JPH05341614A - Multicolor image forming device - Google Patents

Abstract

PURPOSE:To provide a multicolor image forming device in which the total amount of use of developer is reduced, color reproducibility is improved and a developing process is speeded up. CONSTITUTION:In the multicolor image forming device which forms images in many colors on an electrophotographic photosensitive body 1 by performing the developing process plural times by means of a plurality of development units 31-35 corresponding to the specific colors and obtains the multicolor image by transferring the images in the many colors to a transfer material all together, the development unit 34 containing at least one of red, blue and green developers is provided in addition to the development units 31-33 and 35 containing yellow, magenta, cyan and black developers.

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 a specific image signal, and then visualizes it with a developing device corresponding to the specific color. The present invention relates to a multicolor image forming apparatus such as a copying machine, a printer, or a fax machine, in which a multicolor image is formed on an electrophotographic photosensitive member by performing a plurality of steps, and the multicolor image is collectively transferred to a transfer material to obtain a multicolor image. ..

[0002]

2. Description of the Related Art FIG. 4 shows an example of the multicolor image forming apparatus which has been actively studied in recent years. Multicolor image forming apparatus shown in the drawing, the yellow, magenta, cyan, black (these developers are hereinafter, Y, M, C, may be abbreviated as appropriate and B _K.) Accommodating the respective developer 4 developing units 31,3
2, 33 and 35 are formed, and a color image is formed by superimposing four color toner images on the photosensitive drum 1 which is an electrophotographic photosensitive member. Reference numeral 2 is a corona charger, 4 is a transfer means, 5 is a cleaner, 6 is a semiconductor laser, 7 is a pre-exposure lamp, and 8 is a reader section.

An example of multicolor image formation by the multicolor image forming apparatus will be briefly described.

For example, in the case of a color copying machine, a document such as a red, green, blue (these colors will be referred to as R, G, and
It may be abbreviated as B as appropriate. ) Is read as an analog signal value. Then, this analog signal is converted into a digital signal by an A / D converter. And this R, G, B
Of the digital signal of Y, M,
Convert to C signal value. Further, in order to improve the reproducibility of black such as black characters and reduce the amount of toner consumption, as shown in FIGS. 6A and 6B, the black component extraction technology (UCR) is used. , M, C, B _K signal values are converted. In the printer section, first, the electrophotographic photosensitive member is neutralized by means such as light, and then uniformly charged by a corona discharger or the like. After that, image exposure is performed according to the image signal of the yellow component obtained as described above.
Then, the latent image thus obtained is developed by a developing device containing yellow toner to visualize it.

After the charge is removed from the photosensitive member by light or the like, a recharging step is carried out with the yellow toner placed on the photosensitive member. Next, image exposure corresponding to the image signal of the magenta component is performed on the photoconductor on which the yellow toner image is formed, and the magenta toner is developed by the developing device containing the magenta toner. Such a process is similarly performed for the cyan and black components to form a full-color image on the photoconductor and collectively transfer it to the transfer material by the transfer means. By passing the transfer material on which the multicolor image is formed through the fixing device, the toner is melted by heating, for example, and the toner is fixed on the transfer material to obtain a multicolor image.

[0006]

In the above-mentioned multicolor image forming apparatus which is an object of the present invention, the following latent image and development are carried out on the toner image previously formed on the photoconductor. Since the toner images are superposed, one of the problems is that the toner image superposed thereon becomes thin and the color reproducibility is poor. Here, the cause will be described with reference to FIG.

FIG. 5 is a diagram showing changes in the surface potential of the photoconductor in the process of forming a multicolor image in this type of multicolor image forming apparatus. In the figure, for convenience of explanation, the polarity of the photosensitive surface is assumed to be positive, and the description will be made sequentially.

The surface potential of the photoconductor becomes E by uniformly charging the photoconductor with the primary charger.

First image exposure is performed by an image exposure means such as a semiconductor laser, and the surface potential of the exposed portion becomes E '.

By applying a positive developing bias close to the charging potential E to the developing sleeve for the latent image thus formed, the positively charged toner has a relatively low potential E '. The exposed portion is developed to form a first toner image.

In this step, the charge T1 is removed by the pre-exposure lamp or the like, so that the potential T ₁ due to the toner charge is increased.
The electric potential of the toner adhering portion becomes higher. This step is for preventing excessive charging of the unexposed area.

