JP2001337550A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device with which soiling of a backside surface of material to be transferred where a developed image is not transferred can be surely prevented and with which generation of toner soiling such as a black stripe on a transfer surface where the developed image of the material to be transferred due to so called transfer memory can be surely prevented. SOLUTION: In the device, intermediate bias voltage V2 that is between a normal bias voltage V3 and a reverse bias voltage V1 is applied for a set period of time to a transfer device 26 by a power source device 32 about when a leading end or tail end of the material to be transferred P passes through a transfer nip position S between an image carrier 12 and the transfer device 26.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for developing an electrostatic latent image on an image carrier using a developer such as a toner, and electrostatically developing the developed image on a transfer material. The present invention relates to an image forming apparatus such as a printer using an electrophotographic method for transferring images.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus such as a printer using an electrophotographic system has been widely used. An image forming apparatus using the electrophotographic method generally includes an image carrier (a photosensitive drum, an intermediate transfer drum, and the like) formed in a drum shape.
The surface of the image carrier is uniformly charged, and the charged surface of the image carrier is irradiated with laser light to form an electrostatic latent image on the surface of the image carrier, and the charged developer (toner) This is an apparatus capable of electrostatically developing an electrostatic latent image and transferring the developed image to a transfer material (paper, plastic film, or the like) to obtain a print image.

One of the transfer methods for transferring the developed image to a transfer material is to rotate while contacting an image carrier.
Using a transfer roller to which a positive bias voltage having a polarity opposite to that of the developed image is applied, a transfer material is sandwiched between the image carrier and the transfer roller, and the developed image formed on the surface of the image carrier is electrostatically charged. There is known a method in which the image is transferred onto a material to be transferred.

When a transfer material is sandwiched between the transfer roller and the image carrier (during transfer), a positive bias voltage having a polarity opposite to that of the developed image is applied to the transfer roller. When the material to be transferred is not sandwiched between the transfer roller and the image bearing member (at the time of non-transfer), the polarity opposite to the positive bias voltage is used to prevent the normally charged toner of the image carrier from adhering to the transfer roller. Is applied.

[0005]

However, a small amount of the opposite polarity toner is usually mixed in the normally charged toner. However, in a high-humidity environment where the charging voltage of the developer is reduced, the reverse polarity toner is generally used. When the reverse bias voltage is applied (at the time of non-transfer), the polarity toner moves in a direction opposite to that of the normally-charged toner. Therefore, there is a problem that the reverse-polarity toner adheres to the transfer roller and actively stains the transfer roller. .

On the other hand, the timing at which the forward bias voltage applied to the transfer roller during the transfer operation is switched to the reverse bias voltage at the end of the transfer is adjusted so as not to affect the image bearing member inside the rear end of the transfer material (transfer material). (Before the trailing end passes through the transfer position).

However, in such a case, if the transfer image is transferred to the transfer material in a state where the transfer roller is soiled by the opposite polarity toner or in a state where the transfer roller is soiled by some other physical action, When switching to the reverse bias voltage at the end of the transfer, there is a problem that the back surface of the transfer material, that is, the surface on the side where the developed image is not transferred, particularly the back surface of the rear end portion of the transfer material may be stained with toner.

In order to prevent such contamination of the rear surface of the rear end portion of the transfer material by the toner, the timing of switching from the forward bias voltage to the reverse bias voltage is set outside the rear end of the transfer material. (After the rear end of the transfer material has passed the transfer position), the switching to the reverse bias voltage outside the rear end of the transfer material in this way may cause the transfer between the image bearing member and the transfer roller. Since the positive bias voltage is applied to a part of the image carrier in a state where the transfer material is not present,
In the next charging step, an insufficiently charged portion (so-called transfer memory) is formed in that portion of the image carrier.

In the transfer memory, when the interval time between the rear end of the transfer material and the front end of the subsequent transfer material is shorter than one cycle of the image carrier, the transfer of the subsequent transfer material is performed. There is a problem that a toner stain such as a black stripe sometimes occurs on the transfer surface.

In order to solve such a problem, the paper feed sensor detects the passage of the trailing edge of the material to be transferred and detects the passage of the leading edge of the subsequent material to be transferred. By changing the time from when the rear end of the material is detected to when the power supply switches the polarity of the bias voltage applied to the transfer device, the back surface (non-transfer surface) of the rear end of the material to be transferred is An image forming apparatus can be considered that can prevent the toner from being stained with toner or causing black toner stripes on the transfer surface.However, a detection signal is generated due to chattering of the paper feed sensor or wear of the actuator of the paper feed sensor. If the output is shifted, the image forming apparatus malfunctions and reliably prevents the back surface of the rear end of the transfer material from being stained with toner, and the transfer surface from being stained with toner such as black stripes. Rukoto come out is a problem that can not be.

