JPH0950164A - Two-color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sufficient latent image potential contrast in the case of forming the single-color image of a second color to realize a high-density single-color image of the second color in a two-color image forming device in which electrification, exposure, and development are repeated twice to form the superimposed image of the toner images of a first color and the second color on a photoreceptor and by which a two-color image is obtained by transferring the superimposed image on a transfer paper with one transfer process. SOLUTION: In the case of forming the single-color image of the second color, the electrification of the photoreceptor is performed by a first electrifying device whose electrification ability is high, so that the photoreceptor is electrified to V2(=980V), and the potential of a second developing position after dark decay becomes the same VD(=650V) as the one obtained in the case of forming the two-color image. Second exposure solely performed is made the same as the one obtained in the case of forming the two-color image so as to obtain a bright part potential VL2(=150V) at a second developing position and the same potential contrast(500V) as the one obtained in the case of forming the two-color image. Thus, the single-color image of the second color can obtain the same high density as the one obtained in the case of forming the two-color image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention uses an electrophotographic system to
A two-color image of a copying machine or a printer that forms two-color toner images on a photoconductor by using toners of different colors and transfers the two images onto a transfer material at one time to obtain a two-color image. Forming apparatus

[0002]

2. Description of the Related Art As a method for forming a two-color image, two charging means, two exposing means and two developing means are arranged around a photoconductor, and two steps of charging, exposing and developing are carried out during one rotation of the photoconductor. There is a method in which the toner images of the first color and the second color are sequentially formed on the photoconductor to obtain a superposed image of two colors, and these are collectively transferred onto the transfer paper.

According to this method, since a two-color image can be obtained by one rotation of the photosensitive member, there is an advantage that the two-color image can be copied at the same speed as in the case of a single-color image.

FIG. 2 shows a schematic structure of a copying machine used to form a two-color image. This two-color copying machine includes a first charger 2, a first exposure device 3, a first developing device 4, a second charger 5, a second exposure device 6, and a second developing device along the rotation direction of the photoconductor 1. It comprises a device 7, a transfer charger 8 and the like.

When forming a two-color image, the photosensitive member 1 is charged by the first charger 2 and then exposed by the first exposure device 3 to form a first latent image. First developing device 4
To develop a toner image of a first color, and subsequently to charge the photoconductor 1 using the second charger 5, a second exposure device 6 forms a second latent image. The second latent image is developed using the second developing device 7 to form a toner image of the second color, and a superposed image of the toner images of the two colors is obtained on the photoconductor 1.
Then, the superposed image is transferred onto the transfer paper P by the transfer charger 8 to obtain a two-color image on the transfer paper P.

On the other hand, the above copying machine can also obtain a monochromatic image. For example, in the case of a monochromatic image of the second color, the second charger 5, the second exposure device 6 and the second developing device 7 are used.
Will be used.

[0007]

Such a two-color copying machine has twice the number of charging means, exposing means and developing means as compared with a monochrome copying machine which obtains only a normal black image. Since it is necessary to arrange these around the photosensitive member, it is necessary to reduce the size of each means.

Particularly, the space for installing the second charger 5 is
It is narrow because it is sandwiched between the first developing device 4, the second exposing device 6 and the second developing means 5. It is difficult to expand this space, and when trying to move the first developing device 4 upward, the first,
The second exposure devices 3 and 6 have to be moved upward, which increases the height of the entire copying machine and makes it difficult to use. Further, when the second developing device 7 is moved downward,
The transfer paper P and the photoconductor 1 cannot be sufficiently adhered to each other, and an image is disturbed in the transfer process.

Therefore, it is necessary to make the second charger 5 particularly small, but when a scorotron charger is used as the second charger 5, the opening of the charger along the circumferential direction of the photoconductor 1 due to the miniaturization. The width becomes narrow and the charging ability becomes low. Generally, even if the currents flowing into the photoconductors are set to be the same, the charging ability of the charger is low if the opening width is narrow.

For this reason, a sufficient charging potential cannot be obtained during the formation of a monochromatic image with the second color, the potential contrast of the second latent image becomes small, and a sufficient image density cannot be obtained.

