JPH08146777A - Image forming device - Google Patents

Abstract

(57) [Abstract] [Purpose] A contact-type charge imparting member is provided, and a stain preventing mode of a transfer member is executed to prevent stain or adhesion of the member. In an image forming apparatus that applies a bias voltage having a polarity opposite to the normal polarity, even if the charge-giving member charges the photoreceptor to a polarity opposite to the normal polarity, it enables uniform primary charging and improves cleaning performance. To provide an image forming apparatus capable of performing. [Structure] In the contamination prevention mode of a transfer member, the charge removing / separating means 4 discharges with the same polarity as the primary charging polarity of the photoconductor 7.

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 having a contact type charge giving member.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus represented by the conventional Carlson process, prior to formation of a latent image,
The corona discharge method, which is a non-contact method, has been used as a means for uniformly primary-charging the photoconductor, but a large amount of ozone is generated because the space up to the photoconductor is ionized and charges are applied. .

This ozone is generated more in the case of negative discharge, but in recent years, the photoconductor has become an organic photoconductor for negative charging, and the environmental standard for generated gas has become strict. In addition, it is a serious problem.

On the other hand, the contact application method in which a member is brought into contact with the photosensitive member to carry out charging / transferring has an advantage that the voltage applied to the charging member is small and ozone is generated very little. , Has already been commercialized as a roller-shaped or brush-shaped contact member. For example, there is a contact type primary charging device for primary charging and a contact type contact transfer device as a transfer member.

However, since such a contact member is in contact with the photoconductor, it is very likely to be contaminated with toner, and it is difficult to maintain its performance over time. Therefore, in order to remove the toner adhering to these contact members, a voltage having the same polarity as that of the toner is applied to the contact members and the toner on the contact members is re-adhered to the photoconductor, so that the contact It has been proposed to remove stains on components.

When a roller is used as a transfer member of the contact members, a transfer member stain prevention mode is performed to prevent the contact transfer member from being stained with toner. In this mode, a bias voltage having the same polarity as that of the toner between the images on the photoconductor is applied to the contact transfer member to prevent the contact transfer member from being soiled with the toner. try to.

In this mode, for example, in an image forming apparatus having a roller-shaped contact transfer member that comes into contact with a photosensitive member and applies a transfer bias voltage at the time of transfer, in order to remove the toner adhering to the contact transfer member. A bias voltage having a polarity opposite to that of the bias voltage applied to the contact transfer member during normal image formation is applied to the contact transfer member to re-adhere the toner on the contact transfer member to the photoconductor, To clean.

Further, when the transfer paper is not in the contact area between the contact transfer member and the photosensitive member during image formation, the polarity of the voltage applied to the transfer member at the time of transfer to the transfer paper has a polarity opposite to that of the voltage applied to the transfer member. A bias voltage is applied to the contact transfer member to prevent the toner on the photoconductor from adhering to the contact transfer member (see JP-A-51-9840).

[0009]

However, in these prior arts, the positive polarity (-) for the photosensitive member at the time of primary charging and the transfer bias polarity (-) for the transfer by the contact transfer member are positive. -In the image forming apparatus by the positive method, in the stain prevention mode of the contact transfer member,
When a voltage having a polarity (−) and a polarity (+) opposite to that in the transfer mode is applied to the contact transfer member, the photoconductor is charged to a polarity (+) opposite to the regular polarity (usually). The static eliminator used cannot eliminate static electricity, causing irregularities in the primary electrification potential due to the primary electrification device,
Since the amount of charge of the (+) polarity toner is large, there is a problem that it is difficult to clean with a cleaning device.

An object common to each claim of the present invention is to have a contact type charge imparting member, and to prevent the stain or adhesion of the member, a bias having a reverse polarity to the charge imparting member is used. Provided is an image forming apparatus capable of improving a cleaning performance in a device for applying a voltage, which enables uniform primary charging even if a photoconductor is charged with a polarity opposite to a normal polarity by the charge applying member. To do.

