JPH0824344B2 - Color image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus, and more particularly to a color copying machine and a color printer for forming a color image on an image forming body by an electrophotographic method.

[0002]

2. Description of the Related Art In recent years, with the spread of color image devices such as color CRT display devices for computers and videotex terminal devices, the demand for color hard copy is increasing. In addition, various documents in offices are more colored and partially colored, and the demand for color copies is increasing.

As a means for obtaining a color hard copy, one that is low in cost, quick and easy to handle is desired.

The wire dot matrix recording system, the ink jet recording system, the thermal transfer recording system, the electrostatic recording system, the electrophotographic system and the like satisfy these conditions.

The advantages and disadvantages of comparing these various recording systems with the electrophotographic system are as follows.

(1) Wire Dot Matrix Recording Method This method is a method of printing on a paper surface a character or an image composed of a matrix of dot points obtained by striking from behind the ink ribbon with a dot wire. The recording device can be miniaturized and can be manufactured at low cost, but the printing speed is slow and a considerable amount of noise is generated.

(2) Inkjet recording method This method forms characters and pictures in that it is obtained by ejecting minute droplets of ink, but the recording apparatus by this method can be made relatively small, but at high speed. To turn into
It is necessary to use a multi-element nozzle head in which a plurality of elements, which are difficult to manufacture and are very expensive, are arranged in a line. As a further serious problem, nozzle clogging cannot be avoided, and it is difficult to maintain reliability for a long period of time. It is said that the bubble jet method solves these problems, but it is not yet considered sufficient.

(3) Heat-sensitive transfer method In the heat-sensitive transfer method, a thermal head formed by arranging minute heat-generating elements behind an ink film that is melted by heat and transferred to paper is brought into contact with the heat-generating elements to heat the elements to heat the ink film. In this method, a dye is melted or sublimated and transferred onto a recording medium for recording. This method does not have a developing device that handles powder inside the device, so it has a clean and simple structure, but there is a restriction on the paper used because it is affected by the quality and condition of the paper surface to which the ink film is transferred. There is a drawback that the running cost becomes high when the ink film cannot be reused because it requires the ink film for the number of colors to be recorded. There is a problem that the compatible thermal head becomes very expensive. Among the above three methods, the wire dot matrix method of (1) has a limitation on the thickness of the dot wire, (2), (3)
However, it is extremely difficult to stably obtain a resolution of 16 dots / mm or more because the size of the nozzle and the size of the heating element of the head are limited in this method.

On the other hand, in the electrophotographic system, it is difficult to downsize the apparatus because it has a developing device for handling a photoconductor, powder or liquid, but it is easy to obtain a high resolution of 16 dots / mm or more and high speed. There is an advantage that can be recorded in.

Xerox 6500 from Xerox Co., NP-COLOR T from Canon Inc., RICOH COLOR 5000 from Ricoh Co., Ltd.
In an electrophotographic copying machine of a type that reproduces the color tone of a document as it is called a full color process, for example, a photoconductor is corona charged and then a green (G) filter is passed through to expose a document image, and a magenta (M) developer is used. The developed magenta visible image is once transferred onto a copy paper. Then, in the same manner as described above, the photoreceptor is exposed with a blue (B) filter and developed with a yellow (Y) developer, and the obtained yellow visible image is aligned with the magenta image already transferred onto the transfer paper. Transcribe. Further, the same process as above is repeated using the red (R) filter and the cyan developer, and the cyan visible image is transferred so as to match the two previous images, and the obtained image is fixed to finally make a color print. obtain.

That is, according to this method, BGR is applied to the original image.
Color separation is performed, the photoreceptor is exposed for each color, YMC (black if necessary) development is performed, and the toner images are transferred one by one onto the transfer paper on the transfer drum to obtain a full-color image.

An electrophotographic color printer for obtaining a color hard copy is also known, for example, one disclosed in Japanese Patent Laid-Open No. 56-144452.
Here, as shown in FIG. 17, an image by each color signal is written on the photoconductor 301 uniformly charged by the charger 302 by the lasers l ₁ , l ₂ and l ₃ which are exposure means. D _1, D _2, D ₃ in each color developing _{devices, l 1, l 2, l} 3 in written a latent image on the transfer sheet 303 in a different color is developed with toner transfer electrode 304, respectively at a time By transferring, one multi-color hard copy can be obtained per one rotation of the photoconductor.

In the above example, the writing of an image is performed by three lasers, but the one configured to perform this by one laser is disclosed by the present applicant in Japanese Patent Laid-Open No. 60-758.
No. 50 and No. 60-76766. JP 60
A typical example of the -75850 is shown in FIG. A developing unit having one writing unit 334 around the photoconductor 331 and yellow, cyan, magenta, and black toners.
335 to 338 are arranged. First, set the photoconductor 331 to the charger 3
After being uniformly charged by 33, exposure and writing are performed by a laser beam modulated by a yellow image signal, and development is performed by a developing device 335 loaded with yellow toner. Photoconductor 3
During the next rotation of 31, the entire surface is charged and then exposed by a magenta signal, and magenta development is performed by the developing device 336 to form a magenta toner image on the yellow toner image. Further, after charging, exposure with a cyan signal, and cyan development are performed to form a cyan image on the above two-color image, it is transferred onto the transfer paper P at once by the transfer pole 340 to obtain a color hard copy.

The electrophotographic color recording apparatus described above writes an image by separately exposing photoelectric signals corresponding to the images to be developed to yellow, magenta, and cyan.

Further, in addition to the method of adding a color reading device to expose the image of the original on the photoconductor through a color filter and developing it with a developer having a color complementary to the color filter used, the original image is also filtered. There is also a method of projecting on a one-dimensionally arranged optical conversion element such as a line sensor, taking out as an electric output from the line sensor, modulating the laser beam by this signal and performing recording for each color by an electrophotographic method. .

This processing method is basically the same as the method used in the image signal processing such as color printing and color scanner as a color image processing technology in a broad sense. That is, for image formation, color reproduction and color reproduction are performed by combining three color information by color separation of the three primary colors (B, G, R) and an arbitrary combination of the color information.

In contrast to such a method of dividing into three colors to obtain respective color information, there are several methods which are somewhat special, but are obtained by dividing a color into two colors and reading them to obtain a read signal for a limited color. Or is disclosed.

As an example thereof, Japanese Unexamined Patent Publication No. 56-162755, FIG.
There is a technology disclosed by the Nippon Telegraph and Telephone Public Corporation at the 1987 National Conference of the Institute of Electronics and Communication Engineers shown in FIG.

Further, as another example, color signals are separated into two colors through a half mirror and a filter, and a color signal is obtained based on the output of the one-dimensional photosensor obtained for each of them. Is the way.

This was obtained by combining a half mirror and a color filter to separate an original into two components, red and blue.
When the output values from a photoelectric conversion means such as a CCD are Vr and Vb, which are the voltages normalized by the output values on a blank sheet, respectively, the former method uses Vr and Vb as the vertical and horizontal axes of the coordinates, respectively. The output signals are black and white, blue / green, purple, red / orange, and yellow. In the latter method, Va + Vb is used as a luminance signal on the vertical axis and logVa + logVb is used as a hue signal on the horizontal axis to extract each color signal of black, white, blue, green, and red.

