JPH11305525A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the reverse contamination of a transfer material resulted from fogging toner and to provide a print image of good quality by differing the DC voltage value in the movement of a DC charged part to a developing position from that in the movement of a superposed charged part. SOLUTION: A developing sleeve is rotated in non-image formation, and a DC voltage is applied by a developing bias applying means (power source). The DC voltage value at this time is differed depending on the surface state of a photosensitive drum. Namely, the developing bias Vdev-I applied in an area which is the image forming area consists of an AC bias with peak-to-peak voltage of 1600 VPP and frequency of 2200 Hz and a DC bias of -400 V (Vds-1) superposed thereon. On the other hand, with respect to the developing bias (Vdev-NI) in an area B which is the non-image forming area, no AC bias is applied, and the DC bias is switched to a developing weak bias Vds-I as the fogging is minimized.

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 an electrophotographic copying machine and a laser printer.

[0002]

2. Description of the Related Art In a general electrophotographic laser printer, a laser beam modulated in accordance with image data irradiates an image carrier (eg, a photosensitive drum) uniformly charged by a charging means such as a charging roller. Thus, a desired electrostatic latent image is formed. This electrostatic latent image is reversely developed at a development site by a developing unit such as a developing device disposed to face the image carrier, and is visualized as a toner image. This toner image is electrostatically transferred to a transfer material such as paper by a transfer means such as a transfer roller, and then permanently fixed on the transfer material at a predetermined fixing temperature by a fixing means such as a heat fixing device.

FIG. 4 shows an example of a conventional image forming apparatus.

The image forming apparatus shown in FIG. 1 includes a drum type electrophotographic photosensitive member (photosensitive drum) 1 as an image carrier. The photosensitive drum 1 has a negative polarity O having a diameter of 30 mm.
It is composed of a PC photoreceptor and is driven to rotate in the direction of arrow R1 at a process speed of 120 mm / sec. The surface of the photosensitive drum 1 has a charging roller (charging member) 2 to which a DC voltage is applied by a power supply (charging bias applying unit) 2a.
As a result, the surface is charged to a predetermined surface potential. Some power supplies 2a are superimposed with an alternating current in order to obtain uniform charging. The surface of the charged photosensitive drum 1 is irradiated with laser light L modulated according to image data by an image signal writing unit (latent image forming unit) 3, and the irradiated portion (bright portion) attenuates to a predetermined value. An electrostatic latent image is formed.

When this electrostatic latent image arrives at a developing site facing the developing device (developing means) 4 as the photosensitive drum 1 rotates, a power source (developing bias applying means) 4b
As a result, a negatively charged toner is attached from a developing sleeve (developer carrier) 4a to which a developing bias is applied, and a toner image is formed by reversal development. Various developing methods have been proposed. For example, there is a method in which an alternating current is superimposed and applied to the power supply 4b as a developing bias, such as jumping development.

When the toner image on the photosensitive drum 1 reaches a nip portion (transfer site) formed by contacting a conductive transfer roller (transfer member) 5 with the photosensitive drum 1, the toner image is timed. A predetermined transfer bias is applied to the transfer material P supplied to the transfer portion via a power source (transfer bias applying means) 5a, and a charge having a polarity opposite to that of the toner is applied to the back surface of the transfer material P, whereby It is transferred to the surface of the transfer material P.

A transfer material P on which a toner image has been transferred at a transfer site
The toner image is fixed and solidified on the surface by a fixing device (not shown). On the other hand, the toner remaining on the photosensitive drum 1 without being transferred onto the transfer material P (hereinafter referred to as “transfer residual toner”) is removed by the cleaner 6, and the photosensitive drum 1 from which the transfer residual toner has been removed is charged next time starting from charging. For image formation.

[0008] The contact type transfer roller (transfer member) 5 as described above has no adverse effects due to the contamination of the corona charger, since it does not have a wire as an electrode, as compared with a corona charger widely used conventionally. In addition, the generation of ozone and the generation of nitride due to the discharge are almost nil, and the deterioration of the image quality due to the contamination of the photosensitive drum 1 caused by these is almost zero. Further, there are various advantages such as a cost advantage because a high voltage power supply is not required.