Next, the photosensitive member on which the first toner image is formed is charged again uniformly. As a result, a substantially uniform surface potential E is obtained regardless of the presence or absence of toner. At this time, since the toner image is recharged, the amount of charge held by the toner increases, and the toner potential (potential due to the toner charge) also increases (T ₁ → T ₁ ′). Therefore, even if the surface potential E of the photoconductor is uniform, the photoconductive layer surface (under the toner layer)
Potential, the surface potential E (on the toner layer) 'decreases by the amount given, E-T _1' Toner potential T ₁ than the at.

If the second image exposure is performed on the photoconductor with the same amount of light as the first image exposure on the first toner, the potential of the surface of the photoconductive layer is as low as ET ₁ ′. In addition, since the image exposure light amount is attenuated by the toner layer, the surface potential of the photoconductor becomes the exposed portion E ″, which is higher than that in the toner-free portion.

Here, in the same manner as described above, the positively charged toner of a color different from the first toner is developed to form a multiple toner image. However, as described above, even if the first toner image and the second toner image are superposed in the image exposure with the same exposure amount, the contrast of the latent image for developing the second toner image becomes smaller. In addition, the thickness of the first toner layer increases the distance from the photoconductor substrate and reduces the electrostatic capacity, which reduces the amount of the second developing toner.

It has been found that the phenomenon described in (1) above becomes more prominent when the charge is removed thereafter and the third and fourth toner images are overlaid.

In addition to the above-mentioned problems, when the above-mentioned multicolor image forming apparatus is used as, for example, a document copying machine or a printer, there are few monochromatic portions such as yellow, magenta and cyan.
There are many red, blue, and green (especially red) monochromatic areas.

For example, for two-color documents, most of them are black and red. Even in such a case, in the conventional multicolor image forming apparatus, magenta and yellow toners are superposed in order to reproduce red.
Therefore, the color reproducibility of red is inferior to that of a two-color printer that uses red toner, and the two-color image causes the photosensitive drum to rotate three times. Had the drawback of being slow.

Further, when reproducing red as described above, there is a problem that the total toner amount is increased when magenta and yellow toners are used, whereas the toner of red single color is used.

The present invention is intended to solve the above problems. That is, it is an object of the present invention to provide an image forming apparatus capable of improving color reproducibility, improving the speed of a developing process, and reducing the total amount of toner used.

[0020]

In order to achieve the above object, a multicolor image forming apparatus of the present invention performs image exposure based on an image signal of a specific color by uniformly charging an electrophotographic photosensitive member. After that, the step of developing with a plurality of developing devices corresponding to the specific color is performed a plurality of times to form a multicolor image on the electrophotographic photoconductor, and the multicolor image is collectively transferred to a transfer material to perform multicolor image formation. In a multicolor image forming apparatus for obtaining a color image, yellow, magenta,
In addition to four developing devices containing cyan and black developers, a developing device containing at least one developer of red, blue, and green is provided.

[0021]

According to the present invention, in the multicolor image forming apparatus, in addition to the four developing devices containing the yellow, magenta, cyan and black developers, at least one of red, blue and green developers is used. Since the developing device accommodating the toner is included, the total toner amount can be reduced, and therefore, the phenomenon that the consumption of the developing toner amount for the second and subsequent colors is reduced can be greatly suppressed.
When forming a color image, the speed of the developing process can be increased as compared with the conventional case.

[0022]

1 shows a first embodiment of a multicolor image forming apparatus of the present invention. In FIG. 1, 1 is a photosensitive drum, 2 is a corona charger, 31 to 35 are yellow, magenta, cyan, red, and black developing devices, respectively, and 4 is a voltage-applying O.
Transfer means 5 having N and OFF means 5 is also ON and O
Cleaner with FF means, 6 is a semiconductor laser, 7
Is an exposure lamp, and 8 is a reader unit. Developer 3
Nos. 1 to 35 are arranged on the rotating body 3a at equal intervals in the circumferential direction, and one of the developing devices faces the photosensitive drum 1 by the rotation of the rotating body 3a.

The toner used in this embodiment is a polyester-based non-magnetic toner of yellow, magenta, cyan, red and black having a particle size of 8 μm.