The above-mentioned electrophotographic copying machine is the same as a normal single-color electrophotographic copying machine in terms of each color, and the same as a normal single-color electrophotographic copying machine in terms of each color.
A commonly used image density adjustment or fog prevention technology can be applied.

For example, among those that compensate the change in the characteristics of the photoconductor by some means, the one described in Japanese Patent Publication No. 44-2550 is used.
JP-B-49-4337, JP-B-54-92256, JP-A-50-36129 and JP-A-50-81237 for using corona discharge, JP-A-48- No. 31942,
No. 53-146629, and Japanese Patent Laid-Open No. 52-99824 for compensating for characteristic changes depending on time or the number of copies.
Nos. 52-110046 and 56-32153, JP-A-55-87174 and 54-83839 for detecting the factors relating to the image forming process and controlling the image density using some factor.
And No. 53-98830.

[0023]

When the electrophotographic color copier is constructed as described above, a problem not experienced in a monochromatic electrophotographic copier arises, and a stable color image is always reproduced. It becomes difficult to get good.

For example, while the copying machine is being used, the photoconductor and the developer tend to be fatigued or deteriorated with time to deteriorate the reproducibility of the image. The color reproducibility of the overlapping toner images changes when they are overlapped. In addition, the color reproducibility is similarly affected by the change of the exposure amount and the change of the charging state. In particular, the stability of the above-mentioned copying machine for the full-color process is not good, so it is necessary to perform sophisticated and complicated control to overcome this, and it is inevitable that the machine becomes large and expensive. .

Further, in the electrophotographic copying machine, there is a phenomenon called "background fog" in which a small amount of toner adheres to produce a dark white portion when a white portion of an original is copied. This background fog phenomenon occurs when the potential remaining on the photoconductor becomes large under the condition that the toner should not adhere to the photoconductor, and normally the bias voltage for neutralizing this residual voltage is used. Is applied to the photoconductor to prevent this.

The background fog is not so disturbing as in the case of a black and white copying machine, but when it occurs in a color copying machine, it causes a strong sensation due to the color mixture, and gives the same discomfort as when a strong stain is attached.

From this point of view, the prevention of background fog in a color copying machine is a particularly important problem. Also,
Since the occurrence of background fog may differ depending on the color, it is extremely difficult to completely prevent it for each color, and it has been desired to put an effective preventive means into practical use. In particular, in the case of a manuscript with black characters often used in offices, etc., or a color part in a part of the black-and-white screen, a copy with a background fog or a low-contrast copy is not preferable, and such a defect can be solved. Is desired.

On the other hand, it is economical to use the method of FIGS. 19 and 20 with a small number of colors as a color separation method for giving a color signal to an image forming apparatus having a writing system as shown in FIGS. 17 and 18. However, there is a drawback in that the obtained color print is very difficult to see. That is,
When such a method is adopted, when a document having a portion having a chromatic color, that is, a color, is printed on a part of an image including an achromatic color, that is, a black and white halftone, the halftone portion is colored purple in the method of FIG. A copy is obtained, which is very unnatural from the original color impression. Also, when the method shown in FIG. 20 is adopted, the halftone portion is colored green, and there is the same problem as in the above case.

Further, in the full color process described above,
Recently, the reproducibility of coloring with a writing instrument with a light color called a marker pen used for coloring underlines and graphs of documents is poor, and there is a problem that the colored part with the marker pen is reproduced in a muddy color or falls off when copying. there were.

The present invention overcomes the above-mentioned problems, and for example, it is possible to freely perform operations such as erasing a specific color of a document colored with a marker pen or the like, reproducing darkly, or reproducing thinly. Moreover, since a clear image without fog is reproduced at that time-an object is to provide an image forming apparatus.

[0031]

[Means for Solving the Problems] The above-mentioned object is (a)
An original reading unit that scans an original to generate a first digital signal, and (b) processes the first digital signal to correspond to the colors of black and color toners and has a density of more than two levels. a converting means for generating a second digital signal having information, converting means having a conversion table for converting said first digital signal into a second digital signal, (c) said second digital signal to a color toner Given to
A recording signal hand that generates a recording signal by comparing with the obtained threshold value.
And (d) for adjusting the threshold value for each color of toner.
And a recording density input means for inputting from the outside to the color image forming apparatus.

[0032]

The present invention will be described in detail below with reference to examples.

(Embodiment 1) FIG. 1 shows the structure of an image forming apparatus according to the present invention, in which a color image is formed as follows.

In FIG. 1, A is a reading unit and B is a reading unit.
Is a writing unit, C is an image forming unit, and D is a paper feeding unit. 2 is a plan view showing the planar arrangement of the internal elements of the writing unit B, and FIG. 3 is a sectional view showing the structure of the developing device used in the apparatus of the present invention.

In the reading unit A, 1 is a platen glass, and the original 2 is placed on the platen glass 1. The original 2 is illuminated by fluorescent lamps 5 and 6 provided on a carriage 4 that moves on a slide rail 3.
The movable mirror unit 8 is provided with mirrors 9 and 9 ′, moves on the slide rail 3, and in combination with the first mirror 7 provided on the carriage 4, the platen glass 1
The optical image of the upper original 2 is led to the lens reading unit 20.

The carriage 4 and the movable mirror unit 8 are driven in the same direction at speeds of V and 1/2 V by pulleys 11, 12, 13, and 14 driven by a stepping motor 10 via a wire 15, respectively. Standard white plates 16 and 17 are provided on the back surfaces of both ends of the platen glass 1 so that standard white signals can be obtained before the start of scanning the original and after the scanning.

The lens reading unit 20 comprises a lens 21, a prism 22, a first reading substrate 24, a red channel (hereinafter referred to as R-ch) CCD 25, a second reading substrate 26, and a cyan channel (hereinafter referred to as C-ch) CCD 27. It

The original light image transmitted by the first mirror 7, the mirror 9 and the mirror 9'is focused by the lens 21 and is reflected by the dichroic mirror 23 provided in the prism 22.
The ch image and the C-ch image are separated and imaged on the light-receiving surfaces of the R-ch CCD 25 provided on the first reading substrate 24 and the C-ch CCD 27 provided on the second reading substrate 26, respectively. .

As the fluorescent lamps 5 and 6, commercially available warm-color fluorescent lamps are used to prevent a particular color from being emphasized or attenuated based on the light source when reading a color original document, and a high frequency power source of 40 KHz is used to prevent flicker. It is kept warm by a heater using a posistor in order to keep the tube wall at a constant temperature or promote warm-up.

The image signals output from the R-ch CCD 25 and the C-ch CCD 27 are processed by a signal processing unit E which will be described later. In the signal processing unit E, color signals color-separated according to the color of the toner described below are output and input to the writing unit B.

