JPH0535038A - Electrophotographic copying device - Google Patents

Abstract

PURPOSE:To improve consecutive gradation and the reproducibility of a highlight part in forming an electrophotographic color image by a digital exposing system or an analog exposing system and to always form a high-quality color image. CONSTITUTION:Two developing devices in which toner having different coloring density is stored are provided for every color. Namely, a cyan developing device 3C is constituted of a cyan developing device 3Ct in which the toner having thin density is stored and a cyan developing device 3Cc in which the toner having thick density is stored; a magenta developing device 3M is constituted of a magenta developing device 3Mt in which the toner having thin density is stored and a magenta developing device 3Mc in which the toner having thick density is stored; a yellow developing device 3Y is constituted of a yellow developing device 3Yt in which the toner having thin density is stored and a yellow developing device 3Yc in which the toner having thick density is stored; and a black developing device 3BK is constituted of a black developing device 3BKt in which the toner having thin density is stored and a black developing device 3BKc in which the toner having thick density is stored.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention forms a latent image on an electrophotographic photosensitive member by a digital exposure system or an analog exposure system,
The present invention relates to an electrophotographic apparatus such as a color copying machine or a color printer which produces a color image using toners of a plurality of colors.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a conventional digital color electrophotographic apparatus such as a color copying machine. In this example, the color original 11 includes the illumination light source 9 and the light receiving element 10.
It is scanned and read by and converted into an electric signal. This electric signal is converted again into color-separated digital signals corresponding to the four color toners of cyan, magenta, yellow and black.

The surface of the photosensitive drum 1 made of an electrophotographic photosensitive member is previously cleaned by a blade cleaner 5, and the pre-exposure lamp 12 and the pre-electrifier 13 remove the influence of the previous image formation on the photosensitive member. . Next, the photosensitive drum 1 is uniformly charged by the primary charger 6 to bring the surface of the photosensitive member to a uniform potential. Subsequently, on the photosensitive drum 1, the laser beam PWM-modulated by the laser beam scanner 2 is scanned and exposed on the basis of the color-separated electric signal, and an electrostatic latent image is formed.

The developing device 3 includes a cyan developing device 3C, a magenta developing device 3M, a yellow developing device 3Y and a black developing device 3B.
The developing devices made of K and corresponding to the colors of the electrostatic latent images move to directly below the photosensitive drum 1, and the latent image on the photosensitive drum 1 becomes a visible image, that is, a toner image.

On the other hand, the transfer material, for example, the transfer paper 14 contained in the cassette is sent to the transfer device 4 by the sending roller 15. In this example, the transfer device 4 is a transfer drum having a peripheral surface provided with a dielectric sheet, and the transfer paper 14 is adsorbed and carried on the transfer drum 4 by an adsorbing corona discharger 16 and is exposed to light by the action of the transfer corona discharger 7. The toner image on the drum 1 is transferred to the transfer paper 14.

The transfer paper 14 is adsorbed and held until the four color toner images are sequentially transferred, and when the transfer is completed, the transfer paper 14 is separated from the transfer drum 4 by the operation of the separation claw 17. The separated transfer paper 14 is sent to the heating roller fixing device 8 by the conveyor belt 18 to fix the image.

After the fixing is completed, the transfer paper 14 is discharged to the tray 19. The toner remaining on the surface of the photosensitive drum 1 after the transfer is cleaned by the blade cleaner 5 and the next image forming cycle is started.

In order to obtain continuous gradation in the color electrophotographic apparatus having such a structure, the LUT is made to correspond based on the density data of each pixel of each color obtained by the light receiving element 10,
By changing the voltage and changing the scanning width of the laser beam scanner 2 within a unit pixel in accordance with the voltage, so-called "pulse width modulation (PWM)" is used to change the reflection optical density by changing the area, thereby producing continuous gradation. Is getting

[0009]

However, in order to obtain a high maximum density in the solid part, the developer, which is usually used in the developing device, has a high maximum density in each solid portion, and the covering power is large. Therefore, when the image of the low density portion is magnified and observed, the image has thin and high density pixels, and it is recognized as an image without discontinuity and lacking in smoothness. or,
Such an image also has a problem in reproducibility of the highlight portion.

