JPH0876615A - Image forming device - Google Patents

Abstract

PURPOSE: To excellently remove toner, etc., remaining on a contact transfer means for transferring a visible image developed on an image carrier to a material to be recorded. CONSTITUTION: The image forming device which transfers the visible image on the image carrier 1 to the material to be recorded therefrom by the contact transfer means 7 coming into contact with the rear surface of the fed material to be recorded 14, to impart a charge for a transfer is provided with a means 4 for forming an electric field in a direction where a developer is shifted from the transfer means 7 to the image carrier 1 therebetween, when a paper sheet is not passed through and further, a means 16 detecting the electrostatic charge quantity of the developer and a control part 15 controls the size of the electric field or an applying time in accordance with the value of the means 16.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a transfer type electrophotographic apparatus.
The present invention relates to an image forming apparatus such as an electrostatic recording device.

More specifically, the recording material is fed to the transfer portion (contact nip portion between the image carrier and the transfer means) between the image carrier and the transfer means in contact with the image carrier so that the recording material is transferred onto the image carrier. The present invention relates to an image forming apparatus of a type in which a transferable image (toner image) formed and carried is transferred onto a recording material.

[0003]

2. Description of the Related Art Conventionally, in a transfer type image forming apparatus,
Toner as a transferable image corresponding to desired image information, which is formed and carried on an image carrier such as a photoconductor, a dielectric or a magnetic body by an appropriate image forming process such as electrophotography, electrostatic recording, magnetic recording, etc. As a transfer means for transferring an image to a recording material (transfer material, printing paper, printing paper, etc.), a non-contact transfer device using a corona charger has been widely used.

This is because a corona charger is disposed on the image carrier so as to be opposed to each other in a non-contact manner, a recording material is fed between the image carrier and the corona charger, and the back surface of the recording material is fed. In addition, a corona discharge charge having a predetermined polarity for transfer is applied by a corona charger, and the formed and carried toner image on the image carrier is electrically attracted and transferred to the surface of the recording material.

However, this transfer means has to apply a considerably high voltage to the corona charger in order to generate corona discharge, which requires a high voltage power source, and ozone is generated due to the corona discharge. Have problems such as.

For this reason, in recent years, an image forming apparatus has been developed which uses a contact charging type transfer means which only needs to apply a relatively low voltage.

In this system, a charging member such as a conductive roller or a conductive brush is provided in contact with an image carrier as a transfer member, and a recording material is fed to a transfer portion which is a contact nip portion between the two, and the recording material is recorded. By applying a bias voltage to the transfer member, which is in contact with the back surface of the material, to a predetermined polarity for transfer (contact charging), the formed toner image on the image carrier is transferred onto the surface of the recording material. It is the one that is electrically attracted and transferred.

In such a contact charging type transfer means, the voltage applied to the transfer member may be a relatively low voltage and the current may be relatively small, so that the power source can be made compact and lightweight.
It has the advantages of cost reduction and low ozone generation.

On the other hand, the transfer member may be contaminated by the oppositely charged toner attached to the non-sheet passing area on the image carrier and the residual toner after the jam.

In the image forming apparatus as described above, the toner adhering to the transfer member is removed at the time of pre-rotation at the beginning of operation and at the time of non-sheet passing such as a sheet interval during continuous sheet feeding. There has already been proposed a means of applying a reverse polarity voltage (having the same polarity as the toner) to transfer the toner to the image carrier to clean the transfer member.

[0011]

However, when the voltage applied to the transfer member is constant and the charge amount of the developer adhered to the transfer member is low, the contamination of the transfer member is insufficiently removed, and the subsequent transfer material is not sufficiently removed. There is a problem of soiling the back surface of the recording material.