The writing unit B is constructed as shown in FIG. 2, and the laser beam generated by the semiconductor laser 31 is rotationally scanned by the polygon mirror 32 rotated by the drive motor 30, passed through the Fθ lens 33, and reflected by the reflecting mirror 37. The optical path is bent and projected onto the surface of the photosensitive drum 40 to form a bright line 39. 34 is an index sensor for detecting the start of beam scanning, and 35 and 36 are cylindrical lenses for tilt angle correction. Reference numerals 38a, 38b and 38c denote reflecting mirrors which form a beam scanning optical path and a beam detecting optical path.

When the scanning is started, the beam is detected by the index sensor 34, and the modulation of the beam by the first color signal is started. The modulated beam scans on the photoconductor drum 40 that has been uniformly charged in advance by the charger 41. A latent image corresponding to the first color is formed on the drum surface by the main scanning by the laser beam and the sub-scanning by the rotation of the photosensitive drum 40. This latent image is developed by, for example, the developing device 43 loaded with red toner, and a toner image is formed on the drum surface. The obtained toner image, while being held on the drum surface, passes under the cleaning device 46 separated from the surface of the photosensitive drum and enters the next copy cycle. The photoconductor drum 40 is recharged by the charger 41.

Then, the second color signal output from the signal processing section E is input to the writing unit B, and writing is performed on the drum surface in the same manner as in the case of the first color signal to form a latent image. It The latent image is developed by a developing device 44 loaded with a second color toner, for example blue. This blue toner image is formed so as to overlap the already formed red toner image.

Reference numeral 45 denotes a developing device having black toner, which forms a black toner image on the surface of the drum based on a control signal generated by the signal processing section. AC and DC biases are applied to the sleeves of the developing devices 43, 44, and 45, jumping development is performed with two-component toner, and development is performed in a non-contact manner on the grounded photoconductor drum 40.

Details of the developing unit 34 will be described with reference to FIG. 43
a is a toner replenisher, 43b is a sponge roller, 43c and 43
d is a toner stirring member, 43e is a scraper, 43f is a developing sleeve, 43g is a magnet, 43h is an h-cut plate, and 43j.
Is a resistor, 43k is an AC power supply, and 43l is a DC power supply.

The toner supplied from the toner replenishing device 43a is sent to the developing section including the developing sleeve 43f and the developing magnet 43g by the action of the sponge roller 43b and the stirring members 43c and 43d. A cutting plate is provided on the developing sleeve 43f.
A layer of developer 43m composed of toner and carrier is formed whose thickness is regulated to be constant by 43h, thereby developing the latent image formed on the surface of the photoconductor drum 40. 43e is a scraper for scraping off the developer, and scrapes off the developer on the surface of the sleeve 43f after development. The arrow a indicates the moving direction of the developer, and the arrow b indicates the rotating direction of the magnet roller. An AC power supply 43k and a DC power supply 43l are connected to the developing sleeve 43f via a resistor 43j, and the sleeve 43f and the photosensitive drum 40 are connected.
A developing bias is applied during. The material of the photoconductor, the bias voltage, and other image forming conditions will be described in detail later.

The thus-developed toner image according to the first color signal, the toner image according to the second color signal, and the superimposed image of the toner image developed with black toner are fed by the transfer pole 50. It is transferred onto the recording paper 61 sent by the feeding belt 62 and the feeding roller 63 of the set. The transfer paper on which the toner image has been transferred is separated from the photoconductor by the separating electrode 51, and is further conveyed to the fixing device 52 to be fixed and a color hard copy is obtained.

The cleaning device 46 comes into contact with the photosensitive drum 40 after the transfer, and the blade 47 performs cleaning to remove unnecessary toner from the drum surface.

The roller 49 of the cleaning device is for removing a small amount of toner left between the drum surface and the blade when the blade 47 leaves the drum surface in preparation for the next exposure and development after the cleaning. While rotating in the opposite direction to the drum, the contact portion with the drum surface is rubbed to collect the residual toner.

Next, a portion for processing the read signal will be described with reference to FIGS. 4 to 8.

FIG. 4 is a partial sectional view showing details of the reading unit A in FIG. The original image incident on the lens 21 is separated into red and cyan by the dichroic mirror surface 23 of the dichroic prism 22, and the R-ch CCD 25 on the first reading substrate 24 and the Cc on the second reading substrate 26.
h Each is incident on the CCD 27.

The spectral reflection characteristics of the dichroic prism used for color separation are as shown in FIG. In the figure, the vertical axis represents the transmittance (%) and the horizontal axis represents the wavelength (nm). The red component uses transmission and the cyan component uses reflection. The example in the figure shows that the transmittance is about 50% near the wavelength of 600 nm.

The principle of generating a color signal from the color separation information signal in the present invention will be described with reference to FIGS. 6 to 8.

The reflected light image of the original 2 separated into the red component and the cyan component by the dichroic prism 22 is the R-ch CCD2.
5, incident on the C-ch CCD 27 and converted into electric signals. The electric signals output from both CCDs are Amp-R,
Amplified by Amp-C and then analog-digital converter A
/ Dr, A / Dc converted to digital signal and normalized by the output value of the reference color (white). Red component output signal V
r and the cyan component output signal Vc. From the output signals Vr and Vc, the sum signal (Vr + Vc) and the cyan component Vc are (Vr + Vc) in the next color separation signal generator.
The color area designation signal Vc / (Vr + Vc) divided by c) is generated and temporarily stored. The sum signal and the color area designation signal are generated in the signals corresponding to the colors and the densities in the color density signal generating section using a read only memory (hereinafter referred to as ROM).

The relationship between the color difference signal and the luminance signal according to the present invention is shown in FIG. Taking (Vr + Vc) as the luminance signal information on the vertical axis of the graph and Vc / (Vr + Vc) as the color difference signal information on the horizontal axis of the graph, the corresponding position of the input signal is determined by color and density when expressed as the coordinate axis. It The luminance information signal and the color difference signal information have the following properties.

Luminance information signal (Vr + Vc): Vr, Vc (0 ≦ Vr, Vc ≦ 1.
The sum of 0) corresponds to black level = 0 and white level = 2.0, and all the colors exist in 0 to 2.0.

Color difference signal information (Vr / (Vr + Vc), Vc / (Vr + Vc)):
If it is an achromatic color, Vr included in the whole (Vr + Vc),
The Vc component is constant. That is, Vr / (Vr + Vc) ≈ Vc / (Vr + Vc) ≈ 0.5 On the other hand, if it is chromatic, Vr / (Vr + Vc) or Vc / (Vr + Vc) becomes
It is a measure of the hue and saturation of the original, which causes a bias of greater than or less than 0.5. That is, red color 0.5 <Vr / (Vr + Vc) ≦ 1.0 0 ≦ Vc / (Vr + Vc) <0.5 cyan color 0 ≦ Vr / (Vr + Vc) <0.5 0.5 <Vc / (Vr + Vc) Expressed as ≤1.0.

By expressing this as a coordinate system as shown in FIG. 7, it is possible to accurately separate achromatic colors and chromatic colors (red and cyan).