Furthermore, the image obtained by the above method is again
When reproduced by the same method, since the low-density portion is an aggregate of thin lines, "moire" may be formed and the image quality may be significantly deteriorated depending on the scanning pitch and angle of the image reading apparatus.

Further, regarding the properties of the developer used, that is, the toner, the relationship between the toner particle size and the image quality is examined. The particle size of the toner that is normally used is the peak of the average particle size. , But if this distribution is wide,
Toner with a large particle size is apt to scatter during transfer, which causes conspicuous roughness in the highlight portion of the image.
The toner having a small particle size is often attached to the magnetic particles so as not to be separated, and the magnetic particles cannot efficiently give the triboelectric charge to the toner, and scattering and fogging from the developing device increase. Therefore, the distribution should be narrow. As a result, in practice,
At present, a particle size of about 10 μm is used in order to appropriately reproduce fine dots and obtain a high maximum density.

In the conventional digital exposure type electrophotographic apparatus, since such toner is used, there is a problem in continuous gradation, and the highlight portion image is not fine and lacks smoothness. It has the disadvantage of being visible.

On the other hand, in the case of an analog exposure type electrophotographic apparatus, a screen for generating halftone dots is installed on the optical paths of the photoconductor and the original at the time of exposure to reproduce continuous gradation and highlight portions. There is a method of improving the property, and another method is to control the primary charging voltage and the exposure amount of the photoconductor to separate the low-density part and the high-density part, perform exposure and development, and superimpose them on the same transfer paper. Although the gradation effect is improved by using the superimposing effect of transfer, ideal characteristics are not obtained by any of the methods.

Therefore, an object of the present invention is to solve the drawbacks of continuous gradation and reproducibility of highlight portions in electrophotographic color image formation by digital exposure method or analog exposure method, and particularly reproducibility of low density portion. That is, it is an object of the present invention to provide a color electrophotographic apparatus capable of improving the reproducibility of a highlight portion and always forming a high quality color image.

[0015]

The above object can be achieved by a color electrophotographic apparatus according to the present invention. In summary,
The present invention relates to an electrophotographic apparatus for forming a latent image on an electrophotographic photoreceptor and producing a color image by using toners of a plurality of colors, and at least one of the plurality of colors used has a plurality of different properties. The electrophotographic apparatus is characterized in that an image is produced using toner. Preferably, the plurality of toners having different properties are toners having different coloring concentrations or average volume particle diameters.

According to a preferred embodiment of the present invention,
The toner of each color is stored in the corresponding developing device.
Alternatively, it is also possible to store a plurality of toners in a plurality of containers provided in one developing unit and select and use any toner. A plurality of different toners may be mixed and contained, and the toners may be selectively used to develop the latent image.

[0017]

Embodiments of the electrophotographic apparatus of the present invention will now be described in more detail with reference to the drawings.

Embodiment 1 FIG. 1 shows a digital color electrophotographic apparatus which is a first embodiment of the present invention. The basic structure of the electrophotographic apparatus of this embodiment is the same as that of the conventional apparatus shown in FIG. 2, and only the structure of the developing device is different. Therefore, members having the same configurations and functions are designated by the same reference numerals, and detailed description thereof will be omitted.

According to the present embodiment, there are provided two developing devices containing toners having different coloring densities for respective colors.

[0020] That is, the cyan developing device 3C is cyan developing device 3C _c containing a dark thin cyan developer 3C _t and concentrations toner accommodating the density toner; magenta developing device 3
M is a magenta developing unit 3M containing a toner of low density
Magenta developer 3M containing _t and high density toner
_c; yellow developing device 3Y, the yellow developing unit 3Y _c accommodating the dark toners yellow developing unit 3Y _t and the concentration which accommodates a thin toner density; black developing device 3BK is black developer accommodating the thin toner density 3BK _t and a black developing device 3BK _c containing a high density toner.

FIG. 3 shows a laser beam exposure control block diagram for forming a color image.

An electric signal R obtained by color separation of a color original,
G and B are converted into cyan, magenta, and yellow density signals C _O , M _O , and Y _O by the CMY conversion unit 31. For example _{C O = -log 10 R, M} O = -log 10 G, Y O = -l
A process called og ₁₀ B is performed.

Next, in the under color removal circuit (UCR) 32, it is determined whether or not to use black. If black is used, the black component is subtracted from the other C _O , M _O and Y _O. Get burned.

