JPH08248787A - Imag forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device capable of preventing soiling of a transfer rotary body by the toner of the non-paper passing time, without deteriorating the image carrier. CONSTITUTION: In the image forming device, an electrostatic latent image on a photoreceptor drum 1 is developed to the toner image, and the toner image is transferred to a transfer paper 3 by the transfer roller 2, at the non paper passing time of the transfer paper 3, by a regulated current bias applying device 4, transfer bias of the transfer roller 2, the polarity is alternately switched, with the regulated current whose ratio of current value of a reverse polarity corresponding to the current value of the normal polarity is <1, the toner of the first polarity stuck on non image part of the photoreceptor drum 1, and the toner of the second polarity generated by Paschen discharge is prevented from sticking on the transfer roller 2. Switchover of the transfer bias, alternately by the time corresponding to an odd number division length of a peripheral length of the photoreceptor drum 1, during the time of two rotations of the photoreceptor drum 1, after the switchover of the transfer bias, during the time >=one rotation of the photoreceptor 1, the current having the normal polarity is made flowing to the transfer roller 2, and the potential unevenness of the photoreceptor drum 1 is corrected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine.

[0002]

2. Description of the Related Art An electrostatic latent image formed on the surface of an image carrier is developed into a toner image, a transfer material is sandwiched between the transfer rotor and the image carrier, and a transfer bias is applied to the transfer rotor. There is known an image forming apparatus that transfers a toner image on an image bearing member to a transfer material by applying.

In this type of image forming apparatus, when the width of the toner image is larger than the width of the transfer material or when a jam occurs,
The toner directly adheres to the transfer rotary member, and the toner is easily scattered and the subsequent transfer material is easily soiled. In order to solve this problem, Japanese Patent Laid-Open No. 51-9840 discloses that when the transfer material does not exist between the image carrier and the transfer rotary member, the polarity is opposite to that at the time of transfer to the transfer rotary member. A toner image transfer device has been proposed which applies a bias to return the toner attached to the transfer rotary member to the image carrier to clean the transfer rotary member.

(3) The above-mentioned proposed apparatus has a problem in that the instability of the charging polarity of the toner is not taken into consideration. That is, when a bias having a reverse polarity to that at the time of transfer is applied to the transfer rotator, when the electric field strength becomes a Baschen discharge region between the image carrier and the transfer rotator, air is ionized and passes through this region. A part of the toner is charged with the same polarity as that at the time of transfer of the transfer rotary member by the charge of ionization. For this,
When a bias with the reverse polarity to that at the time of transfer is applied to the transfer rotor, a large amount of toner returns to the image carrier, but some toner remains on the transfer rotor and remains contaminated inside the device and transfer material. May not be resolved.

[0005]

In order to solve this problem, in Japanese Patent Laid-Open No. 3-69978, as shown in FIG. 4, a time t2 corresponding to one rotation is applied to the transfer rotary member when the paper is not passed. There is disclosed an image forming apparatus that applies a bias with a predetermined polarity during the period from t3 to t3, and with a reverse polarity during the period from t3 to t4 corresponding to one rotation. There is disclosed an image forming apparatus that maintains the polarity of the residual toner of the transfer rotary member that enters into the reverse polarity to the polarity of the transfer bias.

As disclosed in these publications, it is impossible to switch the bias applied to the transfer rotator.
It is effective to prevent toner contamination. However, if the voltage is simply switched, the image carrier is charged with a polarity opposite to the normal polarity due to Paschen discharge that occurs when a voltage is applied. It has no sensitivity and cannot remove charges by light,
As shown in FIG. 5, the forward and reverse electric potentials generated on the image carrier are not eliminated even in the subsequent steps, and there is a problem in that the electric potential becomes uneven. In this case, even if an attempt is made to reduce the applied voltage to solve these problems, the resistance value of the transfer rotor, which is usually made of conductive rubber, varies depending on temperature and humidity, and the charge degree is low when the resistance is low. Increasingly, the problem cannot be solved.

The present invention has been made in view of the current state of transfer in an image forming apparatus as described above, and an object thereof is to prevent contamination of a transfer rotary member by toner when a paper is not passed. It is to provide an image forming apparatus that does not deteriorate the temperature.

[0008]

In order to achieve the above object, the invention according to claim 1 is characterized in that an electrostatic latent image is formed on an image bearing member and the toner is supplied to the image bearing member. In an image forming apparatus in which an electrostatic latent image is developed into a toner image, and the obtained toner image is transferred onto a transfer material by a transfer rotary member, a transfer bias of the transfer rotary member when the transfer material is not passed. Is provided with bias applying means for preventing the toner in the non-image portion of the image carrier from adhering to the transfer rotary member by switching the polarity with a constant current.

