JPH0355968Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an image forming apparatus using electrophotography.

[Prior art and its problems]

As the amount of information increases, computers are processing this information in large quantities and at high speed. In conjunction with this, there is a need to output the results of processing performed by the computer in print form at high speed. Therefore, electrophotography, electrostatic recording, and the like are widely used as image forming apparatuses that can perform high-speed, large-volume printing. Furthermore, there is a demand for an image forming apparatus that can output two-color images, such as black characters and red underlines, at high speed.

FIG. 2 shows the surface potential of a photoreceptor at each step in a conventional image forming apparatus using electrophotography.

To explain a conventional image forming apparatus, first, the surface of a photoreceptor is uniformly charged to a positive polarity (FIG. 2a).
Next, positive exposure corresponding to the first image information is performed from the photosensitive layer side of the photoreceptor using a laser beam, an LED array, a liquid crystal shutter array, or the like, to form a first electrostatic latent image (FIG. 2(b)). Next, regular development was performed using the magnetic brush development method (development bias V ₀₁ ).
A first color toner, for example, black toner BT, is deposited to form a black toner image (c in the same figure). Next, the surface of the photoreceptor is charged again to positive polarity using a scorotron charger connected to a positive DC power source (d in the figure). Next, positive exposure corresponding to the second image information is performed from the photosensitive layer side of the photoreceptor to form a second electrostatic latent image (see e in the figure). Next, regular development was performed using the magnetic brush development method (development bias V ₀₂ ).
A second color toner, for example, a red toner RT, is attached to form a two-color toner image on the photoreceptor (FIG. 3(f)).

However, as shown in FIG. 2e, when the first color toner image is formed on the photoreceptor, it is recharged and the second exposure is performed, the first color toner image already formed on the photoreceptor is removed. The image blocks the second exposure. In other words, the potential of the first color toner image portion is not sufficiently optically attenuated before the second development is performed. As a result, as shown in FIG. 5F, the second color toner also adheres to the first color toner image, resulting in color mixture. In order to prevent this, if the second developing bias V ₀₂ is made higher than the potential of the first color toner image area, the difference between the second developing bias potential and the potential of the second electrostatic latent image area becomes smaller, and A disadvantage arises in that the density of the second color toner image does not increase.
Therefore, in any case, a clear two-color image cannot be obtained.

[Purpose of invention]

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks of the conventional image forming apparatus, an object of the present invention is to provide an image forming apparatus capable of producing clear images with sufficiently high density and without color mixture.

[Key points of the idea]

In order to achieve the above object, the present invention includes a photoconductor having a photoconductive layer on a transparent and conductive base, a charging means for first charging the photoconductor to a predetermined polarity, and a first charging device. an exposure means for forming a first electrostatic latent image by performing positive exposure on the subsequent photoreceptor corresponding to first image information; and forming a first image by regularly developing the first electrostatic latent image. a first developing means for applying a second charge of the same polarity as the first charge to the photoconductor while carrying the first image; 2 Starting from the base side of the photoreceptor after charging, the second
It is characterized by comprising an exposure means for forming an electrostatic latent image, and a second developing means for properly developing the second electrostatic latent image to form a second image.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing an example of the image forming apparatus of the present invention, FIG. 3 is an enlarged view of the main parts in FIG. 1, and FIG.
The figure shows the surface potential of the photoreceptor at each step in an embodiment of the image forming apparatus of the present invention.

1 and 3, a photoreceptor 1 has a transparent support layer 1c such as a polyethylene terephthalate film, a transparent conductive layer 1b, a photoconductive layer 1a, and a photoconductive layer 1a.
It is constructed in the form of an endless (or endless) belt formed by sequentially laminating the following layers, is stretched between rollers 12a, 12b, and 12c, and is driven in the direction of the arrow shown in the figure.

The photoreceptor 1 is first uniformly charged to a predetermined polarity, for example, positive polarity by the first corona charger 2 (the fourth
Diagram a). Next, the liquid crystal shutter head 4 performs positive exposure corresponding to the first image information to form a first electrostatic latent image (FIG. 4b). Here, as shown in FIG.
b, a fluorescent lamp 4c, and a shield portion 4d, and the liquid crystal shutter 4b is controlled to open and close based on a signal corresponding to the first image information. Light is irradiated from the transparent support layer 1c side of the photoreceptor 1 by the liquid crystal shutter head 4, and the photoreceptor 1 is exposed to the transparent support layer 1c and the transparent conductive layer 1 in this order from the light irradiation side as described above.
b. Since it is composed of the photoconductive layer 1a, the irradiated light reaches the photoconductive layer 1a, and the potential of the exposed area on the photoconductive layer 1a is sufficiently optically attenuated.

The first electrostatic latent image thus formed on the photoreceptor 1 is regularly developed in a magnetic brush type first developing device 5, and a first color toner, for example, black toner, is used to develop the first electrostatic latent image.
BT adheres to the unexposed areas, forming a black first image (FIG. 4c). Here, the bias voltage for the first development is a voltage V ₁ such that toner does not adhere to exposed areas and toner sufficiently adheres to non-exposed areas.
is set to .

