential thereof, and after the transfer of the developer image onto the transfer material by the transfer unit. The separation of the transfer material from the image carrier is unstable. Under the conditions described above, during the pre-transfer exposure to the surface of the image carrier by the pre-transfer exposure means, the leading end in the moving direction of the image carrier in the image forming area on the surface of the image carrier before reaching the exposure area. In this case, the exposure is turned on 0.2 seconds before, and the exposure is turned off at the same time when the rear end of the image forming area in the moving direction of the image carrier passes through the exposure area.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the illustrated embodiment.

Embodiment 1 FIG. 1 is a schematic diagram showing an image forming apparatus according to Embodiment 1 of the present invention (in the present embodiment, an image forming apparatus such as an electrophotographic digital laser printer). It is a block diagram.

The present image forming apparatus operates in the direction of the arrow (clockwise).
A photosensitive drum 1 as an image carrier that is rotationally driven. Around the photosensitive drum 1, a primary charger 2, a developing device 3, a pre-transfer charger 4, a pre-transfer exposing device 5, a transfer charger 6, a separation charger 7, A cleaning device 8 and a pre-exposure device 9 are provided, and the exposure device 1 is located above the primary charger 2 and the developing device 3.
0 is provided.

The photosensitive drum 1 has an a-Si photosensitive layer on a cylindrical drum base formed of aluminum or the like. The photosensitive drum 1 is driven at a predetermined peripheral speed (450 m in this embodiment) in the direction of the arrow by a driving unit (not shown).
m / sec).

The primary charger 2 has a discharge electrode 2b and a metal wire grid electrode 2c in a shield case 2a, and a high voltage power supply for a discharge electrode (a high voltage power supply (+) for applying a positive DC high voltage to the discharge electrode 2b. (Not shown), and a high-voltage power supply for grid (not shown) is connected to the metal wire grid electrode 2c and the shield case 2a which is electrically connected to the metal wire grid electrode 2c. A high voltage is applied to the discharge electrode 2b from a high-voltage power supply (not shown) for the discharge electrode,
By applying a high voltage to the metal wire grid electrode 2c and the shield case 2a from a high voltage power supply for grid (not shown), a predetermined positive potential (400 to 5) is applied to the surface of the photosensitive drum 1 by corona ions generated by corona discharge.
(00 V).

The developing device 3 has a rotatable developing sleeve 3a in which a fixed magnet roller (not shown) is disposed, and the surface of which is metal-plated. The magnetic positive toner is carried on the surface of the developing sleeve 3a, and the toner is adhered to the electrostatic latent image formed on the photosensitive drum 1 by applying a developing voltage, and the toner image is subjected to reversal development (visualization).

The pre-transfer charger 4 is arranged downstream of the developing device 3 in the rotation direction of the photosensitive drum 1, and is configured to correct a toner image on the photosensitive drum 1 by applying a voltage from a high-voltage power supply (not shown). The electric charge is added so that the toner image is easily attracted to the transfer material P such as paper in the transfer portion N.

The pre-transfer exposure device 5 has a plurality of LEDs (not shown).
The pre-transfer exposure device 5, which is a feature of the present invention, is disposed downstream of the photosensitive drum 1 in the rotation direction and in close proximity to the surface of the photosensitive drum 1.

The transfer charger 6 serving as a transfer unit is provided at a transfer portion N between the photosensitive drum 1 and the transfer charger 6 by a transfer voltage applied from a transfer power supply (not shown).
The toner image on the surface is transferred to a transfer material P such as paper.

The separation charger 7 includes a separation charging power supply (not shown).
The transfer material P on which the toner image has been transferred is separated from the surface of the photosensitive drum 1 by the separation charging voltage applied from.

The cleaning device 8 has a cleaning blade 8a, and removes and collects untransferred toner remaining on the surface of the photosensitive drum 1 after the transfer by the cleaning blade 8a.

The pre-exposure device 9 has an LED (not shown) for removing residual charges on the surface of the photosensitive drum 1 after transfer, and is located upstream of the primary charging device 2 in the rotation direction of the photosensitive drum 1. Located on the side.

The exposure device 10 performs image exposure E on the surface of the photosensitive drum 1 uniformly charged by the primary charger 2 with a laser beam in accordance with an input image signal, and converts the surface of the photosensitive drum 1 into an image signal. A corresponding electrostatic latent image is formed.

