JPH0570818B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a printer using electrophotographic technology.

[Prior art]

BACKGROUND ART Today, as the amount of information increases, computers are used to process a large amount of information at high speed. In conjunction with this, it becomes necessary to output the results processed by the computer in a print format at high speed according to the output speed. Therefore, image forming apparatuses that utilize electrophotography or electrostatic recording methods, which can perform high-speed, large-volume printing, are widely used.

Furthermore, as the amount of information becomes more diverse, there is a demand for a two-color image forming apparatus that can output two-color images, such as black characters and red underlines, at high speed.

FIG. 3 shows the potential state of the surface of a photoreceptor in each image forming process in a conventional image forming apparatus using an electrophotographic method. First, the photoreceptor is uniformly positively charged (FIG. 3a). Next, negative exposure L ₁ corresponding to the first image information is performed from the photosensitive layer side of the photoreceptor, which is formed by laminating a photosensitive layer on an opaque and conductive support, and the potential of the exposed area is attenuated by light. , forming a first electrostatic latent image (FIG. 3b). Then, reverse development is performed using a magnetic brush developer.
A first color image (for example, a black toner BT image) is formed on the photoreceptor (FIG. 3c).

Furthermore, the photoreceptor is charged to positive polarity again using a scorotron charger connected to a positive DC power source (Fig. 3 d), and then negative exposure L corresponding to the second image information is performed. _{Step 2} is performed again from the photosensitive layer side to optically attenuate the potential of the exposed area (Fig. 3e).

Then, reversal development is performed using a magnetic brush development method to form a second color image (for example, a red toner RT image) on the photoreceptor (FIG. 3f).

As a result, a two-color toner image is formed on the photoreceptor, and the toner image is transferred to transfer paper and fixed by a fixing device.

[Problems with conventional technology]

In conventional image forming apparatuses such as those described above, especially when a liquid crystal light shutter array is used, the light directed from the light source to the photoreceptor is digitally controlled by opening and closing the shutter, but originally, when the shutter is closed, the light source is Although it is necessary to block the light from the inside, the blockage cannot be achieved sufficiently, and some light leaks (L ₀ ).

As a result, when performing the second exposure, the non-exposed areas are also exposed to light when the shutter is closed, and while the potential of the first toner area hardly decreases, the potential of the non-adherent areas decreases. Therefore, there is a drawback that during the second development, the potential difference with the first toner adhering portion increases, and the first toner mixes into the second developing device due to the action of the electric field.

Furthermore, since the exposure section is installed close to the photoreceptor, scattered toner from each developing device or the like adheres electrostatically or physically to the exposure section, causing a decrease in the amount of light.

[Purpose of the invention]

In view of the above-mentioned conventional drawbacks, the present invention makes the amount of potential drop in the non-image area uniform when performing negative exposure corresponding to the second image information, regardless of whether the first toner is attached or not. , the first during the second development
This prevents toner from entering the second developing device to obtain a good two-color image, and also prevents the toner on the photoreceptor,
An object of the present invention is to provide an image forming apparatus that can prevent scattered toner generated from a developing device or the like from adhering to an exposure section and causing uneven exposure or a decrease in light amount.

[Key points of the invention]

According to the present invention, the above object includes a step of first charging a photoreceptor having a photoconductive layer on a transparent and conductive base to a predetermined polarity; a step of performing negative exposure corresponding to the first image information to form a first electrostatic latent image; a first developing step of reversing developing the first electrostatic latent image to form a first developed image; A second charge of the same polarity as the first charge is applied to the photoreceptor that still carries the first developed image.
a step of charging, a step of performing negative exposure corresponding to second image information from the base side of the photoconductor after the second charging to form a second electrostatic latent image, and a step of forming a second electrostatic latent image. This is achieved by providing an image forming apparatus characterized in that a second developing step of performing reversal development to form a second developed image is sequentially performed.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus of the present invention, and FIG. 2 is an enlarged sectional view of a main part of a liquid crystal optical shutter head. In FIG. 1, the recording apparatus includes a first corona charger 2, a second corona charger 3, a first developer 5, a second developer 6, which are arranged in order on the outer peripheral surface of a transparent photoreceptor 1. Transfer charger 8, separation charger 9,
A cleaner 10, a static elimination lamp 13, and a liquid crystal light shutter head 4 disposed inside the photoreceptor 1.
It is composed of etc.

