JPH04177276A - Image forming device and developing device - Google Patents

Abstract

PURPOSE:To keep the maximum concentration of image and improve a realization of tone at a low concentration side by a method wherein a latent image is formed on an image carrier in such a way a toner image formed with the latent image has a plurality of different concentrations divided in it and a plurality of kinds of developers having different mean particle diameter having the same number as the divided number of concentration are used to develop the latent image and to form the image. CONSTITUTION:Two sets of developing devices 3BS, 3BL; 3YS, 3YL; 3MS, 3ML; 3CS, 3CL are provided for each of colors, respectively, a latent image is formed in such a way as the toner image formed by the latent image is divided into a plurality of different concentrations. The latent image is developed using plural kinds of developers having different mean particle diameter in the same number of the divided concentrations. With such an arrangement, it is possible to keep the maximum image concentration and at the same time to improve a tone realization at a low concentration side.

Description

DETAILED DESCRIPTION OF THE INVENTION Part 1 of the present invention is to form a latent image on an image carrier and develop it with a developer.
The present invention relates to an electrophotographic image forming apparatus that obtains images by visualizing them, and a developing device suitable for use therein. The above-mentioned image forming apparatuses include black-and-white, monochrome, or full-color electrophotographic copying machines, printers,
There are also various other recording devices.

[Startup] Various electrophotographic multicolor image forming apparatuses have been proposed in the past. FIG. 4 is a schematic diagram showing a multicolor electrophotographic apparatus equipped with a typical developing device called a so-called mobile developing device.

The original 11 placed on the original table 20 is exposed to light by the illumination light source 9, the reflected light is read by the light receiving element 10, and the image density of the original 11 is converted into an electrical signal by photoelectrically converting it by a processing device (not shown). do. This converted electrical signal is further separated into electrical signals corresponding to the four developer colors of cyan, magenta, yellow, and black.

On the other hand, the photosensitive drum 1 is cleaned of residual toner on its surface by a cleaning device 5 in advance, and after the influence of the electrostatic latent image formed last time is removed by a pre-exposure lamp 12 and a pre-static eliminator 13, the photosensitive drum 1 is subjected to -wide charging. The surface is uniformly charged by being uniformly charged by the container 6. Based on the electrical signals corresponding to the color-separated cyan color described above, the exposure light source 2 consisting of a laser beam exposure device or the like is modulated and scanned to expose the photosensitive drum 1, thereby producing cyan on the photosensitive drum 1. An electrostatic latent image corresponding to the color is formed. Next, the electrostatic latent image on the photosensitive drum 1 is developed by the cyan developing device 3C, which has been moved to the developing position below the photosensitive drum 1 in advance, and a cyan toner image is formed on the photosensitive drum 1. .

Further, the recording material 14 housed in the cassette 14a is taken out from the cassette 14a by the pickup roller 15,
The image is transported to the transfer drum 4 via a transport path. Transfer drum 4
The drum is constructed by stretching an insulating resin sheet or the like over the opening of a cutout drum, which is a cutout of a portion of a cylinder. The recording material 14 sent to the transfer drum 4 is electrostatically attracted and held onto the transfer drum 4 by an attraction charger 16 and an attraction auxiliary member 21 that brings the recording material 14 into close contact with the transfer drum 4 . The transfer drum 4 rotates in the direction of the arrow in the figure, thereby conveying the transfer material 4 to a transfer section facing the photosensitive drum 1. In the transfer section, the recording material 14 is charged with a corona with a polarity opposite to that of the toner image on the photosensitive drum l by the transfer charger 7 provided in the transfer drum 4 from the opposite side of the photosensitive drum l. , a cyan toner image is transferred onto the recording material 14.

This &ml distribution material 14 is conveyed while being adsorbed and held by the transfer drum 4 without being separated, and is subjected to the transfer of the toner image of the fifth color. The above series of steps is repeated for magenta, yellow, and black, and after the four-color toner image is transferred onto the recording material 14, the charge is removed by the separation charger 22, and the separation claw 17 is assisted. In response, the recording material 14 is separated from the transfer drum 4. The separated transfer material 14 is conveyed by a conveyor belt 18 to a fixing device 8, where the toner image is heat-fixed and mixed with color to form a full-color permanent image, which is then discharged to the outside of the image forming apparatus. .

However, in the conventional electrophotographic multicolor image forming apparatus described above, toner having an average particle diameter of about 12 μm is usually used in order to obtain a sufficient maximum image density. Therefore, the development characteristics exhibit an S-shape characteristic of electrophotography, as shown in FIG.