Similarly, in order to achieve the above object, in the invention according to claim 2, in the invention according to claim 1, the ratio of the reverse bias current value of the transfer bias to the normal polarity current value is smaller than 1. It is characterized by that.

Similarly, in order to achieve the above object, in the invention according to claim 3, in the invention according to claim 1, the switching of the transfer bias corresponds to an odd division length of the peripheral length of the image carrier. It is characterized in that the operations are alternately performed with time, and are performed during an even rotation of the image carrier.

Similarly, in order to achieve the above object, the invention according to claim 4 is the image forming apparatus according to any one of claims 1 to 3, wherein after the transfer bias is switched, the image carrier is formed. During the time of one rotation or more, a current having a normal polarity is applied to the transfer rotary member by the bias applying unit.

[0012]

According to the first aspect of the invention, an electrostatic latent image is formed on the image carrier, the electrostatic latent image is developed into a toner image by the toner supplied to the image carrier, and the obtained toner image is formed. In an image forming apparatus in which a transfer rotator transfers a transfer material to a transfer material, the polarity of the transfer bias of the transfer rotator is switched by a constant current by a bias applying unit when the transfer material is not passed. Both the first polarity toner attached to the non-image portion of the image carrier and the second polarity toner generated by Paschen discharge are prevented from attaching to the transfer rotary body.

According to the second aspect of the present invention, in the operation according to the first aspect of the invention, the ratio of the reverse bias current value of the transfer bias to the normal polarity current value is set to be smaller than 1.

According to a third aspect of the present invention, in the operation according to the first aspect of the invention, the transfer bias is alternately switched at a time corresponding to an odd division length of the peripheral length of the image carrier,
And it is performed during the even rotation of the image carrier.

According to a fourth aspect of the invention, in addition to the effect of the invention according to any one of the first to third aspects, one or more rotations of the image carrier after the transfer bias is switched by the bias applying means. During the period of time, a current having a normal polarity is applied to the transfer rotator.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS.
Will be described with reference to. FIG. 1 is an explanatory diagram showing a configuration of a main part of an embodiment of the present invention, FIG. 2 is a time chart showing a timing of applying a transfer current in the present embodiment, and FIG. 3 is a diagram showing each state of an image carrier of the present embodiment. It is an explanatory view showing the surface potential of.

In this embodiment, as shown in FIG. 1, a rotatable photoconductor drum 1 is provided as an image carrier, and is placed in proximity to the photoconductor drum 1 so as to be electrically conductive as a transfer rotary member. The transfer roller 2 is provided, and the transfer paper 3 is provided when passing the paper.
However, the photosensitive drum 1 and the transfer roller 2 are configured so as to be pressed and nipped and transferred.

A constant current bias applying device 4 for applying a constant current bias to the transfer roller 2 is provided.
In this constant current bias applying device 4, the common terminal T0 is connected to the bias applying point to the transfer roller 2, and the switching terminal T
A polarity conversion switch 7 for switching between 1 and T2 is provided. The negative terminal of the first power source 5 is connected to the switching terminal T1,
The positive terminal of the second power source 6 is connected to the switching terminal T2,
The positive electrode of the power source 5 and the negative electrode of the second power source 6 are connected, and the current setting device 8 is connected between the connection point and the ground. The automatic controller 10 that controls the operation of the constant current bias applying device 4 is connected to the constant current bias applying device 4.

The operation of this embodiment having such a configuration will be described. In the present embodiment, as shown in FIG. 2, when the copy is started at time t1 and the copy is finished at time t2, the automatic controller 10 is activated to make the odd-numbered division length (3 (Division length) at the time of 2 of the photosensitive drum 1
From the time t2 corresponding to the rotation to the time t5, the polarity conversion switch 7 is alternately switched, and the positive polarity toner and the negative polarity toner which are about to adhere to the transfer roller 2 are returned to the photosensitive drum 1.

In this case, the reverse bias current value of the switching bias applied to the transfer roller 2 by the first power source 5, the second power source 6 and the current setting device 8 in advance is higher than the normal polarity current value. It is set to be small. As described above, even if the current value of the reverse polarity is reduced, the amount of toner that is generated by Paschen discharge and returned to the photosensitive drum 1 by the application of the bias of the reverse polarity is relatively small. It can be sufficiently prevented.
Therefore, when the switching bias is applied to the transfer roller 2, the photosensitive drum 1 is not in a strong reverse charging state and deterioration of the photosensitive drum 1 due to reverse charging is prevented.

Next, during the period of one rotation of the photosensitive drum 1 corresponding to the time t6 to the time t7, the polarity conversion switch 7 is switched to the first power source 5 side by the automatic controller 10 to transfer the transfer roller. 2, a current having a normal polarity is supplied, and the current is supplied so that the photoconductor drum 1 is charged to a normal polarity, and as shown in FIG. 3, the positive and negative unevenness of the potential of the photoconductor drum 1 is corrected. Will be possible.