Next, an image forming operation by the above-described image forming apparatus will be described.

At the time of image formation, the photosensitive drum 1 is driven to rotate at a predetermined rotational speed (450 mm / sec in the present embodiment) in a direction indicated by an arrow (clockwise) by a driving means (not shown). The surface is uniformly charged to a predetermined positive potential (400 to 500 V). When the image exposure E by laser light is given to the charged surface of the photosensitive drum 1 by the exposure device 10, the potential of the surface of the photosensitive drum 1 is reduced to the potential of the portion where the image exposure E is performed. An electrostatic latent image corresponding to the information is formed.

A developing device in which a developing voltage having the same polarity as the charging polarity (positive in this embodiment) of the photosensitive drum 1 is applied to the electrostatic latent image formed on the surface of the photosensitive drum 1 at the developing position. The toner charged to the same polarity as the charged polarity (positive polarity) of the photosensitive drum 1 is adhered by the developing sleeve 3a of No. 3 to perform reversal development (visualization) as a toner image.

Then, the surface of the photosensitive drum 1 on which the toner image has been formed is charged by the pre-transfer charger 4, and the LED of the pre-transfer exposure device 5 emits light to expose the surface of the photosensitive drum 1 to pre-transfer.

The surface of the photosensitive drum 1 is charged by the pre-transfer charger 4 and exposed by the pre-transfer exposure device 5, so that the background potential (dark potential) on the surface of the photosensitive drum 1 is changed between the developing step and the transfer step. The transfer material P is reduced in advance and the electrostatic attraction force generated at the time of transfer is weakened, so that the transfer material P can be easily separated from the surface of the photosensitive drum 1 stably after the next transfer process.

When the toner image on the surface of the photosensitive drum 1 reaches the transfer portion N between the photosensitive drum 1 and the transfer charger 6, a paper feed cassette (not shown) is synchronized with this timing.
A transfer material P such as a sheet of paper is conveyed to a transfer portion N, and a transfer charger 6 to which a transfer voltage having a polarity opposite to that of the toner (negative in this embodiment) is applied to the transfer material P and the surface of the photosensitive drum 1 Is transferred. Then, the transfer material P on which the toner image has been transferred is separated from the photosensitive drum 1 by the separation charger 7 and conveyed to a fixing device (not shown), and the toner image is transferred by heating and pressing by the fixing device (not shown). The material P is thermally fixed on the surface and discharged.

On the other hand, the transfer residual toner remaining on the surface of the photosensitive drum 1 after the transfer of the toner image is removed and collected by the cleaning blade 8a of the cleaning device 8. The residual charges on the surface of the photosensitive drum 1 are transferred to the pre-exposure device 9.
And is ready for the next image formation.

Next, the details of the pre-transfer exposure device 5 will be described.

The pre-transfer exposure device 5 is installed downstream of the pre-transfer charger 4 disposed downstream of the developing device 3 with respect to the rotation direction of the photosensitive drum 1 and upstream of the transfer charger 6. A plurality of LEDs are arranged in an array along the rotation axis direction (longitudinal direction) of the photosensitive drum 1, so that the entire surface of the photosensitive drum 1 can be uniformly exposed along the longitudinal direction of the photosensitive drum 1. ing.

A drive voltage (24 V in the present embodiment) is applied to the pre-transfer exposure device 5 from a drive power supply 11, and a control device (CPU) 12 for controlling the entire image forming apparatus turns on light emission (exposure). / OFF is controlled. As shown in FIG. 5, the amount of light emitted from the pre-transfer exposure device 5 is such that no image scattering occurs, that is, the background portion potential> the toner portion potential, specifically, non-exposure at the transfer portion N. The exposure background potential is + with respect to the background potential (+400 V).
It was set to be 300V. The amount of light at this time is
It was 0.05 ± 0.0035 Lux · sec.

Next, regarding the ON / OFF timing of the light emission at this light amount, when the exposure is always ON during the image forming operation (hereinafter, referred to as condition A), an image forming area on the surface of the photosensitive drum 1 (hereinafter, referred to as an image area). ) Alone (hereinafter referred to as condition B), and before and after the image area on the surface of the photosensitive drum 1 in the first embodiment of the present invention (in the present embodiment, in the rotation direction of the photosensitive drum 1). On the other hand, the case where the exposure is performed for 0.1 second (the front end and the rear end of the image area) (hereinafter referred to as condition C) will be described in comparison.