In the above-described image forming apparatus, the bias applied to the charging roller (charging member) 2 requires uniform charging in the image forming area.
Usually, alternating current (AC) is superimposed on direct current (DC),
In other non-image areas, in consideration of the life of the photosensitive drum 1, there is a type in which the photosensitive drum 1 is charged only with direct current, which requires less shaving of the surface layer.

On the other hand, after the main switch is turned on, warm-up of the fixing device, start-up of the scanner motor, and preparation rotation for stabilizing the potential of the photosensitive drum 1 until the image forming operation can be performed. At the time of rotation, at the time of pre-rotation when printing only one sheet, at the time between sheets when printing multiple sheets continuously, at the time of post-rotation to prepare for the next print after printing, etc., each non-image area In order to secure a stable image, a developing blade or the like that is in contact with a developing sleeve 4a, which is a developer carrying member, is usually used in order to make the toner layer uniform and properly charge the toner. The sleeve 4a is being driven.

In some cases, the remaining amount of toner is detected by driving the developing sleeve 4a during the above-described multi-rotation, printing, or post-rotation. That is, the developing sleeve 4
A so-called antenna-type toner in which a developing bias having an AC component is applied to a, and the remaining amount of toner in the developing device is detected by utilizing a change in capacitance between detection conductors disposed opposite to the developing bias. Some devices include a remaining amount detecting unit.

As a result, the following problems occur.

That is, when the developing sleeve 4a is driven in the above-mentioned non-image area, the photosensitive drum 1
The toner is more or less transferred to the upper side, and fogging occurs. Here, when the transfer roller 5 is in direct contact with the surface of the photosensitive drum 1 as described above, the fog toner on the photosensitive drum 1 is removed by the transfer roller 5.
And the transfer roller 5 is soiled. At this time, measures such as applying a bias to the transfer roller 5 so as not to be easily contaminated by toner may be taken.

Further, in a portion of the inter-sheet area of the continuous printing, if the developing bias is normally applied, this portion is slightly covered, and the transfer roller 5 is contaminated with toner between the sheets. Conventionally, the contamination level has been improved by not applying a developing bias to a region including the portion.

[0015] Also, utilizing the time of front multiple rotation and the time of rear rotation,
In order to clean the transfer roller 5 contaminated with toner between sheets, a + bias or a − bias is applied to the transfer roller, and the toner is collected by the cleaner 6 via the photosensitive drum 1. In addition, in the cleaning of an intermediate transfer member such as an image forming apparatus (not shown) that forms a full-color image by superimposing four color toner images on the intermediate transfer member, as in the case of the transfer roller 5 described above, In some cases, the toner on the intermediate transfer body is collected on the photosensitive drum by providing a potential difference between the drum and the transfer residual toner.In this case, the surface potential of the photosensitive drum is also changed according to the applied bias. In some cases, the potential is set to be easily collected.

As described above, the developing sleeve 4a is driven to secure stable development and to detect the remaining amount of toner by using various timings related to the image forming operation. In order to maintain the transfer, cleaning of the transfer roller and the intermediate transfer member is performed.

[0017]

However, in the above-described cleaning of the transfer roller 5 or the like, for example, switching from the application of AC superposition to the charging of only DC in consideration of the life of the photosensitive drum 1 or the charging of the photosensitive drum 1 is performed. When the developing sleeve 4a is driven in order to secure a stable image when the charging is performed while switching the surface potential to a potential setting that facilitates collection, conventionally, no developing bias has been applied in the non-image area. The fog level on the photosensitive drum 1 was sometimes deteriorated.

This is because the surface potential of the photosensitive drum 1 at the developing site when the developing sleeve 4a is driven varies depending on whether the voltage applied to the charging roller 2 during charging is only DC or when the AC component is superimposed on DC. This is because a macro value measured by an electrometer or the like has the same potential, but a microscopic value is not uniform when only direct current is applied. Specifically, observing the fog on the surface of the photosensitive drum 1 when the developing sleeve 4a is driven, it can be seen that the difference is remarkable.