In general, full-color images have higher requirements in terms of image quality than black-and-white images, and there is a tendency for particular importance to be placed on reproducibility of intermediate tones. However, in the conventional electrophotographic multicolor image forming apparatus described above, only the development characteristics shown in FIG. 5 can be obtained, and sufficient continuous gradation cannot be obtained.
Satisfactory reproduction of midtones is not possible.

2. Description of the Related Art Digital multicolor image forming apparatuses have been proposed that attempt to improve continuous gradation by processing electrical signals for original images. but,
Even in such cases, images are usually formed using toner having a large particle size, for example, the same average particle size of 12 μm as described above, in order to obtain a sufficient maximum image density, especially in solid areas. During development, these toner particles do not move one by one from the developing device onto the photosensitive drum to form a toner image, but usually move in clusters of 3 to 4 or more to form a toner image. Are known. For this reason, continuous gradations cannot be obtained in low density areas of the image, resulting in discontinuous step function-like development characteristics, resulting in images lacking in smoothness.

Furthermore, when reproducing an image obtained by the above method using the same method, the scan pitch of the image reading device is In some cases, image deterioration such as moiré may occur depending on the image quality and angle. On the other hand, if you only want to improve the gradation characteristics in low density areas, you can reduce the particle size of the toner used for development. The physical property value (charge amount/toner mass) becomes large, and a sufficient maximum image density cannot be obtained under the same latent image formation and development conditions as in the past. Changing latent image formation or development conditions in order to obtain a sufficient maximum image density will adversely affect the life of the photosensitive drum.

Furthermore, even if a sufficient maximum image density is obtained on the photosensitive drum, sufficient transfer is not easy in the next transfer process due to the large electrostatic attraction force of the toner with a high triboelectric charge amount, and transfer failures often occur. Image defects such as the following occurred, and an image of sufficiently satisfactory quality could not be obtained by any of the methods. Furthermore, it is not easy to produce toner with such a small particle size (it is difficult to produce it stably and inexpensively, and it is not suitable for images that require large amounts of toner, such as full-surface vector images). Ta.

Furthermore, with toner having a single average particle size, the absolute amount of toner held on the photosensitive drum during transfer, and therefore the amount of triboelectric charge, differs between the high density side and the low density side, resulting in uneven transfer characteristics. Another problem occurred in that the transfer characteristics were good on the high density side but poor on the low density side.

Therefore, an object of the present invention is to provide an image forming apparatus that can ensure maximum image density and improve gradation reproducibility on the low density side. Another object of the present invention is to provide a developing device suitable for use in the above image forming apparatus.

The above objects for achieving the following are achieved by an image forming apparatus and a developing device according to the present invention. In summary, the present invention provides image formation in which a latent image is formed on an image carrier, the latent image is developed with a developer to be visualized as a toner image, and the toner image is transferred onto a transfer material to obtain an image. In the apparatus, the latent image is formed such that the toner image thereof is divided into a plurality of different densities, and a plurality of types of developers having different average particle diameters are used as the developer in the same number as the number of divisions of the density. The image forming apparatus is characterized in that the latent image is developed by using the latent image. According to one aspect of the present invention, the plurality of types of developers are provided in separate developing devices according to their average particle sizes, and according to another aspect, the plurality of types of developers have different average particle sizes. The two types of developer have opposite charge polarities depending on their size, and the two types of developer are housed in the same developing device.

Further, the present invention provides a plurality of developer containers each having a developer stirring member containing a developer having a different average particle size, which are installed adjacently so that the openings provided in the developer containers are connected. A common developer carrier is received in the plurality of developer containers through the opening, and each opening is connected to the developer carrier in each opening of the plurality of developer containers. The developing device is characterized in that it is provided with a shutter that opens and closes with a shutter, and further includes a stripping member that strips off the developer on the developer carrier at each of the openings.

Examples of the present invention will be described in detail below.

FIG. 1 is a configuration diagram showing an embodiment of an image forming apparatus of the present invention.

The present invention can be suitably implemented in a multicolor electrophotographic copying apparatus equipped with a movable developing device as described with reference to FIG.

Therefore, in this embodiment, the basic configuration of the image forming apparatus of this embodiment, which is embodied in a multicolor electrophotographic copying apparatus similar to that shown in FIG. The same reference numerals as those shown in FIG. 4 indicate the same members.

Now, a major feature of this image forming apparatus is that two developing devices are provided for each color, as shown in FIG.