The black extraction technique and the red extraction technique used in this embodiment will be briefly described with reference to FIG. For example, assuming that the toner amount at the time of maximum density for a single color is 100, the signal values obtained for reproducing a certain color are Y = 60, M = 40, C = 25 as shown in FIG. Then, as the black extraction technology or processing,
By replacing 25 of Y, M and C with B _K ,
Y = 35, M = 15, C = 0, and B _K = 25. By this process, the total toner amount before the process was 125, whereas the total toner amount after the process was 75, which can be greatly reduced. Further, as a red extraction technique or process, 15 of Y and M are set to R
Replaced with (red), Y = 20, M = 0, C =
By setting 0, B _K = 25, and R = 15, the total toner amount becomes 60, and the toner amount can be reduced to less than half of the initially expected total toner amount.

Next, the operation related to the above embodiment will be described. First, place a color document on the platen and cover it with a cover. Next, if necessary, press the color mode specification button on the operation panel and then the copy button. Then, the document illumination lamp illuminates the document and the reflected light is detected by the light receiving element provided with the B, G, and R filters. The detected analog signal is converted into a digital signal by an A / D converter. Then, the R, G, and B digital signals are converted into Y, M, and C signal values by a known image processing technique. After that, by performing the black extraction processing and the red extraction processing as described above, the signal values of Y, M, C, R, and B _K are obtained,
It is sent to the printer section.

In the printer section, the photosensitive drum 1 is first discharged by the exposure lamp 7 and then uniformly charged by the corona charger 2. After that, image exposure is performed by the laser 6 according to the image signal of the yellow component obtained by the reader unit 8 as described above. Then, the latent image formed as described above is developed by the developing device 31 containing the yellow toner and visualized. After that, the charge on the photosensitive drum 1 is removed by light or the like, and then the recharging step is performed with the yellow toner placed thereon. Next, image exposure corresponding to the image signal of the magenta component is performed on the photosensitive drum 1 on which the yellow toner image is formed, and the magenta toner is developed by the developing device 32 containing the magenta toner. Such a process is similarly performed for cyan, red, and black to form a full-color image on the photosensitive drum, and the image is collectively transferred to the transfer material by the transfer unit 4. By passing the transfer material on which the multicolor image is formed through the fixing device in this way, the toner is melted by heat and fixed on the transfer material, whereby a multicolor image can be obtained.

As described above, in the present embodiment, in addition to the developing device containing yellow, magenta, cyan, and black toners, the developing device containing red toners is provided.
By using the black extraction technology and the red extraction technology, the total toner amount can be greatly reduced, and therefore a great result can be obtained against the phenomenon that the development toner amount for the second and subsequent colors decreases below the target amount. Can be seen. In addition, in the case of the black-red original that is usually used most often, three steps of developing yellow, magenta, and black were conventionally required.
According to the present embodiment, only two steps of red and black development are required, the speed of the development step, that is, the output speed is improved, and the amount of toner used can be reduced as compared with the case of mixing yellow and magenta. Red reproducibility can be improved.

Although the developing device 34 has been described above as containing red toner, it is also included in this embodiment that blue or green toner is stored in the developing device 34 instead of red toner.

FIG. 2 shows a second embodiment of the multicolor image forming apparatus of the present invention. 2, the same members as those shown in FIG. 1 are designated by the same reference numerals.

In the first embodiment, as shown in FIG. 1, five developing devices 31 to 35 are arranged on one rotating body 3a, but in this embodiment, as shown in FIG. Four developing devices 31 to 34 for yellow, magenta, cyan and red are arranged on the rotating body 3a, and a black developing device 35 is arranged on the downstream side thereof independently of the rotating body 3a. Then, using a semiconductor laser as an exposure means, a laser 61 for yellow, magenta, cyan, and red,
It has a two-beam configuration with the laser 62 for black.

To describe the operation of this embodiment, the developing process for yellow, magenta, cyan, and red is performed by rotating the photosensitive drum 1 once for each color as in the first embodiment, and the final color of black is used. Only in the process, charging, image exposure, and development are performed following the red process.

In the present embodiment, when a multicolor image is formed on the basis of a black-and-red original that is usually most often used, the photosensitive drum 1 only needs to be rotated, so that the speed-up of the developing process, that is, high-speed output is possible. As compared with the case of mixing yellow and magenta, the amount of toner used can be greatly reduced, and the color reproducibility is improved.

The developing device 34 can store blue or green toner as in the first embodiment.

FIG. 3 shows a third embodiment of the multicolor image forming apparatus of the present invention. 3, the same members as those shown in FIG. 1 are designated by the same reference numerals.