According to another aspect of the present invention, in the first and third aspects of the invention, even when the photoconductor is charged to the opposite polarity to the normal polarity when the contact transfer member is in the dirt prevention mode, An object of the present invention is to provide an image forming apparatus capable of removing charges and reducing the load on the cleaning device. According to the invention of claim 2, an image forming apparatus capable of reliably obtaining the effect of removing charges on the photoconductor is provided. Is to provide
According to the fourth and fifth aspects of the present invention, an image forming apparatus is provided in which the on / off timing of the output of the charge eliminating separation means is obtained so that unnecessary charges do not remain on the photoconductor.

[0012]

In order to achieve the above object, the present invention is configured as follows. (1). A contact transfer member is used to transfer the visible image on the photoreceptor to the transfer paper, and the toner having the same polarity as the toner is applied to the contact transfer member to remove the toner adhering to the contact transfer member or to prevent the toner adhesion. In the image forming apparatus in which the charge removing and separating means for the transfer paper is provided downstream of the arrangement position of the contact transfer member in the rotation direction of the photoconductor, the charge removing and separating means performs AC discharge. Then, the output of the AC discharge of the charge removing / separating means is turned on in the stain preventing mode of the contact transfer member (claim 1).

(2). In (1), the AC discharge discharge output of the charge removal separation unit when the contact transfer member is in the stain prevention mode is set higher than that during normal image formation (claim 2).

(3). A contact transfer member is used to transfer the visible image on the photoreceptor to the transfer paper, and the toner having the same polarity as the toner is applied to the contact transfer member to remove the toner adhering to the contact transfer member or to prevent the toner adhesion. In the image forming apparatus in which the charge removing and separating unit is provided in the rotation direction of the photoconductor and downstream of the arrangement position of the contact transfer member, the charge removing and separating unit performs DC discharge. When the transfer output and the charging output have the same polarity, the polarity of the output of the charge eliminating / separating means is reversed from the polarity of the output at the time of image formation in the stain prevention mode of the contact transfer member, and the transfer output and the charging output are charged. When the outputs have different polarities, the polarity of the output of the charge removing / separating means is not reversed to that of the output at the time of image formation, and the polarity is output as it is at the time of image formation (claim 3).

(4). (1) or (2) or (3)
In the image forming apparatus described above, the contact transfer member and the photosensitive member are applied when a voltage reverse to that at the time of image formation is applied to the contact transfer member with respect to the transfer when the contact transfer member is in the dirt prevention mode and the output ON timing of the charge eliminating separation means. The output of the static elimination separation means is turned on before the place where the static elimination separation means reaches the output range of the static elimination separation means with respect to the photoconductor (claim 4) (5). In the image forming apparatus described in (1), (2), or (3), the transfer member when the contact transfer member is in the stain prevention mode is executed, and the charge removal separation output is turned off when the transfer output is turned off. After the place where the photoconductor and the photoconductor are in contact with each other falls within the output range for the photoconductor by the static elimination separation unit, the output of the static elimination unit is turned off (claim 5).

[0016]

As a function common to each claim, even if the photoconductor is charged to the opposite polarity to the normal polarity by the charge giving member, it is changed from the charged state to the non-charged state by the charge removing / separating means.

[0017]

【Example】

(one). 1. Correspondence to Claim 1 In FIG. 1 schematically showing the image forming apparatus of the present invention, a photoconductive drum-shaped photoconductor 7 is provided above the photoconductive drum 7 as a contact type charge giving member as a primary charging means. The roller-shaped charging member 1 is always in contact.

In the image forming process, the photoconductor 7 is rotated in the direction of the arrow. A developing device 2 is provided next to the charging member 1 around the photoconductor in the order of the rotation direction, and hereinafter, a roller-shaped contact transfer member 3 as a contact-type charge imparting member, and a charge-separating / separating means 4 for transfer paper. A cleaning device 5 for the photoconductor, a light erasing means 6 and the like are arranged. In addition,
Exposure light is irradiated onto the photoconductor between the charging member 1 and the developing device 2.