The first cyan developing device 3CL is a developing device containing a negatively charged cyan toner having an average particle size of 12 μm, a carrier that imparts an electric charge to the cyan toner, and other charge control agents, lubricants, etc. agent is contained. A second cyan developing device 3C.

contains a developer containing a negatively charged cyan toner having an average particle size of 8 μm, a carrier that imparts an electric charge to the toner, and other charge control agents, lubricants, and the like.

Similarly, the first magenta developing device 3 M L stores a developer containing negatively charged magenta toner having an average particle size of 12 μm, a carrier, a charge control agent, etc. The cyan developing device 3C of No. 2 contains a developer containing negatively charged magenta toner having an average particle size of 8 μm, a carrier, a charge control agent, and the like. First and second yellow developer 3YL
, 3 Ys accommodates a developer containing a negatively charged yellow toner having an average particle size of 12 μm and 8 μm, a carrier, a charge control agent, etc., and the first,
The second black developing devices 3BL and 3BI contain a developer containing negatively charged black toner having an average particle size of 12 μm and 8 μm, a carrier, a charge control agent, etc., respectively.

Next, the flow of full-color image formation in this embodiment will be explained with reference to the sensitometric diagram shown in FIG.

The original 11 placed on the original platen 20 is exposed to light by the illumination light source 9, the reflected light is read by the light receiving element 10, and the image density of the original 11 is converted into an electrical signal by photoelectrically converting it by a processing device (not shown). do. This converted electric signal is further passed through a color separation processing circuit (not shown) and converted into four color separated electric signals of cyan, magenta, yellow, and black. First, an electric signal corresponding to the cyan color of the original image is generated. is taken out and guided to the next gradation correction circuit (not shown).

First, among the electric signals corresponding to the cyan color described above, the signal on the high density side above point A in FIG. 2, in this example, the signal with optical density from 0.75 to 1.50 is The photosensitive drum is uniformly charged to a negative polarity by the primary charger 6 in advance, and the amount of exposure that has been processed and corrected for the original image density according to the gradation correction function B shown in the first quadrant of FIG. 2 is applied to the photosensitive drum. 1 using an exposure light source 2. As a result of this exposure, a curve D (characteristic curve showing a change in development contrast potential with respect to a change in exposure amount) shown in quadrant Ⅰ of FIG. 2 is obtained.
Accordingly, an electrostatic latent image corresponding to the original image density is formed on the photosensitive drum 1.
formed on top. At this time, since a reversal development method was used for exposure, the amount of exposure was set to be large for portions of the original image with high image density.

Next, the developing device 3CL, which has been moved to the developing position in advance, develops the electrostatic latent image on the photosensitive drum 1 by a reversal developing method according to its development contrast potential. The cyan toner image obtained by the development is transferred onto the recording material 14 which is electrostatically attracted and held on the transfer drum 4 in the transfer section by the action of the positive transfer electric field of the transfer charger 7. Ru. As described above, the cyan toner used in the development process has an average particle size of 12 μm, and the density of the toner image on the recording material 14 with respect to the development contrast potential, that is, the density characteristic of the copy image. is shown by curve E shown in quadrant 2 of FIG.

If you refer to Figure 2, it will be even more clear (as can be seen, for the high-density side of the original image, the image density of the copy image with respect to the image density of the original image is finally shown in quadrant ① of Figure 2). As a density characteristic, a gradation characteristic consisting of a straight line GH was obtained.

Next, among the signals corresponding to the cyan color of the original image mentioned above,
Signals on the low-density side below point A in FIG. 2, in this example, signals with optical densities from 0.00 to 0.75 are processed, and the gradation correction function shown in the first quadrant of FIG. 2 is processed. Exposure of an amount corrected for the original image density according to the number C is performed using the exposure light source 2 on the photosensitive drum 1 which has been uniformly charged again by the primary charger 6 in advance. Through this exposure, an electrostatic latent image is formed on the photosensitive drum according to the original image density according to the curve shown in the quadrant (2) of FIG. 1.

Next, the developing device 3C1, which has been moved to the developing position in advance, develops the electrostatic latent image on the photosensitive drum 1 according to its development contrast potential. A cyan toner image different from the previous one obtained by development is applied to the recording material 14 which is electrostatically attracted and held on the transfer drum 4 in the transfer section by the positive transfer electric field of the transfer charger 7. Due to this action, the cyan toner image is overlaid with the previous cyan toner image and transferred multiple times. As described above, the cyan toner used in the development step at this time has an average particle size of 8 μm, and the density of the toner image on the recording material 14 with respect to the development contrast potential of this toner is as follows.
That is, the density characteristics of the copied image are shown by the curve E shown in the quadrant (2) of FIG.