Therefore, the present invention has been made to cope with such a situation, and detects the charge amount of the developer,
By controlling the magnitude or the application time of the voltage applied to the transfer member according to the value, it is possible to remove stains on the transfer member under any environment and prevent the back stain on the following recording material. It is what

[0013]

The above object is achieved by the image forming apparatus according to the present invention. In summary, a contact that develops an electrostatic latent image formed on an image carrier to form a visible image, and contacts the back surface of a transfer material to which the visible image is fed to impart a transfer charge. In an image forming apparatus that transfers from the image carrier onto a transfer material by a charging transfer means, in a direction in which a developer is transferred from the transfer means to the image carrier between the image carrier and the transfer means when the paper is not passed. An image forming apparatus comprising: a means for forming an electric field; and a means for detecting a charge amount of a developer, and controlling the magnitude of the electric field or an application time according to the value. is there.

Further, the image forming apparatus is characterized in that a humidity sensor is used as the means for detecting the charge amount of the developer, or the charge amount of the developer on the image carrier is directly measured.

[0015]

【Example】

(1) Image Forming Apparatus Example FIG. 1 is a schematic diagram of an image forming apparatus according to an embodiment. The image forming apparatus of this example is a transfer type laser printer or copying machine using an electrophotographic process.

Reference numeral 1 denotes a drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image bearing member, which is adhered to a conductive base layer 1b made of aluminum, iron or the like and an outer peripheral surface thereof. For example, a photoconductive layer 1a made of an organic photoconductor is used as a basic constituent layer, and is rotationally driven at a predetermined peripheral speed (process speed) in a clockwise direction indicated by an arrow around a spindle 1d. The conductive base layer 1b is grounded.

The photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the primary charging device 2 during its rotation process.
In this example, the photosensitive drum is negatively charged.

The primary charging device 2 in this example is a contact charging roller, and is a conductive roller 2c such as a metal roller which is a core metal, a conductive layer 2b formed on the outer peripheral surface thereof, and a resistance layer formed on the outer peripheral surface thereof. 2a ₁ and 2a ₂ , both ends of the conductor roller 2c are rotatably supported by bearing members (not shown) and arranged in parallel with the photosensitive drum 1, and a spring (not shown) or the like is pressed. The photosensitive drum 1 is pressed against the photosensitive drum 1 with a predetermined pressing force by means, and is driven to rotate as the photosensitive drum 1 rotates.

Then, an electric contactor 3a is attached to the conductor roller 2c.
By applying a predetermined bias voltage (DC voltage or oscillating voltage) from the power source 3 via the, the peripheral surface of the rotary photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by a contact charging method.

Next, the charged surface is subjected to image exposure processing of the target image information by the image exposure means 5 such as a laser scanner and slit exposure means, and an electrostatic latent image of the target image information is formed on the surface of the photosensitive drum 1. It is formed.

The electrostatic latent image is developed by a developer (toner) carried in a thin layer on the developing sleeve 6a of the developing device 6 to form a visible image (toner image). In this example, development is performed with positively charged toner (positive toner).

At the transfer portion N, which is the contact nip portion between the photosensitive drum 1 and the transfer member 7 in contact with the toner image, the toner image is fed to the transfer portion N from the paper feeding portion side at a predetermined timing. The recording material 14 thus transferred is sequentially transferred.

The transfer member 7 of this embodiment is a contact charging transfer roller, and includes a conductive roller 7a such as a metal roller which is a core metal,
It is composed of a cylindrical conductive layer 7b formed on the outer peripheral surface thereof, and both ends of the conductive roller 7a are rotatably supported by bearing members (not shown) so as to be arranged in parallel with the photosensitive drum 1. It is pressed against the photoconductor drum 1 by a pressing means such as a spring shown in the figure, and is rotated by the rotation of the photoconductor drum 1. A contact nip portion between the photosensitive drum 1 and the transfer roller 7 is a transfer portion N.

