JPH05142913A - Multicolor image forming device - Google Patents

Abstract

PURPOSE:To provide the multicolor image forming device which suppresses the nonuniformity of an electrifying potential and the splashing of toner images and can form high-grade multicolor images. CONSTITUTION:A destaticizing stage consisting of a pre-exposing lamp 8 is provided between a developing stage and an electrifying stage for image formation for the next color toner and a photosensitive drum 1 is uniformly electrified by a corona electrifier 2 again after the destaticization. The magenta, cyan and black toners are developed on the photosensitive drum 1 by the same procedure as before, by which multiclor toner images are formed. The destaticization down to >=1/4 the electrifying potential is necessary for the destaticization before the electrification and the destaticization down to <=3/4 the electrifying potential is executed in order to execute the uniform electrification.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention applies a uniform charge to an electrophotographic photosensitive member, performs image exposure based on an image signal of a specific color to form a latent image, and transfers the latent image to a toner of a specific color. The process of forming a toner image by performing development is repeated in a predetermined order for each of a plurality of preset colors to form a multicolor toner image on the photoconductor, and this is collectively printed on the transfer material. The present invention relates to an electrophotographic multicolor image forming apparatus for transferring a multicolor image.

[0002]

2. Description of the Related Art FIG. 7 shows an example of this type of multicolor image forming apparatus which has been actively researched and developed in recent years. In this example, the multicolor image forming apparatus includes a drum-shaped electrophotographic photosensitive member, that is, an image carrier 1 that is a photosensitive drum, and the photosensitive drum 1 is rotated in the arrow direction. The photosensitive drum 1 is uniformly charged by the charger 2, and then an image exposure based on an image signal of a specific color is applied by the exposure unit including the reader unit 10 and the semiconductor laser 6, and the photosensitive drum 1 is exposed.
A latent image is formed on it. This latent image is a developing device provided with color toner corresponding to the specific color, that is, a yellow developing device 3
1, a magenta developing unit 32, a cyan developing unit 33, or a black developing unit 34 develops a toner image.

Subsequently, the above-mentioned steps are repeated in a predetermined order for each of a plurality of preset colors to form a multicolor toner image on the photosensitive drum 1, and the multicolor toner image is formed on the transfer material P by a transfer charger. A batch transfer is performed by the action of 4, and a multicolor image is obtained by passing through a fixing device (not shown). After removing the residual toner with the cleaner 5, the photosensitive drum 1 is
It is subjected to the next image forming process.

[0004]

However, in the above-described multicolor image forming apparatus, as a first color image forming step, a pre-exposure step is provided before the charging step, and the pre-exposure, charging, image exposure, and development steps are performed. When the toner image of the first color is formed in various steps, and thereafter, the charging, image exposure, and development are performed as the steps of the second color to form the toner image of the second color as described above, FIG. As shown in (Conventional example), the unexposed portion on the photosensitive drum in the image formation of the first color is excessively charged at the time of charging the second color.
In the image formation after the color, the uniformity of charging was impaired and the latent image formation could not be normally performed.

In order to solve this non-uniform charging, the first
An apparatus using a method in which a step of applying uniform pre-exposure to sufficiently reduce the potential on the surface of the photoconductor is added between the color developing step and the second color charging step is also announced.

However, in an apparatus using this method, as shown in FIG. 4 (conventional example), when pre-exposure is performed,
There is a difference in the surface potential between the portion where the toner image is formed and the portion where the toner is absent, and due to the difference in the surface potential, the toner scatters in the non-image portion.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a multicolor image forming apparatus capable of forming a high quality multicolor image while suppressing nonuniformity of charging potential and toner image scattering.