An example in which color gamut division is performed by the above-described separation method is shown in the drawing.

Around Vc / (Vr + Vc) = 0.5 is an achromatic color Vc / (Vr + Vc) <0.5 is a red system Vc / (Vr + Vc)> 0.5 is a cyan system.

Since (Vr + Vc) on the vertical axis corresponds to the reflection density, it can be made to correspond to this output value.

Color difference signal-color in the luminance signal generator,
To generate the density signal, use the ROM (Vr +
An address is designated by Vc) and Vc / (Vr + Vc), and an output corresponding to the combination is generated. FIG. 8 shows a ROM table corresponding to achromatic colors and chromatic colors (red-based colors and cyan-based colors), respectively, in the case where the density signal output obtains a binary value of 0 or 1.

The red table, the cyan table, and the black table in the density signal generator of FIG. 6 are shown in FIG.
It corresponds to the tables shown in (a), (b), and (c).

In FIG. 6, the output of the color difference signal Vc / (Vr + Vc) and the luminance signal (Vr + Vc) generated in the separation signal generator is applied to the red table, the black table and the cyan table at the same time to obtain an achromatic color and a red color. , A color signal output corresponding to any of the cyan colors is generated.

ROM in FIGS. 8B and 8C
The output exists across both gamuts of the table because the gamut separation also expresses that the gamuts overlap each other. For example, an intermediate color between red and cyan such as purple (magenta-purple) It is an attempt to express a mixture of red and cyan in accordance with the color tone. Also, when expressing tea, it is expressed using brat and red.

In the case of FIG. 6, the color signal is also output as the luminance signal. The original image read by the CCD has a color signal and a luminance signal generated for each pixel.

Color Designating Means Color select is selected from blue, black, and black, which are determined by a signal generated from a control unit of the copying machine main body (not shown) and a designation signal generated from a switch of a copying machine operating panel (not shown).
A select signal is generated from a red designation signal (abbreviated as BBR signal), whereby a red buffer, a cyan buffer, and a black buffer are designated and selected. For example, a blue developing device corresponding to a red system signal is operated. When it is present, the signals of the cyan buffer and the black buffer are prohibited and an output signal is sent to the writing unit B to cause the laser diode to emit light to reproduce the image of the red component of the read document. B. Input as color designation signal B. The R signal is used to write and expose each color corresponding to each color developing machine in operation.

FIGS. 9A, 9B and 10 are explanatory views showing the color separation recording signal generator in the embodiment of the present invention.

Since this color separation recording signal generating section is constructed so as not to record the colors in a superposed manner, there is a restriction that, for example, purple or brown cannot be expressed, but the ROM table is held separately for two sheets of red and cyan. It is not necessary and can be put together as one chromatic color table (cyan, red table).

Further, according to FIG. 9A, it is possible to specify four levels of the density of the print to be obtained for each color: no color, light color, standard color, and dark color. In this case, the red table, the cyan table, and the black table, which are accessed by the color difference signal Vc / (Vr + Vc) and the luminance information signal (Vr + Vc), are not 1-bit signals of 0 or 1 but correspond to the four levels of the density. 2-bit grayscale output value is written. Therefore, buffers for 2 bits are used for the buffer 1 and the buffer 2, respectively. By using the configuration shown in FIG. 9A, it is possible to perform colored printing or erasing and printing of a colored portion of an original having a colored portion with a marker pen used as an underline. The color difference-luminance information of the fluorescent marker pen is L1-L in FIG. 9 (b).
2 and the zone between L'1 and L'2, and is erased at the time of copying in a normal monochrome copying machine.

In this embodiment, the fluorescent marker is colored and recorded by changing the threshold value for determining white from L1 to L2 (L'1 to L'2), or from L2 to L1 (L '. The fluorescent marker can be erased by changing from 2 to L'1). This buffer 1, is the output buffer 2 or et al. In view the 9 (a)
A 2-bit grayscale output value corresponding to four levels and a threshold value (threshold value) 7 given as a density defining signal are compared by a comparator, and recording is performed for each color according to the obtained output signal.

The circuit of FIG. 9 (a) can be configured as shown in FIG. In the figure, the color table, that is, the red table and the cyan table have a plurality of ROM tables, and the output levels are made different according to the purpose. The density select switch is set by an operation unit push button (not shown) of the main body of the copying machine, and the stages of "dark", "normal", "light" and "color removal" are designated. When this stage is designated, a table having a threshold level matching each ROM table is selected to emphasize and delete a specific light color.

The image forming conditions in the image forming apparatus of this embodiment were as follows.

Image forming condition (1) Image forming body Photosensitive layer OPC drum diameter 140 mm Linear velocity 58 mm / sec Surface potential Charging potential (potential of non-image area during development) -650 V Exposure area potential -10 V Image exposure condition Light source Semiconductor laser Wavelength 780 ± 20nm Recording density 16dots / mm Developing device Sleeve Made of non-magnetic stainless steel, 18mmφ Linear velocity 20mm / sec, rotating Magnet 8 poles, rotating at 600rpm Magnetic flux density 700 gauss (sleeve surface) Developer carrier Magnetic powder resin dispersion system, average Particle size (weight basis) 20 μm Specific resistance 10 ¹⁴ Ωcm or more Magnetization Approx. 50 emu / g (σ ₁₀₀₀ ) σ ₁₀₀₀ : Magnetization in magnetic flux density of 1000 gauss Toner Red (R) Average particle size (weight basis) 11 μm Average charge amount 10 μc / g (toner concentration 15 wt%) Blue (B) average particle size (weight basis) 11 μm Average charge amount 11 μc / g (toner concentration 15 wt%) Black (K) average particle size (weight basis) 11 μm Average charge amount 12 μc / g (toner concentration 15wt%) Development condition 1.0mm between photoconductor and sleeve Developer layer thickness 0.2-0.8mm (static) (regulated by non-magnetic blade) (common for above) Development bias A (R) DC-500V AC 1.0KV (Actual value) 2KHz B (B) DC-500V AC 1.0KV (Actual value) 2KHz C (K) DC-500V AC 0.8KV (Actual value) 2KHz Development order R → B → K Other process method Transfer Corona transfer fixing Pressurizing with a heating roller Cleaning blade and cleaning roller Photosensitive materials used in the present invention: selenium type, organic compound type, amorphous silicon type, titanium oxide type, zinc oxide type and the like. However, there are many kinds of compounds having various properties, and organic compounds are excellent in the sense that the range of selection is extremely wide.

In the organic compound system, since a charge-generating substance and a charge-transporting substance are often combined to form a photoreceptor,
Each of them is described below.