Therefore, when the DC component of the developing bias applied to the developing sleeve 4a is changed to suppress fog, the charging component is more uniformly charged by applying the DC component to the charging roller 2 and by superimposing the AC component on the DC component. It was found that the developing bias value at which the fog was minimized was different from that in the case where the fogging was performed. The developing bias value may not be 0V. For example, when the developing bias is set to 0 V, a reverse contrast of a potential difference corresponding to the potential of a dark portion on the surface of the photosensitive drum 1 occurs, and the reverse fog (original polarity, that is, the above-described image forming apparatus) , But fog due to toner charged to the opposite polarity is generated, and as a result, the transfer roller 5 is contaminated. In general, the relationship between the inverted contrast and the fog on the photosensitive drum 1 tends to increase as the inverted contrast increases.

Further, when the surface potential of the photosensitive drum 1 is switched when the developing sleeve 4a is driven as described above, the developing bias value at which fog is minimized depends on each potential.

That is, conventionally, when the developing sleeve 4a is driven at the above-described timing, regardless of the value of the surface potential of the photosensitive drum 1 or whether the charging is performed by direct current only or the superposition of direct current and alternating current, etc. However, since no developing bias was applied, the fog level on the photosensitive drum 1 was not always at the minimum. For this reason, depending on the fog level when the bad conditions overlap, the transfer roller 5
For example, even if a cleaning bias is applied to the transfer roller 5, contamination of the transfer roller 5 cannot be sufficiently eliminated, and there is a problem that a back stain on a printed image occurs.

Further, in the case of double-sided printing, the image surface is stained, and there is a problem that print quality cannot be ensured.

In order to avoid these problems, if the driving of the developing sleeve 4a for securing stable development and the cleaning of the transfer roller 5 and the intermediate transfer body are performed at different timings, the wait time and the first time are reduced. This will increase the print time.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and does not extend a wait time, a first print time, or the like, and a toner of a transfer member or an intermediate transfer member that is in contact with an image carrier. An object of the present invention is to provide an image forming apparatus capable of preventing contamination and preventing deterioration of print quality due to toner contamination.

[0025]

According to a first aspect of the present invention, there is provided an image carrier, a charging member for uniformly charging the surface of the image carrier, and a charging member. A charging bias applying unit for applying a DC voltage to the DC carrier or a superimposed voltage of the DC voltage and the AC voltage; and a developing device having a rotatable developer carrier which is arranged opposite to the surface of the image carrier and forms a developing site. Means, and a developing bias applying means for applying a DC voltage to the developer carrier or applying a superimposed voltage of the DC voltage and the AC voltage, wherein the charging bias applying means applies to the charging member. A part of the image bearing member charged by applying only a DC voltage is defined as a DC charged portion, and a part of the image bearing member charged by applying a superimposed voltage to the charging member by the charging bias applying power source is superimposed. When the DC charged portion is moved to the developing site, the DC bias value applied by the developing bias applying unit to the developer carrier during the rotation of the developer carrier during non-image formation. And the DC voltage value differs between when the superimposed charging portion moves.

According to a second aspect of the present invention, there is provided an image bearing member, a charging member for uniformly charging the surface of the image bearing member, and a DC voltage applied to the charging member or a DC voltage and an AC voltage. Charging bias applying means for applying a superimposed voltage; developing means having a rotatable developer carrier which is arranged opposite to the surface of the image carrier to form a developing site; and a DC voltage and an AC voltage applied to the developer carrier. A developing bias application unit for applying a superimposed voltage to the developer carrier, and a detection conductor disposed in the developing unit so as to face the developer carrier, and a developing bias is applied to the developer carrier by the developing bias application unit. In the image forming apparatus that detects a voltage induced in the detection conductor to detect a remaining amount of the developer in the developing unit, the charging bias applying unit applies only a DC voltage to the charging member. A portion of the charged image carrier is a DC charging portion, and a portion of the image carrier charged by applying a superimposed voltage to the charging member by the charging bias application power supply is a superimposed charging portion. At the time of detection of the remaining amount of the developer, the DC voltage value applied to the developer carrier by the developing bias applying unit is determined when the DC charged portion moves to the developing site and when the superimposed charged portion moves. Wherein the DC voltage value is varied.