[0008]

The above object can be achieved by a multicolor image forming apparatus according to the present invention. In summary, the present invention uniformly charges an electrophotographic photosensitive member, performs image exposure based on an image signal of a specific color to form a latent image, and develops the latent image with a specific color toner. A series of steps of forming a toner image by performing the above is repeated in a predetermined order for each of a plurality of preset colors to form a multicolor toner image on the photoconductor, and this is used as a transfer material. In an electrophotographic multicolor image forming apparatus that obtains a multicolor image by batch transfer, the surface potential of the photoreceptor is at least ¼ of the charging potential before charging between each color developing process and the next color charging process. A multicolor image forming apparatus characterized in that it has a pre-charging charge eliminating unit for eliminating charge. The pre-charging static eliminator is, for example, a pre-exposure lamp or a corona static eliminator. Further, it is preferable that the surface potential of the photoconductor after the charge removal before charging is set to 1/4 or more to 3/4 or less of the potential during charging.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A multicolor image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

FIG. 1 shows an embodiment of a multicolor image forming apparatus according to the present invention. The apparatus of this embodiment is the same as the conventional multicolor image forming apparatus described above with reference to FIG. Members having the same structure and function are designated by the same reference numerals, and the description thereof will be omitted. The apparatus of this embodiment is different from the conventional apparatus in that a pre-exposure lamp 8 and a surface electrometer 11 for checking the uniformity of charging are arranged around the photosensitive drum 1.

In this embodiment, the exposure amount of the pre-exposure lamp 8 is controlled by controlling and changing the voltage applied to the pre-exposure lamp by the control means 7.

The yellow, magenta, cyan, and black toners used in this embodiment were all polyester-based nonmagnetic toners having a volume average particle diameter of 12 μm.

Various experiments were conducted below using the multicolor image forming apparatus having the above-mentioned structure. Hereinafter, this experiment will be described.

A color original is color-separated into yellow, magenta, cyan, and black components by an exposure unit including a reader unit 10 and a semiconductor laser 6, that is, a scanner unit, and the image signal is as shown in FIG. The image is output to the multicolor image forming apparatus configured, that is, the printer unit. This document scan is repeated four times for each color.

In the printer unit, the photosensitive drum 1 is uniformly charged by the corona charger 2 until the surface potential of the photosensitive member reaches 600 V, and image exposure is performed based on the yellow component image signal input from the scanner unit. To form a latent image, and the latent image is developed by the yellow toner of the developing device 31.

Between the developing process and the charging process for image formation for the next color toner, a charge eliminating process including the pre-exposure lamp 8 is provided, and after the charge eliminating, the corona charger 2 again charges the photosensitive drum uniformly. Then, in the same procedure as above, magenta, cyan, and black toners are developed on the photosensitive drum 1 to form a multicolor toner image. The potential on the photosensitive drum 1 immediately after charging according to the present invention is shown in FIG. 3 (the present invention). Further, according to the present invention, the scattering of the toner image is prevented, which state is shown in FIG. 4 (the present invention).

The multicolor toner image thus formed was transferred onto a transfer material all at once, and the fixing unit melted and fixed the toner to form a multicolor image.

Incidentally, the developing devices 31 to 34 used in this embodiment.
Is a so-called non-contact developing method in which a developer layer is formed on the developing sleeve to have a layer thickness that does not contact the photosensitive drum 1, and toner is ejected from the developer layer to adhere to the electrostatic image. It was Also, the advantage of this non-contact developing device is that
It is easy to switch the non-operation, and it is difficult to damage the previously formed toner image.

Table 1 shows that in the pre-charging static elimination performed between each color developing step and the next color charging step, the light amount of the pre-exposure lamp 8 is adjusted to reduce the photoreceptor surface potential after the static elimination to 0.
This is an evaluation of the scattering and the charging uniformity when changing from V to 600V.

[0020]

[Table 1]

Here, the pattern used for the evaluation of scattering is shown in FIG. 2A, the amount of toner in the toner adhering portion is 1 mg / cm ^2, and the distance between the toner adhering portion and the toner adhering portion is 1 mm. The amount of splattering was evaluated subjectively in the toner non-adhesion part of No.

The pattern used for the evaluation of the charging uniformity is shown in FIG. 2 (B), and the toner amount in the toner adhering portion is also set to 1 mg / cm ² in the rotational direction of the photosensitive drum. A pattern in which toner adhered portions and non-adhered portions are repeated every 10 cm is developed on the photosensitive drum 1, and the deviation amount between the peaks of the potential at the time of charging when the photosensitive drum 1 is charged to 600 V is measured using the surface electrometer 11. The charging uniformity was evaluated by the measurement.