<Charge Generating Substance> Azo type, for example, JP-A-55-84943, JP-A-55-117151, perylene type, for example, JP-A-55-36849, anthraquinone-type, for example, JP-A-49-48334 Polycyclic quinone type, for example USP 3,992,205 indigoid type, for example JP 47-30331 phthalocyanine type, for example JP 55-59468 quinacridone type, for example JP 47-30332 cyanine type, for example JP 53 -41230, JP-A-54-35734
<Charge-transporting substance> An arylalkane system, for example, JP-A-50-4153, JP-A-5-4153
4-60927 Pyrazoline type, for example JP-A-52-72231, Oxadiazole type, for example, JP-A-50-81151, Hydrazone type, for example, JP-A-54-81847, JP-A-55-745
No. 47 styryl system, for example, JP-A-55-35319, JP-A-55-64243
Cyanine color base, for example JP-A-55-59468, triphenylamine-based, for example USP 3,658,520 phenylenediamine-based, for example JP-A-54-83435, biphenylamine-based, for example JP-B-39-11546, JP-A-39-11546
No. 55-79450 Carbazole type, for example, USP.4,209,327 Desirable combination with organic compound type photosensitive material: It is necessary to have sensitivity to semiconductor laser light and have sufficient color sensitivity in red to infrared. is there. Specifically, for example, as disclosed in JP-A-59-218447, azo pigments or JP-A-59-219752, JP-A-59-214034, and JP-A-59
-155851, JP-A-59-155847, JP-A-55-59468 and JP-A-54-147839, a phthalocyanine compound or complex is used as a charge generating substance.

Further, examples of the charge transport material include those disclosed in JP-A-
Triarylamine derivatives such as those shown in 61-14642 may be used.

Actual Preparation of Photoreceptor: For example, JP-A-52-135
736, JP-A-53-44028, JP-A-53-76036, JP-A-5
A layer construction or manufacturing technique such as 3-58240 may be used.

Developer used in the present invention: On the other hand,
Developers used in such an apparatus include a two-component developer including a toner and a carrier and a one-component developer including a toner. The two-component developer requires control of the amount of toner with respect to the carrier, but has an advantage that triboelectric control of toner particles can be easily performed. Further, especially in a two-component developer composed of a magnetic carrier and a non-magnetic toner, it is not necessary to include a large amount of a black magnetic material in the toner particles, so it is possible to use a color toner that does not cause color turbidity due to the magnetic material. It is possible to form a clear color image.

The two-component developer used in the present invention is particularly preferably composed of a magnetic carrier as a carrier and a non-magnetic toner as a toner as follows.

Carrier: A magnetic material may be used as it is, a resin or the like may be coated on its surface, or a fine powder may be mixed with the resin. The magnetic material is a substance that is extremely strongly magnetized in that direction by a magnetic field. ,
For example, a metal such as iron, cobalt, nickel, etc., an alloy or compound containing an element exhibiting ferromagnetism such as ferrite, magnetite, hematite, and other iron, cobalt, nickel, etc. As a result, an alloy which exhibits ferromagnetism, for example, a Heusler alloy containing manganese and copper such as manganese-copper-aluminum or manganese-copper-tin, or chromium dioxide can be exemplified. The particle size is about 5 μm to 200 μm when it is used as it is, and about the same when the surface is coated with a resin or the like. However, when the fine powder is used, it is desirable that the average particle size is about 0.05 to 3 μm.

Basically, as the carrier-constituting material, those mentioned as the toner-constituting materials described later are used. The carrier particles for increasing delicate dots or lines or gradation are particles composed of magnetic particles and resin, for example, resin dispersion system of magnetic powder and resin or resin-coated magnetic particles, and more preferably Is spherical. Particles having a weight average particle size of preferably 80 μm or less, particularly preferably 40 μm or less and 5 μm or more are suitable. Further, in order to prevent the charge from being injected into the carrier by the bias voltage and attaching the carrier to the image forming surface, or the bias voltage leaking to eliminate the charge forming the latent image, the resistivity of the carrier is set to An insulating material having a resistance of 10 ⁸ Ωcm or more, preferably 10 ¹³ Ωcm or more, and more preferably 10 ¹⁴ Ωcm or more is preferable.

The specific resistance of the toner or carrier was determined by placing the particles in a container having a cross-sectional area of 0.5 cm ² and tapping them, and then applying a load of 1 kg / cm ³ on the packed particles to obtain a load and a bottom electrode. It is determined by applying a voltage that causes an electric field of 10 ² to 10 ⁵ V / cm between and, reading the current value flowing at that time, and performing a predetermined calculation. At this time, the thickness of the carrier particles is about 1 mm. Such a finely divided carrier is prepared by coating the surface of the magnetic material with a resin using the magnetic material and the thermoplastic resin described for the toner,
Alternatively, the particles obtained by making particles with a resin in which magnetic fine particles are dispersed and mixed are well mixed to improve the fluidity of the developer and the charge controllability of the toner to improve the charge controllability of the toner particles or toner particles. In order to prevent aggregation of the carrier from occurring, it is desirable to make the carrier spherical. For such spherical magnetic carrier particles, in the resin-coated carrier particles, magnetic particles should be selected as spherical as possible and the resin should be coated thereon. It is manufactured by using fine particles and then subjecting them to spheroidizing treatment with hot air or hot water after forming dispersed resin particles, or directly forming spherical dispersed resin particles by a spray drying method.

Toner: The toner used in the present invention is manufactured by applying a known method. That is, for example, a binder resin, a fluidity improver, and other substances added as necessary are premixed by using a ball mill or the like and then uniformly dispersed, and then kneaded using a heating roll, and then cooled. And crush, and classify if necessary.

A granulation polymerization method can also be used as a toner manufacturing method. Small particle size For example, toner particle size 1 ~ 10μ
When the toner of m is produced by the granulation polymerization method, a spherical toner is produced, which is applicable to the present invention.

As the binder resin in the present invention,
Resins having various thermoplastic properties can be used, and addition polymerization resins such as styrene resins, styrene-acrylic resins, styrene-butadiene resins, and acrylic resins, condensation polymerization resins such as polyester resins, polyester resins, and polyamide resins. Further, epoxy resin and the like can be exemplified.

Among these resins, styrene o-methylstyrene, a monomer for forming the addition polymerization type resin,
Styrenes such as m-methylstyrene, p-methylstyrene and 3,4-dichlorostyrene; ethylenically unsaturated monoolefins such as ethylene, propylene, butylene and isobutylene; vinyl chloride, vinylidene chloride, vinyl bromide, fluorine Vinyl halides such as vinyl chloride; Vinyl acetates such as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, acrylic Acid n-octyl, dodecyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, n-octyl methacrylate, dodecyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, methacrylic acid Phenyl acid, methacrylic Α-Methylene aliphatic monocarboxylic acid esters such as dimethylaminoethyl and diethylaminoethyl methacrylate; acrylic acid or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile, acrylamide; vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether, etc. Vinyl ethers; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone and methyl isopropenyl ketone; N- such as N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole and N-vinyl pyrrolidone
Vinyl compounds; mono-olefinic monomers such as vinylnaphthalene; propadiene, butadiene, isoprene,
Examples thereof include diolefin-based monomers such as chlorobrene, pentadiene and hexadiene. These monomers can be used alone or in combination of two or more kinds.

Examples of the monomer for forming the condensation type resin include ethylene glycol, triethylene glycol, 1,3-propylene glycol and the like.