The photoreceptor 1 has a photoconductive layer 1a made of selenium or the like, a transparent conductive layer 1b made of a metal oxide film (SnO ₂ , In ₂ O ₃ , etc.), and a transparent support layer 1c made of a film such as polyethylene terephthalate. It is constructed by laminating layers and has an endless belt shape or an end belt shape. The photoreceptor 1 has rollers 12a, 1
2b and 12c and conveyed in the direction of the arrow.

The liquid crystal light shutter head 4 is composed of an SLA (self-occurring [trade name] lens array) 4a, a liquid crystal light shutter 4b, and a fluorescent lamp 4c, and is arranged with the SLA 4a side facing the transparent support layer 1c of the photoreceptor 1. has been done.

The image forming process of the image forming apparatus configured as above will be described. FIG. 4 is a diagram showing changes in photoreceptor surface potential in the image forming apparatus of the present invention. In this embodiment, the entire process shown in FIG. 4 is performed by rotating the photoreceptor 1 twice. During the first rotation, the photoreceptor 1 is first charged to +800V by the first corona charger 2 (FIG. 4a). Next, the first
A first electrostatic latent image is formed by performing negative exposure _L1 corresponding to the image information (FIG. 4b). Here, a liquid crystal optical shutter head 4 is used as a means for negative exposure _L1 , and light is irradiated from the transparent support layer 1c side of the photoreceptor 1. As mentioned above, the photoreceptor 1 includes the transparent support layer 1c, the transparent conductive layer 1b, and the photoconductive layer 1.
a, the potential on the photoconductive layer 1a can be sufficiently optically attenuated. In this way, the potential of the exposed area is optically attenuated to +100V.

On the other hand, the non-exposed area is irradiated with light L ₀ due to the incomplete light blocking of the liquid crystal light shutter head 4, and the light is attenuated to drop to +500V.

Next, the first electrostatic latent image is reversely developed in a magnetic brush type first developer 5 containing a developer formed by mixing a carrier and a positively chargeable black toner BT to form a first image. . Note that the first developing device 5 has +
A bias V ₁ of 400V is applied, and the exposed area (+
Black toner BT adheres to the area (100V), and no toner adheres to the non-exposed area (+500V). In this way, the first color black image is formed (the fourth color
Figure c).

In the next second rotation, the photoreceptor 1 is charged again to a positive polarity using the second corona charger 3, which is a scorotron charger with a positive polarity DC power supply (+900V) connected to the grid. As a result, the unevenness of the potential is smoothed out, and the voltage becomes +800V uniformly in both the toner-adhered and non-adhered parts (Fig. 4d).

Next, negative exposure _L2 based on a signal corresponding to the second image information is first performed at a timing consistent with the first image forming position. In this case as well, light irradiation corresponding to the second image information is performed from the inside of the photoreceptor 1, so the exposed area is sufficiently attenuated and the voltage drops to +100V, and the toner-attached area and the non-toner area are exposed in the unexposed area. Regardless of the attached part, the light L ₀ due to insufficient light shielding of the liquid crystal light shutter causes the light to attenuate uniformly up to +500V, forming a second electrostatic latent image (Fig. 4e). Next, the second electrostatic latent image is reversely developed in a magnetic brush type second developer 6 containing a developer formed by mixing a carrier and a positively chargeable red toner RT.
If a carrier made of a resin mixed with magnetic powder is used, the magnetic brush ears will be extremely soft. Furthermore, since a bias V ₂ of +400V is applied to the second developing device, positively charged red toner RT adheres to the exposed area (+100V), but no toner adheres to the non-exposed area (+500V). Since the electric field formed between the potential of the toner adhesion part (+500V) and the developing bias V ₂ (+400V) is also weak, the black toner BT adhering to the photoreceptor 1 is mixed into the second developing device 6 side. No force works. Furthermore, carriers having a polarity opposite to that of the toner in the second developing device 6 do not adhere to the photoreceptor 1 side.