As a result, as shown in Table 1, when the charging potential is 600 V, the toner scattering used in this embodiment is remarkable when the surface potential of the photoconductor after static elimination is 150 V or less. It was From this, it is necessary to set the surface potential after static elimination to 150 V or more. Regarding the uniformity of charging, it may be better to remove the charge even if it is a little.
It has been found that the charge uniformity is considerably improved by removing the charge to 450 V or less.

Further, the charging potential is 400V, 500V, 7
When the same evaluation was performed for the cases of 00V and 800V, in order to prevent scattering, it is necessary to eliminate the charge up to ¼ or more of the charge potential in the charge removal before charging.
Further, it has been found that it is desirable to eliminate the charge up to 3/4 or less of the charge potential in order to perform uniform charge.

Further, since the toner used in this embodiment has a toner charge amount of about 15 μc / g on the photosensitive drum 1 immediately after recharging after development, it is a toner having a relatively low charge amount. Even with other toners, however, scattering does not occur due to static elimination of 1/4 or more of the charging potential. However, the toner charge amount after recharging is 10
In the case of using an extremely low tribo toner of μc / g or less, it is necessary to remove the charge to 1/2 or more of the charging potential.

FIG. 5 shows another embodiment of the multicolor image forming apparatus of the present invention. In this embodiment, the pre-charging static elimination step is performed by the AC corona static eliminator 9 instead of the pre-exposure lamp and the control means 7 that changes the voltage applied to the AC corona static eliminator.

The toner used in this embodiment is a polyester-based non-magnetic toner of yellow, magenta, cyan and black having a particle diameter of 12 μm.

Also in this example, when the charging potential was 600 V, static elimination of 150 V or more was performed before charging in the same manner as in Example 1, and scattering and good uniformity of charging were obtained. If the uniformity of charging is emphasized, 4
Better results were obtained by removing the charge up to 50 V or less.

From the above, as in the first embodiment, also in this embodiment in which the AC corona charge eliminator is used as the pre-charging static eliminator, static eliminator of ¼ or more of the charging potential is performed before the charging step. As a result, it is possible to uniformly charge the toner in each color process without causing the toner image to scatter. Also, in order to perform uniform charging, 3/4 of the charging potential
It is desirable to eliminate static electricity up to the following.

Further, a similar effect can be obtained by using a DC corona charge eliminator instead of the AC corona charge eliminator as the pre-charging charge eliminator 9.

FIG. 6 shows a two-color image forming apparatus which is another embodiment of the present invention.

In the two-color image forming apparatus of this embodiment, a black toner image and a red toner image are formed while the photosensitive drum 1 makes one rotation, and they are collectively transferred to the transfer material P to form a two-color image. It is a thing.

More specifically, the pre-exposure lamp 8 and the corona charger 2 are provided around the photosensitive drum 1 which rotates in the direction of the arrow.
(2 ₁ , 2 ₂ ), black developing device 34, red developing device 3
5, an exposure unit including a transfer unit 4, a cleaner 5, a reader unit 10, and a semiconductor laser 6 (6 ₁ , 6 ₂ ), and an AC corona discharger 9 are arranged. The electric potential of the photosensitive drum 1 after the charge removal was performed by changing the voltage applied to the AC corona charge remover 9 by the control means 7.

The toner used in this embodiment is a polyester-based non-magnetic black and red toner having a particle diameter of 12 μm.

[0035] In this embodiment, the semiconductor laser 6 is 2 groups 6 _1, 6 ₂ are disposed in correspondence with respective colors of black and a red, while the photosensitive drum 1 is rotated 1, pre-exposure (pre-exposure Lamp 8), charging (corona charger 2 ₁ ), black image exposure (semiconductor laser 6 ₁ ), black development (black developing device 34), and subsequently, pre-charge neutralization (corona neutralizer 9), charging (corona charging) 2 ₂ ), red image exposure (semiconductor laser 6 ₂ ), red development (red developing device 3
5), and batch transfer (transfer charger 4) and cleaning (cleaner 5) are performed.