Desirable developer: In the present invention, it is preferable to use a carrier having a mean particle size of about 5 to 80 μm, most preferably 5 to 40 μm. Also, the average particle size of the toner particle size of 1 to 20 μm is good and 3 to 15 μm.
The most desirable one. Examples of these developers are, for example, JP-A-53-8360, JP-A-61-9660, JP-A-60-252366, JP-A-61-15156, and JP-A-61-6660.
No. 61-9659, 61-662, 61-966
There are No. 3 etc.

Toner: (1) Thermoplastic resin: Binder 80 to 90 wt% Example: Polystyrene, styrene acrylic polymer, polyester, polyvinyl butyral, epoxy resin, polyamide resin, polyethylene, ethylene vinyl acetate copolymer, or the above Mixture of (2) Pigment: Colorant 0-15wt% Example: Black: Carbon black Cyan: Copper phthalocyanine, sulfonamide dielectric dye Yellow: Benzene derivative Magenta: Rhodamine B lake, Carmine 6B, etc. (3) Charge control agent 0-5wt % Plus Toner: Nigrosine type electron donating dye, other alkoxylated amine, alkylamide chelate, pigment, quaternary ammonium salt, etc.

Minus toner: electron-accepting organic complex, chlorinated paraffin, chlorinated polyester, polyester with excess acid groups,
Chlorinated copper phthalocyanine etc.

(4) Fluidizing agent Examples: Colloidal silica, hydrophobic silica, silicon varnish, metal soap, nonionic surfactant and the like.

(5) Cleaning agent (prevents toner filming on the photoreceptor) Example: Fatty acid metal salt, silicon oxide having organic group on the surface, fluorine-based surfactant, etc.

(6) Filler (for the purpose of improving the surface gloss of an image and reducing raw materials) Example: Calcium carbonate, clay, talc, pigment, etc.

In addition to these materials, a magnetic material may be contained in order to prevent fogging and toner scattering.

As the magnetic powder, 0.1 to 1 μm iron trioxide, γ-ferric oxide, 2 chromium dioxide, nickel ferrite, iron alloy powder and the like are used, and 5 to 5 to the toner is used.
Contains 70 wt%.

The resistance of the toner varies considerably depending on the type and amount of magnetic powder, but in order to obtain a sufficient resistance of 10 ⁸ Ωcm, preferably 10 ¹² Ωcm or more, the amount of magnetic substance should be 55 wt% or less. preferable. Further, in order to maintain a clear color as the color toner, the amount of the magnetic substance is preferably 30 wt% or less, and particularly preferably 5% or less.

Resins suitable for the pressure fixing toner, which is plastically deformed by a force of about 20 kg / cm and adheres to paper, include wax, polyolefins, ethylene vinyl acetate copolymer,
Adhesive resins such as polyurethane and rubber are selected.
Capsule toner can also be used.

A toner can be produced by a conventionally known production method using the above materials.

In the constitution of the present invention, in order to obtain a more preferable image, the toner particle size (weight average particle size) is 50 μm.
It is desirable that it is about m or less. In the present invention, the toner particle size is not limited in principle, but usually 1 to 30 μm is preferably used in view of the resolution, toner scattering and conveyance, but 3 to 15 μm is particularly preferable. The weight average particle diameter is a value measured by a Coulter counter manufactured by Coulter.

In addition to the above-mentioned methods, the granulation polymerization method can be used as the method for producing the toner. Particularly, a toner having a small particle size (10 μm or less, especially 1 to 5 μm) can be sufficiently manufactured by a pulverization method, but a granulation polymerization method is more preferable.

(Embodiment 2) FIG. 12A shows the structure of a second multicolor image forming apparatus of the present invention. In this apparatus, a multicolor image is formed as follows.

A document 218 placed on the document table receives light from an illumination light source 213 which moves in the X direction, and its reflected light passes through a mirror 214, a lens 215, and a color separation filter 216, and a CCD image pickup device 217. Is imaged. CCD image sensor 217
Then, the optical information is converted into a time-series electrical signal and sent to the image data processing unit TR (the image reading unit LE).

The image data processing unit TR forms recorded image data by a preprogrammed procedure. As the image data processing unit TR, the one having the configuration shown in FIG. 13 is used. The configuration of FIG. 13 is the same as the color separation recording signal generation of FIG.
Ikube was changed to YMC. The laser optical system 210 emits laser light based on the recorded image data.

On the other hand, the image forming body 201 is the scorotron band electrode 2
The surface is uniformly charged by 02. Then, the image exposure L from the laser optical system 210 shown in FIG. 3B is applied to the image forming body 201 to form an electrostatic latent image. The electrostatic latent image yellow toner is developed by the developing device A containing the toner. The image forming body 201 on which the toner image is formed is again uniformly charged by the scorotron band electrode 202 and is subjected to image exposure L. The formed electrostatic latent image is developed by the developing device B containing magenta toner. As a result, a two-color toner image of yellow toner and magenta toner is formed on the image forming body. In the same manner, cyan toner and black toner are overlaid and developed to form a four-color toner image on the image forming body 201. The four-color toner image is charged by the pre-transfer belt electrode 209 and transferred to the recording paper P at the transfer pole 204. The recording paper P is separated from the image forming body 201 by the separation pole 205 and fixed by the fixing device 206. On the other hand, the image forming body 201 has the removing electrode 207.
And is cleaned by the cleaning device 208.

The cleaning device 208 has a cleaning blade 281 and a fur brush 282. These are kept out of contact with the image forming body 201 during image formation, and
When a multicolored image is formed on 01, it comes into contact with the image forming body 201 and scrapes off the transfer residual toner. After that, the cleaning blade 281 separates from the image forming body 201, and after a short delay, the fur brush 282 separates from the image forming body 201.

The fur brush 282 is the cleaning blade 2.
When 81 moves away from the image forming body 201, it functions to remove the toner remaining on the image forming body 201.

In this multicolor image forming apparatus, each color of the image forming body 201 is developed one by one, but each image exposure must be started from the same position of the image forming body 201.

Further, none of the developing device, the electrodes other than the strip electrode 202, the paper feed, the paper transport, and the cleaning device 208, which are not used during image formation, do not act on the image forming body 201.

FIG. 1 shows a laser optical system 210 used for exposure.
2 (b). In the figure, 212 is a semiconductor laser oscillator, 235
Is a rotating polygon mirror, and 236 is an fθ lens.

The multicolor image forming apparatus of FIG. 12 (a) uses four types of developing devices, but these may have the same or similar structure, and a cross-sectional view of the first developing device A is representatively shown. Figure
Shown in 14. The developer De is conveyed in the direction of arrow G by rotating the magnetic roller 241 having the number of poles of N and S in the direction of arrow F and the sleeve 242 in the direction of arrow G, respectively. The thickness of the developer De is regulated by the bristling regulation blade 243 during the conveyance, and a developer layer is formed. Developer pool 244
A stirring screw 245 is provided therein so that the developer De is sufficiently stirred, and when the developer De in the developer reservoir 244 is consumed, the toner supply roller 246 is rotated to cause a toner hopper 247. Nokara Toner T
Is replenished.