This problem is more remarkable in a high-speed copying machine in which the photoconductor needs to be rotated at a high speed, and the higher the rotation speed, the less the required amount of charging potential can be obtained.

An object of the present invention is to obtain a sufficient latent image potential contrast even when a monochromatic image is formed by the second color,
It is an object of the present invention to provide a two-color image forming apparatus capable of achieving a high-density single-color image with each color.

[0013]

The above object can be achieved by a two-color image forming apparatus according to the present invention. In summary, the present invention relates to a first charging unit for charging a photosensitive member around a photosensitive member, a first latent image forming unit for forming a latent image by exposure, and the latent image for the toner of a first color. Developing means for developing a toner image into a toner image, second charging means for charging the photoconductor, second latent image forming means for forming a latent image by exposure, and the latent image for the toner of the second color. And a transfer means for transferring the toner image formed on the photoconductor onto the transfer material, and the second developing means for developing the toner image on the photoconductor is formed on the photoconductor during one rotation of the photoconductor. In a two-color image forming apparatus, in which a toner image of a first color and a toner image of a second color are sequentially superposed and formed, and a two-color image is obtained by collectively transferring them onto a transfer material, Without forming a toner image, only the toner image of the second color is formed and transferred onto the transfer material to obtain a monochromatic image of the second color. During monochrome image formation, the charging of the photosensitive member, a two-color image forming apparatus and performing with the first charging means or the first charging means, and a second charging means.

Preferably, when the monochromatic image is formed, the photosensitive member can be exposed by using the first exposing means. The photoconductive material of the photoconductor may be amorphous silicon.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 2 is a schematic configuration diagram of a two-color copying machine used in the present invention.

As shown in FIG. 2, the two-color copying machine has a first charging device 2, a first exposing device 3, a first developing device 4, and a second charging device 5 along the rotation direction of the photoconductor 1. The second exposure device 6, the second developing device 7, and the transfer charger 8 are provided. In this embodiment, the photoconductor 1 is configured by providing a photoconductive layer made of an organic semiconductor on a cylindrical conductive substrate. The first charger 2 and the second charger 5 are scorotron chargers.

The two-color image forming process will be described. First, while rotating the photoconductor 1 in the direction of the arrow in the figure, the first scorotron charger 2 uniformly charges the photoconductor 1 to a predetermined potential level, and then, 1 exposure device 3 performs laser beam exposure modulated according to the first image signal to expose photoreceptor 1
A first electrostatic latent image is formed on top. Then, the first electrostatic latent image is developed by the first developing device 4 which holds the non-magnetic toner of the first color (red in this example), and the first color on the photoconductor 1 is developed. A toner image is formed.

Subsequently, the photoconductor 1 carrying the toner image of the first color is recharged by the second scorotron charger 5 to make the potential of the photoconductor 1 uniform and at the same time charged to a predetermined potential level. After that, the second exposure device 6 performs laser exposure on the photoconductor 1 modulated in accordance with the second image signal to form a second electrostatic latent image on the photoconductor 1. Then, the latent image is developed by the second developing device 7 which holds the magnetic toner of the second color (black) to form the toner image of the second color. An overlapping image of the toner images of the first and second colors is obtained.

In the above, the second latent image is developed by non-contact development in which the magnetic toner carried on the toner carrier (not shown) of the second developing device 7 is not brought into contact with the photoconductor 1. As a result, the toner image of the second color can be formed without disturbing the toner image of the first color.

Then, the two-color superposed images are collectively transferred onto the transfer paper P conveyed along the conveying path 10 by using the transfer corona charger 8, and then the transfer paper P is removed by the charge eliminating charger 9. The separated image is sent to the fixing device 11, where the superimposed image is permanently fixed on the transfer paper P, and a two-color image is obtained on the transfer paper P.

After the transfer process, the photoconductor 1 is rotated as it is, the residual toner on the surface of the photoconductor 1 is removed by the cleaning device 11, the residual charge of the photoconductor 1 is erased by the charge elimination lamp 12, and then the photoconductor 1 is again erased. The next image formation is repeated.