According to a third aspect of the present invention, in accordance with the first or second aspect of the present invention, there are provided a plurality of the DC charging portions having different voltage values, and the developer carrier is provided in accordance with the voltage values of the DC charging portions. Are characterized in that the DC voltage value applied to them is made different.

According to a fourth aspect of the present invention, there is provided an image bearing member, a charging member for uniformly charging the surface of the image bearing member, charging bias applying means for applying at least a DC voltage to the charging member, A developing unit having a rotatable developer carrier that is arranged to face the image carrier and forms a development site; a developing bias applying unit that applies at least a DC voltage to the developer carrier; In an image forming apparatus including a transfer member that is pressed to form a transfer portion and a transfer bias application unit that applies a transfer bias to the transfer member, the charging bias application unit applies a predetermined potential to the charging member. A part of the charged image carrier is used as a first charged part, and the charging bias application power source applies one other predetermined potential to the charging member, and the one of the image carrier charged. Assuming that the minute portion is a second charged portion, the DC voltage value applied to the developer carrying member by the developing bias applying means when the developer carrying member is rotated during non-image formation is the first voltage applied to the developing portion. The DC voltage value differs between when the charged portion has moved and when the second charged portion has moved, and the transfer bias applied to the transfer member by the transfer bias applying means is different from the transfer bias. The transfer bias is different between when the first charged portion moves to a site and when the second charged portion moves.

[0029]

Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment 1> The basic configuration of the image forming apparatus according to the present invention is the same as the configuration of the image forming apparatus shown in FIG.

Using the image forming apparatus shown in FIG. 4, first, between the image area of the first transfer material and the image area of the second transfer material during continuous printing as shown in FIG. A portion substantially corresponding to a space between transfer materials (hereinafter, referred to as a "paper space") will be described.

FIG. 2 schematically shows an image area (area A in the figure) and a non-image area (area B in the figure). In this embodiment, the region B corresponds to a superimposed charging portion to which a superimposed voltage obtained by superimposing a DC voltage and an AC voltage is applied as a charging bias, and the region C applies only a DC voltage as a charging bias. Corresponding to the charged DC portion. In the present embodiment, the region A (Vch-I) and the region B
In both cases (Vch-NI), the surface of the photosensitive drum 1 is brought to about -55
It is uniformly charged to 0 V (dark portion potential; Vd). In the image area of the area A, a state is shown in which a laser beam modulated according to the image data is irradiated to form a desired electrostatic latent image. The surface potential (bright portion potential; Vl) of the portion irradiated with the laser beam is about -200V.

The surface of the photosensitive drum 1 on which the electrostatic latent image is formed (the surface of the photosensitive member) is applied with a predetermined direct current to a developing sleeve 4a having a diameter of 20 mm, which is driven to rotate while the toner is carried on the surface. The exposed portion is developed by applying a developing bias (Vdev-I) to which AC is superimposed.

Here, the developing bias Vdev-I applied in the area A, which is an image area, has a peak-to-peak voltage of 1600.
An alternating current bias (development bias (AC)) having a frequency of 2200 Hz at V _PP and a direct current bias (development bias (DC)) of -400 V (Vds-I) are applied in a superimposed manner.

On the other hand, in the area B which is a non-image area, the developing bias (Vdev-NI) is applied with no AC bias so as to minimize fog as described above. Development weak bias Vds
Switching to -1. Here, the development weak bias Vds-1 is
The voltage is set to be smaller than Vds-I of the image area and larger than 0V. In the present embodiment, Vds-1 = -2
Set to 50V. With such a setting, the fog on the photosensitive drum 1 in the area A in the figure can be reduced to almost zero.

In this embodiment, the transfer bias of the transfer roller 5 having a diameter of 20 mm is applied to the transfer material in the area A where the paper is being passed in order to always apply a predetermined charge to the transfer material regardless of the environmental change. Approximately +
A voltage (Vhi) of 3 kV is applied to transfer the toner developed on the photosensitive drum 1 to a transfer material.