In view of the above problems, the present invention can reliably prevent the back surface of the transfer material to which the developed image is not transferred from being stained with toner, and can use a so-called transfer memory to develop the developed image of the transfer material. It is an object of the present invention to provide an image forming apparatus capable of reliably preventing toner stains such as black streaks from being generated on a transfer surface on a side where the image is transferred.

[0012]

In order to solve the above-mentioned problems, an image forming apparatus according to the present invention is arranged such that an image carrier carrying a developed image or a primary transfer image is conveyed between the image carrier and the image carrier. A transfer device for transferring the developed image or the primary transfer image from the image carrier to the transferred material,
The transfer device is supplied with either a forward bias voltage having a polarity opposite to the developed image, a reverse bias voltage having the same polarity as the developed image, or an intermediate bias voltage having a magnitude between these forward bias voltage and reverse bias voltage. A power supply device capable of selectively applying the power, wherein the power supply device is connected to the transfer device before and after the leading end or the rear end of the transfer material passes through a transfer nip position between the image carrier and the transfer device. The intermediate bias voltage is applied for a certain period of time.

According to the image forming apparatus having such a configuration,
Since the power supply unit applies the intermediate bias voltage to the transfer device for a certain period of time before and after the leading or trailing end of the transfer material passes through the transfer nip position between the image carrier and the transfer device, the developed image of the transfer material is Is reliably prevented from being contaminated with the toner on the back surface on which the toner image is not transferred, and the transfer memory is used to prevent toner transfer such as black streaks from being generated on the transfer surface on which the developed image of the material to be transferred is transferred. It can be reliably prevented.

[0014]

Embodiments of the present invention will be specifically described below with reference to the drawings. 1 to 7
FIG. 1 is a diagram referred to for describing an embodiment of an image forming apparatus according to the present invention.

An image forming apparatus 10 according to the present embodiment shown in FIG.
And a photoconductor drum 12 (image carrier) of an OPC photoconductor,
A charging roller 16 connected to a charging power source (not shown) for uniformly charging the surface of the photosensitive drum 12 when the photosensitive drum 12 rotates, and a laser beam L
And an exposure device (not shown) for forming an electrostatic latent image on the surface thereof by exposure, and developing the electrostatic latent image on the photosensitive drum 12 using a developer to form a developed toner image. , Developing sleeve 2 connected to a developing power source (not shown)
1, a transfer roller 26 (transfer device) for transferring the developed toner image of the photoconductive drum 12 to a paper P (transferred material) sent from a registration roller 40, which will be described later, and a photoconductive drum The photosensitive drum 12 includes a charge removing device 30 having a charge removing brush 30a for removing charges from the photosensitive drum 12, and a cleaner 31 for removing toner remaining on the surface of the photosensitive drum 12 after transfer.

The transfer roller 26 is a transfer roller 2
6 is connected to a transfer power supply 32 that applies a bias voltage to the transfer roller 6. The transfer power supply 32 is connected to a bias voltage switching device 34 that drives the transfer power supply 32 to switch the bias voltage applied to the transfer roller 26.

Further, the bias voltage switching device 34
The transfer power supply 32 is connected to a voltage application time control device 36 that controls the time for applying a bias voltage to the transfer roller 26. The voltage application time control device 36 includes:
A registration sensor 42 to be described later and a control circuit 38 for controlling the voltage application time control device 36 as needed are connected.

As described above, the bias voltage applied to the transfer roller 26 is switched by the bias voltage switching device 34 via the transfer power supply 32. Therefore, the power supply device according to the present invention is used in the present embodiment. In the embodiment, it is constituted by a transfer power supply 32 and a bias voltage switching device 34.

The transfer timing of the sheet P conveyed from a sheet tray (not shown) is adjusted to the right of the transfer roller 26 in FIG. 1 to transfer the sheet P to the transfer roller 26 and the photosensitive drum 12. A registration roller 40 that conveys the paper P to a transfer nip position sandwiched therebetween, and a registration sensor 42 that detects whether the leading end or the rear end of the paper P has passed through the registration roller 40 are arranged.