In this embodiment, the AC corona charge eliminator 9 is used as the pre-charge charge eliminator after black development.
Considering the influence of light quantity leakage on the development area and charging area,
Although the pre-exposure lamp was not used, it is also possible to use the pre-exposure lamp instead of the AC corona charge eliminator 9 if the light is sufficiently shielded.

The scattering and charging uniformity in this example were evaluated in the same manner as in Example 1. The evaluation result was that the charging potential was 60 as in Example 1.
In the case of 0 V, when static elimination of 150 V or more was performed before charging, scatter and good uniformity of charging were obtained. Further, when the uniformity of charging was emphasized, better results were obtained by removing the charge up to 450 V or less.

From the above, even when a two-color image is formed during one rotation of the photosensitive drum as in the present embodiment as in the first embodiment, the charging potential is changed before the second color charging process. By eliminating the electric charge by 1/4 or more, it is possible to uniformly charge the toner images in each color process without causing scattering of the toner image. Further, in order to carry out uniform charging, it is desirable to eliminate the charge up to 3/4 or less of the charging potential.

In the multicolor image forming apparatus of the present invention, the photosensitive drum 1 is controlled by controlling the pre-charge elimination as described above.
Since the upper potential becomes significantly smaller than the conventional difference between the portion with the toner image and the portion without the toner image, the photosensitive drum 1
The scattering of the above toner is almost suppressed (FIG. 4), and since the charge is removed before charging, uniform charging can be performed.

The multicolor image forming apparatus of the present invention is not limited to the image forming apparatus described in each of the above-described embodiments, and forms a toner image of two or more colors on the image carrier to form a multicolor image. Can be suitably embodied in an electrophotographic copying machine, a printer, or the like.

[0041]

As described above, in the multicolor image forming apparatus according to the present invention, precharge elimination of ¼ or more of the potential at the time of charging is performed between the developing process of each color and the charging process of the next color. Due to the constitution, the toner adhering portion and the toner non-adhering portion can be uniformly charged, and further, the scattering of the toner image at the time of charge removal can be remarkably reduced, so that a high-quality multicolor image can be obtained. Can be formed.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a pattern for evaluating scattering of a toner image and a pattern for evaluating charging properties.

FIG. 3 is a diagram showing a surface potential of an image carrier immediately after being charged.

FIG. 4 is a diagram illustrating the scattering of toner images.

FIG. 5 is a schematic configuration diagram of another embodiment of the multicolor image forming apparatus according to the present invention.

FIG. 6 is a schematic configuration diagram of another embodiment of the multicolor image forming apparatus according to the present invention.

FIG. 7 is a schematic configuration diagram of a conventional multicolor image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier (photosensitive drum) 2 Charging device 4 Transfer charging device 8 Pre-exposure lamp 9 Pre-charging static eliminator 31-34 Developing device

Claims (3)

[Claims] 1. A uniform charge is applied to an electrophotographic photosensitive member, image exposure is performed based on an image signal of a specific color to form a latent image, and the latent image is developed with toner of a specific color. A series of steps of forming a toner image by
An electrophotographic multicolor system in which a multicolor toner image is repeatedly formed on a photoconductor by repeating the process in a predetermined order for each of a plurality of preset colors, and the multicolor image is obtained by collectively transferring the toner images onto a transfer material. The image forming apparatus is provided with a pre-charging static eliminator for pre-charging static erasing to reduce the surface potential of the photoconductor to at least ¼ of the charging potential between each color developing process and the next color charging process. Image forming apparatus. 2. The multicolor image forming apparatus according to claim 1, wherein the pre-charging static eliminating means is a pre-exposure lamp or a corona static eliminator. 3. The surface potential of the photoconductor after the static elimination before charging is
The multicolor image forming apparatus according to claim 1, wherein the charging potential is 1/4 or more and 3/4 or less.