JPH1026860A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent toner from adhering to a non-image part in the case of color development so as to prevent the toner from scattering and being excessively consumed by excessive toner adhering thereby, the burden on a cleaning device, etc., are lightened, in a reversal developing type image forming device using black toner and color toner. SOLUTION: As to this image forming device, the potential difference of the color toner (bias 1 impressing) between the electrified potential of the non- image part of the photoreceptor and the developing bias potential of the non- image part is larger than that of the black toner (bias 2 or 3 impressing), the potential of the developing bias of the non-image part is the reverse potential to that of the developing bias potential of the image part while making the electrified potential of the non-image part a boundary. Thus, the toner adhering to the non-image part can be surely prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly to an image forming apparatus of a reversal developing type having at least one type of color developing device and using black toner and color toner. It is.

[0002]

2. Description of the Related Art Recently, the number of users requesting a color image has increased, and various electrophotographic images have been used, such as a multi-color copying machine for copying a single-color image and a full-color copying machine for reproducing original colors. A forming apparatus has been proposed (for example, Japanese Patent Application Laid-Open No. 61-254960).
Conventionally, in these image forming apparatuses, as one method of creating a color image, a process of visualizing a latent image created on a photoreceptor with a plurality of color toners, transferring the latent image to recording paper, and fixing the color image to obtain a color copy. Has been done.

[0003]

When the above image forming process is performed in a conventional image forming apparatus, for example, when the potential on the photosensitive member is positive when viewed from the developing device side, a negative toner is used as a developer. In the case of the developing process using, even if the potential of the photoconductor is negative,
It occurs that toner adheres to the photoconductor. In other words, if the potential of the photosensitive member and the potential of the developing sleeve of the developing device are the same, it can be said that toner adhesion occurs.
It is considered that this is because the development start voltage of the developer is low.

As described above, when the electric field of the development start voltage is biased toward the same polarity as that of the toner rather than 0 V, in the case of the reversal development method, the non-image area of the uncharged photosensitive member (image formation is not performed) Area, which is not referred to as non-image area)
When the developing sleeve of 0 V is in contact with the toner, the toner adheres to the non-image area, causing toner scattering, wasteful toner, and a burden on the cleaning device. . It is known that the development start voltage differs depending on the type of the toner. In particular, the black toner and the color toner have different development start voltages.

The present invention has been made in view of the above circumstances, and a purpose thereof is to provide an image forming apparatus using a black toner and a color toner in an optimal non-image area corresponding to the type of toner. To prevent toner from adhering to the non-image area of the photoreceptor in the case of color development, thereby preventing toner scattering and extra toner consumption due to extra toner adhering, and reducing the load on the cleaning device and the like. Is to do.

[0006]

According to the present invention, there is provided an image forming apparatus of a reversal development type using a black toner and a color toner. The color toner has a larger potential difference from the developing bias potential of the portion than the black toner.

In the above image forming apparatus, the developing bias potential of the non-image portion is opposite to the developing bias potential of the image portion with respect to the charging potential of the non-image portion. ).

In the image forming apparatus having the above structure, the potential difference between the charging potential of the non-image portion of the photosensitive member and the developing bias potential of the non-image portion is larger in the color toner than in the black toner, so that the development start voltage is reduced. The developing bias of the non-image portion is set according to the different black toner and color toner, so that toner adhesion to the non-image portion can be prevented, and toner scattering and unnecessary toner consumption can be prevented.

In the above image forming apparatus, the developing bias potential of the non-image portion is opposite to the developing bias potential of the image portion with respect to the charging potential of the non-image portion. Adhesion can be reliably prevented, and toner scattering and unnecessary toner consumption can be prevented.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. First, as an embodiment, an image forming apparatus will be described in which a reversal developing method for developing an exposed portion is used, and in color developing, a single color developing is performed by replacing a unit. In this embodiment, a two-component developer including a carrier and a toner is used as the developer.