The recording material 14 is fed to the transfer portion N and is nipped and conveyed. When the front end of the recording material 14 enters the transfer portion N, a predetermined transfer bias voltage is applied from the power source 4 to the conductor roller 7a, and the back surface of the recording material in contact with the transfer roller 7 has a polarity opposite to that of the toner. The toner image on the photosensitive drum 1 is transferred to the recording material surface by being charged by the contact charging method.

The recording material 14 having the toner image transferred through the transfer portion N is separated from the surface of the photosensitive drum 1 and sent to an image fixing means (not shown), and the transferred toner image is transferred onto the recording material 14. It is fixed as a permanently fixed image on the sheet, and is ejected outside the machine as a print or copy.

On the other hand, the surface of the photosensitive drum after passing through the transfer portion is cleaned by removing residual developer and other adhering substances by the cleaner 8, and further, the static eliminator (static erasing lamp) 1
It is neutralized by 0 and initialized, and is repeatedly used for image formation.

Gears and the like may be attached to the contact charging type charging roller 2 and the transfer roller 7, respectively, and they may be forcibly driven by a driving means such as a motor.

In such a case, the bias (hereinafter referred to as a cleaning bias) applied to the transfer roller 7 at the time of non-transfer, that is, at the time of pre-rotation, at the time of post-rotation, and at the sheet interval (at the time of continuous copy) is referred to as the time of transfer. It is assumed that the toner has an opposite polarity to form an electric field in which the toner is directed toward the photoconductor drum 1, whereby the transfer roller 7 is cleaned. More specifically, when the transfer is not performed, a cleaning bias of +2.5 kV is applied to the transfer roller for one rotation of the transfer roller or more (process speed 105 m
Approximately 500 with φ16mm transfer roller for m / sec
msec) Apply. At the same time, a voltage is applied to the charging roller 2 to charge the surface potential of the photoconductor drum 1 to −400 V, so that the toner on the transfer roller 7 is transferred to the photoconductor drum 1.
It is easy to transfer to.

In the present invention, a well-known humidity sensor is used, the charge amount of the toner is estimated from the humidity in the environment in which the apparatus is used, and the transfer roller 7 is used during the pre-rotation, the post-rotation, and the sheet interval according to the value. Change the cleaning time of.

FIG. 2 shows the tendency of the amount of charge per unit mass of toner (hereinafter referred to as Q / M) with respect to environmental humidity. As shown in this graph, Q
/ M changes. When Q / M is low, the transfer roller 7
Since the upper toner is less likely to transfer onto the photosensitive drum 1, it is effective to lengthen the application time of the cleaning bias. The application time of the cleaning bias necessary to sufficiently clean the transfer roller 7 with respect to this Q / M is as shown in FIG. Therefore, from the detection value of the environment sensor 16, the proper cleaning bias application time can be estimated from FIGS. 2 and 3, that is,
The contents of these figures are stored in the storage means, and the control unit 15 determines the application time based on the measured humidity of the environment sensor 16 and refers to the stored contents in the storage means to control the transfer roller 7. To do. By the above means, the dirt on the transfer roller is sufficiently cleaned under any environment.

[Second Embodiment] The basic configuration is the same as that of the first embodiment.

In this embodiment, a humidity sensor is used to estimate the toner charge amount from the humidity in the environment in which the apparatus is used, and the transfer roller 7 is rotated during the pre-rotation, the post-rotation, and the sheet interval according to the value. Change the cleaning voltage. The cleaning bias required to sufficiently clean the transfer roller 7 with respect to the Q / M predicted in FIG. 2 is as shown in FIG.

Therefore, from the detection value of the environment sensor 16, the applied voltage of the proper cleaning bias is determined as shown in FIGS.
And the control unit 15 controls accordingly.
By any means such as above,
The dirt on the transfer roller is thoroughly cleaned.

[Embodiment 3] In the present embodiment, the charge amount of the toner on the photosensitive drum is directly measured, and the transfer roller 7 during the pre-rotation, the post-rotation and the sheet interval is measured according to the value.
Change the cleaning time of.