[0024] For _{example, BK 1 = α {M in} (C O, M O, Y O)} a + beta, greater than the value L _B there is BK _1, i.e., BK
When ₁ ≧ L _B uses black, and _{C 1 = C O -BK 1 M} 1 = M O -BK 1 Y 1 = Y O -BK 1.

[0025] Also, when BK ₁ <L _B does not use black, and _{C 1 = C O M 1 =} M O Y 1 = Y O.

Further, the masking circuit 33 carries out a masking process in consideration of the unnecessary absorption of toner, and the densities C ₂ , M ₂ , Y ₂ and BK _{2 of} each color are obtained. This processing generally uses the following matrix.

[0027]

[Equation 1]

The coefficient M _ij of the matrix is obtained by processing the data obtained by actually reproducing the color by the least square method.

Then, in the editing process 35, the densities C ₂ of the respective colors,
In the density range lower than a certain boundary density according to M ₂ , Y ₂ and BK ₂ , the toner of low density is used and the corresponding LUT 34
To _C3t , _C3c , M to the pulse width converter 36.
_3t , M _3c , Y _3T , Y _3c , BK _3t and BK _3c are sent out.

FIG. 4 shows conversion characteristics from image input of any one color to output.

The quadrant I is a characteristic that optical density is converted into an electric signal. Quadrant II is a LUT for converting so that the final tone reproduction characteristics (quadrant IV) can be reproduced 1: 1.
Indicates. Quadrant III shows the properties that are transformed by the processes of exposure, development and fixing.

In the present invention, a concentration range lower than a certain concentration A and a concentration range higher than a certain concentration A are separated, and the concentration A from the concentration 0.0 on the low concentration side is reduced.
Up to the LUT of the solid line part of the curve B in the II quadrant,
A straight line F is obtained in the tone reproducibility of the fourth quadrant according to the conversion characteristics of the process when the low density toner in the solid line portion of the curve D of the third quadrant is used. On the other hand, from the density A on the high density side to the maximum density of the original, the L of the solid line part of the curve C in the second quadrant
Based on the conversion characteristics of the process when using the UT and using the high density toner in the solid line part of the curve E in the third quadrant,
In the tone reproduction characteristic of the IV quadrant, the straight line G is obtained, and therefore, the straight line F and G provide the ideal tone reproduction characteristic.

The above conversion is performed for each color having a plurality of toners having different densities. By this method,
By increasing the area of the pixel in the low density area and decreasing the density per unit area of the pixel, an effect similar to that of the density modulation method can be obtained and the reproducibility of the low density area is improved. Reproducibility is also increased.

In this embodiment, two kinds of toners of different shades are used for each color, and the number of developing devices used is twice as large as that of the conventional device. However, with respect to yellow, which has little visual effect, the developing device space and cost are reduced. In this respect, it is not necessary to use two kinds of toner, and therefore, one developing device can be used.

FIG. 5 shows another embodiment of the developing device which can be used in the apparatus of the present invention. In the above embodiment, the number of developing devices is increased as compared with the conventional device, which is not preferable in terms of space and cost. The developer unit of this embodiment can provide an improvement in this respect.

That is, the developing device 3'shown in FIG. 5 has a container 52 for containing a developer made of a mixture of toner and magnetic particles having a low concentration, and a developing device made of a mixture of toner and magnetic particles having a high concentration. A container 53 containing the agent, a developing sleeve 56 rotating in the direction of arrow a in synchronism with the photosensitive drum 1, screw type agitators 54 and 55 for agitating the developer in the containers 52 and 53, and A movable shutter 57 is provided to prevent the developer in the other container from being mixed when the developing operation is performed using the one container.
The developing device 3'having such a structure is provided for each color.

In the developing device 3'having such a structure, when the use of the developer is changed, the developing sleeve 56 is rotated and the developing sleeve cleaner blade 58 is connected to the developing sleeve 56.
To remove the developer on the developing sleeve 56. The removed developer is returned to the corresponding developer container, and the developing sleeve cleaner blade 58 separates from the developing sleeve 56 when the removal of the developer is completed.

