JP3261063B2 - Image forming device - Google Patents

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 color images has increased, and various types of electrophotographic images have been used, such as a multi-color copying machine for copying a single color image and a full-color copying machine capable of 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]

In order to achieve the above object, the present invention provides an image forming apparatus of a reversal development type using a black toner and a color toner, wherein an image is formed on a photoconductor at the time of image formation. Image formation is performed in an image forming apparatus having a non-image area (hereinafter, referred to as a non-image area) in which an area is not formed and charging by a charging unit is not performed.
Non-image area where charging is not performed by charging means
When the portion enters the developing portion, the potential difference between the potential of the non-image portion of the uncharged photoconductor and the developing bias potential of the non-image portion is substantially equal to or greater than the toner development start voltage. When a development bias is applied to the color toner and the development start voltage is lower for the color toner than for the black toner, the potential difference between the potential of the photosensitive member when using the color toner and the development bias potential is different when the black toner is used. The developing bias is set so as to be larger than the potential difference between the potential of the photosensitive member and the developing bias potential.

Further, in the image forming apparatus, the developing bias potential of the non-image area, and a development bias potential and opposite potential of the image portion potential of the non-image portion of the photoreceptor as a boundary toner
It is characterized in that it is changed according to the type of key (claim 2).

In the above-described image forming apparatus, the image
An area where formation is not performed and charging is performed by charging means.
When a non-image portion that does not enter the developing portion, the potential difference between the non-image portion potential of the uncharged photoconductor and the developing bias potential of the non-image portion is substantially equal to or lower than the toner development start voltage. When the development start voltage is lower for the color toner than for the black toner, the potential difference between the potential of the photoreceptor when using the color toner and the development bias By setting the developing bias to be larger than the potential difference between the photoconductor potential and the developing bias potential when using
The developing bias of the non-image portion is set according to the black toner and the color toner having different development start voltages, so that toner adhesion to the non-image portion can be prevented, and toner scattering and unnecessary toner consumption can be prevented.

Further, in the image forming apparatus, the developing bias potential of the non-image area, and a development bias potential and opposite potential of the image portion potential of the non-image portion of the photoreceptor as a boundary toner
By changing the type according to the type of toner, it is possible to reliably prevent toner from adhering to the non-image area, and to prevent toner scattering and unnecessary toner consumption.

[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.
Then, the determined color signal is sent from the color detection device 21 to the main control device 10 as shown in FIG. , 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. When a non-image portion (a non-image region of the photoconductor which is not charged in a region where image formation is not performed) enters the developing portion, a voltage higher than the potential of the photoconductor 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 development is performed such that the potential difference between the potential of the non-image portion of the uncharged photosensitive member and the developing bias potential of the non-image portion becomes substantially equal to or larger than the development start voltage of the toner. When a bias is applied and the development start voltage is lower for the color toner than for the black toner, the potential difference between the potential of the photoconductor when using the color toner and the development bias potential is equal to the photosensitive potential when using the black toner. The developing bias is set so as to be larger than the potential difference between the body potential and the developing bias potential, and the developing bias potential of the non-image portion where toner is not to be adhered is set to the potential of the non-image portion of the photoconductor. The potential is opposite to the developing bias potential of the image portion and is changed according to the type of toner. For example, FIG. 5 shows the charged potential of the image portion of the photoconductor, the potential of the non-image portion, and the developing bias potential. FIG. 5 is an explanatory diagram of a method of setting the developing bias potential in the non-image portion. Regarding the body 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 potential of the non-image portion, and the developing bias potential of the image portion 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 potential of the non-image portion of the photoreceptor. The potential is set according to the type of toner. Is applied, in the case of color 1, 150 V is applied as bias 3 to make the developing potential of (0-150) V, and in the case of color 2, bias 1 is applied.
When a developing potential of (0-100) V was applied by applying 00 V, toner adhesion did not occur 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, the potential difference (developing potential) between the potential of the photosensitive member and the developing bias potential when using color toner is larger than the potential difference (developing potential) between the potential of the photosensitive member and the developing bias potential when using black toner. By setting the developing bias to be large, it was possible to prevent the toner from adhering to the non-image area even in the case of a color toner having a low development start voltage and easily adhering.

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 potential of the photoconductor when using color toner and the developing bias potential (bias 2 or 3 applied) is the potential of the photoconductor and developing bias potential when using black toner. (The bias 1 is applied), and the developing bias is set so as to be larger than the potential difference between the developing bias potential of the non-image area and the developing bias potential of the image area. With the potential (plus potential) opposite to (minus potential), the problem of toner adhesion to the non-image portion 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, there is provided an image forming apparatus of a reversal developing type using a black toner and a color toner, wherein an image forming apparatus is provided on a photosensitive member at the time of image forming. In an image forming apparatus having a non-image area (hereinafter, referred to as a non-image area) in which charging is not performed by a charging unit and where image formation is not performed,
The non-image area which is not charged by the charging means
When entering the image area, the developing is performed so that the potential difference between the non-image area potential of the uncharged photoconductor and the developing bias potential of the non-image area becomes substantially equal to or larger than the toner development start voltage. When a bias is applied and the development start voltage is lower for the color toner than for the black toner, the potential difference between the potential of the photoconductor when using the color toner and the development bias potential is equal to the photosensitive potential when using the black toner. By setting the developing bias so as to be larger than the potential difference between the body potential and the developing bias potential, it is possible to prevent the toner from adhering to the non-image area, so that it is possible to prevent toner scattering and unnecessary toner consumption, The burden on the cleaning device and the like can be reduced.

According to the second aspect of the present invention, in the first aspect,
In the image forming apparatus described above, the developing bias potential of the non-image portion is set to a potential opposite to the developing bias potential of the image portion with respect to the potential of the non-image portion of the photoconductor , and according to the type of toner.
By changing this, it is possible to reliably prevent toner from adhering to the non-image portion, so that 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

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Claims (2)

(57) [Claims] An image forming apparatus of a reversal development type using a black toner and a color toner, wherein an area on which an image is not formed on a photosensitive member at the time of image formation is charged by a charging means. Non-image area (hereinafter referred to as non-image area)
In the image forming apparatus having the charging by and charging means an area where the image formation is not performed
When a non-image portion that is not performed enters the developing portion, the potential difference between the non-image portion potential of the uncharged photoconductor and the developing bias potential of the non-image portion is substantially the same as the toner development start voltage. When the development start voltage is lower than that of the black toner and the development start voltage is higher than that of the black toner, the potential difference between the potential of the photoconductor when the color toner is used and the development bias potential is black. An image forming apparatus, wherein a developing bias is set so as to be larger than a potential difference between a potential of a photoconductor and a developing bias potential when toner is used. 2. An image forming apparatus according to claim 1, and the developing bias potential of the non-image portion, a developing bias potential opposite of the potential of the image portion potential of the non-image portion of the photosensitive member as a boundary
An image forming apparatus characterized by changing according to the type of toner .