In this way, a second color red image is formed, and as a result, a two-color image of red and black is formed on the photoreceptor 1 (FIG. 4f).

Next, the two-color image is transferred to a transfer paper 7 by a transfer charger 8, separated from the photoreceptor by a separation charger 9, and then fixed by a fixing device 11.

The cleaner 10 is retracted from the surface of the photoreceptor 1 during the first rotation of the photoreceptor 1, but during the second rotation, after the transfer paper 7 has been separated, the cleaner 10 is brought into pressure contact with the surface of the photoreceptor 1.
The residual toner on the photoreceptor 1 is removed, and the residual potential on the photoreceptor 1 is further removed by the neutralization lamp 13 in preparation for the next image forming cycle.

On the other hand, since the liquid crystal light shutter head 4 is disposed inside the photoreceptor 1, when the image forming cycle is repeated, the liquid crystal light shutter head 4 will not become dirty at all even if toner is scattered from a developing device or a cleaner. . Therefore, it is possible to maintain a stable amount of light for a long period of time.

The above explanation is based on the case where a two-color image is obtained by two rotations of the photoreceptor using one liquid crystal light shutter head according to the configuration example shown in FIG. It is also possible to obtain two-color images.

In addition, in this embodiment, an example using only two colors has been explained, but the necessary number of developing devices other than red and black can be prepared, and each process of charging, negative exposure, and reversal development can be repeated as many times as necessary. If it is a repeating configuration, 3
It is clear that it is possible to construct a multicolor image forming apparatus with more than one color.

Furthermore, although the present invention has been described using a belt-shaped photoreceptor, the invention is not limited thereto, and similar effects can be obtained even with a drum-shaped photoreceptor.

Further, the optical writing means is not limited to a liquid crystal optical shutter, and may be configured using, for example, an LED (light emitting diode) array, etc., which is driven to blink by controlling a digital signal.

〔Effect of the invention〕

According to the image forming apparatus of the present invention configured as described above, since the exposure of the second image is performed from the back side of the transparent photoreceptor, the potential of the area to which the first toner is attached is the same as that of the area to which the first toner is not attached. The first toner is not taken into the second developing device during the second development.

Therefore, since a good composite image can be obtained, in the case of a two-color image forming apparatus, the color of the second image is
Can maintain clarity for a long time.

Then, during the second development, carrier adhesion to the first toner image area can be prevented.

Further, since the exposure section such as the liquid crystal light shutter is isolated and no stains are caused by scattered toner, the amount of light is stable and a stable image can be obtained over a long period of time.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an example of the image forming apparatus of the present invention, FIG. 2 is an enlarged sectional view of the main part of a liquid crystal optical shutter head, and FIG. 3 is a change in photoreceptor surface potential in a conventional image forming apparatus. 4 are diagrams showing changes in photoreceptor surface potential in the image forming apparatus of the present invention. 1...Photoreceptor, 1a...Photoconductive layer, 1b...
Transparent conductive layer, 1c...Transparent support layer, 2...First corona charger, 3...Second corona charger, 4...Liquid crystal light shutter head, 4a...
SLA, 4b...Liquid crystal light shutter, 4c...Fluorescent lamp, 5...First developer, 6...Second developer, 7...
...Transfer paper, 8...Transfer charger, 9...Separation charger, 10...Cleaner, 11...Fuser, 12a, 12b, 12c...Roller, 13...
...Static electricity removal lamp.

Claims (1)

[Claims] 1. A step of first charging a photoreceptor having a photoconductive layer on a transparent and conductive base with a predetermined polarity, and charging the photoreceptor with a negative value corresponding to first image information after the first charging. a step of performing exposure to form a first electrostatic latent image; a first developing step of reversing developing the first electrostatic latent image to form a first developed image;
A step of performing a second charge of the same polarity as the first charge on the photoconductor while carrying a visible image, and applying negative exposure corresponding to the second image information to the base side of the photoconductor after the second charging. forming a second electrostatic latent image; and reversing and developing the second electrostatic latent image to form a second electrostatic latent image.
An image forming apparatus characterized in that a second developing step of forming a developed image is sequentially performed.