The photosensitive drum 1 based on the image information of the low density portion
While the top exposure is taking place, the agitator 54 and the developing sleeve 56 in the container 52 of developer used rotate.
A developer containing a toner having a low density is uniformly applied to the developing sleeve 56. At this time, the shutter 57 covers the high-concentration side container 53 to prevent the developer in the container 53 from mixing with the developer in the container 52. After the development of the low-density portion is completed in this state, the developing sleeve cleaner blade 58 again cleans the developing sleeve to prevent the developer from being mixed, and the shutter 57 is used to close the container 5 on the low-density side.
Cover 3.

Based on the image information of the high density portion, the agitator 55 and the developing sleeve 56 rotate during the exposure on the photosensitive drum to uniformly develop the developer containing the high density toner. It is placed on No. 56 and developed. At this time, the shutter 57 covers the container 52 on the high concentration side.

By this method, the space occupied by the developing device is greatly reduced as compared with the developing device used in the previous embodiment, and the size of the apparatus can be reduced.

FIG. 6 shows still another embodiment of the developing device that can be used in the present invention. According to the developing device of this embodiment, the mechanical complexity of the developing devices of the first and second embodiments is eliminated.

That is, in the developing unit 3 "of the third embodiment, toners having different coloring densities and having opposite polar charges are put in the same developing container 65.

That is, the developing device 3 "has a container 65, a developing sleeve 61, a charging plate 62, and a stirring screw 63. In the developing device of this embodiment, toner having a low color density is negatively charged, and the color density is low. Assuming that the high toner is positively charged, the photosensitive drum 1 is negatively charged, and a jumping developing system using a two-component developer is adopted, the image forming process according to the present embodiment will be described. .

FIG. 7 shows a reproduction process of low density gradation.

First, initial charging is performed by the primary charger 6 to uniformly charge the photosensitive drum 1 (FIG. 7).
(I)). Then, image exposure by laser output of the low density gradation area portion is performed as determined in the first embodiment,
An electrostatic latent image is formed on the photosensitive drum 1 (FIG. 7B).

On the other hand, the developing sleeve 61 of the developing device 65 is positively charged so that the toner having a low negative charge density is easily attached, and further, the charging plate is separated to separate the toner having a high positive charge density from the developing sleeve 61. 62 is negatively charged and positively charged toner is applied to the developing sleeve 6
1 Separate from above.

In this way, reversal development is performed in a state where the negatively charged toner having a low density is uniformly attached to the developing sleeve 61, and the low density portion gradation area is reproduced (FIG. 7).
(C)).

FIG. 8 shows a reproduction process of the high density gradation part.

First, initial charging is performed by the primary charger 6 to uniformly charge the photosensitive drum 1 (FIG. 8).
(I)). Then, background exposure is applied to form an electrostatic latent image based on the laser output signal of the high density gradation area portion as determined in the first embodiment (FIG. 8B).

On the other hand, the developing sleeve 61 of the developing device 65 is negatively charged, and the charging plate 62 is positively charged, so that only toner having a high positively charged concentration is generated.
It is applied to the developing sleeve 61. Normal development in this state reproduces the high density gradation region (see FIG. 8).
(C)).

With the developing devices according to the second and third embodiments shown in FIGS. 5 and 6, the same number of developing devices as the conventional one can be used to obtain richer continuous tone expression, particularly reproducibility in the low density portion, that is, It is possible to improve the reproducibility of the highlight part. It is preferable in terms of color reproducibility that the toner of the lower layer can be seen through by arranging the toner of low density and good transparency in the upper layer of the transfer paper 14 in the order of superimposing the toner.

Embodiment 2 FIG. 9 shows a digital color electrophotographic apparatus which is a second embodiment of the present invention. The electrophotographic apparatus of this embodiment is shown in FIG.
The apparatus is the same as the apparatus of the first embodiment shown in the above, and only the properties of the developer accommodated in the developing device are different. Therefore, members having the same configurations and functions are designated by the same reference numerals, and detailed description thereof will be omitted.

According to the present embodiment, there are provided two developing units containing toners having different particle diameters for each color.

Prior to the detailed description of this embodiment, the relationship between the toner particle size and the color image quality will be briefly described.

As described above, in the digital exposure type color electrophotographic apparatus, "pulse width modulation (PWM)" is used.
By changing the reflection optical density by changing the area due to
Although a continuous gradation is obtained, the laser beam when the pulse width (t) of the PWM signal becomes an extremely short time such as 10 ns, the beam barely emits to form a latent image. In order to form a toner image by electrophotographic development, it is in an extremely unstable region, and it is usually difficult to achieve stable density formation.