As can be seen more clearly by referring to Figure 2, for the low density side of the original image, the image density characteristics of the copied image relative to the image density of the original image are finally determined as shown in quadrant (2) of Figure 2. , gradation characteristics consisting of direct MOG were obtained.

As described above, by performing each of the latent image formation, development, and transfer steps twice for the cyan color of the original image, all densities corresponding to the cyan color of the original image are printed on the recording material 14. A toner image is formed. By repeating these steps in the same way for magenta, yellow, and black, the final recording material 14
A full-color image is obtained by multiple-transferring four-color toner images onto the image.

When the transfer of the four color toner images onto the transfer material 14 is completed, the recording material 14 is separated from the transfer drum 4 with the charge removed by the separation charger 22 and with the assistance of the separation claw 17. The separated transfer material 14 is transferred to a fixing device 8 by a conveyor belt 18.
There, the toner image is heat-fixed and mixed to form a full-color permanent image, and then discharged outside the image forming apparatus.

As mentioned above, the full-color image obtained in the above manner is produced by using a toner with a small particle size to reproduce the low-density side of the original image. Gradation characteristics consisting of OGH have been obtained, and good image reproducibility can now be obtained even on the low density side.

Further, in this embodiment, a toner having a small particle size, that is, a toner having a large amount of triboelectric charge per mass, is used to develop the low density side of the original image. Conventionally, toner images formed on 5-photosensitive drums have a large difference in absolute amount of toner, and hence charge amount, between the high-density side and the low-density side of the original image, and uniform transfer from the low-1 degree side to the high-density side is impossible. On the other hand, in the present invention, although the absolute amount of toner on the low density side is small as in the conventional case, the amount of charge of each toner image is large, so the amount of toner on the low density side is small. It has become possible to increase the total amount of charge, and it has become possible to obtain uniform transfer characteristics from the low density side to the high density side.

In the above examples, toners having two types of average particle diameters were used for each of the four colors, but the present invention is not limited to this.
Depending on the color, the image density of the document may be divided into three or more types, and toner having an average particle size of three or more types may be used, and it goes without saying that even better image formation can be achieved by doing so. In addition, the image forming process was configured so that development was performed first using the larger toner among toners with different average particle sizes, but conversely, the process was configured so that the toner with the smaller average particle size was developed first. Needless to say, it is okay.

Furthermore, the present invention does not require the use of toners with two types of average particle diameters for all four colors; for example, for colors such as yellow that have little visual impact, toners with small particle diameters and toners thereof are used. A developing device can be omitted. Also, for colors such as black, which are mainly used for character reproduction and are rarely used for halftone reproduction, it is possible to omit small particle size toner and its developer.

Furthermore, it goes without saying that the present invention can be applied not only to full-color image forming apparatuses but also to black-and-white, monochrome, or multicolor image forming apparatuses.

FIG. 3 is a configuration diagram showing a developing device in another embodiment of the image forming apparatus of the present invention.

As a result of further research, the inventors of the present invention found that by making the developing device have a structure as shown in FIG. 3, there was no need to provide two developing devices for each color as in the image forming apparatus shown in FIG. It has been found that the present invention can be implemented in a developing device space, such as a space between conventional development devices. The image forming apparatus of this embodiment is characterized by incorporating one developing device for each color as shown in FIG. 3 instead of the two developing devices for each color in the image forming apparatus shown in FIG.

Hereinafter, a cyan color developer will be described as the developer of this embodiment to avoid complication of explanation, but the same applies to other color developers.

As shown in FIG. 3, the developing device 51 according to this embodiment includes first and second developer containers 52. whose upper surfaces are opened in an arc shape.
53 are installed adjacently so that their openings are connected, and the lower part of the common developing sleeve 56 is received in the first and second developer containers 52, and the first and second developer containers Developer stirring members 54 and 55 such as screws are installed in the first and second developer containers 52 and 53, respectively.
2.53 is supplied to the developing sleeve 56 while stirring to enable the developing operation, and further the first and second
shutters 57 and 58 for opening and closing the openings with respect to the developing sleeve 56 are provided at each of the openings of the developer containers 52 and 53 of the first. A cleaner blade 59, 60 for stripping the developer on the developing sleeve 56 is provided at the upper end of each opening of the second developer container 52, 53.