In this embodiment, as shown in FIG.
Two rotating bodies, a rotating body 3a and a rotating body 3b, are provided, and the rotating body 3a has four members of yellow, magenta, cyan, and black.
The three developing devices 31, 32, 33 and 35 are arranged at equal intervals in the circumferential direction, and the rotating body 3b has three members of red, blue and green.
Two developing units 34, 36 and 37 are provided, and two beams 61 and 62 are formed as in the second embodiment. Reference numerals 21 and 22 are corona chargers.

When all the red, green and blue developing devices are provided as in this embodiment, the preferred operation of this embodiment is as follows.

It is desirable to extract red, green or blue after the black extraction processing according to the image signal of each pixel. That is, as shown in FIG. 7, for example, when the image signal of cyan is the smallest among yellow, magenta, and cyan (a)
Performs red extraction, performs green extraction when the magenta image signal is smallest (b), and performs blue extraction when the yellow image signal is smallest (c). After performing such extraction processing, development is performed in the following procedure.

First, the photosensitive drum 1 is uniformly charged by the charger 21, and then image exposure and development of the yellow component are performed.
The beam 61 and the developing device 31 are used. Next, the charger 22
After performing the image exposure and development of the red component by the beam 62 and the developing device 34, the photosensitive drum 1 is discharged by the pre-exposure of the exposure lamp 7. Subsequently, on the second lap of the photosensitive drum 1, a developing process for magenta and green is performed, on the third lap, a developing process for cyan and blue is performed, and on the fourth lap, a developing process for black is performed. After that, the multicolor image formed on the photosensitive drum is collectively transferred to a transfer material.

According to this embodiment, the amount of toner used can be greatly reduced, and the color reproducibility is also greatly improved. Further, most color originals used in offices or the like are two-color originals of black characters plus red, blue, or green. In the case of such an image, according to the present embodiment, the above two colors are not mixed, so that the colors are not mixed. In addition to the advantages of improved reproducibility and reduction of toner consumption, an image can be output with one rotation of the photosensitive drum, which enables high-speed output.

As a modification of this embodiment, two red, blue, and green developing units 34, 36, 37 can be combined and arranged on the rotating body 3b to perform development.

[0041]

As described above, according to the present invention, toner images are superposed on a photoconductor to form a multicolor toner image, and then the multicolor toner image is collectively transferred to a transfer material, that is, a so-called multicolor toner image. In the image forming apparatus, at least one of red, blue, and green is provided in addition to the four developing devices containing yellow, magenta, cyan, and black developers.
Since the developing device accommodates two developers, it is possible to reduce the total amount of developer used, and thus it is possible to significantly suppress the phenomenon that the amount of developing toner for the second and subsequent colors decreases. Further, since red, blue and green are developed in a single color regardless of the mixture of developers, color reproducibility is improved and the development process is speeded up.

[Brief description of drawings]

FIG. 1 is a schematic view showing a first embodiment of a multicolor image forming apparatus of the present invention.

FIG. 2 is a schematic view showing a second embodiment of the multicolor image forming apparatus of the present invention.

FIG. 3 is a schematic view showing a third embodiment of the multicolor image forming apparatus of the present invention.

FIG. 4 is a schematic diagram showing a conventional example of a multicolor image forming apparatus.

FIG. 5 is an explanatory diagram of changes in the surface potential of a photoconductor in a conventional example.

FIG. 6 is an explanatory diagram of black extraction and red extraction processing.

FIG. 7 is an explanatory diagram of developing unit selection in the third embodiment of the present invention.

[Explanation of symbols]

1: Photosensitive drum 2, 21, 22: Corona charger 3a, 3b: Rotating body 31: Yellow developing device 32: Magenta developing device 33: Cyan developing device 34: Red developing device 35: Black developing device 36: Green developing device 37 : Blue developing device 4: Transfer means 5: Cleaner 6, 61, 62: Semiconductor laser 7: Pre-exposure lamp 8: Reader unit

Claims (1)

[Claims] 1. A step of visualizing with a plurality of developing devices corresponding to the specific color a plurality of times after uniformly charging the electrophotographic photosensitive member and performing image exposure based on an image signal of the specific color. In the multicolor image forming apparatus for forming a multicolor image on the electrophotographic photosensitive member and transferring the multicolor image to the transfer material at a time to obtain a multicolor image, yellow, magenta, cyan, and black developers are used. In addition to the four stored developing devices, red,
A multicolor image forming apparatus comprising a developing device accommodating at least one developer of blue and green.