As described above, in the gradation expression by the PWM method, there is a limit to the minimum pulse width capable of forming the density by the PWM method. If this limit is set to t = 10 ns, it is difficult to reproduce gradation with a pulse width (highlight portion) narrower than this value, and it is possible to obtain a high-quality image that faithfully reproduces the highlight portion. It is difficult. In the narrow pulse width part, light intensity modulation is consequently performed,
As the spot diameter becomes smaller, the peak value of the electric potential at the center of the spot also becomes lower. That is, if the spot diameter is small,
Even if the charges on the surface are the same, the apparent potential decreases.

On the other hand, as the particle size of the toner becomes smaller, the influence of the surface area becomes larger than the volume and the weight thereof. Therefore, if the toner is the same material, the influence of the electric charge becomes large. Therefore, even if the potential of the latent image is apparently small, the toner having a small particle size is more likely to be developed in the portion where the electric charge exists.

Further, the toner having a small particle diameter becomes a thin layer on the paper after the transfer, and the attracting force with the paper is large. Therefore, even if the toner image is exposed to the transfer electric field a plurality of times, the scattering does not easily occur.

FIG. 10 shows the minimum reproduced dot diameter with respect to the toner volume average particle diameter. From this figure, as the toner volume average particle size decreases, the minimum reproducible dot diameter that can be reproduced also decreases, and gradation reproducibility in highlight areas with low image density and high-definition images with less blurring and blurring can be obtained. I understand.

In the present invention, the volume distribution and volume average particle diameter of the toner are those measured by the following measuring method, for example.

As a measuring device, a Coulter counter T
Using an A-II type (manufactured by Coulter), an interface (manufactured by Nikkaki) that outputs a number average distribution and a volume average distribution and a CX-i personal computer (manufactured by Canon) are connected, and the electrolyte is primary sodium chloride. Using 1% NaC
l Prepare an aqueous solution.

As a measuring method, the electrolytic aqueous solution 100 to 1 is used.
0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) as a dispersant is added to 50 ml, and 0.5 to 50 mg of a measurement sample is further added.

The electrolytic solution in which the sample was suspended was placed in an ultrasonic disperser 1
Disperse for ~ 3 minutes, then use Coulter Counter T
According to the type A-II, a particle size distribution of particles of 2 to 40 μm is measured using a 100 μm aperture as an aperture to obtain a volume distribution.

The volume average particle size of the sample can be obtained from the obtained volume distribution.

From the characteristics shown in FIG. 10, particularly when a toner having a volume average particle diameter of 6 μm or less is used, dots of 50 μm or more are faithfully reproduced, and the shading in a highlight portion having a low image density is excellent in reproducibility. Have an impact. However, a toner having a volume average particle size of 6 μm or less has a poor covering power and a low maximum density.
It is understood that the reproducibility range of the shadow portion on the high density side becomes narrow.

On the other hand, in the toner having a volume average particle size of 10 μm or more, as shown in FIG. 10, dots of 80 μm or less have poor reproducibility, but the reproducibility and shadow of the shadow portion on the high density side composed of dots of 80 μm or more are high. It can be seen that the maximum concentration is obtained.

Therefore, a high-quality color reproduced image can be obtained by using a small particle size toner on the low density side and using a large particle size toner on the high density side.

When the above-mentioned facts are expressed with respect to the volume average particle diameter of the toner and the toner particle diameter, the following relationship is derived.

That is, the volume average particle diameter and toner particle diameter of the toner on the highlight side are M ₁ and r ₁ , respectively, and the volume average particle diameter and toner particle diameter of the toner on the shadow side are M ₂ and M ₂ respectively.
If you have a r _{2 and, M 1/2 <r 1} <3 / 2M 1, M 2
90% by volume or more of the toner is included in the range of / 2 <r ₂ <3 / 2M ₂ , and 0 <M ₁ / M ₂ <1 between M ₁ and M ₂ .
Preferably, 2/15 <M ₁ / M ₂ <4/5 is established.

Further, the range of 0.5 μm ≦ M ₁ ≦ 15 μm, preferably 1 μm ≦ M ₁ ≦ 10 μm is satisfied, and M ₁ <
The relationship of M ₂ is established.