In one of the first and second developer containers 52 and 53, for example, the developer container 52, a cyan toner having an average particle size of 12 μm and being charged with a negative polarity, and a carrier that imparts an electric charge to the toner, A developer containing other charge control agents, lubricants, etc. is stored in the other developer container 53, and the other developer container 53 contains cyan toner having an average particle size of 8 μm and having a negative polarity. A developer containing a carrier to be applied, other charge control agents, lubricants, etc. is contained therein.

In order to carry out development according to the present invention using the developing device 51, the following procedure may be performed.

That is, the developing device 51 is moved to the location of the photosensitive drum 1 shown in FIG. 1, and the developing sleeve 56 is made to face the photosensitive drum 1.

For example, a portion of the upper opening of the second developer container 53 of the developing device 51 facing the developing sleeve 56 is connected to the shutter 58.
is moved counterclockwise to close it, and the developer containing the above-mentioned cyan toner having an average particle size of 12 μm contained in the first developer container 52 is supplied to the developing sleeve 56. In the same way as before, the electrostatic latent image on the photosensitive drum 1 corresponding to the high-density side of the original image is developed.

The cyan toner image on the photosensitive drum 1 obtained by the development is similarly transferred onto the recording material 14 adsorbed and held on the transfer drum 4 at the transfer section.

After the transfer of the above-mentioned toner image is completed, while the next latent image is being formed, that is, the latent image corresponding to the low density side of the original image is being formed on the photosensitive drum 1, the upper surface of the first developer container 52 side is The shutter 57 is moved clockwise to close the portion of the opening facing the developing sleeve 56, and the cleaner blade 59 is brought into contact with the developing sleeve 56 by a drive means (not shown) to strip off the developer on the developing sleeve 56. . The developer peeled off from the top of the developing sleeve 56 is returned into the developer container 52 from the upper end of the upper surface opening thereof, and is returned to the developer container 52 by the liner blade 59.
The contact is also released.

Next, the shutter 58 on the side of the second developer container 53 is moved clockwise to open the opening of the developer container 53, and the cyan color with an average particle size of 8 μm stored in the developer container 53 is removed. A developer containing toner is supplied to the developing sleeve 56 to similarly develop the electrostatic latent image on the photosensitive drum 1 corresponding to the lower density side of the original image. A cyan toner image different from the previous one obtained by development is multiple-transferred onto the recording material 14, which is attracted and held on the transfer drum 4 in the transfer section, overlapping the previous cyan toner image. Ru.

In this manner, toner images for all densities corresponding to the cyan color of the original image are formed, similar to the previous embodiment.

When the development of the low-density side of the original image is completed, the developer 51 moves the shutter 58 on the second developer container 53 counterclockwise to close the opening of the developer container 53. The cleaner blade 60 at the upper end of the opening is brought into contact with the developing sleeve 56 by a driving means (not shown), and the developing sleeve 5
6 in the direction opposite to the arrow X, and remove the developing sleeve 56.
Peel off the developer on top. The developer peeled off from the developing sleeve 56 is returned into the developer container 53 from the upper end of its opening, and the cleaner blade 60 is also released from contact with it, preparing for the next development.

The cleaner blades 59 and 60 described above do not only remove the developer on the developing sleeve 56 (but also remove the developer from the developing sleeve 56).
It may also be used as a so-called doctor blade to regulate the layer thickness of the developer carried thereon.

Once toner images for all densities corresponding to the cyan color of the original image are formed on the recording material 14 in the above manner, magenta, yellow, and black colors are developed in the same way as in the case of cyan color. By performing this series of steps for magenta, yellow, and black using a developer having the same configuration as the developer 51, the recording material 1
Four color toner images are multiple-transferred onto the image forming apparatus 4, and then the toner images are heat-fixed and mixed with color in the fixing device 8 to form a full-color permanent image.

In this embodiment as well, two types of developers with different toner particle sizes are used for development, and the lower density side of the original image is developed with the developer containing toner with a smaller particle size. As in the previous embodiment, a full color image of good quality can be obtained.

Furthermore, in this embodiment, the developing device 51 for the original image is configured to include two developer containers 52 and 53 containing two types of developers having different toner particle sizes for a common developing sleeve 56. , compared to the conventional case with one developing device for each color, and the conventional case with two developing devices for each color, in which development can be performed using two types of developers with different toner particle sizes in the developing device space such as between the tracks. The developer space does not become large.