When the registration sensor 42 detects that the leading edge or the trailing edge of the paper P has passed through the registration roller 40, the detection signal is input to the voltage application time control device 36. As will be described later, a timer (not shown) that starts counting a predetermined time until the forward and reverse bias voltages applied to the transfer roller 26 are switched to the intermediate bias voltage or from the intermediate bias voltage to the forward and reverse bias voltages is provided. Built-in.

The operation of the image forming apparatus 10 will be described below. The process speed due to the rotation of the photosensitive drum 12 of the image forming apparatus 10 is 70 mm / sec,
The surface of the photosensitive drum 12 is
The charged photosensitive drum 12 is uniformly charged to 00 V, and the surface of the charged photosensitive drum 12 is irradiated with the laser beam L. The voltage of the irradiated area is reduced to 80 V to form an electrostatic latent image. When the electrostatic latent image reaches the developing area, the developing sleeve 21
Is developed by electrostatically attaching toner to the electrostatic latent image,
A developed toner image (developed image) is formed on the photosensitive drum 12.

A DC bias voltage of 350 V is applied to the developing sleeve 21. When the developed toner image on the surface of the photosensitive drum 12 reaches the transfer nip position where it comes into contact with the transfer roller 26 due to the rotation of the photosensitive drum 12, the paper P is conveyed from the registration roller 40 to the transfer nip position in synchronization with the arrival time. You.

An intermediate bias voltage is applied to the transfer roller 26 during a certain period of time when the leading end of the sheet P passes before and after the transfer nip position, and thereafter, a positive polarity having a polarity opposite to that of the developed toner image on the photosensitive drum 12 is applied. A bias voltage is applied,
As a result, the developed toner image on the photosensitive drum 12 is electrostatically transferred to the paper P.

Thereafter, the discharging brush 30a of the discharging device 30
Thus, the paper P after the transfer is neutralized, and the paper P is conveyed to a fixing device (not shown) via the discharge conveyance path 44 without being wound around the photosensitive drum 12. The toner remaining on the photosensitive drum 12 after the transfer is removed by the cleaner 31 and the photosensitive drum 12 proceeds to the next latent image forming step.

Next, the operation of switching the bias voltage at the start of the transfer of the sheet P by the transfer roller 26 will be described below with reference to FIGS. FIG.
As shown in FIG. 3A, when the registration sensor 42 detects that the paper P has arrived at the registration roller 40, the registration sensor 42 operates at time T1 as shown in FIG. Is changed from H to L.

The voltage application time controller 36 measures the time from time T1 by the timer, and measures the time when the leading edge of the paper P comes slightly before the transfer nip position S as shown in FIG. At T2, the voltage application time control device 36 changes the intermediate bias switching signal output to the voltage switching device 34 from H to L, as shown in FIG.

As a result, the bias voltage switching device 34 controls the transfer power supply 32, as shown in FIG.
The reverse bias voltage V1 applied to the transfer roller 26 is switched to the intermediate bias voltage V2 having a magnitude between the reverse bias voltage V1 and the forward bias voltage V3.

Then, after the transfer time T3 at which the leading edge of the sheet P arrives at the transfer nip position S from the time T2, the leading edge of the sheet P slightly exceeds the transfer nip position S as shown in FIG. When the timer of the voltage application time control device 36 measures that the time T4 has come to the position, the voltage application time control device 36 outputs the intermediate bias switching signal output to the voltage switching device 34 as shown in FIG. Is changed from L to H, and as shown in FIG. 3B, the bias polarity switching signal output to the bias voltage switching device 34 is changed from H to L.

As a result, the voltage switching device 34 controls the transfer power supply 32 to switch the intermediate bias voltage V2 applied to the transfer roller 26 to the positive bias voltage V3 as shown in FIG. Thus, the developed toner image on the photosensitive drum 12 can be transferred onto the sheet P continuously at the transfer nip position S.

Next, the operation of switching the bias voltage at the end of the transfer of the paper P by the transfer roller 26 will be described below with reference to FIGS. FIG.
As shown in FIG. 6A, when the registration sensor 42 detects that the trailing edge of the sheet P has separated from the registration roller 40, the registration sensor 42 operates at time T1 as shown in FIG. The paper trailing edge detection signal output to the control device 36 is changed from L to H.