FIG. 1 is a schematic configuration diagram of a copying machine showing an example of an image forming apparatus to which the present invention is applied. FIG.
Reference numeral 1 denotes a photosensitive member capable of carrying a latent image on the surface, and reference numeral 2 denotes a scorotron charger for uniformly charging the surface of the photosensitive member 1. An exposure light 3 emitted from the exposure light source 12 is intensity-modulated in accordance with an image signal from the control device 10 and writes an image corresponding to the image signal on the uniformly charged photoconductor 1. Reference numeral 4 denotes a developing unit, which can be replaced with a color unit for each unit. Reference numeral 5 denotes a developing sleeve in the developing unit 4, which holds a developer and causes toner to adhere to the photoconductor 1 by a developing bias potential applied thereto. The amount of toner adhered on the photoconductor 1 is also controlled by the developing bias potential. Reference numeral 6 denotes a transfer charger,
Reference numeral 7 denotes a separation charger, 8 denotes a cleaning device, 9 denotes a power supply for applying a developing bias potential, and 11 denotes a charge removing device.

Next, an image forming operation by the copying machine will be described. In FIG. 1, a photoconductor 1 uniformly charged by a scorotron charger 2 is exposed by an exposure light beam whose intensity is modulated by an image signal corresponding to a document.
An electrostatic latent image is formed, developed by the developing unit 4, and visualized. Then, the image visualized by the toner is transferred to a transfer sheet by a transfer charger 6, and the transfer sheet after the image transfer is separated from the photoconductor 1 by a separation charger 7. Then, the separated transfer paper is transferred to the transport device 1.
3 and is fixed by a fixing device (not shown) to obtain a copy image. Excess toner not transferred on the photoreceptor 1 from which the transfer paper has been removed is cleaned by the cleaning device 8, and thereafter, the photoreceptor 1 is discharged by the discharging device 11 to remove the excess charge.

Here, in the image forming apparatus according to the present invention,
The method is characterized by a method of applying a developing bias. Next, an embodiment will be described. First, a method of determining the color of the toner will be described. In the copying machine having the configuration shown in FIG. 1, color development is performed by replacing the developing unit 4. Each unit is provided with a shielding plate as shown in FIG. 2 for each color, and the shape of the shielding plate differs depending on the color. Therefore, the color detection device is turned on and off according to the shape of the shielding plate, and the color of the toner contained in the unit is determined based on the signal.
The determined color signal is sent from the color detection device 21 to the main control device 10 as shown in FIG. 3, and a signal corresponding to the color is sent from the signal generation circuit 22 of the main control device 10 to the developing bias potential application. , And a developing bias output corresponding to the color is output from the high-voltage power supply circuit 9.

Next, the applied voltage of the developing bias will be described. Here, as an example, the image portion of the photosensitive member 1 where the image is formed is negatively charged, and the image portion is exposed to the exposure light beam 3 to form an electrostatic latent image. A reversal developing method of developing with toner is used. In this embodiment, the charging potential is -800 V,
The potential of the exposed portion is set to be -100 V, and a toner having a negative polarity is used. In the image area, a voltage of -600 V is applied to the developing bias,
The toner adheres to the exposed portion, is developed, and is visualized. Further, when a non-image portion (a non-image region of the photoreceptor which is not charged in an area where image formation is not performed) enters the developing portion, a voltage higher than the potential of the photoreceptor 1 is applied to the developing bias, and The setting is made so that the toner does not adhere to the body.

By the way, as shown in FIG. 4, as a characteristic of the toner used in this embodiment, even if the toner has a negative characteristic, the developing potential is negative and the toner adheres to the photosensitive member. However, the development start voltage at which the toner starts to adhere depends on the toner. That is, in the example of FIG. 4, the development start voltage is about 0 V for the black toner, about -150 V for color 1 and about -100 V for color 2, and the development start voltage is particularly different between the black toner and the color toner. Color toner is more likely to adhere to non-image areas.