First, in the case of condition A, the pre-transfer exposure device 5
The exposure by the LED may be turned on during image formation (during rotation of the photosensitive drum 1) in synchronization with the timing of the rotation drive of the photosensitive drum 1. Then, as described in "Problems to be Solved by the Invention", the LED has a characteristic that the light quantity decreases by about 15% due to self-heating of the light emission current for about one minute after the light emission. Fluctuation of the light quantity in the number of sheets until one minute elapses, the light quantity width that stabilizes image scattering and transfer material separation is 0.05 ± 0.0035 Lux.
Sec, that is, the light amount fluctuation is within a range of ± 7%, and it is possible to secure a stable image and separability.

By the way, if the light is constantly emitted during the image formation as in the condition A, it is not possible to guarantee a decrease in the light amount due to the life of the LED itself as described below (the life was calculated under the following conditions).

When the transfer material is intermittently conveyed one by one to output an image, the light emission time is 3 sec per sheet.

LED life: 10 million sheets of image formation (emission life is about 3000 hours) Cumulative light emission time: 3 (sec / sheet) × 10 million (sheets) ≒ 83
This is 33 hours, which greatly exceeds the LED life of about 3000 hours.

In the conditions B and C, the condition B
In this case, since the width of the image area in the rotation direction of the photosensitive drum 1 is 210 mm and the peripheral speed of the photosensitive drum 1 is 450 mm / sec in the present embodiment, the exposure time per transfer material is 210 (mm) / 450 (mm / sec) = 0.47 sec / sheet In the case of the condition C, the image area in the case of the condition B and the front end and the rear end thereof are each further 0.1 second (0.2 in total).
Sec), the exposure time per transfer material is 0.47 (sec / sheet) +0.2 (sec / sheet) = 0.67 sec /
Therefore, the cumulative light emission time is 0.47 (seconds / sheet) × 10 million (sheets) in the case of condition B.
= 1305 hours In the case of condition C: 0.67 (seconds / sheet) x 10 million (sheets)
= 1861 hours. Therefore, the decrease in the amount of light due to the change with time is as follows in the case of the condition B;
305 (hour)) =-8.7% In the case of condition C; -20 (%) / (3000 (hour) × 1
861 (time)) = − 12.4%, and the change in the light amount due to the aging of the conditions B and C falls within the above-mentioned light amount fluctuation range ± 7%.

Next, the difference between the above condition B and the condition C of the present embodiment will be described with reference to FIGS.

FIGS. 2 and 3 show an image area on the photosensitive drum 1 (in the present embodiment, a solid white image with severe separation is assumed).
Is passed through the transfer charger 6 (FIGS. 2 and 3A) and the separation charger 7 (FIGS. 2 and 3B), each corona charge is applied to the transfer material (paper). FIG. FIG. 2 shows the case where only the image area is exposed (condition B), and FIG. 3 shows the first embodiment of the present invention.
FIG. 7 is a diagram of a case (condition C) in which an image area and its front and rear sides (front end side and rear end side) are exposed.

In the case of condition B, as shown in FIG.
In the transfer section N, only the image area portion is exposed to +30
The potential drops to 0 V, and the leading end and the trailing end (in the rotation direction of the photosensitive drum 1) are +400 V because they are not exposed. In this state, when receiving the transfer (the transfer is negative because the photosensitive drum 1 is positively charged, the transfer is negative), as shown in the boundary portion between the leading end and the trailing end of the image area, as shown in FIG.
For example, when viewed from the transfer of the negative discharge at the tip,
The impedance in the direction of the photosensitive drum rapidly increases from 00V to + 300V.

For this reason, the transfer charge of the negative polarity is attracted immediately before the leading end of the image area, while the negative charge of the transfer tends to be insufficient at the leading end of the image area.

In this state, as shown in FIG. 2B, in order to cancel the negative charge received in the transfer, the charge on the back of the transfer material (paper) by the positive electric field is removed by the separation charger 7. However, at the boundary between the front end of the image area where the transfer charge is concentrated and immediately before the front end, a large amount of negative transfer charge is attracted, and the charge for separation is also concentrated. Since the negative charge is small, the charge to be removed is less likely to concentrate, so that the leading end separation of the transfer material (paper) becomes very unstable.

Similarly, the same occurs at the rear end of the image area, and the transfer and separation tend to be unstable.