As described above, according to the present embodiment, the polarity conversion switch 7 is alternately switched at the time corresponding to the odd division length of the entire circumference of the photosensitive drum 1 after the end of the copying operation or at the time of jam, and the temperature is changed. The constant current bias switching operation that does not depend on temperature or humidity is continued for two rotations of the photosensitive drum 1, and the positive polarity toner and the negative polarity toner that are about to adhere to the transfer roller 2 are transferred to the photosensitive drum 1. It is prevented that the toner is attached to the transfer roller 2 and the image quality is deteriorated due to the toner adhering to the transfer roller 2.

When applying this bias, the current value of the reverse polarity is set smaller than the current value of the normal polarity, and the bias of the normal polarity and the bias of the reverse polarity are applied alternately, so that the reverse of the photosensitive drum 1 is applied. It is possible to prevent deterioration due to charging.

Further, after the bias is applied, a current having a normal polarity is supplied to the transfer roller 2 for one rotation of the photoconductor drum 1. Therefore, by supplying a current having a polarity opposite to the normal polarity when the bias is applied, the photoconductor drum 1 is supplied. The potential unevenness occurring at 1 is corrected, and high quality image formation is always possible.

[0025]

According to the first aspect of the present invention, the polarity of the transfer bias of the transfer rotator can be switched by a constant current by the bias applying means when the transfer material is not fed. The charge fluctuation of the image carrier due to the resistance fluctuation of the rotating body is reduced, the deterioration of the image carrier is prevented, and the first polarity toner adhering to the non-image portion of the image carrier and Paschen discharge are generated. It is possible to prevent any of the toner of the second polarity from adhering to the transfer rotator, which enables high quality image formation. According to the invention of claim 2, claim 1
In addition to the effects obtained by the invention described above, since the ratio of the reverse bias current value of the transfer bias to the normal polarity current value is smaller than 1, the charge amount of the image carrier when the reverse bias current of the transfer bias is applied can be reduced. And the fatigue of the image bearing member is reduced.
According to the invention of claim 3, in addition to the effect obtained by the invention of claim 1, the transfer bias is alternately switched at a time corresponding to an odd division length of the peripheral length of the image carrier, and Since it is performed during the even rotation of the image carrier, continuous reverse charging is avoided, the effect of preventing the deterioration of the image carrier is enhanced, the potential unevenness of the image carrier is eliminated, and the uniformity of the quality of image formation is improved. According to the invention described in claim 4, in addition to the effect obtained by the invention described in any one of claims 1 to 3, after the transfer bias is switched by the bias applying means, one or more rotations of the image carrier are performed. Since a current having a normal polarity is applied to the transfer rotator during the time, there is no potential unevenness of the image carrier when the transfer bias is applied, and the image quality during image formation is stable.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a main part of an embodiment of the present invention.

FIG. 2 is a time chart showing a timing of applying a transfer current in the example.

FIG. 3 is an explanatory diagram showing a surface potential in each state of the image carrier of the embodiment.

FIG. 4 is a time chart showing a timing of applying a transfer current in a conventional image forming apparatus.

FIG. 5 is an explanatory diagram showing a surface potential of an image carrier of a conventional image forming apparatus in each state.

[Explanation of symbols]

 1 Photoconductor drum 2 Transfer roller 3 Transfer paper 4 Constant current bias applying device 5 First power supply 6 Second power supply 7 Polarity conversion switch 8 Current setting device 10 Automatic controller

Claims (4)

[Claims] 1. An electrostatic latent image is formed on an image carrier, the electrostatic latent image is developed into a toner image by toner supplied to the image carrier, and the obtained toner image is transferred to a rotating body. In the image forming apparatus in which the transfer material is transferred to the transfer material by switching the polarity of the transfer bias of the transfer rotary member with a constant current when the transfer material is not passing through the non-image portion of the image carrier. An image forming apparatus comprising: a bias applying unit that prevents the toner of (1) from adhering to the transfer rotary member. 2. The image forming apparatus according to claim 1, wherein the ratio of the reverse bias current value of the transfer bias to the normal polarity current value is smaller than 1. 3. The transfer bias is alternately switched at a time corresponding to an odd division length of the peripheral length of the image carrier, and is performed during an even rotation of the image carrier. The image forming apparatus described. 4. The image forming apparatus according to claim 1, wherein after the transfer bias is switched, the transfer rotary member is provided with the image transfer member for one rotation or more. An image forming apparatus, wherein a current having a normal polarity is supplied by the bias applying unit.