The gap between the sleeve 242 and the image forming body 201 is kept so that the developer layer on the sleeve does not come into contact with the image forming body. During this period, a reversal development is performed and a DC bias is applied to apply a developing bias to the sleeve. A power source 248 and an AC power source 249 are connected in series. R is a protective resistance.

The developer and photoconductor used in this example are the same as in Example 1, and the image forming conditions are as follows.

Image forming conditions (2) Image forming body Photosensitive layer a-Se system Drum diameter 160 mm Linear velocity 200 mm / sec Surface potential Charging potential (potential of unexposed area during development) 800 V Exposure area potential 0 V Exposure condition Light source Semiconductor laser Wavelength 780 ± 20nm Recording density 16dots / mm Development device Sleeve Made of non-magnetic stainless steel, 20mmφ Linear velocity 200nm / sec Rotating magnet 12 poles, Rotating at 500rpm Magnetic flux density 800 gauss (Sleeve surface) Developer carrier Magnetic powder Resin dispersion system Average particle Diameter (weight basis) 20 μm Specific resistance 10 ¹⁴ Ωcm or more Magnetization Approx. 50 emu / g (σ ₁₀₀₀ ) σ ₁₀₀₀ : Magnetization in magnetic flux density of 1000 gauss Toner Yellow (Y) Average particle size (weight basis) 9 μm Average charge amount 8 μc / G (toner concentration 15 wt%) Magenta (M) average particle size (weight basis) 9 μm Average charge amount 9 μc / g (toner concentration 15 wt%) Cyan (C) average particle size (weight basis) 9 μm average Charge amount 9μc / g (toner concentration 15wt%) Black (K) Average particle size (weight basis) 9μm Average charge amount 10μc / g (toner concentration 15wt%) Development condition Photoconductor-sleeve 1.0mm Developer layer thickness 0.2- 0.6mm (static) (regulated by non-magnetic blade) (common for above) Developer bias A (Y) DC 600V AC 1.2KV (effective value) 2KHz B (M) DC 600V AC 1.2KV (effective value) 2KHz C ( C) DC 600V AC 1.0KV (effective value) 2KHz D (K) DC 600V AC 0.8KV (effective value) 2KHz Development order Y → M → C → K Other process method Transfer Corona transfer Heat with fixing heat roller Cleaning blade and Fur Brush Next, the developing method will be described.

The developing method of the present invention is not particularly limited, but the developer layer on the sleeve does not rub the surface of the image forming body in at least the second and subsequent developments in order to avoid damage to the formed toner image. It is desirable to use a non-contact developing method. This non-contact method creates an alternating electric field in the development area,
The development is performed without rubbing the image forming body and the developer layer. This will be described in detail below.

In the repetitive development using the alternating electric field as described above, the development can be repeated several times on the image forming body on which the toner image is already formed. The developing device of the latter stage that disturbs the toner image formed on the image forming member in the former stage at the time of developing the toner, or the toner already adhering to the image forming member stores a developer of a color different from the developer of the preceding stage. There is a problem of breaking into.
To prevent this, basically, the developer layer on the sleeve is operated without rubbing or contacting the image forming body. For this purpose, the gap between the image forming body and the sleeve when there is no potential difference therebetween is kept larger than the thickness of the developer layer in the developing area on the sleeve. Experiments by the present inventor have revealed that desirable developing conditions exist in order to more completely avoid the above problems and form each toner image with a sufficient image density. This condition is the gap d between the image forming body and the developer transport body in the developing area.
(Mm) (hereinafter sometimes simply referred to as the gap d), it is difficult to obtain an excellent image even if the values of the amplitude Vac of the AC component of the developing bias that generates the alternating electric field and the value of the frequency f (Hz) are independently determined. , These parameters are closely related to each other.

The process will be described below.

The experiment was carried out by using the multicolor image forming apparatus shown in FIG. 12A, and when a two-color toner image was formed by the developing devices A and B, the voltage of the AC component of the developing bias of the developing device B and The influence of parameters such as frequency was investigated.

First, the developer De accommodated in the developing device B is a one-component magnetic developer, which comprises 7.0 wt% of a thermoplastic resin, 10 wt% of a pigment (carbon black), 20 wt% of a magnetic material, and a charge control agent, which are kneaded and ground. The average particle size was set to 15 μm, and a fluidizing agent such as silica was further added. The charge amount is controlled by a charge control agent.

When an experiment was carried out while changing the above conditions, the amplitude Eac of the AC electric field strength (bias voltage V
The relationship between the frequency (ac divided by d) and the frequency can be summarized, and the results shown in FIG. 15 are obtained.

In FIG. 15, the region indicated by I is a region where development unevenness is likely to occur, the region indicated by II is a region where the effect of the AC component does not appear, and the region indicated by III is that the toner image already formed is destroyed. The easy regions, IV and V, are regions where the effect of the AC component appears, sufficient development density is obtained, and the toner image already formed is not destroyed, and V is a particularly preferable region.

Based on the above experimental results, in the present invention, the amplitude of the AC component of the developing bias is Vac (V), the frequency is f (Hz), and the gap between the image forming body 201 and the sleeve 207 is d in each developing step. (Mm) If the development is carried out under the condition of 0.2 ≦ Vac / (d · f) ≦ 1.6, the image forming body 201
It was concluded that the subsequent development can be performed at an appropriate density without disturbing the toner image formed above. In order to obtain a sufficient image density and not disturb the toner image formed up to the previous stage, it is more preferable to satisfy the condition of 0.4 ≦ Vac / (d · f) ≦ 1.2. Furthermore, it is more desirable to satisfy the region of 0.6 ≦ Vac / (d · f) ≦ 1.0, which is in a slightly lower electric field than the saturation of the image density.

Further, in order to prevent uneven development due to the AC component, the frequency f of the AC component is set to 200 Hz or more, and when a rotating magnetic roller is used as a means for supplying the developer to the image forming body 201, the AC component is It is more desirable that the frequency of the AC component is 500 Hz or higher in order to eliminate the influence of the beat caused by the rotation of the magnetic roller.

Next, an experiment was conducted by using the two-component developer in the multicolor image forming apparatus shown in FIG. The developer De accommodated in the developing device B is a two-component developer consisting of a magnetic carrier and a non-magnetic toner, and the carrier is a fine particle having an average particle size of 20 μm, an oxidation of 30 emu / g and a resistivity of 10 ¹⁴ Ωcm. It is a carrier made by dispersing iron oxide in a resin. The toner used was a thermoplastic resin of 90 wt% and a pigment (carbon black) of 10 wt% with a small amount of a charge control agent added, kneaded and pulverized to have an average particle size of 10 μm. The carrier 80
A developer De was prepared by mixing 20 wt% of the toner with respect to wt%. In this case, the toner is negatively charged by friction with the carrier. The developing device A contains a two-component yellow developer.