As the binder resin used in the toner, a styrene-based copolymer such as a styrene-acrylic acid ester resin or a styrene-methacrylic acid ester resin, or a polyester resin is used.

Now, returning to FIG. 9, the digital color electrophotographic apparatus according to this embodiment will be described. As described above, according to the present exemplary embodiment, the two developing devices that store toners having different particle diameters for each color are provided.

That is, the cyan developing device 3C includes a cyan developing device 3C _S containing a small particle size toner and a cyan developing device 3C _L containing a large particle size toner; a magenta developing device 3M.
The magenta developing unit 3M _L accommodating the magenta toner developing unit 3M _S and large particle size which accommodates the toner of small particle size; yellow developing device 3Y, the yellow developing device 3Y _S and containing a toner having a small particle size The yellow developing device 3Y _L containing a large particle size toner; the black developing device 3BK is composed of a black developing device 3BK _S containing a small particle size toner and a black developing device 3BK _L containing a large particle size toner. To be done.

In this embodiment, as shown in FIG. 11, a toner having an average volume particle diameter of 5 μm is used as the small particle diameter toner, and an average volume particle diameter of 12 μm is used as the large particle diameter toner.
I used the one. The manufacturing method is as follows.

The following materials were melt-kneaded, the melt-kneaded product was cooled, the cooled product was crushed, classified by a fixed wall air classifier, and further classified by a multi-division classifier utilizing the Coanda effect to obtain a volume average particle size. Two types of toner having a diameter of 5 μm and 12 μm were prepared.

[0076]   ・ By condensing propoxylated bisphenol and fumaric acid     100 parts by weight of the obtained polyester resin   (Weight average molecular weight 3300)   ・ Negative charge control agent     (Metal complex of dialkyl-substituted salicylic acid) 4 parts by weight   ・ Colorant 3 parts by weight

The following are used as the above colorants.

Black: a mixture of pigment yellow pigments, pigment red pigments and pigment blue pigments cyan: phthalocyanine pigments magenta: rhodamine pigments yellow: pigment yellow pigments

As in the first embodiment, the photosensitive drum 1 is similar to that shown in FIG.
Also, the laser beam PWM-modulated by the laser scanner 2 is scanned and exposed by the laser beam exposure control as shown in FIG. 4 to form an electrostatic latent image.

Then, for each color, in a density range lower than a certain boundary density, development is carried out with a toner having a small particle size, and from a certain density to a maximum density is developed with a toner having a large particle size.

According to this method, the highlight side is reproduced by the small particle size toner having good reproducibility of the fine dots, and the shadow side is reproduced by the large particle size toner capable of obtaining a high maximum density. Due to its high price, the gradation reproduction range is wide, and a comprehensive improvement in image quality was obtained.

In this embodiment, two kinds of toner having a small particle diameter and a large particle diameter are used for each color, but a color such as yellow, which has little visual effect, is one kind of toner having an average volume particle diameter of 8 μm. You can also respond.

Furthermore, also in this embodiment, the developing devices according to the second and third embodiments shown in FIGS. 5 and 6 can be used, and the number of developing devices is the same as that of the conventional one. It is possible to improve continuous tone expression, particularly reproducibility in a low density portion, that is, reproducibility in a highlight portion.

In this embodiment, a combination of toners having different particle diameters for all colors was used. However, a combination of toners having different coloring densities for one color may be used together with a combination of toners having different particle diameters for another color. It is possible.

Further, it is possible to combine a toner having a high color density and a toner having a small particle size, or a toner having a light color density and a toner having a large particle size.

Third Embodiment In the second embodiment, the digital color electrophotographic apparatus has been described. However, the present invention can be suitably embodied in an analog exposure type color electrophotographic apparatus and reproduces a minute image in a highlight portion. The property is improved by using the toner having a small particle size, and the covering power is increased, the maximum density is increased, the reproduction density region is widened, and the image quality is improved even in the shadow portion due to the large particle toner.

In this embodiment, as shown in FIG. 12, the present invention shows a color electrophotographic apparatus using an analog exposure system.

The electrophotographic apparatus of this embodiment has the same basic mechanical structure as that of the electrophotographic apparatus of Embodiment 2 after exposure,
Only the exposure means is different. Therefore, members having the same configurations and functions are designated by the same reference numerals, and description thereof will be omitted. Also, the same toner as in Example 2 was used.