In forming an image, first, a constant voltage is applied to the charging member 1 after the photoconductor 7 starts rotating in the direction of the arrow. As a result, the photoconductor 7 is charged to a constant potential. Then, a writing device (not shown) irradiates and forms light containing image information to form a latent image on the photoconductor.

Next, while applying a constant developing bias voltage to the developing roller 2a of the developing device 2, toner is supplied to this latent image to visualize the latent image. This visible image is transferred to a transfer paper which is sandwiched between the photoconductor 7 and the transfer roller 3 and sent.

At the time of transfer, a constant bias voltage is applied to the transfer roller 3. After the transfer, a constant voltage is applied to the charge removing / separating unit 4 to separate the transfer paper from the photoconductor 7. Next, the transfer residual toner remaining on the photoconductor 7 is removed by the cleaning device 5, and the residual charge on the photoconductor 7 is removed by the photo-electrification means 6. An image is formed on the transfer paper by repeating the above cycle.

The photo-electrification means 6 has a structure in which needle electrodes are arranged in the axial direction of the photoconductor 7, and when voltage is applied,
A three-dimensional electric field region which is spread and overlaps is formed in a conical region having the tip of each electrode as the apex, and the output range is shown on the surface of the photoconductor 7 in FIG. As described above, the electric field regions are formed so as to be overlapped and continuous with each other on the circular straight line. When viewed in the axial direction of the photoconductor, this electric field region is an output range having a spread indicated by a symbol a.

By the way, while such an image forming cycle is being repeated, a photoconductor 7 called a sheet interval is called.
In the area between the front image area and the rear image area on the upper side, a voltage having a polarity opposite to that at the time of image formation is applied to the transfer roller 3 so that the toner adhered between the papers on the photoconductor 7 is removed. Prevents the toner from adhering to the transfer roller 3. This state is called the contact transfer member stain prevention mode.

In the stain prevention mode of the contact transfer member, the photoconductor 7 is charged with a polarity opposite to its normal polarity. Furthermore, the amount of charge of the toner existing between the sheets will also increase.

For example, in the positive-positive method in which the primary charging output of the charging member 1 and the transfer output of the contact transfer member have the same polarity, the charging member 1 charges the photoconductor 7 to (-), and the exposure light is used to form an image. The charges other than the portions are erased to form a latent image. The latent image is visualized by the developing device 2 with the (+) polarity toner. This visible image is transferred onto a transfer sheet passing between the transfer member 3 and the photoconductor 7 under a bias voltage of (-) polarity applied to the contact transfer member 3. At the time of this transfer, that is, at the time of forming an image on the transfer paper, the charge removal separation means 4 performs AC discharge.

Conventionally, in the stain prevention mode of the contact transfer member, the output of the charge removing / separating means 4 is turned off, and the bias voltage of (+) polarity is applied to the contact transfer member 3. As a result, the transfer member 3 is prevented from being contaminated by the (+) charged toner between the sheets. However, (+) of this transfer member 3
Due to the bias voltage of the polarity, the photosensitive member 7 is also charged by being inverted to the (+) polarity, and such charging becomes an obstacle to the charging of the (−) polarity at the time of the next primary charging and causes uneven charging. is there. Further, as a result of further applying the (+) charge to the (+) polarity toner between the sheets, the charge amount of the toner increases and the burden on the cleaning device 5 increases.

On the other hand, according to the first aspect of the present invention, even when the contact transfer member stain prevention mode is executed, the output of the charge removal separation means 4 is turned on and AC discharge is performed to remove the charge of the photoconductor and toner. To do. This will be described with reference to the timing chart of FIG.

In FIG. 4, the term "photoreceptor drive" indicates the drive of the photoconductor in a diagram, and the photoconductor 7 continues to be driven while the rising state is continued when it is ON. During this driving state, image portions and non-image portions are alternately formed on the photoconductor.

In FIG. 4, the term "development bias" is
The developing bias output state, that is, the magnitude, the polarity, and the timing of the bias voltage applied to the developing roller 2a is shown. While the image portion passes through the facing portion of the developing roller 2a, while the non-image portion passes, A voltage with a larger (-) polarity is applied. The magnitude of this bias voltage is
It is set to an appropriate size so as to control the amount of toner adhered to the developing section.