Next, the photoreceptor 1 enters the second rotation, and the second corona charger 3 charges the photoreceptor 1 to positive polarity again. Here, the second corona charger 3 is a scorotron charger in which a positive polarity DC power source is connected to the grid, and the unevenness of the potential before charging is smoothed out so that both toner-attached and non-adherent areas are uniform. potential (Fig. 4d). Note that the second charging potential setting needs to be lower than the first charging potential setting. This eliminates the need to convert the polarity of the black toner BT, and therefore eliminates the need to perform polarity adjustment before the batch transfer after the red toner RT is formed.

Next, the liquid crystal shutter head 4 performs positive exposure corresponding to the second image information at the same timing as the first image forming position, thereby forming a second electrostatic latent image (FIG. 4e). At this time, since light irradiation corresponding to the second image information (positive exposure) is performed from the transparent support layer 1c side of the photoreceptor 1, the exposed area is sufficiently exposed without being affected by the already formed toner image. The light is attenuated.

The second electrostatic latent image formed on the photoreceptor 1 in this manner is normally developed in a magnetic brush type second developer 6, and a second color toner, for example, a red toner, is applied to the second electrostatic latent image.
RT adheres to the non-exposed areas to form a red second image (FIG. 4f). Since the developer contains a carrier made by mixing and dispersing magnetic fine powder in a resin, the ears of the magnetic brush are extremely soft. Further, the bias for the second development is set to a potential V ₂ to the extent that toner does not adhere to areas other than the second electrostatic latent image area.
is set to . Therefore, the toner in the toner-adhering area of the first color that has already been formed will not be mixed into the second developing device 6, and the carrier having the opposite polarity to the toner in the second developing device 6 will not be mixed into the photoreceptor. It will not stick to the first side.

In this way, a second color red image is formed, and finally a red and black two-color toner image is formed on the photoreceptor 1.

This two-color toner image is transferred all at once onto the transfer paper fed from the cassette 7 by the transfer charger 8, and then the transfer paper is separated from the photoreceptor 1 by the separation charger 9, and transferred to the fixing device. 1
1, a final two-color image is obtained.

Incidentally, during the first rotation of the photoconductor 1, the cleaner 10, which had been retracted from the surface of the photoconductor 1, is removed from the 2nd rotation of the photoconductor 1.
During the rotation, the portion of the transfer paper 7 that has been transferred is pressed against the surface of the photoreceptor 1 before reaching the cleaning position.
Residual toner on the photoreceptor 1 is removed. Further, the residual charge on the photoreceptor 1 is erased by the charge eliminating lamp 13, and the photoreceptor 1 is prepared for the next image formation.

Further, the liquid crystal shutter head 4 is located inside the photoconductor 1 which is configured in a belt shape, and a shield portion 4d is formed at the tip thereof, so that the tip of the liquid crystal shutter head 4 and the photoconductor 1 are closely opposed to each other. Since the exposure area is completely shielded from the surroundings, the liquid crystal shutter head 4 is not contaminated at all, and a stable amount of light is maintained over a long period of time.

According to the configuration shown in FIG. 1, by using one liquid crystal shutter head and rotating the photoreceptor 1 twice, two
Although a color image was formed, it is also possible to similarly form a two-color image by rotating the photoreceptor once using two liquid crystal shutter heads.

In this embodiment, the case of forming a two-color image has been described above, but by repeating the process of recharging, positive exposure, and regular development as many times as necessary, it is possible to form a multicolor image of three or more colors.

[Effect of idea]

As described above in detail, according to the image forming apparatus of the present invention, a sufficiently high image density can be obtained and color mixture does not occur, so that a clear image can be formed.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing an example of the image forming apparatus of the present invention, Figure 2 is a diagram showing the surface potential of the photoreceptor at each step in a conventional image forming apparatus, and Figure 3 is an enlarged view of the main part of Figure 1. 4 are diagrams showing the surface potential of the photoreceptor at each step in an embodiment of the image forming apparatus of the present invention. DESCRIPTION OF SYMBOLS 1... Photoreceptor, 2... First corona charger, 3... Second corona charger, 4... Liquid crystal shutter head, 5... First developing device, 6... Second
Developing device, 10... Cleaner, 11... Fixing device, 1
3... Static elimination lamp.

Claims (1)

[Claims for Utility Model Registration] (1) A photoconductor having a photoconductive layer on a transparent and conductive base, a charging means for first charging the photoconductor to a predetermined polarity, and a first charging device. an exposure means for forming a first electrostatic latent image by performing positive exposure on the subsequent photoreceptor corresponding to first image information;
a first developing unit that regularly develops the first electrostatic latent image to form a first image; and a second charging unit that charges the photoreceptor carrying the first image with the same polarity as the first charging unit. a charging device for forming a second electrostatic latent image by performing positive exposure corresponding to second image information from the base side of the photoreceptor after the second charging; and a second developing means for properly developing the image to form a second image. (2) A developer used in the first developing means and a developer used in the second developing means.
Utility model registration claim No. 1 characterized in that the developer used in the developing means has a different color from each other.
The image forming apparatus described in (1).