On the other hand, in the case of the condition C in the present embodiment, as shown in FIGS. 3A and 3B, the transfer and separation of the front and rear ends of the image area in the case of the above condition B are performed. So that the corona charge excess / deficiency area of the
The area at the front end and the rear end of the image area (the area M in FIG. 3) is also exposed along the rotation direction of the photosensitive drum 1. In the present embodiment, the exposure time in this area M is 0.1 second.

That is, under the condition C of the present embodiment, the control signal is output from the control device 12 to the drive power supply 11 during the pre-transfer exposure, so that the leading end of the image area becomes the exposure area with respect to the rotation direction of the photosensitive drum 1. Turn on the exposure 0.1 seconds before reaching,
The exposure was turned off 0.1 seconds after the rear end of the image area had passed through the exposure area. By exposing the image area and its front and rear sides (front side and rear end side) for 0.1 second in this way, the edge effect of transfer and separation occurring at the front and rear boundary of the image area is shifted to the non-image area. As a result, the uniformity of transfer and separation at the leading and trailing ends of the image area was secured, and stable transfer of the toner image and separation of the transfer material P were achieved.

As described above, in the present embodiment, during the pre-transfer exposure, the exposure is turned on from 0.1 second before the leading end of the image area reaches the exposure area in the rotation direction of the photosensitive drum 1, and the trailing end of the image area is turned on. Since the exposure is turned off 0.1 seconds after passing through the exposure area, uniformity of transfer and separation of the leading and trailing ends of the image area can be secured, and the pre-transfer exposure can be performed. In this case, a high-quality image can be obtained by preventing the toner image from scattering at the time, and the transfer material P can be stably separated.

The ON / OFF timing of the pre-transfer exposure may be controlled in synchronization with the image area, for example, by applying a 0.1 second offset to laser, transfer, developing bias, or the like. A clock used for controlling the image forming operation of the image forming apparatus may be used.

The time of offset from the image area may be determined in consideration of the peripheral speed of the photosensitive drum 1, the type of transfer material P (easiness of separation), the high-pressure response of transfer and separation, and the like. , About 0.2 seconds is sufficient. Therefore,
At the time of the pre-transfer exposure, the exposure is turned on at least 0.2 seconds before the leading end of the photosensitive drum 1 in the image area in the rotation direction reaches the area of the pre-transfer exposure, and after the rotation of the photosensitive drum 1 in the image area. The exposure may be turned off at most 0.2 seconds after the end has passed through the pre-transfer exposure area.

<Embodiment 2> This embodiment is also described using the image forming apparatus of Embodiment 1 shown in FIG. In the first embodiment, during the pre-exposure, the image area and its front and rear sides (front and rear ends) are each exposed for 0.1 second. However, in the present embodiment, the drive power source 11 is controlled by the control device 12. Then, at the time of the pre-exposure, only the image area and its front (front end side) were exposed for 0.1 second. Other configurations and operations are the same as those in the first embodiment, and a description thereof will be omitted in the present embodiment.

At the time of pre-exposure, if the image area and its front (front end side) are exposed for 0.1 second to stabilize the separation of the front end of the transfer material P, then the separation is performed by the rigidity of the transfer material (paper) or its own weight As a result, separation stability close to that of the first embodiment can be obtained.

Therefore, in the present embodiment, exposure is performed from 0.1 seconds before the leading end of the image area passes through the exposure area before transfer until the rear end of the image area passes through the exposure area.

As described above, the photosensitive drum 1 is exposed during the pre-transfer exposure.
In the case of the present embodiment, the exposure is turned on 0.1 seconds before the leading end of the image area reaches the exposure area with respect to the rotation direction, and the exposure is turned off at the same time as the rear end of the image area passes through the exposure area. However, in the same manner as in the first embodiment, uniformity of transfer and separation at the leading end and the trailing end of the image area is ensured. And the transfer material P can be stably separated.

In this embodiment, the exposure is turned on 0.1 seconds before the leading edge of the image area reaches the exposure area in the rotation direction of the photosensitive drum 1 during the exposure before transfer. As described in the first embodiment, the exposure may be turned ON 0.2 seconds before the leading end of the image area reaches the exposure area.

<Embodiment 3> This embodiment is also described using the image forming apparatus of Embodiment 1 shown in FIG.