In the area B between the sheets,
In the case of the above-described reversal development method, since a bias having a polarity opposite to the charging polarity is applied to the photosensitive drum 1 from the transfer roller 5, +3 kV (V
When hi) is applied, a charge memory by the transfer roller 5 occurs. This memory appears as density unevenness of the subsequent print image, and is particularly conspicuous in the case of the contact type transfer roller 5.

Further, while studying a very small amount of fog toner on the photosensitive drum 1, it was found that no toner transfer to the transfer roller 5 was observed when the transfer bias was about +0.5 kV or more.

Therefore, in this embodiment, in order to avoid the drawbacks of the charging memory, in the area B, which is the space between the sheets in the drawing, the transfer bias of the transfer roller 5 is controlled at a constant current of 1 μA, and about +1 kV is applied. Voltage (Vlo) is applied.
With the above setting, fogging toner on the photosensitive drum 1 between sheets can be suppressed as much as possible, and transfer to the transfer roller 5 can be prevented. This makes it possible to prevent back stains on the second and subsequent sheets during continuous printing.

Next, a description will be given of a region C in the figure corresponding to the post-rotation after printing. In consideration of the life of the photosensitive drum 1, the surface of the photosensitive drum 1 in the area C is charged only with direct current, which requires less shaving of the photosensitive member surface layer. Specifically, a state is shown in which the charging means is charged (Vd-H) to about -550 V by applying only a direct current (DC-H) of about 1150 V to the charging means.

As described above, in the present embodiment, in order to secure a stable image in preparation for the next print, the toner layer on the developing sleeve 4a, which is a developing carrier, is made uniform and charge is applied to the toner. In this case, the drive of the developing sleeve 4a (sleeve drive) is executed for a predetermined time after image formation to optimize the image quality, and then the sleeve drive is stopped. The AC of the developing bias is turned off to suppress fog on the photosensitive drum 1.

Here, the difference from the above-mentioned area B is that only a direct current is applied to the charging means in order to form the surface potential of the photosensitive drum 1 at the developing site when the sleeve is driven. The surface potentials of the photosensitive drum 1 in the areas B and C are the same as far as they are measured by a surface voltmeter or the like. However, when the DC component of the developing bias applied to the developing sleeve 4a to suppress fogging is changed, the charging means In the region C to which only the direct current was applied, the development weak bias Vds-2 = −200 V where the fog was minimized was found to be different from the region B. Here, the developing weak bias Vds-2 has an absolute value smaller than Vds-1 (= −250 V) in the image area and is 0%.
It is preferable to set the voltage higher than V.

In this embodiment, the transfer bias is Off.
However, as described above, the transfer bias is about +0.5.
At kV or higher, no toner transfer to the transfer roller 5 is observed, so such a voltage may be applied.

As described above, in the present embodiment, the fog on the photosensitive drum 1 at the time of driving the sleeve at the time of the post-rotation, that is, the non-image area, is brought close to none, and By applying the transfer bias described above, toner contamination of the transfer roller 5 in contact with the photosensitive drum 1 can be suppressed, and a high-quality print image free of back stains and the like can be obtained.

<Second Embodiment> FIG. 2 is a schematic diagram showing a second embodiment. The description of the same parts as in the first embodiment is omitted. The region A in the figure is the same as in the first embodiment, and the region C
An area corresponding to post-rotation after sheet printing is shown, and this area C will be described.

In the present embodiment, as in the first embodiment, the surface of the photosensitive drum 1 in the area C is charged only with a direct current that requires less shaving of the surface of the photosensitive member in consideration of the life of the photosensitive drum 1. . Here, the difference from the first embodiment is that in order to clean the transfer roller 5 after printing, the bias applied to the transfer roller 5 is not turned off, and the transfer bias of ± bipolar is applied to the transfer roller The point is that the adhered toner is cleaned. The details are described below.

For the same purpose as in the first embodiment, the state of each part is shown while the sleeve drive is executed for a predetermined time (about 3 seconds in the present embodiment) and thereafter the sleeve drive is stopped.