In FIG. 4, the term "transfer bias" is
The output state of the contact transfer member 3 is shown. While the image portion passes through the facing portion of the contact transfer member 3, a transfer process onto a transfer paper is performed, and a voltage of (+) polarity is set as a “normal bias”. Is applied. Further, while the non-image portion is passing, the stain preventing mode of the contact transfer member 3 is executed, and the bias voltage of (+) polarity is applied to the contact transfer member 3.

In FIG. 4, "(1) Static elimination separation output (A
The item “C)” indicates the AC output state of the static elimination separation means 4, and the output is started from the time when the leading edge of the first image portion reaches the output range a (see FIG. 3) of the static elimination separation means 4,
After that, the output state is maintained regardless of the image portion and the non-image portion, and thereafter, the output state is maintained until the last image portion passes.

The charge removing / separating means 4 has a function of separating the transfer sheet while the image portion passes, and removes the (+) polarity charged toner adhering to the non-image portion while the non-image portion passes. Perform a function.

As described above, in the positive-positive method, the bias of the primary charging polarity (-) and the reverse polarity (+) by the charging device 1 is applied to the contact transfer member 3, and the toner is attached to the contact transfer member 3. Even if the contact transfer member stain prevention mode is performed to prevent the electric charge, the charge of the photoconductor is discharged by the AC output of the charge separation unit 4.

Therefore, when this photoconductor is primarily charged in the next step, the photoconductor is uniformly charged without uneven charging, and therefore, uneven image does not occur in the following image forming step. Further, the non-image portion between the images on the photoconductor, so-called reverse polarity (+) toner existing between the sheets, is also discharged by the AC output of the charge separation unit 4, so that the burden on the cleaning device 5 is reduced and cleaning is performed. Performance is also improved.

The positive / positive method has been described above.
Since the charge eliminating separation means 4 outputs AC, the charge eliminating function is performed regardless of whether the charge polarity of the photoconductor or the toner is (+) or (-). Therefore, in the positive / positive method. Not only the negative and positive methods also perform the same static elimination function.

(II). Description corresponding to claim 2 When executing the content described in the above "(1) Description corresponding to claim 1", the AC discharge output of the charge removing / separating unit 4 is AC during normal image formation, that is, during transfer. If the discharge output is higher than the discharge output, the charges on the photoconductor can be removed more quickly and reliably.

(3). Description corresponding to claim 3 This is a case of a device in which the output of the static elimination separation device 4 is only DC. When the primary charge output is the (-) polarity, the toner used is the (+) polarity, and the transfer output of the contact transfer member 3 is the (-) polarity, that is, when it is so-called positive, the contact transfer member stain prevention mode If a bias voltage having a polarity (+) opposite to the primary charging polarity is applied to the contact transfer member 3, the photosensitive member 7 also has a polarity (+) opposite to the primary charging polarity (−). It gets charged.

On the other hand, at the time of transfer, a DC voltage having a polarity (+) opposite to the polarity (−) of the voltage applied to the contact transfer member 3 is applied to the charge removing / separating means 4. Even in the contamination prevention mode of the contact transfer member, even if the polarity of the bias voltage applied to the charge eliminating / separating means 4 is reversed from the transfer output polarity and the bias voltage of the charge eliminating / separating device 4 is turned on as it is, the photoreceptor 4 is reversed. The electric charge (+) is not removed.

Therefore, in the third aspect of the present invention, when the contact transfer member is in the dirt prevention mode, the voltage applied to the charge removing / separating means 4 is set to the polarity of the output of the normal charge removing / separating means, that is, at the time of transfer. Switch to the opposite polarity (-) to the polarity (+). The output value at this time is arbitrarily set to an output that can cancel the charge due to the previous transfer output. The timing and polarity of the output of the static elimination separation unit 4 are shown in the section "(2) Static elimination separation output (DC)" of FIG.

The above is the case of the positive-positive method,
Next, consider the case of the so-called negative / positive method, in which the charge separation output is only DC and the polarities of the charging output and the transfer output are different.