In this embodiment, the original 11 is illuminated by the illumination light source 9 and is exposed on the photosensitive drum 1 through the reflecting mirrors 93, 94, the optical lens 91, the reflecting mirror 95, the color separation filter 97, and the reflecting mirror 96. To be done.

FIG. 13 shows the reproduction characteristics of the present invention.
When reproducing on the highlight side, the optimum γ
The photosensitive characteristics are set under such charging and exposure conditions that
Further, a toner having a small particle size is used, and the image characteristic is obtained by the developing characteristic. The image characteristics are designed so that the characteristics on the highlight side are optimum, and the fineness and smoothness of the image are reproduced by the small particle size toner.

On the other hand, on the shadow side, the photosensitive characteristics are set under the charging and exposure conditions such that the optimum γ is achieved in the high density region. Then, with the toner having a particle diameter larger than that used on the highlight side, the image characteristic is obtained by the developing characteristic. As for image characteristics, a large maximum particle size toner having a large covering power is used, so that a sufficient maximum density can be obtained.

By superimposing the image characteristics, the gradation from the highlight to the shadow is adjusted, and in the highlight part, the texture is fine and smooth, and in the shadow, the maximum density is high and the image quality is high. An image was obtained.

This image forming process is performed for all four colors, and the gradation reproduction of each color is optimally performed, so that a high-quality color image with good color balance was obtained.

Furthermore, also in this embodiment, the developing devices according to the second and third embodiments shown in FIGS. 5 and 6 can be used, and the number of developing devices is the same as that of the conventional one. It is possible to improve continuous tone expression, particularly reproducibility in a low density portion, that is, reproducibility in a highlight portion.

[0095]

As described above, according to the color electrophotographic apparatus of the present invention, the gradation reproduction of the conventional color electrophotographic apparatus could not successfully reproduce the gradation of the low density portion and the highlight area. On the other hand, by using a low density or small particle diameter toner having a low covering power, the gradation reproducibility and highlight reproducibility of the low density portion can be greatly improved. Furthermore, since the area on which the toner is on the transfer material can be increased, direct reflection from the transfer material is reduced, and even when toner of different colors is superposed, the density of the toner in the upper layer is If a thin toner is placed, the color of the lower layer can be transmitted, which is advantageous in terms of color reproducibility.

[Brief description of drawings]

FIG. 1 is a structural cross-sectional view of an embodiment of a digital color electrophotographic apparatus of the present invention.

FIG. 2 is a structural cross-sectional view of an example of a conventional digital color electrophotographic apparatus.

FIG. 3 shows an exposure control block diagram for forming a color image according to the present invention.

FIG. 4 shows a conversion characteristic diagram for forming a color image according to the present invention.

FIG. 5 is a sectional view showing another embodiment of a developing device that can be used to realize the present invention.

FIG. 6 is a sectional view showing still another embodiment of a developing device that can be used to realize the present invention.

FIG. 7 is a diagram illustrating a potential of a photosensitive drum for explaining an image forming process according to the present invention.

FIG. 8 is a diagram showing a potential of a photosensitive drum for explaining an image forming process according to the present invention.

FIG. 9 is a sectional view of the configuration of a second embodiment of the digital color electrophotographic apparatus of the present invention.

FIG. 10 is a graph showing the relationship between the average toner particle size and the minimum reproduced dot.

FIG. 11 is a graph showing the relationship between the volume particle size and the volume distribution rate of the toner used in the present invention.

FIG. 12 is a sectional view showing the configuration of an embodiment of an analog color electrophotographic apparatus of the present invention.

FIG. 13 is a diagram showing reproduction characteristics of the present invention.

[Explanation of symbols]

1 Photosensitive drum (electrophotographic photoreceptor) 2 leather beam scanner 3, 3 ', 3 "developer

Claims (2)

[Claims] 1. An electrophotographic apparatus for forming a latent image on an electrophotographic photoconductor and producing a color image using toners of a plurality of colors, wherein at least one of the plurality of colors used has a plurality of different properties. An electrophotographic apparatus characterized in that an image is produced by using the above toner. 2. A plurality of toners having different properties are toners having different coloring density or average volume particle diameter.
Electrophotographic device.