Therefore, in the present invention, the potential difference between the charging potential of the non-image portion of the photosensitive member and the developing bias potential of the non-image portion is made larger for the color toner than for the black toner.
The developing bias potential of the non-image portion where the toner is not to be adhered is changed in accordance with the type of the toner, with a potential opposite to the developing bias potential of the image portion with respect to the charging potential of the non-image portion of the photosensitive member. For example, FIG. 5 shows the charging potential and the developing bias potential of the image portion and the non-image portion of the photoconductor, and is an explanatory diagram of a method of setting the developing bias potential in the non-image portion. As for the charging potential, the portion of about -800 V is the charging potential of the image portion, the portions of about 0 V on both sides thereof are the charging potential of the non-image portion, and in the image portion, the developing bias potential is about -600 V as described above. However, in the non-image portion, the potential is opposite to the developing bias potential of the image portion with respect to the charging potential of the non-image portion of the photoreceptor. The potential is set according to the type of toner. 0 V is applied. In the case of color 1, 150 V is applied as bias 3 to make the developing potential of (0-150) V. In the case of color 2, 100 V of bias 2 is applied (0
When the developing potential was set to (-100) V, no toner adhesion occurred in the non-image area.

As described above, at the current development start voltage, it is found that the color toner is lower than the black toner, and the development bias potential of the non-image portion corresponding to the toner can be set depending on the type of toner. Was. That is, by setting the potential difference (developing potential) between the charging potential of the non-image portion of the photoconductor and the developing bias potential of the non-image portion so that the color toner is larger than the black toner, the development start voltage is reduced. Even in the case of a color toner which is low and easily adhered, it was possible to prevent the toner from adhering to the non-image area.

As described above, in the image forming apparatus of the present invention,
The high voltage power supply circuit 9 for applying the developing bias potential is controlled by the main controller 10 in accordance with the type of the toner detected by the color detecting device 21, and the developing bias of the non-image portion is set to a potential at which the toner does not adhere. As shown in FIG. 5, the potential difference between the charging potential of the non-image portion of the photoconductor and the developing bias potential of the non-image portion is more than the color toner (bias 2 or 3 applied) rather than the black toner (bias 1 applied).
And the developing bias potential of the non-image portion is opposite to the developing bias potential of the image portion with respect to the charging potential of the non-image portion of the photoconductor. The problem of adhesion can be solved.

The present invention can be carried out in a multicolor image forming apparatus in which at least two or more developing units are arranged around one photosensitive member, and the developer uses a carrier. Even if one component does not exist, the same can be applied to an image forming apparatus of a developing process in which a bias is applied to a developing sleeve to perform development.

[0020]

As described above, according to the first aspect of the present invention, in a reversal developing type image forming apparatus using a black toner and a color toner, the charging potential of the non-image portion of the photosensitive member and the non-image portion Since the potential difference between the developing toner and the developing bias potential of the color toner is larger than that of the black toner, it is possible to prevent the toner from adhering to the non-image area. Etc. can be reduced.

According to the second aspect of the present invention, in the first aspect,
In the image forming apparatus described above, since the developing bias potential of the non-image portion is opposite to the developing bias potential of the image portion with respect to the charging potential of the non-image portion, toner adhesion to the non-image portion can be reliably performed. Therefore, toner scattering and unnecessary toner consumption can be prevented, and the burden on the cleaning device and the like can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a copying machine showing an example of an image forming apparatus to which the present invention is applied.

FIG. 2 is a perspective view of a main part of a copying machine showing an example of a detecting unit for detecting a type of toner.

FIG. 3 is a block diagram illustrating a developing bias setting unit.

FIG. 4 is an explanatory diagram of toner adhesion characteristics depending on the type of toner.

FIG. 5 is a diagram illustrating a charging potential and a developing bias potential of an image portion and a non-image portion of a photoconductor, and is an explanatory diagram of a method of setting a developing bias potential in a non-image portion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoreceptor 2 Scorotron charger 3 Exposure light beam 4 Developing device 5 Developing sleeve 6 Transfer charger 7 Separation charger 8 Cleaning device 9 Power supply for developing bias voltage application 10 Control device 11 Static elimination device 12 Exposure light source 21 Color detection device

Claims (2)

[Claims] In a reversal developing type image forming apparatus using a black toner and a color toner, a potential difference between a charging potential of a non-image portion of a photosensitive member and a developing bias potential of a non-image portion is
An image forming apparatus wherein the color toner is larger than the black toner. 2. The image forming apparatus according to claim 1, wherein the developing bias potential of the non-image portion is opposite to the developing bias potential of the image portion with respect to the charging potential of the non-image portion. Image forming device.