First, the cleaning of the -polar toner adhered to the transfer roller 5 will be described. To reduce the potential on the surface of the photosensitive drum 1 so that toner can be easily collected on the photosensitive drum 1 from the transfer roller 5, only about 900 V direct current (DC-L) is applied to the charging means after printing, and about −3.
It shows a state of being charged (Vd-L) to 00V.
The portion charged to Vd-L on the surface of the photosensitive drum 1 is a first charged portion. Here, first, Vneg ≒ −2 kV is applied as a transfer bias for about three turns of the transfer roller 5 in order to clean the negative polarity toner attached to the transfer roller 5. This is because dirt is removed by cleaning for about two rounds, and therefore, in this embodiment, three rounds are taken into consideration in consideration of a margin.

At this time, in order to suppress the contamination of the transfer roller 5, that is, to minimize the fog on the photosensitive drum 1 charged to about -300V, a developing bias applied to the developing sleeve 4a is used. When the AC was turned off and the DC component was shaken, the development weak bias Vds-3 ≒ −50 V at which fog was minimized was obtained. This is different from the portion where DC-H is applied to the charging means described in the first embodiment.

Next, in order to clean the toner of + polarity adhering to the transfer roller 5, Vlo ク リ ー ニ ン グ +1 kV is applied as a transfer bias for about three turns of the transfer roller 5. At this time, in order to increase the surface potential of the photosensitive drum 1 so as to easily collect the toner from the transfer roller 5 onto the photosensitive drum 1, the charging means is set to about −11 as in the first embodiment.
It shows a state in which a direct current (DC-H) of 50 V is applied and the voltage is charged (Vd-H) to about -550 V. The portion charged by DC-H on the surface of the photosensitive drum 1 is a second charged portion. Here, the developing bias value Vds-2 ≒ −200 V at which fog is minimized is obtained. With such a setting, fog toner on the photosensitive drum 1 during cleaning of the transfer roller 5 can be suppressed as much as possible, and transfer to the transfer roller 5 can be prevented.

As described above, in this embodiment, the surface potential of the photosensitive drum 1 at the time of cleaning the transfer roller 5 is adjusted in order to reduce fog on the photosensitive drum 1 when the sleeve is driven at the time of post-rotation. By applying the predetermined developing bias, toner contamination of the transfer roller 5 that is in contact with the photosensitive drum 1 is suppressed, so that a high-quality print image without back stains can be obtained.

Further, since the driving of the developing sleeve 4a and the cleaning of the transfer roller 5 are executed at the same timing, the time until the standby state for receiving the next print is extended to control these. Absent.

In the present embodiment, the cleaning of the transfer roller 5 has been described. However, it goes without saying that the same operation as that of the above-described embodiment can be achieved with respect to the cleaning of the above-mentioned intermediate transfer member.

<Embodiment 3> FIG. 3 is a schematic view showing Embodiment 3 and describes a case where the above-mentioned detection of the remaining amount of toner in the developing device is performed by an antenna type toner remaining amount detecting means. The description of the same parts as in the first embodiment is omitted. An area D in FIG. 3 indicates an area corresponding to a preparatory rotation before printing, and the area D will be described first.

The area D is the area inside the developing device at the time of the pre-rotation, which is the preparatory rotation until the image forming operation can be performed after the main switch is turned on, or at the time of the pre-rotation before printing the first sheet. 5 shows a state in which the remaining amount of toner is detected. That is, in the present embodiment, a magnetic toner is used as a toner, a developing bias having an AC component is applied to a developing sleeve 4a as a developer carrier, and a nonmagnetic detecting conductor 4c (FIG. It is assumed that the remaining amount of toner is detected by a so-called antenna system in which the remaining amount of toner in the developing device is detected by utilizing a change in the capacitance during the period 4).

Here, the charging means needs to uniformly charge the surface of the photosensitive drum 1 in order to stabilize the potential of the photosensitive drum 1, but in this embodiment, the surface of the photosensitive drum 1 in the area D in FIG. In the same manner as in the first embodiment, a direct current (DC-H) of about -1150 V is applied, and the battery is charged (Vd-H) at about -550 V. On the other hand, a developing sleeve 4a opposed to the surface of the photosensitive drum 1 at the developing site
When a developing bias in which an AC component is superimposed is applied while rotating the lens, as described above, fog is more or less generated on the photosensitive drum 1 at the developing portion, and the fog toner is transferred to the transfer roller 5. Therefore, the transfer roller 5 is soiled.