In this embodiment as well, development was performed first using the larger toner among toners with different average particle diameters.
It goes without saying that, as in the previous embodiment, the image forming process may be configured so that the toner having the smaller average particle size is developed first.

Still another embodiment of the image forming apparatus of the present invention will be described.

As a result of further research, the present inventors found that when using two types of developers with different toner particle sizes, if the toners with different particle sizes each exhibit opposite polarity charging characteristics, it would be possible to achieve the same result as before. It has been found that development can be performed using two types of developers having different toner particle sizes in a developing device, and that the present invention can be implemented without providing two developing devices for each color.

The image forming apparatus of this embodiment is similar to the conventional image forming apparatus, and is the image forming apparatus of FIG. 1 equipped with conventional developing devices, one for each color.

In this example, each color developer has two different particle sizes.
It has different types of toner, among which the average particle size is 12μm.
The toner of each color was adjusted to be charged to a positive polarity, and the toner having an average particle size of 8 μm was charged to a negative polarity, and the developer of each color was stored in each developing device.

Then, as in the previous two embodiments, an image is formed on the high-density side of the original image for each color, and then an image on the low-density side is formed, but unlike the previous embodiments, the latent image is formed at this time. ,
The lower the image density of the original image, the thicker the exposure amount.Then, in the next development step, development is performed using the regular development method.Then, when forming a low-density image, the previous development method is used. As in the embodiment, the higher the image density of the original image, the greater the exposure amount, and the next development step was to perform development using a reversal development method.

By charging toners with different particle sizes to opposite polarities and using different latent image forming and developing methods, images with good gradation can be formed using the same number of developing devices as before. It was found that full-color images of good quality were obtained.

In the above example, the toner with large particle size is charged with positive polarity and the toner with small particle size is charged with negative polarity, but it is also possible to charge the toner in the opposite direction (and the order of development may also be reversed). The image forming process may be configured so that the toner having a smaller diameter is developed first.

1. As explained above, in the image forming apparatus of the present invention, a latent image is formed on the image carrier so that the resulting toner image is divided into a plurality of different densities. Since a latent image is developed and an image is formed by using multiple types of developers with different average particle diameters in the same number as the number of divided densities mentioned above, the maximum image density is ensured and the gradation on the low density side is maintained. Images with improved reproducibility can be obtained.

Furthermore, since the developing device of the present invention has a structure in which a common developer carrier is received in a plurality of developer containers, it is possible to use a plurality of types of developers having different average particle sizes in one developing device. Development can be performed.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of an image forming apparatus of the present invention. FIG. 2 is a sensitometric diagram showing the relationship between original image density, exposure amount, development contrast potential, and copy image density in the image forming method using the image forming apparatus of FIG. FIG. 3 is a configuration diagram showing a developing device in another embodiment of the image forming apparatus of the present invention. FIG. 4 is a configuration diagram showing a conventional image forming apparatus. FIG. 5 is a graph showing image characteristics in the image forming apparatus shown in FIG. 1: Photosensitive drum 2: Exposure power source 3CL to 3Bg, 51: Developing device 9: Illumination light source 14: Transfer material 52.53: Developer container 54.55: Developer stirring member 56: Developing sleeve 57.58: Shutter number Figure 1 Figure 2 Original ■1 Figure 4 (V) Development contrast potential

Claims (1)

[Scope of Claims] 1) An image in which a latent image is formed on an image carrier, the latent image is developed with a developer to be visualized as a toner image, and the toner image is transferred onto a transfer material to obtain an image. In the forming device, the latent image is formed such that the toner image is divided into a plurality of different densities, and the developer is a plurality of types of developers having different average particle diameters in the same number as the number of divisions of the density. An image forming apparatus characterized in that the latent image is developed using the following. 2) The image forming apparatus according to claim 1, wherein the plurality of types of developers are housed in separate developing devices depending on their average particle diameters. 3) The plurality of types of developers are two types of developers whose charging polarities are opposite depending on the size of the average particle size, and the two types of developers are housed in the same developing device. 1. The image forming apparatus according to 1. 4) A plurality of developer containers each equipped with a developer stirring member containing a developer having a different average particle size are installed adjacently so that the openings provided in the containers are connected, and the plurality of developer containers are A shutter that receives a common developer carrier through the opening in the developer container and opens and closes each opening of the plurality of developer containers with respect to the developer carrier. A developing device further comprising: a stripping member for stripping off the developer on the developer carrier at each of the openings.