In the negative-positive method, the primary charging polarity is (-).
It is polar, and the electric charge in the image area is erased during exposure,
(-) Charge remains in the non-image area. This image portion is visualized with toner charged in the (-) polarity. At the time of transfer, the contact transfer member 3 is charged to the (-) polarity, and the charge removing / separating unit 4 is charged to the (-) polarity.

In the contact transfer member stain prevention mode, the contact transfer member 3 is charged to the (-) polarity which is the polarity of the toner, and the charge on the photosensitive member 7 is the (-) polarity which is the primary charging polarity. Therefore, the output of the charge removing / separating unit 4 is also output with the (-) polarity which is the polarity at the time of transfer. Take the
The timing and polarity of the output of the static elimination separation means 4 are shown in FIG.
"(3) Static elimination separation output (DC)" of.

In this way, since the polarity of the primary charging of the photoconductor is matched, even in the case of the device in which the charge removing / separating means 4 outputs only DC, the primary transfer is performed on the photoconductor that has passed through the contact transfer member stain prevention mode. No unevenness occurs during charging,
Therefore, image unevenness does not occur. Whether the output value of the charge removing / separating means 4 at this time is the same as or different from that at the time of transfer is determined in consideration of the charge strength of the photoconductor and the toner and the like. May be arbitrarily selected and set.

(4). Description corresponding to claim 4 As can be said with respect to each of the above-described embodiments of claims 1 to 3, the timing of turning on the output of the charge removing / separating means 4 in the dirt prevention mode of the contact transfer member will be considered. Try.

In any of the embodiments corresponding to any of the claims, since the surface charge of the photoconductor 7 after passing through the contact transfer member 3 must be removed, at least the on-timing of the charge separation output is transferred. A place where the transfer roller 3 and the photoconductor 7 are in contact with each other when a voltage having the same polarity as that of the toner is applied to the roller 3 (a portion indicated by a symbol b in FIG. 3A).
Is the output range a for the photoconductor 7 by the static elimination separation means 4.
It must be turned on before reaching (see Figure 3).

In the example in which the transfer member 3 is arranged on the upstream side in the rotation direction of the photoconductor and the charge removing / separating means 4 is arranged on the downstream side in the rotation direction, the output timing of the charge removing / separating means 4 is the contamination of the contact transfer member. In the prevention mode, the contact transfer member 3
Of course, it does not matter even if the voltage for is applied. By such control, the static elimination function of the necessary region on the photoconductor by the static elimination separation unit 4 is surely performed.

(5). Description corresponding to claim 5 As can be said with respect to each of the above-described embodiments of claims 1 to 3, the timing of turning off the output of the charge removing / separating means 4 in the stain prevention mode of the contact transfer member will be considered. Try.

When the output of the charge eliminating separation means 4 is off, consideration is made in accordance with the contents explained in the above-mentioned section "(4). Description corresponding to claim 4". The timing of turning off the output of the charge removing / separating means 4 is at least the output range a of the charge removing / separating means 4 to the photoconductor 7 at a position b where the photoconductor and the transfer roller 3 were in contact with each other when the transfer output of the contact transfer member 3 was turned off. After entering. That is, the output of the static elimination separation means 4 is turned off after waiting for the timing where the place b enters the output range a. By such control, the static elimination function of the necessary region on the photoconductor by the static elimination separation unit 4 is surely performed.

In each of the above embodiments, each polarity is an exemplification, and each of the embodiments can be implemented with a polarity opposite to the illustrated polarity.

(6). Description of Control System The control system of the image forming apparatus shown in FIG. 1 will be described with reference to FIG. The central processing unit 100 controls the operation of all members of the image forming apparatus. The central processing unit 100 sends a command to the photoconductor drive power source 102 via the drive control circuit 101 to drive the photoconductor 7. As a result, the photoconductor 7 is driven at the timing shown in FIG.

The central processing unit 100, via the developing bias control circuit 103, commands the developing roller 2a to apply a predetermined developing bias voltage to the developing at a predetermined timing. The mode of this application is as shown in the timing chart of FIG.