In this embodiment, the diameter of the photoconductor 1 is about 1.
00 mm, the rotation speed of the photoconductor 1 is 200 to 400 mm /
In second, the opening width of the first scorotron charger 2 in the circumferential direction of the photoconductor is 30 to 40 mm, and the opening width of the second scorotron charger 5 in the same direction is 10 to 20 mm.

FIG. 3 shows a two-color image forming process by a potential diagram of a photosensitive member. Although the charging polarity of the photoconductor 1 is originally negative, it is the same in principle as the positive polarity, so the following description will be treated as positive for convenience.

After uniformly charging the photoconductor 1 to the potential VD = 650V, the first negative exposure is performed to set the potential VL1 = 15.
The first electrostatic latent image is formed by setting it to 0 V (FIG. 3A).
Then, using the first color toner charged to the positive electrode,
A bias VDC1 is applied to the toner carrier of the developing device 4 to perform reversal development, and toner is attached to the exposed portion to form a toner image T1 of the first color (FIG. 3 (b)).

Next, the photoconductor bearing the toner image of the first color is recharged to the potential VD (FIG. 3c)). After this,
A second negative exposure is performed to form a second electrostatic latent image by setting the potential to VL2 = 150V (FIG. 3 (d)), and then the second development is performed using the second color toner charged to the positive electrode. A developing bias VDC2 is applied to the toner carrier of the container 7 to perform reversal development as in the case of the first color to form a toner image T2 of the second color (FIG. 3 (e)). As a result, a superimposed image of two color toner images is obtained on the photoconductor.

The details of the present invention will be described with reference to FIG. FIG.
Shows changes in the potential of the photoconductor during latent image formation. In FIG. 1, curves a, b, and c represent potentials when a two-color image is formed.

The photosensitive member is charged to V1 (= 730) by the first charging.
After being charged to V) (curve a), the first exposure is performed in the middle of dark decay to divide into a light portion of the light receiving portion (curve b) and a dark portion of the non-light receiving portion. The dark portion potential continues to be attenuated to VD (= 650V) at the first developing position, and the light portion potential becomes VL1 (= 150V) at the first developing position after being optically attenuated. When the toner of the first color adheres to the bright portion due to the first development, the potential of the bright portion rises by the charge held in the toner layer.

Subsequently, the dark portion and the bright portion are charged to V3 (= 710V) again by the second charging. Although the second charger 5 has a lower charging ability than the first charger 2, the dark portion is charged to about 600V and the light portion is charged to about 200V immediately before the second charging, and thus the second charger 5 is charged to V3. The current is less likely to flow in the bright portion having a lower electric potential than that in the dark portion, and charging can be performed in a short time. Therefore, the second charger can also charge.

After the second charging, the second exposure is carried out again to divide into a light portion (curve c) and a dark portion, and the dark portion potential is V at the second developing position.
D (= 650V), the light potential is VL2 (= 150V)
And At this time, since a sufficient potential contrast VD-VL2 = 500V is obtained as the second latent image, a bias VDC2 (VD-about 100V) of an appropriate value is applied to the second developing device.
= 550V is an appropriate value), a sufficient developing electric field VDC2-VL2 = 400V can be secured, and a toner image of the second color with high density and no fog can be formed.

On the other hand, the curves d and e in FIG.
2 shows a potential change during formation of a single color image of the color. In this case, charging is performed only by the second charger 5, and unlike the case of forming a two-color image, the entire surface of the photoconductor at zero potential must be charged. Does not provide sufficient potential. The potential after the second charging is S1 (= 50
0V), SD (= 410V) at the second developing position,
The bright portion potential (curve e) after the second exposure is SL2 (= 50) at the second developing position even if the light is attenuated to the minimum residual potential.
V), and the potential contrast of the second latent image is SD-SL2
= 360V, which is low. Therefore, the proper developing bias VDC
When 2 (SD-about 100V = 310V) is applied, the developing electric field is VDC2-SL2 = 260V, which is about 2/3 of that at the time of two-color image formation. Therefore, a sufficient concentration cannot be obtained.