Similar to the above-mentioned case, when an experiment was conducted under different conditions, the relationship between the amplitude Vac of the AC electric field strength and the frequency f could be arranged and the results shown in FIG. 16 were obtained.

In FIG. 16, a region indicated by I is a region where development unevenness is likely to occur, a region indicated by II is a region where the effect of the AC component does not appear, and a region indicated by III is destruction of the toner image already formed. Areas IV and V where the occurrence is likely to occur are areas where the effect of the AC component appears, sufficient development density is obtained and the toner image already formed is not destroyed, and V is a particularly preferable area.

Based on the above experimental results, the inventor of the present invention, in each developing step, the amplitude of the AC component of the developing bias is Vac, the frequency is f (Hz), and the gap between the image forming body 201 and the sleeve 207 is d.
(Mm), if development is carried out under the condition that 0.2 ≦ Vac / (d · f) {(Vac · d) -1500} /f≦1.0, the image forming member 201
It was concluded that subsequent development can be done at an appropriate density without disturbing the toner image formed above. In order to obtain a sufficient image density and not disturb the toner image formed up to the previous stage, it is more preferable to satisfy 0.5 ≦ Vac / (d · f) {(Vac · d) -1500} /f≦1.0. preferable. In particular, if 0.5 ≦ Vac / (d · f) {(Vac · d) -1500} /f≦0.8 is satisfied, a clearer multicolor image with no color turbidity can be obtained, and even if operated many times. It is possible to prevent mixing of different color toners into the developing device.

Further, in order to prevent uneven development due to the AC component, the frequency of the AC component is set to 200 Hz or higher as in the case of using the one-component developer, and it rotates as a means for supplying the developer to the image forming body 201. Experiments have shown that when a magnetic roller is used, the frequency of the AC component should be 500 Hz or higher in order to eliminate the influence of the AC component and the beat generated by the rotation of the magnetic roller.

The image forming process based on the present invention is as described above, but the toner images formed on the image forming body 201 are not destroyed and the subsequent toner images are sequentially formed on the image forming body at a constant density. In order to develop the image, as the development is repeated, toner with a large amount of charge is sequentially used. The amplitude of the electric field strength of the AC component of the developing bias is gradually decreased. The frequency of the AC component of the developing bias is gradually increased. Or, it is preferable to employ any combination thereof.

That is, toner particles having a large charge amount are more likely to be affected by the electric field. Therefore, if the toner particles having a large charge amount adhere to the image forming body 201 in the initial development, the toner particles may return to the sleeve in the subsequent development. The above is to prevent the toner particles used in the former stage from returning to the sleeve in the latter stage development by using the toner particles having a small charge amount in the initial stage development. Is a method of preventing the toner particles already adhering to the image forming body from returning by sequentially decreasing the electric field strength as the development is repeated (that is, as the development is performed in the subsequent stage). As a specific method for reducing the electric field strength, there are a method of sequentially lowering the voltage of the AC component and a method of widening the gap d between the image forming body 201 and the sleeve 207 in the subsequent development. Further, is a method of preventing the return of the toner particles already adhering to the image forming body 201 by sequentially increasing the frequency of the AC component as the development is repeated.

These methods are effective when used alone, but more effective when they are used in combination, for example, by sequentially increasing the toner charge amount and sequentially decreasing the AC bias as the development is repeated.
Further, when the above three methods are adopted, it is possible to maintain an appropriate image density or color balance by adjusting the DC bias, respectively.

(Embodiment 3) A third embodiment of the present invention will be described.

In this embodiment, only the read signal processing section E of the first embodiment is changed to the signal processing section of FIG.

The signal processing section E of this embodiment is a chromatic red,
The 4-level signals output from the buffer 2 output from the cyan table and the buffer 1 output from the black table are given to the binarized comparator, and a fixed threshold value,
A dither memory in which the dither matrices (a), (b), (c), and (d) are stored can be switched and selected, so that the writing can be performed by the writing unit B that performs writing and recording with a binary signal. This makes it possible to reliably perform recording with a large change range and less dirt and background fog.

[0135]

According to the present invention, the second digital signal is transferred to the toner.
Generate a recording signal by comparing it to a given threshold for color.
In addition, in order to adjust the threshold for each toner color
Since it is input from outside, coloring with a marker pen etc.
To erase or reproduce a specific color of the original
User can freely set the recording density input method
It's easy to do, and it's clear without any fogging.
Images are reproduced.

[0136]

[0137]

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of a color image forming apparatus of the present invention.

FIG. 2 is a plan view of a writing section B in FIG.

FIG. 3 is a sectional view of the developing device in FIG.

FIG. 4 is an explanatory view showing the arrangement of a reading portion in FIG.

FIG. 5 is a graph showing the spectral characteristics of the dichroic prism used in the present invention.

FIG. 6 is a block diagram showing a configuration of a signal processing unit of the present invention.

FIG. 7 is an explanatory diagram showing the principle of color signal processing in the present invention.

FIG. 8 is an explanatory diagram showing an example of a color separation signal generator of the present invention.

9A is a block diagram showing an outline of a signal processing unit of FIG. 1 embodiment of the present invention, and FIG. 9B is an explanatory diagram when a threshold value needs to be changed in FIG. 9A.

FIG. 10 is a block diagram showing a modification of the first embodiment.

FIG. 11 is a block diagram showing a third embodiment of the present invention.

FIG. 12 is a configuration diagram showing a second embodiment of the present invention.

FIG. 13 is a block diagram of an image data processing unit TR according to a second embodiment of the present invention.

FIG. 14 is a sectional view of the developing unit in FIG.

FIG. 15 is a graph showing concentration characteristics when electric field strength and frequency are changed.

FIG. 16 is a graph showing concentration characteristics when electric field strength and frequency are changed.

FIG. 17 is an explanatory diagram showing a conventionally known image forming apparatus.

FIG. 18 is an explanatory diagram showing a conventionally known image forming apparatus.

FIG. 19 is an explanatory diagram relating to a conventional color signal processing method.

FIG. 20 is an explanatory diagram relating to a conventional color signal processing method.

[Explanation of symbols]

 20 Lens reading unit 22 Dichroic prism 23 Dichroic mirror 25, 27 CCD 31 Semiconductor laser 40 Photoconductor drum 41 Charger 43, 44, 45 Developer 46 Cleaning device 50 Transfer pole 51 Separation pole 52 Fixer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shunji Matsuo 2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica Stock Company Examiner Kiyoshi Baba (56) References JP 57-44825 (JP, A) JP 58 -211168 (JP, A)

Claims (1)

[Claims] 1. (a) a document reading means for scanning a document to generate a first digital signal; (b) processing the first digital signal to correspond to black and color toner colors, and a converting means for generating a second digital signal having more graduated density information than binary converting means having a conversion table for converting said first digital signal into a second digital signal, (c) said first 2 Apply digital signal to toner color
A recording signal hand that generates a recording signal by comparing with the obtained threshold value.
And (d) for adjusting the threshold value separately for each color of toner.
A color image forming apparatus , further comprising: a recording density input means for inputting from outside .