An example of a method of measuring the charge amount of toner will be shown below.

FIG. 5 is a schematic view of the image forming apparatus of this embodiment. A predetermined developing bias voltage is applied from a power source 17 to the developing sleeve 6a of the developing device 6. Since the developing sleeve 6a and the photosensitive drum 1 are not in contact with each other, the current flows only when the toner is transferred from the developing sleeve 6a onto the photosensitive drum 1.

Here, a constant area on the photosensitive drum 1 is uniformly charged to about -700 V, and a black belt-shaped constant area toner image is formed by the developing device 6. Since the amount of toner on a certain area changes according to Q / M, the current value accompanying development is measured as shown in FIG. Therefore, the value of Q / M can be obtained by measuring the developing current at this time with the ammeter 18. Based on this Q / M, an appropriate cleaning bias application time is determined according to FIG.
It is controlled by the control unit 15.

By the means as described above, the dirt on the transfer roller is sufficiently cleaned under any environment.

[Fourth Embodiment] The basic configuration is the same as that of the third embodiment.

In this embodiment, the toner charge amount on the photosensitive drum is directly measured, and the cleaning voltage of the transfer roller 7 during the pre-rotation, the post-rotation and the paper interval is changed according to the value.

By the same means as shown in Example 3, Q /
The value of M is measured, an appropriate cleaning bias is determined according to FIG. 4, and the control unit 15 controls it.

By the above means, the dirt on the transfer roller is sufficiently cleaned under any environment.

In the above-mentioned embodiments, the case where the transfer roller is used as the transfer means has been described, but the present invention is not limited to the roller type, and the present invention is a member such as a transfer belt or a transfer brush. It is also possible to apply to.

[0044]

As described above, according to the present invention, the cleaning condition of the transfer member is changed according to the charge amount of the toner in the image forming apparatus which transfers the transfer member by contacting the transfer member with the photosensitive drum. It is possible to sufficiently remove the stains on the transfer member under any environment and avoid the back stains on the recording material that follows.

[Brief description of drawings]

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

FIG. 2 is a graph showing the relationship between environmental humidity and toner Q / M.

FIG. 3 is a graph showing the relationship between toner Q / M and the application time of a cleaning bias required for proper cleaning.

FIG. 4 is a graph showing the relationship between the toner Q / M and the applied voltage of the cleaning bias necessary for proper cleaning.

FIG. 5 is a schematic view of an image forming apparatus according to another embodiment of the present invention.

FIG. 6 is a graph showing a current value associated with development on a certain area on a photosensitive drum.

[Explanation of symbols]

1 ... Image carrier (electrophotographic photosensitive drum) 2 ... Primary charging device (contact charging roller) 3, 4, 17 ...
Biasing power source 5 ... Image exposing means 6 ... Developing device 7 ... Transfer member (contact charging transfer roller) 8 ... Cleaner 10 ... Static eliminator 14 ... Recording material 15 ... Control section 16 ... Environment sensor 18 ... Ammeter

Claims (3)

[Claims] 1. An electrostatic latent image formed on an image bearing member is developed to form a visible image, and the visible image is brought into contact with the back surface of a recording material to which a transfer charge is applied. In an image forming apparatus that transfers from the image carrier onto the recording material by the contact charging type transfer device, the developer is transferred from the transfer device to the image carrier between the image carrier and the transfer device when the paper is not passed. An image characterized by having a means for forming an electric field in the direction of causing the electric field, and further having means for detecting the charge amount of the developer, and controlling the magnitude of the electric field or the application time according to the value. Forming equipment. 2. A means for detecting the charge amount of a developer,
The image forming apparatus according to claim 1, wherein a humidity sensor is used. 3. A means for detecting the charge amount of a developer,
The image forming apparatus according to claim 1, wherein a means for directly measuring the charge amount of the developer on the image carrier is used.