Therefore, in the present embodiment, in order to suppress the transfer roller contamination, that is, about -550 V
When the DC component of the developing bias applied to the developing sleeve 4a is changed in order to minimize the fog on the photosensitive drum 1 which is charged to the developing roller 1, the developing weak bias Vds-4 ≒ −280V at which the fog is minimized is obtained. became. After the detection of the remaining amount of toner is performed for a predetermined time, the state in which the developing bias is turned off and the sleeve driving is stopped is shown in the figure.

Further, similarly to the above-described embodiment, during the sleeve driving, the transfer means is provided with Vlo-1 ≒ +
0.5 kV is applied to prevent fog toner transfer to the transfer roller 5.

Next, FIG.
The regions A and B in the middle will be described. The surface of the photosensitive drum 1 in the region A and the region B is uniformly charged to about -550 V by applying a direct current to a charging means in both the regions A (Vch-I) and B (Vch-NI). (Potential of dark part; Vd).

Here, the area A (Vdev-I) and the area B
In (Vdev-NI), a developing bias in which an AC component is superimposed is applied while the developing sleeve 4a is driven to rotate. In the present embodiment, in this area, the remaining amount of toner is detected by an antenna method. It is assumed that.

First, as the DC component of the developing bias in the area A, Vds-I = -400 V which is set to obtain an appropriate image is applied because it is an image area. During this time, the transfer material is passed between the photosensitive drum 1 and the transfer roller 5 is not contaminated. Next, in the region B, it is necessary to apply a developing bias value that minimizes fog as described above. At this time, the developing weak bias Vds−5 = −370 V, and the region D
It turned out to be different. That is, the developing bias that minimizes fog is different between the case where only DC is applied to the charging unit and the case where the AC component is superimposed on DC and charged more uniformly.

Here, the developing weak bias Vds-4 is V
It is preferable to set the voltage to be smaller than ds-5. this is,
This is because, when only the direct current is applied to the charging means to charge the photosensitive drum 1, there are minute charging defects that cannot be measured by the surface voltmeter.

Further, as in the above-described embodiment, Vlo ≒ + 1 kV is applied to the charging means to prevent the transfer of fog toner to the transfer roller 5.

As described above, in the present embodiment, the fog on the photosensitive drum 1 when the sleeve is driven in the non-image area and when the sleeve is driven at the time of post-rotation is brought close to zero, and the predetermined amount By applying a bias, toner contamination of the transfer roller 5 that is in contact with the photosensitive drum 1 is suppressed, so that a high-quality print image free from back stains or the like can be obtained.

As described above, the present invention has been described with reference to the case where the surface of the photosensitive drum 1 is negatively charged and the transfer roller 5 is used as the transfer means as shown in FIG. 4. However, the present invention is not limited to this. Not the photosensitive drum 1
It goes without saying that the present invention can also be applied to a device that is charged or a device that uses an intermediate transfer member or a transfer belt as a transfer unit. Here, the charging member is not limited to the charging roller 5, and the developing method is not limited to the jumping developing method. Needless to say, other charging means and developing means can be used.

Further, depending on the image forming apparatus, the speed and resolution (dpi) of the apparatus can be varied and the density can be controlled depending on the image forming apparatus.
The settings of the amount of laser light for writing an image signal, the developing bias, the potential Vd of the dark portion of the photoconductor, and the potential Vl of the bright portion are changed, and the present invention is applied in an optimized form according to these settings. Of course, you can do that.

[0067]

As described above, according to the present invention,
During non-image formation, the DC voltage value applied to the developer carrier by the developing bias applying unit is made different depending on whether the DC voltage portion or the superimposed voltage portion on the image carrier is used, so that the back side of the transfer material due to fog toner is formed. The generation of stains can be prevented, and a high quality print image can be obtained.

It is also possible to extend the life of the transfer member, prevent image density unevenness caused by the charge memory of the image carrier by the transfer member, reduce the load on the cleaner,
For example, it is possible to prevent wasteful consumption of toner.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing potential states of an image area and a non-image area on the surface of a photosensitive drum before and after printing in the first embodiment.