The central processing unit 100 sends a command to the output control circuit 104, and based on this command, the transfer bias power supply 105 applies a predetermined voltage to the contact transfer member 3 at a predetermined timing. The mode of this application is as described in the description of each claim. Specifically, it is as shown as the transfer output in the timing chart of FIG.

The central processing unit 100 sends a command to the output control circuit 106, and based on this command, the static elimination separation bias power source 107 applies a predetermined voltage to the static elimination separation means 4 at a predetermined timing. The mode of this application is as described in the description of each claim. Specifically, FIG.
In the timing chart of (1) static elimination separation output (AC),
(2) Static elimination separation output (DC), (3) Static elimination separation output (D)
C) is as shown respectively.

[0054]

As an effect common to each claim, it is possible to perform uniform primary charging and improve cleaning performance. According to the second aspect of the present invention, image unevenness and cleaning failure can be avoided more reliably. In the inventions of claims 4 and 5, since the on / off timing of the transfer charge elimination separation output is defined according to the reverse charge region on the photoconductor, unnecessary charges may remain on the photoconductor. Absent.

[Brief description of drawings]

FIG. 1 is a front view illustrating the configuration of an image forming apparatus according to the present invention.

FIG. 2 is a block diagram illustrating a control system of the image forming apparatus according to the present invention.

FIG. 3 is a diagram illustrating an output range on a photoconductor of a charge removing / separating unit according to the present invention.

FIG. 4 is a timing chart illustrating the operation of each process member according to the present invention.

[Explanation of symbols]

 3 Contact transfer member 4 Static elimination separation means

Claims (5)

[Claims] 1. A contact transfer member is used to transfer a visible image on a photoconductor onto a transfer paper, and toner is removed from the contact transfer member to remove or adhere to the contact transfer member. In the image forming apparatus, in which the voltage of the same polarity is applied, and the charge removing / separating unit of the transfer paper is provided downstream of the arrangement position of the contact transfer member in the rotation direction of the photoconductor, the charge removing / separating unit is An image forming apparatus, wherein an AC discharge is performed, and an output of the AC discharge of the charge removing / separating unit is turned on in a stain prevention mode of the contact transfer member. 2. The image forming apparatus according to claim 1, wherein the AC discharge output of the charge removing / separating means when the contact transfer member is in the stain prevention mode is higher than that during normal image formation. 3. A contact transfer member is used to transfer a visible image on a photoconductor onto a transfer paper, and toner is removed from the contact transfer member to prevent the toner from adhering to the contact transfer member. In the image forming apparatus, in which the voltage of the same polarity is applied, and the charge removing / separating unit of the transfer paper is provided downstream of the arrangement position of the contact transfer member in the rotation direction of the photoconductor, the charge removing / separating unit is DC discharge is performed, and when the transfer output and the charging output have the same polarity, the polarity of the output of the charge removing / separating means is reversed from the polarity of the output at the time of image formation in the stain prevention mode of the contact transfer member. In the case where the transfer output and the charging output have different polarities, the polarity of the output of the charge removing / separating means is not reversed to that of the output at the time of image formation, and the polarity is outputted as it is at the time of image formation. Forming equipment. 4. The image forming apparatus according to claim 1, 2 or 3, wherein an image is formed on the contact transfer member with respect to the timing of transfer when the contact transfer member is in the stain prevention mode and the output ON timing of the charge eliminating separation means. It is characterized in that the output of the charge eliminating separation means is turned on before the position where the contact transfer member and the photoreceptor are in contact with each other when the voltage opposite to that at the time of formation is reached within the output range of the charge eliminating separation means to the photoreceptor. Image forming apparatus. 5. The image forming apparatus according to claim 1, 2 or 3, wherein the transfer output is turned off with respect to the timing of the transfer and charge removal separation output being turned off when the contact transfer member is in the dirt prevention mode. At this time, after the place where the transfer member and the photoconductor are in contact with each other falls within the output range for the photoconductor by the static elimination separation unit, the output of the static elimination separation unit is turned off.