The voltage application time controller 36 measures the time from the time T1 by the timer, and measures the time when the rear end of the paper P is slightly before the transfer nip position S as shown in FIG. At time T2, the voltage application time control device 36 changes the intermediate bias switching signal output to the bias voltage switching device 34 to H, as shown in FIG.
To L.

As a result, the bias voltage switching device 34 controls the transfer power supply 32, as shown in FIG.
The forward bias voltage V3 applied to the transfer roller 26 is switched to the intermediate bias voltage V2 having a magnitude between the reverse bias voltage V1.

Then, after the transfer time T3 at which the rear end of the sheet P arrives at the transfer nip position S from the time T2, the rear end of the sheet P is slightly less than the transfer nip position S as shown in FIG. When the timer of the voltage application time control device 36 measures that the time T4 has come to the past position, the voltage application time control device 36 outputs the intermediate voltage to the bias voltage switching device 34 as shown in FIG. The bias switching signal is changed from L to H, and the bias polarity switching signal output to the voltage switching device 34 is changed from L to H, as shown in FIG.

Thus, the voltage switching device 34 controls the transfer power supply 32 to switch the intermediate bias voltage V2 applied to the transfer roller 26 to the reverse bias voltage V1, as shown in FIG. Thus, the operation of transferring the developed toner image on the photosensitive drum 12 to the sheet P is completed.

As described above, according to the present embodiment, the paper P
Of the photosensitive drum 12 and the transfer roller 2
6 before and after passing through the transfer nip position S between
2 applies the intermediate bias voltage 12 to the transfer roller 26 for a certain period of time, and since the absolute value of the intermediate bias voltage V2 is smaller than the reverse bias voltage V1, the intermediate bias voltage V2 is directly switched from the forward bias voltage V3 to the reverse bias voltage V1. As in the case described above, it is possible to reliably prevent the rear surface of the rear end portion of the sheet P from being stained with the toner.

Since the absolute value of the intermediate bias voltage V2 is smaller than the forward bias voltage V3, the intermediate bias voltage V2 is switched from the reverse bias voltage V1 in a state where the sheet P does not exist between the intermediate bias voltage 12 and the transfer roller 26. As in the case where the positive bias voltage V3 is applied to a part of the intermediate bias voltage 12, toner stains such as black stripes are generated on the transfer surface of the transfer memory P on which the developed toner image is transferred by the transfer memory. This can be reliably prevented. Such a phenomenon occurs particularly remarkably in a so-called positively charged single-layer type OPC photoconductor, so that a remarkable effect of the present embodiment is recognized.

Next, according to a second embodiment of the present invention,
An image forming apparatus using a positively charged single-layer OPC photosensitive drum 52 will be described with reference to FIG. The image forming apparatus in FIG. 2 has the same configuration as the image forming apparatus 10 in FIG. 1, but includes a developing sleeve 51, a positively charged single-layer type OPC photosensitive drum 52, a scorotron charger 53, a cleaner 54,
It comprises a static eliminator 55 and a transfer roller 56. The surface potential of the photosensitive drum 52 is 400V, the developing bias potential
V, the same effect as in the first embodiment can be obtained by performing the above control at an arbitrary value between 500 V and -2800 V. Further, when the charge eliminator 55 is provided to perform the light elimination as in the present embodiment, the generation of the transfer memory is suppressed to some extent.

In the second embodiment, the photoconductor drum 52 of the OPC is described. However, the photoconductor of a-Si (amorphous silicon), which makes the toner stain on the rear surface of the rear end portion relatively light, is relatively small. Even in the case of a drum or a photosensitive drum of a laminated type negatively charged OPC, there is no problem even if the above control is adopted. By the way, the a-Si photosensitive drum is OP
The reason why the generation of transfer memory is smaller than that of the photosensitive drum of C is that the photosensitive drum of a-Si has low film resistance and low charging ability, but is difficult to be charged even in reverse charging. This is because a-Si is less susceptible to the influence of the reverse charge, and a-Si is sensitive to the reverse charge, so that the transfer memory can be eliminated by removing the charge.

In the above-described embodiment, the case where the developed image on the photosensitive drum 12 is transferred to the sheet P by the transfer roller 26 has been described. Can be applied to the case where the developed image on the intermediate transfer drum on which the primary transfer is performed is secondarily transferred to the sheet P by the transfer roller 26.