On the other hand, the curve f shows the potential change during the formation of the second color monochromatic image according to the present invention. In this case, the photoconductor 1 is charged by the first charger 2 instead of the second charger 5. Since the first charger has few restrictions on the installation space like the second charger, a relatively wide opening width can be adopted, and a high potential can be obtained by setting a large charging current. V2 (= 980V) of the photoconductor by the first charger
When charged to, the potential at the second developing position after dark decay coincides with VD (= 650V), which is exactly the same as when forming a two-color image. Further, by making the only second exposure the same as the second exposure when forming a two-color image, a bright portion potential VL2 (= 150 V) is obtained at the second developing position, and the same potential as when forming a two-color image is obtained. A contrast (500V) is obtained. As a result, it was possible to obtain the same high-density single-color image as when forming the two-color image even when forming the single-color image with the second color.

According to the above, since the first charger 2 is used when forming the monochromatic image of the second color, the frequency of use of the first charger is increased. For this reason, there is a possibility that contamination due to the discharge dust collection effect of the first charger may be accelerated, which may raise inconveniences such as an increase in the number of maintenance operations. And so on,
There are no particular problems because dust discharge means such as a blower is often installed.

Example 2 In this example, an inorganic semiconductor was used as the photosensitive material of the photosensitive member 1. The organic semiconductor used in Example 1 has a small electrostatic capacity and is easily charged, but an inorganic semiconductor, such as amorphous silicon, has a high surface hardness and excellent durability, while it has a large electrostatic capacity, and thus is hard to be charged and has a saturated potential. Is also low.

Therefore, when the monochromatic image formation with the second color is performed by only the first charging as in the first embodiment,
In some cases, the desired dark part potential cannot be obtained at the second developing position. Therefore, in the present embodiment, not only the first charging but also the second charging as the auxiliary charging is performed so that a desired dark part potential is obtained.

FIG. 4 is a diagram showing a potential change when a latent image is formed on a photosensitive member using amorphous silicon. 4, parts having the same contents as those in FIG. 1 are designated by the same reference numerals. In FIG. 4, curves a, b, and c represent potentials when a two-color image is formed.

The photosensitive member is charged to V1 (= 460) by the first charging.
After being charged to V) (curve a), the first exposure is performed (curve b), and the dark portion potential VD (= 400V) and the light portion potential VL1 (= 50V) are obtained at the first developing position. After the first development is performed to form the toner image of the first color, the second charge is performed and then the second exposure is performed (curve c) after charging to V3 (= 440V), and at the second development position. Dark potential VD (= 40
0 V) and the bright part potential VL2 (= 50 V) are obtained. Since the potential contrast VD-VL2 = 350V of the second latent image is small, the toner carrier of the second developing device 7 and the photoconductor 1 are brought close to each other, or the electric charge of the toner is increased, By performing the second development with the improved development efficiency, it is possible to obtain the toner image of the second color in which the high density is maintained.

In FIG. 4, reference numeral g indicates a potential change when a monochromatic image is formed by the second color. Even if the photosensitive member is charged to the saturation potential V2 (= 520V) by the first charging, V4 (= 340) is charged at the second developing position due to the subsequent dark part decay.
V) (curve h), and the potential contrast becomes insufficient. In order to prevent this, auxiliary charging is performed by the second charging. That is, immediately before the second charging position (V5
The second charging is performed at a potential of 410 V), and V3 (=
440V). As a result, the same potential contrast as when forming a two-color image was obtained even when a single-color image was formed using the second color, and it was possible to obtain a high-density single-color image that was formed using the second color.

Embodiment 3 In each of Embodiments 1 and 2 described above, the second exposure device 6 is used to form the bright portion potential when the monochromatic image of the second color is formed.
However, the first exposure device 3 can also be used.

In this type of two-color copying machine, a manuscript image is usually decomposed into a two-color image by a reading device called a reader and read, the read image information is converted into an electric signal, and then exposure is performed based on this signal. The photosensitive member is exposed while modulating the emission time and emission intensity of the laser beam for use.