FIG. 2 is a schematic diagram showing potential states of an image area and a non-image area on the surface of a photosensitive drum before and after printing according to a second embodiment.

FIG. 3 is a schematic diagram showing potential states of an image area and a non-image area on the surface of a photosensitive drum before and after printing according to a third embodiment.

FIG. 4 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus to which the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier (photosensitive drum) 2 Charging member (transfer roller) 2a Charging bias applying means (power supply) 3 Latent image forming means 4 Developing means (developing device) 4b Developing bias applying means (power supply) 5 Transfer member (transfer roller) 5a Transfer bias applying means (power supply) 6 Cleaner A Image area B Superimposed charging area (inter-paper area) C DC charging area (post-rotation area) D Pre-rotation area

Claims (4)

[Claims] An image bearing member, a charging member for uniformly charging the surface of the image bearing member, and charging for applying a DC voltage to the charging member or applying a superimposed voltage of a DC voltage and an AC voltage. Bias applying means, developing means having a rotatable developer carrier which is arranged opposite to the surface of the image carrier to form a developing site, and applying a DC voltage to the developer carrier or applying a DC voltage and an AC voltage And a developing bias applying unit for applying a superimposed voltage to the image forming apparatus, wherein the charging bias applying unit applies a DC voltage only to the charging member, and a part of the image carrier charged as a DC charging part. Further, when the charging bias application power source applies a superimposed voltage to the charging member and a part of the image carrier that is charged is a superimposed charging portion, when the developer carrier rotates during non-image formation, Regarding the DC voltage value applied to the developer carrying member by the developing bias applying unit, if the DC voltage value is different between when the DC charged portion moves to the developing site and when the superimposed charged portion moves. An image forming apparatus, comprising: 2. An image carrier, a charging member for uniformly charging the surface of the image carrier, and charging by applying a DC voltage to the charging member or applying a superimposed voltage of a DC voltage and an AC voltage. Bias applying means, developing means having a rotatable developer carrier which is disposed opposite to the surface of the image carrier and forms a developing site, and applying a superimposed voltage of a DC voltage and an AC voltage to the developer carrier; A developing conductor for applying a developing bias to the developer carrying member by the developing bias applying unit. An image forming apparatus that detects a voltage induced in the developing unit and detects a remaining amount of the developer in the developing unit, wherein the charging bias applying unit applies a DC voltage only to the charging member and is charged. When a part of the carrier is a DC charging part, and a part of the image carrier that is charged by the charging bias application power supply applying a superimposed voltage to the charging member is a superimposed charging part, Regarding the DC voltage value applied to the developer carrying member by the developing bias applying unit, if the DC voltage value is different between when the DC charged portion moves to the developing site and when the superimposed charged portion moves. An image forming apparatus, comprising: 3. The method according to claim 2, further comprising a plurality of the DC charging portions having different voltage values, wherein a DC voltage value applied to the developer carrier is changed according to the voltage values of the DC charging portions. The image forming apparatus according to claim 1. 4. An image bearing member, a charging member for uniformly charging the surface of the image bearing member, charging bias applying means for applying at least a DC voltage to the charging member, A developing unit having a rotatable developer carrier arranged to form a developing site; a developing bias applying unit for applying at least a DC voltage to the developer carrier; and a transfer unit pressed against the image carrier to form a transfer site. An image forming apparatus comprising: a transfer member to be configured; and a transfer bias applying unit that applies a transfer bias to the transfer member, wherein the charging bias applying unit applies a predetermined potential to the charging member to charge the image bearing member. A part of the image carrier is a first charged part, and a part of the image carrier charged by the charging bias applying power source applying another predetermined potential to the charging member is a second charged part. Then, when the developer charging member is rotated during non-image formation, the DC bias value applied to the developer carrying member by the developing bias applying means moves when the first charged portion moves to the developing part. And when the second charged portion has moved, the DC voltage value is different. Further, regarding the transfer bias applied to the transfer member by the transfer bias applying means, the first charged portion is applied to the transfer portion. An image forming apparatus, wherein the transfer bias is different between when the image forming apparatus moves and when the second charged portion moves.