In the above-described embodiment, the outer diameter of the photosensitive drum 12 is 30 mm, the process speed of the image forming apparatus 10 is 70 mm / sec, the surface of the photosensitive drum 12 is The voltage of the irradiation area irradiated with the beam L is 80 V, and the DC bias voltage applied to the developing sleeve 21 is 350 V
However, it is needless to say that the present invention does not need to be limited to such values and can take other values.

In the above embodiment, the case where the intermediate bias voltage V2 is between OFF (0 V) and the positive bias voltage V3 has been described. However, the intermediate bias voltage V2 may be OFF. May have a magnitude between OFF and the reverse bias voltage V1. In any case, it is desirable that the intermediate bias voltage V2 is close to OFF.

In the above embodiment, the case where the material to be transferred is paper has been described. However, the material to be transferred in the present invention is not limited to paper, and other materials such as a plastic film may be used. it can.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and may be variously modified based on the technical idea of the present invention. Can be changed.

[0044]

As described above, according to the image forming apparatus of the present invention, the power supply device is provided before and after the leading or trailing end of the transfer material passes through the transfer nip position between the image carrier and the transfer device. Since the intermediate bias voltage is applied to the transfer device for a certain period of time, it is possible to reliably prevent the back surface of the transfer material on which the developed image is not transferred from being stained with the toner, and to use the transfer memory to transfer the developed image of the transfer material. It is possible to reliably prevent the toner from being stained such as black stripes on the transfer surface on the side to be transferred.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing the position of a sheet of paper P for each time;
2A shows the position of the leading end of the sheet P at time T1, FIG.
2B shows the position of the leading edge of the sheet P at time T2, and FIG.
(C) is a diagram showing the position of the leading edge of the sheet P at time T4.

3A and 3B are time charts showing a relationship between each signal and each time, FIG. 3A is a time chart of a sheet leading edge detection signal, FIG. 3B is a time chart of a bias polarity switching signal, and FIG. (C) is a time chart of the intermediate bias switching signal.

FIG. 4 is a time chart showing a temporal change in the polarity and magnitude of a bias voltage applied to a transfer roller 26 at the start of transfer.

FIG. 5 is a diagram showing the position of the paper P for each time;
FIG. 5A shows the position of the rear end of the sheet P at time T1, FIG.
FIG. 5B shows the position of the rear end of the sheet P at time T2, FIG.
(C) is a diagram showing the position of the rear end of the sheet P at time T4.

6A and 6B are time charts showing a relationship between each signal and each time, FIG. 6A is a time chart of a paper trailing edge detection signal, and FIG. 6B is a time chart of a bias polarity switching signal; FIG. 6C is a time chart of the intermediate bias switching signal.

FIG. 7 is a time chart showing a temporal change in the polarity and magnitude of a bias voltage applied to the transfer roller 26 at the end of transfer.

FIG. 8 is a schematic configuration diagram illustrating an image forming apparatus according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Photoreceptor drum 16 Charging roller 21 Developing sleeve 22 Paper guide 26 Transfer roller 30 Static eliminator 30a Static elimination brush 31 Cleaner 32 Transfer power supply 34 Bias voltage switching device 36 Voltage application time control device 38 Control circuit 40 Registration roller 42 Resist Sensor 51 Developing sleeve 52 Photoreceptor drum 53 Scorotron charger 54 Cleaner 55 Static eliminator 56 Transfer roller A Arrow L Laser beam P Paper S Transfer nip position T1, T2, T3, T4 Time V1 Reverse bias voltage V2 Intermediate bias voltage V3 Forward bias Voltage

Claims (3)

[Claims] An image carrier for carrying the developed image or the primary transfer image; and transferring the developed image or the primary transfer image from the image carrier to a material to be transferred conveyed between the image carrier. A transfer device that causes the transfer device to have a forward bias voltage of the opposite polarity to the developed image, a reverse bias voltage of the same polarity as the developed image, or an intermediate bias having a magnitude between these forward and reverse bias voltages. A power supply device capable of selectively applying any one of voltages, wherein the power supply device is provided before and after a leading end or a trailing end of a material to be transferred passes a transfer nip position between the image carrier and the transfer device. Wherein the intermediate bias voltage is applied to the transfer device for a certain period of time. 2. The image forming apparatus according to claim 1, wherein the intermediate bias voltage is obtained by turning off the positive bias voltage or reducing the absolute value of the positive bias voltage. 3. The image forming apparatus according to claim 1, wherein the intermediate bias voltage is obtained by turning off the reverse bias voltage or reducing the absolute value of the reverse bias voltage.