At this time, the reading operation of the reader and the exposure of the photosensitive member are performed in parallel in synchronization with each other. However, the image forming position on the photosensitive member is changed to the exposure position within the time for transferring the signal to the laser after reading. If it does not come, naturally, an image memory for temporarily storing the signal is always required. Since the second exposure is performed later than the first exposure, an image memory for storing the signals for the second exposure is indispensable. This memory capacity becomes more necessary as the time from the signal transfer to the exposure start time is longer.

Since the first exposure device 3 is in a non-use state during the formation of a monochromatic image of the second color, if the first exposure device is used instead of the second exposure device 6, the exposure start time is advanced, and It is not necessary to use the image memory of.
This is advantageous because power consumption can be saved and the memory can be used for other signal processing.

FIG. 5 shows the potential change when the first exposure device is used to perform exposure when forming a monochromatic image of the second color. 5, parts having the same contents as those in FIG. 1 are designated by the same reference numerals. Curves f and c in FIG.
The potential at the time of forming a monochromatic image with the second color described in
The light portion is formed by exposure (curve c).

On the other hand, the curve i shows the case where the bright portion is formed by the first exposure. The exposure amount of the first exposure is set so that VL2 can be obtained at the second developing position after the light portion potential after exposure is darkly attenuated. This makes it possible to take advantage of the above-mentioned non-use of the memory while maintaining the high density of the monochrome image of the second color.

[0045]

As described above, according to the present invention, charging,
By repeating the cycle of exposure and development processes twice, a superimposed image of the toner image of the first color and the toner image of the second color is formed on the photoconductor, and the superimposed image is formed on the transfer paper in one transfer process. It is a two-color image forming apparatus that obtains a two-color image by transferring the image onto the two-color image forming apparatus. Wide area charging is possible when forming a single color image without forming the first color toner image and transferring only the second color toner image onto the transfer material to obtain a second color single color image. Since the charging is performed by using the first charging device having a high charging ability or both the first charging device and the second charging device, sufficient potential contrast is obtained for the latent image of the monochromatic image of the second color. It was possible to obtain a high-density monochromatic image of the second color. In addition, the first charger and the first exposure device cause a second
When the latent image of the monochromatic image of the color is formed, the image memory required when the second exposure device is used is unnecessary, and the power consumption can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a potential change in a latent image forming process in an example of the present invention.

FIG. 2 is a schematic configuration diagram of a two-color copying machine used in the present invention.

FIG. 3 is a potential diagram of a two-color image forming process.

FIG. 4 is a diagram showing a potential change in a latent image forming step according to another embodiment of the present invention.

FIG. 5 is a diagram showing a potential change in a latent image forming step in still another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 1st charging device 3 1st exposure device 4 1st development device 5 2nd development device 6 2nd exposure device 7 2nd development device 8 Transfer charging device

Claims (3)

[Claims] 1. A first charging device for charging a photosensitive member around the photosensitive member.
A charging unit, a first latent image forming unit that forms a latent image by exposure, a first developing unit that develops the latent image with a toner of a first color to form a toner image, and a second unit that charges the photoconductor. A charging unit, a second latent image forming unit that forms a latent image by exposure, a second developing unit that develops the latent image with a toner of a second color to form a toner image, and is further formed on the photoconductor. A toner image of a first color and a toner image of a second color are sequentially superposed on the photoconductor during one rotation of the photoconductor. Then, in a two-color image forming apparatus that obtains a two-color image by batch-transferring onto the transfer material, the transfer material is formed without forming the toner image of the first color but only the toner image of the second color. When the monochromatic image is formed by transferring the image onto the monochromatic image of the second color, the charging of the photoconductor is
A two-color image forming apparatus, which is performed using a first charging unit or a first charging unit and a second charging unit. 2. The two-color image forming apparatus according to claim 1, wherein the exposure of the photoconductor is performed by using the first exposure means when the monochromatic image is formed. 3. The two-color image forming apparatus according to claim 1, wherein the photoconductive material of the photoconductor is amorphous silicon.