In the present embodiment, when stable transfer and separation can be performed at normal times (for example, when a rigid transfer material (paper) having a basis weight of 80 g / m ² or more is used, or when normal temperature and humidity are used) Environment, or in the case of image formation in which a toner image is transferred to only one side that is advantageous for separation, etc.)
FF or pre-transfer exposure is performed only on the image area.

In this embodiment, in the case of severe separation conditions (when the temperature and humidity are high and the absolute moisture content is high, or when the transfer material used is thin paper or recycled paper having a basis weight of 70 g / m ² or less (for example, EW-500, EN-500 manufactured by Canon Sales Co.
In the case of paper having low rigidity, or in the case of double-sided image formation in which a toner image is transferred to both sides of a transfer material, etc.), as in the second embodiment, the end of the image area passes through the exposure area. Exposure was performed from one second before the rear end of the image area passed through the exposure area.

This is because, when the temperature and humidity increase, the absolute moisture content of about 18 g / m ³ increases the moisture absorption of the transfer material, lowering the stiffness (rigidity) of the paper, and the transfer material having a basis weight of 70 g / m ^3.
waist of the transfer material itself and below the m ² (stiffness) is less likely to separate drops. Further, when an image is formed (transfer-separated) on the second side during double-sided image formation, the transfer material curls due to the fixing action on the first side, making it difficult to separate.

Other configurations and operations are the same as those of the first embodiment, and the description thereof will be omitted in the present embodiment.

As described above, only when the separation is severe, during the pre-transfer exposure, the exposure is started from 0.1 second before the leading end of the image area reaches the exposure area in the rotation direction of the photosensitive drum 1.
N, and in the present embodiment in which the exposure is turned off at the same time as the rear end of the image area passes through the exposure area, the transfer of the front end and the rear end of the image area is performed in substantially the same manner as in the first embodiment. Since the uniformity of separation is ensured, scattering of the toner image at the time of exposure before transfer can be prevented, a high-quality image can be obtained, and stable separation of the transfer material P can be performed.

In this embodiment, the exposure is turned on from 0.1 seconds before the leading end of the image area reaches the exposure area in the rotation direction of the photosensitive drum 1 during the pre-transfer exposure only under severe separation conditions. However, as described in the first embodiment, the exposure may be turned ON 0.2 seconds before the leading end of the image area reaches the exposure area.

[0071]

As described above, according to the first aspect of the present invention, at the time of the pre-transfer exposure, the leading end of the image forming area on the surface of the image carrier in the moving direction of the image carrier before reaching the exposure area. The exposure is turned on at least 0.2 seconds before, and the exposure is turned off at least 0.2 seconds after the rear end of the image carrier in the image forming area in the moving direction of the image carrier has passed through the exposure area. It is possible to ensure uniformity of transfer and separation of the leading and trailing ends of the area, prevent scattering of the developer image at the time of exposure before transfer, and obtain a high-quality image, and transfer material Can be separated stably.

According to the second aspect of the present invention, at the time of exposure before transfer, the front end of the image forming area on the surface of the image carrier in the moving direction of the image carrier reaches at most 0.2 mm before reaching the exposure area. The exposure is turned on from the second before, and the exposure is turned off at the same time as the rear end of the image carrier in the moving direction of the image forming area passes through the exposure area, thereby preventing scattering of the developer image at the time of exposure before transfer. A high-quality image can be obtained, and stable separation of the transfer material can be performed.

According to the third aspect of the present invention, under the condition that the separation of the transfer material from the image carrier becomes unstable, the pre-transfer exposure means performs the pre-transfer exposure to the image carrier surface.
The exposure is turned on at least 0.2 seconds before the leading end of the image carrier in the image forming area in the moving direction of the image forming area on the surface of the image carrier reaches the exposure area, and the rear end in the moving direction of the image carrier in the image forming area is long. By turning off the pre-transfer exposure at the same time as passing through the exposure area, even under severe conditions where the transfer material is severely separated from the image carrier, scattering of the developer image during the pre-transfer exposure is prevented to achieve high quality. An image can be obtained, and stable separation of the transfer material can be performed.

[Brief description of the drawings]

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

FIGS. 2A and 2B show transfer material (paper) when an image area on a photosensitive drum passes through a transfer charger and a separation charger when only an image area is exposed before transfer. The figure which showed typically a mode that corona charge is provided.

FIGS. 3 (a) and 3 (b) show the image area and the image area on the photosensitive drum in the case of Embodiment 1 in which the pre-transfer exposure was performed before and after the image area passed through the transfer charger and the separation charger. FIG. 4 is a diagram schematically showing a state in which corona charges are applied to a transfer material (paper).

FIG. 4 is a schematic configuration diagram showing an image forming apparatus in a conventional example.

FIG. 5 is a diagram for explaining the occurrence of toner scattering due to pre-transfer exposure.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum (image carrier) 2 primary charger (charging means) 3 developing device (developing means) 3a developing sleeve 4 pre-transfer charger 5 pre-transfer exposure device (pre-transfer exposure means) 6 transfer charger (transfer means) 7) Separation charger 8 Cleaning device 8a Cleaning blade 9 Pre-exposure device 10 Exposure device (exposure means) 11 Drive power supply 12 Controller

Claims (4)

[Claims] A movable image carrier; a charging unit configured to charge the image carrier by applying a charging voltage; and an electrostatic latent image corresponding to image information by exposing the charged image carrier to an image. Exposing means for forming a developer, developing means for inverting and developing the electrostatic latent image with a developer charged to the same polarity as the charging polarity of the image carrier to form a developer image, and transferring the developer image An image forming apparatus provided with a transfer unit that transfers the toner image onto a material, wherein the developer unit is provided downstream of the developing unit and upstream of the transfer unit along the moving direction of the image carrier, and a developer image is formed by the developing unit. A pre-transfer exposure unit for exposing the surface of the formed image carrier to reduce the surface potential thereof; and performing a pre-transfer exposure on the image carrier surface by the pre-transfer exposure unit, the image carrier surface In the moving direction of the image carrier in the image forming area at Exposure is turned on at least 0.2 seconds before reaching the exposure area, and is 0 at most after the rear end of the image forming area in the moving direction of the image carrier has passed through the exposure area. 2. The image forming apparatus, wherein the exposure is turned off after 2 seconds. 2. A movable image carrier, charging means for charging the image carrier by applying a charging voltage, and an electrostatic latent image corresponding to image information by exposing the charged image carrier to an image. Exposing means for forming a developer, developing means for inverting and developing the electrostatic latent image with a developer charged to the same polarity as the charging polarity of the image carrier to form a developer image, and transferring the developer image An image forming apparatus provided with a transfer unit that transfers the toner image onto a material, wherein the developer unit is provided downstream of the developing unit and upstream of the transfer unit along the moving direction of the image carrier, and a developer image is formed by the developing unit. A pre-transfer exposure unit for exposing the surface of the formed image carrier to reduce the surface potential thereof; and performing a pre-transfer exposure on the image carrier surface by the pre-transfer exposure unit, the image carrier surface In the moving direction of the image carrier in the image forming area at Turning on the exposure for at least 0.2 seconds before reaching the exposure area, and turning off the exposure at the same time as the rear end of the image forming area in the moving direction of the image carrier passes through the exposure area. An image forming apparatus comprising: 3. A movable image carrier, charging means for charging the image carrier by applying a charging voltage, and an electrostatic latent image corresponding to image information by exposing the charged image carrier to an image. Exposing means for forming a developer, developing means for inverting and developing the electrostatic latent image with a developer charged to the same polarity as the charging polarity of the image carrier to form a developer image, and transferring the developer image An image forming apparatus provided with a transfer unit for transferring to a material, the transfer unit being provided downstream of the developing unit and upstream of the transfer unit along a moving direction of the image carrier, and a developer image is formed by the developing unit. A pre-transfer exposure unit that exposes the surface of the formed image carrier to reduce its surface potential, and after the transfer unit transfers the developer image onto the transfer material, the image carrier of the transfer material Under conditions where separation from the body becomes unstable, At the time of exposing before transfer to the image carrier surface by optical means, at least 0.2 seconds before the leading end in the moving direction of the image carrier in the image forming area on the image carrier surface reaches the exposure area. An image forming apparatus, wherein the exposure is turned on, and the exposure is turned off at the same time when the rear end of the image forming area in the moving direction of the image carrier passes through the exposure area. 4. The condition under which the separation becomes unstable is such that when the basis weight of the transfer material is 70 g / m ² or less, and when an image is formed by transferring a developer image to both surfaces of the transfer material, The image forming apparatus according to claim 3, wherein at least a case of high humidity is included.